Other causes of mold damage
In addition to common factors such as materials, processes, and stress, there are many other easily overlooked causes of mold damage. Although these factors have little impact when acting alone, their long-term accumulation will significantly shorten the mold life and need to be prevented through full-process control.
Improper use of mold lubrication and release agents is a hidden source of damage. Excessive application of release agent decomposes at high temperatures, producing corrosive gases (such as hydrogen fluoride). These react with the mold’s oxide layer, forming loose corrosion products, reducing surface hardness and accelerating wear. Testing at a die-casting plant found that excessive use of fluorinated release agent reduced mold surface hardness from 45HRC to 38HRC, and the wear rate increased by twofold. Insufficient or uneven application can lead to mold sticking, requiring greater force during demolding and causing cavity strain. This is particularly true in aluminum alloy die-casting, where unlubricated core surfaces are prone to metallurgical bonding with the molten aluminum, resulting in aluminum sticking. Each cleaning removes surface metal from the mold, leading to dimensional deviations. The correct approach is to use atomized spraying to ensure even coverage of the release agent (5-10μm thickness). Select a non-corrosive, water-based release agent and inspect the mold surface weekly for corrosion.
Neglecting maintenance can exacerbate mold damage. After prolonged use, the vent grooves of a mold can become clogged with metal debris and slag, preventing air from escaping the cavity. This increases the impact pressure of the molten metal during filling, leading to localized excessive forces in the cavity. Statistics show that molds that fail to regularly clean the vent grooves have a 40% increased probability of cavity cracking. Maintaining the ejector mechanism is equally important. When the clearance between the ejector pin and the guide bushing exceeds 0.1mm due to wear, unbalanced loading can occur during ejection, leading to localized deformation of the cavity. Inadequate lubrication of the ejector pin can cause sticking, resulting in bending stress on the core during demolding of the die-cast part. Furthermore, improper mold storage can cause damage. For example, if a mold without anti-rust oil is stored in a humid environment (humidity > 60%) for more than a week, surface rust will form. Grinding away the rust will reduce cavity dimensional accuracy. Therefore, a closed-loop management system of “production-maintenance-storage” is necessary. Clean the vent grooves every shift, inspect the ejector mechanism monthly, and thoroughly clean and apply anti-rust oil before storage.
Wear caused by external impurities should not be underestimated. Non-metallic inclusions (such as sand and scale) in die-casting raw materials can enter the mold cavity with the molten metal and embed themselves into the mold surface under high pressure, causing abrasive wear. Due to insufficient raw material purity (impurity content 0.05%), an aluminum alloy die-casting mold developed dense scratches on the cavity surface after 50,000 cycles, with the roughness increasing from Ra 0.8μm to Ra 3.2μm. Furthermore, an excessively high proportion of recycled material (over 50%) increases the amount of oxide inclusions in the molten metal, accelerating mold wear. Experimental studies have shown that for every 10% increase in the recycled material proportion, mold life decreases by 5% to 8%. Raw material impurities should be removed through processes such as magnetic separation and filtration, with the recycled material proportion controlled at less than 30%. A ceramic filter (with a precision of 50-100μm) should be installed at the injection chamber entrance to intercept large impurities.
Defects in design details can lead to localized damage. If the mold parting surface lacks a venting step, gas compression generates high pressure during mold closing, causing wear on the parting surface. Insufficient parting surface inclination (<0.5°) can cause friction during mold opening, resulting in step-like damage. Insufficient guiding accuracy in the core pulling mechanism can also cause damage. When the clearance between the slider and the guide groove exceeds 0.05mm, the core will vibrate during pulling, causing the core to collide with the cavity and cause chipping. Due to poor slider guidance, a molded home appliance mold experienced a 0.5mm chipping of the core after 10,000 cycles. Analysis showed the clearance was as high as 0.08mm. Refined design details are needed: a 0.1-0.2mm venting step should be provided on the parting surface, guide keys should be added to the core pulling mechanism to maintain a clearance of ≤0.03mm, and a 1-2mm radius should be added to the core root to reduce stress concentration.
Sudden injuries caused by operational errors and equipment failures can have serious consequences. If foreign matter (such as residual die-cast parts) remains in the mold cavity during mold closing, the mold can be forced shut, generating significant impact force and potentially causing fractures in the cavity or core. This type of damage often occurs in automated production lines due to sensor failure. In one case, a photoelectric sensor misjudged the clamping force to 1.5 times its rated value, resulting in cracks in the fixed mold plate and repair costs exceeding 100,000 yuan. Failures in the injection system (such as pressure loss) can cause the molten metal to fill at excessive pressure, instantly exceeding the mold cavity’s force limit and causing plastic deformation. Equipment maintenance should be strengthened, including regular calibration of sensors and pressure valves, the implementation of dual safety interlocks (such as mechanical limit switches and pressure monitoring), and the performance of a “cavity clear” check before operation to minimize the risk of sudden injuries.
