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May 18, 2000

3 Min Read
PIM troubleshooting

This chart provides information on PIM troubleshooting: molding problems, analysis, causes, and remedies. The information comes from Thermat Precision Technology Inc. (Corry, PA).

PIM troubleshooting: Molding problems, analysis, causes, and remedies

· distortion
· flash
· incomplete filling
· separation
· sticking

· injection pressure profile: high/no peak in transition period

· poor transition from speed (filling) to pressure control (packing)

· adjust transition point/ use different transition trigger
· reduce final injection speed

· flash
· porosity and voids
· sink marks

· cavity pressure profile follows injection pressure profile closely in packing period
· low injection pressure during filling

· powder mixture is too liquid; melt temperature is too high
· filling by jetting

· reduce nozzle/barrel temperature profile
· check actual melt period temperature in nozzle/barrel

· cracking
· distortion
· incomplete filling
· inconsistent surface finish
· lamination
· porosity and voids
· rough surface texture

· large difference between injection pressure and cavity pressure profiles
· high injection pressure during filling

· powder mixture is too viscous, melt temperature is too low
· filling by multiple jetting

· increase nozzle/barrel/ mold temperatures
· check viscosity of melt by extrusion (should be liquid, but not too thin)
· adjust filling speed profile

· cracking
· sink marks

· drop in injection pressure later in packing cycle causes drop in cavity pressure

· molded compact is cooling and shrinking, but gate has not frozen off yet after packing

· increase packing times for the early stages of the packing pressure profile

· sink marks
· lamination

· large difference between injection and cavity pressure profiles in middle of packing cycle

· gate has frozen off, but compact is still liquid, cooling and shrinking· reduce initial (low- pressure) packing period for skinning

· distortion 
· rough surface texture
· weldline cracking

· large difference between injection and cavity pressure profiles at proper melt viscosities

· melt is solidifying before mold cavity is completely filled

· increase mold temperature
· increase injection speed profile

· distortion
· flash 

· injection pressure for initial packing much higher than for end of filling

· initial packing pressure unnecessarily high

· reduce initial packing pressure

· cracking
· distortion
· separation
· sticking
· weldline cracking

· injection pressure profile high during filling

· filling speed profile not adjusted according to viscosity/shear rate behavior

· adjust injection speed profile to reduce injection pressure during filling

· part/sprue fracture during ejection 

· injection pressure much higher than cavity pressure in packing

· packing pressure higher than gate can transfer

· reduce packing pressure profile

· porosity and voids

· drops or peaks in injection pressure profile during filling· entrapped air in metered feedstock in front of screw

· adjust metering back-pressure and speed
· check feedstock shape and size consistency 

· cracking
· sink marks
· surface defects 

· injection pressure profile for packing lower than for end of filling

· insufficient packing pressure to overcome feedstock viscosity

· increase packing pressure profile

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