Livonia, MI - C & B Machinery has been awarded an order by GM for two special double disc grinding systems to finish grind both coplanar and non-coplanar connecting rods for the auxiliary 1.4L engine in the electrically powered Chevy Volt.
Double disc grinders grind both sides of flat parts at the same time using opposing wheels. The C & B Double Disc Grinder is equipped with horizontal spindles. All four faces of the Volt's connecting rods are ground simultaneously to extremely tight tolerances. The Turbo version of this connecting rod has unparallel (or non-coplanar) surfaces (the crank end is 1.2mm narrower than the pin end).
The challenge was to produce this non-coplanar connecting rod from a parallel or coplanar rod. C & B Machinery developed this grinding system to remove 1.8mm of metal stock from the crank end and 0.6mm from the pin end in one cycle. All four faces are ground simultaneously, and the production rate is roughly 200 parts per hour.
This grinding process (to the best of C & B's knowledge) is unique. Similar, conventional methods have been attempted by other manufacturers in the past, but never proved successful.
The first grinder which shipped to GM earlier this year 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 tolerances 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:
1. Unloads finish ground parts.
2. Positions every part in front of a camera, which ensures the part, is oriented correctly.
3. Places the part into an automatic gaging system that 100% inspects:
o Pin end thickness
o Crank end thickness
o Step relationship
4. Places the part in the outgoing automation
Traditionally, only coplanar connecting rods (pin end and crank ends are the same width) have been ground on double disc grinders. Additional grinding steps have been needed for stepped or "non-coplanar" connecting rods.
On the C & B grinder, two different widths on the same connecting rod can be ground in one pass through the machine, saving time, improving quality and reducing costs.
Like the Chevy Volt, this machine employs the use of Green Technology. There are no hydraulics on the machine and the motors used require less energy than more conventional machines. Additionally the coolant filtration system uses no disposable filter media.
General Motors is to be commended for its faith in a hometown manufacturer to get the job done.
C & B Machinery designs and builds production grinding equipment for automotive and other high volume grinding applications. In addition to its own line of double disc grinding systems, the company rebuilds and services other major brands of grinding machines. C & B is privately owned and employs a highly trained staff of service technicians, machine builders as well as in-house control and mechanical engineers.
Mr. Chris Cox