*2.2. Mould Base Material*

The selection of material for mould base parts depends on the product that needs to be manufactured. Choosing suitable materials can help a company to save costs and time. The materials of the mould base are divided into four types, which are mild steel, high-alloy steel, stainless steel, and tool steel, as tabulated in Table 2 [83–87].


**Table 2.** Types of mould base material with examples [81–87].

Mild steel is a type of iron that has varied levels of carbon added to it and no addition of other elements. There are different percentages of carbon where the carbon content ranges from mild, to medium, to high. Examples of carbon steel are carbon steel 1018 and 1050 [83,86]. High-alloy steel is a variety of steel that is alloyed with additional components ranging from 1 wt. % to 50 wt. % through the addition of carbon to enhance the material's different qualities.

High-alloy steel is therefore made of iron that has been alloyed with additional elements including copper, chromium, and aluminium. It can also alloy more than two metals. Examples of alloy steel are alloy steel AISI 4130 and AISI M2 [35]. Stainless steel provides excellent corrosion resistance and machinability. Stainless steel is a class of iron-based alloys notable for their corrosion and heat resistance.

Furthermore, stainless steel is produced by adding chromium at a rate of about 11% and the use of stainless steel is selected because it does not corrode or oxidise. Stainless steel does not require stress relief because its material qualities are stable. Examples of stainless steel are stainless steel 420, 316L, and 17-4 PH [88,92,93]. Tool steel refers to a range of carbon and alloy steels that are especially well-suited to be produced into tools.

In addition, tool steel contains elements such as tungsten, vanadium, cobalt, and molybdenum [94]. These elements are used to improve hardenability and generate harder and more thermally stable carbides. Examples of tool steels are tool steel O-1, A-6, S-7, D-2, P-20, and H13 [83,88]. RT is the AM technology that refers to the manufacturing methods of tooling [94–96].

Injection mould bases can be made from a wide variety of materials. However, selecting the right mould base material is essential for making high-quality components, since different materials have different properties.

#### Selecting Mould Base Material

Material selection for the mould base is important because it will affect the performance of the mould. Selecting the suitable material during the tool-making stage can reduce cost. Several factors need to be considered, which are strength, good wear resistance, excellent surface finish, dimensional stability, machinability, and corrosion resistance. First, highly compressive loads must be able to be absorbed by the material without cracking or splitting. Next, good wear resistance is needed so that the mould can be used longer. Good surface finish is also vital to be considered because it will affect the product surface. Other parameters also need to be considered so that the product can be used longer, and to save cost and time. An example of this consideration is the use of H13 which is selected because

it can perform well at high temperatures, and has high dimensional stability, hardness, and wear resistance [97]. The recommended mould material for transparent products is stainless steel AISI 420, which has a hardness of up to 54HRC [98].

On the other hand, mould inserts are assembled in a mould base and form the cavities where the molten plastic will be injected to form the products. Therefore, the material of the mould insert is an important aspect that will have a direct impact on the defects of the moulded parts produced.

## *2.3. Mould Insert Material*

The material of a mould insert will affect the cooling time of a product as it influences the overall cycle time of the injection moulding process [36]. Other than that, improving cooling time can also reduce defects such as shrinkage and warpage [90,99,100]. Tool steel material takes longer to achieve the ejection temperature than pure copper (Cu) and beryllium copper (BeCu) as tabulated in Table 3 [86]. This is because Cu and BeCu have higher thermal conductivities which can remove more heat than tool steel material. It is important because the temperature needs to be evenly distributed from the cavity to the core of the mould [84]. Although pure copper is proven to be the best according to simulation results, other factors need to be considered in choosing the mould insert material, including properties such as hardness. The hardness of BeCu is higher compared to pure copper and other properties that need to be considered are, namely, durability and resistance to non-oxidising acids.

**Table 3.** Simulation results of mould inserts by researchers [100].


However, the materials used to fabricate mould inserts for the product designed in the development stage do not have to be the same as materials used for the hard tooling (mould used for mass production) because the product design is not yet finalised and there are still some tests and evaluations to be carried out, as well as a need to improve the product's features in terms of ease of assembly and reliability tests in order to ensure the high quality of product. An alternative material of mould inserts for low production in the product development industry is in high demand, especially in the effort to reduce the expenses in the research and development stage.
