Todays’ Machining World Archives March 2008 Volume 04 Issue 03
Dear Shop Doc,
We are trying to stamp our company logo on components produced on our CNC Swiss type machines. In the past we’ve had no problems, but we’ve recently taken on a new project where the parts are much smaller. Now the parts are either getting bent or the impression is not being fully formed. Our typical process is to machine all the features of the component and stamp on the last operation. We’ve tried different brands of tools and have even tried to use a “roll stamp,” but we still have the issues with small components.
Bent Logo
Dear Mr. Logo,
I have the solution to your problem. Most of the difficulties in machining micro-precision parts can be attributed to work holding and rigidity. The reason why you haven’t seen these problems on large components is because the “machined” portion of the component was strong enough to withstand the stamping process. But now that you are making a smaller part you don’t have the same strength in the partially machined component. Let’s look at what you can do in this particular application.
One of the great benefits of Swiss-type machining is that the material is being fed through a guide bushing into the cutting tools. When the guide bushing is adjusted properly and the material is consistent, the guide bushing acts as your support. When you incorporate Swiss-type machining with the limitless possibilities in CNC programming, you may forget that when you are moving the material back and forth (Z-axis movements) you must realize that if you removed any material from the outside diameter, the component is no longer supported by the guide bushing. So, if you machined the entire component (before parting off) and then try to stamp your logo, the part is not being fully supported. Even though the part is still attached to the bar stock it is still not very rigid. This also keeps the impression from being fully formed because the part is pushing away from the stamping tool at an angle.
Here’s a couple of tricks I’ve used in the past to solve this problem. If your machine has an extra tool position opposite of the stamping tool, put a support tool in that extra position. Next, program the position of the support tool, in the X-axis, into the part. For example, if the diameter you are stamping is .060″, position the X-axis to a diameter of .058″. This will push the part about .001″ in the direction of the stamping tool, and when you stamp the part it will be held rigid by the support tool. If your machine doesn’t have the extra X-axis try this: machine your outside diameter to the linear position of where the logo is supposed to be (plus clearance for your stamping tool), stamp your logo, and then go back to finishing the outside diameter. This will keep the bar stock at its original diameter and supported by the guide bushing.
David Cogswell
Regional Manager at Gosiger Inc.
