Case Study: Another Layer of Confidence in Quality and Speed

  • Apr 6, 2012
  • Pratt Miller

Reading Time: 5 minutes

With tighter tolerances and increased customer requirements, Pratt Miller turns to Zeiss quality inspection solutions.

Customers know they can count on Pratt Miller Engineering (New Hudson, MI) to quickly get quality products over the finish line. While Pratt Miller is well known for its commitment to motorsports—with design, fabrication and testing services on display through the General Motors factory American LeMans Series Corvette Racing and SCCA World Challenge Cadillac Racing teams—it is much more. Pratt Miller provides cutting-edge engineering and manufacturing solutions for clients in the motorsports, automotive, aerospace, commercial and military industries.

Pratt Miller started out as a small motorsports engineering and fabrication shop when it opened its doors in 1989, and has grown into an innovative solutions provider spanning several industry sectors. Since 2009, Pratt Miller has doubled its total sales stemming from both existing and new customer orders. With the addition of new employees, less time to manage customer orders, tighter tolerances and increased customer requirements it needed a more advanced quality inspection solution.

In March of 2011, Pratt Miller installed a Zeiss (Maple Grove, MN) CMM in its quality inspection lab to help meet those needs. The company had analyzed key factors, such as part volume sizes, target tolerances and available floor space, to determine that the CONTURA G2 10/12/6 with VAST active scanning would be the best solution for its new and growing requirements. Pratt Miller chose the VAST XT sensor for its fast scanning speed, allowing the company to gather more data and get better information.

Prior to the Zeiss CMM, Pratt Miller was measuring parts with several different sized portable measuring arms and various hand tools, including micrometers, bore and height gages. However, the company needed increased turnaround, repeatability and accuracy to meet its new targeted tolerances. Manual measurement with the portable measuring arms and hand gages required consistent technique to get consistent numbers and that was very difficult. Internal design tolerances were reaching 2 ten-thousandths-of-an-inch and some of its customers had tolerances of five microns on certain dimensions. With some pre-production runs increasing in size—with hundreds of a particular kind—repeatable results were critical.

The majority of the parts that Pratt Miller inspects are prototypes, such as clutch plates for electronically controlled limited slip differentials, suspension components for military vehicles and racecar chassis components. During development, these parts go through several revisions with the customer and have increasingly critical tolerances as they get closer to the finished, production stage.

Spindles for the various race programs, including Corvette Racing and Cadillac Racing, are examples of some of the more complicated parts that Pratt Miller designs and manufactures internally. These parts, often referred to as life-critical parts, are especially important and must be thoroughly measured. Spindles are measured on the CMM several times—initially during first article inspection, just before they leave for outside processing, a sampling when they return after heat treatment, and then one more final inspection after grinding operations are complete.

“Some more complicated parts, such as hubs, can take up to two months from start to finish, including all of the outside processing steps, which account for well over half of the processing time, and their associated inspection,” explains Frank Wilson, quality assurance manager at Pratt Miller. Speed and repeatable accuracy are critical to keeping long lead parts such as these on the tight timelines required by motorsports, as well as other industry sectors Pratt Miller has expanded into. About 12 parts a day on average are measured using the Zeiss CONTURA G2, which includes re-inspection of used parts, however, daily volume fluctuates significantly depending on current manufacturing programs and can be in excess of 100 parts some days.

The CONTURA G2 is saving Pratt Miller a significant amount of time with its inspections. For example, inspection time for an upright was reduced from two hours with the manual gages to 20 minutes with the Zeiss CMM. The company also can measure all locations and sizes on the part with only one measurement tool, versus 10 to 20.

The CONTURA G2 has been getting more use than expected recently because of increased awareness of its capabilities. Pratt Miller even had to get a second set of fixturing to prepare other parts waiting to be inspected. All operators are up to speed on the CALYPSO metrology software programs and Pratt Miller has received a lot more high-tolerance orders due to its new capabilities. “The local service and support has been great in helping us maximize our CMM use,” says Wilson.

One surprise Pratt Miller had was when it decided to use the CONTURA G2 to measure the suspension setup gages for racecars to better understand their impact on setup variations. In an effort to maximize setup consistency and performance, these gages were measured to determine the effect of assembly tolerance stack-ups on the accuracy of the gage. The CMM allowed the company to quickly find where improvements could be made.

One of the most beneficial features of the CALYPSO metrology software for Pratt Miller has been the graphical outputs. The company can now visually examine circularity and true position to locate and rework high spots into tolerance. “We couldn’t do this before. This visualization helps me quickly show coworkers what is happening versus having to draw multiple sketches,” states Wilson. “It helps us to avoid frustration and it gives us a much stronger handle on quality. For example, sometimes a part’s edge can become ‘tri-ovaled’ due to pressure from the chuck jaws. This part may be within specifications, but there is still room for improvement and the graphical visuals help us communicate that need.” Another benefit has been the mirror feature in CALYPSO, which they realized was excellent for dealing with left and right components on race cars. In some instances, it has saved Pratt Miller a day’s worth of programming time.

“The CONTURA is still new to us and we’re still realizing new ways to integrate it more and more into our environment,” says Wilson. “We still have a prototype environment and mentality, but we hope to do more statistical analyses with the CMM in the future.” While Pratt Miller manufactures some part runs that number in the hundreds, the majority are small batches of approximately 20 pieces, some of which are quite intricate. One current benefit is that it helps the company monitor machining operations, such as determining if the end mill is wearing out towards the bottom, based on if a bore is being tapered.

As Pratt Miller acquires new customers, it’s noticing more and more requirements, especially in the defense industry. Fortunately, the company’s specialty shop mindset has been adapting by adding new technologies and processes for these new requirements. Of course, Pratt Miller still anticipates many more motorsport projects in addition to providing engineering support, including development of newer, green prototypes. If it keeps growing at its current rate, the company could need an additional CMM, and a second shift.

The CONTURA G2 has given Pratt Miller a higher degree of confidence in its measurements and has improved communication with the graphical reports. “The CNC control automates part measurement, gives us complete confidence, and frees up our time to perform other tasks,” says Wilson. Customers often come to Pratt Miller because they are in a crunch and need a quick turnaround. The CONTURA G2 increases throughput without rushing the job, something that could have led to errors in the past. “Once you see how much more accurate and repeatable the measurements are with the ZEISS CMM, you realize that it is invaluable. It adds another layer of confidence to our day,” says Wilson.

Carl Zeiss Industrial Metrology

(763) 744-2409


About 12 parts a day on average are measured using the Zeiss CONTURA G2 and can be in excess of 100 parts some days.

Inspection time for an upright was reduced from two hours with the manual gages to 20 minutes with the Zeiss CMM.

The company also can measure all locations and sizes on the part with only one measurement tool, versus 10 to 20.

Michael Gibbons


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