Is In-Process Gaging for You?

Many shops have a built-in option on their multifunction CNC lathes that they’re not taking advantage of: in-process gaging. There’s a perception that in-process gaging adds a lot of cycle time, but for many manufacturers this option will likely save time and/or resources overall. It can also reduce your scrap rate and eliminate operator error. Let’s explore the pros and cons and see if in-process gaging might be the best solution for you.

Is In-Process Gaging for You?

I work on Okuma’s multifunction machines, such as the MULTUS series of CNC lathes. Many people who buy these machines include the probe option (such as those offered by Renishaw, Blum and Marposs) with their purchase. But, as time goes by, they don’t really use it. If you’re only doing one or two parts at a time, and then changing your setup for another part, this makes sense. But if the following applies to you, it would be very beneficial to look at in-process gaging:

• You’re doing long runs of the same part, or a family of parts
• You’re trying to hold tight tolerances of .001” or less
• Your scrap rate is high
• You’re having problems with operator error
• You have materials that are inconsistent from one part to the next

In-Process vs. Post-Process Gaging

In-process gaging gives you the ability to check the part as you're actually making it, so for those tight tolerances you can semi-finish the feature, probe it and adjust your offset, then make your finish cut if you need to. (Watch this video to see a short demonstration of this.) With post-process gaging (which a lot of automotive manufacturers use), the part is cut complete on the machine and then a robot takes that part and puts it into a gage. The gage checks it, and then provides feedback to the machine such as an offset change for the next part.

Cycle Time vs. Scrap Rate

Unfortunately, the part that was already completed could be a bad part. Normally, when that happens the gage also sends a signal to tell the robot to stop running until someone can investigate why the part was bad. If the part was within the set tolerance range that was good, now we adjust the offset up for the next part being cut. In-process, it's going to take a little more cycle time. Post-process is all external to the what's going on in the machine, so it's typically a little quicker, and that's why the automotive users deal with the post processing. With high volume runs, they want the shortest cycle times possible. But you may be paying a high price for that cycle time with higher scrap rates. In other industries such as aerospace and medical, where material costs can be very high, it may make sense to incorporate in-process gaging.

Eliminates Operator Error

In-process gaging also takes the possibility for operator error out of the process. With in-process gaging the machine will make a semi-finished cut, check the part, change the offset and make the finish cuts. Or, for tolerances that are not as critical, you can probe the finish size without the semi-finish cut and adjust the tool offset for the next part. This eliminates the operator having to stop the machine and go in with a hand-held gage to check the part. If he reads the gage wrong, or offsets the wrong tool, he may scrap the part.

If you have an Okuma multifunction CNC lathe, chances are good you already have a probe option. If you want some training on using this tool, feel free to contact us or your local distributor.

Kevin Kraieski is Senior Application Engineer, Okuma America Corporation.