How to Choose Mold Materials? 3 Dimensions to Avoid Cracking and Deformation Issues
In mold production, “cracking” and “deformation” are the most frustrating problems for enterprises — minor cases lead to trial mold failure and waste of tens of thousands of yuan in costs; major cases delay product launch cycles and even result in loss of customer orders. The root cause of these issues often lies in the critical link of “mold material selection”.
Our team has been deeply engaged in the mold industry for over 20 years, serving clients in medical equipment, military communication, daily necessities and other sectors. We have witnessed numerous cases where wrong material choices led to problems. Today, we will share three core dimensions — material performance matching, application scenario adaptation, and processing & maintenance compatibility — to help you avoid the pitfalls of mold cracking and deformation, and make the right material choices with fewer detours.
1. Dimension 1: Focus on “Core Material Performance” to Prevent Cracking and Deformation from the Source
The essence of mold cracking and deformation is that the material performance cannot withstand the “pressure, temperature, and wear” during production. Before selecting materials, clarify these 3 key indicators and match them to your specific needs:
1.1 Hardness and Toughness: Balance is Key to Avoid “Brittleness and Easy Cracking”
- Misconception: Many people believe “the higher the hardness, the better” and blindly choose high-hardness materials, only to find the mold cracks once it endures impact.
- Correct Approach: Select a balanced value based on the mold’s stress conditions —
For example, stamping molds (commonly used for metal processing) need to withstand repeated impacts, so materials with “high toughness + medium hardness” are required, such as Cr12MoV (hardness: HRC 58-62, moderate toughness). It not only resists wear but also prevents cracking during stamping.
For injection molds (commonly used for plastic processing), the stress is relatively mild, so P20 (hardness: HRC 28-32) is a good choice. It has stronger toughness and is less prone to deformation caused by internal stress from temperature cycles.
1.2 Heat Resistance: Tackle “High-Temperature Aging” to Prevent Deformation and Failure
- Hidden Risk: If the mold is used in high-temperature molding scenarios (such as injection molding of nylon or PC plastics), insufficient heat resistance of the material will cause “softening and deformation at high temperatures”, leading to product dimension deviations.
- Selection Tip: Choose heat-resistant materials based on the molding temperature —
For injection molding of conventional plastics (e.g., PP, PE), P20 is sufficient (heat resistance ≤ 300℃);
For high-temperature plastics (e.g., PC, PA66) or military product molding, H13 (heat resistance ≤ 600℃) or even 718H is needed. 718H has stronger heat resistance and thermal fatigue resistance, making it less likely to crack during long-term high-temperature use.
1.3 Corrosion Resistance: Avoid “Environmental Erosion” to Extend Mold Lifespan
- Easily Overlooked Point: If the production environment involves corrosive materials (e.g., acidic plastics, disinfection environments in the medical industry), ordinary materials will be corroded, resulting in surface pitting and subsequent cracking.
- Solution: Prioritize corrosion-resistant materials such as S136 (a stainless steel material with strong corrosion resistance, suitable for medical molds). Alternatively, apply surface treatments (e.g., chrome plating) to ordinary materials to enhance their corrosion resistance.
2. Dimension 2: Adapt to “Application Scenarios” — Choose “the Most Suitable” Instead of “the Best”
In many cases, mold cracking and deformation are not caused by poor material quality, but by “mismatch between materials and scenarios”. Based on the multi-industry cases we have served, special attention should be paid to these 3 scenarios:
2.1 Medical Equipment Molds: Safety First, with Precision as a Priority
- Requirements: Medical products have extremely high demands on mold cleanliness and stability. They also need to come into contact with medical liquids and disinfection environments, so no harmful substances should be generated due to material issues.
- Material Selection: Prioritize S136 — it not only has corrosion resistance (resistant to disinfectant erosion) but also excellent polishing performance (mold surface roughness Ra ≤ 0.02μm, meeting medical cleanliness standards). Meanwhile, its strong toughness prevents deformation during long-term production, avoiding product dimension deviations that affect usage safety.
2.2 Military Communication Molds: Withstand Extreme Environments and Resist Fatigue
- Requirements: Military products are often in extreme environments such as low temperatures and vibrations. Molds need to withstand repeated impacts without micro-cracks (which would affect signal transmission).
- Material Selection: Recommend 718H or H13 — 718H has good low-temperature toughness (remaining stable at -40℃ to avoid low-temperature cracking), while H13 has strong thermal fatigue resistance, making it suitable for high-frequency molding needs of military products. We once customized a mold with 718H for a military client, and it maintained no deformation after continuous production of 50,000 products.
2.3 Daily Necessities Molds: Cost-Effectiveness First, with Wear Resistance
- Requirements: Daily necessities have large production volumes (e.g., plastic basins, cups). Molds need to be used frequently, so the key is to prevent “wear and deformation” while controlling costs.
- Material Selection: P20 is sufficient for ordinary daily necessities (cost-effective, wear-resistant, suitable for mass production); if the product requires high gloss (e.g., transparent water cups), upgrade to 718H — its polished surface is smoother, reducing product defects.
3. Dimension 3: Consider “Processing and Maintenance” to Avoid “Right Material, Wrong Usage”
Choosing the right material is only the first step. Improper processing and maintenance can still lead to cracking and deformation. These 2 details must be noted:
3.1 Processing Technology Compatibility: Even Good Materials Are Wasted with Wrong Processing
- Case: A client once chose high-quality H13 material for a mold, but the quenching temperature was too high (exceeding 1050℃) during processing, making the material brittle and causing direct cracking during trial molding.
- Suggestion: Match processing technology to material characteristics —
For example, Cr12MoV requires “low-temperature quenching + multiple tempering” to avoid coarse grains; excessive cutting should be avoided during P20 processing to prevent internal stress (unreleased internal stress leads to deformation during later use). Our factory has a professional processing team that customizes processing plans based on different materials to minimize problems from the source.
3.2 Daily Maintenance: Extend Lifespan and Reduce Cracking Risks
- Key Actions: Clean the mold promptly after use (to avoid corrosion of the surface by residual plastic scraps); regularly inspect the cooling system (uneven cooling causes large local temperature differences in the mold, leading to deformation); apply anti-rust oil when the mold is not in use for a long time to prevent rusting and cracking.
Finally: 3 Questions to Ask Yourself Before Choosing Materials
- Will the mold be used for injection molding, stamping, or other processes? What are the stress and temperature requirements?
- What is the product’s usage environment? Are there special requirements such as corrosion resistance or low-temperature resistance?
- What is the expected lifespan of the mold? Is it for mass production or small-batch customization?
If you are still unsure about the selection, you can contact us — with 20 years of industry experience and accumulated multi-industry cases, we can accurately recommend materials based on your product characteristics, helping you avoid cracking and deformation issues and ensuring your mold is durable and reliable.