The reason of Weld lines in SMC molding process and solution

What is the reason for the occurrence of weld lines in SMC molding process

The weld seam line issue does indeed have a significant impact on product quality You pay attention to the detail of the weld seam line, which indicates that you have a good control over the process stability during the production process. This is a common difficulty in SMC molding process, mainly related to material flow and welding.

Material factors

Resin content: Low resin content can lead to insufficient welding strength and the formation of obvious welds.

Fiber length/distribution: Long fibers or uneven distribution can hinder melt flow and cause poor fusion.

Thickener compatibility: Thickening too quickly can cause the melt to solidify prematurely before merging.

Mold Design

Gate position/quantity: When multiple gate melts converge, uneven pressure can easily cause cold joints.

Flow channel structure: Narrow flow channels or excessive corners can cause a decrease in melt temperature and a deterioration in the welding effect.

Exhaust system: Poor exhaust can cause gas to accumulate at the welding surface, forming bubbles or weak welds.

process parameters

Molding temperature: If the temperature is too low, it will reduce the fluidity of the melt, resulting in insufficient fusion; If it is too high, it may cause the resin to solidify prematurely.

Closing speed/pressure: If the closing speed is too slow or the pressure is insufficient, it cannot push the melt to fully melt.

Holding time: Insufficient holding time can cause cooling shrinkage of the fusion surface, resulting in the formation of gaps.

Operating Specifications

Mass weight/placement: Insufficient mass weight or placement off center can cause uneven flow of the melt.

Preheating time: Insufficient preheating of the sheet will reduce its initial flowability and affect the quality of welding. 

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