The part was a hardened thin-walled steel sleeve. The customer was dissatisfied with the results he was obtaining from a bore grinding process using a vitrified-bonded CBN wheel. Grinding pressure was too high, which resulted in deformation of the part and poor roundness results. The only viable solution at the time was to slow down the process to an unacceptable cycle time of 45-seconds. The production requirement was to be under 35 seconds.
In addition to the slow cycle time and part deflection, the customer also complained that after the dressing cycle, they were seeing a size drop along with increased taper that only corrected itself after grinding 2-3 parts.
After reviewing the wheel and dresser designs, Meister engineers decided to have a closer look at the dressing process. It was determined the dress process was unnecessarily dulling the CBN wheel, causing it to build too much pressure during the grind cycle. This resulted in quill deflection which, in turn, caused the taper and size control issues after dress as well as the part deflection and roundness problems. Using the Meister Dress Calculation Tool, the following chart shows the changes that were made to improve the dressing process and the grinding results.
A screen shot of the full calculation tool can be seen by clicking the thumbnail image to the left.
Results/Conclusions: Moving from a counter-directional to a uni-directional dress (both wheel and dresser rotating in the same direction), combined with a faster dress traverse rate resulted in a more open and aggressive cutting wheel, so the customer was able to increase feed rates and get the cycle time down from 45 seconds to 35 seconds, while keeping the roundness in spec. Furthermore, taper and size control dramatically improved, so there were no more dimensional issues after dressing. As a bonus, since the wheel was cutting more efficiently, the customer found he could increase skip dress from 10 to 13 parts, allowing a much improved wheel life.
Would you like your own copy of the Meister Dress Calculation Tool? Download it HERE.