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CMMs Stake Their Claim

Bruce Morey
By Bruce Morey Senior Technical Editor, SME Media

With the growth of new sensing methods for metrology, from lasers to X-rays, one might think the venerable CMM might be fading from view. Nothing could be further from the truth.

An eternal truth is that manufacturing will always push the limits on cost, performance, and especially quality. “Tolerances never get looser, they always get tighter,” remarked Gene Hancz, product specialist, CMM of Mitutoyo America Corp. (Aurora, IL).

That is one reason why the fixed-bed coordinate measuring machine, or CMM, has remained a vital tool. Even as new sensing technologies have entered the field of metrology, the CMM remains one of the most accurate tools available. They are mostly variants of the basic bridge-style CMM, according to Hancz, with a moving bridge that traverses over a part fixtured to a table and a probe that moves up and down. Scales in each axis determine position X, Y, and Z of the point. Articulating probes that rotate independently and rotary tables provide additional degrees of freedom.

Suppliers have also created many variants on the basic idea of the bridge-style CMM to meet evolving needs—and reduce cost. Take, for example, the horizontal arm CMM with a cantilevered probe attached to a single support. While automatic, extremely accurate machines that measure ever larger parts will easily grab attention, there is still a place for the humble, manually operated CMM equipped with a touch trigger probe, or even a hard ball. Another reason the CMM remains relevant is that the technology is getting better while the value increases. “When I started in the business, a small manual CMM might have cost the same as what you can get today in a computer-controlled CMM, with twice the accuracy and twice the measuring volume,” said Hancz.

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The Zcat, available through Fowler, sitting on the bed of a milling machine and measuring a part that is still clamped.

He reports that even simple manual CMMs remain popular, especially with smaller job shops that need to measure just a few parts at a time. “It is vital to purchase the right piece of equipment for the right application. Many times, people ask for the highest accuracy possible, which would be in our LEGEX series, capable of measuring almost a 0.25 micron. But these get very expensive, both in purchasing the machines and housing them in rooms where the temperature and humidity are tightly controlled,” he explained. They are necessary to a few applications, but not very many.

In fact, he thinks the biggest trend in the field is near-line or in-line quality measurements using CMMs. This led Mitutoyo to develop its MACH line of CMMs, designed for high-speed measurements in-line or near-line in conjunction with CNC machine tools. For example, the MACH-3A is a horizontal arm CMM optimized for high-speed measuring of long, cylindrical parts, such as crankshafts. The latest is MACH Ko-ga-me, an in-line CMM that can be configured either stand-alone or integrated into a workcell.

As CMMs move into production, monitoring their health becomes vital. This trend mirrors the evolving Smart Factory, and Hancz points to the MTConnect standard that Mitutoyo supports. “In my opinion, it is a fundamental technology standard for the future of in-line or near-line machine monitoring,” he said.

Growth and Skill Set

“There is still plenty of growth in the CMM market,” agreed Angus Taylor, president of Hexagon Manufacturing Intelligence (North Kingstown, RI). He concurred that growing quality demands are boosting the CMM market. He also observed that many of the CMMs Hexagon is selling are placed in production environments, though placement in quality rooms is still a big part of the market.

“But, aside from its use in production, the biggest concern we have is the skill set of [users]. We have customers who would like to acquire more equipment, but do not have the people with the skill sets to write programs for them,” he remarked. Like any good manager, he sees opportunity rather than crisis in that observation. “That means more automation and, frankly, opportunity for us to help customers by writing the inspection programs for them,” he said.

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Mitutoyo’s MACH Ko-ga-me is a compact, three-axis CNC CMM that can be integrated into an automated cell for in-line production or configured for stand-alone applications. Modifications can be made on the fly and when critical changes in the manufacturing process occur.

Automation could include robotic loading of parts into and out of CMMs, but he also ties it into information that could feed the process itself. “One of the key elements here is our Q-DAS software,” he said, referring to the statistical software company Hexagon acquired that analyzes data from metrology devices for decision-making. “With that, we start to monitor things like tool wear and more specifically [data] on a feature, and track data from specific features,” he said.

In response to both production requirements and the need to make CMMs easier to use, in May Hexagon announced its new Global S CMM platform, which debuted at the Eastec show. According to the company, the Global S is the initial offering in Hexagon’s Enhanced Productivity Series (EPS). The new platform features smart technologies such as user experience (UX) enhancements, measurement software and advanced green options. The EPS platform simplifies the creation, execution and analysis of measurement routines, and the inspection process is faster because the Global S platform is fully integrated with iPC-DMIS CMM software for the collection, evaluation, management and presentation of manufacturing data, according to Hexagon Manufacturing Intelligence.

Other trends that Taylor sees are the growing emphasis on noncontact metrology and integration of equipment into smart or interconnected factories. “Our new optical probing system for use on CMMs is dramatically improving throughput for, say, turbine blade and blisk inspections,” he remarked. “In all areas, with noncontact technologies we will be collecting data faster and gaining a better understanding of features and of individual parts.”

Multitasking and Application Specific

“One trend I see across multiple industries is people wanting to be more productive with their CMM,” said David Wick, product manager for Carl Zeiss Industrial Metrology Technology LLC (Maple Grove, MN). This means measuring diverse parts on the same equipment, maximizing the investment. A key element in this strategy is employing the maximum number of sensors available on CMMs. Today, in addition to the venerable touch trigger and scanning analog probes, CMMs are now often equipped with laser line scanners and even surface roughness sensors. Zeiss introduced a new confocal white light sensor for its Accura class of CMMs in 2016.

With CMMs growing in flexibility, they may start to supplant devices purpose-built for a specific measurement, such as form measurement. “On our latest version of the Prismo CMM, equipped with a rotary table and latest Calypso software, you can now take form measurements of many different shapes, such as cylinders or ball bearings,” said Wick. Another common application is reverse engineering, using a laser line scanner to measure a part whose CAD model is nonexistent, then create a model from the point cloud. One system, many measurements. This is especially useful to small or medium-sized enterprises who are frequently tasked with multiple jobs or low-volume parts.

Among larger organizations, he sees the ways CMMs are used evolving in different ways. These customers want more application-specific installations that are interconnected with the factory and world around them. “We are getting more requests for automation, robot loading and palletization,” he explained. “People want to measure 10 parts at a time instead of one, requiring more applications knowledge.” A good example is using the Zeiss Gear Pro software, an option for its Calypso software, to create a gear-specific installation. Gear Pro will measure cylindrical, bevel, and worm gears as well as rotors, and also measure the hobs that cut them. Other packages include turbine blades or erosion electrodes.

He also observed, like others interviewed, that CMMs are more accepted on the shop floor. For harsh environments, offerings like the DuraMax HTG with its IP54 rated cabinet that maintains accuracy over a wide temperature range—15° to 40°C—increases its utility. For integration into automation, Wick also noted that Zeiss software now communicates directly with robot loaders in any robot vendor’s native language.

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Some CMMs are more capable for the shop floor, such as the DuraMax HTG shown here coupled with automation. Its IP54 rated cabinet that maintains accuracy over a wide temperature range of 15°C to 40°C.

This brings up the issue of data security. The company announced in May that it is partnering with Cisco to build a secure data transmission platform to connect Zeiss devices (e.g. measuring machines) in the field to higher-level systems within the Industry 4.0 environment. The goal is integrated security. This involves the joint development of a solution for monitoring Zeiss measuring machines. It will allow the fast provisioning of global services, such as remote subject matter expert and help-desk support.

A New Approach to CMM — Portability

While bridge-style CMMs and their variants are doing nicely in the marketplace, thank you, there is always room for variants. The programmability of a CMM from a CAD file has always been one of its hallmarks, but even the smaller versions are not particularly portable. Enter the 30 lb zCat portable CMM from Fowler High Precision (Auburndale, MA). Looking something like a coffee caddy with an extension arm equipped with a Renishaw TP20 touch trigger probe, the device is both portable and programmable.

A key difference compared to other CMMs is that it is a radius machine, with two axes rather than three. It has a measuring volume of 700-mm radius (about the center axis) by 250 mm in height. Its accuracy specification is then in two dimensions: [3.0 + D/100-mm (radius)] microns and [5.0 + L/100 mm (linear)] microns. “Unlike other portable devices, this is a truly direct computer controlled portable CMM,” said Jeff Petersen, international sales manager of zCat LLC, the recently formed producer of the machine (partially owned by Fowler).

Why a portable and programmable CMM? For Fowler, it was the next logical addition to its metrology hand tool catalog, according to Petersen. “Our typical tool was a single axis or linear scale type device, really good for what they were meant to do but simply not able to do the detailed 3D measurements a typical CMM can do,” he explained. “A CMM, on the other hand, is usually relegated to a special room and operated by a highly trained person.” Their dream was to bring a CMM right next to the CNC machine making the parts, operated by personnel with far less training in programming CMMs.

Since its introduction in 2014, the device has been “going well,” according to Petersen. “Some customers are buying their second and third machine,” he said.

Process Beyond CMMs

Renishaw’s invention of the touch-trigger probe is often credited with starting the CMM revolution back in the day, enabling direct computer control while increasing accuracy and repeatability over the hard-ball probes it replaced. Since Renishaw is a (key) component supplier to the metrology world that includes—but is not confined to—CMMs, Denis Zayia has a unique perspective as vice president of sales and marketing, and former CMM business manager for Renishaw LLC (West Dundee, IL). “There is a lot more focus today on metrology being the driver to understanding processes, providing feedback for control of variables and to verify final outcome,” he observed. Renishaw probes have now evolved into an independent five-axis measuring system, the REVO, which delivers high-speed scanning, noncontact inspection, and surface finish analysis on a single CMM.

He believes there is a place for data acquisition and monitoring throughout the manufacturing cell, including the machine tool, the CMM in the quality room, and flexible gages on the shop floor. While gaining in importance on the shop floor, CMMs have traditionally been viewed as a bottleneck. “With an appreciation for the whole process, you need to avoid allowing CMMs to be that bottleneck,” he said. “The five-axis system is designed to overcome this. On-machine probing can have its challenges. You principally want your machine tool to be cutting metal or otherwise creating parts,” he said. In the past, it typically has not recorded data, losing the history of the measurement. But today’s software has overcome this.

Each component—the machine tool, the CMM, and the flexible gage—has its respective role to play, and Renishaw provides probes and equipment for each phase. Its Equator gaging system was built with this “whole process” in mind. A quality room CMM is often best used in mastering a part for use on the Equator gage, which resides on the shop floor next to the machine tool and is immune to temperature variations as opposed to the CMM.

“A balanced and efficient approach is required when establishing workload to each component based on familiar criteria,” he said. “Expensive, low-volume parts can be inspected on the machine tool itself. High-volume parts are better off inspected and mastered on the CMM and then remastered on the flexible gage. Each additional part is then compared to the known master with the offset data being fed back into the machine tool. The balancing act results in increased efficiency, throughput and cost savings.”

Intelligent Manufacturing

With his unique perspective, how does Renishaw’s Zayia see the future? “A factory with direct process control and intelligent manufacturing, with decisions being made on the shop floor based upon the data collected. In addition, an increase in additive manufacturing along with related improvements in throughput, metrology and availability of additional materials,” he said.

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