torsdag 12 januari 2017

Injection Moulding and Thinking Ahead

Have a quick look at this picture. What do you see? If your answer is "an injection moulded front panel of some sort" your answer is correct. So why this image? Because it illustrates two things, one of which is very important, the other actually being a minor thing.

What this illustrates is the importance of thinking ahead when designing your components. This part wasn't originally done by me, it was done by a colleague of mine. He did an ok job with it, basically doing what he could to replicate an existing part. But he missed a couple of crucial things. This part is injection moulded, so draft angles are required. We normally go for 0,5 degrees on relatively short surfaces and wherever there is contact between parts of the tool we go for somewhere in the range of 3-5 degrees. The draft angles at the openings, which clearly need to be 3-5 degrees, were not done when I received the model. Also, we need to be as structured as possible when designing parts, striving to keep it so that it's easy to see in the model tree what has been done and avoiding using an excessive number of operations (e.g. let's say we have a number of screw bosses with reinforcement ribs and a few fillets, then we would make one screw boss complete with ribs and fillets and pattern it as a whole instead of making each boss as a separate entity). This model was not easy to understand.

As I was given the model to finish it up to send to the intended supplier for evaluation I found a couple of issues. Not only did it have a lot of operations which could have been avoided but as I tried adding the 5 degree draft angle at the openings, the software protested. The shape was simply too advanced for the software to accept. Catia will sometimes protest to things that seem very simple. The solution was to go back to where the cutouts were created and re-do the surfaces defining the cutout. Ok, fine, that gave me the required angle. But then the shell operation wouldn't agree. In the end, I redid almost the entire model.
This could have been avoided had my colleague simply thought of the required draft angle around the openings much sooner and strived to keep the model more structured. It's a mistake we all make at some point, forgetting about something specific to manufacturing or not keeping models structured, but it really shows the importance of thinking ahead when designing stuff.

What is that other thing that this image illustrates? The importance of having an easy-access tool for snapshots. I know Catia has one, I've used it many times, but I have not been able to find this kind of tool in Inventor. I found a way to create the image but it was by no means quick and it did not produce the image I actually wanted. I could of course have used the print screen option and then cropped the image to include only that which I wanted to show but that should not be needed now should it?
Of course, I could have missed something in which case you may feel free to educate me further.

torsdag 9 januari 2014

The rear suspension is getting somewhere

Last time the rear suspension was giving me headaches, it was very frustrating. Well, it turned out that some of that was due to constraints initially set between one of the control arms and the upright. What I did now was to make a skeleton for the suspension, i.e. I inserted a part into the product which defines the pivot points on the chassis. This way I managed to get a rough estimation of where the pivots should be. Which means it's now back to measuring the drawings and figuring out where the suspension should attach to the frame... I also need to examine the suspension and decide what kind of joint should be used where, it doesn't seem appropriate to use only ball-joints but maybe I'm missing something.

Pictures speak a thousand words, so here's what I have for you today: