Defects such as short shots, flashes, sink marks, bubbles, deformation, burning and color difference often occur in injection molding production. Following the troubleshooting principle of from simple to complex, easy to difficult, process first then hardware, external inspection first then mold inspection can effectively reduce downtime and avoid blind commissioning. This standardized process is applicable to mold trial and mass production on site.
1. On-site Appearance and Basic Status InspectionAfter finding defective products, conduct visual inspection and basic environment check without changing any parameters first. Judge the defect source by observing the distribution rule of defective products: full-cavity abnormality, single-cavity defect or random scattered defects. Check raw material conditions to confirm no mixed materials, excessive recycled materials or material breakage caused by bridging in hoppers. Inspect workshop temperature, humidity, ventilation and equipment for water leakage and oil leakage. Finally, exclude secondary damage generated in post-processing and transportation links.
2. Raw Material Pretreatment VerificationUnqualified raw material pretreatment is a common cause of molding defects. For hygroscopic materials including PA, PC, PET and TPU, check the temperature, duration and air volume of drying equipment. Excess moisture will lead to bubbles, silver streaks and reduced transparency. For thermally decomposable materials such as PVC and POM, confirm storage period and environment to prevent premature aging. When using color masterbatch, color powder and additives, check mixing ratio and uniformity to eliminate color difference and mottle. Ensure raw material conveying pipelines are sealed to prevent foreign impurities from mixing in.
3. Troubleshooting by Fine Adjustment of Injection Process Parameters
If raw materials are qualified, adjust process parameters preferentially, which is the lowest-cost and most efficient solution. Follow the rule of single variable and small-range adjustment, and change only one parameter each time. Check barrel and nozzle temperature first: properly lower temperature for burning and silver streaks, and raise temperature for short shots and flow marks. Adjust injection pressure and speed: excessive pressure and speed cause flashes, while insufficient parameters lead to filling shortage.
Optimize packing pressure and time for sink marks and dents. Reduce back pressure and screw speed to relieve product whitening and internal stress. Adjust cooling time and mold temperature to solve deformation and demolding problems. Large-scale parameter modification is forbidden to prevent new defects.
4. Inspection of Equipment Operating StatusIf parameter adjustment fails, inspect the operation of injection molding machine. Observe the stability of mold opening, closing speed and pressure. Insufficient mold clamping force is the main cause of large-area flashes. Check injection and plasticizing actions to eliminate screw slipping and position deviation. Verify hydraulic system for stable oil pressure and no leakage. Calibrate temperature control system to ensure thermocouples and heating rings work normally, as temperature deviation will cause material decomposition or poor fluidity. Also check the liquid level and quality of hydraulic oil and lubricating oil.
5. Inspection of Mold Movement and StructureAfter eliminating equipment faults, focus on mold inspection. Check the action sequence of mold opening, closing, core pulling and ejection to remove jamming and uneven ejection, which will cause local flashes, deformation and surface scratch. Inspect venting system, clean carbon deposits and plastic residues in vent grooves. Blocked or under-sized vent grooves will result in burning, short shots and bubbles. Check the clearance of parting lines, inserts and ejector pins. Excessive clearance causes flashes, while too narrow clearance leads to scratch and mold sticking. Inspect cooling water channels for blockage, as uneven mold temperature will bring about inconsistent shrinkage and warpage.
6. Inspection of Auxiliary Systems and Peripheral Accessories
Check supporting auxiliary equipment. Verify the operation parameters and water flow of mold temperature controllers and chillers. For molds equipped with hot runner and vacuum venting systems, check vacuum degree, pipeline tightness, hot runner temperature and nozzle leakage. Improper use of release agent will leave surface blemishes. Calibrate the positioning accuracy of automatic manipulators and fixtures to avoid product deformation and collision damage during picking.
7. Judgment on Mold Precision, Wear and Mold RepairIf all above inspections cannot solve problems, the mold has inherent defects such as insufficient precision, long-term wear or unreasonable design. Check cavities and cores for wear, rust and peeling of polishing layer. Mold eccentricity, unreasonable gate position and uneven wall thickness cannot be solved only by process adjustment. Evaluate and carry out mold repair work such as polishing, gap matching, gate modification and vent groove re-opening. After trial run and verification, fix the optimal process parameters and formulate standard operation specifications to prevent recurring problems.
The standardized troubleshooting sequence guides on-site staff to locate faults efficiently. Combine defect types with targeted inspection to further improve efficiency and ensure stable production of injection molding workshops.
