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Articles About SPC
Today, as part of filling a typical gear hobbing or shaping machine order, engineers are required to perform an SPC acceptance test. This SPC test, while it is contractually necessary for machine acceptance, is not a machine acceptance test. It is a process capability test. It is an acceptance of the machine, cutting tool, workholding fixture, and workpiece as integrated on the cutting machine, using a gear measuring machine, with its work arbor and evaluation software, to measure the acceptance elements of the workpiece.
Statistical Precess Control (SPC) and statistical methods in general are useful techniques for identifying and solving complex gear manufacturing consistency and performance problems. Complex problems are those that exist in spite of our best efforts and the application of state-of-the-art engineering knowledge.
You're already a veteran of the computer revolution. Only you and your controller know how much money you've spent and only your spouse knows how many sleepless nights you've had in the last ten years trying to carve out a place in the brave new world of computerized gear manufacturing. PC's, CNCs, CAD, CAM, DNC, SPC, CMM: You've got a whole bowl of alphabet soup out there on the shop floor. Overall these machines have lived up to their promises. Production time is down, quality is up. You have fewer scrapped parts and better, more efficient machine usage.
Part I of this paper, which appeared in the January/February issue of Gear Technology, described the theory behind double-flank composite inspection. It detailed the apparatus used, the various measurements that can be achieved using it, the calculations involved and their interpretation. The concluding Part II presents a discussion of the practical application of double-flank composite inspection -- especially for large-volume operations. It also addresses statistical techniques that can be used in conjunction with double-flank composite inspection, as well as an in-depth analysis of gage R&R for this technique.
A common goal of gear manufacturers is to produce gearing that is competitively priced, that meets all quality requirements with the minimum amount of cost in a timely manner, and that satisfies customers' expectations. In order to optimize this goal, the gear manufacturer must thoroughly understand each manufacturing process specified, the performance capability of that process, and the effect of that particular process as it relates to the quality of the manufactured gear. If the wrong series of processes has been selected or a specific selected process is not capable of producing a quality part, manufacturing costs are greatly increased.