Original Date: 09/20/2004
Revision Date: 01/18/2007
Best Practice : Inspection
Forest City Gear’s production gears are inspected in its inspection laboratory to ensure they are being manufactured to the required parameters and tolerances to meet customers’ needs.
One of the factors that contribute to the quality of any gear, whether generated by shaping, hobbing, or grinding, is having and using high quality, calibrated inspection equipment. Forest City Gear (FCG) has three coordinate measuring machines (CMMs) dedicated to gear inspection and a surface roughness tester for inspection measurements for all sizes of shaped or hobbed gears. Areas of measurement include, but are not limited to, gear profile, lead, spacing, run out, root diameter, internal diameter, external diameter, and surface roughness. FCG’s customers receive reports of all inspections, and the company keeps copies of all inspection records for 10 years.
Currently, FCG uses an industry approved statistical sampling plan for the amount of gears to be inspected based on the lot or batch size of the job order with higher frequency for higher quality. Current in-process shaped or hobbed gears are inspected to Level IV and occur on orders from as small as one part to more than 500,000 parts (one part can consist of multiple machined sections). The inspection process begins on the production floor at one of the shapers or hobbers. Machine operators are notified by the Traveler when to take the part for inspection. The part is removed from the production floor after it is machined and allowed to cool to ambient conditions. It is delivered to the laboratory for inspection, and then mounted in the jig or holding fixture on the CMM table. A carbide tipped spherical probe (stylus) is used as the measuring medium. The machine’s software draws a profile between pre- programmed tolerances of the part as the stylus passes over the material. The stylus is verified at least once a day using a master gear and a calibrated set of shop grade gage blocks to a tolerance of ± 20 micro inches. For surface roughness inspection, the part is mounted on the test rail, and the stylus is drawn over the surface of the shaped or hobbed machined section and displayed on the graphics screen with the parameters of the surface finish.
FCG’s Gear Lab is separated from the production floor, has its own independent temperature control system, and the large CMMs are secured to the floor by resilient mounts preventing any unwanted backlash or vibrations that could affect the measurements. The CMMs are re-calibrated annually by an outside calibration activity using calibration standards that are traceable to the National Institute of Standards and Technology (NIST) to tolerances of ± 10 micro inches.
FCG is transitioning from its current ISO 9001:2000 compliancy to AS 9100 compliancy. Since inspection greatly contributes to the quality of manufacturing, FCG will make a smooth transition to be AS 9100 compliant because its inspection equipment is some of the best in industry and its measuring tools and test equipment are traceable to NIST.
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