Injection moulding warpage

In summary, therefore, processing, and in particular injection moulding, can introduce limited chemical degradation, local polymer orientation, orientation of short fibre reinforcements, internal stresses, warpage, shrinkage and defects such as weld lines and voids. 

To improve the notched impact strength and to prevent hydrolysis induced embrittlement of PBT, PBT-styrenic blends have been thoroughly investigated. In comparison with ASA-PC, blends of ASA and PBT generally have to be compa-tibilized in order to yield acceptable mechanical properties. In the case of glass fibre reinforced PBT-ASA blends, an added and important bonus is reduced warpage properties on injection moulding in comparison with reinforced PBT. 

R. Zheng et. al., Thermo viscoelastic Simulation of Thermally and Pressure Induced Stresses in Injection Moulding for the Prediction of Shrinkage and Warpage for... 

S. P. Walsh, Shrinkage and Warpage Prediction for Injection Moulded Components, Journal of Reinforced Plastics and Composites, vol. 12, 1993. 

CR grades are available both as homopolymers and copolymers. Copolymer-based CR grades for injection moulding flow well and are highly resistant to warpage and internal stresses. These grades find application in thin-walled packaging for food and... 

Heat deflection temperature is a single point measurement and does not indicate longterm heat resistance of plastic material. However, it may be used to distinguish between those materials that are able to sustain light loads at high temperatures. The heat deflection temperature of a specimen is affected by the presenee of residual stresses. Warpage of the specimen due to stress relaxation may lead to erroneous results. In addition, injection-moulded specimens tend to give a lower heat defleetion temperature than compression-moulded specimens. This is because compression-moulded speeimens are relatively stress fiee. 

Injection moulding Processing cost high in comparison to amorphous materials. Mould cooling critical. Warpage and dimensional tolerances difficult. 

Injection moulded articles represent only a small proportion (5%) of the consumption of LDPE and LLDPE. This proportion is not insignificant, however, considering the total volume of 300,000 tonnes per year. LDPE and LLDPE parts produced by injection moulding are used in a wide range of applications, for example, for domestic storage containers and closures in cosmetic, food, and pharmaceutical applications. High environmental stress crack resistance and low warpage are required for LLDPE applications. 

Liquid crystal polymer materials offer many advantages over conventional thermoplastics in injection moulding, including low mould shrinkage, minimum warpage and distortion, fast cycle time, ability to mould thin parts, low moisture absorption, and excellent chemical resistance. The mechanical properties are comparable to those of materials filled with short glass fibres. 

The warpage simulation with in-mould constraint effect in injection moulding , Yi-Hui Peng et al, Moldex3D paper. 

Certainly in the case of many co-injection techniques, differences in mould shrinkage and thermal expansion can lead to problems such as sink marks, warpage and residual stresses. With over-moulding techniques, differences in shrinkage or the coefficient of linear thermal expansion (CLTE) can produce high stresses between restrained materials. The result in both cases can be the same, premature failure. 

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