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by Bill Wilde

Applications and operating modes for surface roughness analysis are changing. Although coordinate measuring machines are commonplace on the shop floor, you’re likely to see more surface-measuring devices appearing there, measuring surface roughness or contour practically in real time. Just as likely, you’ll see these same surface-analysis devices operating automatically, thanks to computer numeric-controlled technology.

CNC surface analysis has found a place in the manufacturing cells of first- and second-tier automotive suppliers, where the demand for automation and in-line operation is highest. Automated, in-line form measurement is also increasing among power transmission components and electronic parts manufacturers. It’s become a standard for industries that manufacture components with safety- or finish-sensitive requirements, have high added value or require 100 percent inspection. As a general rule, the higher the tolerances for metal-to-metal contact parts, the more in-line measurement you’ll find. The same goes for large parts because new technology has made it easier to bring the measurement function to the workpiece.

Develop, apply, automate

CNC surface roughness measurement isn’t a revolution in quality assurance; it’s just the next logical step in developing and applying surface-analysis equipment. For the same reason that manufacturers have moved coordinate measuring machines and other dimensional measuring devices to the plant floor--the need for real-time measurement integrated into the workflow--more surface-related measurements are showing up on part prints. The obvious benefits of in-line, automated inspection to process control are especially important given increasing demands for improved productivity and higher accuracies. If a print specifies a parameter to a given tolerance, then the faster and closer to real time you can check that parameter, the better--for quality, process control and the bottom line.

Several engine manufacturers have begun integrating surface-roughness testing into their engine-deck milling operations to ensure that mating parts seal properly in the finished engines. Originally, these manufacturers performed surface-roughness testing to satisfy ISO 9001 or QS-9000 requirements, but they’ve found that automated, in-line surface measurement can reduce the incidence of seal failures.

Why choose CNC form measurement?

The interest in automated form measurement is chiefly due to its higher speed and ability to execute complex measurement routines. Additionally, today’s measuring devices are robust and user-friendly. Good ideas tend to proliferate, and as the number of shop floor surface measurement applications increase, so does the range of instruments tailored to specific needs.

CNC-driven surface analysis is the result of increased productivity demands on the shop floor as well as the need to perform complex measuring routines on multisurfaced workpieces. The automotive market, its supply chain and the aerospace/defense industries require flexible but fast surface analysis equipment that can work in harmony with diverse manufacturing processes.

The near-machine models of today’s form measuring equipment don’t require the clean-room atmosphere and pinpoint temperature control of older models. The new breed of affordable shop floor surface- analysis instruments perform as well at 60° to 80° F as a 1990-era lab instrument in a temperature-controlled clean room. They measure at submicron levels right on the plant floor, next to a machining or turning center.

Given proper setup--which is critical for the CNC surface-roughness measuring machines--near-machine form measurements can be one-keystroke operations for each measurement. Typically, the time needed per surface measurement on the floor is about one-quarter or less than that required in the lab. Essentially, the cost disappears because operators make each measurement within the existing machine-cell cycle. Measuring with CNC machines is so quick and simple that it becomes feasible to increase the inspection frequency--even to 100 percent. With proper setup, near-machine form measurement requires no more skill than it takes to secure a part.

Surface analysis has also proved useful for nonmetallic parts more often associated with noncontact measurement. With the higher accuracies now possible with larger surface equipment, optics have partnered successfully with surface-roughness analysis. For example, the finishes on medical devices, especially implant components, are a critical attribute both to ensure FDA compliance and the devices’ long-term reliability.

When to make the change

If your organization adheres to an industry standard, the sooner you change to shop floor form measurement, the better off you’ll be. For example, companies that make automotive OEM parts with roundness, contour or surface-roughness callouts on their prints will need real-time form measurement to meet ISO 9001 or ISO/TS 16949 standards. And unless they meet those standards shortly, they’ll be bumped off the qualified suppliers list.

But aside from ISO 9001, ISO/TS 16949 and other mandates, deciding when to move to real-time form measurement is really up to you. The key is to look at the cost-benefit ratio in terms of your market’s quality expectations, i.e., the economic payoff to your operation in light of today’s lower prices. In some cases you should also look at product liability risks, especially if you’re running a job shop where customers’ prints specify form-related standards that you’re simply ignoring for now. Although at one time you perhaps couldn’t afford to use real-time form measurement, today the dilemma is whether you can afford not to.

How do you start moving toward CNC surface-analysis measurement? What equipment and functions should take the highest priority? From a process control standpoint, first look at the parameters you must measure. Multifunctional equipment such as Mitutoyo’s CS-3000, which can measure surface roughness and contour with one pass and using one detector, saves time and money through increased productivity and reduced setup time. From a part-function standpoint, however, the priorities are different. If you produce a lot of flat or contoured parts, moving surface measuring equipment out to the machine early in the production process will increase productivity over the long run.

Keep selection quick and simple

What should you look for when selecting equipment? First, remember that you’re buying a multipurpose, CNC-controlled production device, not a general-purpose lab instrument. Focus on the most cost-effective machine for the part-auditing task at hand. You’ll want to consider speed, versatility and flexibility. Also, focus on the most capable unit that will reliably achieve the resolution needed to meet present and anticipated print specifications covering form measurement. A resolution of 1 µin. is often more than enough for shop floor surface measurement. Consider multidetector equipment for productivity as well as ease of use.

Don’t waste money on resolution or neat features that you’ll never need on the plant floor. Dollar for dollar, you’re better off with focused, in-line form instruments placed right in the cells than with a single, overqualified instrument placed where it can be shared.

Sixfold growth in five years

What’s ahead for real-time surface measurement? Progressive manufacturers of high-volume finished and contoured parts are making room for surface analysis measurement solutions on their shop floors. They’re demanding machines with speed and the ability to automate complex routines. The leaders will invest in both benefits, the followers just the former.

Real-time surface measurement, especially automated solutions, are expected to expand at least sixfold during the next five years. This new technology is also expected to pay its way through product cost savings and increased yields, as well as ISO 9001 and ISO/TS 16949 compliance.

About the author

Bill Wilde is marketing manager for Mitutoyo America. He has been with the company for 10 years and is responsible for marketing strategy, branding and strategic planning. Visit the Mitutoyo Web site at www.mitutoyo.com.