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quality improvement


cycle time is not adversely impacted because the workpiece is off the ma- chine before it’s measured. In the past, this advantage was offset by the fact that any process anomalies discovered by the gage are likely to be present in more than one high-value part because of the time lag between machining and inspection. In modern gantry loaded gaging systems, however, this is no longer the case because inspection time is a small fraction of machine cycle time and workpieces are not accumulated prior to gaging. In a modern system there is nearly always time available to generate pro- cess compensation signals before a new machining cycle begins. Lag time between inspection and compensation may still be a consideration, however, when adding an end- of-line gage to an older, conveyor-based system. Another historical limit of end-of-line solutions was that


In this view from inside of the machine tool, a dual-diameter WRG bore gage is inserted into the spindle, with the part fi xture visible below. It is possible to have multiple gages stored in the toolchanger for measuring different size diameters.


they introduce a single point of failure into the system. If the gage is damaged, or out of use for any reason, nothing gets inspected until it is repaired. The user was then faced with the no-win decision of either shutting down production or taking the risk of producing parts while the gage is repaired.


What Happens When the Gage Is Bypassed? Here again, modern systems are suffi ciently robust that this is no longer a practical disadvantage. Even without the end-of-line gage, today’s machines and systems are suffi ciently stable and robust that they can reasonably be expected to continue producing good parts for a time while the gage is bypassed. That period is likely to be short since a modern end-of-line gage will be highly modular permitting lit- eral “plug-and-play” replacement of components in minutes. The third traditional downside of an end-of-line solution was a lack of fl exibility to handle part changes and/or part families without extensive and costly modifi cations. Once again, technology has substantially overcome this limitation. The Marposs M125 Flex is an example of this. CNC servo technology lets it accurately position the gage plugs to handle families of parts and Wide Range gaging capability.


Where bore locations change in addition to bore sizes, changeover consists of selecting from previously program- med gaging and calibration cycles, while multiple size mas- ters are already in place. Thus, the end-of-line gaging ma- chine can check batch-of-one parts without intervention. End-of-line solutions still constitute the lion’s share of high-volume production gaging applications, but they are not the only choice for a modern, cellular manufacturing system. Putting the gages in the machine is a viable alternative.


The Gage in the Machine A modern gage is sized to fi t the automatic toolchanger of the CNC machines used in automotive manufacturing. That makes it easy to incorporate the gaging routine into the over- all process. It also makes it possible to implement a gaging solution that requires no additional fl oor space and utilities in an already cramped manufacturing environment. An in-machine gage can check a workpiece while it’s


still fi xtured exactly as it was machined to virtually eliminate variables introduced by factors like variations in clamping force and temperature changes. Repairable anomalies can be fi xed immediately while on the machine since the part is still fi xtured, and at worst only one scrap part is produced. An in-machine gage almost always costs much less than a special gaging machine designed for end-of-line measurements


44 — Motorized Vehicle Manufacturing 2016


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