CNC hobbing machine Operator

[ambarish]

Does any one has any experience of being CNC hobbing machine operator ??
I want to ask certain questions on it.. Very Urgent ..
Thank You

[ambarish]

Would like to know: 1) if anyone has come up with an inspection "standard" which governs acceptability of the "step" (at root) which is often generated
2) DFCE excess
3) Dent Marks

[RICHARD ZASTROW]

Explain "dent" DFCE "excess

[ambarish]

Hi Richard,
Dent is a scratched part or a impression of a blow on the surface of the gear.. while DFCE excess is the excessive flick shown on a gear rolling tester by the dial indicator .In our company the Gear manufactured on the CNC hobbing machine should be less than 0.045 microns.. if it exceeds the value its know as excessive.. I hope i have answered ur question Sir..
Thank You

[RICHARD ZASTROW]

ambarish If I am understanding , the dent is an impression in the surface you are attempting to measure. The DFCE is the movement of two gears in mesh as displayed by an indicator while the gears are rotated against each other. There are potentially many causes of the "dent". Not being familiar with your production process, I would be hesitant to attempt the explaination. First, recutting chips often cause this to occur. Solution is sufficient coolant flow or air blast to clear ALL chips from cutting zone. Second is excessive backlash in the system. Cause can be in gearing backlash, particularily in the worm/gear interface driving either the hob or the workpiece. This will also show itself at the start of a cut and again at the feed out of the cutter when the cutter is not applying side pressure to the workpiece.

[ambarish]

Thx Richard .. ur solution of giving sufficient coolant(Cutting Oil) to the machine can be the perfect one.. for air blast i think dry hobbing is neccessary .. i aint using that.. Will this be the solution even for broaching machine ? i m askin bcz the coolant flow given to the broaching machine is in right manner and direction of the pipes is perfectly directed towards to the fixture ,blank gears and the tool (Broach).. But still dents do come.. so what can we do in such cases? Sry i am outta topic 2.) what abt the step at root..?
Ur solutions r giving me positive directions.. please do help ..Once again thanks for ur reply

[RICHARD ZASTROW]

ambarish My reply was to your problem on a hobbing machine. Direct coolant flow at the cutting zone and air blast after cutting area, thus clearing chips after cut and before entering cutting zone again. This avoids recutting chips. As to boaching, the same will apply. Regardless if the broach is a vertical or horizontal machine, chips must be flushed from the tool. Have you tried broaching? That might eliminate your step problem. Another possible solution is to process the gears on a gear shaper still keeping chips cleared.

[ambarish]

we do have shaping machines as well as hobbing machines.. but i m an operator on hobbing machines..i have tried broaching also.. its vertical..and for clearing chips we rub a brush against it. do u know any other method for clearing chips on the broach? Any Kaizen Technique? Acc to my knowledge broaching will cause spline damage.. m askin abt the step @ root after the gear is manufactured.. Thx Richard .. Keep replyin .. its helping me a lot

[RICHARD ZASTROW]

ambarish I do not understand "step at root". Is this a deeper axial cut as the hob breaks out at the end cut? Or is the step to the side as the hob breaks out? These types of steps can usually be traced to dull cutters causing excessive cutting pressure. As the hob breaks out, the pressure is reduced and the workpiece moves into the hob. The same results can occur if either the workpiece or cutter setup are not rigid enough. Often a heavy first cut followed by a lighter second finishing pass will relieve "spring" in the setup and remove the step. I hope this helps.

[ambarish]

On the root of the Gear a line comes..thats called as a step at root..
this step at root is caused because of blunt on hob..however ur all replies r good enough and i appreciate it.. Can u suggest me some Kaizen Techniques for reducing all these defects.. Ty Sir..

[RICHARD ZASTROW]

ambarish If what you are describing is an additional depth at the root that is part of the form ground into the hob cutter itself, you may be describing what is called "protruberance". If so, this is a cutter designed to leave grinding or shaving material on the flanks of the tooth. that additional stock is to be removed in later operations. If this is the case, you must leave the additional stock on the flanks during the first operation.

[ambarish]

what is protruberance... m not aware of this term.. Thx for ur reply