Machining center with onboard CMM

[geesamand]

Hello everyone,

My company has no machining centers, only a single CMM. Part of our business is refurbishing used machines. This involves CMM measuring the critical used pieces, sending out to perform any machining repairs (usually sleeving and remachining damaged bore features), and bringing the pieces back in for a CMM inspection to verify the repair. All of this is well and good, however it has inefficiencies and can be difficult to balance against support for building new standard machines.

I know that many modern machining centers have built-in CMM ability. I don't need a 3 micron CMM for this kind of work; even a 10 micron CMM would probably work. So it would be interesting for us if there was a large table machine that would permit us to do both inspection and machining repairs on the same platform. Our largest workpiece might be 100" deep x 80" x 80", but an average workpiece fits within a 30x30x30 box. The machining would not be heavy-duty stuff, it would be precision boring within cast iron and low carbon steel, and we can afford to go slow if that helps. So this machine would be used for CMM inspection only, or repair followed by CMM confirmation of the repair.

I know CMM brands and product lines but not machining centers. Is there machinery that supports the kind of dual-purpose work I'm describing? Does the CMM portion of the machining center work like a regular CMM? What brands or machines might make sense for this type of activity?

Thanks,

David

 

[MikeHalloran]

While it would be nice to have some measuring capability on a machining center for checking purposes, I can't see the logic of tying up a fast automated machine to use part of it for the slow, agonizing, aggravating CMM process.



Mike Halloran
Pembroke Pines, FL, USA

 

[geesamand]

I could swear I've seen onboard inspection on milling machines, similar to the way gear grinders can self-inspect. If I'm mistaken, that kind of ends this search.

The type of machining center used to repair these components is not a high output CNC. Our repair work is always uniquely per piece. We repair rather than replace because we the parts are decades old and new pieces are not practical. Most of the cost is setup.

One thing surprises me - I'm skimming over the specs for horizontal machining centers and I see no mention of accuracy. While it's obvious that the accuracy of a part is highly variable and not as easy to boil down like the x/y/z probing uncertainty of a CMM, how would I begin to compare the accuracy of various machines?

 

[BrianE22]

You can put a probe into the spindle and measure some part feature dimensions. For instance, say you bored a hole in a part. You could then load the probe and have the mill slowly move it across the bore diameter. When the probe makes contact with the edge of the bore the mill can see where the x or y position of the machine is at and compare that to acceptable limits. If it's outside the limits the machine can halt or ring a bell or something. See "machine tool probes" at

http://www.renishaw.com.

Statically, CNC mills can get to where they are supposed to be within maybe .0001/.0002 inches. Dynamically it's a different story - way too many force variations to be able to pin down a dynamic accuracy. As the saying goes, you get what you pay for. The expensive machines will do better dynamically.

 

[MikeHalloran]

One way to estimate the _likely_ _relative_ accuracy of multiple machine tools is to compare the shipping weight.

In machine tools, heavy is good.



Mike Halloran
Pembroke Pines, FL, USA

 

[CastMetal]

Get what you pay for will always be true, but for 10 micron even the "budget" brands with the right options would be acceptable. Certain Haas machines come with a finer pitch ball screw that is listed as accurate to .0002" / 5 micron. For more complicated measuring routines like BrianE suggested you will have to spend some time writing custom macro programs but they can be a huge time saver. For example the machine could take the measurements, adjust the cutter compensation, and re-machine the problem dimensions automatically.

Comprehension is not understanding. Understanding is not wisdom. And it is wisdom that gives us the ability to apply what we know, to our real world situations

 

[mfgenggear]

Gees

we do first articles on every first part in every lot.
that works for us.
depending on the cost of each part. an extra part is added for set up.
it is the sacrificial lamb.

Mfgenggear
if it can be built it can be calculated.
if it can be calculated it can be built.

 

[AaronH]

How about this?

Link

 

[geesamand]

Yes, that's the kind of technology I've envisioned.