Research on Micro-Triangular Pyramid Array-Based Fly-Cutting Technology Using the Orthogonal Test Method

Abstract

The copper mold of the micro-triangular pyramid (MTP) is a key component of MTP plastic film manufacturing, and its optical functional surface comprises micro-triangular pyramid arrays (MTPAs). The edge burrs of MTPAs severely affect the optical properties of MTP plastic film. To solve the problem of excessive edge burr of MTPA machining using the fly-cutting method, the orthogonal experimental method was used to optimize the four influencing factors: fly-cutting speed, feed speed, cutting depth, and cooling mode. The results show that the impact of these influencing factors on surface roughness, the projected area of the exit edge burr, and exit edge burr thickness are ranked from largest to the smallest as follows: fly-cutting speed, feed speed, cutting depth, and cooling mode. The factors affecting tool nose wear in descending order are fly-cutting speed, feed speed, cooling mode, and cutting depth. The optimal conditions for minimizing the thickness of the edge burr were a fly-cutting speed of 7.85 m/s, a feed speed of 50 mm/min, a finishing cutting depth of 15 μm, and using compressed air with oil mist for cooling. This study lays a foundation for improving the anti-reflection performance of MTP plastic film.

1. Introduction

As green energy is attracting considerable attention, solar panels with higher energy conversion efficiency are increasingly required [1]. Covering the solar panel substrate with a layer of micro-triangular pyramid (MTP) films can effectively improve its anti-reflective performance [2,3,4]. While the copper mold is the critical component for MTP film fabrication [5], its functional surface comprises micro-triangular pyramid arrays (MTPAs) (Figure 1a,b). Therefore, the surface quality of MTPAs determines the anti-reflective effect of MTP films. The main cutting methods for MTPAs are fly cutting [6,7], ultrasonic cutting [8,9,10], grinding [11], diamond micro-chiseling [12], and planing [13]. Among these methods, the fly-cutting method is widely used because of its fast cutting speed, small cutting force, small cutting deformation, and high surface quality of the machined MTPAs [14].

Researchers have conducted numerous studies on MTP processing using the fly-cutting method. Dong et al. studied the micro-structured arrays after fly-cutting processing. They found that the processed MTPAs had a clear structure and good surface quality, and some of the edges had burrs [15,16]. The edge burr significantly affects the surface quality of MTPAs. Thus, the removal of the edge burr is vital. Huang et al. found that recutting along the previous tool path effectively removed the edge burrs of MTPAs. However, repetitive positioning errors in the machine tool during repeated cutting led to tool deflection and tool nose wear [17,18]. Fu et al. removed burrs using ultrasonic cleaning. However, the material surface exhibited varying degrees of damage [19,20]. Therefore, removing burrs from the edges of MTPAs remains challenging. To improve the anti-reflective properties of MTP films, researching the edge burr removal process without reducing the surface quality of MTPAs is imperative.

Accurate characterization of edge burrs is the basis for burr removal. Researchers have conducted numerous constructive works on characterization methods for microstructural edge burrs. Qiao et al. used the height of the micro-burr as an evaluation index to optimize cutting parameters [21,22]. Medeossi et al. [23] measured the width of a micro-burr using optical scanning methods and used it as an evaluation index to optimize the cutting scheme. Sharan et al. used image processing methods to extract the projected area of burrs [24], which was used to evaluate the burr removal rate. Li et al. [25] used the unit-length-volume method of the V-groove edge burr to improve the accuracy of burr characterization to a certain extent. MTPA edge burrs are rollover burrs, making it challenging to characterize the thickness of curly burrs. Therefore, the characterization method needs to be further improved (Figure 1c,d). The smaller the thickness of the edge burr, the easier it is to break and fall off [26,27]. Hence, the characterization of the thickness of the edge burr is essential.

Figure 1. The effect of edge burrs on the energy conversion efficiency of high-performance solar panels. (a) Process of micro-triangular pyramid (MTP) thin film fabrication. (b) Structure of solar panels with high anti-reflection performance. (c) Micro-triangular pyramid arrays (MTPAs) are processed using the fly-cutting method observed using a scanning electron microscope (SEM) [28]. (d) An enlarged view of the crimped burr of the yellow dashed line area in (c).

Figure 1. The effect of edge burrs on the energy conversion efficiency of high-performance solar panels. (a) Process of micro-triangular pyramid (MTP) thin film fabrication. (b) Structure of solar panels with high anti-reflection performance. (c) Micro-triangular pyramid arrays (MTPAs) are processed using the fly-cutting method observed using a scanning electron microscope (SEM) [28]. (d) An enlarged view of the crimped burr of the yellow dashed line area in (c).

This study used the orthogonal experimental method to optimize the fly-cutting process of MTPAs, aiming to improve surface quality and reduce edge burrs. The four influencing factors, namely, fly-cutting speed, feed speed, cutting depth, and cooling method, were optimized using an orthogonal experimental method focusing on surface roughness, edge burr thickness, edge burr projection area, and tool nose wear as evaluation indexes. The range method was used to process the results of the orthogonal experiment to determine the optimal level of each influencing factor. In addition, the edge burr was characterized using the dual parameters of edge burr thickness and projected area. To prevent the contamination of the MTPA surface by inclusions in the circulating cutting fluid, reduce production costs and energy consumption, and improve operator safety, in this study, minimum quantity lubrication (MQL) was used for cooling and lubrication during fly cutting [29,30,31]. The working surface was vertically fixed to facilitate the dislodgement of micro-scraps and to prevent micro-scraps from scratching the surface of the workpiece. The influencing factors affecting the surface quality and burr residue of MTPAs were investigated, providing a basis for low burr residue and a high surface quality MTPA fly-cutting process.

2. Materials and Methods

2.1. Experimental Platform and Materials

A WN-5V250 five-axis machine (Weino, Putian, China) was used for the experiment. The machine controls the relative positions of the tool and the workpiece through three moving axes and two rotary axes in concert, while the machine spindle drives the inserts to rotate rapidly, enabling the MTPA fly-cutting machining (Figure 2b). The three linear axes have a resolution of 0.1 μm, the rotary axis (A) has a resolution of 0.001°, and the rotary diameter of the fly cutter disc is 100 mm. The air vortex generated by the rapid rotation of the fly cutter assembly caused some of the micro-scraps to re-adhere to the surface of the workpiece, and a suction device was installed to accelerate the fall of the micro-scraps. In addition, to prevent thermal deformation of the workpiece material and the machine tool, the cutting environment temperature was maintained at 25 ± 0.2 °C using an air-conditioning cooling system. Previous experiments have confirmed that the experimental platform can process 100-micron-level MTPAs [28] (Figure 1c).

The workpiece was 30 mm × 30 mm brass bar material grade C28000 (Tongyuan, Dongguan, China). Optical emissions spectrometer (OES) (SpectroMAXx BT) (Soectro, Kleve, German) measurements showed a Cu content of 61.16% and a Zn content of 37.96%, indicating that the chemical compositions met the requirements of the ASTMB36/B36M-23 standard [32]. Considering that the workpiece is easy to clamp, the workpiece was designed as a stepped bar, with a large section and small end diameter of 30 mm and 10 mm, respectively. The large end was mainly used for clamping, while the small end was used for machining (Figure 2b).

2.2. MTPA and Tool Design Parameters

The MTPA consists of MTP units of the same size. The three sides of the MTP are isosceles right triangles, the base is equilateral triangles, and the height (a) of the base triangle is 100 μm (Figure 1c). The geometric parameters of the MTP can be obtained from Equations (1)–(5), as shown in the green font in Figure 2a.

$$a=\sqrt{3}l/2,$$

(1)

$$b=\sqrt{2}l/2,$$

(2)

$$\delta =\mathrm{a}\mathrm{r}\mathrm{c}\mathrm{s}\mathrm{i}\mathrm{n}(b/a),$$

(3)

$$H=b·cos\delta ,$$

(4)

$$\beta =\pi -2\delta ,$$

(5)

where l is the length of the bottom side of the MTP, a is the height of the bottom side, b is the length of the edges, H is the total height of the MTP, δ is the angle between the side and the bottom, and β is the angle relative to the side.

A single crystal diamond tool was welded to a standard-type SEHT1204 [33] fly cutter according to the geometry of the MTP. Because of the use of forming method processing, the diamond tool was a molding cutter. The two cutting edges of the diamond tool were symmetrically distributed. The angle β was 70.5°, the rake angle of the tool γ₀ was 0°, the back angle α₀ was 10°, the radius of the tool nose arc r₀ was 1 μm, and the radius of the cutting edge arc r₁ was 0.5 μm, as shown in the blue font in Figure 2a.

2.3. Orthogonal Experimental Design

2.3.1. Orthogonal Experimental Factor Levels

MTPAs’ surface roughness and burr residue are not only related to the machine tool but also the cutting process and cooling method. The cutting process includes fly-cutting speed, feed speed, cutting depth, and the three related cutting elements. The MTP fly cutting in this study consisted of roughing and finishing. The primary purpose of roughing is to remove a large amount of material, and finishing is to ensure the quality of the workpiece. When roughing, the fly-cutting speed was 3.66 m/s, the feed speed was 70 mm/min, the cutting depth was 40 μm, and the cooling method was compressed air. The cutting process of this study was directed towards the finish machining. Both roughing and finishing cutting trajectories were the same, and their cutting trajectories are shown in Figure 3.

The cooling method is essential for the fly-cutting method because of the high cutting speed and the amount of heat generated. The inclusions in the circulating coolant might contaminate the surface of the MTPA. Thus, compressed air containing a cooling medium (ethanol and cooling oil) was used for cooling during fly cutting (Figure 4). Among the cooling methods, ethanol had an excellent cooling effect, preventing the diamond tool from burning due to the cutting heat. The cooling oil has a good lubrication effect, which can prevent the machining of sticky tools. Uniform, pure compressed air cooling was used, and the cost was low. Therefore, choosing the best cooling method among pure compressed air, compressed air containing ethanol, and compressed air containing oil mist in the MTP fly-cutting process is necessary. The pressure of the compressed air was 0.77 MPa.

In summary, the orthogonal experimental method was adopted, with the fly-cutting speed, feed speed, cutting depth, and cooling method as the four factors. Based on previous studies [28], the levels of each factor were determined. An L9(3⁴) four-factor, three-level orthogonal table was used, with the specific factor levels shown in

Table 1. Four-factor three-level orthogonal table.

Factors	Levels
	1	2	3
Fly-cutting speed v	5.23 m/s	7.85 m/s	10.47 m/s
Feed speed F	50 mm/min	100 mm/min	150 mm/min
Finishing cutting depth ap2	5 μm	10 μm	15 μm
Cooling method	Compressed air	Compressed air containing ethanol	Compressed air containing oil mist

. Nine groups of orthogonal experiments were conducted, as shown in

Table 2. Orthogonal experimental program and results.

Test	Four Factors				Four Indices
	Fly-Cutting Speed v (m/s)	Feed Speed F (mm/min)	Finishing Cutting Depth ap2 (μm)	Cooling Method	Surface Roughness Sa (nm)	Edge Burr Thickness D (μm)	Edge Burr Projection Area S (μm2)	Tool Nose Wear N (μm)
1	1 (5.23)	1 (50)	1 (5)	1 (Compressed air)	21	0.3	3.2	0.5
2	1	2 (100)	2 (10)	2 (Compressed air containing ethanol)	22	0.4	3.3	0.4
3	1	3 (150)	3 (15)	3 (Compressed air containing oil mist)	24	0.6	3.4	0.5
4	2 (7.85)	1	2	3	27	0.2	4	0.6
5	2	2	3	1	29	0.3	4.2	0.8
6	2	3	1	2	31	0.6	4.7	1
7	3 (10.47)	1	3	2	35	1.4	5.1	2
8	3	2	1	3	38	1.6	5.3	2.1
9	3	3	2	1	39	2	5.5	2.4

. Based on the specific experimental protocol mentioned, nine workpieces and single crystal diamond tools were prepared.

2.3.2. Orthogonal Experimental Indices and Measurement Methods

Surface roughness Sa, edge burr thickness d, edge burr projection area S, and tool nose wear N were used as evaluation indices. The MTP edge burr and surface roughness directly affected the optical function of the optical units. Among them, the thickness of the edge burr directly reflects the difficulty of removing the edge burr. The smaller the thickness of the edge burr, the easier it is to remove. The projected area of the edge burr directly reflects the effective area of the optical function. The smaller the projected area of the edge burr, the larger the effective area of the optical function. The amount of tool nose wear is a direct response to tool life. The smaller the tool wear, the higher the number of MTPAs that can be processed.

Two non-contact measurement methods, namely SEM (Crossbeam 550) (Zeiss, Oberkochen, German) and confocal laser scanning microscopy (CLSM) (VK-X3000) (Keyence, Osaka, Japan), were used to prevent scratching the surface of the workpiece during measurement. The details were as follows: the tilt angle of the SEM stage was adjusted to obtain the morphology of MTPA from different viewing angles. When the SEM stage was standing upright (shown in the upper right corner of Figure 5a), the complete morphology of the MTPA was obtained, and the projected area of the edge burr S was counted using the Image J 1.8.0 graphic processing software, as shown in the lower left corner of Figure 5a. The tilting angle of the SEM stage was adjusted (shown in the upper right corner of Figure 5b) to obtain the thickness of the edge burr D, as shown in the lower left corner of Figure 5b. A CLSM was used to obtain the three-dimensional morphology of the MTPA and measure the surface roughness Sa on the side of the MTP, as shown by the black dashed line in Figure 5c. The tool nose wear N was analyzed using a CLSM, as shown in the upper right corner of Figure 5d.

3. Results

3.1. Orthogonal Experimental Results

Because an L9(3⁴) orthogonal table with four factors and three levels was used, there were nine groups of orthogonal experiments, as shown in Table 2. The levels of the four influencing factors for each group of experiments are shown in the left half of Table 2, and the measurement results for each group of experiments are shown in the right half.

3.2. Range Analysis Results

The MTP side surface roughness Sa, edge burr thickness D, edge burr projection area S, and after machining tool nose wear N were used as test indexes for range analysis. The range method requires only a small amount of calculation to determine the degree of influence of each factor on the test index. As shown in

Table 3. Range analysis of influencing factors.

Text Index		Factor
		Fly-Cutting Speed	Feed Speed	Finishing Cutting Depth	Cooling Method
Surface roughness Sa (nm)	${\overline{k}}_1$	22.33	27.67	30.00	29.67
	${\overline{k}}_2$	29.00	29.67	29.33	29.33
	${\overline{k}}_3$	37.33	31.33	29.33	29.67
	R	15.00	3.67	0.67	0.33
Edge burr thickness D (μm)	${\overline{k}}_1$	0.43	0.63	0.83	0.87
	${\overline{k}}_2$	0.37	0.77	0.87	0.80
	${\overline{k}}_3$	1.67	1.07	0.77	0.80
	R	1.30	0.43	0.10	0.07
Edge burr projection area S (μm2)	${\overline{k}}_1$	3.30	4.10	4.40	4.30
	${\overline{k}}_2$	4.30	4.27	4.27	4.37
	${\overline{k}}_3$	5.30	4.53	4.23	4.23
	R	2.00	0.43	0.17	0.13
Tool nose wear N (μm)	${\overline{k}}_1$	0.47	1.03	1.20	1.23
	${\overline{k}}_2$	0.80	1.10	1.13	1.13
	${\overline{k}}_3$	2.17	1.30	1.10	1.07
	R	1.70	0.27	0.10	0.17

, ${\overline{k}}_i$ represents the mean value of the ith (i = 1, 2, 3) level test index of each factor. R is the range value and reflects the magnitude of change of the test index.

The R value determines the primary and secondary influences of each test factor on the test index. The optimal program was selected for each test index (

Table 4. Determination of experimental factor priorities and selection of optimal programs.

Test Index	Influencing Factors (Primary→Secondary)	Optimal Program
		Fly-Cutting Speed v (m/s)	Feed Speed F (mm/min)	Cutting Depth ap2 (μm)	Cooling Method
Surface roughness Sa (nm)	v→F→ap→Cooling method	5.23	50	15	Compressed air containing ethanol
Edge burr thickness D (μm)	v→F→ap→Cooling method	7.85	50	15	Compressed air containing oil mist
Edge burr projection area S (μm2)	v→F→ap→Cooling method	5.23	50	15	Compressed air containing ethanol/oil mist
Tool nose wear N (μm)	v→F→Cooling method→ap	5.23	50	15	Compressed air containing oil mist

). The influences of primary and secondary factors on the surface roughness, projected area of the exit edge burr, and exit edge burr thickness were the same. These influencing factors—fly-cutting speed, feed speed, cutting depth, and cooling mode—were ranked from largest of smallest as fly-cutting speed, feed speed, cooling mode, and cutting depth. In terms of tool nose wear, the factors influencing it from greatest to least impact were fly-cutting speed, feed speed, cutting depth, and cooling mode.

The best process for each index was then determined based on the minimum value of ${\overline{k}}_i$ for each index in Table 3. Small surface roughness was achieved under the following optimal conditions: a fly-cutting speed of 5.23 m/s, a feed speed of 50 mm/min, a cutting depth of 15 μm, and using compressed air containing ethanol for cooling. The thickness of the edge burr was minimized under the following conditions: a fly-cutting speed of 7.85 m/s, a feed speed of 50 mm/min, a finishing cutting depth of 15 μm, and using compressed air with oil mist for cooling. The edge burr projection area was minimized under the following conditions: a fly-cutting speed of 5.23 m/s, a feed speed of 50 mm/min, a finishing cutting depth of 15 μm, and using compressed air containing ethanol for cooling. Tool nose wear was minimized under the following optimal conditions: a fly-cutting speed of 5.23 m/s, a feed speed of 50 mm/min, a finishing cutting depth of 15 μm, and using compressed air containing oil mist for cooling. The fly-cutting speed had the most significant impact on the four test metrics compared with the other three factors, followed by the feed speed.

3.3. Experimental Verification of the Optimal Program

The smaller the thickness of the edge burr, the easier it is to remove the edge burr; considering this, the optimal program for minimizing the edge burr was subsequently verified through experiments. The optimal program for minimizing edge burr thickness based on range analysis is shown in Table 4. Compressed air with a fly-cutting speed of 7.85 m/s, a feed speed of 50 mm/min, a cutting depth of 15 μm, and the use of compressed air containing oil mist for cooling were selected for experimental verification. The results showed that the PTMA had a clear outline, as shown in Figure 6a. The edge burr thickness was about 0.15 μm, which is smaller than the edge burr thickness of the nine experimental groups in Table 2, as shown in Figure 6b. The experimental results thus verify the effectiveness of the optimal scheme based on the range analysis.

4. Discussion

4.1. Fly-Cutting Speed

The fly-cutting speed v mainly influenced the four test indexes. Generally, a higher fly-cutting speed results in a lower cutting force, reduced plastic deformation of the material, and smoother workpiece surface roughness. However, except for edge burr thickness, the surface roughness, the projected area of the edge burr, and the tool nose wear monotonically increased as the fly-cutting speed increased (Figure 7). As the fly-cutting speed increased, the edge burr thickness first decreased slightly and then increased significantly.

In micro fly-cutting machining, only the tip and a small part of the cutting edge of the whole diamond tool participates in cutting, making the tool nose easy to break. Due to the increase in rotation speed, the wear on the diamond tools was intensified, breaking the cutting edge and tip of the tool at different degrees [34]. The cutting edge and tip contour were mapped on the workpiece surface, making the workpiece surface rougher. At the same time, the tool wear caused the tool to become dull, increasing the cutting force and workpiece material deformation. This phenomenon led to more outlet edge burrs and machining cutter marks (Figure 8a). No machining cutter mark was observed when the tool was not worn (Figure 8b).

The thickness of the edge burr can be directly determined by the plastic deformation of the edge produced by fly cutting: the greater the plastic deformation of the edge, the greater the edge burr thickness. With an increase in the fly-cutting speed, the cutting force decreases, and the plastic deformation of the edge also decreases. However, further increases in fly-cutting speed may lead to greater tool nose wear and more significant plastic deformation of the edge material due to dull tools.

4.2. Feed Speed

The second top-ranking influencing factor of the four test indexes was the feed speed. As the feed speed increased, surface roughness, edge burr thickness, projected edge burr area, and tool nose wear increased (Figure 9). According to the literature [13], the expression of the main cutting force can be obtained from Equation (6), where a higher feed speed results in larger shear stress ${\tau }_s$, larger cutting force F_y, and increased tool wear, leading to larger surface roughness and increased edge burrs. Therefore, among the three feed speeds of 50, 100, and 150 mm/min, the optimal feed speed was 50 mm/min.

$$F_y=\frac{{\tau }_s{a}_w{d}_c\mathrm{c}\mathrm{o}\mathrm{s}({\beta }_e-\gamma )}{sin\phi \mathrm{c}\mathrm{o}\mathrm{s}(\phi +{\beta }_e-\gamma )},$$

(6)

where τ_s is the shear stress, a_w is the cutting width, d_c is the uncut chip thickness, β_e is the friction angle, γ is the front tilt angle, and φ is the shear angle.

4.3. Cutting Depth

The third influencing factor on the four test indexes (surface roughness, edge burr thickness, projected edge burr area, and tool nose wear) was the cutting depth. As the finishing cutting depth increased, the surface roughness, edge burr projection area, and tool nose wear became smaller, while the edge burr thickness increased and then decreased (Figure 10).

Figure 11a,b show the cutting diagram of the diamond tool turning three times. The finishing cutting depth a_p2 was not the actual cutting depth a_pa2 of fly cutting, and the difference between the finishing cutting depth a_p2 and the actual maximum cutting depth a_pam2 during fly cutting was large, as shown in Figure 11c. As shown in Figure 11d, with each turn of the tool, the actual cutting depth of the finishing a_pa2 first increased and then decreased. The geometric relationship between fly-cutting speed v, feed speed F, feed rate f, and actual maximum depth a_pam2 is shown in Equations (7) and (8).

$$f=F/n$$

(7)

$$a_{pam2}=R-\sqrt{{(R-a_{p2})}^2+{(\sqrt{R^2-{(R-a_{p2})}^2}-\frac{f}{2})}^2}$$

(8)

If the fly-cutting speed v = 5.23 m/s and feed speed F = 50 mm/min, then the feed rate f = 50 μm/r and a_p2 = 5 μm, 10 μm, and 15 μm can be obtained using Equations (7) and (8). The actual maximum cutting depths a_pam2 were 0.35, 0.49, and 0.61 μm. When a_p2 values were 5 and 10 μm, the actual maximum cutting depth a_pam2 was less than the tool edge radius of 0.5 μm, resulting in plowing and scuffing of the tool and the material. When the a_p2 was 15 μm, the actual maximum cutting depth a_pam2 exceeded the tool edge radius of 0.5 μm, resulting in a weak plowing and scrubbing effect, reduced tool nose wear, reduced surface roughness, and decreased edge burr. Therefore, among the three a_p2 values of 5, 10, and 15 μm, the optimal a_p2 value was 15 μm.

4.4. Cooling Method

The weakest influencing factor of the four test indexes (surface roughness, edge burr thickness, projected edge burr area, and tool nose wear) was the cooling method. When compressed air with oil mist was used for cooling, the tool nose wear became small, resulting in fewer exit edge burrs (Figure 12). The lubricating effect of the oil mist reduced the tool and workpiece friction and the tool wear. The cutting edge of the tool remained intact, reducing the possibility of burrs caused by tool breakage. The surface roughness of the workpiece was relatively minimized when cooled with compressed air containing ethanol. Due to the excellent cooling effect of ethanol, the continuous volatilization of ethanol during machining removed most of the heat, minimizing the thermal deformation effect on the workpiece and resulting in the lowest surface roughness of the workpiece.

5. Conclusions

In this study, to solve the problem of excessive burrs on the edges of fly-cutting MTPAs, which affects the anti-reflective performance of MTP films, the fly-cutting MTPA process was optimized using the orthogonal experimental method under the state of the vertical machining surface. The following conclusions were drawn.

• The four influencing factors of orthogonal experiments were the fly-cutting speed, feed speed, cutting depth, and the cooling method. Among them, the cooling method adopted the MQL to prevent impurities in the circulating working fluid from contaminating the surface of the MTPA. The four evaluation indexes of orthogonal experiments were surface roughness, edge burr thickness, edge burr projection area, and tool nose wear. Among them, edge burr thickness and edge burr projection area were used to characterize the curly edge burr.
• The primary and secondary factors affecting the surface roughness, the projected area of the exit edge burr, and the exit edge burr thickness were the same, ranked in descending order as the fly-cutting speed, feed speed, cutting depth, and cooling method. In contrast, the factors affecting the amount of tool nose wear were ranked as fly-cutting speed, feed speed, cooling method, and cutting depth.
• The projected area of the edge burr was minimized under the following optimal conditions: a fly-cutting speed of 5.23 m/s, a feed speed of 50 mm/min, a finishing cutting depth of 15 μm, and using compressed air containing oil mist for cooling. The optimal conditions for minimizing the thickness of the edge burr were as follows: a fly-cutting speed of 7.85 m/s, a feed speed of 50 mm/min, a finishing cutting depth of 15 μm, and using compressed air with oil mist for cooling.
• The plasticities of different metal materials varied, and the residual amount of edge burrs produced by cutting MPTAs was also different. Cutting force and cutting heat affect MPTAs. Therefore, the influence of different metal materials, cutting forces, and cutting heat on MPTAs is the focus of subsequent research. The optimized fly-cutting process can only minimize the thickness of the edge burrs; it cannot remove them altogether. To completely remove the edge burr, it is necessary to develop a new technology, which will be the subject of future research.