| Sr. No. |
Problem / Trouble |
Probable Cause/s |
Remedy |
| 1. |
Blisters/bubbles |
| - |
Heating too rapidly |
| - |
Excess Moisture |
| - |
Uneven heating |
| - |
Wrong sheet type or formulation |
|
| - |
Lower heater temperature
Use slower heating
Increase distance between heaters and sheet
Blow air across sheet surface during heating. |
| - |
Predry sheet
Preheat sheet
Heat from both sides
Do not remove moisture barrier film until ready to use.
Request sheet supplier to provide dry sheets |
| - |
Check heater output, power consumption
Use pattern heating |
| * |
Check for runaway heating elements
Obtain correct formulation |
|
| 2. |
Incomplete Forming, poor Details |
| - |
Sheet too cold |
| - |
Clamp frame cold prior to sheet insertion |
| - |
Applied pressure too low |
|
| - |
Heat sheet longer
Raise heater temperatures
Use more heaters
Change to more efficient heater design
If problem localized, check heater bank for problems. |
| - |
Preheat frame |
| - |
Increase air pressure
Use plug, silicon slab rubber, or bladder as pressure assist. |
|
| 3. |
Scorched sheet |
|
| - |
Shorten heat cycle
Use slower, soaking heat
Move heater bands farther from sheet |
|
| 4. |
Blushing or color intensity change |
| - |
Insufficient heating |
| - |
Excessive heating |
| - |
Mould too cold or hot |
| - |
Assist too cold |
| - |
Sheet is stretched too far |
| - |
Sheet cools before fully Formed |
| - |
Poor mould design |
| - |
Polymer not suitable |
| - |
Excessive, poor use of regrind |
|
| - |
Lengthen heating cycle
Raise heater temperature
Change to more efficient heaters. |
| - |
Reduce heater temperature
Shorten heating cycle
If localized, check heater efficiencies |
| - |
Warm mould or lower temperature |
| - |
Heat assist |
| - |
Try heavier gauge sheet
Try more elastic formulation
Change mould design |
| - |
Transfer sheet faster
Increase forming rate
Increase mould, plug temperature |
| - |
Reduce draw ratio
Increase draft angles (taper) of mould
Increase corner radius |
| - |
Change sheet formulation
Change polymers |
| - |
Retest regrinds for problems
Check percentage of regrind. |
|
| 5. |
Whitening |
| - |
Stretching below forming temperature |
| - |
heet dry colored |
|
| - |
Increase sheet temperature
Increase forming speed |
| - |
Poor extrusion
Polymer unsuitable for pigmentation
Local blemishes removed with hot air gun
Hot air gun can be used to diminish or eliminate whitened surface on formed part |
|
| 6. |
Webbing, bridging, wrinkling |
| - |
Sheet too hot, drape into forming area |
| - |
Resin melt strength too low, sheet sag. |
| - |
Orientation mismatch |
| - |
Excess draw ratio, poor mould design/layout |
| - |
Extrusion direction of sheet parallel to space between moulds |
|
| - |
Shorten heating cycle
Increase heater distance
Lower heater temperatures
Air cool just before forming |
| - |
Change to lower M.I.olefin
Increase orientation
Use minimum sheet temperature possible
Profile temperature of sheet |
| - |
Use very low heater temperature
Increase or decrease TD to MD orientation ratio. |
| - |
Redesign mould
Use plug / ring assist
Use female mould rather than male mould
Use assist blocks to pull out wrinkles
Increase draft angles
Speed up assist and/or mould travel
Redesign grid/plug assists. |
| - |
Move sheet 90 degrees in relation to space between moulds |
|
| 7. |
Nibs or nipples on formed parts |
|
| - |
Reduce heating cycle
Reduce heater temperature |
|
| 8. |
Excessive sag |
| - |
Sheet too hot |
| - |
Sheet area excessive |
| - |
Melt index too high |
|
| - |
Reduce heating cycle
Reduce heater temperature |
| - |
Patten heat to reduce sheet center temperature
Add sag bands |
| - |
Use lower MI resin |
|
| 9. |
Sag variation between sheet banks |
| - |
Wide sheet gage Variation |
| - |
Sheet made from different resins, not a homogeneous mixture |
|
| - |
Replace sheet with proper gage tolerance |
| - |
Control regrind percentage and quality
Avoid resin mix-ups |
|
| 10. |
Chill marks, striations |
| - |
Plug assist temperature too low |
| - |
Mould temperature too low |
| - |
Poor mould temperature control |
| - |
Sheet too hot |
| - |
Wrong forming Techniques |
| - |
Ghosts in details, rim on Roll-fed |
|
| - |
Increase plug temperature
Use wooden, synthetic plug
Cover plug with wool, felt, fabric |
| - |
Increase mould temperature |
| - |
Reconfigure cooling, heating channels
Add more coolant channels
Increase coolant flow rate
Increase coolant channel diameter |
| - |
Reduce heating cycle
Cool sheet surface with air prior to forming
|
| |
Change forming rate Correct forming technique |
| - |
Matched die mould misaligned
Mould hesitates in-travel
Check guides, alignment |
|
| 11. |
Surface blemishes |
| - |
Indentations |
| - |
Mould too hot |
| - |
Mould too cold |
| - |
Improper mould Composition |
| - |
Rough mould surface |
| - |
Dirt |
| - |
Atmospheric dust |
| - |
Scratched sheet |
| - |
Drag marks on roll fed sheet |
|
| - |
Mould surface too smooth-roughen
Sheet cast against smooth roll, air trapping |
| - |
Reduce mould temperature |
| - |
Increase mould temperature |
| - |
Change mould material
Try machined aluminum moulds |
| - |
Polish mould
Use aluminum moulds |
| - |
Clean mould, sheet |
| - |
Clean thermoforming area
Enclose formers
Use filtered air for blow off |
| - |
Review sheet handling procedures
Use surface paper protection
Polish sheet prior to forming |
| - |
Use sag band to keep sheet from touching mould edge
Increase mould daylight |
|
| 12. |
Shiny streaks on part |
| - |
Sheet over heated in this Area |
| - |
Bad sheet |
|
| - |
Lower heater temperature in scorched area
Shield heater with screen wire to reduce overheating
Slow heating cycle
Increase heater to sheet distance |
| - |
Check with sheet supplier |
|
| 13. |
Post-forming shrinkage, distortion |
| - |
Time on mould too short |
| - |
Mould too hot |
| - |
Too much sheet orientation |
|
| - |
Increase cooling time
Decrease coolant temperature
Use free surface cooling to water mist
Check for restricted coolant flow
Use cooling fixturess |
| - |
Reduce mould temperature
Increase coolant flow rate |
| - |
Replace sheet |
|
| 14. |
Warped parts |
| - |
Uneven part cooling |
| - |
Poor polymer distribution in part wall |
| - |
Poor mould design |
| - |
Poor part design |
| - |
Mould temperature too low |
| - |
Part removed too early |
| - |
Part cold formed |
|
| - |
Change coolant channel configuration
Check for blocked coolant channels
Direct free surface cooling to warped area |
| - |
Use prestretching or plug assist
Poor temperature uniformity
Out-of-spec. sheet thickness |
| - |
Redesign rim area to slitter |
| - |
Large flat areas should include ribs, corrugations
Crown large radius areas |
| - |
Increase mould temperature to just below polymer set temperature |
| - |
Part must be below set temperature |
| - |
Increase sheet temperature
Increase hold down pressure
Increase forming rate |
|
| 15. |
Poor material allocation |
| - |
Improper sheet sag |
| - |
Sheet thickness variation |
| - |
Hot, cold spots |
| - |
Cold mould |
| - |
Sheet pulls from rails |
| - |
Sheet slips from frame |
|
| - |
Try mounting mould on top pattern
Try sag bands
Use sheet with higher orientation
Increase speed of forming
Use resin with higher M.I. |
| - |
Gauge all sheet, contact sheet supplier
Set guidelines with sheet supplier |
| - |
Check heater elements
Go to pattern heating |
| - |
Increase mould temperature
Change coolant channel configuration
Check for channel plugging |
| - |
Air cool rails prior to heater
Move rails in to grasp more sheet
Use drag bands at rail edge
Increase rail tooth bite, e.g.longer teeth |
| - |
Adjust frame alignments
Increase frame clamp pressure
Sheet gauge variation
Heat frames prior to inserting sheet
If retainer springs are used, change to higher temper springs |
|
| 16. |
Shrink marks |
| - |
Mould surface too smooth |
| - |
Part shrinking during Forming |
| - |
Inadequate air pressure |
|
| - |
Roughen mould surface
Change to lower conductivity mould material |
| - |
Increase forming pressure
Increase mould temperature
Reduce free surface cooling |
| - |
Increase air flow rate
Increase air pressure
Increase cycle time under pressure |
|
| 17. |
Very thin corners |
| - |
Incorrect forming technique |
| - |
Sheet too thin |
| - |
Sheet temperature Variation |
| - |
Variation in mould Temperature |
| - |
Incorrect polymer |
|
| - |
Try plug assist |
| - |
Increase sheet thickness |
| - |
Check material allocation
Switch to pattern heating
Increase forming rate |
| - |
Change coolant line configuration
Check free surface cooling |
| - |
Use slitter polymer
Use more elastic polymer |
|
| 18. |
Part sticks in mould |
| - |
Part temperature too high |
| - |
Inadequate draft |
| - |
Mold undercuts |
| - |
Sticking in one spot |
| - |
Very smooth surface Olefins |
|
| - |
Increase cooling time
Lower mould temperature
Reduce heating cycle time |
| - |
Rework mould for more draft
Use female mould |
| - |
Remove part early, then fixture until cool
Consider more sophisticated ejection system
Use pulling cores, break away frame
Decrease depth of texture |
| - |
Uneven mould temperature
Uneven sheet temperature prior to forming |
| - |
Add antiblock to polymer
Roughen mold surface slightly
Try female mould if excessive shrinkage |
|
| 19. |
Sheet sticks to plug |
| - |
Plug temperature too High |
| - |
Wooden plug |
| - |
Plug speed too high |
|
| - |
Reduce plug temperature
Use dry mould release
Use permanent mould coating
Use felt/wool/fabric covering
Coat with lubricant |
| - |
Switch to temperature controlled plug material |
| - |
Reduce plug penetration rate
Increase air pressure behind plug
Decrease air pressure ahead of plug |
|
| 20. |
Sheet tears while Forming |
| - |
Mould design |
| - |
Sheet too hot |
| - |
Sheet too cold |
| - |
Improper polymer |
| - |
Forming conditions improper |
|
| - |
Increase corner radius |
| - |
Decrease sheet temperature
Preheat sheet, then bring to forming temperature slowly
Sheet thickness may not be uniform |
| - |
Increase heating time
Preheat sheet |
| - |
Change forming technique
Depth of draw excessive for polymer, see resin supplier |
| - |
Decrease plug penetration rate
Increase inflation rate
Increase draw down rate |
|
| 21. |
Corner cracking in service |
| - |
Stress concentration |
| - |
Under designed |
|
| - |
Increase radii
Corner too cold during forming
Increase mould temperature
Increase sheet temperature
Increase forming rate
Prestretch sheet
Decrease free surface cooling
Decrease plug rate of penetration
Change to ESCR resin |
| - |
Re-evaluate design |
|
| 22. |
Heating unit moves too slowly |
| - |
Compressed air working pressure is too low |
| - |
Heating traverse regulating valve is already set. |
| - |
Rubber cuff seal on traverse cylinder leak |
|
| - |
Arrange for correct air pressure, set pressure regulator correctly |
| - |
Screw out knurled screws |
| - |
Renew the seal |
|
| 23. |
Heating unit moves too fast |
| - |
Regulator valve for heating unit traverse is wrongly set |
|
| - |
Screw down knurled screws |
|
| 24. |
Feed drive motor does not run or cuts out |
| - |
Motor contactor is open Circuited |
|
| - |
Check contactor for correct setting and functioning. |
|
| 25. |
Main drive motor does not run or cuts out |
| - |
Motor contactor is open circuited |
|
| - |
Check contactor for correct setting and functioning. |
|
| 26. |
Motor runs, m/c. remains stationary friction clutch slips |
| - |
Safety friction clutch slips. Hard object or several beakers blocking forming station |
|
| - |
Stop drive, vent brake, traverse lower tooling bridge down, clean the tooling. When re-starting check for backlash between drive and forming unit |
|
| 27. |
Main drive motor does not run when auto simulator is switched ON |
| - |
Counter is defective motor contactor is defective |
|
| - |
Change the counter, exchange the motor contactor |
|
| 28. |
M/c. will not start on Auto simulator |
| - |
Key push button is not depressed |
| - |
Limit switch "Heating forward" is not contacted |
| - |
Limit switch is defective |
|
| - |
Depress key push button |
| - |
Check position of limit switch |
| - |
Exchange the limit switch |
|
| 29. |
Heating unit moves forward, but no sheet feed |
| - |
Timer switch forming heating period is defective |
| - |
Timer switch for feed period is defective |
|
| - |
Change the timer switch |
| - |
Change the timer switch |
|
| 30. |
Scrap surround tears |
| - |
Friction setting of clutch is too high |
|
| - |
Reduce friction setting on the knurled nut |
|
| 31. |
Scrap surround does not come away |
| - |
Friction setting of clutch is too low |
|
| - |
Increase friction setting of clutch on the knurlled nut |
|
