5 most important design guides for injection molding plastic parts

5 most important design guides for injection molding plastic parts


Injection molding is used to produce plastic parts in small and large volume series. In contrary to rapid prototyping, injection molding manufacturing requires  the manufacturing of a mold or a tool, which is a time consuming process and usually made of expensive steel. It requires a up front high investment in this tooling. It is thus important to avoid mistakes in the beginning and during the toolmaking process and thus a perfect designed plastic parts it of utter importance.

That Is why we describe hereunder the top 5 most important design rules or guides.

the 5 design rules:

1 Applying a Draft All vertical walls oriented normal to the direction of mold pull will need to have draft ideally at 1 degree minimum.

When you use texturised walls the draft has to be at least 3 degrees.


This is all necessary to pull the part out of the mold core. Otherwise part sticks to the core and it Is difficult to release the product.


2 Uniform Wall Thickness


Injection molding is all about flow of molten thermoplastic material, so the flow in the mold must be as smooth as possible to create uniform cooled products.  The best way to design your part is to design uniform wall thicknesses.
3 Shrinkage and Warpage Considerations


Thick sections Should be hollowed out


4 Watch The Sharp Corners


Round edges ; The edges and corners should be round and even. The final product should be as smooth as possible. The radius for interior edges should be at least 0.5 multiplied by the wall thickness. Whereas for exterior edges, the radius should be equal to the sum of the radius and wall thickness of the interior edges.


Use radii when possible and avoid sharp transitions between wall sections.



5 Positionize the partling at a strategical surface The parting line is a physical line that  will appear where the two halves of a mold meet. In many cases, parting lines can be easily seen and felt, but it’s more than an aesthetic issue. The placement of the parting line dictates how the mold opens (and therefore the direction in which you need to add draft to the part’s features), and it can influence both the cost of mold tooling and any required post-processing.

You can often improve a part’s appearance and functionality by placing the parting long along an edge rather than on a flat surface. This helps to hide the seam and also reduces the chances of flash (excessive material around where the mold comes together).