Common product defects and their causes in the injection molding process

Drooling

a. Incomplete drying of the material or moisture in the material

b. Pre-molding speed (screw speed) is too fast

c. Nozzle temperature is too high

d. Bad material return (powder)

e. Insufficient reabsorption

f. Insufficient nozzle contact force

g. Mismatch between nozzle and mold gate sleeve size

h. Dirty nozzle contact surface (resulting in uneven surface)

Unstable pre-molding

a. Unreasonable or unstable return ratio

b. Backpressure is too low

c. Long material rod bridging

d. Damp material

e. unreasonable temperature (too high) at the lower material

Flying edge

a. Inaccurate parameter setting (turning point too low, holding pressure too high, shooting speed too fast, temperature too high)

b. Dirty mold 

c. Insufficient clamping force

d. Mold problem (damaged)

e. Equipment problem (unstable pressure)

f. Nozzle temperature is too low

g. Uneven plasticization (long material rod, too fast screw speed, too low back pressure, etc.) causing cold material

h. Unstable closing of check valve due to too small suckback

Insufficient mold filling

a. Inaccurate parameter setting (too high-pressure turning point, too low holding pressure, too slow injection speed, too low temperature)

b. Dirty mold

c. Nozzle temperature is too low, unreasonable structure

d. Damaged check valve or barrel

e. Gates, runners are too small

f. Unclean material (including trash)

g. Moisture in the material

h. Equipment problems (insufficient pressure)

I. Misalignment of injection table

h. Unstable closing of check valve due to too small suction

Inadequate mold filling from time to time

a. Injection speed is too low (especially for PA, POM)

b. Insufficient melt temperature for large products

c. Uneven plasticization (backpressure too low, speed too fast)

d. Insufficient nozzle temperature

e. Damaged check valve or barrel

f. Impurities

g. Dirty mold

h. Incomplete drying of material or moisture in the material

I. Injection table is not aligned

h. Unstable closing of the check valve due to too little suction

Scorch

a. Dirty molds

b. Inaccurate parameter setting (shooting speed too fast)

c. Incomplete drying of material or moisture in the material

d. Too much-clamping force

e. Mold problems (poor exhaust)

f. Too much reabsorption

g. The barrel is not sealed at the second joint

Denting

a. Gate, runner size too small

b. Nozzle opening is too small

c. Inaccurate parameter setting (holding pressure too low, holding time too short, turning point too high, material or mold temperature too high)

d. Uneven plasticization (backpressure too low, speed too fast)

e. For large products, melt temperature is not enough

d. Damaged check valve or barrel

e. Injection table not aligned

Product deformation

a. Wrong waterway connection

b. Product extrusion 

c. Uneven product ejection

d. Insufficient cooling time

e. Too low injection speed

f. Too much pressure causing mold sticking

g. Uneven plasticization causing internal stress

h. Uneven mold temperature distribution

Dimensional instability

a. Unstable parameter control (mold temperature, material temperature, holding pressure too low or too high, cooling time)

b. Unreasonable or unstable return ratio

c. Damage to check valve or barrel

d. Unstable closing of check valve due to too small suction

Unstable weight

a. Inaccurate parameter setting (mold temperature, material temperature, holding pressure is too low or too high, cooling time, holding time is not enough)

b. Nozzle temperature is too low 

c. Holding time is too short

d. Damaged check valve or barrel

e. Unstable return ratio

f. Unstable closing of check valve due to a too-small suction

The product is prone to breakage

a. Melt temperature is too high or too low

b. Wet material

c. Injection speed is too low or too high

d. Mold temperature is too high or too low

e. Fusing marks

f. Impurities

g. Uneven plasticization (too low back pressure, too fast rotation speed, long material rod for return material)

h. Sharp edge of the mold

i. Unstable return ratio

Weld marks

a. Injection speed is too slow

b. Melt temperature too low

c. Mold temperature is too low

d. Poor air venting

d. Color masterbatch; uneven plasticization

e. Mold, product design unreasonable

Skin delamination

a. Wet material

b. Trash material

c. Color masterbatch has problems

d. Shooting speed is too fast