by Rob Titus
How to improve your cylindrical grinding process
There are many factors to consider when developing a stable and efficient cylindrical grinding process. Having the correct grinding wheel is a must, but there are many other factors that need to be taken into consideration.
1.) Dressing the grinding wheel
The grinding wheel is dressed to make a dull grinding wheel sharp again. The more parts the grinding wheel grinds, the duller the grinding wheel becomes. Single point dressing diamonds, when new, will create a sharp grinding wheel after dress. The more the single point tool is used, a flat will develop on the diamond, due to wear. It is important to rotate the single point diamond frequently to avoid a large flat from developing. This flat creates a wider contact area between the diamond and the grinding wheel, which in turn creates a dull grinding wheel. This in turn can result in excessive grinding forces, excessive heat generation, and/or chatter.
The better option for dressing is a rotary dressing. This requires an electric rotary dresser spindle and a rotary dresser diamond disk to be mounted to the spindle. The rotary dresser diamond has diamonds around the entire diameter of the disk and rotates at a proportional speed to the grinding wheel. Rotary dresser diamonds wear at a much slower pace than a single point diamond, therefore they produce a much more consistent dress, which in turn produces a much more consistent grinding process.
2.) Grinding wheel balancing
Having a properly balanced grinding wheel will result in a more stable grinding process. Static balancing of a grinding wheel outside the machine can be time consuming. This involves manually placing the wheel/wheel flange on a balance stand and manually shifting weights to get the assembly balanced.
A more efficient method of wheel balancing is done by an automatic wheel balancer. An automatic wheel balancer consists of a balance head, vibration sensor and balance controller. After installing a new grinding wheel on the grinding wheel spindle, the grinding wheel spindle can be turned on and the controller will display the amount of vibration. By the simple press of an “auto balance” button, the weights in the balance head automatically start moving to reduce the amount of vibration to a desired level. Manually balancing a grinding wheel can take up to 30 minutes whereas an automatic wheel balancer can balance a grinding wheel in 30 seconds.
This is an area often overlooked in a cylindrical grinding process. The main purpose of coolant is lubrication at the point of contact between the grinding wheel and the workpiece being ground. This reduces heat, reduces wheel wear, and improves surface finish. Coolant pressure/velocity is much more important than the amount of coolant. A general rule of thumb is the coolant velocity should be 80-100 per cent of the grinding wheel velocity. This allows the coolant to penetrate the air barrier created by the rotation of the grinding wheel.
Equally important is that the coolant is directed into the grinding zone. This requires a coolant nozzle that will allow the coolant to flow out of the nozzle in a solid tight stream, rather than fanning out, thus getting more coolant at the point of contact between the grinding wheel and the workpiece. Coolant cleanliness will also have an effect on the grinding process. If the coolant is not being filtered properly or the coolant system is not properly maintained, grinding chips (swarf) will then be pumped back into the grinding zone, affecting surface finish and grinding wheel life.
Taking these things into consideration when developing a grinding process will put you on the right path to stable and efficient grinding. SMT
Rob Titus is the Okuma product grinder specialist.