What are the defects in injection molding?
Top-10 Injection Molding Defects And How To Fix Them
- Flow Lines.
- Sink Marks.
- Vacuum Voids.
- Surface Delamination.
- Weld Lines.
- Short Shots.
- Warping.
- Burn Marks.
What are the common defects in injection molding products and why?
Insufficient injection-molding machine performance (shot capacity, plasticizing capacity, etc.) Gate cross-section surface area is too small. Molded product thickness is too thin. Poor gas venting.
What are molding defects?
Technical Information｜Molding Defects and Countermeasures
- 1) Insufficient resin amount.
- 2) Insufficient injection pressure.
- 3) Low filling speed.
- 4) Low resin temperature.
- 5) Insufficient release of air from the mold.
- 6) Too small runner or gate diameter.
- 7) Long runner.
- 8) Thin wall thickness of the molded product.
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 causes voids in injection molding?
Voids form when the outside layer of the part cools faster than the inner layer of the part. This causes the inner layer of the part to basically pull-apart causing the void to form. While good part design dictates having a uniform wall thickness, sometimes thicker walls cannot be avoided.
What causes shrinkage in injection Moulding?
What causes shrinkage in injection moulding? Volumetric shrinkage is caused by thermal contraction, which affects all polymers (semi-crystalline and amorphous), and influences how the material changes in volume as it transitions from a liquid to a solid.
What causes cold slug in injection molding?
Cold slugs – A small non-uniform area on the part caused by an improperly heated piece of plastic becoming attached to the part. Flow marks – A wavy pattern or discoloration caused by a slow injection speed which allows the material to cool too quickly.
What causes high gates in injection molding?
Injection fill speed is too high. The speed at which resin enters the mold has a big impact on finished parts. If the mold is filled too quickly, the molten plastic will react to the flow restriction at the gate.
How do you fix voids in injection molding?
To solve voids or sinks, try slow fill rates, use of gas counterpressure, or increasing backpressure. Ensure the runner or gate is not freezing too early and that longer hold times will allow more packing during the second stage.
What causes splay in injection molding?
Splay is caused by tiny gas bubbles that are dragged across the surface of the part when the mold cavity is filled. Splay is usually caused by water that is absorbed within the plastic granules. As the mold fills, the steam migrates to the surface of molded part. It is these steam bubbles that you see as Splay.
What is the main reason of voids?
There are several factors that can come into play when voids are discovered and they can be caused by either machine (process), mold, or material issues. The most common cause of voids would be the process and there are some adjustments you can make to better fill the part out and reduce your risk of void defects.
How do you prevent shrinkage in injection molding?
Decreasing shrinkage – If you desire a decreased shrink rate, add cooling time in the injection mold, lower the mold surface temperature, decrease component wall thickness, decrease the resin melt temperature during injection, increase resin injection speed, and increase packing density or holding pressure.