TOP TEN BORE GRINDING PROBLEMS and how to solve them…TODAY! (part-5)

Fluctuations After Dress

Size Shift at DressProblem: You are grinding a lot of parts between dressing cycles. Every part looks fine until you dress the wheel. Then the first one or two parts on the next cycle look horrible. It could be size or surface finish but something is thrown off after dress.

Solutions: When you come in and run the rotary dresser across the wheel, whether you like it or not you are changing the top layer of the abrasive, and that could result in an unacceptable shift in part quality in the next parts off the machine.

Change your dressing parameters: If you are experiencing this problem, the first thing to do is collect some data on your process. Say you are grinding 100 parts between dress cycles. Assemble all the data for size, surface finish, roundness, taper, etc. for those 100 parts and determine if some aspects of your process are drifting. It could be that the first part after dress looks so bad because the process has drifted too far and the newly dressed wheel is bringing that into focus.

If this is the case, it is very likely that you need to change the parameters you use to dress the wheel. This is easy enough to do if you use Meister’s Dressing Calculation Tool, which was designed to assist you in setting up the optimal parameters for rotary dressing of vitrified CBN and Diamond grinding wheels.  (Click on the link to download it.)

Keep in mind that the way you dress a new wheel is not the same as the way you redress a wheel as it is being used cycle after cycle thereafter. During the first dress you may want to make several passes to get the new wheel nice and round. Subsequent dresses generally require only a single pass to re-establish the desired wheel condition. If you are using the new wheel approach for your redress cycles, then you might be over-dressing and very well get the type of problems we are discussing here. If you optimize your dressing parameters, this problem could go away.

Increase Dress In-Feed. Sometimes the unexpected change is what the dress cycle does to bring your process back to where you want it to be. For example, as you grind 100 parts they continue to be straight and with good finish but the size is getting smaller and smaller because your wheel is getting smaller and smaller too. So you come in and dress the wheel. The machine should compensate for that and your size should come right back up to where you want it. But it doesn’t. It keeps on getting smaller. The most likely reason for this is that the wheel wore more than the amount of the dress. Therefore you may need to increase the dress infeed on the wheel and the machine compensation will then bring the part size back to where it should be.

Dress more frequently. Another solution is to dress more frequently. For example if you are dressing 5 microns every hundred parts, maybe you should dress 2-1⁄2 microns every fifty parts. Your wheel life will be exactly the same but maybe that change in size after dress will only be half as much because you are dressing more often. This will only work, however, if your machine has enough resolution to accurately remove thinner layers during a dress cycle.

Check the condition of your dresser. If the steps above do not produce the desired results, you might want to take a look at your dresser to make sure that it still has all of its diamonds. Dressing wheels are tough but they do wear out over time. We run into this one more often than you might think!

About joelcassola

Joel Cassola is a commercial journalist who has written feature articles and case histories for clients in more than 100 trade magazines.
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