NCDMM and GKN Aerospace Proving the Viability of Sustainable Machining Cells
Although many civilians may not understand what sustainable machining cells are, the concept is at the core of new efforts within the Department of Defense (DoD) to manufacture sustainable products, which are less expensive and better for the environment. Recently the United States Air Force, GKN Aerospace and the National Center for Defense Manufacturing and Machining (NCDMM) collaborated to test and to collect data proving that machine cell improvements enabled quantifiable costs savings, reductions in water use and recycling of thousands of gallons of materials. And if that were not enough, the new technology increased tool life by more than 33 percent and reduced energy consumption.
This article describes the project, how it was created and the measurable value derived. The leaders from this unique collaboration have demonstrated their vision of an improved way to machine tools that will better equip war fighters and do it more cost effectively while also benefitting the environment. One can only estimate the full impact if approaches in machine cells, as described below, were applied across-the-board within the defense industry.
During the late 1980s, the term “lean” manufacturing became a model for discussing production principles and methods. Out of those principles arose the “work cell” concepts for sustainable manufacturing. The need for ever greater efficiencies drove the evolution toward machine cells. In a production environment, one machine cell performs many tasks at the same station. Today machine cells are commonplace in many manufacturing facilities. “Lean” and sustainable manufacturing concepts continue to focus on producing products with improved quality at lower costs while also considering improvements in cell inputs, machining process and waste outputs.
Recent technology developments in computer modeling, alloys and chemical compounds allow production experts to construct methods that evolve the machine cell toward ever smarter use of limited resources and ever greater control over waste streams.
DoD initiated the move towards sustainability with release of its Strategic Sustainability Performance Plan.1 Many defense suppliers who provide machined parts now have incentives to embrace the sustainable machine cell not only to support DoD goals, but also to support their own productivity and savings goals.
The sustainable machine cell is a contemporary machine cell on steroids that produces heightened outcomes. Not only does it produce a product that minimizes waste, but it exploits new points of improvement at the task level. Consumables range from the initial block of material to be machined to the tools and materials used to create a part. Optimizing the amount of consumable reduces cost and requires fewer amounts of resources.
This reduces stress on the consumable market. With fewer resources used, less disposable waste is generated. Less waste requires reduced energy and less cost to make the waste returnable to the environment.
Shorter production cycle times reduce energy requirements and increase volume productivity. Finding time optimized sequences and new technologies that enhance tool effectiveness encourages quicker cycle times. Improving efficiency reduces energy costs. Using better lubricants can reduce friction, and advanced automation techniques can maximize energy benefits for equipment. As a company requires less energy for manufacturing processes, it is less dependent on current and long-term availability of energy. If a company is restricted to its energy usage by local constraints, such as peak demand hours, requiring less energy allows more flexibility to the production process. When energy becomes more costly or difficult to procure because of lack of fuels or weather conditions, the manufacturer requires less energy, which results in less drain on the overall energy infrastructure.
Beginning a Sustainable Machine Cell Case Study
The Air Force (AF) Manufacturing Technology (ManTech) Program funded a research effort conducted in collaboration between NCDMM and GKN Aerospace – St. Louis. The DoD-stated ManTech program focus is centered on manufacturing technologies and processes, and enabling production capabilities that reduce the acquisition and sustainment cost of weapon systems. The Sustainable Machine Cell effort was under the auspices of DoD’s ManTech initiative to create and generate methods to accelerate adoption of a sustainable manufacturing philosophy within the defense aerospace industry. This would ensure that it is on the leading edge of addressing social, resource conservation and environmental stewardship challenges. The initial focus of the effort was on sustainable manufacturing for machining metallic component parts for aerospace structures and engines.
NCDMM, a non-profit formed to develop and deliver manufacturing solutions to DoD and its industrial base, helps assure readiness and sustainment of needed defense systems using new methodologies and affordable solutions that reduce/avoid cost and reduce lead times. Traditionally, the organization focused on metrics, such as improved part quality, but now it also considers sustainability metrics involved in areas like resource conservation, waste stream reductions and energy efficiency improvements of the manufacturing operation. In many cases, these measurements are byproducts of or complimentary to its previous focus areas. NCDMM recognizes the need to focus on the most efficient use of natural resources while ensuring compliance to increasingly stringent environmental health and safety regulations, and minimizing energy intensity and environmental impact of manufactured components.
GKN Aerospace – St. Louis specializes in production of aviation grade aluminum, titanium and carbon fiber parts used in aircraft fuselage, wings and flight control surface assemblies. The fabrication operations manufacture metal and composite structural components primarily for the F/A-18E/F, C17 and other Boeing military aircraft programs. When GKN Aerospace took ownership of the plant, its management agreed with the International Association of Machinists and Aerospace Workers (IAMAW) union to improve significantly the competitiveness of the St. Louis fabrication operations. Contributing to the development of a sustainable machine cell was deemed a perfect activity towards achieving that goal by both the plant’s management and union.
NCDMM and GKN Aerospace staff worked together in their respective areas of expertise to detect areas of improvement, to design and test these potential areas, to analyze resulting test data and to turn results into practices that can be used throughout DoD’s machining supply chains.
In December 2010 the team focused on minimizing and optimizing inputs and outputs required to transform NCDMM and GKN material into defense aerospace products that support U.S. military forces, transports and helicopters. The assessment delivered a roadmap for technology solutions to reduce operational energy consumption and waste products at various tiers within the manufacturing enterprise of GKN. Through second quarter FY2011, sustainable technologies effecting energy consumption and consumables were implemented with consideration to return-on-investment and available resources.
Developing a Baseline. The team’s initial task was to create a baseline environment from which to take control values and to provide common starting points when exercising various components, materials and processes. The machine cell was comprised of a machine center that was routinely used for conventional fabrication of titanium aerospace components. GKN Aerospace designed a titanium (Ti-6Al-4V) test piece that represented common design features for aerospace structural components. The test piece acted as a benchmark to evaluate the machine tool’s capabilities, the current state in titanium metal removal process and equipment efficiencies. The part was used to evaluate a machining process based on metal removal rate, cycle time and cutting tool life while maintaining specific part quality requirements. Three existing machine cell tasks were targeted for improvement: coolant recycling, cutting tool performance and optimized path planning.
Recycling Coolant. GKN Aerospace – St.Louis used a semi-synthetic coolant with limited success. The coolant required regular adjustments to maintain proper acidity and continuous monitoring for bacterial growth. Additionally, the semi-synthetic coolant emulsified machine oils and was not designed to be a recyclable product. And contaminants, such as tramp oil, machining fines and dirt, reduced effectiveness of the cutting fluid and eventually required the fluid to be replaced prematurely.
GKN evaluated six alternative cutting fluids for machining aluminum and titanium alloys. The evaluation considered cost-per-gallon, ability to remove residue from machined components, cutting fluid maintenance requirements, disposal costs, cutting tool performance, sump stability, machine tool maintenance, fluid management and ability to recycle the product. Based on test data collected, GKN selected TRIM MicroSol 585XT working fluid from Master Chemical Corporation (MCC). The new fluid also allowed GKN to implement a centrifuge recycling system also supplied by MCC.
The transition to a new cutting fluid was seamless with no negative impact on the machining operations. During three months of operation, GKN Aerospace realized the following savings:
- reduced coolant usage 7.5 percent per pound of aluminum/titanium generated chips,
- reduced both raw coolant and water consumption by 11.2 percent when compared to 2009 values,
- reduced waste fluid disposal requirements,
- eliminated anti-bacterial, anti-stain, acidity balancers and defoamer additives,
- recycled 13,775 gallons of metal cutting fluid in December 2010 and January 2011, and
- improved working conditions by using a more employee-friendly cutting fluid.
Cutting Tool Performance. An industry standard Kennametal RPF cutter was used in the machine center for most of the titanium facing operations in the baseline test. In 2011, Kennametal released Beyond Blast Technology (BBT), a new cutting tool technology that creates the potential for increased productivity and improved tool life. BBT uses a patented through-the-insert cooling technology to direct cutting fluids through the insert and to more effectively deliver fluids to the interface between insert and chip. The BBT cutting tool replaced the standard RPF cutter in the sustainability test.
At its Advanced Manufacturing Laboratory in Latrobe, Pa., NCDMM conducted a life test of the BBT cutter. First, a test piece was fabricated using the RPF cutter and GKN accepted machining parameters. Then, using identical cutting parameters the test piece was fabricated using a BBT cutter. Analysis found the BBT technology increased tool life by more than 33 percent per cutting edge.
The BBT cutter is a round insert with six effective cutting edges compared to two effective cutting edges of an oval RPF insert. This geometry provides three times the number of edges and three times the tool life. Total improvement with extended tool life per edge and increase in number of effective edges resulted in more than a 300 percent increase in tool life.
Optimized Path Planning. Advances in tool path software allow an end user to maximize the time a cutting tool is engaged with a work piece and stabilize the cutting conditions in a machining operation. These improvements result in increased metal removal rates, decreased power spikes, reduced wear on a machine tool, reduced energy consumption and increased tool life.
NCDMM and GKN investigated a variety of software path planning packages to maximize machine efficiencies and to improve titanium alloy removal rate. After analysis of each package’s fundamental operations, the team selected Volumill Universal software to evaluate software capabilities and to conduct machining trials using the Sustainable Machining Cell. Volumill is an ultra-high performance tool path optimization technology that improves tool path using high-speed continuous tangential motion rather than sharp, interrupted movements. Benefits include maximizing the time a cutting tool is engaged with a work piece, stabilizing the cutting conditions, increased metal removal rates, decreased power spikes, reduced energy consumption and increased tool life.
Early testing showed a 205 percent increase in metal removal rates for pocketing operations conducted on a GKN standard test component. A review of the machine tool load indicated reduction in per unit power consumption as well as overall power consumption during machining operation. The advanced tool path allowed additional features to be machined with fewer tools. Additional testing has begun to examine the possibility of producing even more efficiencies by combining this progress with other advanced technologies, such as extreme high flute cutting tools. The testing team anticipates data results will show configuration revisions can double machine output, extend tool life, reduce energy consumption and machine downtime while creating a more productive and competitive manufacturing enterprise in the global marketplace.
In response to a sustainability request by the Air Force, GKN Aerospace and NCDMM pooled their individual areas of expertise to test and to collect data that proved the viability of a sustainable machine cell. This information will benefit all branches of DoD as it demonstrates that machine cells can be cost- as well as resource-effective.
NCDMM provided the experience in research and analysis while GKN Aerospace provided practical implementation of designed testing. Baseline testing and data monitoring and collection provided detailed metrics that proved valuable cost and resource savings. Based on data collected from the coolant recycling process, GKN Aerospace is forecasting a $6,000 monthly savings through implementation of the cutting fluid recycling process, water consumption reduction of 11 percent and increased recycling of more than 13,000 gallons of material.
New tooling technology increased tool life by more than 33 percent per cutting edge, thus reducing machine cell power consumption as well as initial resources to manufacture the tool. Lowering power consumption reduced load meter spikes during heavy cuts, and lower loads provided use of smaller tools and chip load. Overall, energy consumption reduction could reach as much as 20 percent.
Complex path planning provided by the latest software produces stable cutting conditions, significantly improved MRR and reduced cycle time, reduced tool loads and improved tool life, and reduced machine cell power consumption.