Burning While Grinding

[1plus1]

We have been creep feed grinding parts for months now on some casting parts and everything has been running well until recently. The parts have been showing burning along some of the edges. The grinding wheel is fairly new, coolant is ok, and the program and dressing has not been changed. We have to dress the wheel every fourth part to keep proper form and dimensions and usually the third part shows little or no burn, but the first and second part after dress show unacceptable burning. It is only a cosmetic issue, but we need to stop it. Any ideas?

 

[griffengm]

1plus1,
Questions:
Is the wheel the same in ALL respects, type, manufacturer, bond, etc?
How do you determine that "coolant is ok"? If nothing has changed with the coolant (see q1), then has your water source changed (assuming water soluble?
How is coolant distrbution managed, how do you control where it hits the part/wheel?
New operator?
Fixture change?
Sorry if some of there seem so elementary but as my old buddy Charlie used to say "The answer has got to be something so simple that we'll al say 'DUH' when we find it.

Griffy

 

[1plus1]

The wheel is the same in all aspects, coolant is at proper mixture, we have tried adjusting where the coolant hits at various angles - only helped slightly, same operators for seven months, and same fixture. The only possibility I can think of is that the castings have more material to remove than before. Another person stated that the wheel is to "tight" after the dress and is not letting coolant penetrate to cool sufficiently, that is why the third part shows little or no burn because the wheel has "broke down" enough to allow coolant to penetrate. He didn't say how to dress the wheel to help. It's got us stumped.

 

[damc]

Many factors can effect burning.What size is your wheel and RPM? Is your coolant under pressure or flood. Is the speed of the dresser the same? Try speeding it up slightly. What kind of diamond are you using? A sharp single point will cut the grains instead of breaking them out which is desirable but will give the wheel a "harder" effect. If you are dressing slowly you could be packing the wheel.Coolant released under pressure will help clean the wheel and keep the part cooler. Any possibility the casting material has changed in any way?

 

[1plus1]

The coolant is under pressure. I am not sure what the size and RPM of the wheel is, but i will find out. I am under another assignment right now. The casting matterial has not changed according to vendor, but we might have our metalurgist check it to make sure. We have changed dressers to no avail, however we might try to increase dressing speed to "loosen" up the wheel a bit. Good idea. We are trying to make a double pass on the rough, instead of single pass. I will keep you updated.

 

[jck26]

As Griffy said it could be simple. Check to make sure that you have a "wind deflector" in place to remove the film of air that surrounds the wheel as it spins. It may look like the coolant is reaching the wheel when in fact it is not happening. This is a basic feature used on many centerless grinders to insure coolant contact.


jck26

 

[griffengm]

1plus1,
Sorry if this seems too elementary but where is your coolant hitting the part and wheel? Jck26's notion of spoiling airflow made me wonder about this.
If your wheel is not carrying enough coolant into the cut it might explain why your wheel is loading. Coolant after the cut(on top of the Part?) may cool the part but may be flung from the wheel by the time a given section of the wheel reengages the material.

Griffy

 

[1plus1]

Thanks for all of the ideas, but the problem is solved. I don't have the exact details just yet, but our programmer changed the program. I will find out from the ME, who was assigned to the case , exactly what was changed. He is going to examine the programs before and after. From what I understand from the programmer is that he made a double pass on the rough grind intead of a single pass and changed some speeds and feeds. He wouldn't give me any specifics, so I am waiting on the ME report. It added one minute to the cycle time which will cost us some production numbers, but we will still get the numbers we need. My only guess is that the casting vendor may have changed castings and there is added material. We should have kept a watch on this, but we didn't. Vendor denies changing anything, but it wouldn't be the first fib from a vendor. I will post the exact changes when they become available.