Why do molds need repair after a period of normal production?
As precision-manufactured industrial products, molds inevitably experience performance degradation during use. Therefore, under normal circumstances, plastic molds need repairs after a period of normal production to ensure continued production. The reasons for this necessary modification and its causes are analyzed below. Furthermore, these repair costs are a significant component of the overall manufacturing cost. Extending the production cycle and reducing repairs during it are determined during mold manufacturing through design, material selection, and other factors.
1. Molds in production mode suffer wear and tear due to impacts and friction at high temperatures
During production, raw materials melt and reform within the mold cavity, repeatedly undergoing melting and peeling of the raw material, causing changes to the mold surface. Simultaneously, each production process involves mold parting and closing. This process can potentially deform components such as ejector pins, altering the mold surface roughness (crucial for optical lens products), leading to poor mold closing and increased product defect rates.
Repair processes include electrical discharge machining (EDM), ejector pin replacement, and surface polishing.
2. During production, the mold surface is corroded by gas, simultaneously causing venting channel blockage
The injection molding jobs involve heating raw materials to a molten state and then reforming them under pressure. During this process, the decomposition and volatilization of the raw materials release gases that react with the cooling condensate to form an acidic solution, corroding the mold surface. Clogged venting channels due to carbon buildup, if not cleaned promptly, can lead to defects such as increased product defect rates due to higher pressure. Regardless of the venting design, the mold is inevitably affected by minute amounts of acid corrosion throughout the production process. Repeated exposure over a certain number of cycles accumulates, causing a quantitative change in acid corrosion that impacts mold precision. Involve heating raw materials to a molten state and reshaping them under pressure. During this process, gases released from the decomposition of raw materials combine with cooled condensate to form acidic liquids that corrode the mold surface. When venting channels become clogged and fail due to carbon buildup, failure to clean them promptly leads to increased product defect rates, such as components subjected to excessive pressure.
The molds need repair, involve adding a surface coating and clearing air passage blockages.
3. Lubrication System Failure Due to Continuous Production
Depending on the materials used in injection molding, the temperature throughout the process can range from 180 to 250 degrees Celsius, with some specialty materials requiring temperatures exceeding 350 degrees Celsius. As mentioned above, each production cycle involves the mold undergoing a period of high temperature and pressure, followed by cooling. The grease used to maintain mold operation will gradually carbonize after a period of normal production, leading to lubrication failure and ultimately accelerating mold wear.
The repair process involves replacing the lubricating material.
4. Prolonged exposure to high temperatures causes thermal fatigue cracks in the mold
Repeated exposure to the same high temperature and high pressure during operation can trigger thermal fatigue in metals. Over time, this can lead to surface cracks. Failure to detect and repair these cracks promptly will ultimately affect product quality due to deteriorated surface finish and increased tolerances.
The repair process involves visually inspecting for cracks. If cracks are found, they are refilled and appropriate post-processing is performed.
5. Variations in mold inserts can lead to a deterioration in the overall structural integrity of the mold
The metal material used for the inserts in the mold may differ from the mold itself. After experiencing the thermal expansion and contraction cycles during the production cycle, the different thermal expansion systems of the metals can cause the fit clearance between the insert and the mold body to exceed the reasonable range after a period of operation. This results in excessive gaps between the mold parts, affecting the quality of the finished product. In severe cases, it can damage the mold.
The repair process involves testing the gap by opening and closing the insert. If it significantly exceeds the reasonable tolerance range, the insert needs to be replaced.
Conclusion
The aforementioned problems occur at different times; therefore, timely inspection and repair of the molds are essential and crucial for ensuring product quality. If you are unfamiliar with these matters, you can check out the Honju blog for more mold-related knowledge.
