A Model of Collaboration

The engineers at Diversified Machine Systems (DMS) specialize in accommodating custom requests, but a recent order for a high-speed machining center was especially unusual in that it had to integrate with the customer’s existing 10ft x 35ft universal fixture table. That request may not seem all that uncommon, except the table is installed over a large pit in the factory floor with a reinforced concrete foundation for greater tolerance and improved accuracy.

The table is a key component that the customer, Cessna Aircraft Co., plans to use to increase its production capabilities significantly with the addition of a DMS 5-axis overhead moving gantry CNC router.

The custom-built DMS machine is a large-format sidewall gantry that has solid walls and doors with a reinforced base with an integrated Flexible Tooling System for machining large sheet metal and composite parts.

By integrating the universal fixture table with the new custom machining center, Cessna operators can perform multiple tasks without having to stop and change the tooling setup. The time savings that can be achieved with this type of technology can be substantial, and result in lower job costs with improved throughput.

In addition to added capacity, several new product offerings – Cessna’s Citation Latitude and Longitude business jets – utilize components larger than the manufacturer’s current equipment could efficiently produce. According to Jason Neal, director of process engineering for Cessna, it was time to rethink the procedure.

“Rather than simply increasing the scale of our current technology, we believed it was time to re-assess how we produced our parts,” Neal says. “Our teams determined the best fit for Cessna was a combination of larger equipment that utilized more flexible tooling solutions.”
 

Give & Take

Cessna has a good track record with router manufacturer DMS, Neal adds, already having purchased five different models of custom machines for various departments involved in aircraft parts production. Therefore, the Cessna engineers were comfortable taking the next steps in determining what would best serve their needs.

“The process that we used with Cessna is similar to most clients in how we service the needs of these unique application requirements,” says DMS CEO, Patrick Bollar. “For each machine purchase, we’ll go and meet with Cessna, review their parts requirement and their manufacturing process, review the size and types of parts that they want to cut on the machine, and check the specifications such as tolerances and accuracy requirements.”

DMS engineers take this feedback to its engineering department back at company headquarters, where they begin the design process for the client and proceed with the custom machine specifications. The final approvals on a machine are then mutually agreed upon before purchasing or manufacturing starts.

“For accuracy, tolerances, and repeatability, DMS as an OEM adheres to a tight corporate standard which generally meets or exceeds our clients’ expectations,” says Ed Hilligrass, DMS’ executive vice president.

“From time to time, companies ask us to deliver specific machine tolerances, some that are achievable, some that aren’t. Either way, the discussion becomes a bit of a fact-finding mission, as well as an education process that covers a wide variety of variables – any of which can have an impact on achieving a specific machining tolerance,” Hilligrass adds. “Based on these types of discussions, it’s our responsibility as an OEM to clearly explain the capabilities of our products and advise if expectations are achievable.”

Hilligrass notes that DMS primarily uses a Fagor control system; the Fagor control is very feature-rich with capabilities such as RTCP, volumetric compensation, and high speed surface accuracy. Fagor also supplies absolute linear scales with integrated thermal capability. In addition, DMS uses a range of HSD spindles for any application.
 

Finding a Solution

Economics was a driving factor in designing the new router. Neal notes that in the past, Cessna used static holding fixtures on its routers.

“We typically manufactured a unique holding fixture for each part that was machined on the routers,” Neal says. “Each holding fixture costs thousands of dollars, and with hundreds of parts going across this process, it doesn’t take long for other options to become financially feasible.”

The solution chosen for the new system combines gantry routing with a universal bed-of-nails style holding fixture that adjusts to the unique geometry of each part.

“When the operator selects the N/C program for the cutter path, the table will dynamically adjust to support the formed part to prepare it for trimming by the router,” Neal explains. “Select a new part and the table adjusts according to the new geometry.”

A dynamic fixturing system avoids the traditional steps of building a dedicated tool, the store-deliver-store-again cycle of the tool, and maintaining the unique tools, Neal says.

“We expect the new system to provide long-term benefits of lower non-recurring costs for new parts, lower logistic/maintenance costs for static fixtures, and improved part quality related to accuracy of the machine and tools always being in good condition.”

The sheet metal parts applicable to the new system are stretch-formed aircraft skins, Neal states.

“The composite parts would be larger, gently sloping aircraft structure such as fairings or cowlings,” he adds.
 

Collaboration Has Benefits

“DMS has gained a lot of value in our processes in the collaboration with Cessna,” Hilligrass says. “It’s helped us develop a model of collaboration that we've been able to use as a model with other large scale clients, especially in the global composites industry, with being able to answer broad scale needs and common issues with a proper manufacturing response.”

Hilligrass notes this experience has applications on an international level, not only through sales, but also with engineering and product development such as complete enclosures and limited workspace to meet global health and safety standards.

“Cessna is one of the first DMS clients who started to look at composite parts for their aircraft, and they were looking for a competitive CNC machine that could work with these newer composite materials,” Hilligrass continues.
 

“One of the early challenges through our collaboration with Cessna was that they needed to contain the composite dust so that the workers weren’t breathing it in during their shift,” he explains. “Cessna originally built a room around our machines to accommodate this new safety requirement, but then they found that while they were trying to filter and recirculate the air from the same enclosure, the process caused static charge particles to get within the more exposed electrical components of the machine, which would cause premature component failures. This prompted design changes to electrical cabinets and how we integrated and sealed our motors and drives. We also installed a sealed air conditioner within the system to provide a constant temperature and dust filtration for the electrical cabinet and components of the machine.”

Another benefit of the two companies’ collaboration has been to improve communication between machine maker and end user.

“It’s helped us improve how we communicate our machine’s features and functions, in order to make them more understandable and useable by our customers,” Hilligrass says. “The clarity around the terminology when they’re asking for certain functionality when they’re not industry-standard terms has helped them in their buying decision. Ultimately, both these process improvements have helped us understand our customer better, from providing machine specification through our customer training and service.”

Cessna Aircraft Co.
Witchita, Kan.
www.cessna.com

Diversified Machine Systems Inc.
Colorado Springs, Colo.
www.dmscncrouters.com

About the author: Eric Brothers is senior editor for AMD and can be reached at 330.523.5341 or ebrothers@gie.net.