DYLARK Resins vs. Polypropylene Warpage Study

Injection molded thermoplastic parts can lose dimensional stability and distort immediately after ejecting from the mold. Warpage is also a common occurrence in injection-molded parts caused by a multitude of variables, such as molding conditions, process variability, uneven cooling, gating and design. These variables result in residual stresses in the molded part that effect the warpage and shrinkage of the part. Generally, if shrinkage is uniform, the part does not distort or change its shape. Warpage typically results when shrinkage is non-uniform and stresses are created within the part. Depending on the part’s stiffness when this occurs, it may cause the part to distort or even fracture in the long term.

The part and mold designer can improve the dimensional stability of a product by considering some critical variables early in the development phase:

  • Material Selection
  • Part Design
  • Wall Thickness Variations
  • Gate & Runner Locations and Dimensions
  • Molding Conditions
  • Cooling Line Layout

Warpage ultimately leads to fit and finish issues in the assembly and performance of the automotive interior system. Assembly and performance problems increase costs by requiring an OEM to add more steel/plastic structures or require tooling modifications to correct the assembly. Therefore, choosing a material that provides excellent dimensional stability – such as DYLARK resin – improves the overall benefits from cost, performance and manufacturing standpoints.


The finite element model with a manifold system represents the model used in the PP warpage study.

NOVA Chemicals’ DYLARK engineers conducted a warpage study to demonstrate the dimensional performance of DYLARK resins compared to various Polypropylene (PP) material grades. The study was conducted on a typical instrument panel with eight drops using Moldflow MPI 4.1 software with the following assumptions:

  • Uniform Wall Thickness (2.5 mm)
  • Uniform Cooling Temperature (No Cooling Lines)
  • Cooling Time 20 Seconds
  • Overall Cycle Time of 60 Seconds
  • No Constraints
  • Flow and Warp Only

The following matrix illustrates the increase in the maximum deflection (%) seen in the various grades of PP relative to DYLARK 480P

Based on the results of the study, DYLARK resins exhibit excellent dimensional stability. The performance of DYLARK 480P16 reduced injection-molding problems and overall costs for automotive interior fit and finish issues in the interior instrument panel assembly.

In a recent study with an automotive OEM, a floor console design utilizing a glass-filled polypropylene substrate and an ABS outer panel was replaced with a DYLARK substrate and polypropylene outer panel. The DYLARK substrate provided the stiffness and dimensional characteristics required to reduce the cost and improve the quality of the overall console system.

Additional benefits of DYLARK resins include processing ease and excellent long-term property retention – essential characteristics for materials used in safety-related products like instrument panels. DYLARK resins are also utilized in other automotive interior applications, including consoles and interior trim components, because of these same performance characteristics.

DYLARK resins continue to be a preferred material for automotive instrument panel substrates for more than 20 years. The unique combination of stiffness, impact consistency, chemical resistance, urethane foam adhesion, thermal stability and low cost make DYLARK resins the choice substrate for more than two-thirds of the soft instrument panels (IP’s) produced in North America. More than 90 million vehicles on the road today contain DYLARK IP’s.

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