Injection Moulding Design

Your masterclass in product design and development

Protolabs’ Insight video series

Our Insight video series will help you master digital manufacturing.

Every Friday we’ll post a new video – each one giving you a deeper Insight into how to design better parts. We’ll cover specific topics such as choosing the right 3D printing material, optimising your design for CNC machining, surface finishes for moulded parts, and much more besides.

So join us and don’t miss out.


Insight: Injection Moulding Design



Hi and welcome to this week’s insight video. Having done several of these videos, I thought it was about time that you met some of the experts here at Protolabs.  So, this week let me introduce you to Dom Corpuz, our Application Engineer.






You can probably guess that we are going to focus on injection moulding this week and get Dom to answer some questions and show you how you can design better parts.

Now we had a chat earlier and decided that if we tried to cover everything then we’d be here for hours, so let’s hone it down to some core elements and give you some pointers on where to find extra information for more complex features.

So, what are we going to talk about today Dom?



Thanks Natalie. When it comes to injection moulding, we always need to think about the actual manufacturing process.  It’s great for producing cost effective parts in high volumes, but some design features require a bit of thought to achieve what you want.

So today, using this design cube as an aid, I’m going to talk to you about wall thickness, coring out, ribs, the use of side action cams and undercuts. 



So, let’s start with wall thickness.  Why is it important?



Getting the wall thickness right will help manage the weight and strength of your part and it can also affect how it looks.  Now you might think that the thicker the better, but parts that are too thick can produce ugly sink, warp and internal voids.  If you look carefully, you can see an example of having too thick a wall here on the this cored out section.



So, what is the ideal wall thickness then Dom?



Well, that depends on what material you are using to manufacture your part from. You will find that each material has recommended wall thickness guidelines to help.  This is where you need to work with your chosen supplier.



Okay so it’s not a good idea to have walls that are too thick or too thin. Is there anything else that will help with the parts strength and integrity?



Absolutely.  If you are looking for structural integrity then your part should contain ribs, ramps and / or gussets. 

Ribs and gussets can help support structures but again if you make them too thick, they can cause sink on the other side of the part.  So, for example, instead of designing a boss with a wall that is too thick, you can strengthen them with gussets.

When it comes to designing support ribs, we generally recommend that it is between 40 to 60 percent of the thickness of adjacent surfaces.

And finally, a small ramp helps the molten plastic flow between levels because generally smooth transitions between geometries are best.



That brings us onto the use of side action cams.  First of all, what is a cam?  And second what would I use it for?



A cam is a pin actuated side action that moves with the mould. It’s like an automatic insert that enables us to produce parts that would not be possible using a simple straight pull mould.

They are normally used for producing undercuts but you can also use them to create the inside core of a tube like this.  It allows you to design more features for your part, but it does add to the cost.  At Protolabs we generally allow up to 4 cams in a design.

Another option is to add and remove manual inserts but as this involves an extra process, you’ll need to consider the cost of doing this.



Okay thanks for that Dom. We’ve been through your list to design parts that are easily manufactured using injection moulding, I’m guessing that there is far more that you could speak to us about and probably more complex features that could be included?



Absolutely Natalie.  I’ve only really covered some of the basics there.  There are other tricks of trade such as producing living hinges, the use of text, overmoulding, thinking about producing your product or part in parts and then assembling it separately. I really could go on for hours.



So, if I want to learn more about the does and don’ts where do I go for some more information?



It’s always worth talking to your supplier, but I realise that this is not always practical when you are sitting in front of your CAD.

I find that design aids such as this Design Cube plus this Torus help.  The design cube shows you what to do and also what not to do. 

The Torus shows you some more complex designs that are possible and some different approaches that you can take to get particular features.  Some of these options will cost you a bit more of course, but it helps to know what you can achieve.



That’s great thanks Dom. As you said we could go on, but I think we’d better stop there.  So, I’ll wish you all a great weekend and see you next week.



With special thanks to Natalie Constable.

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