30 Common Problems and Solutions in Injection Molding

1. Causes and Solutions for Product Flashing When the Machine is First Started and Glue Shortage After a Period of Production: When the machine is first started up, the molten glue in the injection molding machine barrel takes a long time to heat up, resulting in low viscosity and good fluidity, making the product prone to flashing. After a period of production, the molten glue continuously dissipates heat, causing insufficient glue, high viscosity, and poor fluidity, leading to glue shortages. Gradually increasing the barrel temperature after a period of production can solve this problem. 2. During the production process, increasing injection pressure and speed can sometimes be ineffective. Why? After a period of production, the molten glue continuously dissipates heat, causing insufficient glue, high viscosity, and poor fluidity, leading to glue shortages. Increasing the barrel temperature can solve this problem. 3. Causes and Solutions for Oval Products: Oval products are caused by uneven glue injection, which creates uneven pressure around the product, resulting in an oval shape. Use three-point glue injection to ensure uniform glue injection. 4. Mold Requirements for Precision Products: Mold materials must have good rigidity, minimal elastic deformation, and a low thermal expansion coefficient. 5. Purpose of the Product Acid Resistance Test: The purpose of the acid resistance test is to detect the internal stress of the product and the location of the internal stress points, so as to eliminate the internal stress. 6. Causes and Solutions for Cracking of Metal Inserts in Products: When inserts are placed in a product, internal stress is generated when hot molten plastic meets the cold insert during injection molding, reducing the product's strength and making it prone to cracking. During production, the inserts should be preheated. 7. Reasonable Mold Vent Point Selection and Selection Methods: Improper mold venting not only fails to achieve effective venting, but can also cause product deformation or dimensional changes. Therefore, the mold venting point must be appropriate. Mold venting points should be located at the point where the product is finally filled with plastic and where air is trapped and burned. 8. Causes and Solutions for Brittle Product Cracking: Brittle product cracking occurs when too much sprue and regrind is used, or when the material remains in the feed pipe for too long, causing the rubber to age and become brittle. Increase the proportion of new material, reduce the number of sprue material recycling cycles (generally no more than three times), and prevent the rubber from remaining in the feed pipe for extended periods of time. 9. Causes and Solutions for Fiber-Fibered Products: This is caused by low melt or mold temperatures, resulting in insufficient injection pressure, which prevents the glass fiber from properly bonding with the plastic within the glue, leading to fiber-fibering. Increase the melt and mold temperatures, and increase the injection pressure. 10. Impact of Inlet Temperature on the Product: Excessively high or low inlet temperatures can cause unstable material return and feed rate, affecting product size and appearance. 11. Causes and Solutions for White Spots in Transparent Products: White spots on transparent products can be caused by cold glue entering the product or dust in the material. Increase the nozzle temperature, add a cold well, and store the raw materials carefully to prevent dust from entering. 12. What is the injection capacity of an injection molding machine? Injection capacity PW = injection pressure (kg/cm²) × injection volume (cm³) / 1000. 13. What is the injection horsepower of an injection molding machine? Injection horsepower (PW) (kW) = Injection pressure (kg/cm²) × Injection rate (cm³/sec) × 9.8 × 100% 14. What is the injection rate of an injection molding machine? Injection rate (V) (cc/sec) = л/4 × d² × rd²: barrel diameter (r): material density. 15. What is the injection thrust of an injection molding machine? Injection thrust (F) (kgf) = л/4 (D12 - D22) × P × 2. D1: cylinder inner diameter (D2): piston rod outer diameter (P): system pressure. 16. What is the injection pressure of an injection molding machine? Injection pressure (P) (kg/cm²) = [л/4 × (D12 - D22) × P × 2] / (л/4 × d²). 17. What is the plasticizing capacity of an injection molding machine? Plasticizing capacity W (g/sec) = 2.5 × (d/2.54) 2 × (h/2.54) × N × S × 1000/3600/2h = screw front end thread depth (cm) S = raw material density 18. What is system pressure? How is it different from injection pressure? System pressure (kg/cm2) = the highest working pressure set in the hydraulic circuit. Injection pressure refers to the actual pressure of the injection molding machine. The two are not equal. 19. Requirements for hydraulic oil for injection molding machines: (1) Appropriate viscosity and good viscosity performance (2) Good lubricity and rust resistance (3) Good chemical stability, not easy to vaporize into colloid (4) Good foaming properties (5) Low corrosion to machine parts and sealing devices (6) Ignition point (flash point) requirements, low freezing point. 20. The Impact of Hydraulic Oil Viscosity on Injection Molding Machines: When the system's operating temperature is high, a higher viscosity oil should be used; conversely, a lower viscosity oil should be used. When the system's operating pressure is high, a higher viscosity oil should be used because sealing is more difficult at high pressures, and leakage is a major concern. Conversely, when the system's operating pressure is low, a lower viscosity oil should be used. When the hydraulic system's working components operate at high speeds, the oil flow rate also increases, increasing pressure loss while minimizing leakage. Therefore, a lower viscosity oil should be used. Conversely, when the working components move at low speeds, a higher viscosity oil should be used. 21. Release Setting: The correct release position equals the rubber ring's travel position + the screw's overrun distance. 22. The Importance of Release Position Setting: If the release position is set too high, it will cause the material to absorb oxygen, causing oxidation and bubbles. If the position is set too low, the pressure in the barrel will be high, resulting in excessive shear forces, causing the material to break down and the nozzle to drool. The position error should not exceed 0.4mm. 23. Setting the melt position: Melt position = Product weight / (Maximum stroke / Maximum melt volume). 24. Main advantages of gas-assisted injection molding (GAM): It can evacuate the core of thick materials to create hollow tubes, saving material and shortening cycle time. Using gas during injection molding evenly distributes pressure. As the plastic cools and solidifies, the gas expands to compensate for the plastic's volumetric contraction. This reduces internal stress in the molded part, thereby improving the shape stability and eliminating deformation and warping. 25. Piston rod outer diameter is smaller in the middle and larger at both ends. This is caused by uneven product shrinkage due to overheating of the center-hole needle, resulting in a smaller piston rod outer diameter in the middle and larger at both ends. The center-hole needle can be made of phosphor copper, a material with faster heat dissipation, and the mold can be vented in the center of the part. 26. Cracking of spherical surfaces after screen printing: This is caused by stress on the part surface. Increase the mold temperature to reduce stress. Annealing can be used to relieve stress. 27. The problem of the nozzle edge of the eyeglass frame being easily broken. High injection pressure and holding pressure lead to residual internal stress at the nozzle edge, causing the product to break easily. Minimize the injection pressure and holding pressure as much as possible, and appropriately increase the mold temperature to solve the problem. 28. The problem of the four pillars of the electrical housing being easily cracked when screwing. Due to the presence of a waterline on the pillars, the product assembly pillars are prone to cracking. Increase the mold venting, appropriately increase the mold temperature, and speed up the injection speed to reduce the waterline. 29. The problem of product deformation. Product deformation is mainly caused by uneven thermal shrinkage or deformation caused by the internal stress of the product itself. 30. The problem of bubbles in the transparent PC housing. Insufficient raw material drying, uneven glue thickness in the product, poor mold venting, and easy decomposition of raw materials can all cause bubbles in the product. Thoroughly dry the raw material, increase the mold venting, and minimize uneven glue thickness.