China How to Carry out Synchronous Debugging of Ejection Mechanism in Plastic Mold Assembly
The synchronization performance of ejection system is critical in plastic mold assembly. Out-of-sync movement of ejector pins, ejector blocks and reset parts may cause product whitening and deformation, or even pin fracture and mold collision in serious cases. The ejection system must be fully debugged during assembly to ensure smooth and consistent ejection and reset. During injection production, molds work under alternating hot and cold conditions, and metal components will expand with heat. Static dimension measurement alone cannot guarantee reliable operation, so static assembly inspection and thermal simulation test must be combined to check synchronization deviation and reduce failures in trial mold and mass production.
1. Pre-inspection and Cleaning Check of Parts
Check the appearance of parts, eliminate collision, bending and burr defects, re-measure the actual length of each ejector part, and store parts with different lengths separately to avoid height difference caused by mixed assembly. Thoroughly clean iron filings and cutting oil remaining in each hole of ejector plate, check the smoothness of inner wall of guide hole. If there are tool marks or scratches on hole wall, polish and repair in advance to prevent ejector pin scratch after assembly. Check the design stroke at the same time, confirm that the demolding distance meets product requirements, reserve safety allowance to prevent mold collision caused by excessive ejection stroke. For slender ejector pins and thin-wall ejector tubes which are easy to deform, check straightness separately. Slightly bent parts cannot be directly put into assembly to avoid jamming during ejection operation.
2. Pre-assembly and Level Calibration of Ejector Plate
The ejector plate is the carrier of the whole ejection mechanism, and its levelness directly determines the uniformity of ejection force distribution. Assemble the ejector bottom plate and ejector panel first, install reset rod and limit screw, and place the component on flat workbench. Use dial gauge to verify the parallelism of the two plates, adjust and eliminate height difference caused by plate warping to ensure the overall level of ejector plate. Push the ejector plate manually to slide back and forth along the guide post, check whether the sliding resistance is uniform without local jamming. Once unsmooth sliding is found, carry out research and repair in time to prevent eccentric load of ejector pin caused by inclined ejector plate after assembly. Parallelism deviation of ejector plate will directly disperse ejection force, part of ejector pins bear extra load, and fatigue fracture is easy to occur after long-term mass production. During pre-assembly, check the thread state of ejector plate screw hole, clean iron filings inside thread to ensure uniform stress during subsequent locking and avoid screw thread slipping.
3. Ejector Parts Assembly and Equal-height Lapping
Install all kinds of ejector parts in turn, ensure the tail of ejector pin is closely attached to the counterbore of ejector panel without suspended gap. After assembly, close the mold to fit the cavity, polish the end face of all ejector parts, unify the height, make the ejector end face flush with the cavity parting surface, and strictly control the height error. For composite ejection structure with multiple types, prioritize the height consistency of main bearing ejector parts, and fine ejector pins can be compensated slightly. Check the fitting gap between ejector parts and template holes at the same time, reserve thermal expansion allowance to prevent locking or flash at high temperature operation. Equal-height lapping cannot polish a large amount at one time. Adopt multiple small amount polishing, compare after each polishing to avoid ejector pin sinking caused by excessive polishing and leaving dents on product surface. For appearance part molds, the polishing treatment of ejector pin end face should also be completed synchronously to prevent scratching product surface during ejection.
4. Reset Mechanism and Synchronous Limit Debugging
Select springs with consistent specification when assembling reset springs to ensure unified compression amount and uniform elastic force. Push the ejector plate manually to complete full-stroke reciprocating action, observe the reset state of reset rods, confirm all reset rods contact the A plate bottom surface at the same time and complete synchronous reset. Adjust the limit screw to ensure that when ejection is in place, all positions of ejector plate touch the limit at the same time, and there is no local advance limit or delay limit. For composite ejection structure with angle lifter and flat ejector, check the movement timing separately to avoid part interference during ejection. Check the free length of springs before assembly. The difference of free length of reset springs used in one set of mold is controlled in a small range. If elastic force gap is too large, part of reset rods return first and others lag, resulting in inclined ejector plate. The locking torque of limit screw needs to be unified to prevent screw loosening during use and changing ejection stroke.
5. Dynamic Verification and Gap Trimming After Mold Closing
After the whole mold assembly is completed, carry out dynamic test by opening and closing mold manually many times. Observe the action of ejection mechanism in the whole process, check whether there is scraping and blocking during movement of ejector pins and ejector blocks. Use feeler gauge to detect the fitting gap of each moving pair, check the guide gap of ejector plate and eliminate unilateral friction phenomenon. Carry out fine trimming for positions with small gap, take both normal temperature assembly state and size change after mold heating into consideration. Slow operation is required for dynamic test, observe the operation state of ejection mechanism in the whole stroke repeatedly. Many jamming problems only appear in the middle of stroke. The ejector pin hole gap needs to be judged combined with molding raw materials. For raw materials filled with glass fiber, the gap can be appropriately reduced to lower the probability of flash. For ordinary soft rubber raw materials, reserve slightly larger gap to avoid locking risk after high temperature expansion. After all trimming is completed, clean polishing debris in holes again. Residual debris will wear the hole wall and amplify gap deviation after long-term use.
6. Thermal Pre-verification and Assembly Completion
Heat the mold to mass production working temperature, test the reciprocating ejection action manually again, verify the synchronization state of mechanism after thermal expansion, and confirm no jamming of mechanism at high temperature. Repeat full-stroke tests many times to confirm all ejector parts eject and reset synchronously without time difference. After test, clean impurities inside mold, apply suitable lubricating grease, lock all fixing screws, record ejection stroke, limit size and other key parameters, and retain assembly records. Thermal verification is a very critical step. The gap qualified under normal temperature assembly state will shrink after metal expansion when mold is heated, and the originally smooth mechanism may jam. Many hidden synchronization problems in assembly stage can only be exposed after mold heating. After mold assembly enters the mold test stage, fine-tune ejection synchronization parameters combined with actual product demolding state. Avoid various molding defects caused by asynchronous ejection from assembly source, and improve mass production stability of mold. In subsequent production maintenance links, refer to this assembly record, regularly check the synchronization state of ejection mechanism, replace aging springs and worn ejector pins in time, and continuously guarantee stable mold production.
