Freesteel Blog » Intelligent machining algorithms

Intelligent machining algorithms

Wednesday, January 11th, 2006 at 11:52 pm Written by:

The first thing to note is there’s a huge amount of literature on all this stuff which we should be browsing through. I found an article yesterday in the University Library that was relevant. Unfortunately, the authors published it in The Journal of Manufacturing Systems (Vol 23 #3), so I can’t make a link for you because this — one would assume — publically funded research is password protected. There are other interesting journals hosted on the same site which might occasionally have relevant articles, but which the academic establishment has seen fit not to let the public have access to for reasons I’m not going to explain right now.

Anyway, here is the simple idea.

You separate the intelligent planning operation from the dumb manufacturing operation, and make the manufacturing operation reliable enough so that it is unable to do any damage no matter what it gets from the planner.

The result is the task can safely be separated into these two components, and you can buy the manufacturing operation from somewhere, and take risks with the planning operation because its results are not critical.

This is a very general pattern. Consider a team of postmen. The manufacturing operation is executed by the postman. He sets off with a sorted bag of mail. He takes the top letter out of his bag, walks to the address written on the front and delivers it. Repeat until bag is empty, then go home.

Clearly, we the mail gets delivered even if the planning operation is very stupid and fills the postmen’s bags at random at the start of the day. It might take all day, with postmen going all over town and crossing each other’s as well as their own paths, but the right end result would be reached.

A first level of planning operation would take all the mail in a postman’s bag and very cleverly sort it so that his rounds would take the shortest route. This is the infamous Travelling Salesman Problem.

The second level of planning would be to give each postman an optimal set of mail with regards to the route he would follow with such a set of post. This optimal answer is uncomputable, so we shouldn’t worry about finding it out.

Ultimately, with regards to the planning operation, there is no right or wrong answer. All plans work, but some work better than others. Since the post office has to solve the same problem each morning, they work to a template. They assign each postman a route, and all the routes together cover the city. Now for each letter they know exactly which bag it belongs in and what order. The postmen still work to the algorithm outlined above, and take shortcuts on their route if they have a short load.

This pattern, of functional division between a planning and manufacturing modules, is not completely general. For example, the operation of an assembly line cannot be separated in this way. It matters which order you lay down the parts as to whether you get the right result.

I don’t happen to know the technical term for this observation, because it’s just an idea which anyone can make up. However, I am sure that CNC machining fits into the pattern if you have the right machining operation.

If you don’t mind how many layers of paint may get applied to the same place, the job of spray-painting an object until it is covered fits this paradigm. You keep doing it from different angles until all the surfaces are coated.

If your machining operation is roughing, then this limitation does not apply. There is no physical effect of machining air. However, classic finishing routines which assume a limited level of stock on the model don’t fit this scheme.

A machining strategy, such as a variant of the Adaptive Roughing generalized to work in different planes in five axis, would be suitable. Once the basic algorithm is complete, and it can rest-rough against any set of previous toolpaths without gouging, over-loading the tool, or colliding the tool holder, the planning operation becomes simple and non-critical. Every plan that it comes up with would work, even stupid ones. Obviously, it doesn’t have to be very complicated to automatically choose directions where walls are aligned. And if you have parts that are similar to one another, you can work to a template. If you don’t know which template fits the best, run the algorithm on all of them and pick the best.

This is all some way off, but it was good to see the idea demonstrated on a few parts in that academic paper I couldn’t give you a link to. There may be other ideas for automating the machining process, but this one is one I can separate into stages which I know all can work. It also gets across the idea that Adaptive Roughing might ultimately be a piece of a larger puzzle. It just has to be available to be used.

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