When it comes to precision grinding, chatter marks can pose a real challenge, especially with the pressure of meeting production deadlines. This problem is typically only identified when products get to the QC stage for quality inspection, and parts have already been ground within the required tolerance. Identifying the problem at this stage of production leads to unnecessary costs as parts usually must be scrapped or reworked.
As common as this scenario is, it is paramount to correct the problem in avoidance of incurring extra costs. With over 40 years of experience in local manufacturing of specialised abrasives, we at Grinding Techniques, understand both the cost, and other implications of this phenomena. Grinding Techniques’ research and development team in conjunction with their business development team can provide a range of solutions on how to avoid chatter marks with practical options of how to counteract this, should it occur during production.
The following steps may be taken but it should be noted that one must try one step at a time.
Reviewing grinding fluid for its cleanliness and for instance increasing the mixture from perhaps a 3% to around 6 to 7% could minimise chatter marks during application.
Secondly, checking for any possible machine vibrations that could aid in the creation of chatter marks during application should be considered. This could be from within or around the machine and even from other machinery in the vicinity that could cause floor vibrations to be transferred to the grinding machine during application, this should be eliminated at all costs. The grinding machine’s belts should not be damaged and should be tensioned correctly and spindle bearings should not have any play or be worn. Make sure that the spindle bearings of the machine are not worn, if there is any play on the spindle bearings, replace them immediately.
One other major cause of chatter marks usually results from taking too big of a cut by simply reducing the infeed of the grinding wheel and allowing for a lighter cut from the material or slowing down the traverse speed should assist you in reducing or eliminating chatter marks.
Another common cause of chatter marks is grinding wheels acting too hard, the general rule of thumb in grinding is to use a grinding wheel with a soft grade on harder materials and a harder grade wheel on softer materials. When a grinding wheel acts too hard, there are two possibilities to fix the problem either change the specification to a softer grade, if the job doesn’t need to be ground urgently or make the wheel act softer by firstly slowing down the speed of the wheel generally, for every 5 M/S that you decrease the grinding wheel speed, it will act one grade softer, or one grade harder when increasing the speed of the grinding wheel. If this is not possible the workpiece speed can be increased. This will enable the wheel to break down more and act softer. Alternatively, the infeed rate of the grinding wheel can be increased. It is however important to remember that a vitrified wheel breaks down under pressure. Taking too light of a cut will just cause the wheel to rub against the surface of the grinding wheel and will lead to l clogging. By increasing the infeed, more pressure is added which will allow the wheel to start breaking down.
If you are traverse grinding, increase the traverse speed of the grinding wheel as this will make it break down more. A final way of making the wheel act softer on application is to decrease the diameter of the grinding wheel, as a wheel gets smaller, the peripheral speed of the grinding wheel decreases, allowing it to act softer.
Another approach is to make changes to your dressing parameters. By taking a heavier cut, and increasing the traverse rate of the dresser, the wheel will open and make it cut more freely, but this will however leave a rougher surface finish. Grinding the part in two stages, first rough grinding and leave a little bit of material on the part, and then moving over to a finishing grinding process to close the face of the wheel slightly to get the desired finish should assist you in obtaining the correct finish.
By taking some of these precautionary measures, chatter marks can be minimised, if not completely avoided during application. Whatever assistance you require when it comes to precision grinding, our application specialists at Grinding Techniques are ready and available to assist you with any concerns or advise you might require.