Benefits of dummy workpieces: General Industry Coverage

Dear Doc: I creep-feed-grind nickel alloys for the aerospace industry. Some of our grinders use a dummy workpiece; some don’t. What’s your take on dummy workpieces?

The Doc Replies: I’m a fan of dummy workpieces—also called false nips—but only in certain situations. Let’s take a look at when they’re useful.

Dummy workpieces are used to help get coolant to the hot spot (see figure) when the wheel is entering the workpiece (when up grinding) and when the wheel is exiting the workpiece (when down grinding). In shallow-cut surface grinding, the main benefit of coolant is lubrication, not heat removal. Here, a dummy workpiece might help a little.

However, when creep-feed grinding, the main benefits of the coolant are lubrication and heat removal. Here, you must have good cooling—and in this case, a dummy workpiece can help a lot.

Dummy workpieces are used to help get coolant to the hot spot. Image courtesy of J. Badger

But that depends on where you put the workpiece. When up grinding, if you don’t have a dummy, the coolant will deflect off the wheel (a) at the entry point. A dummy workpiece will help catch the coolant and carry it to the hot spot. Here, you put the dummy at the entrance (b).