Determining Four Mold Design Schemes
Time：2026-10-13 08:56:17 / Popularity： / Source：
I. Determining Parting Surface, Number of Cavities, and Arrangement
Determining mold design scheme is essentially determining mold structure. The first issue in determining mold design scheme is determining mold opening direction and parting surface. After determining parting surface and gate type, gate location is then determined. Once these two are determined, dimensions of runner are naturally determined based on dimensions of product. After parting surface, runner, gate, and ejection method are determined, mold base specifications and model are selected, and basic structure of mold is thus determined.Generally speaking, when production batch is small, dimensions are large, and high precision is required, a single-cavity mold is suitable; when production batch is large and production costs need to be reduced, a multi-cavity mold is used. When using a multi-cavity mold, a balanced arrangement is required. If cavity balance cannot be achieved, even with identical cavity dimensions, products will often exhibit inconsistent dimensions, leading to incomplete or overfilled filling, resulting in burrs, reduced molding efficiency, and other abnormal phenomena. Therefore, thorough consideration is necessary when using multi-cavity molds.
II. Side Core-Pulling Mechanism and Part Ejection Method
When part has lateral protrusions and recesses, molding and demolding method must be carefully considered. Mold structure should consider methods such as flap molding, side core pulling, lifters, or rotating threaded cores. For part ejection, ejector pins are commonly used, but ejector plates can be used to avoid leaving ejector pin marks on part. Other ejection methods include ejector tubes, ejector blocks, and pneumatic ejection; the most suitable ejection method for molded part must be determined. For cold slug demolding in main runner, three-plate molds use main runner pull rods, while two-plate molds use main runner push rods.Both sliders and lifters are common demolding structures. Some fasteners utilize both sliders and lifters to demold plastic parts. Difference is that lifters, compared to sliders, also provide an ejection function. Lifters have various designs, each with significant differences in structure and lifespan. A specific analysis should be conducted for each case to select appropriate lifter structure. Generally, lifters are considered less stable than sliders, with higher wear and failure rates, but they occupy less space, resulting in a more compact mold structure.
III. Determining Mold Machining Method
After determining detailed mold structure, machining method must be determined. In actual machining, suggestions from CNC programmers and on-site fabrication personnel can be adopted. These suggestions are for roughing and semi-finishing to achieve correct shape. Determination of machining method discussed here involves pre-determining during design phase which machining method can achieve required shape and is the most economical. Therefore, it is necessary to illustrate special machining methods used, heat treatment methods, and methods that require disassembling into two or more parts for assembly using existing machining equipment, etc. When machining molded parts, special machining methods can be used for complex shapes with many curved surfaces, while other shapes should be machined using ordinary machine tools as much as possible. Degree of polishing of molded part surface must be determined along with machining method. In addition, hardness requirements of sliding parts that may wear and areas that may generate flash must be determined.IV. Impact of Insert Removal on Mold Structure
Insert removal directly affects mold structure. There are two main categories of insert removal: partial insert assembly and full insert assembly. Full insert assembly is generally suitable for medium to large-sized plastic parts. Insert removal is closely related to mold cost, and its impact on mold cost is complex. Insert removal directly affects ordering specifications of mold steel, machining process and process arrangement of mold parts, and organization of production in mold workshop. Therefore, from a techno-economic perspective, reasonable insert removal can improve processing efficiency of mold workshop equipment; conversely, unreasonable insert removal will waste machining time and cause difficulties in mold assembly.Location of insert removal has a significant impact on design of cooling circuit, thus affecting injection molding cycle. When disassembling inserts in a mold core, process should prioritize convenience, ease of processing, material conservation, and cost reduction, while ensuring customer appearance requirements and good molding quality as much as possible. Following principles should be considered when disassembling inserts:
1. For a given product, specific parts requiring insert removal depend primarily on actual processing capabilities at processing site and product's specific structure. Generally, areas with complex shapes, difficult processing, challenging molding, or multiple mating parts requiring repeated adjustments should be considered for insert removal.
2. Inserts should ideally not be removed from product's exterior surfaces. If insert removal is unavoidable, method must be confirmed with customer before proceeding.
3. For large, assembled molds, insert structures should be as regular as possible, with length and width dimensions rounded down to minimize processing errors caused by mechanical precision issues and effectively prevent assembly misalignment leading to mold closing difficulties.
4. When product structure contains through holes and blind holes, inserts are generally used to cover corresponding molding locations.
5. Disassembly of inserts requires consideration of machining datum for each insert to ensure machining and assembly accuracy.
6. Experienced technicians should review feasibility of insert disassembly.
Number and location of inserts are crucial and must be closely integrated with company's mold manufacturing process, stroke, parameters, and machining range of existing machine tools, taking into account injection molding venting and mold polishing. Inappropriate insert disassembly may hinder utilization of insert functions and advantages, waste machining time, weaken mold cooling, potentially affect mold strength and rigidity, causing irreparable damage. Poor insert segmentation also makes mold assembly difficult, lacking assembly datum.
