Finding Treasure In Your Grinding Process
By Tom Cappadona, Meister Abrasives USA
Since grinding is generally last step in the manufacturing process, it is frequently the last item to be considered for optimization. At this point there may be a heightened sense of urgency for getting grinding out of the way quickly to get manufacturing up and running and parts out the door. Even more unfortunate, there may be a temptation to use grinding as a means of correcting dimensional inadequacies that were created in other manufacturing phases. This makes the grinding process less efficient and cost-effective while it disguises other causes of lost manufacturing profitability.
I am happy to report, however, that many of the customers with whom I routinely visit and consult have bought into the concept that treasure is to be found in optimizing their grinding processes and it is worth going after the right way. If you are one of these I offer a few tips that could help make your grinding process treasure hunt more effective.
1. Divide and Conquor
If you are not getting what you want from your grinding process it would be nice if you could simply try a different wheel, or machine, or change feeds, speeds and dress cycles and bingo you’ve got it. Unfortunately it’s usually not that simple. Over the years I have created a spread sheet of parameters that can be adjusted to improve grinding performance. At present, I have 82 variables on this sheet. And I seem to add more every year.
There are just too many variables to be adjusted simultaneously in the hope that near perfection will result. Based on experience, I will choose the settings I believe most likely to achieve good results and then I will pick one variable, change it, see what happens, then move on to the next most likely. With this approach I may reach my goal in an hour and a half or a day and a half but I will get there without backtracking.
2. Make Big Changes First
This is counter-intuitive. You might think that if you are trying to fine- tune something that you should make a lot of fine adjustments. However, your first goal is to test the parameter to see if it has much influence on what you are trying to improve. If you just make a small change it is usually very hard to see the difference it makes in the end result.
It’s kind of like trying to climb the specific branch of a tree when you are lost in the leaves. If you climb out to the end you will quickly know whether you are on the right branch or not. If you make a small change, then you may be lost in the little details for a long time.
So select a single variable and start making some big changes to it. First make a big change in one direction. Does it help or does it hurt? Then try going in the other direction. If that has little influence on the result you want then go on to the next thing.
3. Talk It Through
If the cause of a grinding problem is not immediately obvious it usually helps to talk it over with an experienced co-worker or supplier. Frequently if I can get some accurate feedback from my customers over the phone, I can make suggestions that they can try on their own without me being there.
Here’s an example. Recently a customer could not get the surface finish he needed using a diamond wheel to grind a profile in a carbide part. I asked him to send me the feed rates and his dressing parameters. He knew the dressing parameters were wrong as soon as he pulled them out of his grinding machine. Once he was pointed in the right direction by someone who wasn’t so buried in the problem, he found and fixed that problem on his own. However, that change by itself did not make the surface finish problem entirely go away.
So then I had him looking at the process he was using to make the profile. We slowed down his feed rate and his surface finish came in. The problem, we determined, was that the small grinding wheel radius was effectively creating threads on the part. It was as if my customer was attempting to trace the edge of the table with the head of a pin instead of using more of the grinding wheel (a larger radius) to do the work.
So we now had to decide how we were going to eliminate the “surface threading effect”. And this brings us to our 4th treasure hunting tip:
4. Get your priorities straight
For him, there were three parameters he could change for this part and any one could be adjusted to bring in the finish: the feeds, speeds and the radius on the edge of the wheel. It’s up to him to decide what he’s going to change depending on his primary objective.
This company wanted to use a smaller radius because they felt it gave them more flexibility to grind a wider variety of parts with a single wheel. Changing the feed rate to make it slower would improve, but that would make for a longer cycle time and lost productivity. So in this case the customer chose to increase RPM of the part so it rotated faster.
Other companies will have different optimization priorities which can include achieving higher surface finish or profile quality, increasing throughput and reducing costs. The cost-reduction item can be further refined according to abrasive costs, grinding process costs or total manufacturing process costs.
The steps you take in your search for grinding process treasure will be guided by which of these considerations is highest on your list of objectives. Without establishing your priorities early on, you could lose a lot of time marching off in the wrong direction. When there is treasure at stake, you’’ll want to avoid this sort of backtracking as much as possible.
We will have more grinding process trouble-shooting (i.e. treasure hunting tips) for you in future posts on this blog.