Design of injection molded wedge
The design of the injection molding wedge block is the key to ensuring the stable position of the mold side core pulling mechanism during the injection molding process. It is mainly used to prevent the side core pulling slider from retreating or deflecting under the pressure of the plastic melt, ensuring the structural dimensional accuracy of the side holes, side recesses, etc. of the product. The wedge block is usually installed in the fixed mold part. During the mold closing process, it contacts the inclined guide column or locking surface on the side core pulling slider. The lateral force generated by the mold closing force locks the slider tightly in the working position. During the injection molding pressure holding stage, the wedge block withstands the lateral pressure of the melt on the slider to prevent the slider from moving and causing flash or dimensional deviations on the product. For example, when molding a plastic gear with a side hole, the wedge block needs to firmly lock the side core pulling slider to prevent the melt pressure from pushing the slider back, ensuring the position accuracy and aperture size of the side hole.
The wedge block’s structural form depends on the side core pulling mechanism and mold structure. Common configurations include integral and modular. Integral wedge blocks are integrally machined with the fixed platen, offering a strong and rigid structure and suitable for applications with high side core pulling forces. However, this approach is more challenging to manufacture, requires more material, and results in high maintenance costs. Modular wedge blocks, secured to the fixed platen with bolts or pins, are simple to manufacture and easily replaceable, making them suitable for molds with small to medium side core pulling forces. When worn, the wedge block can be replaced separately, reducing mold maintenance costs. The wedge block’s working surface is typically designed with a bevel. The angle of the bevel must match the angle of the guide pins, typically 2-3 degrees greater than the guide pins. This ensures that when the mold is closed, the wedge block contacts the slider before the guide pins, preventing damage to the guide pins from excessive lateral forces. For example, if the guide pins have a 15-degree inclination, the wedge block’s bevel angle can be designed to be 17-18 degrees.
The material selection and heat treatment process of the wedge block directly affect its service life and locking performance. Since the wedge block needs to withstand large lateral pressure and friction during operation, it is necessary to use high-strength, high-wear-resistant materials, such as Cr12MoV or SKD11 alloy tool steel. After quenching, the hardness reaches 55-60HRC, which improves its surface hardness and wear resistance. At the same time, low-temperature tempering is used to eliminate internal stress to ensure that the wedge block will not crack during use. The working surface of the wedge block needs to be ground, and the surface roughness is controlled below Ra0.8μm to reduce friction resistance when in contact with the slider and avoid premature wear of the slider or wedge block due to surface roughness. For large wedge blocks, tempering treatment is also required to improve the toughness of the core to prevent breakage when subjected to large loads.
The fit accuracy between the wedge block and the slider is an important factor in ensuring the locking effect. The fit clearance needs to be strictly controlled. If the clearance is too large, the slider cannot be effectively locked, causing the slider to move under the action of the melt pressure; if the clearance is too small, the mold closing resistance will increase, exacerbating the wear of both. Usually the fit clearance should be controlled between 0.01-0.03mm. The flatness and verticality of the inclined surface of the wedge block can be ensured through precision machining to ensure a close fit with the locking surface of the slider. During the assembly process, it is necessary to adjust the installation position of the wedge block or grind the inclined surface to ensure uniform fit and reliable locking. In addition, the installation position of the wedge block must be accurate, and its center line should be parallel to the movement direction of the slider to avoid poor contact between the wedge block and the slider or eccentric load due to installation deviation, which affects the locking effect and mold life.
The strength calculation of the wedge block needs to be performed based on the size of the side core pulling force to ensure that it will not deform or be damaged under the maximum lateral pressure. The strength calculation mainly considers the width and thickness of the inclined surface of the wedge block and the allowable stress of the material. The calculation formula is: F = σ × A, where F is the maximum lateral force, σ is the allowable stress of the material, and A is the load-bearing cross-sectional area of the wedge block. Based on the calculation results, the geometric dimensions of the wedge block are determined. For example, for a mold with a side core pulling force of 50kN, Cr12MoV material (allowable stress of approximately 1500MPa) is selected, then the load-bearing cross-sectional area of the wedge block must be no less than 33.3mm², and it can be designed as a rectangular cross-section with a width of 20mm and a thickness of 2mm. In actual design, the safety factor must also be considered. Usually, the calculated dimensions are enlarged by 1.2-1.5 times to cope with sudden loads or fluctuations in material properties. Once the design is complete, finite element analysis software can be used to simulate the forces acting on the wedge block, examining its stress distribution and deformation, optimizing its structural dimensions, and ensuring that its strength and rigidity meet operational requirements. Through rational structural design, material selection, and precision control, the wedge block effectively ensures the operational stability of the side core pulling mechanism, improving the dimensional accuracy and quality consistency of injection molded products.
