The service life of injection molds is influenced by multiple factors, mainly including mold materials, design, manufacturing processes, use, and maintenance. Here is a detailed analysis:
Mold Materials
Wear Resistance: During the injection molding process, there is friction between the mold surface and the plastic melt. Poor wear resistance of the material can lead to surface wear and a decrease in dimensional accuracy, affecting the mold's service life. For example, when producing glass fiber-reinforced plastics, due to the high hardness of glass fibers, significant wear is inflicted on the mold. Therefore, mold steel with good wear resistance is required.
Toughness: Molds are subjected to impact and alternating stresses during mold opening, closing, and injection holding processes. Insufficient toughness can easily result in cracks or even fractures. For large injection molds, because of the high injection pressure, the material needs to have good toughness to resist impacts.
Corrosion Resistance: When injection molding involves plastic with corrosive additives or when the mold operates in a humid environment, if the mold material has poor corrosion resistance, it will be corroded and rusted, reducing surface quality and accuracy. For instance, when producing PVC plastics, the hydrogen chloride gas generated from its decomposition is corrosive. Therefore, mold steel with good corrosion resistance should be used, and protective treatments should be carried out.
Mold Design
Rationality of Structural Design: A reasonable structure can ensure uniform force distribution on the mold and avoid stress concentration. For example, improper design of the parting surface, gate location, and number of gates in the mold can lead to uneven plastic flow, causing excessive local pressure and accelerating mold wear.
Design of the Cooling System: A good cooling system can uniformly cool the molded parts, shorten the molding cycle, and reduce the stress caused by thermal deformation. If the cooling is uneven, local overheating of the mold can occur, degrading the material properties and affecting the service life.
Strength and Rigidity Design of the Mold: The mold needs to have sufficient strength and rigidity to withstand the injection pressure and clamping force. Insufficient strength and rigidity can cause mold deformation, leading to a decrease in the dimensional accuracy of the molded parts and premature mold damage.
Manufacturing Processes
Machining Accuracy: High machining accuracy can ensure the dimensional accuracy and surface quality of the mold, reducing wear and damage caused by excessively large or small fitting clearances. For example, if the fitting clearance between the core and cavity exceeds the tolerance range, flash will occur, and the dimensional accuracy of the molded parts will be affected.
Surface Treatment Quality: Surface treatments such as chrome plating and nitriding can improve the mold's surface hardness, wear resistance, corrosion resistance, and demolding performance. However, improper treatment processes, such as uneven chrome plating layer thickness or defective nitriding layers, can reduce the treatment effectiveness and affect the mold's service life.
Heat Treatment Quality: Heat treatment can improve the mold material's properties, enhancing its strength, hardness, and toughness. However, improper heat treatment parameters, such as excessively high quenching temperatures or insufficient tempering, can result in uneven internal material structure, generate internal stresses, and reduce the mold's service life.
Use and Maintenance
Control of Injection Molding Process Parameters: Unreasonable settings of injection pressure, temperature, holding time, and cooling time can increase the mold's load. For example, excessive injection pressure can cause the mold cavity to expand, accelerating wear; excessively high temperatures can soften the mold material, reducing its hardness and wear resistance.
Mold Installation and Debugging: Improper installation and debugging, such as non-level mold installation or loose fastening, can cause vibrations and displacements during the injection molding process, leading to increased mold wear.
Daily Maintenance and Care of the Mold: Regular cleaning, lubrication, inspection, and repair of the mold can promptly detect and address problems, extending the mold's service life. For example, timely removal of residual plastics and impurities on the mold surface can prevent surface scratches; regular lubrication of moving parts can reduce friction.
In addition, production volume and product complexity also affect the mold's service life. A large production volume leads to rapid accumulation of mold wear; complex product structures make mold forming more difficult, increasing the likelihood of wear and deformation. These factors need to be comprehensively considered during mold design and use.
