Check the material in the hopper, check the feed throat for resin agglomerates, machine capacity not enough
Increase the gate, runner, and sprue size, use the nozzle with a higher diameter hole, try with a higher MFI material, check the nozzle for blocks.
Provide adequate venting, reduce the clamping force.
Balance the runner design , cavity location
Increase the size of cold slug well, provide cold well for sub runners.
Rearrange the cooling line of mould to provide a uniform cooling
Maintain a uniform melt cushion, check the back flow valve and, repair if needed
Use a bigger machine.
Flash
Material too hot
Excessive feed
Erratic feed
Poor parting line or matting surface
Erratic cycle time
Injection pressure is too high
Insufficient clamping force
Foreign matter or flash acting as high spot on mould land.
Mould platens are warped , Clearance in vents, knock-outs, etc. are too great
Insufficient venting causing material from cavity to flow out
Injection pressure unevenly distributed in the mould
Reduce material temperature, increase cycle time, decrease mould temperature
Reduce feed
Check the feeding system.
Reface the parting time , matting surface
Maintain uniform cycle time.
Decrease the injection pressure, decrease the hold on pressure, decrease the injection hold time,
Use wherever necessary bigger machine if available, reduces number of cavities; adjust the mechanism to increase the clamping force.
Inspect mould land and clean carefully.
Check the clearance and adjust
Inspect vents and clean in case of blockage, enlarge vents, if needed.
Cavity and runner layout should be balanced
Sprue sticking
Excessive pressure
Nozzle not aligned with sprue bush
Sprue puller too small
Material too cold at nozzle and sprue unable to breakaway.
Nozzle orifice greater than sprue bush orifice.
Material too hot, Sprue breaking at component end.
Sprue held up in sprue bush due to inadequate taper
Hot material ,
Excessive material
Insufficient draft · Improper fit between sprue bushing and nozzle.
Under cuts or rough surface.
Long plunger dwell
Reduce pressure
Realign the nozzle with a sprue bush.
Increase the undercut, Increase the size of sprue puller.
Increase the nozzle temperature until the sprue breaks from the nozzle.
Change the nozzle with a lower Dia orifice or increase the dia of sprue bush orifice
Decrease the cylinder temperature, increase the moulding cycle time, and increase the cooling time in the mould.
Give adequate taper in the sprue bush, use mould release agents, remove burrs on the sprue.
Decrease material temperature.
Decrease size of the sprue extended nozzle and short sprue bushing
Increase draft angle.
Hole size in nozzle should be smaller than in the sprue bushing.
Eliminate undercuts and polish the surface.
Reduce plunger forward time
Sink marks
Not enough plastic in the mould to allow for shrinkage due to thick sections, bosses, ribs etc.
Not enough feed
Injection pressure too low
Plunger forward time to short
Unbalanced gates
Injection speed too slow
Plastic too hot· Variation in mould open time
Excessive cushion in front of the plunger
Gate location, it's size and design· Insufficient packing.
Part sections uneven
Product too hot when ejected.
Restriction in flow
Local hot spot in the moulds.
Reduce pressure or temperature accordingly
Reduce feed
Reduce plunger forward time.
Eliminate undercuts, polish and provide sufficient draft
Maintain constant mould open time.
Polish rough cavity surface to correct finish, adjust mould temperature to obtain proper shrinkage
Polish the mould well
Provide a release taper
Check the ejector system , provide extra ejector pins
Eliminate undercuts with a proper design, polish and provide sufficient draft.
Check the alignment of the core and cavity.
Replace the mould with a hardened metal.
Reduce the injection pressure, reduce the feed material, reduce the screw forward time.
Maintain a constant feed cushion, balance the gates and runner for uniform filling.
Use a mold release spray, adjust the mould temperature to retain the components on the ejection side. use an undercut runner to keep the parts on the ejection side
Check and clean the mould deposits.
Part sticking to the mould.
Injection pressure or cylinder temperature too high
Excessive feed
Plunger forward time too long
Undercuts in mould
Variation of mould open time
Improper finish
Rough surface of the mould
Inadequate release taper in mould cavity.
Ejection system not designed properly
Undercuts in the mould cavity.
Misalignment of core and cavity
Mould made of soft porous steel.
Over packing of the plastic material.
Uneven pressure in cavities.
Parts sticking to injection side.
Mould deposit causing sticking
Redesign and increase injection pressure
Increase feed
Increase injection pressure.
Increase plunger forward time.
Restrict flow through gates near sprue.
Raise mould and cylinder temperature
Reduce cylinder and mould temperatures, decrease cycle time.
Use of timers for mould open time
Reduce feed
Locate the gate at the thick section of the part, increase the gate size and reduce gate land
Increase the injection pressure.Increase the hold pressure time, check back the flow valve for leakage.
Redesign the part with an even wall thickness
Decrease the cylinder temperature, increase the cooling time in mould, reduce the mould temperature.
Increase the gate, runner and sprue size, provide a proper venting in the mould, balance flow and filling in cavity.
Redesign the cooling pattern in the mould
Flow lines and folds
Cold material
Cold mould
Gates to small
Non uniform section thickness.
Increase plastic temperature
Increase mould temperature
Enlarge gates.
Eliminate heavy bosses and ribs.
Poor surface finish
Cold material
Cold mould
Slow injection
Poor flow within mould cavity
Poor mould cavity finish
Contamination of material
Material wet
Mould surface too cold
Poor mould surface
Inadequate injection pressure.
Insufficient hold pressure time.
Increase plastic temperature
Increase mould temperature
Increase injection speed.
Redesign parts.
Polish mould cavity surface to correct finish
Check the feed material for contamination, purge the injection cylinder, clean the feeding system, check the quality of regrind added
Preheat the material, use hopper dryer
Increase the mould surface temperature
Polish the mould
Increase the injection pressure
Increase the hold pressure time
Warpage
Excessive orientation in the material which manifests itself in differential shrinkage in the direction of flow and vertical to it. Orientation increases as material becomes too viscous, the wall becomes thinner, runner becomes narrower and longer
Temperature distribution in cylinder is uneven
As a result of over - loading of moulding due to excessive or too long follow up pressure
Components ejected too hot
Port design with uneven thickness
Mould coating uneven
Distortion due to internal strain
Ejection knockout pins working unevenly.
Gate location not proper
Distortion of heavy section only.
Avoid orientation
Watch cylinder design
If possible use follow -up pressure lower than injection pressure, shorten follow-up pressure.
Reduce the cylinder temperature, increase the mould cooling time, place in the jig after moulding, and increase the mould temperature.
Design the part with an even wall thickness and strengthen it with ribs.
Maintain a uniform temperature in the mould, use a cold mould.
Increase / decrease the injection pressure, increase the mould cooling time, increase the overall moulding cycle.
Check the knock out pin levels and set evenly, increase the knock out area.
Gate location should be in such a way that the material flows from the thick to thin section, gate runner system design for balanced filling.
Increase the mould cooling time, maintain uniform melt temperature, slowly cool the part in warm water, place in a shrink jig after ejection.
Fracture cracks
Internal stress due to metal inserts with coefficient of thermal expansion different from the plastic material.
Internal stress due to improper mould design
Embrittlement due to thermal degradation
Parts ejected too fast
Ejector system defective.
Internal stress due to cold metal insert.
Use higher molecular weight materials, increase wall thickness, and anneal the moulded parts.
Check the mould design and change if necessary.
Reduce the cylinder temperature, use faster moulding cycle.
Give more cooling time in the mould.
Check the ejection system for a smooth operation.
Warm the insert before use, thicken the section in the area of crack, use toughened materials.
Brittleness of component
Material is too hot
Material too cold
Mould surface too cold
Reground material in excess quantity
Bad quality regrind
Rate of injection too slow
Original part design too thin
Product not conditioned
Reduce the cylinder temperature, shorten the over all cycle time, machine is too big, change to a smaller machine.
Increase the cylinder temperature, increase the nozzle temperature, decrease the screw speed,
Increase the mould temperature, control the flow of coolant to the mould
Avoid using regrind, use less percentage of regrind
Check regrind for contamination, moisture degraded polymer, check the regrind melt index.
Increase the injection rate, maintain the minimum feed cushion.
Redesign the part to strengthen the weak areas
Condition the part as per the raw material manufacturer's recommendation.
Bubbles and voids
Internal shrinkage after the outer surface sets.
Material too hot
Insufficient venting in the mould resulting in entrapment of air
Condensation on cavity surface
Moisture in material
Injection rate to fast
Restriction to flow of material
Increase the injection pressure, rate, time, Increase the size of the gates, runners, and sprue, increase the screw forward time.
Decrease the cylinder temperature, reduce the moulding cycle time.
Provide vents at the point of final fill, decrease the injection speed, decrease the mould clamping force, increase the gate size, change location.
Reduce the flow of coolant through the mould, wipe the cavity surface with a solvent
Preheat the material thoroughly, use hopper dryer
Decrease the injection rate.
Eliminate restrictions, increase the gate and runner size.
Discolouration
Contamination of material
Wet material
Degradation of material, colourant, additives
Degradation of material due to gas entrapment
Too much stress on component
Charred material in cylinder or nozzle coming out with material.
Check the moulding material, purge the heating cylinder, check the feed system and hopper
Preheat the material, use a hopper dryer
Decrease the overall moulding cycle, use small machine, check the residence time of the material, reduce the screw speed, use colourants and additives which will withstand processing temperature.
Provide proper venting, relocate the gates, and decrease the mould clamping force.
Check the ejection system
Purge the cylinder completely, remove and clean the nozzle.
Nozzle droofing and foaming
Nozzle temperature very high
Material too hot
Nozzle orifice too large.
Moisture in the material.
Decrease the nozzle temperature,
Decrease the cylinder temperature, decrease the cylinder moulding time
Use a nozzle with a small orifice, use the reverse taper nozzle, use a nozzle with shut off valve.
Preheat the material, use hopper dryer
Scorching
Material over heated
Thermocouple burnt out
Temperature controller malfunctioning
Regrind not of good quality.
Improper shutdown procedures.
Moisture in material
Gas entrapment
Rate of injection too fast
Constant degrading
Reduce the cylinder temperature, decrease the moulding cycle time, and remove dead spots in the cylinder, screw, and nozzle assembly.
Check all thermocouples and change, if necessary.
Check for the sticking of relays, check for the controllers connected to the wrong heaters, check if the relays are functioning properly.
Segregate and check regrind critically for contamination, excess moisture or degraded polymer.
Purge the machine thoroughly, clean the nozzle and start moulding afresh
Preheat the material , use a hopper dryer
Vent the cavities properly, relocate the gate position,
Decrease the injection speed, decrease the injection pressure, increase the size of gates.
Use a colourant which can withstand the processing temperature
Weld lines
Material too cold
Mould too cold
Injection pressure too low
Gas entrapment
Part too thin at weld
Capacity of the machine lower
Contamination of material
Poor flow of melt
Increase the cylinder temperature, increase the overall moulding cycle
Increase the mould temperature, throttle the flow of coolant in the mould
Increase the injection pressure, increase the screw forward time, increase the rate of injection, increase the size of gates, runners and sprue, use multiple gates and runners.
Provide vent in cavities, relocate the gate, decrease the mould clamping force.
Thicken the part at the weld line
Change to a bigger machine.
Check the material, check the feeding system.
Use a higher MFI material, use an external lubricant
Dimensional variations
Inconsistent moulding cycle
Feeding system malfunctioning particularly in the plunger type machines.
Inconsistent melt cushion while injection.
Malfunctioning of non return valve
Uneven back pressure adjustment
Malfunctioning of temperature control system.
Insufficient plasticizing capacity
Incorrect runner, gate dimensions
Uneven mould filling
Distortion during ejection
Incorrect mould dimensions
Ununiform mould temperature
Packing of cavity not enough.
Maintain uniform moulding cycle
Check the feed system and adjust for uniform feed.
Maintain a uniform melt cushion, check the non-return valve for wear and tear.
Check and replace the valve if necessary
Arrange for a uniform back pressure.
Check the heater bands, check the thermocouples.
Use bigger machine
Check and provide a proper runner gate system.
Design the mould for uniform filling of cavities.
Check the knock-out pin system and correct it
Machine the mould cavity and core for proper dimensions with proper allowances for shrinkage.
Maintain a uniform mould temperature
Use a higher injection pressure. Increase the screw forward time.
Jetting
Melt injected directly into the cavity
Melt temperature is not enough
Adjustment of the injection rate
Gate size to small
Direct the material flow to hit the wall and flood the cavity.
Increase the cylinder temperature, increase the moulding cycle time.
Increase or decrease the injection rate.
Increase the gate size and flare the gate
Gate smear
Mould temperature not enough
Injection rate too fast, gate too restricted.
Increase the mould temperature
Decrease the injection rate, increase the gate size, flare the gate, change the gate location.
