Management of grinding operation and problems

I have found from my practice for management of grinding operation and problems, often there are small things that affect grinding process and it is important to take care of.

Hereby I have divided management of grinding operation problems in two sections, those are ‘effective problem management’ and ‘grinding operation problem and management’ us under.

Section – 1. Effective problem management

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

First, a concrete grasp of the facts is necessary. 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 cured 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 mentioned below. However, there are also disadvantage for each item as shown.

Remedy	Disadvantage
making the grain size finer	grinding ability is generally reduced
if using a vitrified grinding wheel, changing to a resin bond grinding wheel	peripheral wheel speed and grinding fluid price are also problems
improving mechanical precision	huge expenses are required
increasing spark-out time frequency	Increase cycle time
changing grinding fluid	depending upon type of machine or wheel it may 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
• work piece
• grinding fluid
• operation method/cycle

It is important not to focus too steadily on any one of these. Since the process of solving major problems becomes a valuable bit of technical data, it is necessary that it be preserved. As for usual data, this should be organized in control charts or graphs.

Section – 2. Grinding operation problems and management

• In the case of chatter and scratch

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
	Unbalance wheel	1.  Re-balance wheel 2.  Re-balance wheel also after first       dressing 3.  Stop wheel rotation after grinding       fluid pouring is finished
	Oval or uneven wheel	1.  Resurface wheel before and after       taking balance
	Hard wheel	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	Rough Wheel	1.  Use fine grain size wheel
Irregular chatter	Unacceptable placement of work piece	1.  Eliminate looseness in placement 2.  Check center rest and revise if       necessary 3.  Lubricate correctly
	Unbalance work piece	1.  Balance the work piece 2.  Use large scale grinding machine
	Unacceptable dresser	1.  Use a sharp diamond 2.  Replace diamond with worn down       edges 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.  Lubricate 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	Soft wheel	1.  Use a hard grade wheel
Wide distribution of dots	Wheel glazing	1.  Balance the wheel and conduct      dressing 2.  Remove adhering fluid from wheel       surface

• In the case of spiral marks and scratch

Condition	Cause	Management
Fine spiral scratches	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 that wheel surface and       work piece are parallel and avoid       uneven placement of one side of       work piece to wheel surface 2.  Reduce wheel pressure 3.  Use a fixed rest 4.  Reduce the wheel feed
Spiral marks (stripes)	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 until       there are no more sparks
	Rough Dressing	1.  Make dressing depth of cut       shallow and slow down the feed
	Incorrect finish grinding	1.  Firstly, speed up the feed and       remove the spark from the rough       finish 2.  Finally, slow down the feed and       finish with an empty depth of cut
	Unacceptable alignment	1.  Check the alignment of the work       piece center 2.  Check the alignment of the wheel       axis with work piece
Isolated deep scratch	Unacceptable dressing	1.  Use sharp diamond 2.  Brush wheel surface after dressing       (A bristle brush is acceptable)
	Entry of rough grain or outside substance	1.  Remove with dressing 2.  Replace wheel if amount is large
	Resin bond wheel deterioration	1.  Avoid chemical solution type and       use soluble type instead 2.  Limit level of alkaline to Ph 9 3.  Protect against summer rise in       grinding fluid temperature
	Accidental fallout abrasive grain	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       work piece 2.  Perform operation using wheel in       soft gentle way 3.  Pour grinding fluid evenly and       sufficiently

• Unsuitable grade of grinding wheel, loading and glazing

Condition	Cause	Management
Poor sharpness of cut (Loading, Glazing, Burn mark of processing surface, Chatter occurring at the same time)	Hard grade wheel	1.  Increase work piece speed, wheel       feed and wheel pressure 2.  Reduce number of wheel rpm,       wheel diameter and thickness 3.  Apply dressing from time to time       using a sharp dresser 4.  Don't stop at the stopping point of       the coming and going table 5.  Carefully select grinding fluid       (water soluble type) Increase the       magnification of grinding fluid 6.  Use a coarse grain size or a soft       grade wheel
Wheel over consumption non-grinding tapered work piece scratch on wheel shedding	Soft grade wheel	1.  Reduce work piece speed, wheel       feed and wheel pressure 2.  Increase number of wheel       rotations, wheel diameter and       wheel thickness 3.  Make dressing depth of cut       shallow, increase feed 4.  Do not release wheel from work       piece on both sides of table 5.  Make grinding fluid magnification       thinner
Higher load on wheel	Improper wheel	1.  Use coarse grain size wheel 2.  Use soft grade wheel 3.  Use coarse structure wheel
	Improper dressing	1.  Use sharper diamond 2.  speed up the dressing feed 3.  Clean wheel surface after dressing
	Improper grinding fluid	1.  Use fluid with good cleanliness 2.  Apply fluid in balanced and       generous way 3.  At time of central lubrication, use       caution for grinding fluid cleaning
	Improper Operation	1.  Perform operations using wheel in       a soft, gentle way (Refer to poor       sharpness of cut listing)
Wheel glazing	Improper wheel	1.  Check choice of wheel abrasive       grain for the work piece material,       whether it is proper or not. 2.  Use a wheel which has coarse       grain size, soft grade and coarse       structure
	Improper dressing	1.  Dress normally with sharp dresser 2.  Speed up the dresser feed 3.  Deepen the dresser depth of cut
	Improper grinding fluid	1.  Choose a fluid with good       lubricating ability (water soluble       type) 2.  Apply fluid in a balanced and       generous amount 3.  Devise a method for applying       grinding fluid
	Improper Operation	1.  Increase depth of cut 2.  Perform operations using wheel in       soft, gentle way (Refer to poor       sharpness of cut listing)

• Work piece accuracy, burn marks, cracks

Condition	Cause	Management
Imperfect roundness	Imperfect alignment of center rest	1.  Open center hole accurately 2.  Grind and lap the center hole, or       remove the dust 3.  Regrind the center point 4.  Lubricate the center hole and point       sufficiently 5.  Eliminate looseness from center       rest
	Imperfect dressing	1.  Line up the machine's various       conditions   with the grinding       position and dressing position
	Unbalance in work piece	1.  Use a balance weight
	Improper operation	1.  For longitudinal feed, do not       release wheel from work piece (if       not doing so, the end of the work       piece will be tapered) 2.  Reduce pressure on depth of cut 3.  Use harder wheel 4.  Use a rest for a long or thin work       piece
Imperfect cylindricity (will be tapered)	Improper wheel	1.  Use a harder wheel 2.  For plunge cutting, make wheel       width larger than work piece width
	Imperfection dressing	1.  Bring diamond edge into contact       with grinding point
	Improper operation	1.  Review placement of the rest 2.  Check table feed whether it is       smooth or not. 3.  Leave at least one third of wheel       width by horizontal feed
	Work piece expansion	1.  Apply a great deal of grinding fluid 2.  Use caution in lubrication method 3.  Reduce depth of cut, quicken the       feed
	Residual stock removal	1.  Use a harder wheel 2.  Review pre-finishing and replace       wheel after a certain interval 3.  Make sure spark out time is proper.
Grinding burn marks and grinding cracks	Improper wheel	1.  Use a hard grade, coarse structure       wheel 2.  Perform operations using wheel in       soft, gentle way (Refer to poor       sharpness of cut listing) 3.  Make fine dressing, apply       occasionally
	Improper grinding fluid	1.  Apply grinding fluid in generous,       uniform way 2.  Devise lubricating method so that       grinding point is lubricated       (Central lubrication etc.) 3.  Use fluid with good lubricating       ability (Straight oil type is       recommended) 4.  If water soluble type with high       viscosity
	Improper operation	1.  Reduce depth of cut 2.  Speed up the feed, do not grind in       one place 3.  Do not stop wheel while in contact       with work piece
	Improper heat treatment of work piece	1.  It might be possibility that the       tempering temperature too low. 2.  It might be possibility that there is       unstable structure remaining at       the work piece.
Warp of thin work piece	Improper operation	1.  Reduce clamping force if using       collates, diaphragm chuck,       hydraulic power chuck, magnet       chuck 2.  Insert an iron plate of proper       thickness between chuck and work       piece if using magnet chuck.
	Improper grinding fluid	1.  (Refer to grinding burn marks and       cracks listing)
	Improper wheel	1.  Same as above