Case Study: The Optimized CMM
October 1, 2007
Reliable and consistent performance is essential in any industry to ensure customer satisfaction and increase the pool of high-yield customers. For Pratt and Whitney (East Hartford, CT), a manufacturer of aerospace components, reliable and consistent performance of its coordinate measuring machines (CMMs) proved to be a decisive factor in achieving high customer satisfaction levels and operating profitability.
Pratt and Whitney, a United Technologies Company, designs, manufactures and services aircraft engines for a variety of customers, including commercial airliners and the military. Its North Berwick, ME, parts center employs about 1,622 people and manufactures a variety of jet engine components ranging from bearing housings to stators, airfoils and vanes. The plant’s primary role within the company is to cost-efficiently produce high-volume parts.
At Pratt and Whitney, CMMs have been an integral part of the manufacturing process from the very beginning. Shortly after the facility opened its doors in 1979, the company purchased several WMM 850 CMMs from Carl Zeiss IMT Corp. (Maple Grove, MN) that were dedicated to the inspection of airfoils. Over time, the company added a number of new product lines such as bearing housings and blade seals, which required the addition of more CMMs, including a Prismo and an Eclipse from Carl Zeiss. “In 2004, our customers required us to certify our manufacturing processes,” says Marcel LaBrecque, project manager. “That’s when we started our process certification initiative.”
Time to UpgradeThe process certification initiative revealed that the existing CMM infrastructure, consisting mainly of older operating systems, outdated algorithms and touch-probing technology, had an adverse effect on accuracy and repeatability. A comprehensive gage repeatability and reproducibility (GR&R) study was performed on several CMMs to assess their measuring capabilities. While the CMMs maintained accuracy, results varied from machine to machine. “We were not able to provide our customers with consistent and reliable measuring results,” says LaBrecque. “The tighter the tolerances that we had to meet, in one instance ±0.0005 inch, the more challenging it became in terms of getting correlation between one system and another. We were just not able to cost effectively achieve these accuracies with touch probing technology.” LaBrecque knew that it was time to upgrade and that this step involved additional research and testing to justify the investment.
Success with ScanningLaBrecque had heard about the benefits of Calypso CAD-based software and scanning technology from Carl Zeiss through literature and online forums. He decided to have Carl Zeiss perform a GR&R study on one of the parts using Calypso software combined with scanning technology. The study produced significantly better results than the existing CMM infrastructure. In addition to a drastic improvement in CMM resolution of almost 500%, the report also showed that the desired accuracy of ±0.0005 inch could be achieved with Vast scanning technology-previously one of the biggest challenges when using touch-probing technology. With Vast, operators are able to check a wider range of feature tolerances including form, size and location.
The decision to upgrade the CMMs was made, and at the beginning of 2005, the first MC850 was upgraded to Vast scanning technology and Calypso. The remaining 12 CMM retrofits were completed by March 2006.
The success was not only evident with the conversion to scanning technology and Calypso software, but also with the purchase of the Contura CMMs with the Rotating Dynamic Sensor (RDS) head. “In the past, we had been using the PH9 and PH10 probes which have 7.5-degree increments. The RDS offers 2.5-degree increments and gives us increased flexibility and allows us probe features that previously we were not able to inspect,” says LaBrecque.
As far as the software is concerned, there are several reasons why LaBrecque champions Calypso. But the most important one is its ease of use. “I’ve been involved with CMMs for the past 27 years,” he says, “and this software has to be the most user friendly that I’ve experienced. This is important to us, because at our company we don’t have programmers to write code. We have layout inspectors who know how to inspect parts and the CMM is a tool they use to do their job. With Calypso, you put a part on the CMM, start scanning and by default you generate a measurement plan. With object-oriented programming, our operators use the features of the design drawing. It is possible to make corrections and changes to existing measuring programs, as well as generate partial measuring runs from an entire CNC program. It has been very successful with our workforce, which is contingent to our success.”
Pratt and Whitney now uses 30 CMMs to inspect the wide range of parts it manufactures, operating in four shifts including weekends. Within a month, 1,200 parts are filtered through the quality area. “Sometimes we inspect multiple parts such as a series of bearing housings,” says LaBrecque. “They require 100% verification, something that can really bog down our process. So, the CMMs are a definite advantage. In addition, we also were able to expand our measuring capabilities to the production floor. In the past, our quality assurance group primarily used the CMMs.
“The equipment we now have is reliable, but most importantly, our customers are happy. We showed them the actual data that we collected during the study, which included both the results prior to using Calypso and the improvements with Calypso. We proved that scanning technology is allowing us to improve the accuracy and repeatability on our measuring devices and, above all, provides them with consistent and reliable data,” says LaBrecque.
Benefits of StandardizingBecause of the success experienced with Calypso, LaBrecque is recommending an upgrade to every CMM at the facility, including all non-Zeiss CMMs. “The trend today is toward standardizing technology and software. The benefits of using common architecture include not only data consistency and reduced cost, but also flexibility and interoperability. With the standardization of our 13 Zeiss CMMs, we are starting to see these benefits,” says LaBrecque.
- Standardizing CMM technology and software gives Pratt and Whitney the benefits of data consistency and reduced cost, as well as flexibility and interoperability.
- VAST scanning technology and Calypso provide consistent, reliable CMM measuring results, even at tolerances that had been troublesome with touch-probing technology.
- CMM resolution improved almost 500%.
Carl Zeiss IMT Corp.