Machined Castings 1

[drawoh]

I am reviewing several packages of casting drawings that may or may not have been done in SolidWorks. I have just got my hands on some DFMA communication, and now I know which features in my part were machined after casting. I have a new job and my understanding is that I am the in-house expert on mechanical[ ]DFMA.

If I were designing a casting in Solidworks, I would model and document the casting. I would then attach the casting model to an assembly, and I would model and document the machining, at the assembly level. I can now see what features are cast, and what features are machined in. I have the option of copying the machining drawing and created a new part based on the unmodified original casting.

What do people think of this? How do you manage castings? Can you make a good argument for doing this some other way?

--
JHG

 

[moon161]

Assembly features is one option, and a pretty easy way to do it.
WHere I work now, we use two configurations of a part- as cast and as machined. The machined features are surpressed in the as-cast configuation.

Another possibility is a derived part. You start an empty part, then insert | part | select, and use move/copy bodies to locate it.

 

[TheTick]

Castings can be modeled fnished-to-raw, or raw-to-finished. Either is fine, as long as the information is correct.

Nearly all casting operations are material removal. From a manufacturing perspective, it make sense to model accordingly, raw-to-finished.

From the design side, function matters most, so finished-to-raw makes more sense (though is more difficult to manage in nearly every respect).

What does not make sense is to micromanage the manufacturing process from within the design environment. A vendor or manufacturing department should be able to work from the pair of raw and finished models (plus drawings and specs) and create their own process from there.

My preference is to model raw casting, then finish in a separate PART (not assembly), beginning with an insert part feature. Capabilities of assembly features are too limited.

Also, don't lean on the design department and CAD system to solve problems that really need to be solved in the MRP system. Those guys also have a job to do. Make sure they do it.

 

[Jboggs]

We don't do any castings where I work but we do LOTS of machined weldments. Our methods might be useful in castings.

I was taught to model the weldment as a multi-body (non-merged) part in the as-welded state. When you declare a part to be a "Weldment" in Solidworks it automatically creates "As Welded" and "As Machined" configurations. It changes the the Solid Bodies feature to a Cut List (and keeps track of the counts of various identical parts). It also sets the default Boss Extrude mode to non-merged so that any new features automatically become separate rather than merged bodies.

Then as you go through the "machining" process of adding various Cut Extrudes, drilled and tapped holes, etc. you have to make sure that those features are suppressed in the As Welded configuration. We have found it very helpful to also assign a certain color (we use a deep bright brown) to all machining features as they are created. This makes it very easy to identify them in the model.

Then in the drawing its easy to start with the As Welded configuration and fully define it and all its sub-components. Cut List creation is automatic. Then on a separate sheet you can show the various machining steps, any geometric tolerances, hole callouts, etc.

The biggest challenge for us was in learning the details of working with a multi-body part, and there are several.

Its all still one single part, not an assembly.

 

[Gupta65]

I used to make casted parts for pumps and we followed raw to finish. There were 2 methods which were used; one was separate files (for finished ones, we would insert the raw into new file and create the finished one) and second method was configuration. So you can opt for either method depending on your preferences.

Deepak Gupta
SOLIDWORKS Champion and Expert
SW 2022 SP0.0, 2021 SP5.1 and 2020 SP5.0
Boxer's SOLIDWORKS Blog

 

[drawoh]

What does not make sense is to micromanage the manufacturing process...

I am looking at drawings of permanent mouldings showing remarkably accurate tolerances. Definitely, there is clean-up machining. Definitely, precise tolerances are being met, some of them by casting, by the looks of it. There is minimal indication on the drawings how these tolerances will be met. They have been having problems with this part, mostly solved by the time I arrived.

I am looking at this from a management point of view. What is going to happen next time, and what are the red flags I need to see? We are in between the designers and the fabricators. I have a new job, and my role seems to be to provide guidance to our customers.

I firmly believe in not telling fabricators how to do their jobs. On the other hand, if I am looking at a casting drawing, I need to know what is cast and what is machined.

--
JHG