[cheeserolle]

hi guys! i'm new to the site and i would like to hear opinions from the experts in the field of metalworking... my concern deals with causes of burrs..

i became a trainee in a manufacturing firm where they fabricate gears to be used in transmission of vehicles... in line with that, deburring certain output is imperative to meet standards...

the personnel in the company attribute occurrence of burrs with unsharpened gear cutters... i've read articles listing causes why burrs occur, informing me that dull cutters are not the sole reason of having burrs in a workpiece; causes includes nature of material being process, immediate environment of the workpiece, etc...

to those who are familiar with the issue, i would like to ask for a rough estimate... what percent of the problem can be attributed to unsharpened cutters? meaning to say, what percent reduction of instances in having burrs may be solved by properly adhering to change cutter schedule...

thanks in advance!

[RICHARD ZASTROW]

Since I do not know the specifics of the workpieces and cutting tools I can not give possible specific answers. I will attempt to give some more general answers.

1.) Yes, dull cutters can cause excessive burrs.

2.) The material being cut. Cast iron=nearly zero burrs, chipping may be more of a problem. Steel could result in serious burrs.

3.) Cut direction may cause excessive burrs. Climb cutting moves the burr to the bottom. This refers to gear hobbing.

4.) If gears can be stacked, only one side of a stacked pair will have the larger burrs.

5.) Most gear hobbing machines can be equipped with a deburring attachment (scraper blade) to remove burrs as they are being created.

6.) A 2-cut cycle can be employed to improve gear accuracy (quality, finish etc.) and reduce burrs.

7.) When sharpening hobs, great care must taken to retain the original geometry ground into the cutting face of the teeth. For example, if the original face was ground with a neutral angle then reground to a positive angle, the tooth profile will change. If the original helix angle was 7 degrees and is reground to some other angle, the tooth profile will also change. Totally unacceptable for automotive transmissions. Probably will cause noisy transmissions.

Hope that helps.

Dick Z

[ctate2000]

I would say that burrs from hobbing will caused by one of four factors (or a combination):

1. Dull cutters
2. Chip load
3. Improper cutting speed
4. Improperly applied cutting fluid

Burrs increase in size due to an increase in the volume of heat in the primary shear zone. Energy is released in the form of heat when the chip is formed. This heat increases the ductilty of the material adjacent to the shear zone. Increaseing the ductility will increase the amount of plastic deformation the material can withstand before shearing. The increase in ductility is the primary reason you start to see poor surface finishes and large burrs when the cutting tools get dull or the coolant is removed. Large chip loads and cutting speeds that are to high can cause the same effect as they also increase the amount of heat in the shear zone.

[cheeserolle]

thanks to the replies! by the way, i think i have a wrong thread title, it should be causes of burrs...

[RICHARD ZASTROW]

An old axiom: don't make burrs, then you will not have to remove them.

Point is you can do things to reduce or not cause burr formation. Extra elements in the cutting cycle can be more economical than removing burrs. Backing up with waste throw-away material for example. Heavy roughing cut followed by a light finish cut often produces easily removed burrs.

Dick Z