A coordinate measuring machine by Carl Zeiss Pty Ltd
has helped a top contractor land an order for a Mars Science Lab (MSL) project from NASA.
An MSL top-tier contractor, Andrew Tool has been employing coordinate measuring machines (CMM) in their manufacturing processes, but the new project demanded intricate measurements, tight tolerances and heat treatments. The short time frame was also an additional challenge for the company.
Carl Zeiss had already demonstrated its capabilities at Superior Tool, a sister company to Andrew by supplying a PRISMO CMM, according to President Bruce Hanson who decided to replicate and build on this capability at Andrew.
Andrew Tool is a unique machine shop with over 30 years of expertise in five-axis milling, EDM (electrical discharge machining) and grinding. Andrew Tool services customers in the aerospace, defence, medical and microelectronic industries, supplying parts that often require extremely tight tolerances.
Andrew Tool decided to go with a ZEISS coordinate measuring machine as the best option for the Mars Rover project, which required the company to manufacture actuators (gearboxes) for the next Mars Rover, Curiosity.
Designed to weigh over 10,000 lbs, five times the weight of the current rovers, the new Rover will carry more than 10 times the weight in scientific instruments compared to the current Spirit or Opportunity rovers. The propulsion system’s power and torque therefore needed to be more robust, and the unit’s wheels considerably larger than previous designs. These changes, according to NASA engineers will help prevent problems that the current Rover, Spirit is encountering such as getting stuck in a sand pile.
Andrew Tool had to adhere to several parameters in order to help NASA make their new actuator design a success. Many of the parts had very deep pockets, small radii added to the challenge, along with extremely tight tolerances, which were tied to different gear pitch diameters. The parts were very labour intensive with thousands of points of data measured on individual parts.
The VascoMax material used for the actuator parts changes the size slightly during heat treatment. As a result, many of the part features were machined and inspected to process dimensions that allowed for this size change if the feature was not going to be final finished post heat treatment. Additionally, position tolerances of 0.0005mm, geometric control of 0.002mm, and size control within 0.0025mm, even on relatively large dimensions added to the challenge.
These challenges coupled with a demanding 18-month timeline and AS9100 certification requirements made it critical for Andrew Tool to bolster its CMM capabilities for precision and speed.
Andrew Tool decided to purchase the ZEISS ACCURA coordinate measuring machine with the VAST XT gold active scanning sensor that offered the range they needed while the VAST technology and automatic stylus rack system increased flexibility and productivity when determining size, form and position.
The VAST XT gold is an excellent product for the complex and heavy stylus configurations required in measuring MSL’s actuators.
Brent Helgeson, Metrology Applications Manager at Concept Machine was very responsive in efficiently diagnosing the correlation problems, therefore enabling Andrew to quickly get up to speed with their new CMM. Additionally, a probing strategy for some of the features and proper alignment sequences to achieve correct results were developed and refined to achieve consistently correct results.
According to Bryant Broderick, Quality Control Engineer at Andrew Tool, the ZEISS ACCURA CMM helped them execute the project by providing timely, accurate and understandable in-process reporting.
The project included 14 different part numbers with quantities ranging from four to 12 in addition to setup parts. Each part was successfully measured up to 60 times by the ZEISS CMM to ensure accuracy every step of the way through all of the different processes including milling, gear cutting, heat treatment and stabilisation.
The temperature compensation feature was especially helpful because they were able to check parts right off the machine tool and relay the results to the toolmaker.
The CALYPSO software’s robust reporting capability was a great asset for the AS9100 certification process required by NASA, which involved ensuring documentation for all the critical paths of each part throughout the manufacturing process. CALYPSO software easily documented the information electronically each time the part was measured.
Ongoing training continues to drive Andrew toward the goal of using the ACCURA to its full capacity. Andrew Tool even acquired a new customer after another NASA supplier saw several of the MSL actuator parts and was impressed with the precision and complexity of the parts.