The Importance of Uniform Wall Thickness in Injection Moulding

If you have ever taken apart a plastic part, you will have noticed that the wall thicknesses of these parts are uniform in size. Wall thickness determines the success or failure of a part to a large extent. It is one of the most important rules of injection moulding design. In this article, we will explain why uniform injection moulding thickness is important and the defects that can result if it is not uniform.

The importance of uniform wall thickness

1 Costs

Thicker walls require more plastic material to fill. They also require more time to cool. More material and longer injection moulding machine times will only increase production costs.

2 Shear stress

The shear stress of plastics in flow is affected by changes in wall thickness. The shear stress of a flowing plastic moving at a constant filling rate increases as the wall thickness decreases. Uneven wall thicknesses can therefore lead to varying degrees of shear stress. This is a major contributor to plastic warpage.

3 External appearance

Uneven wall thickness can affect the aesthetics of the injection moulded part. Defects such as warpage and shrink marks may occur due to uneven wall thickness. Surface issues such as flow lines may also be noted.

4 Cooling speed

Thicker parts take longer to cool. Parts with uneven wall thicknesses must remain in the mould until the whole part has cooled. This results in increased cycle times and the overall manufacturing process.

5 Gating challenges

Gating is done from thicker parts to thinner parts. Uneven wall thicknesses can cause molten plastic to flow from the thinner part to the thicker part. This can cause problems as the plastic material may start to cool in the thinner part, effectively preventing flow to the thicker part. This results in defects such as sinking and warping.

air filter injection molding machine DV-2100DS

Although injection moulding is one of the best methods of manufacturing parts, there are still a number of factors that can lead to defects in the final product. Due to the moulding process and the thickness of the plastic used, a variety of defects can occur, such as 'warpage' due to uneven shrinkage in different parts of the product, and 'shrinkage' when the plastic material does not cool completely in the mould.

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