In the production process of precision injection mold, wear is always a key factor affecting the service life of the mold and product quality. The wear of the mold is not caused by a single reason, but the result of the interaction of multiple factors, which cover material properties, processing technology, mold design, use environment and other aspects. Understanding these causes of wear is crucial to extending the life of the mold and ensuring production stability.
The characteristics of the plastic material itself are the primary factor causing mold wear. Different types of plastics have different effects on the mold during the molding process. When engineering plastics containing reinforcing fillers such as glass fiber and carbon fiber are injected into the mold cavity under high temperature and high pressure, these high-hardness fillers are like fine "sandpaper". As the melt flows, it continuously washes the mold surface, causing wear in the mold cavity, runner and other parts. Some plastics will decompose and produce corrosive gases at high temperatures. For example, polyvinyl chloride will release hydrogen chloride gas when heated. These gases will react chemically with the mold steel, causing corrosion on the mold surface, thereby accelerating the wear process. Even for ordinary plastics, when the melt flows in the mold, it will cause a certain degree of wear on the mold surface due to friction.
Whether the process parameters are set reasonably during the injection molding process is directly related to the degree of wear of the precision injection mold. If the injection pressure is too high, the plastic melt will rush into the mold cavity at a high speed with a large impact force, especially at the gate, runner corners and other locations, which is prone to cavitation effect. The strong pressure released at the moment of bubble bursting will cause microcracks on the mold surface. As the number of production times increases, these microcracks gradually expand, causing the mold surface material to peel off. Frequent and drastic changes in mold temperature will also cause thermal fatigue damage to the mold. When the high-temperature plastic melt is injected into the mold, the mold surface temperature rises sharply and then cools rapidly. This repeated thermal expansion and contraction will produce thermal stress on the mold surface. Under long-term action, small cracks will appear on the mold surface, reducing the strength and wear resistance of the mold.
If there are defects in the structural design of the precision injection mold, it will also accelerate wear. Unreasonable runner design, such as using right angles instead of arc transitions at the runner corners, will cause turbulence in the plastic melt when flowing, increasing the scouring force on the mold wall; improper position of the exhaust groove will cause local air entrapment, resulting in high temperature and high pressure, and carbonization and corrosion of the mold surface. If the clearance between mold inserts is too large, the plastic melt can easily penetrate into the gap to form flash. During the mold opening process, the pull of the flash will cause the edge of the insert to wear. If the mold support structure is not stable enough, the mold will deform during the injection molding process, which will lead to uneven force between the components and cause local excessive wear.
The precision problem in the manufacturing process of precision injection mold also buries hidden dangers for subsequent wear. Insufficient mold surface machining accuracy and high roughness will increase the resistance to the flow of plastic melt, increase the friction between the melt and the mold surface, and accelerate wear. Improper heat treatment process of mold steel leads to uneven mold surface hardness or failure to meet design requirements. When subjected to injection molding pressure and friction, the lower hardness parts will wear first. During assembly, if the coaxiality deviation of the guide pin and guide sleeve, the ejector reset is inaccurate, etc., the mold will generate additional lateral force or collision during the opening and closing process, resulting in increased wear of related parts.
The matching degree between automation equipment and mold also affects mold wear. When the robot grabs the product, if the clamping force is too large or the clamping position is improper, the product will generate a large reverse pulling force on the mold core, which may cause the core to bend, deform or wear in the long run. During the process of automated warehousing and handling, if the mold collides with peripheral equipment, the mold surface will be damaged, especially if the key parts such as guide pillars and guide sleeves are damaged, which will affect the mold clamping accuracy and cause more serious wear problems.
Inadequate daily maintenance is an important factor in accelerating mold wear. After the mold is used, if the residual plastic in the flow channel and cavity is not cleaned in time, these residual plastics will carbonize and harden at high temperatures, becoming "abrasives" for the worn mold. If the moving parts of the mold, such as guide pillars and sliders, are not regularly added with lubricating oil or grease, the friction coefficient between the parts will increase and the wear rate will be significantly accelerated. When the mold is idle for a long time, if it is not properly anti-rust treated, the mold surface is prone to rust in a humid environment. The rust layer will not only affect the surface quality of the mold, but also fall off during the injection molding process, aggravating the mold wear.
The factors that cause precision injection mold wear during the production process are complex and diverse, from raw material characteristics, process parameter control, to mold design and manufacturing, equipment matching, and maintenance, each link may have an impact on mold wear. Only by fully understanding these factors and taking targeted measures in each link of production can we effectively reduce mold wear, extend mold service life, and ensure efficient and stable operation of precision injection molding production.
