In injection molding, excess thin material burrs appearing on the edges of products, commonly known as flash, not only affect the appearance but also increase the cost of trimming processes, and in severe cases, directly cause product scrap. Flash problems occur frequently in daily processing. Identifying the causes and making targeted adjustments can effectively reduce this defect.
I. Main Causes of Flash
1. Insufficient Mold Closing Force: Insufficient mold closing pressure, when the molten material is injected under high pressure, will open the mold gap, and the plastic will overflow along the gap, forming flash at the edges. Long-term mold wear and tear, and poor fit between the mold parts, can also cause the same problem.
2. Inappropriate Injection Parameters: Injection pressure and holding pressure set too high, resulting in excessive impact force of the molten material; injection speed too fast, causing the material to expand and be compressed instantaneously, can all break through the mold seal, producing burrs. High barrel temperature and mold temperature, with excessive plastic fluidity, also easily lead to overflow and flash.
3. Mold Malfunctions
Wear or deformation of the mold parting surface, loose or misaligned guide pillars and bushings, leading to gaps when the mold closes; excessively deep or large venting grooves cause molten material to overflow from the venting points, forming flash.
4. Raw Material and Equipment Factors
Excessively fluid plastic raw materials increase the difficulty of control during molding; inconsistent tension of equipment tie rods, machine level deviation, uneven force during mold closing, and enlarged local gaps cause overflow.
II. Practical Mitigation and Solutions
1. Stabilize the Mold Closure Foundation
Match the standard clamping force according to the product size and molding area to ensure a tight mold fit. Regularly inspect the mold mating surfaces, promptly grind and repair any wear or deformation, tighten mold components, and eliminate closing gaps.
2. Optimize Injection Molding Process Parameters
Gradually reduce injection pressure and holding pressure, slow down the injection speed, and reduce the impact force of molten material extrusion. Reasonably control the material temperature and mold temperature to avoid excessively thin material flow and adapt to the molding characteristics of the raw material.
3. Mold Inspection and Maintenance: Regularly clean debris and waste from the parting surface to prevent foreign objects from lifting the mold; standardize the depth of the venting grooves, promptly repairing and adjusting any excessively large areas to ensure smooth venting and prevent material leakage.
4. Standardized Material Selection and Equipment Adjustment: Select plastic raw materials with suitable flowability as needed; regularly calibrate the equipment level and evenly tighten the machine's tie rods to ensure balanced force during mold closing, eliminating material overflow from a hardware perspective.
By properly controlling the process, maintaining the mold, and adjusting the equipment, the rate of flash defects can be significantly reduced, the finished product qualification rate improved, and subsequent processing losses minimized.
