Injection Molding Design Tips for Plastic Medical Part (1)

Whenever you begin a design project involving plastic medical injection molding, your goal is to have the component injection molded, you must consider many things that will save time and money during the production phase of your injection molding project. At the beginning, this foresight will help you to understand the limitations and challenges faced of the plastic medical injection molding product.

Next, we will show you 10 considerations are by no means exhaustive, but they will bring you very close to where you need it and guide you in the right direction. Details are as follows:

1. Consider the Parting Line

Try to imagine your plastic medical part is being molded. Visualizing the empty cavity space that the liquid plastic will fill to mold into a plastic component. Inevitably, when cavity space is filled, your medical part will have to be ejected from it. To make that happen, the two mould halves must to separate, leaving behind your plastic injected component in one side of the mold (preferably the side where you plan on ejecting from). You need to visualize and plan for where this "parting line" will be to ensure that your plastic medical part does not get trapped in the mould.

2. Uniform Wall Thickness

Try and make the wall thickness of your plastic part. Uneven wall thickness increases the possibility of sink marks, warpage, voids, molded-in stress, longer cooling times, and even material flow restrictions. If wall thickness must be uneven, you should better let it have a smooth transition. The minimum wall thickness allowed for your plastic injected component depends on the size of the part and the material. 

3. Avoid Undercuts

It is not very difficult to mold your plastic part when undercutting on your component, what’s more difficult is to demold it. The undercut portion of the plastic component will get trapped inside the plastic medical mould once the part is cooled and hardened, the portion must depend on other mold actions to eject from the mold. Many times, undercuts are a necessity for part function. Side actions and lifting mechanisms will have to be introduced to your tool to deal with the ejection problems of your medical part. This is unavoidable in sometimes, but if you want save the cost on tooling, trying to redesign to eliminate necessary tooling costs is worth. 

4. Consider Shrinkage and Warpage 

All materials shrink at different rates and varying degrees when do the cooling process of your medical injection molding operation. Shrinkage occurs where there is a difference between corresponding linear dimension of the plastic mould and the molded component. Warpage is a dimensional distortion in a molded plastic caused by excessive residual stress in the part. Material considerations, part geometry considerations, tooling considerations, and processing considerations all play a part.

5. Watch the Sharp Corners

Avoiding sharp corners as much as possible. These will result in weak points and then lead to part failure and cracking. Adding radii to sharp corners can reduce the molded-in stress. Radii redistributes the stress more evenly and facilitates the flow of the material and ejection from the plastic medical mold. Stresses rapidly amplify when inside corner id less than 25% of the nominal wall thickness of the component.

These are the 5 detail points of plastic medical mould production, the rest of which you can see in another article: Injection Molding Design Tips for Plastic Medical Part(2). As a professional China plastic medical mould manufacturer, we will try our best to provide you with any solution you need.