DEFECT SUGGESTED SOLUTION
• Bubble or blister on the sheet
• Incomplete forms and details
• Color change of a sheet
•Excessive moisture
•Heating too fast
•Irregular heating.
•Insufficient vacuum
•Slow vacuum displacement
• Insufficient heating of a sheet.
• Excessive heating
• Low mold temperature.
• Pre-dry sheet.
• Dry both sides of sheet at 140°F (60°C)
• Reduce furnace temperature.
• Increase distance between sheet and heater.
• Check and fix the furnace.
• Check heating elements.
• Eliminate obstructions in vac-uum system
• Increase number of holes
• Increase their diameter
• More tank and vacuum pump capacity.
• Leakage.
• Check vacuum system for possible leaks.
• Use vacuum canals in possi-ble areas.
• Increase temperature or heat-ing time.
• Reduce heating time.
• Reduce furnace temperature.
• Heat mold.
POSIBLE CAUSE
DEFECT SUGGESTED SOLUTION
• Color change of a sheet.
• Excessive warping or bend-ing of a sheet
• Cooling marks on a formed piece.
• Low temperature of mechanical support
• Too much thinning of a sheet.
• Sheet cooling before its formi-ing is completed.
• Mold wrongly designed.
• Inadequate material
• Sheet too hot
•Sheet too big.
• Sheet too hot.
• Insufficient temperature of support.
• Mold low temperature (Shrinking stops at contact with mold or cold support).
• Heat mechanical support.
•Increase sheet thickness.
• Place sheet more quickly on the mold.
• Increase vacuum speed.
• Heat mold and mechanical support.
• Reduce mold depth.
• Improve vacuum air flow.
• Use more curved radiuses.
• Change material.
• Reduce heating time.
• Reduce furnace
• If possible, reduce sheet size
• Use screens, mainly on cen-ter of sheet (only infrared heating furnaces).
• Reduce mold temperature. .
• Reduce heating time.
• Raise support temperature. .
• Use soft flannel filter on sup port surface
• Raise mold and/or support -temperature, without exceed ing temperature range.
• Soften and/or round mold critical areas.
POSIBLE CAUSE
DEFECT SUGGESTED SOLUTION
• Small wrinkles or circular marks..
• Bending variation of sheet.
• Wrinkles while forming.
• Very shiny lines or zones.
• Bad surface aspect of piece.
• Sheet too hot
• Too big vacuum bores.
• Sheet irregular temperature.
• Excessive heating of sheet.
• Excessive bending of sheet.
• Insufficient vacuum..
• Over heating sheet on shine area.
• Defect caused by air caught on flat surface of mold.
• Insufficient vacuum.
• Reduce mold temperature.
• Reduce heating time..
• Refill and bore again smaller diameter.
• Check there are no drafts in furnace, deflectors must be incorporated.
• Reduce furnace temperature.
• Reduce heating time.
• As far as possible, more dis-tance between 2 heaters and sheet (only infrared heating furnaces)
• Reduce molding range tem-perature.
• Check vacuum system.
• Increase vacuum canals or ori-fices.
• Use screens to reduce heat on zone.
• As far as possible more dis-tance between 2 heaters and sheet (only infrared heating fur-naces).
• Reduce heating time.
• Sandblast mold surface.
• Increase number of vacuum ori-fices
• If marks are isolated, increase number of vacuum orifices in affected area.
POSIBLE CAUSE
DEFECT SUGGESTED SOLUTION
• Piece surface bad aspect
• Excessive distortion or shrinking after removing a piece off a mold.
• Excessive thinning of walls of a piece
• Excessive mold temperature.
• IInsufficient mold tempera-ture..
• Superficie del molde demasia-do áspera o rugosa.
• Dirty sheet.
• Piece removed too fast.
• Inadequate forming tech-nique.
• Material thickness variation.
• Uneven sheet heating.
• Sheet at excessive tempera-ture.
• Cold mold.
• Sheet not firmly fastened to frame.
• Reduce mold temperature.
• Increase mold temperature.
•Soften mold surface.
• Make mold of other material.
• Clean sheet.
• Prolong cooling cycle.
• Move the piece to a cooling template.
• Use refrigerant.
• Use water spray steam to reduce piece temperature.
• use electric ventilators to cool piece inside the mold.
• Use different forming techni-que: vacuum with return, pres-sured air and mechanical sup-port, pressured air and return with vacuum.
• Check material meets quality norms and /or complain.
• Check furnace operation.
• Reduce furnace temperature.
• Reduce heating time.
• Heat mold.
• IIncrease closing pressured.
• Check possible sheet thick-ness variation.
POSIBLE CAUSE
DEFECT SUGGESTED SOLUTION
• Pieces twist
• Shrinking marks on corners.
• Bubble stretches unevenly.
• In deep forming, thin cor-ners.
• Piece cooled wrongly.
• Uneven wall thickness distri- bution.
• Wrongly designed mold.
• Wrongly designed piece.
• Insufficient mold temperature.
• Mold surface too smooth.
• Insufficient vacuum.
• Insufficient sheet temperature.
• Sheet uneven thickness.
• Insufficient pressured air.
• Wrong forming technique.
• Thin sheet
• Sheet unevenly heated
• Mold wrongly heated.
• Adjust cooling cycle.
• Use pre-stretching mechanical or technical support.
• Sheet might be unevenly heat-ed.
• Increase vacuum orifices.
• Modify mold
• As far as possible, curve a little flat areas.
• Increase mold temperature.
• Sandblast mold surface.
• Check vacuum system.
• Add more orifices.
• Check furnace operation con-dition
• Use cooling screens (Only infrared radiation heating fur-nace.).
• Longer heating time at lower temperature.
• Incorporate an air distribution system with deflectors.
• Change forming technique.
• Increase sheet thickness.
• Check furnace operation.
• Use screens to change heat distribution.
• Change furnace temperature.
POSIBLE CAUSE
DEFECT SUGGESTED SOLUTION
• Piece sticks to mechanical support.
• Piece sticks to mold.
• Corners of formed piece shatter once in use..
• Mechanical support (wood).
• Mechanical support (metal).
• Piece high temperature.
• Mold insufficient exit angle.
• Wooden mold.
• Piece wrongly designed.
• Effort concentration on a piece.
• Apply removing agent.
• Cover with soft felt or flannel.
• Apply removing agent.
• Lower support temperature.
• Cover with felt or flannel.
• Longer cooling time.
• Reduce mold temperature.
• Give 1° and 3° angle
• Change matrix.
• Apply removing agent.
• Redesign piece.
• Increase mold curve radius.
• Increase thermoforming tem-perature.
• Make sure piece is wholly formed before it cools below forming temperature.
POSIBLE CAUSE
APPENDIX
ABSORBENCY
Fraction of radiant energy taken by a sheet.
CAVITY
Depression of a vacuum made mold, machine finished or a combination of both,.
depending on the number of depressions, it may have one or several cavities.
CONDUCTION
Energy transferred by directly touching a solid.
CONVECTION
Energy transferred by the movement of a fluid current.
COOLING MARKS
Marks caused by using wrong temperature on a plastic sheet, derived from inadequate heating.
CO-POLYMER
Polymer composed of tow different kinds of monomers.
CYCLE
Complete repetitive sequence in the thermoforming process, which consist in: heating, forming, cooling and removal.
DIMENSIONAL STABILITY
Capacity of a piece to keep the accurate shape and dimension of the mold used.
ENTHALPY
Inner energy of a system.
HEAT TRANSFER COEFFICIENT
Effectiveness measure of energy transported between a fluid current and a solid surface.
HOMO-POLYMER
Polymer made of only one monomer INFRARED
Part of electro-magnetic spectrum, between the range of visible light and the range of radio waves. Radiant heating is the range at which infrared heaters are used to heat a sheet. Wave length is 0.08” to 0.4”
Glossary
MELTING TEMPERATURE
Range of temperature at which a crystalline polymer turns from a solid rubber-like state into a viscous-elastic liquid.
MOLDING TEMPERATURE
A piece temperature at which it can be removed without deforming.
PRESSURED AIR SHAPING
Difference of pressure exceeding two atmospheres (30 Psi.).
RADIATION
It is the transfer or exchange of electromagnetic energy.
REFLECTIVITY
Fraction of radiant energy reflected on a sheet surface.
RESIN
Another name to call a polymer or plastic material.
SCRAP
Material waste that is not part of the final piece.
TENSION
External charge exerted on a defined area.
THERMAL DIFFUSIVENESS
Transmission index of calorific energy in a material.
TRANSMITTANCE
Fraction of energy that is transmitted through a sheet.
TRI-POLYMER
Polymer composed of three different kinds of monomers.
VACUUM TANK
Tank between the vacuum pump and the mold, that allows you to apply pressure even-ly during forming.