1. Decomposition of resin

1. Purge sufficiently.

2. Lower the resin temperature.

3. Shorten the resin residence time.

2. Substances retained inside the cylinder for an extended period of time

3. Mixing in of foreign substances

1. Purge sufficiently.

1. The resin temperature and pressure are too low at the time of fusing the flow front.

1. Increase the mold temperature.

2. Increase the resin temperature.

3. Increase the injection speed.

4. Increase the holding pressure.

5. Expand the gate.

2. Gas removal imperfections

1. Strengthen the gas vent on welded parts.

3. Design imperfections

1. Establish a weld relief.

2. Correct the thickness in places and change the pattern of inflow to welded parts.

1. Water, gas, and other volatile components and air trapped at the time of plasticization

1. Dry the materials sufficiently.

2. Do not increase the resin temperature too much.

3. Lower the screw rotation speed. Increase the screw back pressure.

4. Strengthen the gas vent (particularly on runners).

2. Generation of air pockets due to an imbalance of flow inside the cavity

1. Adjust the injection speed.

2. Strengthen the gas vent.

3. Mixing in of foreign substances

1. Purge sufficiently.

1. Gas removal imperfections

1. Lower the injection speed. (If there are restrictions on shape, etc.) Adjust the V/P switchover value. Conduct multi-stage injection.

2. Strengthen the gas vent.

3. Lower the resin temperature.

2. Residual decomposition of residue inside the cylinder

1. Purge sufficiently.

1. Mixing in of hardened resin at the tip of the nozzle

1. Increase the nozzle temperature. (In the case of nozzle-touch molding) Increase the mold temperature.

2. Expand the resin sump.

3. Move the cylinder forward and back for each shot cycle

1. This occurs when resin moves from a narrow area to a wide area, and shoots out in string form and flows without touching the mold.

1. Increase the gate size.

2. Change the gate position. (Shorten the straight distance after passing through the gate.)
-(a) Move the gate to a position at which the flow will hit the core.
-(b) Move the gate to a thin area.
-(c) Use a tab gate.

3. Lower the speed of passing through the gate.

4. Increase the mold temperature.

5. Increase the holding pressure.

1. Insufficient pressure

1. Increase the holding pressure.

2. Increase the mold temperature. Increase the resin temperature.

3. Increase the gate size.

4. Increase the injection speed.

2. Gas removal imperfections

1. Lower the holding pressure.

2. Lower the injection speed.

3. Strengthen the gas vent.

1. The pattern of flow remains on the surface due to changing flow speed when passing through a corner or an area with uneven thickness.

1. Radius the corners.

2. Put a slight gradient on or radius areas at which the thickness changes.

1. The outer surface is pulled (dented) in due to shrinkage inside, caused by insufficient cooling of thick or rib areas or insufficient cavity pressure.

1. Lower the mold temperature.

2. Expand the sprue, runner, and gate.

3. Increase the holding pressure. Increase the dwell time.

4. Ensure that cushion remains until the gate seals.

5. Make the rib thickness about 1/3 of the base thickness.

6. Make thick areas thinner.

1. Mixing in of foreign substances

1. Purge sufficiently.

2. Air entrapment

1. Lower the screw rotation speed. Increase the screw back pressure.

2. Lower the amount of decompression (suck back).

3. Increase the temperature of the rear part of the cylinder.

3. Shear delamination

1. Increase the resin temperature. Increase the mold temperature.

2. Expand the gate.

3. Lower the injection speed.

4. High gas generation

1. Do not increase the resin temperature too much.

2. Dry the materials sufficiently.

3. Shorten the residence time.

4. Lower the holding pressure.

5. Lower the injection speed.

6. If recycled materials are being used, reduce the ratio.

1. Anisotropy due to fiber orientation

1. Increase the thickness.

2. In the case of molded articles with ribbing, design gates so that the flow travels lengthwise, and make the rib and base orientation the same.

1. The amount of resin supplied to the inside of the cylinder is inconsistent, or no resin is supplied.

1. Adjust the screw rotation speed. Lower the screw back pressure.

2. Increase the temperature of the back part of the cylinder.

3. If recycled materials are being used, make the size of the pulverized material the same as that of the virgin pellets as much as possible. Remove dust as much as possible.

2. Molding machine imperfections

1. The check ring or screw has become worn.

1. Overfilling of the rib or boss

1. Lower the holding pressure.

2. Lower the mold temperature.

2. Mold design imperfections

1. Increase the draft of the area around the cavity, the boss, and ribs, etc. Or, add ejector pins.

2. Polish the cavity surface in the pulling direction of the molded articles.

3. Insufficient crystallization

1. Increase the mold temperature and increase the degree of crystallization.

1. Gas-caused void
Mixing in of gas (moisture, resin decomposition gas, air) generated inside the cylinder or during filling

1. Increase the holding pressure. (Expand the gate, runners, sprue.)

2. Put the gate as close as possible to the location at which the void is generated (thick area).

3. Dry the materials sufficiently.

4. Lower the resin temperature.

5. Shorten the molding cycle.

6. Lower the screw rotation speed. Increase the screw back pressure.

7. Lower the injection speed.

8. Strengthen the gas vent.

2. Vacuum void
In the case of thick molded articles with quickly hardening surfaces, the resin in the center is pulled toward the surface due to cooling/shrinkage. This makes the center area insufficiently filled.

1. Put the gate at the thickest part of the molded article.

2. Expand the gate, runners, sprue, and nozzle as suitable for the thickness of the molded article. Gate thickness should be at least 50% to 60% of the molded article thickness.

3. Increase the holding pressure. Increase the dwell time.

4. Ensure that cushion remains until the gate seals.

5. Ensure the operation of the check ring to prevent backflow during dwelling.

6. Increase the mold temperature.

7. Lower the injection speed.

1. Adhesion/accumulation of decomposed resin and additives on the mold surface

1. Lower the resin temperature.

2. Dry the materials sufficiently.

3. Shorten the residence time.

4. Lower the injection speed.

5. Increase the mold temperature.

6. Strengthen the gas vent.

7. If recycled materials are being used, reduce the ratio.

8. Clean the cavity.

1. Mold deposits

1. See the section for mold deposits.

2. Imperfections in adhesion to the cavity

1. Increase the holding pressure. Increase the dwell time.

2. Expand the runner and the gate.

3. Increase the mold temperature.

4. Increase the resin temperature.

5. Increase the injection speed.

3. Insufficient crystallization

1. Increase the mold temperature and increase the degree of crystallization.

1. Ejection performance is poor.

1. See the section for ejection failure.

2. Embrittlement of molded items due to resin deterioration and hydrolysis

1. Lower the resin temperature.

2. Shorten the residence time.

3. Dry the materials sufficiently.

3. Mixing in of foreign substances

1. Purge sufficiently.

4. Insufficient crystallization

1. Increase the mold temperature and increase the degree of crystallization.

1. The resin temperature is too high.

1. Lower the resin temperature, particularly the nozzle temperature.

2. Lower the screw rotation speed. Lower the screw back pressure.

3. Dry the materials sufficiently.

4. Increase the amount of decompression (suck back).

1. The sprue tip has not solidified.

1. Lower the resin temperature. Lower the nozzle temperature.

2. Lower the mold temperature.

3. Increase the mold opening speed. Increase the size of the mold opening.