C & B Machinery Develops Double-Disc Grinding System for GM

2011 1.4L I4 Chevrolet Volt EngineGRINDING VOLT RODS

Traditionally, only coplanar, or parallel, connecting rods have been ground on a double-disc grinder, which simultaneously grinds both sides of flat parts using opposing wheels, according to grinding machine builder C&B Machinery. That’s because the part path through the wheels only allowed grinding of coplanar rods, with additional operations required for stepped rods, and there was no method to dress a step into the grinding wheels.

However, General Motors sought a machine that could grind a noncoplanar connecting rod in a single setup for the auxiliary 1.4-liter engine in the Chevy Volt plug-in hybrid electric vehicle. GM requested a quote from C&B for two such machines. (The crank end is 1.2mm narrower than the pin end on the turbo version of the connecting rod.)

Recipricator Double Disc Grinding Machine

C & B Machinery DG-2H-RE/30 Double Disc Connecting Rod Grinding System

After analyzing alternate methods of double-disc grinding and material handling, C&B developed a CNC double disc grinder to remove 1.8mm of stock from the crank end and 0.6mm from the pin end in one cycle. According to the company, the process is unique and represents the first successful attempt to grind a stepped connecting rod with this technology on a production basis.

By grinding two different widths on one connecting rod in a single pass through the machine, GM saves the cost of buying another machine to reduce the crank end and improves part quality, noted Chris Cox, C&B vice president. “When processing connecting rods of this type on two different machines, which is a more conventional approach, it is very difficult to hold the relationship, or symmetry, of the faces from crank end to pin end,” he said, adding that parts float between the wheels in a double-disc grinder and are not clamped. “By grinding the four faces simultaneously we were able to hold much tighter tolerances.”

The first grinder shipped to GM in 2010 produced flatness and parallelism of the rod faces within 4-microns on average, repeating within 1-micron! Size range is held within 25% of print tolerance and repeats within 3-microns. The step relationship from crank face to pin face is held within a range of 6-microns.

This state of the art Grinding System is equipped with a robot that places the ground parts into an automatic gauging system that 100% inspects the crank end thickness, pin end thickness and step relationship. The system is designed such that the grinder will automatically correct itself should any of the three characteristics drift beyond preset limits.

The entire cell which is comprised of the grinder, automation, robot, gauging system and coolant filtration system is monitored and controlled by a single Human Machine Interface (HMI).

Chevy VoltSimilar to the Volt getting better mileage than cars powered only by gasoline, Cox noted that the motors on C&B’s special double-disc grinding machines require less energy than conventional machines due to the process using 25% less horsepower.

For more information, contact C&B Machinery, Livonia, Mich., at (734) 462-0600 or www.cbmachinery.com.

Super-Abrasive Double-Disc Grinder for Ceramic Discs

CBV2-16-RB Double Disc Grinder Workzone | C & B Machinery

The workzone of the CBV2-16-R/B double-disc grinder that C & B Machinery developed for Island Ceramic Grinding.

Ceramic Discs

Ceramic discs manufactured by Island Ceramic Grinding in Gilroy, Calif.

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.”