Solutions to Defects of Plastic Injection Molding Parts
Solutions to gas holes
1. Adjust molding conditions to improve fluidity. For example, increase the resin temperature, mold temperature, injection pressure and speed.
2. Adding an exhaust groove and setting a push rod at the place where the weld is generated is also conducive to exhaust.
3. Minimize the use of release agents.
4. Set the process burr to the place where the weld seam is generated; cut and remove it after forming.
5. If only the appearance is affected, the position of the weld seam can be changed. The location which generates the weld bond is regarded as a dark smooth surface, and modify it.
Solutions to cracks
1. The mold is too cold; adjust the mold temperature.
2. The cooling time is too long; shorten the cooling time.
3. Plastic and metal inserts shrink differently. Preheat metal inserts.
4. The ejection device tilts unevenly, and the ejection cross-sectional area is small or the distribution is improper. Adjust the ejector device or reasonably arrange the number and position of ejector pins.
5. The production slope is not enough, and correctly design the demoulding slope.
Ripples on the product
1. The material temperature is low and the modulus is large, which increases the material temperature.
2. The injection pressure is high; reduce the injection pressure, and vice versa, increase injection pressure.
3. Increase mold temperatures or injection pressure.
4. The injection speed is too slow; increase the injection speed.
5. The gate is too small; properly expand the gate.
The brittle strength of the product being reduced
1. If the material temperature is too high, the decomposition of the plastic will reduce the material temperature and control the staying time of the material in the barrel.
2. The internal stress of the plastic and insert is too great; the insert can’t be preheated; ensure that there is a certain thickness of plastic around the insert.
3. The plastic is recycled for many times, and the recycling ratio is controllable.
4. Preheat and dry the plastic containing water raw materials.
Being difficult to demold
1. The mold has poor structure of ejection devices and improve ejection design.
2. The draft angle of the mold cavity is not enough; design the mold correctly.
3. The mold cavity temperature is inappropriate; properly control the mold temperature.
4. There are seams or storage of materials in the mold cavity; clean the mold.
5. The molding cycle is too short or too long; correctly control the injection molding cycle.
6. The mold core has no air inlets; change the mold.
Unstable product sizes
1. The machine circuit or oil circuit system is unstable; adjust electrical equipment or oil pressure systems.
2. The molding cycle is different. Control the molding cycle to make it consistent.
3. The size of the plastic particles is different; use uniform plastic.
4. The mixing ratio of recycled materials and new materials is uneven. Control the mixing ratio to make it uniform.
5. The material feeding is uneven; make the feeding uniform.
Peeling and layering of parts
1. Different plastics are mixed with a single type of plastic.
2. Different brands of plastics are mixed.
3. Poor plasticization will increase the molding temperature.
4. Foreign matter is mixed in; clean up raw materials, and remove impurities.
Melt marks
1. The temperature of the plastic is too low; increase temperatures of nozzles and molds.
2. There are too many gates; reduce the gate or change the position of the gate.
3. Atomized release agents are used too much; use less release agents.
4. The injection speed is too slow; increase the injection speed.
5. The mold temperature is too low; increase the mold temperature.
6. The injection pressure is too low; increase the injection pressure.
7. The mold doesn’t exhaust well; increase mold exhaust holes.
Adjustment for injection
1. Temperatures of the barrel and nozzle are low; increase temperatures of the barrel and nozzle.
2. The mold temperature is low; increase the mold temperature.
3. The feeding volume is not enough; increase the feeding volume appropriately.
4. When the manufactured parts exceed the maximum injection volume of the injection molding machine, an injection molding machine with a larger injection volume should be selected.
5. The runner and gate are too small; increase the size of the gate appropriately.
6. The injection pressure is too low or the injection speed is too slow. Increase injection pressure, temperatures and speeds.
1. Adjust molding conditions to improve fluidity. For example, increase the resin temperature, mold temperature, injection pressure and speed.
2. Adding an exhaust groove and setting a push rod at the place where the weld is generated is also conducive to exhaust.
3. Minimize the use of release agents.
4. Set the process burr to the place where the weld seam is generated; cut and remove it after forming.
5. If only the appearance is affected, the position of the weld seam can be changed. The location which generates the weld bond is regarded as a dark smooth surface, and modify it.
Solutions to cracks
1. The mold is too cold; adjust the mold temperature.
2. The cooling time is too long; shorten the cooling time.
3. Plastic and metal inserts shrink differently. Preheat metal inserts.
4. The ejection device tilts unevenly, and the ejection cross-sectional area is small or the distribution is improper. Adjust the ejector device or reasonably arrange the number and position of ejector pins.
5. The production slope is not enough, and correctly design the demoulding slope.
Ripples on the product
1. The material temperature is low and the modulus is large, which increases the material temperature.
2. The injection pressure is high; reduce the injection pressure, and vice versa, increase injection pressure.
3. Increase mold temperatures or injection pressure.
4. The injection speed is too slow; increase the injection speed.
5. The gate is too small; properly expand the gate.
The brittle strength of the product being reduced
1. If the material temperature is too high, the decomposition of the plastic will reduce the material temperature and control the staying time of the material in the barrel.
2. The internal stress of the plastic and insert is too great; the insert can’t be preheated; ensure that there is a certain thickness of plastic around the insert.
3. The plastic is recycled for many times, and the recycling ratio is controllable.
4. Preheat and dry the plastic containing water raw materials.
Being difficult to demold
1. The mold has poor structure of ejection devices and improve ejection design.
2. The draft angle of the mold cavity is not enough; design the mold correctly.
3. The mold cavity temperature is inappropriate; properly control the mold temperature.
4. There are seams or storage of materials in the mold cavity; clean the mold.
5. The molding cycle is too short or too long; correctly control the injection molding cycle.
6. The mold core has no air inlets; change the mold.
Unstable product sizes
1. The machine circuit or oil circuit system is unstable; adjust electrical equipment or oil pressure systems.
2. The molding cycle is different. Control the molding cycle to make it consistent.
3. The size of the plastic particles is different; use uniform plastic.
4. The mixing ratio of recycled materials and new materials is uneven. Control the mixing ratio to make it uniform.
5. The material feeding is uneven; make the feeding uniform.
Peeling and layering of parts
1. Different plastics are mixed with a single type of plastic.
2. Different brands of plastics are mixed.
3. Poor plasticization will increase the molding temperature.
4. Foreign matter is mixed in; clean up raw materials, and remove impurities.
Melt marks
1. The temperature of the plastic is too low; increase temperatures of nozzles and molds.
2. There are too many gates; reduce the gate or change the position of the gate.
3. Atomized release agents are used too much; use less release agents.
4. The injection speed is too slow; increase the injection speed.
5. The mold temperature is too low; increase the mold temperature.
6. The injection pressure is too low; increase the injection pressure.
7. The mold doesn’t exhaust well; increase mold exhaust holes.
Adjustment for injection
1. Temperatures of the barrel and nozzle are low; increase temperatures of the barrel and nozzle.
2. The mold temperature is low; increase the mold temperature.
3. The feeding volume is not enough; increase the feeding volume appropriately.
4. When the manufactured parts exceed the maximum injection volume of the injection molding machine, an injection molding machine with a larger injection volume should be selected.
5. The runner and gate are too small; increase the size of the gate appropriately.
6. The injection pressure is too low or the injection speed is too slow. Increase injection pressure, temperatures and speeds.
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