At the Michigan facility of the Global Engine Manufacturing Alliance (GEMA), IMPCO Machine Tools can boast that it is one of two American machine tool builders involved in the cooperative venture of DaimlerChrysler, Mitsubishi, and Hyundai.

The Lansing, MI, manufacturer has delivered two flexible two-station microfinishing systems for crankshaft polishing to GEMA’s Dundee facility.  The plant, and others like it in South Korea and Japan, will produce a family of different-size four-cylinder engines.

The IMPCO microfinishing process and statistical process control will be used to guarantee correct circular geometry, straightness, and surface finish of main and pin journals and other surfaces on crankshafts for the 1.8L, 2.0L, and 2.4L engines. The result will be reduced manufacturing cost and consistent part quality for the engine manufacturer.

According to a company spokesman, microfinishing—the final operation on the crankshafts before assembly—will eliminate the need to match journal diameters to bearings and will help improve engine performance because of the ability of the process to consistently meet tight part specifications.

IMPCO’s WORLDSTAR Model 1640 microfinishing systems are capable of production rates of 60 parts per hour with IMPCO’s patented FlexShift part-transfer solution and up to 120 parts per hour with conventional tooling. The IMPCO 1640 series microfinishers can accommodate crankshafts up to 760mm (30") in length with a maximum swing of 203mm (8").

The FlexShift linear synchronous transfer system within the two-station microfinishers not only costs 50 percent less and uses 20 percent less floor space than a gantry-type transfer system but also installs more rapidly. The internal transfer can be loaded manually or with automation and provides a 25 percent faster part transfer time than gantries.

The IMPCO systems are designed to GBQ Level II microfinish, with optional size control, five main journals and four pin journals, and conventionally microfinish one oil seal. GBQ, standing for Generating Bearing Quality, is a proprietary metal removal process that enables manufacturers to accurately remove an amorphous material layer of just a few microns that remains on the crankshafts after grinding. Parts also typically exhibit geometry and form errors as a result of previous processes and differing material hardnesses.

The IMPCO process allows very close control of surface finish, bearing ratio, geometry, and size of bearing journals. IMPCO Size Control utilizes in-process gaging to control the amount of material removed from the parts in each cycle, ensuring correct bearing size.

Considered the world’s tightest tolerance process for material removal, GBQ microfinishing uses a non-compressive, coated abrasive film backed by patented, precision-shaped non-resilient tooling for full, consistent part-to-abrasive contact. The film is automatically indexed after each cycle to present fresh abrasive to each workpiece and thereby help to achieve consistent finish specifications.

Used with accurately applied coolant, pressure, part-rotational speed, and tooling oscillation, the GBQ process reliably improves shaft surface texture, roundness, and straightness to predetermined specifications, as well as the tightest tolerances in automotive manufacturing today.

Following the process
Crankshafts are transferred from the grinding operations and automatically loaded into the first station. The part is centered between a fixed-quill headstock, which provides servo-driven part rotation, and a pneumatically-operated tailstock.

The abrasive microfinishing film is applied by horizontal arms, which close around the part and press the abrasive against the crankshaft at predetermined pressures for a specific time to achieve the desired surface finish and geometry. Independent of part rotation, the part is also oscillated while rotated.

Importantly, within each station, the crankshafts are FlexShifted left to right to present journals to the tooling, saving time, floor space, and machine cost. This procedure also allows the manufacturer to use less tooling to complete each part without inhibiting required production.

The sequence of operations in both stations in the machines proceeds this way after the machine is loaded with customer automation: advance headstock and tailstock, advance microfinishing arm slide, close microfinish arms, GBQ microfinish with Size Control, two pin journals, three main bearing journals, microfinish an oil seal surface; open microfinish arms, return arm slide and index film, then FlexShift to present the remaining two pin journals and three main journals of the crankshaft to the abrasive microfinishing film. A part-exchange shuttle between the two stations is accomplished with an IMPCO-designed transfer.

The second station proceeds likewise: advance microfinishing arm slide, close microfinish arms, GBQ microfinish with Size Control two pins, three mains, open microfinish arms, return arm slide and index film, return headstock and tailstock, and microfinish the remaining two pins and three mains.

Within each two-station machine, the crankshafts are finished to GBQ Level II ready for assembly.

Checking the results
Surface finish achieved on main and pin journals was statistically held to a part-print spec maximum limit of 0.15mu Ra with a process capability of 1.33Cpk. Journal parallelism, roundness, straightness, waviness, and other attributes are consistently within part-print allowances and much improved over incoming conditions.

Manufacturers of precision shafts are increasingly using microfinishing to achieve extremely tight part-surface finish and geometry specifications required for many products from pumps and compressors to automotive engines and transmissions. IMPCO microfinishing process is widely used in the auto industry to improve the geometry and surface finish of crankshaft bearings, increasing bearing life by increasing the contact area compared with conventional finishing.

All tooling maintenance is accomplished from a single location at the front of the machine. Microfinishing tooling is within easy, safe reach from the front of the machine, and operators can easily observe tooling. It is also designed to be simple to changeover or expand for future production needs.

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