|
Problem
|
Cause
|
Solution
|
|
Bubbles or blisters |
Extremely quick heating |
Decrease temperature of the heater.
Increase the distance between the heater and the sheet.
Blow air through the surface of the sheet during the heating. |
| Excessive humidity |
Pre-dry or preheat both faces of the sheet. |
| Inadequate material |
Use another resin. |
|
Incomplete forming , poor details |
Very cold sheet
|
Increase the time of heating the sheet.
Increase the temperature of the heater.
Use more resistances.
Change to a design of more efficient heater.
|
| Insufficient vacuum pressure |
Check if there's obstruction of the holes of the vacuum.
Increase the number of holes.
To increase the diameter of the vacuum holes |
| Application of vacuuming was not sufficiently fast |
Use grooves instead of vacuum holes.
Increase the vacuum line, avoiding extremely marked angles (~90°). |
| Pressure applied slowly |
Increase the pressure of air.
Use an assisting piston.
|
| Burnt sheet |
Extremely hot sheet surface |
Decrease the heating cycle.
Separate a little more the resistances of the sheet.
Consider convection heating |
| Change in the intensity of coloration |
Insufficient heating |
Increase the heating cycle.
Increase the temperature of the heater.
Use more efficient heaters. |
| Excessive heating |
Reduce the temperature of the heater.
Decrease the heating cycle.
Consider heating for convection, cooling of the surface. |
| Extremely cold mold |
Increase the mold temperature |
| Extremely cold assistant |
Heat the assistant. |
| Sheet cooling before completing the stretching |
Quicker transfer of the sheet toward the mold.
Increase the forming speed.
Increase mold or assistant temperature. |
| Sheet stretched beyond limit |
Use higher thickness or more elastic resin. |
| Poor design of the mold |
Increase de-molding angles.
Increase corner radios |
| Whitening |
Stretching below the forming temperature |
Increase the sheet temperature.
Increase the forming speed
|
| Dry pigmented Sheet. |
Poor extrusion.
Non available material for pigmentation. |
| Wrinkles
|
Extremely hot sheet
|
Use short heating cycles.
Increase the distance among the heaters.
Decrease the temperature of the heaters.
Place cold air exactly before the forming
|
| Low resistance in Melting the resin |
Use resin of smaller index of fluency.
Increase the orientation.
Use low temperatures of the heater.
|
|
Misalignment in orientation
|
Increase or Decrease the orientation. |
| Insufficient vacuum |
Check vacuum system.
Increase the number of vacuum holes.
|
| Poor design of mold |
Use vacuum assistant.
Use female mold instead of male mold. |
| Nipples |
Extremely hot sheet |
Reduce the heating cycle.
Decrease the temperature of the heater. |
| Extremely long vacuum holes |
Cork the holes and drill again with a smaller wick.
Use vacuum grooves. |
| Excessive warpage |
Extremely hot sheet |
Reduce the heating cycle.
Decrease the temperature of the heater.
|
| Resin of high index of fluency |
Use a different resin or with smaller fluency index
|
| Extremely long sheet area |
Use meshes or other systems to provide heat to the sheet, reducing the relative temperature in the center
|
| Bulging varies from sheet to sheet |
Variation in the temperature of the sheet |
Check that there are not air currents around the heaters. In such a case, protect with meshes to eliminate them. |
|
Fabricated sheet with different resins (non homogeneous mixes )
|
Control the quality and the percentage of utilized regrind.
Avoid mixtures of resins. |
| Striation |
Low temperature of the assistant |
Increase the assistant's temperature.
Use a synthetic assistant.
Recover the assistant with wood or cloth.
|
| extremely low temperature of the mold |
Increase temperature of the mold. |
| inadequate control of temperature of the mold |
Increase the number of cooling channels.
Check the flow of water in the piston.
|
| Bright stripes |
Local over heating |
Decrease the temperature of the heater in the brilliant area.
Reduce the heating cycle.
Increase the distance heater-sheet. |
| Excessive shrinkage after molding/distortion |
Extremely short time of the piece in the mold |
Increase the cooling cycle.
Decrease the temperature of the refrigerating agent.
Use spray to cool the piece in the mold quicker.
|
| Extremely hot mold |
Decrease the temperature of the mold.
Increase the flow speed of the refrigerating agent.
|
| Warpage pieces |
Uneven Cooling |
Add cooling channels.
Check that there are not obstructed cooling channels
Cool the piece to at the same speed, both sides. |
| Poor material distribution in the walls of the piece |
Use an assisting piston or pre-stretching.
Place vacuum holes in the areas with defects.
|
| Poor mold design |
Add vacuum holes. |
| Low mold temperature |
Increase the temperature of the mold just below the temperature of the material. |
| Shrinkage marks |
Inadequate vacuum |
Use vacuum grooves.
Check if there are obstructed holes
or inadequate holes in surface area. |
| Extremely flat mold surface |
Modify the surface of the mold with sand treatment. |
| Contraction of the piece during the molding |
Increase the formed pressure
Increase the temperature of the mold.
Change to a less elastic material.
Reduce the surface free of cooling. |
| Inadequate pressure of air |
Increase the flow speed of the air.
Increase the pressure of the air.
Increase the time of the cycle under pressure. |
| Extremely thin corners |
Inadequate forming technique |
Use an assisting piston. |
| Extremely thin sheet |
Increase sheet gauge. |
| Variation in the temperature of the sheet |
Check the temperature profile
Increase the forming speed |
| Variation in the temperature of the mold |
Change the configuration of the cooling channels.
Adjust the temperature control system. |
| Poor thickness distribution on the walls of the piece |
Inadequate bulging of the sheet |
Use a different forming technique, as mounting the mold in the upper platen, pre-stretching for bubble welding.
Increase the orientation in the sheet. |
| Variations in the sheet thickness |
Adjust the caliber of the sheet. |
| Extremely cold mold |
Adjust the temperature control system. Heat the mold evenly till reaching the appropriate temperature. |
| Cold or hot areas in the sheet |
Improve the heating technique.
Check that all the heating elements are working. |
| Sticking in the mold |
Temperature of the mold or of the extremely high sheet |
Increase the cooling cycle.
Decrease the temperature of the mold.
Reduce the heating cycle. |
| Insufficient tolerances for de-molding |
Increase de-molding taper angle.
Use a female mold.
Extract the piece as soon as it is possible. |
| Wooden mold |
Lubricate the mold with
demolding agent |
| Surface of the rough mold |
Polish the surface of the mold, especially the corners.
Use releasing agent.
Use Teflon spray or Zinc stearate . |
| Adherence of the sheet to the assisting piston |
Extremely high assistant temperature |
Reduce the temperature of the piston.
Use releasing agent.
Use a cloth coating. |
| Wooden assisting piston |
Recover with lubricant.
Use a cloth coating |
| extremely high speed of the assistant |
Decrease the speed of penetration of the assisting piston.
Increase the pressure of air behind the assistant.
Decrease the pressure of the air before the assistant. |
| Tear of sheet during forming process |
Design of the mold |
Increase the radio of the corners. |
| Extremely hot sheet |
Reduce the heating cycle.
Decrease the temperature of the sheet.
Preheat the sheet, and then take it to the temperature of forming slowly.
|
