As part of its ongoing effort to diversify its customer base, C & B Machinery has developed a double-disc grinding system equipped with diamond-impregnated grinding wheels arranged for grinding the faces of various ceramic discs used in the telecommunications and permanent magnet industries.
The Model CBV2-16-R/B is now in use at Island Ceramic Grinding in Gilroy, Calif. The machine is actually a re-engineered system developed from a used machine carcass, but now designed to increase quality and product throughput, thereby reducing unit production cost. During runoff, the grinder achieved production rates of 300 parts per hour, effectively doubling output over previous grinding methods.
Double-disc grinding involves removing material from a part with parallel surfaces. The stock removal takes place on both faces of the component simultaneously, with the grinding occurring on the faces of the grinding wheels. Disc wheels are attached to diametrically opposed spindles, each contained in a heavy-duty precision grinding head assembly. For this particular process the spindles are vertically opposed and the parts are introduced to the grinding wheels via a rotary carrier system.
The design challenge for C & B Machinery was to provide a solution that fit within Island Ceramic Grinding’s budget. “A typical re-engineered grinding system means starting from a blank sheet of paper and completely stripping the machine of all commercial and most OEM components,” according to Chris Cox, vice president at the machine builder. The solution involved adapting new state-of-the-art feed systems and CNC controls to the machine, along with newly designed tooling. The result is essentially a turnkey system that is 20-30% less expensive to acquire than a comparable “new” machine.
In this case, C & B Machinery scaled back the updates in order to meet the customer’s budget. A simple PLC control replaced relay logic, and the mechanical wheel-feed systems were remanufactured and reinstalled. Careful attention was paid to balancing the spindles, which is critical to grinding with super abrasives.
The grinding wheel spindles were outfitted with variable-frequency drives that allow the grinding wheel surface speed to be programmable. Changing the speed of wheels, in essence, changes the “hardness” and cutting characteristics. This is a useful for adapting to changes in the material to be ground or variations in stock removal.
“Considering the expense of diamond grinding wheels, the ability to program the speed of the wheels allows easier and more cost effective optimization of the grinding process. It limits the necessity to experiment with and stock multiple grades of grinding wheels,” Cox explained.
Also, the machine is also outfitted with new digital readout displays for the grinding axes. This allows the operator to make very small adjustments (0.000050 in. increments) for precise size control.
Precise alignment of the wheelheads and tooling make it possible to achieve extremely flat and parallel parts, as compared to more conventional surface grinding methods.
“The trick to grinding ceramic components on a double disc is not to be in a hurry. In other words,” Cox continued, “the stock removed from the part is very small as compared to metal components. This is in order to keep the parts from chipping or even disintegrating when they enter the grinding wheels. Depending on the parent stock, multiple grinding passes may be required. Even still, this is a much faster method of producing higher quality parts than conventional surface grinding. It doesn’t hurt to have hundreds of years of grinding experience either.”
