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:

• Unloads finish ground parts.
• Positions every part in front of a camera, which ensures the part, is oriented correctly.
• Places the part into an automatic gaging system that 100% inspects:
  • Pin end thickness
  • Crank end thickness
  • Step relationship
• 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.

C&B Machinery’s latest Non-Coplanar Connecting Rod grinding system does the work of three machines.

C&B Machinery of Livonia, Michigan has improved productivity and flexibility of their double disc non-coplanar connecting rod grinding system first introduced in 2009 for the Chevrolet Volt 1.4L auxiliary engine.

The first grinding system produced a stepped connecting rod from a parallel (or coplanar) rod. The 1.4L Chevy Volt connecting rod has a 1.2mm symmetrically smaller crankshaft end width, and both the pin and crank ends of the rod are ground in one sequence. At the time, the system was considered the most advanced double disc grinder ever produced by C&B.

This latest system, recently shipped to Eston Manufacturing Division of Linamar Corporation, is grinding a 1.8L connecting rod with a symmetrical reduction of the pin end of 3.8mm. As before, the challenge was to produce this part from a coplanar connecting rod in one operation. Stock removal from the pin end of the connecting rod is 5mm and stock removal from the crank end is 1mm. Previously, this connecting rod required three grinding operations to complete and the crank and pin end were ground on two separate machines.

C&B’s application engineers took the challenge to task developing a special tooling package and unique 2-stage grinding cycle which first rough grinds the pin end to a stock condition equal to the crank end. It then finish grinds the crank and pin end of the connecting rod simultaneously. Grinding the crank and pin ends at the same time produces much better symmetry between the two. Additionally the grinder easily exceeds Eston’s 1.67 Ppk requirements for size, parallel and flatness.

The grinding system also includes a post process gaging system with automatic feedback to the grinding wheel infeed servos providing automatic compensation for wheel wear. The gage also inspects step relationship between the crank and pin end faces.

The C&B model DG2H-SA/30 Connecting Rod grinding system has the ability to grind parallel parts, non-coplanar parts, pin end only or crank end only configurations with very simple changeover. This bodes well with today’s manufacturing requirements — lower production rates, better flexibility and a never-ending demand for lower machining costs per piece.

With models utilizing up to 42” diameter grinding wheels, large diesel connecting rods can also be produced in this manner.