The service life of an injection mold is a comprehensive issue, deeply influenced by multiple stages such as design, manufacturing, usage, and maintenance. Mold life typically refers not to time, but to the total number of acceptable injection-molded parts it can produce (number of cycles).
The following are the main factors affecting the service life of an injection mold, divided into several key aspects:
Mold Design & Construction
This is the most critical determining the innate lifespan of a mold. Excellent design can significantly extend mold life.
- Steel Selection:
- Core Factor: The material, hardness, toughness, wear resistance, corrosion resistance, and thermal stability of the mold steel directly determine its lifespan.
- Cavity/Core: Typically uses pre-hardened steel (e.g., P20), quenched steel (e.g., H13, S136, NAK80), etc. High-hardness steel is wear-resistant but may be less tough; high-toughness steel has good impact resistance but may be less wear-resistant. Selecting the appropriate steel based on the plastic material (e.g., whether it contains glass fiber or other reinforcements) and production requirements is crucial.
- Mold Base: Typically uses lower-grade steel (e.g., S50C), but its strength and hardness must also be guaranteed; otherwise, overall precision is affected.
- Design Rationality:
- Strength & Rigidity: Whether the core, sliders, lifters, and other key components have sufficient thickness and support to avoid deformation or cracking under long-term injection pressure.
- Cooling System Design: Uniform and efficient cooling reduces thermal stress fatigue (crazing) in the mold, greatly extending its life while also improving production efficiency. Uneven layout of cooling channels causes excessive temperature differences and internal stress.
- Venting System Design: Good venting avoids trapped air burns and prevents corrosion and damage to the mold surface from high-temperature, high-pressure gases.
- Ejection System Design: Rational layout of ejector pins, sleeves, sufficient draft angles—all avoid scratching and wear on the mold surface during part ejection.
- Parting Line Design: The selection of the parting line should avoid sharp and thin steel sections to prevent chipping or cracking under clamp force and injection pressure.
- Runner & Gate Design:
- Gate location and size affect the speed and direction of melt filling. An improper gate may cause the melt to directly impact small cores or inserts, leading to bending or breakage.
Mold Manufacturing & Processing
Precise manufacturing is the foundation for realizing the design blueprint and ensuring mold life.
- Machining Accuracy & Fit Clearance: The machining accuracy and fit clearance of components like the mold core, sliders, and lifters must be strictly controlled. Excessive clearance causes flash (burrs) and accelerates wear; insufficient clearance causes jamming and galling.
- Surface Treatment: Processes like heat treatment (quenching, nitriding), electroplating (chromium), PVD/CVD coating greatly enhance the surface hardness, wear resistance, and corrosion resistance of the mold. For example, nitriding can significantly increase surface hardness, extending life several times over.
- Stress Relief: Stress relief annealing after rough machining and heat treatment eliminates internal machining stresses, preventing the mold from deforming or cracking due to stress release during use.
- Polishing Quality: A high-gloss cavity surface not only improves product appearance but also reduces ejection resistance, lowering the risk of wear and scratching.
Molding Operation & Usage
Improper operation is the “number one killer” of molds. Even the best mold cannot withstand rough handling.
- Molding Process Parameters:
- Excessively High Injection/Packing Pressure: Increases the molding pressure on the mold, subjecting it to huge mechanical stress, potentially causing core bending, insert displacement, or plate deformation.
- Excessively High Barrel and Mold Temperatures: Aggravate thermal fatigue in the mold, making crazing more likely, and also accelerate mold wear.
- Excessively Fast Injection Speed: Creates high-pressure impact on cores and inserts, especially damaging to delicate features.
- Mold Protection:
- Low-Pressure, Low-Speed Mold Closing: Low-pressure protection parameters must be set correctly. Otherwise, if a part fails to eject or foreign material (e.g., metal parts) is present, high-pressure clamping can directly crush or even crack the mold core.
- Mold Height Adjustment: Incorrect adjustment of the machine’s clamp stroke can cause the mold to be clamped too tightly, damaging both the mold and the machine under long-term overload operation.
- Cleaning & upkeep:
- Promptly clean mold surfaces, vent slots, and ejector pins of dirt and material residue during production to avoid crushing the mold.
- Use suitable rust preventives and release agents. Poor quality or excessive release agent can corrode the mold or build up on surfaces.
Maintenance & Care
Regular, professional maintenance is essential for keeping the mold in optimal condition and extending its effective life.
- Regular Maintenance Schedule: Establish and strictly follow a regular maintenance plan including cleaning, rust prevention, lubricating moving parts (guide pillars, ejector pins, sliders), and checking fastening screws.
- Timely Repair of Damage: If slight wear, scratches, or cracks are found, stop using the mold immediately and repair it. Small issues left unaddressed can quickly develop into serious damage.
- Proper Storage: When not in use for extended periods, the mold must be thoroughly cleaned, coated with rust preventive, and stored in a dry, ventilated environment to prevent rust and corrosion.
Plastic Material
- Corrosiveness: Some plastics (e.g., PVC, flame-retardant materials) decompose during processing, producing corrosive gases that attack the mold runner and cavity. Corrosion-resistant steel (e.g., S136H) or stainless steel is required.
- Abrasiveness: Plastics filled with glass fibers (GF), mineral fillers, etc., are extremely abrasive to molds, acting like “grinding compounds.” High-hardness, high-wear-resistant steel (e.g., hardened alloys) or surface hardening treatments are essential.
To improve mold life, it is essential to control it from the design source, manufacture it with exquisite craftsmanship, operate it with standardized procedures, and maintain it with a scientific attitude, forming a closed-loop management throughout its entire lifecycle