Add Flexibility to Gaging Systems

May 5, 2003
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As the global trend toward outsourcing and decentralization of manufacturing continues to gather momentum, business managers and process designers alike find themselves facing a new set of challenges. Simply put, while production batch sizes for any given part get smaller and smaller, moving rapidly toward the "batch-of-one" ideal, customer quality demands are either at the "no-defects-ever" point, or soon will be.

Caught firmly between the batch-of-one rock and the no-defects-ever hard place, manufacturers must find new strategies to keep both their customers and their shareholders satisfied. In today's environment, those strategies nearly always include flexibility as a key component.

As used today, the term flexibility in manufacturing most commonly refers to the use of a single machine that can not only perform multiple operations on a workpiece, but can also accommodate a range of different parts within a given size envelope. Flexible systems tend to be cellular and nonsynchronous, as opposed to traditional in-line dedicated synchronous manufacturing systems. As such, they require different approaches to both production monitoring and process control.

Part of the process
In the past, gaging was often viewed as a parasitic cost that was included in a production facility only because someone required it to be there. But as flexible manufacturing takes hold, gaging technologies are increasingly being recognized as an integral part of any process, due to their dual role in process monitoring and control.

Process monitoring, the traditional inspection of in-process or finished parts, will help meet the no-defects-ever goal by weeding out bad parts. But only when gaging is coupled with a sophisticated capability for feeding information back into the process does it really make a contribution to overall productivity. With well-designed feedback and control, gaging systems can eliminate the production of bad parts, rather than merely finding them before they are shipped.

In a nonsynchronous, cellular environment, the gages need to be physically close to the production processes they are controlling to keep the feedback loop as short as possible. Even though statistical methods are used to accumulate information from several parts before generating a feedback signal, keeping the gages close to the process minimizes the potential amount of scrap that can be generated by an out-of-control process.

The most cost-effective integration of gaging into a manufacturing process is achieved by including the gage supplier in the simultaneous engineering team that is assembled for the project. Like other key contributors, the gage supplier should be brought on board early so that others can benefit from the supplier's experience and knowledge. Treating gaging as an afterthought is often a costly mistake.

Which technology?
The objective is to match the capabilities of the gaging system to the parameters of the manufacturing process. The first step in selecting the appropriate technology is to look at the cycle time and changeover time of the operation.

If cycle and changeover times are relatively long, a simple modular gaging system that can be reconfigured manually is often the most cost-effective solution. On the other hand, if the cell is highly automated and producing at high volume, a more sophisticated gaging system is probably required to keep it under control. It all depends on the process itself, the cycle and changeover times, and what the gaging system is expected to accomplish.

If flexibility is the only requirement, an advanced optical gaging system is often the best choice. Such a system delivers the ultimate in flexibility because it requires no part-touching components and can be instantly reconfigured.

One of the prices of that flexibility is that the optical gage requires clean parts to achieve accurate measurements. That, in turn, means it is usually not the best choice for use next to a machining center, unless the process also includes an intermediate washing and drying operation. A reconfigurable pneumatic or contact gage is usually a better choice for handling as-machined parts without difficulty.

In an automated, high-volume flexible cell using computer numerical control grinders to finish lobes and mains on a family of automotive camshafts, for example, an optical system might be most appropriate. In a turning or milling cell producing partially machined components that need to be gaged before they are passed to subsequent operations, a contact-electronic style gage is more likely to be the best choice.

The danger lies in the temptation to include technology for its own sake, based on the assumption that newer and smarter is always better. A simple electronic gage or even a machine-mounted touch probe feeding data to a processor with enough intelligence to meet application requirements is often all that is needed. The goal is to install just enough capability, and not more than is needed, to optimize and control the process.

Trade-offs
Understanding the trade-offs among flexibility, cost and operational compatibility is critical if the gaging system is to make an optimum contribution to the quality and productivity of the process. Flexibility is never free, and in many cases, a high-degree of flexibility is unnecessary where gaging systems are concerned.

For example, if a family of parts can be handled by manually moving or changing a few details on a gage, and there is ample time within the production cycle for the machine operator to make those changes, then flexibility -- at least in terms of gage automation--probably should not be a primary criterion in selecting the gaging solution. Likewise, if a limited number of similar features need to be measured, a set of simple manual gages may provide all the capability required, and at a much lower cost than a more complex automatic gage.

Similar trade-offs exist for the decision on whether to gage every part or to sample production every X number of parts. Tolerances also matter. Achieving flexibility in a measuring system that requires accuracy to tenths is achieved at a much lower cost than if accuracy is required in microns.

In sum, there are no one-size-fits-all solution to flexible gaging applications and there are no exact linear relationships that can be used to evaluate these trade-offs. Nevertheless, understanding the trade-offs and the long- and short-term implications of each decision is critical to the success of the application. The best way to manage this analysis is through a team effort that recognizes gaging as a key process element from the beginning of the project.

How to spend it
There is a bit of folk wisdom that says, "If the only tool you have is a hammer, eventually everything begins to look like a nail." The point is that limited options tend to result in less than optimal solutions. If any member of the team comes to the table with preconceptions about the best solution, or resource limitations that constrain the range of options that can be considered, the ultimate solution will almost certainly be less than optimal.

If the machine tool supplier can provide only vertical spindle machining centers, for example, it is unlikely that the potential productivity contributions of horizontal spindle machining centers or turn-mills will be adequately explored during process development. In the same vein, a gaging supplier who can provide only highly automated systems or only modular manual gages or only air-type gages will probably not be able to offer an objectively optimal solution for the specific process being developed.

Getting the most for your money means taking advantage of the best technology available to meet the needs of your specific process, regardless of what that technology may be. The wider the range of potential solutions any contributor to the process can offer, the more likely it is that the process will be optimally productive.

Realistically, getting the most for your money also requires making some educated guesses about the future. Flexible machines and processes are inherently reconfigurable, which means equipment purchased today for one application will likely be used in the future for another. To the extent possible, such future uses should be factored into today's decisions, even when they result in higher initial cost. Over the long term, the ability to reconfigure and reuse system components, including gaging equipment, will nearly always result in lower capital and operating costs.

Flexibility clearly is the way of the future for global manufacturing. Succeeding in this environment requires new ways of thinking about manufacturing systems as a whole and about the components from which they are built. Process monitoring--inspection and detection--is only part of the answer. The real success stories of the next decade will result from tightly integrated process monitoring and control systems that close the loop on quality. The best of these will be produced by simultaneous engineering teams in which gaging considerations play a strategic role from the beginning of the process development effort.

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