Potentials of Additive Manufacturing for Cutting Tools: A Review of Scientific and Industrial Applications

Abstract

Additive manufacturing (AM) techniques enable new design concepts for performance improvements and functional integration in a wide range of industries. One promising application is in additively manufactured cutting tools for machining, improving process reliability on the one hand and increasing tool life and process productivity on the other hand. Compared to conventional manufacturing processes, AM allows for new and complex geometrical designs, enables the production of individualized parts, and offers new possibilities for alloy composition and material design. This work gives a comprehensive and systematic review of scientific as well as industrial activities, studies, and solutions regarding AM cutting tools and their fields of application. Four different areas are identified, including cooling and coolant supply, damping and vibrational behavior, lightweight design and topology optimization, and functional integration. Thus, the relevant and promising approaches for the industrialization of AM cutting tools are highlighted, and a perspective is given on where further scientific knowledge is needed.

1. Introduction

With a global market size of USD 379 billion in 2023, machining is by far the most relevant manufacturing process [1]. In 2023, machine tools worth USD 88.6 billion were produced [2]. Machining processes with a defined cutting edge, such as turning, milling, drilling, threading, and broaching, are applied in all fields of industries, from transportation, such as in the automotive and aerospace industries, through defense to medical applications [3]. Although cutting is one of the oldest manufacturing processes, it continues to undergo a high level of innovation. These include, among other innovations, digital solutions and process monitoring, process simulation and control, new process kinematics, sustainable machining approaches, and innovative tool concepts [4,5,6,7,8]. In Germany, precision tools for machining, such as end mills, cutting inserts, turning tools, and indexable millings tools, reached a yearly turnover of EUR 9.9 billion in 2022 [9]. Recent developments in cutting tools are found, e.g., in new substrate materials and coatings, micro- and macroscopic tool design, optimized application scenarios, and process monitoring [10,11,12,13]. The objective of the ongoing developments and innovations is to enhance process efficiency and sustainability, as well as reliability.

In this context, additive manufacturing (AM) technologies offer a variety of possibilities to support improvements in tool performance. Compared to conventional manufacturing processes, AM allows for new and complex geometrical designs, enables the production of individualized parts, and offers new possibilities for alloy composition and material design [14,15,16,17]. Polymers, composites, metals, and ceramics can be processed via different AM techniques, unleashing potential in all areas of cutting tool development [18,19]. AM is a constantly growing market, reaching a yearly revenue of USD 15 billion in 2021 for all AM services and products and an estimated growth rate of up to 20% [20]. In many fields of application, AM techniques already exhibit high technology readiness levels (TRL) [21].

A multitude of AM cutting tools have been showcased in the research environment and industrial applications in recent years [22,23,24]. However, most of the examples and products presented have not yet achieved market penetration or have only been used as prototypes or demo tools. Reasons for this can be found in the lack of understanding of the possibilities of AM techniques for cutting tool design and the resulting performance improvements, reservations about the operational readiness of layer-by-layer manufactured tools, and cost-intensive production [25,26]. In order for AM tools to be widely used, the application potential for functional improvements must be identified and understood. Based on this understanding, future research demands for an industrialization of AM cutting tools can be derived. A comprehensive overview of the fields of application of AM cutting tools in science and production is missing to date.

This paper aims to provide a comprehensive and systematic review of scientific—as well as industrial—activities, studies, and solutions regarding AM cutting tools and their fields of application in machining. The review highlights the relevant and promising approaches for the industrialization of AM cutting tools and determines the research requirements pertaining to additive manufacturing and cutting technology. First, relevant AM techniques are introduced, and studies regarding processable cutting tool materials are summarized. Substrate materials, such as cemented carbide and ceramics, but also steel materials for tool carriers, are examined. Second, the potential applications of AM in improving cutting tool functionalities are reviewed, identifying four areas of applications. These areas, namely, cooling and cutting fluid supply, damping and vibrational behavior, lightweight design and topology optimization, and functional integration, are discussed in detail. Based on this review, the current challenges of, and future requirements for, the industrialization of AM cutting tools are determined in the last step.

2. Fundamentals of Additive Manufacturing

Additive manufacturing (AM) techniques are found in a variety of industry sectors, such as aerospace, medical technology, and tool making [17,27]. AM is not only used for rapid prototyping purposes but is also applied for small-lot production [28,29,30]. Thus, AM techniques are also used for the prototyping, development, and production of cutting tools. In the following section, relevant AM techniques are introduced. Furthermore, processable materials, with a focus on their application in cutting tools, are summarized.

2.1. AM Process Variants

As part of the DIN 8580 main group 1 “primary shaping processes” [31], additive manufacturing is defined as a “process of joining materials to make parts from 3D model date, usually layer upon layer, as opposed to subtractive manufacturing (…) fabrication” according to DIN EN ISO/ASTM 52900 [32]. AM technologies can be grouped into seven process categories, representing all machine concepts and materials. Plastic, metallic, and ceramic materials can be processed in liquid, powder, or dense form. A further subdivision can be made regarding the acquisition of the final part properties (single-step and multi-step processes) [32]. With the first patent in only 1984, AM is still undergoing many technological breakthroughs and process innovations today.

Four AM process categories are especially important regarding cutting tool fabrication as they allow us to process metallic, composite, and ceramic materials. The relevant techniques are schematically illustrated in Figure 1. In vat photopolymerization (VPP), a liquid photopolymer is selectively cured via light-activated polymerization (also called stereolithography). Powder bed fusion (PBF) techniques use thermal energy to fuse regions of a powder bed selectively. In binder jetting (BJT), a liquid bonding agent is selectively deposited to join powder materials. In directed energy deposition (DED), thermal energy is used to fuse materials by melting them as they are deposited. The energy source is provided by laser, electron beam, or UV light, depending on the process [33]. For the AM of metallic materials in the form of powder or wire, laser powder bed fusion (PBF-LB), electron beam powder bed fusion (PBF-EB), and DED are the most commonly used processes [34]. PBF-LB, in particular, will be the focus of this review. Each AM technology offers advantages and drawbacks for the manufacturing of cutting tools, summarized in

Table 1. Comparison of advantages and disadvantages of relevant AM processes (data from [20,35,36,37,38]).

AM Process	Advantages	Disadvantages
VPP	High geometrical complexity and accuracy; processing of metal and ceramic (composite) materials	Limited material range; green part only (sintering needed, undesired shrinkage)
PBF	Manufacturing of dense metallic parts. Depending on the material, no need for additional heat treatment. High geometrical complexity and accuracy	Limited part size; melting process introduces residual stress; low build rate; processing of weldable materials only; high production costs
BJT	Processing of metal and ceramic (composite) materials; low production costs; high scalability; no support structures needed	Low density; green part only (sintering needed, undesired shrinkage)
DED	High build rate; manufacturing of dense metal parts; large build volume; high material utilization; possibility of functional graded materials	Limited geometrical accuracy and complexity; melting process introduces residual stress; processing of weldable materials only

.

2.2. AM Market Relevance

AM techniques are particularly utilized in high-value sectors, such as in automotive, aerospace, and biomedicine, where highly complex and often individualized designs are implemented [17]. Prototyping still accounts for 24% of the market, end-consumer products for 34%, while metal tooling represents only 3.5%, as shown in Figure 2 [20]. The leading industrial sectors for AM applications are aerospace (17%), followed by the medical and dental sectors (16%), and the automotive industry (15%) [20]. The overall size of the AM industry is predicted to grow sixfold by 2031 compared to 2021, with the PBF-LB process achieving the highest growth rates in the metal AM market [20,39]. Nickel-based alloys, steel, and titanium were the most commonly used metals in AM in 2021, comprising 68% of the market share, as illustrated in Figure 2 [20].

AM techniques offer advantages such as geometrical freedom of design, near-net-shape fabrication, fast availability of complex parts, and high resource efficiency [40]. The key drivers of AM over conventional manufacturing techniques are shown in Figure 3. AM can provide cost advantages, particularly for individualized, complex parts with small lot sizes [16]. However, compared to conventional manufacturing, AM typically results in higher surface roughness, limited part sizes, and increased production and material costs [16,41,42]. The process route includes additional steps, such as powder removal, heat treatment, and post-processing, which add to energy, resources, and cost consumption [43]. Technological limits often hinder competitive mass production. In most AM techniques, build rates in layer-by-layer manufacturing are constrained by physical boundary conditions such as energy input or powder deposition. For instance, in PBF-LB, increasing the laser beam diameter, laser power, scanning speed, or layer thickness can lead to overheating of the melt pool, strong spatter formation, internal defects, coarser structures, and increased surface roughness [44,45,46]. The relatively low productivity and the need for elevated temperatures and inert gas throughout the process, combined with the energy-intensive powder production, contribute to the high environmental impact of AM compared to conventional machining [47,48].

Thus, AM can only be economically and ecologically viable when its technical advantages over conventional manufacturing are fully exploited [49]. These advantages include functional integration, lightweight and topologically optimized design, the processing of new alloys, or fast prototyping of parts during product development [14,16,50].

Figure 3. Key drivers for the application of additive manufacturing techniques (data from [51,52]).

Figure 3. Key drivers for the application of additive manufacturing techniques (data from [51,52]).

2.3. Processable Materials Relevant to the Application in Cutting Tools

To identify the potential of AM for cutting tools, the materials used must be considered. These include metal materials for tool carriers and tool holders on the one hand and substrate materials on the other. Tool carriers, mostly manufactured from steel alloys, can be equipped with either indexable cutting inserts, usually tungsten carbide-based, or brazed cutting edges, such as polycrystalline diamond (PCD). Tool substrates or cutting tool materials, which form the cutting edge, must withstand the thermo-mechanical loads from the cutting process. In general, materials that are hard, temperature-resistant, and strong, such as tool steels, cemented carbides, ceramics, and superhard materials like diamond, are required for such applications [3]. Given its advantages, high market penetration, relevance, and TRL, the focus is on the PBF-LB process [53,54].

2.3.1. Materials for Tool Carriers

Due to the dynamic loads, contact with emerging chips, and high temperatures encountered in use, materials for cutting tool carriers must have high strength, wear resistance, temperature resistance, and stiffness [55,56]. To be processable in PBF-LB, materials need to be weldable, resistant to crack formation during solidification, and available in spherical powder form with a particle size between 10–100 µm. The key characteristics of powder for PBF-LB include flowability, moisture resistance, and a well-defined particle size distribution with a spherical shape [57]. Various materials have been investigated, including Ni-based superalloys, Co-Cr alloys, tool steels, stainless steels, Ti-, Al-, Cu-, and Mg-based alloys, precious and refractory metals, intermetallic compounds, and high-entropy alloys [38,58,59,60,61,62]. Material properties and microstructures of PBF-LB-manufactured materials can differ significantly from conventionally manufactured cast and wrought materials of the same composition due to grain refinement, anisotropic and elongated grain growth, and internal metallurgical defects [63,64,65].

Table 2. Suitable steel materials for the application in PBF-LB-manufactured tool carriers (H: hardness, Rm: tensile strength).

Steel Material	As-Built Properties	Ref.
X40CrMoV5-1 (H13, 1.2344) Conventional, heat-treated cast material	H = 540–615 HV; Rm = 1430 MPa	[66]
X40CrMoV5-1 (H13, 1.2344)	H = 706–894 HV; Rm = 835–1236 MPa	[67,68]
X37CrMoV5-1 (H11, 1.2343)	H = 506 HV	[69,70]
X3NiCoMoTi18-9-5 (18Ni-300, 1.2709)	H = 333–341 HV; Rm = 1056–1096 MPa	[71,72]
X5CrNiCuNb17-4-4 (17-4 PH, 1.4548)	H = 258 HV	[73]
30CrNiMo8 (AISI 4340, 1.6580)	Rm = 1009–1016 MPa	[74]
16MnCr5 (AISI 5115, 1.7131)	H = 330 HV; Rm = 1050 MPa	[75]
18MnCrMoV4-8-7 (1.7980)	H = 405 HV	[76]

provides an overview of suitable steel materials for AM tool carriers.

Tool steels, case hardening steels, quenched and tempered steels, and maraging steels are commonly used for tool carriers. Processing steel alloys with higher carbon content in PBF-LB is challenging due to their tendency to form cracks. In carbon martensitic steels, such as tool steels, these cracks occur because of the changes in specific volume during phase transformation in the solid state [77]. This phenomenon happens when the molten material cools below the martensite start temperature. The martensite, with its high strength, hinders the reduction of residual stresses, leading to crack formation [78]. A preheating system can improve processability by reducing thermal gradients and thermally induced residual stresses [79].

Several tool steels with varying carbon contents have been investigated for PBF-LB, including hot-working steels such as H13 (X40CrMoV5-1, 1.2344) and H11 (X37CrMoV5-1, 1.2343), as well as maraging steels like 18Ni-300 (X3NiCoMoTi18-9-5, 1.2709) [67,68,69,71]. Nearly carbon-free maraging steels with a high Ni-content, such as 1.2709, are easier to process due to their relatively ductile martensitic microstructure. In contrast, carbon-containing tool steels develop a harder and more brittle martensitic matrix without precipitates, leading to higher thermal stresses and a greater tendency to crack during PBF-LB [80]. If the mechanical properties and wear resistance of the component are not crucial, precipitation-hardening steels like X5CrNiCuNb17-4-4 (17-4 PH) can be used to improve the PBF-LB processability [72,73]. Additionally, hot and cold working steels with lower martensite start temperatures can be used to reduce crack formation [81]. Although H13 does not offer the highest mechanical properties among tool steels, it is widely used in injection and die mold fabrication due to the favorable combination of toughness, wear resistance, and fatigue strength [82,83]. H13 also has cost advantages compared to maraging and other tool steels [84]. It can be processed in PBF-LB using a preheated build platform at approximately 200–300 °C, with the main challenge being cracking due to fast solidification [67,85,86,87]. Depending on conditions, as-built specimens have achieved densities of up to 99.7% and hardness values of up to 60 HRC with a tensile strength of 1025 MPa [67].

Few investigations have been conducted on other steel alloys suitable for tool manufacturing. Zumofen et al. successfully processed steel 30CrNiMo8 (1.6580, AISI 4340) with a density of 99.8% and a tensile strength of 1098 MPa after heat treatment [74]. Schmitt et al. investigated case hardening steel 16MnCr5 (1.7131, AISI 5115), achieving densities above 99.75% with a tensile strength of 995 MPa and a hardness of 235 HV10 after heat treatment [75]. PBF-LB processing of low-alloy case hardening steel 18MnCrMoV4-8-7 (1.7980, “Bainidur AM”) promises good processability and favorable mechanical properties. Bartels et al. investigated the microstructure and microhardness of this steel depending on the PBF-LB process parameters and subsequent heat treatment [76]. Bainite-like microstructure formation was confirmed in both the as-built stat and after tempering at 600 °C without preheating. The material achieved a relative density exceeding 99.7% across a broad parameter range, with as-built state hardness values of 405 HV1. Processing of 1.7980 in DED-LB was investigated by Bartels et al. and Kreß et al. to manufacture hybrid components and to deposit wear-resistant WC-reinforced coatings [88,89,90]. In addition to steel tool carriers, titanium is also used in some tool carriers, particularly for lightweight designs [91,92].

Recent investigations aim to accelerate alloy development through in situ alloying by mixing pure elemental powders [93]. The processability is challenging due to the differences in melting point, viscosity, density, and thermal conductivity [94]. Hantke et al. achieved the processability of low-stress specimens without preheating using low-transformation temperature H13 steel fabricated from pre-alloyed ferropowders [78]. Other approaches involve mechanical alloying by ball milling as a powder preparation. Narvan et al. functionalized H13 with VC particles, significantly improving the mechanical properties compared to standard H13 powder [95]. Köhler et al. blended TiC carbides with H13 powder for an improvement in isotropic microstructure and hardness [96]. Pannitz et al. nano-coated maraging tool steel 1.2709 powder with silicon carbide and few-layer graphene. Although the process window shrank, the build rate increased significantly due to the enhanced absorption behavior of the metal powder [97]. Bareth et al. utilized multi-material processing for combining 1.2709 tool steel with copper alloy CW106C [98].

It is important to note that the post-processing of AM parts introduces new challenges to machining compared to conventionally processed materials. AM materials often exhibit higher strength and hardness in the non-heat-treated as-built state. Along with the anisotropic microstructure and mechanical properties, this can cause direction-dependent machinability. These factors can lead to varying thermo-mechanical loads on the tool and workpiece, as well as differences in chip formation mechanisms, tool wear, tool deflection, and surface roughness. Other post-processing techniques, such as abrasive flow machining or laser peening, can help reduce surface inaccuracies and anomalies in AM as-built parts if needed [99,100].

This review demonstrates that a wide range of materials suitable for tool carriers, particularly in PBF-LB, is available. AM of tool steels presents no significant challenges, as these steels exhibit mechanical properties comparable to those of conventionally manufactured steel alloys. However, tool steels often incorporate numerous expensive alloying elements. Therefore, the development of new low-alloy steels specifically designed for AM, which retain adequate mechanical and thermal characteristics for cutting tools, is crucial for reducing the costs associated with powder materials. Avoiding heat treatment to minimize the post-processing efforts while concurrently achieving the desired microstructure and mechanical properties in line is especially important. The rapid development and testing of new alloy compositions that possess favorable characteristics for use in tool carriers, such as hardness, toughness, and heat resistance, are feasible in AM. Furthermore, the influence of layer-by-layer manufacturing on microstructure anisotropy, such as grain growth in the build direction, and mechanical properties, such as residual porosity, must be thoroughly evaluated to ensure machinability performance, including vibration behavior and fatigue strength, for industrial applications [101]. This evaluation is essential for building trust in these new manufacturing methods. Moreover, the design and implementation of clamping and referencing elements are critical for minimizing AM build times, material usage, and post-processing efforts.

2.3.2. Materials for Tool Substrates

PBF-LB processing of cutting tool materials is challenging, primarily due to low weldability, a tendency to crack formation, and the anisotropic and inhomogeneous microstructure caused by the local heat-affected zone. Additional challenges include lack-of-fusion defects and resulting porosity, and different melting points of the alloying elements, which can lead to evaporation. Furthermore, the geometrical accuracy and surface quality are limited, necessitating subtractive post-processing. On the other hand, new material compositions can be developed and tested much faster [102,103,104,105].

Table 3 provides an overview of the suitable cutting tool substrate materials processed using different AM techniques. These materials include high-speed steels (HSS), tungsten carbide (WC-Co), and ceramics, each offering distinct advantages for specific applications. HSS steels are characterized by their high flexural strength and favorable toughness properties. These attributes make HSS ideal for tools with sharp cutting edges, such as those used in broaching, threading, drilling, and orthogonal turning. Cemented carbide comprises carbides (e.g., tungsten, W) within a soft binder matrix (e.g., cobalt, C), exhibiting high hardness, compressive strength, and hot wear resistance. These properties make cemented carbide, especially tungsten carbide, the most commonly used material in metal machining applications. Ceramics, particularly oxide ceramics like aluminum oxide (Al₂O₃), are noted for their high compressive strength, chemical resistance, and high melting temperatures. These characteristics make ceramics suitable for high-productivity applications. All three materials have been successfully processed using AM. The subsequent sections will present detailed accounts of their AM processing and applications.

HSS types such as M50 (80MoCrV42-16, 1.3551), M2 (HS-6-5-2C, 1.3343), and ASP2030 (HS6-5-3-8, 1.3244) have been proven processable with adapted preheating systems and process parameters, reaching hardness values of up to 65 HRC with a relative density of 99.5% [106,107,108,109,110]. Several studies analyzed the fabrication of Al-, Ti-, and steel-based metal matrix composites by PBF-LB, either by processing prepared powder or by initiating a reaction in situ during the build process [111]. Additionally, PBF-LB of tungsten carbide (with a Co-content of 17%) has been successfully carried out with powder bed preheating temperatures of up to 1000 °C [112].

Kelliger et al. tested non-coated PBF-LB as-built grooving inserts made from HS6-5-3-8 (ASP2030) in orthogonal cutting experiments of different materials [113]. All inserts withstood the thermo-mechanical loads. Coated and heat-treated tools for M10 tap cutting and forming were PBF-LB-manufactured using the same substrate material and tested in 42CrMo4+QT (1.7225) and X5CrNi18-10 (1.4301) [105]. When comparing conventionally and additively manufactured tools, no significant difference in tool wear behavior and torque progression was detected. Koruba et al. deposited HS11-2-5-8 (S390PM) by wire DED [114]. The developed process is intended for the future repair of broaching tools.

Table 3. Suitable materials for the application in additively manufactured cutting tool substrates (σ: flexural strength).

Material	AM Process	Alloy	Properties	Ref.
HSS	Conventional PM steel	ASP2030 (HS6-5-3-8, 1.3244)	H = 990 HV (heat-treated)	[105]
	PBF-LB	M50 (80MoCrV42-16, 1.3551)	H = 789 HV (as-built); H = 803 HV (heat-treated)	[107,109]
		M2 (HS-6-5-2C, 1.3343)	H = 640 HV; Rm = 1300 MPa (as-built)	[106,108]
		ASP2030 (HS6-5-3-8, 1.3244)	H = 654–817 HV (as-built); H = 991 HV (heat-treated)	[110,113]
	DED	HS11-2-5-8 (S390PM)	H = 791–825 HV (as-built)	[114]
WC-Co	Conventional sintered	WC-10%Co	H = 1450–1590 HV (heat-treated)	[115]
	PBF-LB	WC-18%Co	H = 820–840 HV (as-built)	[116]
		WC-17%Co	H = 584–663 HV (as-built); H = 900–1050 HV (heat-treated)	[112] [102]
		WC-12%Co	H = 863 HV (as-built); H = 1086–1106 HV (heat-treated)	[117]
	PBF-EB	WC-13%Co	H = 915–970 HV (as-built)	[118]
	BJT	WC-12%Co	H = 1050–1306 HV (heat-treated)	[119,120,121,122]
		WC-10%Co	H = 1119 HV (heat-treated)	[119]
	Slurry-based three-dimensional printing (3DP)	WC-10%Co	No information	[123]
Ceramics	Conventional sintered	ZTA	H = 1799 HV (heat-treated)	[124]
	VPP	ZTA	H = 1833 HV; σ = 779 MPa (heat-treated)	[124]
		SiAlON	No information	[104]

Table 3. Suitable materials for the application in additively manufactured cutting tool substrates (σ: flexural strength).

Material	AM Process	Alloy	Properties	Ref.
HSS	Conventional PM steel	ASP2030 (HS6-5-3-8, 1.3244)	H = 990 HV (heat-treated)	[105]
	PBF-LB	M50 (80MoCrV42-16, 1.3551)	H = 789 HV (as-built); H = 803 HV (heat-treated)	[107,109]
		M2 (HS-6-5-2C, 1.3343)	H = 640 HV; Rm = 1300 MPa (as-built)	[106,108]
		ASP2030 (HS6-5-3-8, 1.3244)	H = 654–817 HV (as-built); H = 991 HV (heat-treated)	[110,113]
	DED	HS11-2-5-8 (S390PM)	H = 791–825 HV (as-built)	[114]
WC-Co	Conventional sintered	WC-10%Co	H = 1450–1590 HV (heat-treated)	[115]
	PBF-LB	WC-18%Co	H = 820–840 HV (as-built)	[116]
		WC-17%Co	H = 584–663 HV (as-built); H = 900–1050 HV (heat-treated)	[112] [102]
		WC-12%Co	H = 863 HV (as-built); H = 1086–1106 HV (heat-treated)	[117]
	PBF-EB	WC-13%Co	H = 915–970 HV (as-built)	[118]
	BJT	WC-12%Co	H = 1050–1306 HV (heat-treated)	[119,120,121,122]
		WC-10%Co	H = 1119 HV (heat-treated)	[119]
	Slurry-based three-dimensional printing (3DP)	WC-10%Co	No information	[123]
Ceramics	Conventional sintered	ZTA	H = 1799 HV (heat-treated)	[124]
	VPP	ZTA	H = 1833 HV; σ = 779 MPa (heat-treated)	[124]
		SiAlON	No information	[104]

Processing tungsten carbide in PBF-LB is challenging due to the material’s high melting point and its tendency to crack formation, which requires preheating temperatures of up to 1000 °C. [112]. Additionally, brittle η-phases can form due to local carbon and cobalt evaporation [102,125,126]. Currently, AM WC-based parts exhibit lower strength and hardness compared to conventionally manufactured parts. Initial attempts at PBF-LB manufacturing of tungsten carbide cutting tools have been made in various areas. Fortunato et al. examined a scudding tool for gear manufacturing made from W5C17Co powder. The tool withstood the applied loads but exhibited weak strength and hardness [127]. Schwanekamp PBF-LB-processed WC-Co 83/17 with an 800 °C preheating temperature to manufacture cutting inserts for turning operations [128]. The performance in turning AlCuMgPb was comparable to conventional inserts of the same composition. However, small defects on the cutting wedge surface led to adhesive wear progression. In turning 42CrMo4, significant wear occurred in the AM test sample. Lower cobalt contents led to a porous microstructure and a substantial reduction in performance [102,128,129]. Several other investigations on PBF-LB processing of WC-Co have been conducted, most of which were with a cobalt content of 17% or higher [103,116,130,131].

An alternative and promising AM technique for processing hard and difficult-to-weld materials is BJT, which has a process characteristic close to conventional powder-metallurgy and offers easier process stability [132,133]. This process is employed by the tool manufacturer Kennametal Inc. [134]. Coarser grain structures greater than 2.5 µm, with cobalt contents as low as 10%, have been successfully processed. Alternative cemented carbides, such as cermets (cemented carbides based on titanium carbide and titanium nitride with a nickel and cobalt binder phase), have been processed using various AM techniques, including PBF-LB, selective laser sintering (SLS), DED, fused filament fabrication (FFF), BJT, and others [3,135].

AM of ceramic materials for cutting tools has been successfully applied in VPP processes [136,137,138,139]. Weigold et al. manufactured SiAlON ceramic cutting inserts via VPP for turning cast iron GJV-45 [104]. Although the geometrical accuracy of the AM inserts was not as precise as that of conventional inserts, the tools showed a comparable cutting force and tool wear. Liu et al. processed zirconia-toughened alumina (ZTA) ceramic to include a chip-breaking geometry into a cutting insert [124]. In turning gray iron GJL-250, tool wear and surface roughness were reduced compared to conventional tools of the same geometry.

In addition to PBF-LB, BJT, and VPP, other adapted AM techniques have also shown promise for cutting tool applications. Kernan et al. used slurry-based three-dimensional printing (3DP) to manufacture CNMG cutting inserts with chip-breaking geometry and a 10% Co-content [123]. After sintering and sinter-HIP, the relative density was nearly 100%. No performance tests were conducted. Traxel et al. deposited Co-Cr-W superalloy structures on a stainless-steel substrate via DED, creating cutting inserts for machining SS304L [140]. The company VBN Components developed a hybrid carbide material, WC-Cr3C2-CoCr, with high thermal and wear resistance, for processing in both EBM as well as PBF-B [141].

This review establishes that the AM of cutting substrate materials is still in its developmental stage. The most promising AM techniques for processing tungsten carbide alloys are PBF-LB and BJT. These techniques can achieve defect-free and dense builds of samples. For the processing of complex geometries necessary for the near-net-shape of internal and external structures in cutting tools—such as chip chambers in end mills, cutting inserts with textured surfaces, complex chip-breaker geometries, or cutting fluid supply channels—defect-free fabrication that prevents crack formation is essential. The application of tungsten carbide cutting tools in the machining of steel alloys and difficult-to-cut materials, such as titanium or nickel-based alloys, requires a defined grain size and cobalt content. Fine and submicron grain tungsten carbides, with grain sizes ranging from 0.2 to 1.3 µm, are beneficial in applications where high toughness, wear resistance, hardness, and strength of the cutting edge are required, particularly in milling operations [3,115]. Typically, cutting tools contain cobalt in proportions between 5% and 15%, balancing high wear resistance with high toughness [3,142]. For milling difficult-to-cut materials, the cobalt content is usually below 10%. However, AM processes have primarily been successful with Co-contents above 10%, necessitating a reduction to enable the use of these tools in a wide range of machining applications. Higher cobalt contents and coarser grain structures remain of interest for specific applications, such as rock milling. In summary, while significant progress has been made in the AM of cutting substrate materials, further research is needed to refine these techniques and compositions to fully meet the requirements of industrial applications.

3. Potentials of Additive Manufacturing for Improved Tool Functionalities

Even though metal tooling comprises only 4% of overall AM applications (see Figure 2), it offers a variety of potential benefits for cutting tools. As discussed in the previous section, numerous materials applicable to tool carriers, as well as tool substrates, have been proven to be processable. The general advantages of AM, including the ability to create complex and lightweight designs and to individualize tools, allow for a wide range of functional improvements in existing tool types as well as new developments. For the literature review, keywords such as “AM cutting tool”, “PBF-LB cutting tool”, “AM coolant channel”, “AM damping”, and others were searched across standard databases and search engines, including Google Scholar, ResearchGate, ScienceDirect, and SpringerLink. Reviewing the state-of-the-art, four main potentials for improved functionality in AM cutting tools can be identified. These include cooling and cutting fluid supply, damping and vibrational behavior, lightweight design and topology optimization, and functional integration, as depicted in Figure 4, which will be discussed in the following sections.

3.1. Potentials for Improved Cooling and Cutting Fluid Supply

Irrespective of the machining process, cutting fluids (also called metalworking fluid (MWF) or lubricoolant) have two essential functions. Their cooling capability ensures the removal of heat from the contact zone of the cutting process, reducing temperatures in the tool, the workpiece, and, to a limited extent, the structure of the machine tool. Their lubricating effect in the contact zone reduces friction between the tool and the workpiece. Secondary functions include chip evacuation from the machining area, defined chip breakage, improved surface finish, increased machining accuracy through reduced workpiece and machine tool distortion, corrosion protection, and, depending on the fluid’s composition, lubrication of slideways [143,144,145,146].

In challenging machining operations that generate a high amount of heat, cutting fluid is supplied internally through the cutting tool. Supply variants include minimum quantity lubrication (MQL), cryogenic cooling, or high-pressure cutting fluid supply [3,147]. Internal fluid supply improves efficiency and effectiveness as the fluid can be more precisely directed to the areas where it is needed. The fluid is delivered to the cutting zone through internal supply channels and outlet nozzles in the tool holder or through the cutting wedge itself. Thus, the distance between the nozzle and cutting zone is much shorter compared to an external supply, resulting in a more focused free jet with higher dynamic pressure and higher fluid velocity. Chip evacuation and heat dissipation can be improved and the cutting force, as well as tool wear progression, can be reduced [148,149,150]. The different methods of internal cutting fluid supply are summarized in Figure 5. These include supply into the gap between the emerging chip and tool on the rake and/or flank face, supply through the cutting tool itself or through a discharge orifice, supply through textured or porous structures on the rake face, or indirect cooling through a closed cooling circuit.

Exploiting the geometrical freedom of design is one of the greatest potentials for AM cutting tools, enabling the adaptation and improvement of cooling concepts for higher efficiency and effectiveness [152]. Pressure losses within the supply system can be reduced, and the cutting fluid-free jet can be individually adjusted using adapted nozzle geometry, targeting the thermally stressed areas of the cutting edge. Increasing the jet focus can result in augmented local mechanical jet force, thereby improving chip formation or chip breakage [153]. Consequently, the contact area between the chip and tool, and thus the cutting force, can be reduced [154,155,156,157]. Table 4 summarizes the discussed solutions, categorized according to the tool type and workpiece material tested during machining. Examples of AM cutting tools with an adapted cutting fluid supply are shown in Figure 6.

Table 4. Adapted cooling and cutting fluid supply in PBF-LB cutting tools.

Tool Type	Workpiece Material	Ref.	Main Findings
Turning tool holder	CGI-450	[158,159,160]	Integration of dual nozzle geometries for CO2-snow supply, design of a Ranque–Hilsch vortex tube for cold air generation, higher cooling rate
	CGI-250	[161]	Improved wetting of cutting edge due to large amount of small outlet nozzles (diameter d = 0.25 mm); comparable cutting forces to conventional tool
	Ti-6Al-4V	[162]	Combination of MQL and LN2 cooling in PBF-LB-manufactured grooving tool, increase in tool life and productivity due to improved and combined cooling of rake face and major and minor flank face
	Ti-6Al-4V	[163]	Internally cooled turning tool holder with copper heat sink; combination of external cutting fluid supply and internal cooling reduced overall ecological impact
	-	[164,165,166,167]	Grooving tool with combined cooling of rake face and major and minor flank face
Indexable milling tool	42CrMo4 + QT	[168]	Single-row milling tool with rake face cooling as a combination of L-shaped and round nozzles; tool life increase of 67%
	Ti-6Al-4V	[169]	Single-row milling tool with combined cooling of rake and minor flank face with three round nozzles (diameter d = 1.5 mm); no tool life increase
	Ti-6Al-4V	[170]	Life cycle assessment of single-row milling tool with rake face cooling as a combination of L-shaped and round nozzles; tool life increase of 45%
	Ti-6Al-4V	[171]	Helical milling tool with individualized nozzle design (combination of L-shaped and elliptical nozzles directed on rake face); tool life increase of 27%, chip volume reduction of 25%
	-	[172,173]	Side-milling cutter with increased tool life due to improved cooling and lubrication (two nozzles directed towards rake face)
	Ti-6Al-4V	[174]	Single-row milling tool with cooling of major flank face with five round nozzles; 60% increase in tool life
	-	[175]	Tool carrier (material: 1.4404) for PCD inserts with adapted circular channel design; no machining tests
Drilling tool	bone	[176,177]	Internally cooled bone drill (material: 1.4404) with conformal cooling, reduction of temperature in the cutting zone
	-	[178,179,180,181]	Indexable drill with triangular supply channels; reduced pressure losses and increase in conveyed volume flow
Threading tool	42CrMo4 + QT	[105,182]	Thread cutting and forming tools from ASP2030 with adapted nozzle design (elliptical and triangular nozzles)—no significant improvement remained for tool life
Form turning tool	Ti-6Al-4V	[183]	Form turning tool of WC-17%Co with internal cutting fluid supply on rake and flank face (round and elliptical nozzles) without any subsequent post-processing; no catastrophic failure in turning test

Table 4. Adapted cooling and cutting fluid supply in PBF-LB cutting tools.

Tool Type	Workpiece Material	Ref.	Main Findings
Turning tool holder	CGI-450	[158,159,160]	Integration of dual nozzle geometries for CO2-snow supply, design of a Ranque–Hilsch vortex tube for cold air generation, higher cooling rate
	CGI-250	[161]	Improved wetting of cutting edge due to large amount of small outlet nozzles (diameter d = 0.25 mm); comparable cutting forces to conventional tool
	Ti-6Al-4V	[162]	Combination of MQL and LN2 cooling in PBF-LB-manufactured grooving tool, increase in tool life and productivity due to improved and combined cooling of rake face and major and minor flank face
	Ti-6Al-4V	[163]	Internally cooled turning tool holder with copper heat sink; combination of external cutting fluid supply and internal cooling reduced overall ecological impact
	-	[164,165,166,167]	Grooving tool with combined cooling of rake face and major and minor flank face
Indexable milling tool	42CrMo4 + QT	[168]	Single-row milling tool with rake face cooling as a combination of L-shaped and round nozzles; tool life increase of 67%
	Ti-6Al-4V	[169]	Single-row milling tool with combined cooling of rake and minor flank face with three round nozzles (diameter d = 1.5 mm); no tool life increase
	Ti-6Al-4V	[170]	Life cycle assessment of single-row milling tool with rake face cooling as a combination of L-shaped and round nozzles; tool life increase of 45%
	Ti-6Al-4V	[171]	Helical milling tool with individualized nozzle design (combination of L-shaped and elliptical nozzles directed on rake face); tool life increase of 27%, chip volume reduction of 25%
	-	[172,173]	Side-milling cutter with increased tool life due to improved cooling and lubrication (two nozzles directed towards rake face)
	Ti-6Al-4V	[174]	Single-row milling tool with cooling of major flank face with five round nozzles; 60% increase in tool life
	-	[175]	Tool carrier (material: 1.4404) for PCD inserts with adapted circular channel design; no machining tests
Drilling tool	bone	[176,177]	Internally cooled bone drill (material: 1.4404) with conformal cooling, reduction of temperature in the cutting zone
	-	[178,179,180,181]	Indexable drill with triangular supply channels; reduced pressure losses and increase in conveyed volume flow
Threading tool	42CrMo4 + QT	[105,182]	Thread cutting and forming tools from ASP2030 with adapted nozzle design (elliptical and triangular nozzles)—no significant improvement remained for tool life
Form turning tool	Ti-6Al-4V	[183]	Form turning tool of WC-17%Co with internal cutting fluid supply on rake and flank face (round and elliptical nozzles) without any subsequent post-processing; no catastrophic failure in turning test

Figure 6. Examples of additively manufactured cutting tools with adapted cutting fluid supply: (a) grooving tool with five nozzles (reprinted with permission from Ref. [165]. Karl-Heinz Arnold GmbH), (b) drill with triangular channels (reprinted with permission from Ref. [178]. MAPAL Präzisionswerkzeuge Dr. Kress KG), (c) thread former with elliptical nozzles (developed by EMUGE-Werk Richard Glimpel GmbH & Co. KG and MTI of RWTH Aachen University), (d) side-milling cutter with two nozzles (reprinted with permission from Ref. [173]. Karl-Heinz Arnold GmbH), (e) milling tool with L-shape and round nozzles, and (f) helical milling tool with L-shaped and elliptical nozzles.

Figure 6. Examples of additively manufactured cutting tools with adapted cutting fluid supply: (a) grooving tool with five nozzles (reprinted with permission from Ref. [165]. Karl-Heinz Arnold GmbH), (b) drill with triangular channels (reprinted with permission from Ref. [178]. MAPAL Präzisionswerkzeuge Dr. Kress KG), (c) thread former with elliptical nozzles (developed by EMUGE-Werk Richard Glimpel GmbH & Co. KG and MTI of RWTH Aachen University), (d) side-milling cutter with two nozzles (reprinted with permission from Ref. [173]. Karl-Heinz Arnold GmbH), (e) milling tool with L-shape and round nozzles, and (f) helical milling tool with L-shaped and elliptical nozzles.

Lakner et al. transferred their findings on workpiece material-dependent cutting fluid supply strategies to PBF-LB-manufactured milling tool carriers made from tool steel 1.2709. These tools featured adapted nozzle geometries specifically designed for cutting 42CrMo4 + QT (see Figure 6e) and Ti-6Al-4V ($D$ = 63 mm, $z$ = 6). In roughing 42CrMo4 + QT, the tool life increased by up to 67%. However, no improvements were detected in the machining of Ti-6Al-4V [151,168,169].

Kelliger et al. developed single and multi-row indexable milling tools with adapted channel and nozzle designs for roughing Ti-6Al-4V; see Figure 6f. The tool carriers were PBF-LB manufactured from low-alloy case hardening steel 18MnCrMoV4-8-7. The comparison between conventional and AM manufacturing routes revealed no measurable differences in the performance behavior of the tools. However, due to the adapted cutting fluid supply, the tool life increased by 27–45%. In a life cycle assessment, the sustainability of the PBF-LB-manufactured tool, compared to the conventional tool, was confirmed with a 15% reduction in the total CO₂-equivalent. Abrasive flow machining (AFM) of the internal channels increased the conveyed volume flow rate at a given supply pressure but led to an undefined widening of the cross-sectional geometry [101,170,171,184].

Heep developed PBF-LB-manufactured turning tool holders (SCLNL-2020/PCLNL-2020/CLNL-2020) from austenitic stainless steel 316L (X2CrNiMo17-12-2, 1.4404) with different cooling channel and supply designs for turning cast iron GJV-450. The geometrical freedom of AM allowed the creation of a two-substance nozzle in combination with a Ranque–Hilsch vortex tube for cold air generation in combination with cryogenic CO₂-cooling with channel diameters between 0.7–1 mm. This channel arrangement separated the gas flow into hot and cold streams. A comparison to conventional CO₂-cooling in turning experiments was not provided [158,159,160].

Abele et al. modified a multifunctional drilling and turning tool, Ceratizit EcoCut, to enhance the cutting fluid supply. The tool was PBF-LB-manufactured by stainless steel powder X5CrNiCuNb16-4 (1.4542) with channel diameters of 0.25 mm for an extensive and homogenous fluid distribution. Due to the implementation of the channels and the change in material compared to the conventional reference tool, the static stiffness was reduced by approximately 21%. The tool was tested in turning cast iron CGI-250 with tungsten carbide cutting inserts, resulting in comparable cutting forces. No tool life tests were performed [161].

Grooving tool holders from 1.2709 tool steel, specifically designed for emulsion cooling, cryogenic cooling, and MQL, were PBF-LB-manufactured and tested by Lubkowitz et al. By adapting the channel and nozzle designs, two different cooling mediums could be supplied simultaneously, with an additional nozzle on the flank face cooling the corner of the cutting edge. Combining emulsion and MQL increased process productivity and reduced tool wear [162].

Kelliger et al. developed M10 threading tools for thread cutting and forming with an adapted cutting fluid supply; see Figure 6c. The tools were PBF-LB-manufactured from HSS ASP2030 powder and tested on 42CrMo4 + QT (1.7225) and X5CrNi18-10 (1.4301) for manufacturing through-hole and blind-hole threads and were compared to conventionally manufactured tools of the same HSS substrate. The adapted cutting fluid supply with elliptical nozzles enabled a more homogenous and wide-spread fluid distribution along the cutting edge. However, no significant variations in friction conditions or tool life were detected [105,182].

Denkena et al. presented a PBF-LB-manufactured 6 mm bone drill made from 316L stainless steel [176,177]. A helical cooling channel, with a diameter of 1.6 mm near the cutting edge, allowed a conformal cooling of the tool with a closed water-cooling circuit, lowering the temperatures in the cutting zone compared to the conventional reference tool and preventing damage to the cell tissue. Ward et al. tested a PBF-LB-manufactured internally cooled turning tool holder containing an additional heat sink made of copper alloy [163].

Beyond scientific exploration, product-mature AM cutting tools with an adapted cutting fluid supply have been introduced in the past years, some featuring patented engineering solutions. Since 2014, Mapal, Aalen, Germany has offered indexable drilling tools with diameters between 8–13 mm, incorporating triangular channels following the helix course; see Figure 6b [178,179,180,181]. This design increased the volume flow by 100% compared to a conventionally manufactured tool. The AM tool, made from 1.2709 tool steel, is printed on a conventional preform. Rosswag, Pfinztal, Germany patented an AM indexable side-milling cutter with an adapted channel design; see Figure 6d [172,173]. According to the company, the tool achieved a 50% longer tool life compared to the conventional tool. Arno Werkzeuge, Ostfildern, Germany offers a patented grooving tool with four cutting fluid supply directions; see Figure 6a [164,165,166,167]. The triangular nozzles are directed toward the rake face, the flank face, and the side faces of the insert. Similar tools with an adapted fluid supply are available for Swiss-type automatic lathes [185]. Furthermore, the company introduced a hybrid turning tool holder with an AM head that allows for an adapted cutting fluid supply. According to the company, the tool life was increased by 100% compared to the conventional tool with an internal cutting fluid supply [164]. Iscar, Migdal Tefen, Israel sells a PBF-LB-manufactured indexable milling tool with an adapted cutting fluid supply, which is optimized through computational fluid dynamic (CFD) simulations [186]. Ceratizit, Mamer, Luxemburg presented a PBF-LB indexable milling tool with flank face cooling for machining Ti-6Al-4V, claiming a 60% higher service life compared to a standard tool [174]. Further examples were introduced by companies such as Neher Group, Ostrach, Germany [187], Hartmetall-Werkzeugfabrik Paul Horn, Tübingen, Germany [188,189], and Seco Tools, Erkrath, Germany [190]. Kennametal, Pittsburgh, PA, USA holds patents on AM cutting tools, including indexable tool carriers with triangular channel cross-sections [191] and indexable cutting tools with porous or grid-like core structures for reducing weight and transporting coolant [192].

The review highlights the significant potential of AM to enhance the design of internal cutting fluid supplies in cutting tools. The geometrical freedom afforded by AM enables innovative design concepts that reduce flow losses and improve the targeting of cutting fluid to thermally stressed areas of the tool. An optimal cutting fluid supply design is highly dependent on the workpiece material, cutting parameters, and the resulting thermo-mechanical load on the tool. Consequently, the individualized design of the nozzle size, number, arrangement, and orientation has been shown to extend tool life and increase productivity through higher cutting speeds or feed per tooth [193,194]. Significant improvements have been demonstrated, particularly in turning and milling applications, as well as in more specialized processes such as form turning. Tool carriers made from steel alloys exhibit considerable potential in these applications. However, for drilling and threading, the improvements are relatively modest, making it challenging to justify the additional costs associated with AM. To date, the benefits of enhanced cutting fluid supply design have been proven for only a few materials, notably Ti-6Al-4V, cast iron, and quenched and tempered steel. The potential for turning and milling tools in other difficult-to-cut materials, such as nickel-based alloys, still needs to be assessed. The results indicate that the degree of improvement varies significantly depending on the workpiece material, ranging from no improvement to an increase in tool life of up to 70%. Previous designs have been mainly tested empirically, without systematic variations and assessments of different geometrical characteristics of channels and nozzles, such as geometry, orientation, and alignment. For the optimal individualized design that considers economic and ecological factors, including manufacturing costs, energy consumption, tool wear, and productivity, a holistic model is required. Such a model would enable efficient and reliable prediction of the effectiveness and efficiency of a cutting fluid supply design variant during the design phase, reducing experimental efforts while considering the specific boundary conditions of the process.

3.2. Potentials for Improved Damping and Vibrational Behaviors

Process vibrations can limit productivity and reliability during machining, particularly in turning and milling. Restrictions in the choice of process parameters, such as unintended chattering, can arise, especially in tools with long overhangs due to insufficient dynamic stiffness [195]. Measures for damping include passive systems (which do not require external energy), semi-active systems, and active systems that convert external energy into a mechanical force based on the supplied energy [196]. Passive systems, in particular, hold potential for AM cutting tools as they can be internally integrated without the need for additional electronics. As depicted in Figure 7, AM processes enable the manufacturing of damped components using either the principle of particle damping or structural damping [197]. In particle damping, energy dissipation occurs due to the inelastic collisions and friction between powder particles [198,199]. Structural damping, on the other hand, is achieved through geometry or material modifications. Improved damping characteristics can be realized through customized lattice structures [200]. Additionally, porous or graded materials can alter the mechanical properties of a component, thus enhancing its damping characteristics [201].

Vogel et al. investigated structured, particle-filled tool holders for turning and milling with passive damping characteristics, resulting in an adapted vibration behavior that increased productivity and quality; see Figure 7 [204]. A PBF-LB-shrink-fit chuck was manufactured from 1.2709 powder on a conventional HSK-63A preform. The AM structure contained four internal cavities, each half-filled with WC-ZrO₂ powder (particle diameter 0.4–0.6 mm). During the milling of Al7075 with a two-teeth 10 mm diameter end mill, the critical depth of cut could be increased by 12.5% compared to the conventional reference shrink-fit chuck. A similar result was obtained with hollow turning tool holders made from 1.2709 in turning Ti-6Al-4V [202,205,206]. The cavity contained an integrated structure with ellipsoidal hollow elements. When half-filled with WC-ZrO₂ powder, the natural frequencies were shifted and reduced in amplitude by more than 80% in both feed and cutting directions. However, fully filled cavities, with or without internal element structures, exhibited a lower damping capability attributed to the combination of particle friction and elastic collision between the particles and the internal structure. These findings were applied to an AM hydraulic chuck, where powder-filled grid structures were arranged near the largest vibration amplitude at the tool center point. When milling high-strength EN AW-7075 aluminum, the critical cutting depth was increased by 146% [203].

Iscar, Migdal Tefen, Israel presented a PBF-LB-manufactured groove turning tool with internal damping [207]. Compared to state-of-the-art damped tool holders, this design eliminates the need for additional assembly and is intended to be less expensive. The chatter-free depth of cut was significantly increased compared to a non-damped tool holder of the same geometry. Kennametal, Pittsburgh, PA, USA patented lightweight cutting tools with integrated lattice or honeycomb structures [208], while Siemens, München, Germany holds several patents on AM components featuring particle-filled internal structures and components with adapted moments of inertia and/or coolant absorption [209,210].

The potential for improved damping behavior through AM design has not yet been fully exploited. Similar to the enhancements in cutting fluid supply, the benefits of improved damping are highly dependent on the specific process boundary conditions. It is crucial to assess the costs of AM-based damping solutions compared to conventional damping methods to validate their advantages. Fundamental scientific research could further investigate the possibilities of vibration-absorbing AM structures. Combining damping functionalities with other functions, such as cutting fluid supply or the integration of active damping elements within the structure, could enhance the industrial benefits and expand the versatility of AM tool or tool holder applications across various machining operations and workpiece materials. Further testing on other high-interest workpiece materials is necessary. Improved damping behavior is particularly beneficial in machining scenarios involving long overhangs, such as those found in die-and-mold or e-mobility applications with steel and aluminum, and the production of aircraft structural components from titanium.

3.3. Potentials for Lightweight Design and Topology Optimization

Lightweight cutting tools reduce the moving mass, which in turn lowers energy consumption during machining. Reducing the mass, particularly in the outer area of a rotating tool, can enable higher cutting speeds while maintaining constant vibration tendencies, thereby increasing productivity without compromising surface quality [211,212]. Examples of AM lightweight tools are shown in Figure 8.

Abele and Scherer developed a method for PBF-LB-manufactured structure-optimized indexable cutting tools [213,214]. Their optimization of an indexable milling tool for roughing aluminum AlSi11 achieved a 27% reduction in weight. The tool was hybrid manufactured using a conventional preform, which reduced the manufacturing time by 32% compared to a fully additive design.

Hanzl et al. presented a finite element method (FEM) analysis for a lightweight milling tool incorporating lattice structures [215]. By implementing a cluster-arranged body-centered cubic lattice structure within the inner volume of a six-tooth indexable milling tool ($D$ = 125 mm), natural frequencies were lowered by 33% compared to the solid structure. However, the lattice-structured tool exhibited a lower stiffness and greater deformation. The tool, manufactured in PBF-LB from 1.2709 tool steel, was tested in milling nickel-based alloy Inconel 718. The expected improvements in lightweight design could not be verified in the experiment [216].

Uhlmann et al. used topology optimization to redesign a six-edge indexable milling tool, reducing its total weight by 29%, with only a slight decrease in torsion strength [217]. Fürstmann designed and tested a structure-optimized turning tool holder with a closed cooling circuit and manufactured using PBF-LB [218,219].

Several lightweight AM cutting tools have been introduced in the context of electric mobility component production [220]. Lightweight construction was utilized in the design of a PBF-LB-manufactured multistage boring tool for stator bores by Ceratizit, Mamer, Luxemburg, reducing the total tool weight to 17 kg [221]. Kennametal, Pittsburgh, PA, USA presented various integrated design concepts for a similar tool, combining carbon fiber with PBF-LB-manufactured parts to achieve a total tool weight of 7.3 kg; Figure 8a [23,222]. The tool is used in automotive production. Mapal, Aalen, Germany offers a hybrid manufactured bell tool for external machining, featuring a conventional HSK-63 tool holder and a PBF-LB-manufactured head with soldered PCD cutting inserts [223].

Figure 8. Examples of additively manufactured cutting tools with lightweight structures: (a) multistage boring tool for e-mobility applications (reprinted with permission from Ref. [222]. Kennametal Inc.), (b) reamer with integrated lattice structure (reprinted with permission from Ref. [224]. MAPAL Präzisionswerkzeuge Dr. Kress KG), (c) turning tool holder with closed cooling circuit (data from [218]), and (d) indexable milling tool (reprinted with permission from Ref. [91]. Iscar Ltd.).

Figure 8. Examples of additively manufactured cutting tools with lightweight structures: (a) multistage boring tool for e-mobility applications (reprinted with permission from Ref. [222]. Kennametal Inc.), (b) reamer with integrated lattice structure (reprinted with permission from Ref. [224]. MAPAL Präzisionswerkzeuge Dr. Kress KG), (c) turning tool holder with closed cooling circuit (data from [218]), and (d) indexable milling tool (reprinted with permission from Ref. [91]. Iscar Ltd.).

PBF-LB manufacturing of a reamer with an internal lattice structure allowed a reduction of weight from 390 g to 172 g, enabling an increase in cutting speed and productivity in use due to lower inertia; Figure 8b [224]. The higher manufacturing costs were offset by improved process reliability during use [225]. Iscar, Migdal Tefen, Israel introduced a lightweight PBF-LB-manufactured indexable milling tool, HELI2000, made from titanium alloy, which increases tool stability, particularly in long-reach deep cavities; Figure 8d [91]. Sandvik Coromant, Sandviken, Sweden introduced a similar development with the CoroMill 390 cutter [92]. Rolls-Royce, Blankenfelde-Mahlow, Germany holds a patent for PBF-LB-manufactured tool carriers with an optimized cutting fluid supply, lightweight design, and damping features that are achieved through topology optimization, as well as loose powder particles that remain in closed cavities [226].

Based on the review, the potential for lightweight AM cutting tools is assessed as high. AM enables the fabrication of topology-optimized structures that are unachievable with conventional manufacturing techniques. These optimized structures can significantly reduce weight while maintaining or even enhancing the mechanical properties and performance of the tools. However, weight optimization in cutting tools is generally reasonable only for specific applications rather than for general use. Lightweight cutting tools are of particular interest in scenarios involving high-moving masses, such as rotating tools with large diameters. Reducing the tool’s weight can lead to significant improvements in dynamic performance, reducing inertia and enhancing speed and precision. Despite the promising potential, extensive use cases of lightweight AM cutting tools are still limited, indicating that their application remains specialized and tailored to specific needs.

3.4. Potentials for Functional Integration

Another potential of AM cutting tools is the integration of additional or improved functions. These may involve additional geometrical features, as well as the integration of sensors and electronics into the tool’s structure, with examples shown in Figure 9.

Mapal, Aalen, Germany offers a hydraulic chuck with a conventional tool holder and PBF-LB-manufactured functional area, including the expansion sleeve; Figure 9d [178,227]. By replacing soldered junctions with an integrated AM shaft, the maximum operating temperature could be significantly increased to 170 °C. Komet, Mamer, Luxemburg developed a hybrid PBF-LB-manufactured screw-in indexable milling tool from 1.2709 tool steel for PCD inserts; Figure 9a [228]. Through redesigning the axis angle and chip flutes, the number of teeth, and thus the productivity, was increased by up to 42%. Gühring, Albstadt, Germany equipped a PCD face milling tool for machining aluminum components with an AM chip-guiding element to prevent chips from hitting the machined surface [229].

Figure 9. Examples of additively manufactured cutting tools with additional integrated functions: (a) Indexable milling tool with PCD inserts (reprinted with permission from [228]. Ceratizit S.A.), (b) sensor-integrated milling head (reprinted with permission from [230]. Fraunhofer Institute for Laser Technology), and (c) hydraulic chuck (reprinted with permission from [178]. MAPAL Präzisionswerkzeuge Dr. Kress KG).

Figure 9. Examples of additively manufactured cutting tools with additional integrated functions: (a) Indexable milling tool with PCD inserts (reprinted with permission from [228]. Ceratizit S.A.), (b) sensor-integrated milling head (reprinted with permission from [230]. Fraunhofer Institute for Laser Technology), and (c) hydraulic chuck (reprinted with permission from [178]. MAPAL Präzisionswerkzeuge Dr. Kress KG).

As shown in Figure 4, additional equipment can be internally integrated with AM components; for example, by interrupting the process and removing the powder from the intended cavity. Initial successful attempts to integrate thermocouples, strain gauges, or piezo actuators into PBF-LB components suggest future applications for cutting tools in process monitoring and control; Figure 9c [231,232,233,234,235,236]. However, no experimental validation of integrated electronics in AM cutting tools has been presented yet. Multi-material AM allows for the integration of sensors into cutting tools, such as embedded thermocouples, to measure temperatures in the contact zone [237,238,239].

The potential for functional integration in AM cutting tools remains highly individualized. Integrating electronics into tools via internal cavities or printed sensors can provide valuable insights into the cutting process. For example, temperature sensors placed closer to the cutting edge can offer real-time data on thermal conditions. Similarly, acceleration sensors can monitor vibrations, and piezo actuators could be used to actively control and inhibit these vibrations. Monitoring each individual cutting edge of a milling tool can improve maintenance and tool management, preventing failures and optimizing performance. The integration of additional functions in AM tools requires creative research and development efforts.

4. Derived Research Needs for AM Cutting Tools

The presented examples demonstrate the versatile potentials of additive manufacturing for application in cutting tools. Comparing additive to conventional manufacturing techniques, AM often proves to be more expensive, more energy-intensive, and more time-consuming. As post-processing of the AM blank is usually required, it adds additional process steps. Cost reduction can be achieved by improving both the manufacturing process chain and the tool’s use phase. The additional production costs of AM cutting tools can only be justified by improved performance during application. To enable broader acceptance and industrialization of AM cutting tools, it is essential to fully exploit the potential of AM. Based on the review of the state-of-the-art, the following research and development needs are derived:

• Design of the internal cutting fluid supply: The geometrical design of AM cutting tools, particularly regarding the internal cutting fluid supply, often lacks a systematic methodology. CFD simulations can optimize the design for desired fluid flow [240,241]. However, achieving an optimal cutting fluid supply requires a deeper understanding of the relationships between heat generation and dissipation during machining, the cooling and lubrication effect of the supplied cutting fluid, and the resulting tool wear phenomena. Currently, there are no systematic design guidelines for optimizing a cutting fluid supply based on the cutting process, workpiece material, and process parameters while also considering the design possibilities of AM.
• Geometrical tool features: AM techniques such as PBF-LB and BJT allow for the processing of hard materials, such as cemented carbide, applicable for the cutting wedge. Research has primarily focused on developing the AM process rather than on exploring the additional potentials of AM regarding the integration of geometrical structures. These potentials can be harnessed for the individualized, process-specific designs of favorable tool micro-geometry, such as flank face modifications, complex chip-breaking geometries, and textured or porous structures that improve frictional conditions. Integrated channels for enhanced cooling or chip-breaking geometries that do not require subsequent post-processing are also possible. Compared to conventional pressing and sintering, AM offers highly flexible geometrical variations that allow for rapid development and designs tailored to specific machining conditions.
• AM for repair of cutting tools: The feasibility of tool repair has been demonstrated in DED processing of HSS for broaching tools [114]. However, the machining performance of such repaired tools remains unexplored. From a sustainability perspective, AM holds great potential for material savings and extending tool life. Thus far, the entire process chain for AM cutting tool repair has not been fully explored. Future developments could include continuous and automatic acquisitions of local tool wear on each cutting edge, preparation for repair (for example, grinding, blasting, or chemical ablation), AM repair, and post-processing of the cutting edge via grinding and coating.
• Functional integration of sensors and actuators: The manufacturing of complex geometries and new AM process variants allows the integration of electronics such as sensors and actuators [236]. This enables real-time monitoring and control of the cutting process. Compared to existing systems, AM offers advantages regarding the compactness of the integrated electronics, proximity of sensors and actuators to the region of interest, and ease of mounting. Further developments in self-sufficient energy supplies, such as energy harvesting and the printing of electronic components, could lead to a deeper understanding of the cutting process and enable online process control.
• Processable alloys for tool substrate and tool carriers: AM facilitates the processing of new alloys, enabling rapid alloy development. On the one hand, low-cost steel alloys with sufficient mechanical properties can reduce tool costs, especially for tool carriers. The PBF-LB manufacturing of tool carriers should allow their use in the as-build state without the need for heat treatment. On the other hand, in situ alloying or high-entropy alloys could lead to the development of new tool substrates, replacing rare and costly elements like cobalt [11]. AM offers the potential to process new alloy compositions that are not feasible with conventional sintering techniques. Thus, process-specific alloy designs for cutting tool substrates tailored to the process requirements, such as hardness, toughness, and high-temperature strength, are possible.
• Multi-material manufacturing: Multi-material processing is possible with various AM techniques. Combining different materials within a single geometry can offer favorable characteristics such as enhanced heat dissipation, damping behavior, and tool stiffness [242,243,244,245]. For example, a tough, vibration-absorbing core combined with a hard, wear-resistant outer skin could benefit milling tool carriers. Including thin heat-transmitting copper structures in the cutting wedge could enable sensor integration as well as controlled heat dissipation or heat input, either increasing or reducing the cooling of the cutting wedge during machining. This could help reduce alternating thermal loads in interrupted cutting, preventing thermal crack formation in brittle substrate materials [246].
• Increase in AM productivity and efficiency: Improvements in AM processes require innovations in process control and AM machine technology. For PBF-LB, these could include adapted scanning strategies, faster powder deposition, increased laser power, or an increased number of simultaneous lasers, as well as the intelligent use of available build volume [247,248,249,250]. Tool manufacturers aim to print AM tool carriers on conventional preforms, such as with HSK-taper [178,190,222]. This approach reduces build times, eliminates the need for referencing elements for subsequent subtractive post-processing, and limits the AM process to the geometrically complex volume area.
• Holistic economic–ecological assessment: Additional economic and ecological costs of AM can often be compensated in the use phase of the tool due to improved functionality and performance compared to conventionally manufactured tools [251,252]. However, evaluating the lifecycle costs of AM cutting tools across their entire lifecycle—from manufacturing to use—remains challenging. Optimization models can help identify ideal operating points for AM cutting tools with individualized designs, such as those optimized for the cutting fluid supply or damping characteristics. Verifying these improvements can increase the acceptance of AM cutting tools in industrial applications.
• Integrated process chain from AM to post-processing: Reliable and repeatable post-processing of the as-built tool is essential for all functional surfaces through various machining processes. To reduce individual setup efforts in the machine tool, clamping and referencing elements need to be considered during the design phase [253]. The process chain requires continuous referencing of the part in the AM machine as well as in the subsequent machining operation [254,255].
• Application of alternative AM processes: In addition to the established AM processes such as PBF, DED, BJT, and VPP, emerging AM techniques currently under research may become significant for the manufacturing of cutting tools. Tool steels have been successfully processed in low-cost FFF for tool carrier production [256]. Cold-spray AM, a solid-state powder deposition technique, shows potential for depositing steel alloys for tool carriers as well as WC-Co, ceramics, and metal–ceramic composites for tool substrates or coatings [257]. Due to its high deposition rates, flexibility in powder selection, and favorable compressive stress of the as-built part, its application in cutting tool fabrication is plausible [258,259]. However, further research is needed to identify suitable material compositions with optimal performance characteristics during machining and to evaluate the resulting tool properties, particularly in terms of wear resistance and strength.

5. Summary and Outlook

In this paper, state-of-the-art additively manufactured cutting tools were reviewed, and research needs for further industrialization of this innovative tool type were derived. PBF-LB has proven to be particularly important for the manufacturing of tool carriers, and it also allows for the processing of hard materials such as HSS and WC-Co. Additionally, BJT and further developed process variants of VPP enable the processing not only of metal materials but also ceramics. The processability of new material alloys, the geometrical freedom of design, and the possibility for individualization allow for the development of new and adapted concepts for AM cutting tools. The main potentials of AM cutting tools lie in the areas of cooling as well as the cutting fluid supply, damping characteristics, lightweight design, and functional integration, such as internal printed electronics. Compared to conventional manufacturing methods, these improved functionalities have beneficial impacts on tool life, process reliability, machining productivity, and sustainability. The examples summarized in this paper demonstrate the operational readiness of AM cutting tools. The identified research needs provide numerous opportunities to enhance AM cutting tools further and contribute to the industrialization of these promising tool concepts.