techview
Data-Driven Quality Needs Quality-Driven Data
W
hen Henry Ford started building the Model T, com- ponents such as bearings and gears were often assembled with hammers or an arbor press. In the hands of a skilled worker who knew what a successful operation felt like either could produce an acceptable level of quality. That all changed when hydraulic presses replaced hu- man muscle with a push button so the operator never felt anything. Operator skill was replaced by gages and other postprocess inspection technologies. Direct Part Data from those inspections was the input
for the fi rst generation of data-driven quality technologies. The natural evolution of this approach focused on increasing manufacturing precision. The theory was that perfect compo- nents would yield perfect assemblies and eventually do away with the need for all that expensive postprocess inspection. It was a good theory, but it didn’t work out quite as planned. The problem is that the technology to meet those tolerances is not free. The ultimate result is a dimensionally perfect product that nobody can afford to buy. But there are hundreds of assemblies in the typical auto- mobile that don’t need that kind of precision at all. Neverthe- less, as long as they’re put together with a “dumb” hydraulic press there really isn’t a practical alternative. What was needed was a press that can “feel” how the components go together like Henry Ford’s skilled workers did. Fortunately, that technology exists. It combines a servo- driven electric press equipped with sensors and a computer to analyze the process and adjust it in real-time. Process Data is the input for the second generation of data-driven quality technologies. The technology is particu- larly useful in assemblies such as control arms which com- bine heavy-duty stampings with resilient components that are diffi cult to position accurately and repeatably. Manufacturers typically specify a fi nished geometry for the assembly, but leave the job of achieving it to the supplier. This is known as a phantom dimension.
Achieving a phantom dimension with conventional tool- ing is extremely diffi cult. The “press and hope” followed by
Glenn Nausley
President Promess Inc. Brighton, MI
the “measure, sort and re-work” approach is not very cost effective. But a Process Data driven “press-measure-press” process can improve the quality of phantom-dimensioned assemblies signifi cantly. In fact, it’s quite possible that the tolerances on the com- ponent parts can be loosened to reduce manufacturing costs with no impact on the fi nished product’s functional quality. That points the way to a third generation of data-driven qual- ity based on looking at quality the way a consumer does. A consumer doesn’t care how precisely a part was machined, they measure quality in different terms. Does it work? Does it “feel” like a quality product? And, does it last long enough to represent a reasonable value for the money spent?
Consumers don’t expect perfection and they are not willing to pay for it. Function is the consumer’s measure of quality and it ought to be the manufacturer’s as well. Functional Data is the input for the third generation of data-driven quality. This approach uses the intelligence of the servo/sensor/computer system to measure the function of the assembly while it’s being assembled instead of the force/ distance measure used in Process Data-driven operations. Riveting is an excellent example. Assemblies such as hood latches typically are made from stampings held to- gether with a rivet. Peen the rivet too much and the latch is stiff, peen it too little and it feels sloppy. By measuring the force needed to actuate the latch while the rivet is being peened by a servo-press it’s possible to produce consistent function even though the components have wide dimensional variations. The consumer gets a quality impression when the latch is used and the manufac- turer gets an opportunity to loosen tolerances and reduce production costs.
In a sense, the Functional Data-driven operation has re-
turned assembly quality assurance to its roots. But today the feel of a good assembly is no longer in the hands of a skilled craftsman, it’s in the intelligence of an electromechanical system that brings it a full step closer to perfection.
35 — Motorized Vehicle Manufacturing 2015
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