China Key Points to Grasp in Injection Mold Development for Small Product Projects
Small plastic products feature compact size and multi-cavity layout, demanding high precision, stable molding performance and controllable processing cost. Missing details in project planning, mold design, machining, assembly and trial molding can easily lead to batch defects and delayed schedules. During project development, product evaluation, mold scheme, process reservation, cost and delivery timeline should be coordinated comprehensively, to ensure smooth project implementation.
1. Product Structure and Tolerance Evaluation
In the early stage of the project, prioritize checking the uniformity of wall thickness of small products to avoid shrinkage, burn marks and insufficient filling caused by partial over-thickness or thinness. Focus on checking undercut, small holes, thin ribs and other features, evaluate whether to adopt angle lifter, slide or insert structure, simplify complex demolding mechanism as much as possible and reduce the probability of jamming fault of mold in later stage. At the same time, distinguish appearance size and assembly function size against drawing tolerance requirements, determine the compensation benchmark of shrinkage rate. For multi-cavity molds, evaluate cumulative tolerance brought by size deviation of each cavity, confirm alternative scheme of tolerance relaxation with product side in advance, and prevent repeated mold modification due to unqualified size in mold test stage.
2. Cavity Layout and Gating System Scheme
Most small products adopt multi-cavity layout. The cavity layout prioritizes stress balance and flow balance to avoid filling time difference of melt in different cavities, resulting in insufficient material and shrinkage in some cavities. The runner design selects short runner and small cross-section runner as far as possible to reduce waste. Hot runner scheme can be selected for appearance parts to reduce gate marks, and calculate temperature control pressure loss of hot runner at the same time. The gate position should avoid product appearance surface and assembly matching area. Point gate and submarine gate are preferred for thin-wall small parts to prevent long gate residue and increase post-processing procedures. Evaluate gate shear heat to avoid material burning.
3. Exhaust and Cooling System Design
Small parts fill fast, gas carried by melt front is difficult to discharge quickly, which is easy to produce burning, weld line and bubble defects. Exhaust grooves are set at melt end and weld line position, and the depth of exhaust groove is controlled to match raw material characteristics to prevent flash. Cooling system is the key to stable molding of small parts. The space of small mold is compact, the layout of cooling water channel needs to be close to cavity and core surface with reasonable water channel spacing to avoid local hot spots. Small standard parts are selected for water channel connectors, which cannot interfere with ejector pins, inserts and screws. Ensure uniform temperature in all areas of mold, reduce product warpage and shorten molding cycle.
4. Ejection Mechanism and Mold Strength Check
The space of ejection mechanism of small plastic parts is narrow. The selection of ejector pins, flat ejectors, ejector blocks and other parts should take both strength and assembly space into account, and standardized ejection accessories are preferred to reduce the difficulty of spare parts procurement in later stage. For thin-wall small parts, control uniform ejection force to prevent ejection whitening and penetration. Although the product volume is small, the cavity pressure during high-speed injection is not low. It is necessary to check the strength of cores, inserts and templates to prevent bending deformation of thin cores under pressure. Precision guide posts and guide sleeves are selected for guiding and positioning structure, and positioning pins are added for multi-cavity molds to ensure mold closing precision and prevent parting surface flash.
5. Material Selection and Processing & Assembly Control
Select mold steel according to product use environment and raw material type. Pre-hardened steel is selected for ordinary mass production small parts, wear-resistant steel for glass fiber reinforced raw materials, and high polishing mold steel for mirror surface appearance products. Control CNC and EDM processing precision in processing stage, reduce manual polishing allowance, control tool marks and avoid too long polishing time in later stage. Control gap during assembly stage, reserve thermal expansion gap for ejector pins, slides and angle lifters. After assembly, carry out mold closing inspection to confirm no interference and check all moving parts slide smoothly.
6. Mold Test, Verification and Mass Production Handover
The first mold test focuses on verifying filling, exhaust and cooling effect, record process window, confirm product appearance, size and assembly performance, adjust mold in batches instead of modifying mold a lot at one time. After mold test is qualified, carry out small batch trial production, continuously observe mold wear and check wear risk of moving parts. Sort out mold drawings, spare parts list and standard process parameters at the end of the project, complete handover of mold maintenance instructions, clarify vulnerable parts list to provide support for long-term mass production maintenance in later stage. Record documents synchronously in the whole process of project development, update problems timely, reduce communication deviation, control mold cost, take long-term mass production stability into account, and ensure on-time delivery of small product projects.
