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How To Design Plastic Molded Parts

Certain tasks in the plastic molding industry need to be left for the experts. This is what most newly employed design engineers in the industry will say to their supervisors when assigned a project to come up with complex plastic molded part designs. It is easy to think that way if you are new at the job, but do you just throw in the towel before even putting your hands on the job just for a trial?

Plastic Molded parts design

If you are the one who had given up in part design, I got you! We will walk together in this step-wise guide and learn how to come up with the best intricate plastic mold designs. Flow with me to the end and grasp all you can. Here’s the guide

First step: Maintain Wall thickness

The most basic rule to remember is always to maintain plastic part wall thickness at a uniform. Doing this will prevent you from many other manufacturing errors that rogue designers make. When your parts’ walls are uniform, you eliminate the risk of warping, and you’ll have the fill and fit properly because any potential contraction is minimized. It is recommended that wall thickness variations be less than 10% for plastics that can easily shrink. Higher variations pose a risk in the resulting quality of the plastic part. 

Step Two: maintain rounded edges

After ensuring that your walls are of uniform thickness, the same principle should apply for all corners and edges. The transition between the wall thickness and the edges should be unnoticeably smooth to keep the right flow of material. 

The radius of the interior edges should be half that of the wall thickness while the exterior edge radius is kept equal to that of the sum of the interior radius and the wall thickness. All this is to keep the entire wall thickness of the plastic part is uniform, and doing this will prevent any stress concentration.

Step Three: Make the thick parts hollow

Whenever the plastic past has a thick section, you are likely to have that part sunken or warped. To avoid warping and sinking, any thick parts should be limited to the standard values by keeping them hollow. However, even the hollow part tends to be weak and must, therefore, be reinforced with rib structures. The rib structures must be stiff and strong but of lesser wall thickness to that of the main plastic part. Using rib designs can help to keep the horizontal protrusions stiff, but the rib thickness must remain lesser than the wall thickness. 

Plastic Mold Design

Step Four: Craft the right draft angles

All vertical walls should have a draft angle to ease the process of ejecting the plastic part from the mold. Failure to put a draft angle on your vertical walls makes the part surface to be spotty during the ejection of the mold.

According to the plastic material suppliers and molders, the recommended draft angle is 2 degrees on the minimum. For parts with taller vertical features, draft angles of up to 50 degrees are allowed. From the engineers POV, the draft angle should be raised at the rate of one degree per 25mm. This is to mean if a feature (could be a rib) is 100mm tall, the draft angle should be increased by 4 degrees. We can call that our rule of thumb when it comes to crafting the right draft angle.

These are the four easy ways that will make you a pro in designing plastic molded parts. There is no need of letting your company or your employer outsource for design engineers to get the job done. With these simple-to-follow guide, you are good to go in making the best plastic molded parts.


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