5 Tips Before

You Start Designing

For Plastic Injection Molding

Plastic Injection Molding is probably one of the most versatile and readily accessible processes that you can utilize to manufacture your products. However, due to it being such a flexible solution, it does sometimes occur that important design aspects and considerations get foolishly overlooked. Here are some tips to avoid this from happening to you.


Simply put, if you have a good grasp on the plastic injection molding process and suitable qualities your chances of running a successfully finished product in the future are realistic.


It is recommended that you take just a few minutes to familiarize yourself with some principles of design which you wish to incorporate into your plastic injection mold design.


Here are some plastic injection molding design tips to guide you in the right direction.


1. The Injection Molding Process

The mold consists of two halves that are hollowed out as a negative image of the part you want to manufacture. Hot, melted plastic or rubber passes through the gate and gets injected into the mold (part) after which it is allowed to cool down. Once cooled, the two halves of the mold release and the part is revealed and removed.


Highlighting the process


There is a small opening in the mold itself that allows the melted plastic to be injected, known as the gate. Once the part has cooled down, it needs to be removed either automatically or manually from the completed part. The position of the gate is important in injection mold designing — it’s well known in the industry that you would ideally locate the gate at a thicker, intersectional area of the part where it can be removed hassle free without interfering with the structural integrity of your new part.


Removing the gate will likely leave a scar on your part, which should be taken into consideration as it will affect the appearance of the part.


During the cooling process


When the liquefied plastic or rubber material cools and solidifies, shrinkage will occur. Remember, this has to be taken into consideration not only when determining part dimensions but also when adding design elements such as radiuses to corners and decisions on wall thickness.

During the part release


As the two halves of the part separate to release the molded part you will notice a line that runs through the part. This line is known as the “parting line” and is a normal occurrence as the mold is made out of two halves. It is advised that you design your part to plan for the parting line location.


2. Considering Wall Thickness


Some plastic injection molding shops will tell you that they can only produce injection mold parts with a uniform wall thickness. Although this will make it more convenient to manufacture your parts, it is not essential to the process. However, different wall thicknesses can make for a more complicated process; this is a result of the cooling process mentioned above.


Areas, where the wall is thicker, will cool down and solidify slower than thinner areas. Now consider the shrinkage during the cooling down process, this is a direct result of poorly designed molds and products that can lead to hot, liquid resin or moisture shifting to areas of the part where it is not meant to be.


Don’t be alarmed


You can manage this potential problem by designing your part with manufacturability in mind; it’s a matter of thinking practically. Thicker areas can, for example, be located at lower portions of a mold, allowing gravity to help keep still-cooling material where it belongs.


3. Incorporate Draft


The taper is a good way of allowing finished parts to leave the walls of the mold much more smoothly with very little friction and can be added to your part depending on the material and the product design. The parts surface remains unscathed, and the process becomes much more efficient.


4. Etch or Mill in Texture

Instead of adding a second finishing process after injection molding to create texture on your product, you can incorporate the desired finish, pattern or texture right into the mold. Etching or milling your mold to create a finish gives you a greater degree of control and also uniformity over the look and feel of your part. This saves not only time but also money by incorporating two processes into one.


5. Get to Know Your Materials


This tip covers everything we’ve already covered above, but it’s important to take note of the following:
Material selection is one of the most critical considerations in designing your part. It factors into many aspects of the process, including the shrinkage factor, cooling time, flexibility and more. Various materials differ in wall thickness or require different degrees of a draft.


Should you seriously be considering an Injection Mold Company in China, it would be wise to have a contract in place before production starts to ensure that your interests are protected.


This article merely touches on what you need to know before you get your plastic injection mold project started, but it can get more complicated as you go along. The best tip we can give you though, is to use common sense.


If you have any questions you’d like to ask our qualified consultants please feel free to leave a comment below and we’ll get back to you.