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Views: 0 Author: Site Editor Publish Time: 2026-06-24 Origin: Site
| 1. What Are Injection Mold Materials? |
| 2. Key Factors in Injection Mold Material Selection |
| 3. Common Injection Mold Materials |
| 4. How to Choose the Right Injection Mold Material |
| 6. FAQ |
Choosing the right injection mold material is an important step in every plastic injection molding project. The mold material not only affects the initial tooling cost, but also influences mold life, part quality, surface finish, production stability, cycle time, and long-term maintenance.
In this guide, we will introduce three common types of injection mold materials and explain how to choose the right mold material for your specific plastic injection molding project.
Injection mold materials refer to the metal materials used to manufacture the main components of an injection mold. These components may include the mold base, core, cavity, inserts, sliders, lifters, wear plates, and cooling-related mold components. During the injection molding process, these mold parts must withstand repeated clamping force, injection pressure, high temperature, plastic flow, friction, wear, and continuous production cycles.
Common injection mold materials include different types of injection mold steel, such as P20, 718H, H13, S136, 420 stainless steel, and NAK80. Each mold steel has its own advantages in machinability, hardness, wear resistance, corrosion resistance, polishing performance, and mold life. For some prototype molds or low-volume production projects, aluminum injection molds may also be used because aluminum alloy is easier to machine and can help shorten mold lead time.
In many production molds, copper alloy is not usually used for the entire mold. Instead, copper alloy mold inserts are often applied in specific areas where better thermal conductivity is needed. For example, copper alloy inserts can help improve cooling performance around deep ribs, thick-wall areas, or hot spots inside the mold.
The purpose of injection mold material selection is to make sure the mold can meet the real production requirements of the project. A suitable plastic injection mold material can improve mold durability, reduce the risk of wear or corrosion, maintain part accuracy, support better surface quality, and help the mold run more stable during long-term injection molding production.
Choosing the right injection mold material is not only about checking the material name or resin price. In a real plastic injection molding project, material selection should be based on product performance, mold design, molding stability, and total cost. A suitable material can help reduce defects, improve production efficiency, and make the final plastic parts more reliable.
The first factor in injection molding material selection is the actual function of the product. Different plastic injection molding materials have different strength, toughness, flexibility, heat resistance, chemical resistance, and durability.
For example, electronic housings may require flame resistance and dimensional stability. Automotive parts may need higher strength, heat resistance, and impact resistance. Outdoor products should consider UV resistance and weather resistance. Medical or industrial parts may need good chemical resistance and stable long-term performance.
Therefore, before choosing any injection mold material, it is important to understand where the part will be used, what load it needs to bear, and whether it will contact heat, moisture, chemicals, or outdoor conditions. The material must match the real working environment, not just the basic product shape.
Material performance directly affects mold design. Different injection molding materials have different shrinkage rates and flowability, which can influence part size, tolerance, warpage, filling balance, and gate design.
For precision parts, shrinkage and dimensional stability are very important. If the shrinkage is not properly considered during mold design, the final part may have assembly problems or unstable dimensions. For thin-wall parts, long-flow parts, or complex structures, material flowability is also critical. Poor flowability may cause short shots, weld lines, flow marks, or high injection pressure.
This is why injection mold material selection should be combined with DFM analysis and mold design review. A proper injection molding material comparison can help engineers choose a material that is easier to mold and more stable in production.
Injection molding material cost should not be judged only by resin price. A cheaper material may increase the risk of defects, longer cycle time, higher scrap rate, poor surface finish, or unstable production. In many cases, the lowest resin price does not mean the lowest total cost.
For mass production, the selected material should have a stable processing window, reliable supply, reasonable cycle time, and good molding consistency. Materials that require special drying, high mold temperature, or strict processing control may increase production difficulty and cost.
A practical injection molding material selection guide should consider both material performance and total production cost, including resin price, mold design difficulty, cycle time, defect rate, secondary processing, and long-term product reliability. The best material is not always the cheapest one, but the one that gives the best balance between quality, performance, and cost.
Aluminum is often used for prototype molds, low-volume production molds, and some fast-turnaround tooling projects. Compared with steel, aluminum is lighter and easier to machine, which can help shorten mold manufacturing time and reduce initial tooling cost.
One of the biggest advantages of aluminum injection mold material is its good thermal conductivity. It can transfer heat quickly, which may help shorten cooling time and improve molding efficiency for certain plastic parts. This makes aluminum molds attractive for product development, small-batch production, and projects that need quick market testing before investing in a hardened steel mold.
However, aluminum also has clear limitations. Its hardness and wear resistance are lower than steel, so it is not ideal for long-term high-volume production or abrasive injection molding materials such as glass fiber reinforced plastics. If the part has complex sliders, tight tolerances, high polishing requirements, or long production life, aluminum may not be the best choice.
Aluminum molds are commonly used for:
Prototype plastic injection molding
Low-volume injection molding
Product testing before mass production
Short lead time tooling projects
Simple plastic parts with moderate tolerance requirements
From an injection molding material comparison point of view, aluminum is suitable when speed and lower initial cost are more important than mold life. But for mass production, engineers should carefully compare aluminum with steel to avoid future maintenance or replacement costs.
3.2 Steel
The table below summarizes several commonly used mold steels in injection mold manufacturing, including their main features, typical applications, and selection notes.
Mold Steel | Main Features | Common Applications | Selection Notes |
P20 | Pre-hardened steel, good machinability, moderate hardness, cost-effective | General plastic injection molds, ABS/PP/PE parts, household products, simple housings | Suitable for medium mold life and standard surface requirements |
718 / 718H | Better hardness and polishability than P20, good dimensional stability | Automotive parts, appliance housings, electronic housings, medium-volume production molds | A common choice for better surface finish and longer mold life |
S136 / S136H | Stainless mold steel, good corrosion resistance, excellent polishing performance | Transparent parts, medical plastic parts, optical parts, high-gloss products, corrosive plastics | Suitable for high surface requirements and materials that may release corrosive gas |
NAK80 | Pre-hardened steel, excellent polishing, good EDM performance, stable hardness | High-gloss plastic parts, cosmetic parts, precision housings, electronic products | Good for products requiring fine surface finish and stable mold performance |
H13 | High toughness, high heat resistance, good wear resistance after heat treatment | High-temperature plastics, engineering plastics, inserts, sliders, lifters, high-wear mold components | Suitable for demanding molding conditions and reinforced materials |
420 / 2316 | Stainless steel with good corrosion resistance and polishability | Medical parts, transparent parts, PVC-related products, molds requiring rust resistance | Often used when both corrosion resistance and surface quality are important |
Copper alloys are not usually used to build the entire injection mold, but they are very useful in specific mold areas that need faster cooling or better heat transfer. In injection mold design, copper alloy inserts are often used around deep ribs, thick walls, hot spots, cores, bosses, or areas where normal cooling channels are difficult to arrange.
The biggest advantage of copper alloy injection mold material is excellent thermal conductivity. It can help remove heat faster from local areas, reduce cooling time, improve dimensional stability, and reduce defects such as sink marks, warpage, and uneven shrinkage.
Common copper alloy applications include:
Core inserts for deep or narrow structures
Cooling inserts near thick wall areas
Inserts around bosses and ribs
Hot spot cooling areas
Precision parts with strict dimensional control
Plastic parts that require shorter cycle time
However, copper alloys also have limitations. Compared with steel, they usually have lower hardness and wear resistance. They are also more expensive than common mold steels, so they are normally used only in selected mold areas instead of the whole mold. For abrasive plastics, such as glass fiber reinforced injection molding materials, engineers need to carefully evaluate wear resistance and insert protection.
Choosing the right injection mold material should be based on more than material price. A good decision needs to consider production volume, plastic resin type, part structure, surface requirements, mold life, cooling performance, and long-term injection molding material cost.
For prototype testing or low-volume production, aluminum may be a practical choice because it is easier to machine and can shorten tooling lead time. It is suitable for product validation, market testing, and simple plastic parts with limited production quantity.
For medium- or high-volume injection molding, steel is usually more reliable. Steel injection mold material offers better hardness, wear resistance, polishability, and longer mold life. It is more suitable for mass production, tight tolerance parts, and products that need stable long-term molding performance.
In injection mold material selection, the lowest upfront tooling cost is not always the best option. If the mold wears quickly, needs frequent repair, or cannot support future production, the total cost may become higher.
Different plastic injection molding materials have different effects on the mold. Some resins are easy to process, while others may require higher mold temperature, stronger mold structure, or better corrosion and wear resistance.
For common injection molding materials such as ABS, PP, PE, or PC/ABS, general mold steels such as P20 or 718 may be suitable for many standard projects. For transparent parts, medical plastic parts, or high-gloss products, S136, NAK80, or other steels with good polishing performance may be preferred. For glass fiber reinforced plastics such as PA-GF or PBT-GF, the mold material should have stronger wear resistance. For corrosive materials, stainless mold steel or anti-corrosion treatment should be considered.
This is why injection molding material comparison should not only compare plastic resin properties, but also evaluate how the resin will affect the mold during long-term production.
The part structure also influences injection mold material selection. A simple housing and a precision component with sliders, lifters, deep ribs, thin walls, or tight assembly features may require different mold materials.
If the product requires high dimensional accuracy, the mold material must have good stability and resistance to deformation. If the product has a high-gloss or transparent surface, the cavity steel should have good polishing performance. If the part has textured surfaces, the mold material should support stable texture quality after machining or etching.
For complex plastic parts, it is also important to check whether local cooling needs improvement. Copper alloy inserts can be used in some hot spots, deep cores, or thick wall areas to improve cooling efficiency and reduce molding defects such as sink marks, warpage, or uneven shrinkage.
Choosing the right injection mold material is an important step in building a reliable and cost-effective plastic injection molding project. Aluminum, steel, and copper alloys each have their own advantages and limitations. The best choice should be based on product structure, plastic resin type, production volume, surface requirements, mold life, cooling performance, and overall injection molding material cost. A proper injection molding material selection guide can help reduce mold modification risks, improve molding stability, and support better long-term production results.
Alpine Mold is a professional injection mold manufacturer with rich experience in custom plastic injection molds and injection molding production. We provide engineering support from DFM analysis, mold design, mold manufacturing, mold trial, to mass production. If you have a new injection molding project, please feel free to send us your 3D drawings, material requirements, production quantity, and surface finish details. Alpine Mold will help review your project and provide a suitable mold quotation.
In some cases, yes. However, it depends on the plastic resin, shrinkage rate, processing temperature, flow behavior, and part tolerance. If the new plastic injection molding material has very different shrinkage or molding conditions, the existing mold may need modification. Before changing resin, it is better to ask the mold manufacturer to review the part design and mold structure.
Some injection mold materials need heat treatment to improve hardness, wear resistance, and mold life. For example, certain mold components such as inserts, sliders, lifters, or high-wear areas may require hardening or surface treatment. Whether heat treatment is needed depends on mold steel grade, plastic resin type, production volume, and part structure.
To recommend a suitable injection mold material, the mold manufacturer usually needs the 3D drawing, plastic resin type, expected production quantity, surface finish requirement, part tolerance, product application, and whether mass production is required. With this information, engineers can make a more accurate injection molding material comparison and suggest a suitable mold material.
Yes. Different mold materials have different machining difficulty, hardness, heat treatment requirements, polishing performance, and availability. Aluminum molds are usually faster to machine, while hardened steel molds may require longer manufacturing time. If the project has a tight delivery schedule, mold material selection should be discussed early during the DFM stage.
It is possible in some cases, but it is not recommended unless necessary. Once mold manufacturing has started, changing the injection mold material may affect machining process, heat treatment, mold structure, cost, and delivery time. That is why injection mold material selection should be confirmed before tooling begins.
