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
- Moving: Change the gate positions. Change the part thickness.
- 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 causes 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 are the possible defects that can be observed in injection molding and what are their causes mention four defects causes?
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.
How can welding defects be prevented?
Remedies:
- Preheat the metal as required.
- Provide proper cooling of the weld area.
- Use proper joint design.
- Remove impurities.
- Use appropriate metal.
- Make sure to weld a sufficient sectional area.
- Use proper welding speed and amperage current.
- To prevent crater cracks make sure that the crater is properly filled.
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.
How do you prevent knit lines in injection molding?
How to Prevent Knit Lines
- Increase material temperature: Higher temperatures on both materials prevent one section from cooling too quickly.
- Increase injection speed and pressure: Faster-moving materials will meet more quickly so one doesn’t cool too soon.
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.
What is mold material defects?
Description: Flow lines are lines, streaks, or patterns that show up on the prototype, caused by the molten plastic passing through the mold or gate. Causes: These defects are caused by the varying speeds of the molten plastic as it changes direction through the contours and bends in the mold.
What are sink marks?
Sink marks appear as depressions on the surface of a molded part. These depressions are typically very small; however they are often quite visible, because they reflect light in different directions to the part.
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.
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
