How to Select the Model of Injection Mold Base
The scientific selection of injection mold base models is a core link to ensure mold accuracy, production efficiency and service life. The selection process needs to comprehensively consider product size, mold structure, injection molding machine specifications and production batch. First, determine the projected area and cavity layout of the product to calculate the required mold opening/closing force and mold base load-bearing capacity, then select the standard mold base series according to the template size and T-slot spacing of the injection molding machine, determine the length and width specifications of the mold base through the core and cavity size and the structural parameters of sliders and inserts, and finally match the template thickness and structural details. The whole process needs to realize the matching of mold strength, rigidity and production rhythm, so as to avoid the problems of insufficient mold base strength, interference with the injection molding machine and low production efficiency caused by improper selection.
1. Clarify the Core Selection Basis and Constraints
Before selecting the mold base, it is necessary to sort out the core constraint conditions to ensure that the selection is targeted. First, confirm the product size, wall thickness, cavity number and layout, calculate the projected area of the product and the total projected area of the mold, so as to determine the clamping force required by the injection molding machine and the load-bearing capacity of the mold base. Second, confirm the model and parameters of the matched injection molding machine, including the maximum mold thickness, minimum mold thickness, template size, T-slot spacing, ejection stroke and other parameters, to ensure that the mold base size can be installed and used normally on the injection molding machine. Finally, clarify the mold structure, such as whether there are sliders, lifters, inserts, hot runners and other special structures, so as to reserve sufficient installation space in the mold base selection.
2. Select the Standard Mold Base Series and Specification
At present, the commonly used standard mold bases in the industry include the Chinese national standard (GB/T 12555), the LKM standard (Longsheng mold base) and the DME standard (American standard), etc. The LKM standard is the most widely used in the Chinese market, with complete specifications and high versatility. According to the mold structure, it is divided into two categories: two-plate mold base and three-plate mold base. The two-plate mold base is suitable for direct gate, point gate and other conventional structures, with simple structure and low cost; the three-plate mold base is suitable for products with multiple cavities, fine nozzles and automatic demolding, with complex structure and high cost, and is selected according to the product gating system design.
After determining the series, select the mold base size according to the core and cavity size. The length and width of the mold base should be 30–50 mm larger than the outer dimension of the core and cavity, so as to reserve sufficient space for the cooling system, positioning system and locking mechanism. For molds with sliders and lifters, it is necessary to reserve the movement space of the sliders on the basis of the core and cavity size, and appropriately increase the length and width of the mold base by 50–100 mm to avoid interference between the sliders and the mold base or the injection molding machine template.
3. Determine the Template Thickness and Structural Matching
The template thickness directly determines the rigidity and strength of the mold, and is the core parameter to prevent mold deformation and product dimensional deviation. The thickness of the A plate (cavity plate) and B plate (core plate) is determined according to the cavity depth, product size and injection pressure. For small and medium-sized molds with conventional injection pressure, the thickness of the A and B plates is generally 40–80 mm; for large-sized molds or molds with high injection pressure, the thickness should be increased to 80–120 mm, and the strength check should be carried out through finite element analysis to avoid template deformation caused by insufficient rigidity.
The thickness of the support plate, backing plate and top plate is matched according to the ejection system and mold structure. The support plate is used to improve the overall rigidity of the mold, and the thickness is generally 20–40 mm; the top plate and top back plate are used to install the ejection mechanism, and the thickness is determined according to the ejection stroke and the number of ejector pins, generally 15–30 mm. For molds with hot runners, it is necessary to select a mold base with a thickened A plate or add a hot runner mounting plate to meet the installation requirements of the hot runner system.
4. Match the Standard Parts and Special Structure Requirements
After determining the basic model of the mold base, it is necessary to match the standard parts and special structures to ensure the normal operation of the mold. The guide pillar and guide bush are selected according to the mold size and precision, and the high-precision guide pillar and guide bush are used for precision molds to ensure the positioning accuracy of the mold. The ejection system is matched according to the product demolding requirements, and the number and position of ejector pins are reasonably arranged to avoid product deformation during demolding. For molds with sliders, it is necessary to reserve the installation space of the slider locking mechanism, oil cylinder or spring in the mold base, and select the mold base with a side lock or oil cylinder mounting hole.
For mass production molds, it is necessary to select a mold base with a thickened template and high-strength materials, and add a cooling system and wear-resistant inserts to improve the service life of the mold; for trial molds and small-batch production molds, a standard mold base with conventional thickness can be selected to reduce the mold cost.
5. Final Check and Verification
After completing the mold base selection, conduct a comprehensive check to ensure that all parameters meet the requirements. First, check whether the mold base size matches the injection molding machine, including the mold thickness, length and width, ejection stroke, etc., to avoid installation interference. Second, check whether the mold base has sufficient space for the core and cavity, cooling system, ejection system and slider structure to avoid structural interference. Finally, check the strength and rigidity of the mold base to ensure that it can withstand long-term injection pressure and opening/closing force without deformation. For special molds such as precision molds and large molds, it is necessary to conduct finite element simulation analysis to verify the rationality of the mold base selection.
