CONTACT INFORMATION:

Advanced Plastic Consultants LLC
Ed Bearse
4806 Ridge Rd
Lake, MI 48632

Phone:  (989) 588-0494
Fax:      (989) 588-0061

 


















Bad surface markings

Pockmarks due to entrapment over smooth mold surface
Blast mold surface with grit or glass beads

Poor vacuum
Add vacuum holes
(If pockmarks are in isolated area, add vacuum holes in this area, or check for plugged vacuum holes or vacuum leak)
Directionally sand from problem area to vacuum holes
Check entire vacuum system for leaks

Mold is too hot
Reduce mold temperature

Mold is too cold
Increase mold temperature

Improper mold composition
Avoid phenolic or other “heat sink” glossy molds
Use aluminum molds where possible

Mold surface is too rough
Change mold material
Sandblast mold surface with #30 grit

Dirt on sheet
Clean sheet
Use ionized-air blow

Dirt on mold
Clean mold

Dust in atmosphere
Clean thermoforming area
Isolate area, if necessary, and supply filtered air
Use ionized air

Contaminated sheet materials
If regrind used, be sure to keep supply clean
Store different materials separately
Check supplier of sheet
Use co-extruded sheet with virgin
Scratched sheet
Separate colored sheets with film
Replace sheet


Blisters or Bubbles

Heating too rapidly
Lower heater temperature(s)
Use screening over heaters
Increase distance between heater(s) and sheet
Blow chilled air across sheet surface during heating

Excess moisture
Pre-dry sheet 1-4 hours at 150°F
Heat from both sides
Lower heater temperature
Request moisture-proof wrap
Do not remove sheet from moisture-proof wrap until ready to use
Obtain dry material from supplier

Uneven heating
Screen for uniform heat by attaching baffles, masks, or screen
Check heater for proper operation
Confirm screen location
Adjust individual heater temperatures for uniformity


Blushing or change in color intensity or gloss

Insufficient heating
Lengthen heating cycle
Raise heater temperature

Excessive heating
Reduce heater temperature
Shorten heating cycle
If consistently in one spot, check associated heater
Blow refrigerated air across high-gloss surface
Lower temperatures on high-gloss surface

Mold is too hot or too cold
Adjust mold temperature

Assist is too cold
Warm assist, or use syntactic foam or felt-covered plug

Sheet being stretched too far
Use heavier gauge sheet
Change mold design
Change forming technique

Sheet cools before it is completely formed
Move mold into sheet faster
Increase rate of vacuum withdrawal
Be sure molds and plugs are hot

Poor mold design
Reduce depth of draw
Increase draft (taper) of mold
Enlarge radii

Sheet material not suitable for job
Try different sheet formulation or a different plastic material

Uncontrolled use of regrind
Control percentage and quality of regrind

Color shift in substrate
Assure that substrate under high-gloss material has not shifted


Chill marks or “mark-off” lines on part

Plug assist temperature too low
Increase plug assist temperature
Use syntactic foam plug assist
Cover plug with cotton flannel or felt

Stretching stops when sheet meets cold mold (or plug)
Increase mold temperature (do not exceed “set temperature” for particular resin)
Relieve molds in critical areas

Inadequate mold temperature control
Increase number of water-cooling tubes or channels
Check for plugged water flow

Sheet too hot
Reduce heat
Heat more slowly
Lower surface temperature of sheet
Before forming, use forced air to slightly chill surface of hot sheet contacting mold

Driving tool too far into sheet
Decrease amount tool travels through sheet frame


Excessive shrinkage or distortion of part after removal from mold

Removed part is too hot
Increase cooling time
Use cooling fixtures
Use fan to cool part faster on mold


Incomplete Forming or Poor Detail

Vacuum not drawn fast enough
Start vacuum as tool first hits sheet
Add vacuum surge and/or pump capacity
Enlarge vacuum line and valves, avoiding sharp bends at tee and elbow connectors
Check for vacuum leaks
Check vacuum system for minimum of 25 inches of Hg pressure

Additional pressure needed
Use 20- to 50-psi air pressure on part opposite mold surface (assure mold will withstand this pressure)
Use frame assist
Use plug or other pressure assist

Wrong material
Insure that sheet is produced at the proper thickness

Sheet too cold
Heat sheet longer
Raise heater temperature
Check heaters for proper operation
Increase number of heaters
Increase watt density

Clamping frame not hot before inserting sheet
Pre-heat clamping frame before insertion of sheet by cycling machine

Insufficient vacuum and/or compressed air
Check vacuum holes for clogging
Increase number of vacuum holes
Check for vacuum or air leak
Remove any 90-degree angles in vacuum system

Excessive mold wear
Check seal between clamp frame and vacuum box
Use pinch frame to create seal
Make sure mold surface is sand or bead blasted
Directionally sand, from problem area to nearest vacuum hole


Nipples on mold side of formed part

Sheet too hot
Shorten heating cycle
Reduce heater temperature
Reduce temperature of sheet surface that contacts mold
Increase time between heating and forming

Vacuum holes too large
Plug holes and re-drill with smaller bit


Non-uniform pre-stretch bubble

Uneven sheet gauge
Consult sheet supplier
Heat sheet slowly in a “soak” type heat

Uneven heating of sheet
Check heater section for non-functioning heaters
Check heater section for missing screens
Screen heater section as necessary

Stray air drafts
Enclose or otherwise shield or screen machine
Check clamping-frame air cylinders for leaks

Non-uniform air blow
Baffle air inlet in pre-stretch box


Part sticking to mold

Mold or sheet temperature too high
Increase cooling cycle
Slightly lower mold temperature to not much less than that recommended by resin manufacturer
Lower surface temperature on side of sheet that contacts mold

Not enough draft in molds
Increase taper
Use female mold
Remove part from mold as early as possible (if above “set temperature,” use cooling jigs)

Mold undercuts
Use stripping frame
Increase air-eject pressure
Remove part from mold as early as possible (if above “set temperature,” use cooling jigs)
Change mold design for undercut to break away

Wooden mold
Lubricate with wax
Use Teflon spray or zinc stearate
Lower surface temperature on side of sheet that contacts mold

Rough mold surface
Polish corners or entire mold
Use mold spray
Use Teflon spray or zinc stearate
Lower surface temperature on side of sheet that contacts mold


Part warpage

Uneven part cooling
Add more water channels or tubing to mold
Check for plugged water flow
Cool part at same rate on both sides

Poor wall distribution
Improve pre-stretching or plugging techniques
Use plug assist
Check for non-uniformity of sheet heating
Check sheet gauge

Poor mold design
Add moat to mold at trim line
Add vacuum holes
Check for plugged vacuum tubes

Poor part design
Break up large, flat surfaces with ribs, where practical
Make large, flat surfaces concave or convex

Mold temperature too low
Raise mold temperature to just below “set temperature” of sheet material


Poor wall-thickness distribution

Improper sheet sag for forming
Use different forming technique
Use vacuum snap-back technique
Use billow vacuum snap-back
Use billow-up plug assist or vacuum snap-back into female mold
Use resin with different melt-index

Variations in sheet gauge
Consult supplier regarding commercial tolerances and improve quality of sheet

Hot or cold spots in sheet
Improve heating technique to achieve uniform heat distribution − screen or shade as necessary
Check to see that all heating elements are functioning

Stray drafts and air currents around machine
Enclose heating and forming areas

Too much sag
Use screening or other temperature control in center areas of heater banks
Use material with higher melt strength

Mold too cold
Provide uniform heating of mold to bring to proper temperature
Check temperature control system for scale or other stoppage

Sheet slipping out of frame
Adjust clamping frame to provide uniform pressure
Check for variation in sheet gauge
Heat frames to proper temperature before inserting sheet
Check for non-uniformity of heat causing cold areas around clamp frame
Install screws in clamp frame


Sag variation between sheet blanks

Variation in sheet temperature
Check for air drafts through oven
Use solid screens around heater section to eliminate drafts

Wide sheet-gauge variation
Replace with sheet that has proper gauge tolerance

Sheet made from different resins − not a homogeneous mixture
Control regrind percentage and quality
Avoid resin mix-ups

Clamp frame air leaks
Check for air leaks on clamp frame cylinders


Scorched Sheet

Outer surface of sheet is too hot
Shorten heat cycle
Use slower, soaking heat (lower heater temperature)
Mover heater bands further from sheet
Check heaters for proper operation


Sheet sticking to plug assist

Improper metal plug assist temperature
Reduce plug temperature
Use mold release
Coat plug with Teflon material
Cover plug with felt cloth or cotton flannel
Use syntactic-foam plug

Wooden plug assist
Cover plug with felt cloth or cotton flannel
Grease plug with wax
Use mold-release compress
Use Teflon spray or zinc stearate
Laminate wood plug surface with syntactic foam


Shiny streaks on part

Sheet overheated in streaked area
Lower heater temperature in scorched area
Shield heater with screenwire to prevent overheating
Slow heating cycle
Increase distance between heater and sheet

Bad sheet
Check with sheet supplier


Shrink marks on part, especially in corner areas (inside radii of molds)

Inadequate vacuum
Check for vacuum leaks
Add vacuum surge and/or pump capacity
Check for plugged vacuum holes
Add vacuum holes

Mold surface too smooth
Grit-blast mold surface with #30 grit

Part shrinking away (may be impossible to eliminate on thick sheet with vacuum only)
Use 20- to 30-psi air pressure on part opposite mold surface, if mold will withstand this pressure
Add moat to mold just outside trim line


Tearing of sheet when forming

Mold design
Increase radius of corner

Sheet too hot
Decrease heating time or heater temperature

Closing speed between mold and sheet too high
Reduce rate of closure

Sheet too thin
Use thicker sheet or adjust process for thinner sheet

Wrong material for application
Check with sheet supplier on grade used in sheet

Sheet moisture
Pre-dry sheet


Too much sag

Sheet too hot
Shorten heater cycle
Reduce heater temperature

Melt index too high
Use different resin or one with lower melt index

Sheet area too large
Profile heat the sheet
Use screening or other means of shading or giving preferential heat to sheet, thus reducing relative temperature of center of sheet


Too-thin corners in deep draws

Improper forming technique
Check other techniques, such as billow-up plug assist, etc., to pre-stretch sheet

Sheet too thin
Use heavier gauge

Variation in sheet temperature
Profile sheet heating − adjust heating as needed by adding screens to portion of sheet going into corners, or by lowering panel heat temperature
Crosshatch sheet with markings prior to forming, so movement of material can be accurately checked

Variation in mold temperature
Adjust temperature-control system for uniformity

Improper mold design
May need to use plug assist or change to male tool

Improper material selection or poor sheet
Consult sheet supplier or raw-material supplier to be sure proper material is correctly extruded


Webbing, bridging, or wrinkling

Sheet too hot, causing too much material in forming area
Shorten heating cycle
Check operation of heaters
Lower heater temperature
Increase heater distance
Insert screen in areas of excess sag

Melt strength of resin too low (excessive sheet sag)
Change to higher melt-strength resin
Use minimum sheet temperature possible
Profile temperature of sheet

Insufficient vacuum
Check vacuum system
Add more vacuum holes
Directionally sand tool from problem area to nearest vacuum holes
Increase size or number of vacuum holes

Vacuum rate too fast
Slow down vacuum rate
Restrict main vacuum line

Insufficient sheet stretching
Drive tool farther into clamp frame

Extrusion direction of sheet parallel to space between molds
Move sheet 90 degrees in relation to space between molds

Draw ratio too great in area of mold, or poor mold design or layout
Redesign mold
Use plug or ring mechanical assist
Use female mold instead of male
Add take-up blocks to pull out wrinkles
Increase draft and radii where possible
If more than one article is being formed, move articles farther apart
Speed up assist and/or mold travel
Redesign grid, plug, or ring assists
Use recessed pocket in web area


Whitening of sheet

Cold sheet stretching beyond its temperature-yield point
Increase heat of sheet
Increase speed of drape
Increase speed of vacuum
Reduce time between heating and molding
Increase tool and/or plug temperature



Site constructed by ChipChap with template by Illusive Design