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Grinding wheel Structure of grinding wheel Abrasive grain (artificial abrasice) Grain size Grade Structure Bond Bond subdivision symbols Grinding wheel specification and indication method Grinding wheel's shapes and size Process of grinding wheel Grinding operations and how to select grinding wheel Basic conditions for selection Prerequisite for selection standart by JIS. Standard selection of grinding wheel by JIS. Processing conditions Management of grinding operation problem Grinding wheel safety Treatment and storage Installation Points of caution when using Safety level Protective equipment CBN and Diamond wheels Bond characteristics Application examples by bond Concentration Indication Wheel shape symbols Truing and dressing Basic conditions on wheel selection

Relationship between machanical conditions and grinding results

Management of grinding operation problems

1. Effective problem management
2. Grinding operation problems and management

Effective problem management
Since specific technologies are noted in sention.2 regarding grinding wheel problem management, in this section general examples of problem management are given.

First, a concreate grasp of the facts is nessary. For instance, the claim that the grinding wheel itself is hard is vague and may easily be mistaken. As well, making judgments based simply upon numerical figures can also cause mistakes.

So far dressing has been made every 20 units, but with the 15th unit, a shear is produced at the edge and the product becomes inferior, the lift span of one wheel declines from 20 to 15 days.

So far dressing has been made every 20 units but with the 15th unit, loading curred and the wheel life span for one unit goes from 20 to 15 days.

In such cases, if we think simply of dressing interval and wheel life span, it seems that the treatment solving the problem is identical. However, treatment for the shear at the edge is completely different from that for loading. The treatment should be opposite because the grinding wheel is soft for case and hard for case.

Second, think sufficiently about mutual relations. For instance, if it is desired to improve surface roughness, there are methods such as,

• making the grain size finer
• if using a vitrified grinding wheel, changing to a resinoid grinding wheel
• improving mechanical precision
• increasing zero-cutting (spark-out) frequence
• changing grinding fluid

However, there are also disadvantages for each item:

• grinding ability is generally reduced
• peripheral wheel speed and grinding fluid price are also problems
• huge expenses are required
• depending on the grinding machine type it is impossible
• depending upon type of machine or wheel it is impossible

In such cases there is a strong tendency to change only the grain size as an acceptable method to prevent efficiency from declining. However, if mutual relations and actual on-site conditions are not carefully considered, it will take many months to solve the problem after conduction all the above methods with successive failures. There was the case when the problem was finally solved by making the dressing feed finer. In logical terms this was the most correct method.

We must think of the grinding process in terms of 5 related items:

• Machine
• Wheel
• Workpiece
• Grinding fluid
• Operation method

It is important not to focus too teavily on any one of these. Since the process of solving major problems becomes a valuable bit of technological data, it is neccessary that it be preserved. As for usual data, this should be organized in control charts or graphs. The data for each wheel should be filled in on the back of the inspection card and such feedback to the wheel macturer can prove to be extremely efficient.

 

Grinding operation problems and management

Machine vibrations, chatter and scratch to the finished surface

In the case of chatter

Condition	Cause	Management
Wave appears in the same internal	Machine vibration	1.Check foundation and positioning method 2.Replace or adjust belt and gears 3.Check spindle and motor balance 4.Recheck moving parts
	Wheel unbalance	1.Retake wheel balance 2.Retake balance also after resurfacing 3.Stop wheel rotation after grinding fluid pouring is finished
	Wheel isn't round	1.Resurface wheel before and after taking balance
	Wheel is hard	1.Use a soft grade wheel 2.Use a rough grain size wheel 3.Reduce peripheral wheel speed 4.Reduce depth of cut
Narrow, deep and regular chatter	Wheel is rough	1.Use fine grain size wheel
Irregular chatter	Unacceptable placement of workpiece	1.Eliminate looseness in placement 2.Check center rest and revise if necessary 3.Lubricate correctly
	Workpiece unbalance	1.Take balance of workpiece 2.Use large scale grinding machine
	Unacceptable	1.Use a sharp diamond 2.Replace diamond with worn down adges 3.Make sure there is no looseness in diamond holder 4.Don't protrude dresser for too long
Both regular and irregular chatter appear	Thrust feed looseness	1.Conduct thrust inspection 2.Lublicate 3.Conduct feed equipment inspection
Chatter appears in a wide range for a long time	Unbalanced movement and vibration of wheel axis	1.Check to see if wheel axis is round 2.Check for curves in wheel axis
Even spread and short with contact chatter	Bearing looseness	1.Undertake wheel bearing fitting 2.Revise thrust 3.Reduce peripheral wheel speed
Wide and various deep irregular streaks	Wheel is soft	1.Use a hard grade wheel
Wide distribution of dots	Wheel glazing	1.Take wheel balance and conduct dressing 2.Remove adhering fluid from wheel surface

In the case of search and spiral mark

Condition	Cause	Management
Fine spiral streaks (Scrarches)	Unacceptable dressing	1.Replace broken diamond 2.Slow down dressing feed 3.For installing, make a bottom placement of 15 degrees and a side placement of 30 degrees 4.Confirm the holder placement 5.Make shallow dresser depth of cut 6.Make sure holder does not touch wheel 7.Begin dressing from end face of wheel, not from the surface mid-point 8.Make sure the final dressing feed is in the opposite direction from the grinding feed 9.Make sure the dresser feed is even 10.Round the end face of the wheel
	Unacceptable grinding operations	1.Make sure wheel surface and workpiece are parallel and avoide uneven placement of one side of workpiece to wheel surface 2.Reduce wheel pressure 3.Use a fixed rest 4.Reduce the wheel feed
Spiral stripes (Spiral marks)	Contact condition of wheel end face	1.Round the wheel end face
	Grain size difference between rough finished wheel and finished wheel is too great	1.For rough finished wheels, use wheel with finer grain size 2.For finished wheel, use rougher size grain wheel, reduce the depth of cut and feed and finish untill there are no more sparks
	Dressing is rough	1.Make dressing depth of cut shallow and slow down the feed
	Finished grinding is incorrect	1.Firstly, speed up the feed and remove the strak from the rough finish 2.Finally, slow down the feed and finish with an empty depth of cut
	Inacceptable alignment	1.Check the alignment of the workpiece center 2.Check the alignment of the wheel axis with workpiece
Isolated deep scratch	Unacceptable dressing	1.Use sharp diamond 2.Brush wheel surface after dressing (Abristle brush is acceptable)
	Entry of rough grain or foreign substance	1.Remove with dressing 2.Replace wheel if amount is large
	Resinoid wheel deterioration	1.Avoid chemical solution type (JIS W-3) and use soluble type (JIS W-2) instead 2.Limit level of alkaline to Ph 9 3.Protect against summer rise in grinding fluid temperature
	Abrasive grain accidental fallout	1.Use a wheel with a hard grade 2.Use abrasive grain with rise in grinding fluid temperature
Various lengths and widths with irregular scratches	Dirty grinding fluid	1.Keep tank clean on regular basis 2.Check function of filtration equipment 3.Keep inside of safety cover clean
	Dust and debris	1.Inspect the dust collection function, especially the suction opening 2.Undertake cleaning of the operations area
Checkered pattern	Unacceptable grinding operation	1.Do not press wheel too far into workpiece 2.Perform operation using wheel in soft gentle way 3.Pour grinding fluid evenly and sufficiently

Unsuitable grade of grinding wheel, loading and glazing

Workpiece precision, burn marks and cracks