Analysis of reasons for Warpage of Plastic Injection Molding Products-1

With the development of the plastics injection molding industry, people have higher and higher requirements on the appearance and performance of plastic injected parts. The degree of warpage deformation is one of the important indicators for evaluating product quality, and it is more and more concerned and valued by mold designers. Mold designers hope to predict the possible warpage of plastic parts during the design phase in order to optimize the design and then they can improve the efficiency and quality of injection molding, shorten the mold design cycle and reduce costs. I take this change to analyze the factors affecting the warpage of injection molded products during the design process of plastic injection molds.

1. Effect of the mold structure on the warpage of plastic injection products:In terms of mold design, themain factors affecting the deformation of plastic parts are pouring system, cooling system and ejection system.

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Technical Problem 7 from Fiberglass Compression Molding-- Warpage

Technical Problem 7 from Fiberglass Compression Molding-- Warpage 

Description 1:The Fiberglass Compression Molding part is slightly warped. 

Condition 1:Warpage due to shrinkage during hardening and cooling. 
Solution:To cool fiberglass molding parts in fixture.To use low or no shrinkage resin. 

Condition 2：The temperature of half mold is higher than other half.
Solution:Reduce mold temperature difference.

Description 2:The Fiberglass Compression Molding part is seriously warped.
Condition:Particularly long process cause fiberglass orientation and then result in warpage.Solution:To increase the feeding area,shorten the process and use low shrinkage or shrink free resin.

Technical Problem 6 from Fiberglass Compression Molding--Mucosa

Technical Problem 6 from Fiberglass Compression Molding--Mucosa 

Description 1:The Fiberglass Molding part is difficult to remove from the mold, and the fiberglass sheet sticks to the mold in some areas.

Condition 1:Mold temperature is too low.
Solution:Increase the mold temperature. 

Condition 2:Solidifying time is too short.
Solution:Extend solidifying time. 

Condition 3:It is too long to open the outer packaging of Fiberglass sheet.
Solution:Always keep the Fiberglass sheet sealing before using them.

 
Condition 4:Without special treatment before using new molds or long-term unused molds.
Solution:To use release agent to help demoulding for first several cyclings. 

Condition 5:The mold surface is too rough.Solution:better surface polishing.

Description2:It is difficult to demould the solidified fiberglass molding parts.In some areas
the fiberglass raw material sticks to the mold, and the surface of the final parts has some 

microholes and scars.

Condition:The feeding area is too large, the air can not be discharged, and the air impedes solidifying.
Solution:Reduce the feeding area and add small sheet at the top of the large sheet.

Technical Problem 5 from Fiberglass Compression Molding--Swell.

Technical Problem 5 from Fiberglass Compression Molding--Swell. 

Description:a semicircular swell on the surface of solidified fiberglass compression molding part.

Condition 1:Entrapped air between fiberglass sheets.Solution:Remove the interlayer air by pre-pressing method and reduce the feeding area to facilitate the discharge of air. 

Condition 2:The tooling temperature is too high (evaporation of monomer).Solution:low tooling temperature. 

Condition 3:Solidifying period is too short (evaporation of monomer).Solution:Extend solidifying period.

Condition 4:There is dry fiber.Solution:Reduce the viscosity of the resin.Install more work rolls in the impregnation area, and heat the dip rollers.Replace the glass fiber.

Condition 5:There are burrs in the cavity of fiberglass compression  tooling.Solution:Carefully remove the burrs in cavity of tooling.

Condition 6:Fiberglass sheet is too soft.Solution:Increase the thickening of fiberglass SMC raw material or increase the content of thickener.

Technical Problem 4 from Fiberglass Compression Molding--Many small surface holes.

Technical Problem 4 from Fiberglass Compression Molding--Many small surface holes. 

Description:if there are too many small holes in the surface it will be difficult to release the fiberglass molding products. 

Condition 1:The feeding area is too large, and the surface air is not discharged due to the short process.
Solution:Reduce the feeding area and add small material sheet at the top of the large sheet.

Condition 2:The clipping edges are too large.   Solution:Repair clipping edges. 

Condition 3:There is dry fiber.The initial viscosity of the resin paste is too high. The glass fiber is not fully saturated.
Solution:Reduce the initial viscosity of the resin paste, increase the work roll in the impregnation area, and replace the glass fiber.

Condition 4:Pre-gelled area on the fiberglass molding part. Solution:Reduce mold temperature and add inhibitor to resin paste. 

Condition 5:SMC material dry.
Solution:When using the anti-seepage film to wrap the SMC material, the quantity of zinc stearate can not be prepared too much. 

Condition 6:Fiberglass SMC material too soft.
Solution:Increase thickening time or increase thickening temperature to increase thickening viscosity level. 

Condition 7:Insufficient pressure.    Solution:Increase fiberglass molding pressure.

Technical Problem 3 from Fiberglass Compression Molding-Internal cracking

Technical Problem 3 from Fiberglass Compression Molding-Internal cracking

Description:Due to excessive shrinkage stress in individual layers of thick-walled products, bosses or ribs.

Solution:Reduce the feeding area so that the fibers are better interwoven between the layers and reduce

 the molding temperature.

Chapter 2--Gas assistance system for Pressure Reduction technology in Plastic Injection Molding

Principle:

 In fact, pressure must be generated in the production of molded plastic parts. In general, the pressure in the cavity is caused by a slight shrinkage, and its effect is cumulative, and this cumulative effect will eventually lead to the defective plastic injection parts. Typically, when the part is removed from the mold for the first time, it can resist the effect of the in-mold pressure on the structure of injected plastic parts. Plastic parts can cause slight deformation or cracking only at high temperature. In practical applications, all the mold parameters can cause a slight deformation, resulting in in-mold pressure. When these forces act together on the same part, a large amount of extra stress is generated. The forces acting on the part result in the generation of pressure. When the pressure is very small, it will not have a significant impact. However, if the pressure is high enough, the in-mold pressure becomes a factor that must be considered because the combined action with the external force will exceed the maximum value that the  plastic injected partscan withstand.The most serious result is part’s fracture.

Technical Problem 2 from Fiberglass Compression Molding-Coking

Technical Problem 2 from Fiberglass Compression Molding-Coking

Description:The surface areas of fiberglass parts which are incompletely filled is dark brown or black. 

Condition:Trapped air and Styrene vapor are compressed to raise the temperature to the ignition point.

Solution:To improve the feeding method so that the air flows out with the raw material, and no trapping occurs. If brown spots appear in the blind holes, you can use the three-half mold structure or use the ejector pin to exhaust air.

More information please check: http://www.olimyfiberglass.com/

Chapter 1--Gas assistance system for Pressure Reduction technology in Plastic Injection Molding

    To designers of injected plastic parts the internal pressure of the cavity is one of the headachy problems.Due to the pressure, the mold will be deformed by heat, and even some parts will break. How to better solve this problem?

    Gas assistance systems can solve the problem of pressure.In fact the gas assistance system can automatically correct many of the problems caused by the internal pressure of the cavity. With the finite element analysis technique for the target,the gas assistance system can be designed as a very accurate gas assistance system component.The analysis of the above components is carried out using Moldflow software. The analysis results show that these components can effectively overcome a series of problems caused by the existence of pressure in the injection mold cavity.

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Technical Problem 1 from Fiberglass Compression Molding:cavities unfully filled

Technical Problem 1 from Fiberglass Compression Molding:cavities unfully filled

Condition 1:Not fully filled at the edge of Fiberglass Compression Mold.
1.Reason:Insufficient feeding Fiberglass SMC material---Solution:Increase the quantity of feeding
2.Reason:Molding temperature is too high--Solution:Decrease molding temperature.
3.Reason:The closing time of SMC Pressure Machine is too long, and the Fiberglass SMC is solidified before the mold is filled.--Solution:Shorten closing time.
4.Reason:Molding pressure is too low--Solution:Increase molding pressure.
5.Reason:Feeding area is too small--Solution:Increase feeding area

Condition 2:Not fully filled in small area on the edge of the Fiberglass Compression Mold
1.Reason:Insufficient feeding--Solution:Increase the quantity of feeding.
2.Reason:Material loss before mold closing--Solution:More careful discharge.
3.Reason:The distance between upper and lower cavities is too large or the fitting length is too short.--Solution:Reduce the fitting clearance and increase the fitting length.
    If the defect is small,increase the molding temperature or add excess Fiberglass SMC material.

Condition 3:Although the entire edge is full filled but some areas are not full filled
1.Reason:Insufficient feeding--Solution:Increase the quantity of feeding.
2.Reason:Air failed to drain--Solution:Improve feeding method.
3.Reason:Air in the blind hole cannot be discharged--Solution:Use three-half mold structure or allow air to be discharged from the ejector pins.If the defect is small to increase
  the pressure.