Solutions to Flash on the Parting Surface of Plastic Molds

In plastic mold production, flash on the parting surface is a common problem affecting product appearance and efficiency. It increases flash trimming time, reduces yield, and even causes mold crushing and deformation, shortening mold life. Essentially, it is excess material formed by molten plastic squeezing into parting surface gaps under injection pressure. To solve it completely, systematic treatment from mold, process, equipment and maintenance is needed. Below are practical, on-site applicable solutions.

Optimize Mold Structure and Precision

Mold precision and structure are the core causes of flash. First, check parting surface flatness, ensuring no depressions, deformation or tool marks. Re-grind if there are depressions to ensure tight fitting after clamping. For large parting surfaces, arrange support columns and ejector pins reasonably to prevent template elastic deformation under injection pressure—ensure supports fit the parting surface tightly.

Insufficient clamping force and template deformation also cause flash. Increase template thickness and optimize mold base structure to enhance rigidity. Unreasonable vent depth is another cause: control vent depth at 0.015~0.025mm for common plastics; excessive depth allows plastic to flow in, forming flash. Poor positioning accuracy leads to clamping misalignment—ensure guide pillars/bushings fit smoothly, and positioning pins are firm to avoid offset.

For worn, damaged or collapsed parting surfaces (especially around sliders, lifters and inserts), repair them in time by welding and precision grinding to restore flatness and fitting.

Adjust Injection Molding Process Parameters

Process adjustment is a direct on-site solution, focusing on reducing cavity pressure, template deformation and over-filling. Reduce injection pressure appropriately (on the premise of full product filling) to prevent template opening. Lower injection speed, especially at the end of filling—excessive speed causes instant pressure peaks, leading to parting surface opening. Adopt segmented injection: fast filling in the early stage, slow down and reduce pressure in the later stage.

High material and mold temperatures reduce plastic viscosity, making it easier to seep into gaps—adjust temperatures according to material characteristics to avoid over-thinning. Excessive holding pressure and time cause over-compaction, continuously applying high pressure to the parting surface. Reduce them if there is no product shrinkage. Adjust filling switching position to switch from injection to holding pressure earlier, avoiding over-filling and relieving cavity pressure.

Check Injection Molding Equipment

Equipment issues are often overlooked but important. Confirm sufficient machine clamping force—calculate based on product projection area and increase if necessary to resist injection pressure. Check machine plate parallelism: uneven plates cause uneven mold force and local gaps; calibrate regularly.

Worn clamping mechanisms and excessive pin gaps affect clamping accuracy—repair or replace worn parts in time. Check hydraulic system pressure stability: fluctuations cause unstable clamping force and intermittent flash—maintain the hydraulic system for stable pressure output.

Standardize Production and Mold Maintenance

Daily maintenance prevents recurring flash. Clean the parting surface thoroughly before production to remove residual plastic and foreign matter, which cause poor clamping. Strictly control the production process to avoid mold crushing, which damages the parting surface.

Maintain molds regularly: grind and maintain parting surfaces, sliders and inserts to keep precision. Establish a mold use record to track flash patterns, predict problems and conduct preventive maintenance, reducing downtime.

Conclusion

Flash affects production efficiency, cost and mold life. The effective solution is coordinated improvement of mold precision, injection process, equipment status and daily maintenance. Mastering these methods solves on-site problems, avoids defects from design, ensures smooth production, high yield and long mold life—an essential skill for mold and process engineers.