From Minnesota to Mars and Beyond

“We had to modify all of our programs to allow for the thermal growth that happens during heat treatment. Feeds, speeds, and many of the tools had to be altered because of the material change as well. Additionally, VascoMax has a strong tendency to creep and move during machining, creating a requirement for multiple in-process stress relieving steps. Mastercam was a tremendous help in streamlining the conversion process. ”

- Jim Breth, CNC Programmer, Andrew Tool & Machining, Plymouth, MN

Printable Profile

While the term "boutique" isn't often used as an adjective defining a job shop, it is an apt way to describe Andrew's niche as a provider of fine products along with extra attention to detail and service for discerning customers. With a 28-person staff, it is also small, flexible, and quick to respond to market demands, while embracing new technology and methods. Precision parts for fussy industries, such as medical and aerospace, are Andrew's specialty, and it's the story of Curiosity's actuators that serves as the telling tale about the company and its distinguishing attributes.

The Challenge

The titanium material proved to be the most challenging aspect. In fact, the initial run of parts failed, not because of anything Andrew did, but because of the mechanical application. The actuators simply did not function properly, and galled during final assembly and testing at NASA's Jet Propulsion Laboratory. After a great deal of angst, JPL was forced to abandon the weight saving benefit of titanium and specify a proven space flight material, VascoMax C300, in spite of the payload penalty.

In December of 2008, NASA announced that the MSL launch would have to be delayed two years because of technical issues with the rover's actuators (motors and gear boxes) that control everything in the rover that moves, including the wheels and robotic arms.

"They're absolutely crucial to the success of the mission," McCuiston was quoted as saying at the 2008 briefing. "Without them, we'd basically have a metric ton of junk on the surface of Mars."

The Solution

The company credits Mastercam for making the transition from titanium to VascoMax an easier process than it would've been without the software.

Benefits

Mastercam gives programmers a choice of how they want to cut out pockets
Mastercam's advanced multiaxis option gave Andrew the ability to get the shortest tool while maximizing the tool's cutting surface
Mastercam's reseller, Prototek Engineering, helped Andrew get up to speed quickly in 5-axis programming

Project Details

The Mars Science Laboratory (MSL) known as "Curiosity" is a NASA rover scheduled to launch September 15, 2011. Its mission is to determine the planet's habitability and analyze samples scooped up from the soil and powders drilled from rocks. Curiosity will weigh over 10,000 lbs. (five times as heavy as the current rovers) and carry over ten times the weight in scientific instruments as the current Spirit or Opportunity rovers. Contributing to the next generation rover is a contract manufacturer called Andrew Tool & Machining in Plymouth, Minnesota, a supplier to one of NASA's top tier subcontractors. One of the engineers there had developed a working relationship with Andrew's co-owner, Bruce Hanson, while working at other companies. They stayed in touch, and the fellow called Bruce to find out if he knew anyone who could produce the actuator parts successfully, perhaps even Bruce's company. Evidently a number of shops had tried and failed, and as a result the MSL actuator timeline was seriously behind schedule.

Specifically, the project resulted in Andrew creating all of the actuator components, first in titanium and then in VascoMax, only on a much tighter, more demanding timeline. Very deep pockets (almost a 20:1 ratio) and small radii were the hallmarks, along with extremely tight tolerances, many of which were tied to multiple gear pitch diameters. Being able to successfully partner with Forest City Gear in Illinois was absolutely critical to the project's success. Positional tolerances of 0.0002" diameter, geometric control of 0.00008" and size control within +/-0.0001", even on relatively large (5.00" range) dimensions, created plenty of challenge. Additional issues related to deep pockets with small tools in nasty material added to the challenges.

"If we didn't have five-axis machining and the Mastercam options to remove the material out of the pockets, we would've really struggled," says Breth. "The software gives programmers a choice of how they want to cut out pockets, which I find a helpful, flexible feature. For example, some of the MSL parts had numerous rib features that were 1.250" deep with .065" corner radii that went around a 360 degree profile. I used the 'Advanced Multi-axis' option to achieve this operation. First I programmed as a standard surface pocket, and then I converted it into a 5-axis toolpath. This gave us the ability to get the shortest tool while maximizing the tool's cutting surface. This would not have happened without the Advanced Multi-axis option".

In addition to the machining challenges, the manufacturing process was rather cumbersome. Controlling feature sizes to achieve post-treatment tolerances of .0005 (without additional post-heat treat machining) requires careful command of the entire process. Features with tolerances closer than .0005 were finished post-heat treatment. Like most heat treatable materials, VascoMax changes size through heat treatment. Fortunately, the size change is minimal and predictable. Andrew created pre-heat treat process drawings of every part, and the new drawings became the foundation of the whole project.

Andrew shipped the last of the "Curiosity" actuator components in October of 2008. In total, the project spanned 18 months.