Flash, also known as burrs, is a common molding defect in injection molding, which frequently appears on the parting surface of plastic molds. It not only spoils the appearance and dimensional accuracy of finished products and increases extra trimming work, but also may lead to assembly jamming and functional failure. Repeated flash will also accelerate mold wear and shorten its service life. This defect is rarely caused by a single factor, but results from the combined effects of mold conditions, injection parameters, raw material properties and equipment operation. Analyzing its root causes and adopting targeted solutions can effectively improve molding conditions and ensure continuous and stable production.
1. Mold-related Causes and CountermeasuresThe mold condition is the decisive factor for the sealing performance of the parting surface, and most persistent flash problems originate from the mold itself. Long-term mold opening and closing, as well as impact from high-pressure melt, will reduce the fitting precision of the parting surface. Excessive gaps between mating surfaces are the most direct cause. If the parting surface is worn after long production runs, or poorly fitted during initial processing, high-temperature and high-pressure plastic melt will overflow through gaps and form flash. Collision damage and chipping on the parting surface will also destroy its tight fit. For minor wear, grind and re-fit the parting surface to reduce clearance. For chipped and sunken areas, perform surfacing welding followed by fine grinding to restore full contact.
Insufficient mold clamping force and template deformation are also common triggers. When the melt fills the cavity under high pressure, it will generate reverse force to prop the mold open. Templates with insufficient rigidity will deform slightly and widen the parting gap. To solve this problem, add support pillars and thicken backing plates to enhance overall rigidity. Correct and repair templates with permanent deformation in a timely manner. Besides, worn guide pins, guide bushes and positioning components will cause misalignment during mold closing, resulting in uneven gaps. It is necessary to replace worn parts regularly and clean glue residues and metal debris on the parting surface before each mold closing.
2. Improper Injection Parameters and Adjustment MethodsEven for well-maintained molds, unreasonable process settings can also produce flash. Excessively high injection pressure and holding pressure are major inducements. Excessive pressure will force the parting surface apart during cavity filling. It is advisable to gradually lower the pressure within a reasonable range, ensuring no shrinkage or short shot on products, and shorten the holding time to avoid long-term pressure load on the cavity.
Excessively fast injection speed creates strong instantaneous impact from the melt, which easily breaks the seal of the parting surface. It is recommended to adopt segmented speed control: maintain normal speed for runner filling and slow down in the later stage of cavity filling to reduce impact. Too high barrel and mold temperature will lower melt viscosity, making the material more likely to seep into tiny gaps. Appropriately reduce temperature according to material characteristics to increase melt consistency.
3. Influences of Raw Materials and Improvement MeasuresPlastic raw materials have a notable impact on flash formation. Materials with high fluidity are more prone to overflow. If product performance allows, select materials with moderate fluidity or reduce the proportion of lubricants and plasticizers. Damp raw materials will produce steam inside the barrel, causing unstable cavity pressure and accompanying defects such as air bubbles and silver streaks. Raw materials must be fully dried before production, and stored in a dry environment. Mixing different types of plastics is forbidden, as foreign materials will change flow characteristics and raise defect risks.
4. Equipment Failures and Daily Management
Malfunctions of injection molding machines will cause abnormal clamping and injection actions. Insufficient clamping cylinder pressure, worn crankshaft and offset clamping position will lead to inadequate actual clamping force. Regularly calibrate clamping parameters, inspect hydraulic systems and replace aging sealing parts. Correct the parallelism of movable and fixed templates to ensure smooth mold closing.
Combined prevention and control are essential to avoid recurring flash. Conduct first-piece inspection after startup and mold change, and stop production to troubleshoot once slight flash is found. Formulate a regular mold maintenance schedule to clean the parting surface and inspect positioning parts. Follow the principle of gradual adjustment during parameter debugging, and keep detailed records of mature process parameters to form standard operating specifications.
Flash reflects multiple hidden problems in production. Distinguish between temporary parameter issues and permanent mold defects, and handle them pertinently. Reasonable parameter setting, standardized material management and regular maintenance of molds and equipment can eliminate flash fundamentally, guarantee product quality, cut maintenance costs and realize efficient injection production.
