How to extend the service life of MIM powder metallurgy molds

The main cause of MIM mold wear: continuous abrasion of the mold cavity by metal powder in feedstock, which is far more severe than common plastic injection molds. Core strategies: mold material selection + surface strengthening + product structure optimization + injection process control + regular maintenance.

1. Mold Material Selection & Heat Treatment

1. Select high wear-resistant mold steel.

General options: S136, NAK80. For mass production with high wear requirements: ASP23, S390 powder high-speed steel, hardness HRC58~62.

Ordinary soft steel such as P20 is not recommended, as metal powder will quickly scratch the cavity.

2. Vacuum quenching plus multiple tempering to fully eliminate internal stress, prevent microcracks during long-term production, maintain the toughness of the steel substrate and avoid coating chipping.

2. Cavity Surface Strengthening (the most effective life-extending method, service life can be increased by 2~3 times)

1. PVD coating (TiN / TiCN / CrN / AlTiN) 【industry preferred】

2~5 μm ultra-thin hard ceramic film with low friction coefficient, excellent wear resistance and anti-sticking property. It causes minimal deformation and is suitable for precision MIM cavities. Coatings are prioritized for gates, thin ribs and small core pins.

TiCN: best resistance to abrasion from metal powder; CrN for titanium alloy feedstock with corrosion resistance; AlTiN for high-temperature resistance.

2. Gas nitriding / ion nitriding

5~8 μm hardened layer, lower cost than PVD. Suitable for simple cavities; precision control for complex micro-features is relatively challenging. It can be used alone or combined with PVD.

Note: Coatings are not permanent. Gates suffer the fastest wear. Worn molds can be stripped, repolished and recoated.

3. Product & Mold Structure Optimization (reduce stress and wear)

1. Replace all sharp corners with R0.2~R0.5 fillets to avoid stress concentration, coating chipping and cavity cracking.

2. Design reasonable draft angle to prevent cavity surface damage during demolding.

3. Keep gates away from tiny cores. Install reinforced inserts at gates. Gates are high-wear zones. Only worn inserts need replacement instead of the whole mold.

4. Polish the cavity to Ra0.1μm or below to reduce scratching from metal powder and lower sticking risk.

4. Injection Molding Process Control (reduce abnormal wear)

1. Feedstock quality control: stable powder particle size, minimize coarse particles; uniformly dispersed feedstock to prevent agglomerated hard particles from scratching the cavity.

2. Do not blindly increase injection pressure and speed. High pressure and high speed will accelerate erosion on cavities and cores.

3. Maintain stable mold preheating temperature (100~160℃) to reduce thermal cyclic stress. Pause production appropriately after 4~6 hours of continuous operation to release thermal stress.

4. Use MIM-compatible release agent properly to reduce green part sticking and avoid cavity / ejector pin damage caused by forced ejection.

5. Inspect vent slots regularly to prevent powder accumulation, which may lead to indentation and scratching on cavity surfaces.

5. Routine Preventive Maintenance (factory implementation standard)

1. Clean the cavity after each production run: blow away residual metal powder with compressed air and remove accumulated material with special detergent. Powder residue is the main source of continuous wear. Apply high-temperature grease to guide pins and ejector pins.

2. Periodic inspection by shot count: check cavity surface, ejector pins, insert wear and coating condition every 10,000 shots. Repair minor wear in time via laser welding, polishing and recoating before large-area damage occurs.

3. Long-term storage: conduct rust removal and anti-rust treatment under constant temperature to protect cavities and coatings from corrosion.

4. Wear repair: adopt laser welding (low heat input and minimal mold deformation). The mold can be repolished and re-coated with PVD after repair. A mold can be refurbished 1~2 times to greatly extend its total service life.

6. Common Pitfalls

Do not apply PVD coating directly on molds with substrate microcracks, otherwise the coating will peel off easily.

High-hardness coatings cannot withstand heavy impact. The ejection system must run smoothly.

Avoid long-term over-pressure and high-speed injection, which accelerates gate erosion.

Powder metallurgy, Metal Injection Molding, powder metallurgy gears

Guangming Group, a professional manufacturer and supplier based in China, focuses on the R&D and manufacturing of metal forming technology and wear-resistant materials. Our factory supplies powder metallurgy parts made by metal compaction and metal injection molding.

The company has a high-caliber talent team. The founding team comes from Guangzhou Research Institute of Non-ferrous Metals, a national ministerial-level research institute, with rich industry experience and strong R&D capabilities, providing continuous innovation momentum for the company.

The group has obtained 5 invention patents and more than 30 utility model patents. It has passed IATF16949, ISO9001-2015, ISO14001 and intellectual property management system certifications, and owns international trademark registrations. It is an innovative enterprise in Guangdong Province, a Guangzhou Science & Technology Little Giant Enterprise, a director unit of Guangdong Powder Metallurgy Industry Technology Innovation Alliance, and an initiator of Guangzhou Advanced Powder Metallurgy Cluster Promotion Center.