What causes weld lines in injection molding?

What causes weld lines in injection molding?

Causes: Weld lines are caused by the inadequate bonding of two or more flow fronts when there is partial solidification of the molten plastic. Remedies: Raise the temperature of the mold or molten plastic.

How do you fix weld lines in injection molding?

Remedies

1. Moving: Change the gate positions. Change the part thickness.
2. Improving the quality: Increase melt and mold temperature. This will allow the flow fronts to interfuse more. Increase ram speed. Optimize runner system design.

What are the cause of weak weld lines?

The main reason for weld-line weakness is a lack of polymer chain entanglement across the junction of the two flow fronts. A major contributing factor is air entrapped at this junction; the flow-fronts do not actually meet due to gas trapped between the fronts.

What is a weld line in plastic?

WHAT IS THE WELD LINE? When two or more plastic streams meet at different temperatures as the plastic is filling the mold cavity, the two streams may not correctly mix together. When this happens, it forms a weld line.

How can welding defects be prevented?

Remedies:

1. Preheat the metal as required.
2. Provide proper cooling of the weld area.
3. Use proper joint design.
4. Remove impurities.
5. Use appropriate metal.
6. Make sure to weld a sufficient sectional area.
7. Use proper welding speed and amperage current.
8. To prevent crater cracks make sure that the crater is properly filled.

What are the defects in plastics?

Common Defects

• Blister. A blister is a raised area on the plastic surface, very similar to the medical condition of the same name.
• Burn Marks. Burn marks are generally caused by problems similar to blistering.
• Burrs.
• Embedded contaminates.
• Flow marks.
• Lamination.
• Sink marks.
• Short mold.

What are welding lines called?

In manufacturing, the Weld line or Knit line or Meld line is the line where two flow fronts meet when there is the inability of two or more flow fronts to “knit” together, or “weld”, during the molding process. These lines usually occur around holes or obstructions and cause locally weak areas in the molded part.

What causes voids in injection molding?

Voids. A void occurs during cooling while the part is inside or outside the mold, usually in thick sections. In thick sections of a part, the center cools slowly and the polymer shrinks more, pulling away from itself to form a bubble.

Where do weld lines occur in a plastic part?

Weld lines occur in plastic injection molded parts in the area or plane where two or more streams of material fuse together as the mold cavity fills with material. It is well know that weld lines create weak areas in molded parts.

What are the common weld defects?

What are common weld defects?

• Lack Of Penetration or Incomplete Penetration.
• Lack Of Fusion or Incomplete Fusion.
• Undercut.
• Spatter.
• Slag Inclusions.
• Cracks.
• Porosity.
• Overlap.

What are the types of welding defects?

Following are the types of welding defects:

• Porosity and Blowholes.
• Undercut.
• Weld crack.
• Incomplete fusion.
• Slag inclusion.
• Incomplete penetration.
• Spatter.
• Distortion.

What are molding defects?

Molding defects often caused by process problems

• Flow lines. Flow lines appear as a wavy pattern often of a slightly different color than the surrounding area and generally on narrower sections of the molded component.
• Burn marks.
• Warping.
• Vacuum voids / air pockets.
• Sink marks.
• Weld lines.
• Jetting.

Why do weld lines form in injection molding?

Weld or knit lines are perhaps the most common and difficult injection molding defect to eliminate. Weld lines occur when part or tool design features—like holes or ribs—split the melt flow and the separate flows do not meld completely when they meet.

What do you need to know about injection molding defects?

11 Injection Molding Defects and How to Prevent Them 1 Flow lines. Flow lines appear as a wavy pattern often of a slightly different color than… 2 Burn marks. Burn marks typically appear as black or rust-colored discoloration on an edge… 3 Warping. Warping is deformation that can occur in injection molded products when different parts…

How to prevent flow lines in injection molding?

Here are some common remedies for flow lines in injection-molded products: Increase the injection speed, pressure and material temperature to ensure the material fills the mold before cooling Round the corners of the mold where wall thickness increases to help keep flow rate consistent and prevent flow lines

What causes hair like line in injection molding?

The hair-like weld line is the result of weak material bonding, which lowers the strength of the part. Two or more fronts of polymer or other molten material need to maintain a certain temperature when colliding.

https://www.youtube.com/watch?v=iOV-K73qE-8