How to Solve the Frequent Breakage of Injection Mold Ejector Pins
Frequent breakage of injection mold ejector pins is a common problem that can significantly impact production efficiency.
1. Optimize Ejector Pin Design
Reasonable Selection of Pin Size: The diameter and length of the ejector pin should be determined based on the size, shape, and required demolding force of the product. If the pin diameter is too small, it is prone to breakage due to stress concentration when withstanding the demolding force. For example, for large plastic products, pins with larger diameters should be selected to disperse the demolding force. The length of the ejector pin should not be excessive. An excessively long pin is prone to bending deformation during the demolding process, leading to breakage. Ensure the pin length is sufficient to complete the demolding action while minimizing unnecessary length.
Optimize Pin Layout: The distribution of ejector pins should be even to avoid concentrating the demolding force on a few pins. When designing the mold, the location of the ejector pins should be arranged reasonably based on the shape and structural characteristics of the product. For example, for circular products, a circularly evenly distributed pin layout can be adopted; for products with irregular shapes, the number of pins should be appropriately increased at the edges of the product and in areas with complex internal structures.
2. Improve Mold Machining Accuracy
Improve the Machining Quality of Pin Holes: The dimensional accuracy, shape accuracy, and surface roughness of the pinhole have a significant impact on the service life of the ejector pin. The tolerance of the pinhole diameter should be controlled within a reasonable range. Generally, a suitable clearance fit with the pin is required. Excessive looseness will cause the pin to wobble during movement, while excessive tightness will increase the friction between the pin and the hole wall. The straightness of the pinhole is also important. A bent pinhole will cause the pin to be subjected to lateral forces during movement, making it prone to breakage. When machining pin holes, high-precision machining equipment, and processes, such as electrical discharge machining or CNC machining centers, should be used to ensure the accuracy of the pin holes. The surface of the pinhole should be smooth, with a roughness generally required to reach Ra0.8 - Ra1.6μm. The surface quality of the pinhole can be improved through processes such as grinding and polishing to reduce friction between the pin and the hole wall.
Ensure Mold Assembly Accuracy: When assembling the mold, ensure the coaxially of the ejector pin and the pinhole. If the ejector pin and the pinhole are not coaxial, the pin will be subjected to uneven forces during movement, easily causing deviation and wear, and eventually leading to breakage. Professional measuring instruments can be used to detect and adjust coaxially, and the assembly process should strictly follow the assembly process requirements.
3. Select Suitable Pin Material
Select Materials Based on Mold Requirements: Different injection molding processes and product requirements require the selection of different materials for ejector pins. For general injection molds, high-quality mold steel such as SKD61 can be used to make ejector pins. This type of steel has good toughness, wear resistance, and corrosion resistance.
Ensure Material Quality: Choose a reputable material supplier to ensure the quality of the ejector pin material. The purity, microstructure, and other factors of the material will affect its performance. When purchasing ejector pin materials, check the material quality inspection report and conduct sampling inspections to prevent the use of inferior materials.
