June 2010: What are your recommendations to minimize/control plastic parts warpage?

some nanoAdditives can minimize the warpage of plastic parts.

1) Improve cooling system
2) Increase cooling time
3) add support or stiffen the part by addding supporting ribs........

Nan-O-Sil ASD has been proven very effective in several polymers like PP, nylon, PBT and more.

http://www.nanosilasd.com/

Even better it's inexpensive and works on glass fiber filled plastics too.

For glass fiber filled plastics, replacing some glass with mica can lower warpage while keeping good properties.

Another way to lower warpage is to intentionally disrupt fiber orientation to get a more isotropic material.

Certain organoclays can aid in shrinkage control, and a very low levels (<5%), as well as improve surface appearance.

older generations of nucleating agents (and pigments) can often increase warpage in PP parts. Newer generations of nucleating agents (Hyperform technologies) promote uniform shrinkage and faster cooling and can thus REDUCE warpage in PP parts

Depends upon
1. Performance
a) Identify application requirement
» Mechanical (Load, Impact, Stiffness etc)
» Thermal (Temperature Range)
» Environmental
b) Identify chemical environment
c) Identify Special needs
» Outdoor or UV exposure
» Light transmission (Opaque to transparent)
» Fatigue & creep requirement
» Painting Requirement

2. Surface Quality
verify surface gloss , finish
3. Manufacturing
Verify Manufacturing consideration
» Injection molding - PP, ABS, PC, PBT, HDPE etc
Plastic Materials not possible in Injection molding - Thermoset Plastics - Bakelite,
» Blow molding - PP, PP+EPDM ,LDPE , HDPE, EVA, PET
Plastic Materials not possible in Blow molding - PP+TF, PP+GF
» Thermoforming - Glassutech, Resinated felt, PP+Jute etc
» Vaccum forming - ABS, HIPS, Acrylic , PS, PVC etc

4. Assembly
5. Cost

Apart from the suggestions given, another important point is providing a fixture to cool the part in a controlled way after taking out the component from mould. Fixtures can be made of wood, aluminium, copper etc. The fixture material selection depends on the speed of heat conductivity required.

In-depth analysis and optimization of plastic parts and molds will enable efficient and expert level of final part / mold design which will help to minimise/control plastic part warpage.
Following some of the areas where we have to concentrate
1. Feed system design
a. Gate Location b.Automatic Runner Balancing c.Hot Runner Systems d. Dynamic Feed Systems
2. Mold cooling simulation
3. Plastic flow simulation
4. Molding processes
a. Gas-Assisted Injection Molding b.Co-Injection Molding c.Injection-Compression Molding d.Blow molding e.Vaccum forming f. Thermoforming g. Compression molding
5. Material composite
a. Fiber Orientation - Understand and control the orientation of fibers within fiber-filled plastics to reduce shrinkage variations across the molded part and to minimize or eliminate part warpage.
b.Warpage Prediction - Uncover and isolate the primary causes of warpage that results from process-induced stresses. Identify where warpage is likely to occur, and optimize part design, material choice, and processing parameters to control part deformation before building the mold.

Most all the above refers to injection. Warpage can be serious in extrusion too. It relates to speed of cooling, alignment of extruder and takeoff, and asymmetry of profile and its cooling. Does anyone have experience with additives that increase/decrease warpage of extruded products?

Foam with SCF will be effective;
If with organclay will improve the quality further.

Closed loop melt pressure control, remedies the issue of shrinkage and warp by delivering the melt to the mold with millisecond controlled pressure, and combining the signal from a mold transducer to transition to a hold and pack pressure that allows the material morphology to relax. This provides consistent stress levels and uniform shrinkage.

Maximize set temperature to upper limit of polymer suggested temperature, minimize fill pressure & profile incremental as well as pack phase in decremental order so as to release stress within mold itself before demolded at room temperature. However, for medium to higher thickness parts both speed & pressure need moderate settings. Sequential gating preferred for larger parts.

You can consider going with an amorphous polymer over a semicrystalline one from the beginning since amorphous polymers tend to warp less. Another thing you need to do, especially if molding with semicrystalline resins is to ensure good even cooling of the part. Make sure you achieve a reynolds number of at least 100 on your water flow to ensure turbulent flow and proper cooling. My favorite is to go with gas assist to reduce warpage. www.wilchron.com

per the question on extrusion, the nucleating agents referenced are also effective in extruded polyolefins

irst of all try to avoid warpage, by optimised uniform cooling (use common sense and simulation). Don't save on this one.

Second, add clays or other additives to "suppress" the stresses / forces that drives warpage

As a last, sometimes gas assisted molding may help, but mosy often it only fixes cosmetic problems like sink marks, rather than warpage (stiffening effect is often overrated.

warpage is a result of induced internal stresses during moulding process. Stresses are caused due to temprature differentials across the section. Therefore gradient of thermal balance or heat exchange should be uniformly mantained in mould.

Warepage is a big issue!
Warping, Part Distortion is shows up as parts being bowed, warped, bent or twisted beyond the normal specification outlined on the drawing. 
Possible Solutions:
Adjust melt Temperature (increase to relieve molded-in stress, decrease to avoid overpacking). stress, decrease to avoid over packing). stress, decrease to avoid over packing).
Check gates for proper location and adequate size.
Check mold knockout mechanism for proper design and operation.
Equalize/balance mold temperature of both halves.
Increase injection-hold.
Increase mold cooling time.
Relocate gates on or as near as possible to thick sections.
Try increasing or decreasing injection pressure.

Warpage is caused by differential cooling, differential shrinkage, and/or orientation effects. It is difficult to combat all three, but improvements can be made through tool design (cooling circuit primarily, inclusion of high heat transfer inserts), part design (maintaining nominal wall thickness is always desired), and processing (gate locations for balanced fill, filling and packing paramters, melt and mold temperatures, cooling time)

Variation in wall thickness causes differential shrinkage causes warpage
Use of amorphous material to reduce warpage
Stiffners are to be provided for more warpging areas to have structural rigidity to prevent warpge

Hello Allan Griff
Extrusion warpage of sheet made with crystalline polymers (PP etc) can also be controlled by the use of forced cooling in the case of thick (greater than 3 mm) sheet.
Warpage of flat vacuum forming (V/F) products can be considerably reduced by immediate trimming away of unformed sheet. Also mould temp can influence warpage.

To understand how to reduce warpage, one needs to understand the causes of warpage. Post molded warpage occurs when you have non-uniform material shrinkage. Several factors relate to this, such as non-uniform wall sections, molded in stress from high packing pressures, non-uniform cooling. There are more, but these tend to be the most common. As I read the comments, it becomes clear the best approach to is to start with good engineering practices and designs. If you don't have knowledge then seek experts. However through my experience, if I had to choose the most common item that cause warpage, it would be non-uniform mold cooling. There are new cooling technologies that address this issue. Ritemp Cooling Technologies is the most advanced cooling system and when properly applied can eliminate warpage.

No quick answers - lot of items to consider. Based on 25+ years experience as a consultant (corexdg.com) - some quick tips:
1. Understand cause of problem before making tool changes
2. Have the product design, material selection and final tool design reviewed by a outside expert with the required experience and proper simulation software tools. Do not rely on toolmaker or feedback from material supplier.
3. With crystalline materials (tougher to fix) focus effort first on improving the cooling layout and second on moving or adding gates to randomize flow.
4. -With amorphous materials (easier to fix) wall thickness typically dominates cause of warpage. Gate in thicker sections. Make sure runner and gate is properly sized and thicker sections of part can be adequately packed. Sometimes small wall thickness changes within tolerance limits can fix the problem.
5. With glass filled crystalline materials the anisotropic shrinkage effects resulting in higher warpage (toughest to fix). Try to randomize flow.
6. With all materials, make sure tool is running properly before any tool changes are made. Bad venting, flashing, or difficult ejection can result in processor having to make changes to temperatures and fill times which can affect warpage.

Hi, Warpage is outcome of Differantial Shrinkage!
One of the way to controlle warpage is to minimise the shrinkage.Shrinkage occurs, when polymer cools from molten stage to solid stage .It is directly proportional to Tempreture differance.Hence higher melt tempreture will result in Higher shrinkage & evantually higher warpage, if cooled unevenly. It is recomanded to have Optimum Melt tempreture just for easy flow inside the mould.
With higher (optimum) hold pressure , you could pack more material in to the mould , componseting volume shrinkage occured as a result of cooling melt inside the mould. This will reduce shrinkage & warpage.
Yes, The hold pressure stage has to be adjusted , steps to be added according to part Geometry , so that pushing in material only componseting the volume shrinkage without causing stress concentration . Generally , Holding pressure steps are used to reduce the hold pressure with respect to time.
Very High Injection Speed cause higher polymer chain orientation in one(Flow) direction and less in transverse direction, causing differantial shrinkage when cooled . This results in warpage. But very low speed will cause cooling of flow path (wall thickness) before comple part filling , and will not transfer Packing /Hold pressure to extreme ends of part . This will result in higher shrinkage/sink marks in those areas & result in differantial shrinkage and hence warpage.
It is observed that warpage can be minimised by-
1.Increasing injection pressure
2.Increasing holding Pressure
3.Increasing Hold time
4.Decrease mould tempreture
5.Decreasing (optomising) melt tempreture.
6.Decreasing (optimising) injection speed.
7.Increase cooling time.
Ofcourse Part geometry is one of the Most importent aspect deciding Warpage. Keeping Uniform Wall thickness is always advised.