Process Forming Systems (PFS) manufactures a number of high-precision ceramic tools for the metal container industry requiring complex inside and outside profiles. This includes necking dies, punches, doming tools and a number of tools for can end manufacturing. A critical component in the quality of aluminum can manufacture is tooling inspection.
Many of these tools have highly complex contours. The shapes consist of multiple radii and tangent angles. It is critical that sizes be maintained and blends between different radii be consistent for high-quality can production. Three tooling profiles critical to the quality of can production are the punch profile, doming die profile and the necking die profile. Necking dies have the most complex geometries and, depending on the can, there may be three to ten different profiles.
As can makers are speeding up lines and reducing metal gauge, the demands on equipment, particularly tooling, are increasing. Changes in necking diameters from 206 to 204 and 202 require ever more precise control of necking die geometries. Previous profile specifications of 0.001 inch to 0.002 inch are now 0.0002 inch to 0.0005 inch. These tolerances were beyond the capabilities of PFS's existing inspection methods. However, improved tooling quality can mean big paybacks for can makers by reducing spoilage and downtime. PFS needed the in-house capability to provide that kind of quality to their customers.
Through 1994, PFS's necking die inspection process was to form a cast of each die and inspect the casting with a 50× optical comparator, with which they could only measure to a 0.001 inch profile with confidence. This method also has a number of other drawbacks.
Because this method is labor intensive, each part must be individually cast and inspected. Even at 50×, the comparator has limited resolution, leading to a large degree of subjectivity and interpretation. Also, because they were not actually examining the die itself, reliability of the inspection could be compromised by errors in the casting process. And there was no hard copy of the results they were basically comparing a shadow to a line on a transparency, the line representing the desired shape. This in turn means they lack documentation for customers, and they have to reinspect the dies upon delivery.
Finally, optical comparators and conventional tracers are 2D machines. Tracing machines are limited in that they can only show a single element of the part, and cannot look at the profile as a 3D surface. Most of the parts PFS processes with a profile tolerance specify with a profile of a surface, which to correctly verify must be inspected as a 3D surface related to a datum surface.
PFS found all too often that it had to use an off-site metrology lab that had a 3D scanning CMM, which could also measure the profile tolerances to 0.0002". But this was time consuming and expensive. PFS grinding machines often sat idle while waiting for inspection results. Also they were forecasting the need to inspect hundreds of necking dies in 1994 and 1995. Therefore, it became imperative that they develop an in-house capability to inspect critical profiles and be able to provide real-time feedback to the grinders.
Roger Casto, formally head of Coors Metrology and a consultant to PFS, convinced the company to consider buying its own scanning coordinate measuring machine (CMM). He believed that the right CMM could eliminate a lot of drawbacks of the comparator inspection in the process. A scanning CMM allows 3D profile inspection, as well as the flexibility to perform many other types of measurements. Diameters, lengths, concentricity and roundness all can be inspected along with profile in the same setup. A CMM is also the only practical way to inspect the complex and irregular geometry found on tools such as score knives.
The CMM had to have 3D continuous-contact scanning to measure the contours and complex geometries of the dies, especially the necking dies. It had to have sufficient machine accuracy to inspect profile tolerances to the level of 0.0002 inch. It had to be able to run unattended to free up the inspector for other duties. It had to have hard-copy output for customer documentation. And it had to cost less than $150,000.
PFS considered scanning CMMs built by a number of major suppliers but all were eliminated due to cost or machine capabilities. Mr. Casto brought PFS's attention to Electronic Measuring Devices, Inc. (EMD) of Flanders, New Jersey. EMD had recently started building its own continuous-contact scanning CMM utilizing its patented Sceptre system. EMD had been providing this system with its continuous-contact analog scanning probe and software to CMM OEMs, and selling it as an upgrade/conversion kit to companies with any motorized CMM.
Their new machine, known as the Legend IMC (integrated metrology center) was well within PFS's budget, had the accuracy and 3D scanning capability they were looking for and met every other requirement on their list.
PFS took delivery of the Legend IMC in January 1995 and it has been in use ever since. To date, the CMM is living up to its promises and their requirements. It can run unattended, allowing it to run during off shifts or load it up at night and come back in the morning to look at the results. It is allowing PFS to legitimately measure to the tolerance levels requested by customers, and it supplies hard copy documentation for customers, which reduces their need to reinspect PFS's tooling.
PFS found that, because the Legend IMC measures the die itself instead of a cast of the die, it reduces the inspection time on necking dies by 25 percent, and has greatly improved the accuracy and reliability of the measurement.
The CMM also helped to improve the manufacturing process of the dies themselves. The cycle time is fast enough so that PFS can use it for in-process verification. Operators don't have to wait until the end of a run to complete the inspection. In effect, it allows PFS to correct things as they come up during the manufacturing process.
PFS also found that the hard copy documentation is useful in communicating required corrections to the machine operators, instead of trying to remember what was seen visually on a screen.
What surprised PFS most was the flexibility of the Sceptre system software. The software had a straightforward programming style and allowed a lot of customization, especially in formatting report output. It didn't force the user to turn out canned reports as some software packages might require.
Essentially, PFS wanted a continuous-contact scanning CMM to measure precision ceramic tooling because of complex geometries and tight tolerances. With the increased emphasis on quality control, and the certification requirements of ISO 9000, it was very important to have hard documentation of the inspection results. The Legend IMC met and surpassed what PFS was looking for in a continuous-contact scanning CMM. MMSblog comments powered by Disqus