Assembly of injection molded struts
As a crucial support component in the mold structure, injection molding stays are primarily used to enhance the rigidity of the mold cavity or core, preventing deformation caused by excessive melt pressure during the injection molding process, which can affect the dimensional accuracy and surface quality of the plastic product. The quality of their assembly is directly related to the overall performance and service life of the mold, so strict adherence to specifications is crucial during the assembly process to ensure precise alignment of each step.
First, the selection and pretreatment of injection molding struts are essential for assembly. Studs are typically constructed from high-strength alloy steels such as S45C and SKD61 to ensure sufficient compressive strength and wear resistance. Before assembly, the diameter, length, and number of struts must be determined based on the mold’s structural characteristics and stress conditions. Generally speaking, the strut diameter should be calculated based on the cavity’s load area and melt pressure, while the length should match the mold plate thickness to ensure a tight fit between the upper and lower plates after assembly. Furthermore, struts undergo rigorous pretreatment, including surface rust removal, degreasing, and precision testing. Through precision grinding, the parallelism of the strut’s end faces is controlled to within 0.01mm/m, with a surface roughness of Ra0.8μm or less, to minimize stress concentration and poor contact after assembly.
Secondly, positioning and marking the assembly position are crucial. When determining the mounting position of the support on the mold template, it is important to consider the mold’s force analysis results and place the support in areas of the cavity subject to greater stress, such as the cavity bottom and corners, to ensure uniform force distribution. During positioning, high-precision equipment such as jig boring machines and CNC milling machines can be used to ensure the accuracy of the support mounting holes. The diameter of the mounting hole should maintain a reasonable clearance with the diameter of the support, generally adopting a transition fit of H7/m6. This ensures smooth installation of the support and prevents loosening after assembly. When marking, tools such as a height vernier caliper and a stylus should be used to precisely mark the center of the mounting hole on the template surface. Dot punching should be used to accurately locate the hole, providing an accurate basis for subsequent drilling. Furthermore, the verticality of the mounting hole should be checked, with a deviation within 0.02mm/100mm to prevent additional stress caused by tilting the support after assembly.
The press-fitting and fixing operations during the assembly process require strict control. For the support columns of small molds, a manual press can be used for press-fitting. During press-fitting, flat pads should be placed on both ends of the support column to avoid deformation or damage to the support column due to direct knocking. During the press-fitting process, pressure should be applied slowly, and a dial indicator should be used to monitor the verticality of the support column to ensure that its axis remains perpendicular to the plane of the template. For the support columns of large molds, a hydraulic press can be used for press-fitting. By controlling the press-fitting speed and pressure, smooth assembly can be achieved. After the support column is pressed into place, it needs to be fixed. There are two common fixing methods: one is to use spot welding to fix the contact between the two end faces of the support column and the template to prevent the support column from loosening during use; the other is to apply anaerobic glue to the mating parts of the support column and the mounting hole to enhance the connection strength through bonding. After fixing is completed, the end face of the support column needs to be ground to make it flush with the template surface to avoid interference during the mold closing process.
Post-assembly inspection and adjustment are critical steps in ensuring the performance of the support pins. First, use a dial indicator to check the verticality and flatness of the support pins to ensure they meet design requirements. If verticality is out of tolerance, correct it by grinding the support pin end faces or adjusting the mounting hole position. Next, perform a mold closing test to check the contact between the support pins and the upper and lower mold plates to ensure that the support pins are evenly loaded when the mold is closed. Apply red lead powder to the support pin ends and observe the contact marks after mold closing. If the marks are unevenly distributed, grind the support pins until the contact area reaches at least 80%. Furthermore, mold trials are required to verify the dimensional accuracy and surface quality of the plastic product through injection molding tests. If mold deformation is detected due to improper support pin assembly, the position or number of the support pins should be adjusted promptly. During the mold trial, monitor the temperature of the support pins. If localized overheating occurs, it may be due to insufficient assembly clearance or uneven load, and should be addressed promptly.
Finally, the maintenance and care of injection molding struts is crucial for extending the mold’s lifespan. During mold use, the struts should be regularly inspected for wear and tightening. Any looseness or severe wear should be promptly replaced. For molds used over a long period, the struts can be periodically nitrided to improve their surface hardness and wear resistance. During storage, the mold should be kept closed to prevent deformation of the struts due to uneven force over time. Furthermore, attention should be paid to mold cleanliness to prevent plastic residue or oil from accumulating on the strut surfaces, which could affect their load-bearing properties. Through scientific and rational assembly, testing, and maintenance, injection molding struts can fully realize their supporting role, ensure stable mold operation, and improve the quality and production efficiency of plastic products.
