Cutting cycle time: General Industry Coverage

Dear Doc: I surface grind 20 “×12 “×0.5 ” steel plates using a 14 “-dia., 1 “-wide WA46IV5 wheel. I must remove 0.025 ” of stock on both sides, doing it in 0.0004 ” passes and dressing 0.0004 ” before every pass. It’s taking 12 to 15 hours to grind this plate and cycle time is killing me. What can I do?

The Doc Replies: There are two keys to reducing cycle time: mixing up your dressing and being smart about your cross-feed. I’d do the following:

First, dress the wheel aggressively by taking a 0.0012 ” DOC and racing the diamond across the wheel as fast as it will go. Then, take a fast finish dress with no infeed to clean the grits you’ve missed. This will give you a super-sharp wheel that will generate less heat and reduce grinding forces by as much as 80 percent, depending on the initial dressing.

Second, grind with a 0.001 ” DOC in each pass using the original table speed. That’s two and a half times the material in each pass! But don’t worry about burn and the motor stalling because you’ve opened the wheel, grinding forces and heat will be much lower and your machine should be able to handle it.

Finally, here’s the kicker: make sure the grinding overlap ratio is less than 1.0:1.0. That means for a 1 “-wide wheel, cross-feed will be around 0.95 “. That’s imperative to reduce cycle time. When rough grinding, you don’t want to “regrind” material to improve the surface finish because you don’t care about surface finish. Therefore, use nearly 100 percent of that wheel for roughing—not 10 percent for roughing and 90 percent for regrinding, which is all too common.

Now, the surface finish is going to be a disaster, but don’t worry. Continue to grind until you’ve removed 0.0238 ” of material, leaving 0.0012 “.