What is the cause of weld marks in TPE injection molding?

Mondo Technology Updated on 2024-02-05

In the process of injection molding, TPE products will sometimes inevitably cause welding marks due to various reasons, when this situation occurs, it will undoubtedly cause inconvenience to our use, thereby affecting the molding quality of TPE products. So do you know what happens when there are weld marks in TPE injection molding? Here's what you know:

Weld mark phenomenon of TPE injection molding:

Weld mark refers to the fact that in the injection product with holes or the product with multi-point feeding, the melt cannot be completely fused when converging in the mold cavity and forms a linear groove at the confluence. When the molten material is converging in multiple streams in the cavity due to the incoherent flow rate and the interruption of the mold-filling material flow, the main reason for the fusion joint is that it cannot be completely fused. In addition, if the melt is sprayed at the gate, a weld will also be formed, and the strength of the entire product will be reduced due to the low strength of the weld.

Causes and treatment measures of weld marks in TPE injection molding:

Reason 1: The material has poor fluidity, the flow rate is too slow, and the temperature of the material flow front is low, so that several strands of material flow cannot be fully fused when converging and weld marks are generated.

Treatment: Choose a material with good fluidity or add lubricant to increase the flowability and ensure that it can be fully integrated.

Reason 2: Poor mold exhaust, so that the mold cavity pressure is too large, and the material flow is not smooth.

Treatment measures: reduce the clamping force appropriately or re-determine the gate position, but before that, check whether there is a foreign object blocking the vent hole; The venting system or the overflow groove at the weld joint can be used to make the exhaust good and the weld joint can be separated from the workpiece.

Reason 3: The cold material blocks the flow of the melt.

Treatment measures: increase the size of the cold material well.

Reason 4: The design of the mold gating system is unreasonable, the gate position is not properly designed or there are too many gates, the process is too long, and the forward material flow can not be fully integrated.

Treatment measures: shorten the process and reduce the temperature difference of the material flow; If the gate is too small and the runner resistance is too large, the gate size should be increased.

Reason 5: The melting temperature is too low, the mold temperature is too low, the injection pressure is too low, and the injection speed is too slow, which will reduce the temperature of the material flow forward and accelerate it, and it cannot be fully integrated.

Treatment: Increase the values of these process parameters appropriately.

Reason 6: Excessive condensation and lubricant on the surface of the mold near the seam surface, and the melt can not be well integrated.

Treatment measures: Thoroughly clean the mold surface to avoid excessive lubrication of particles and mold surface.

Reason 7: The structural design of the product is unreasonable, if the product is too thin or the thickness difference is too large or there are too many inserts, it will cause poor welding.

Treatment measures: When designing products, it should be ensured that the thinnest part of the product is greater than the minimum allowable wall thickness during molding, and the wall thickness should be consistent as much as possible to reduce the use of inserts.

To sum up, this is the cause of the phenomenon of weld marks in TPE injection molding and the treatment measures. When it is impossible to avoid the generation of weld marks from the process and mold, you can attach an "adjustment piece" to the weld mark when designing the TPE product, so that the weld mark appears on the adjustment sheet, and then cut it off.

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