New components call for new processes.

With new components often come new processes. When the Visteon plant in Connersville, IN, was assigned production of scroll compressors for automotive climate control systems, it turned to CIMTEC centerless microfinishers from IMPCO Machine Tools, Lansing, MI, on two critical components.

At the heart of the new high-RPM scroll-type compressor is an eccentric crankshaft and bushing. At Visteon, a North American source of these parts for Ford Motor Co, Detroit, MI, there are eight classes of shaft and bushing assembly sizes with 4[micro] difference between each class. The bushing diameters must be precisely matched to other compressor components in these size ranges.

The scroll compressors are for the Connersville plant, which is to ramp up to 1 million bushings and shafts each year.

Visteon was looking for a process that could economically handle millions of parts at high production rates while consistently meeting journal surface texture and geometry specs. Seeking a consistent seal surface finish on the eccentric shafts and superior load-bearing surface bushings for the compressors, Visteon decided to invest in two CIMTEC Model 50 centerless microfinishing machines equipped with the GBQ microfinishing process.

The abrasive-tape based CIMTEC machines maintain necessary production rates and improve surface texture within predetermined classes. Available only through IMPCO, the GBQ microfinishing process is specified for many parts, such as crankshafts and camshafts, that must precisely, continually, and reliably transfer power and torque.

Visteon specifications for the eccentric bushing--a bearing surface--required surface finish to be improved to 8[micro]" Ra from an incoming measurement of up to 16[micro]" on the journal; roundness was to be improved at least 30%, while straightness and taper had to be maintained. Stock removal is expected to be less than 0.0002" on diameter for the bushings. The shaft must have a seal surface, so it has a no-lead (straight-line) microscratch specification, 0.8 Rz DIN to 0.32 Rz DIN. This allows it to rotate without lubricant being pushed or pulled into the compressor body by turning or grinding lines left on the shaft by previous operations.

The GBQ process uses a noncompressive, coated abrasive film backed by patented nonresilient tooling. This assures full, consistent part/abrasive contact throughout the finishing cycle. The film is automatically indexed after each cycle, presenting fresh abrasive to each workpiece, helping assure that consistent finish specifications are achieved.

Used with consistently applied coolant, pressure, part rotational speed, and tooling oscillation, the patented GBQ process used in the CIMTEC machine reliably improves shaft surface texture, roundness, and straightness to predetermined specifications.

To accommodate varying production requirements, the CTMTEC machine's process parameters--including shoe pressure, oscillation frequency and stroke, drive roller speed, cycle duration, and amount of abrasive tape index--are fully adjustable.

In operation, the scroll compressor shafts are carried into the CIMTEC on a small pallet and mechanically pushed onto the drive rollers which rotate the parts. As the parts turn, the abrasive film is pressed onto the diameters for a specific time and at consistent pressure. At the end of the cycle, the parts are rotated out of the work area by a transfer mechanism, and onto unload automation. The total cycle is 16 sec, during which the parts are finished, ready for gaging, washing, and final assembly.

Visteon completes two bushings at a time on one machine and two shafts at a time on the second machine. This has helped it improve required throughput to easily meet demand.

When equipped with a standard integral coolant supply and filtration unit, and electrical enclosure, the Model 50 can be located on the shopfloor as required.