I work on these things all the time and it seems to me I've seen non-cast ones but I can't actually say.. I'll have to look more carefully at the mechanical as usually I'm focused on the electrical. That said big castings have a lot going for them since these machines need to be insanely heavy to do their jobs. The bigger they are the stiffer they are and that's better for machining finish and accuracy. I can't see five tons of more processed plate being cheaper than lightly processed castings.
Generally, you would expect to see casting for most tooling structures: The cast shape is a "known" irregular, highly stressed FOUNDATION for all subsequent machining and assembly. A welded-together assembly will stretch, move, flex under welding, and carry unknown heat stress levels after each welding seam. The net is a more expensive total process - because even after welding, you still have to align the fabricated walls and fixtures and footings and sides together and machine all of the same surfaces already cast at one time in one single mass.
Consider even a hand tool like a drill: cast it in plastic because of the complex shape, rather than gluing together the different individual pieces. Clamp the final halves together mechanically.
Whilst machines like press brakes and shears are commonly made from plate , I have never seen Lathes, milling machines, or radial drills made of anything but castings.
B.E.
You are judged not by what you know, but by what you can do.
Yes, many modern machine tool structures are weldments. The main reason castings were used previously was due to cost. In order to get the necessary vibration damping, machine tools have historically needed a lot of mass in their structure, which was typically cheaper to accomplish with good ol gray iron than with steel. Improved analytical methods in recent decades have given us the ability to get the damping of a good heavy iron machine from lighter welded machines while casting prices have skyrocketed, and on top of that linear rails have become a low-cost alternative to machined ways. Linear rails allow a bit of adjustment to the ways, which allows the base weldment to be a bit less than ideal, often milled and not even surface ground much less scraped to a precision finish. I dont recall which of our VMCs are weldments but know several are, as is the Haas TL2 manual&cnc lathe I just finished using.
I've done machine shops since 16 or so. And been around many different makes. And have seen expensive ones ruined from dropping, castings cracked etc. Castings are more economical, if you have a large expensive over regulated industry to do it. Not so easy for a small operation that is why I'm asking. Personally I have not seen major parts made of weldments.
The Lincoln welder company used to publish a book about using weldments for machinery instead of castings, remember they have a vested interest in this.
B.E.
You are judged not by what you know, but by what you can do.
CWB1, from a machining standpoint, each has their advantages and disadvantages. That should not be a determining factor in choosing the best process/materials for a machine element.
It is better to have enough ideas for some of them to be wrong, than to be always right by having no ideas at all.
