Warpage in Compression Moulding SMC and DMC: Understanding the Causes and Solutions

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Compression moulding is a widely-used manufacturing process for various materials, including Sheet Molding Compound (SMC) and Dough Molding Compound (DMC). SMC and DMC are composite materials made up of resins, fiberglass reinforcement, and fillers. Compression moulding is known for its ability to produce intricate and detailed parts with high precision and consistent quality. It is widely used in industries such as automotive, aerospace, electronics, and consumer goods to produce a wide range of components, including seals, gaskets, automotive parts, and electrical housings. This process allows for efficient mass production of parts with excellent structural integrity and dimensional accuracy.

Definition of warpage in compression moulding

Warpage is a common challenge encountered in the compression moulding process of Sheet Molding Compound (SMC) and Dough Molding Compound (DMC) products. It refers to the distortion or deformation of a part from its intended shape during or after the moulding process. Warpage adversely affects the product's quality and functionality, leading to deviations from the desired dimensions.

Causes of Warpage in Compression Moulding:

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A. Non-uniform Material Distribution:

An uneven distribution of the SMC or DMC material during compression moulding can lead to variations in shrinkage and cure rates, resulting in warpage. This can occur due to improper material placement or inadequate compression force.

B. Cooling Inconsistencies:

Inadequate or non-uniform cooling of the part can cause differential shrinkage, leading to warpage. Rapid cooling or improper cooling techniques can result in varying rates of contraction across the part, causing it to deform.

C. Uneven Mould Temperature:

Fluctuations in mould temperature can cause variations in the cure process, leading to different degrees of material shrinkage. Variations in shrinkage rates can result in dimensional inconsistencies and warpage.

D. Residual Stresses:

During the compression moulding process, internal stresses can build up within the material as it cures and solidifies. The release of these internal stresses upon demoulding or during cooling can cause the part to warp.

E. Mould Design and Venting:

Inadequate venting or improper mould design can lead to trapping of air or gasses within the part during the curing process. This can create uneven pressure distribution and cause warpage.

Solutions for Warpage in Compression Moulding:

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Optimize Material Distribution and Compression:

Ensure uniform material placement within the mould to minimize variations in shrinkage and curing rates. Apply adequate and evenly distributed compression force to achieve consistent material consolidation and reduce warpage.

Stabilize Mould Temperature:

Maintain a stable and uniform mould temperature throughout the moulding process. Use heating or cooling mechanisms to control the temperature and reduce variations in material shrinkage rates, thereby minimizing warpage.

Address Residual Stresses:

Apply post-moulding processes like annealing or stress-relieving treatments to minimize and release residual stresses. These processes help reduce warpage by allowing the part to settle and stabilize.

Optimize Mould Design:

Ensure proper mould design considerations to reduce warpage-inducing factors. Optimize the gating and venting designs to minimize the chances of air or gas trapping, which can cause uneven pressure distribution and warpage.

Implement Mold Release Agents:

Apply suitable mold release agents to promote easy and uniform part demoulding. Proper use of release agents reduces the stress on the part during demoulding, mitigating warpage.

Validate Mold Temperature Uniformity:

Regularly check and validate the temperature uniformity within the mould using thermal analysis techniques or sensors. Make necessary adjustments to the heating or cooling systems to ensure consistent temperature distribution and minimize warpage.

Perform Iterative Process Optimization:

Conduct systematic trials and process optimization to identify and fine-tune parameters that affect warpage. Iteratively adjust material formulations, moulding conditions, and process parameters to minimize warpage and achieve optimal part quality.

Warpage Prevention Fixture:

A warpage prevention fixture is a specially designed tool or jig that helps control and reduce the warpage post-compression moulding process. It supports the moulded part shape and applies strategic forces or constraints to minimize distortion and achieve dimensional accuracy.


Warpage is a common occurrence in compression moulding of SMC and DMC products, resulting from causes such as non-uniform material distribution, cooling inconsistencies, uneven mould temperature, residual stresses, and inadequate venting. By implementing strategies like proper material placement, optimal cooling techniques, consistent mould temperature control, controlled release of residual stresses, and optimal mould design, manufacturers can mitigate warpage issues during the compression moulding process. This helps ensure the production of high-quality SMC and DMC parts with dimensional accuracy and minimal distortion, improving overall product performance and customer satisfaction.

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