Carleton has applied lean six sigma tools in the development of the Microclimate Cooling Unit (MCU) for the US Military. This miniature vapor compression cooling unit is used by the Army to address the thermal burden of helicopter and ground vehicle personnel. The main objective was to optimize cooling performance by minimizing environmental heat gain and improving cooling power, while at the same time minimizing hidden factory costs associated with adjusting each unit for optimum output.
As this was an existing program, the DMAIC (Define, Measure, Analyze, Improve, Control) tool kit was used. In the "Define" phase, the first step was to create a project charter. This charter identified the key goals and objectives of the program, identified business benefits of doing the process, and identified key metrics and team members, as well as suppliers. The project charter would also serve as a living document that would be updated as the program progressed. Next, a process flow diagram was created. This diagram would map out each step of the assembly process in order to best determine where issues could arise and where gains could be made. A cause and effect diagram was also created to address the factors that would affect the MCU cooling power. These factors are split up into six categories (Manpower, Method, Machine, Measurement, Materials and Environment).
The next step in the DMAIC process is Measurement. A review was made of existing engineering studies related to environmental heat gain minimization and process capability improvement. In addition, the Cpk for the MCU was recorded over a one month span and rolled throughput yield values were calculated for the MCU. Gage R&R studies were implemented to insure the capability of Assembly and test instrumentation.
During the Analyze phase, detailed Failure Modes & Effects Analysis (FMEA) studies were completed for the MCU and MCU Compressor build processes. The results were put into a pareto chart to identify key risks in each case. An additional goal of the analyze phase was to gather relevant system data so that a baseline could be produced. This was done by collecting data for the entire production build for the previous year. A statistical analysis was completed and mean cooling power, standard deviation and Cpk were calculated. A screening Design of Experiments (DOE) analysis was also completed during this phase in preparation for running a much more detailed DOE during the Improve phase.
As part of the Improve phase, a high design resolution DOE was completed to determine a transfer function that would accurately describe the system with regards to key input factors. Main effects / marginal means plots were then created to examine which of the factors would have the largest impact on cooling power when changed. Through this examination, it was determined that when the level of a key factor was decreased, mean cooling power increased and standard deviation decreased. With this correlation in hand, a monte carlo expected value analysis was carried out using the transfer function derived during the DOE. The results of this analysis showed that by optimizing the key factor setting, mean cooling power would increase by 4% and Cpk would increase by 36%. It also allowed the Carleton team to view the effect of key factor interactions on the critical performance outputs. Design decisions were made to minimize hidden factory effort and produce the most capable design in assembly and test.
Finally, the last phase of the process is the control phase. Control plans were implemented on the shop floor to sustain and support continual improvement. Carleton utilizes several different forms of control charts (IMR, X-bar charts, P charts, etc) to control key variables and prevent problematic issues from occurring.
In addition to applying Six Sigma techniques Carleton actively utilizes Lean Manufacturing to support Value Stream Flow and Improvement. By addressing the value stream in its entirety Carleton can support and continually improve a lean flow of information and material from the time of order to the delivered MCU. Every process in the value stream is included to support the best quality, lead time, and cost for our customer.
Carleton utilizes cross functional business teams to create a current state value stream map to capture the value stream flow. Once the current state is captured the team will create a future state identifying kaizen and six sigma improvement opportunities. The continual improvement is focused on creating a pull system from the customer using kanban signal systems through Carleton's gemba all the way to the supply chain.
Sales and Marketing personnel work with the customer to actively manage and support contracted and variable demand. This information is communicated to Carleton business support personnel including, contract administrators, procurement, planning, engineering, quality and operations. The value stream will be setup to meet the customer takt time.
To support the flow of material from the supply chain to Carleton, procurement teams setup supply chain kanban to efficiently control and minimize inventory in the value stream. Kanbans are sized to support takt time and lead time. To improve value stream lead time Carleton has dedicated supply chain Black Belt support personnel to train and support the supply chain. These Black Belts work closely with the Military Aircraft Team at Carleton for Dock to Stock quality initiatives for MCU supplied parts.
Once the material arrives at the Carleton shop floor the operation is ready to support the effort. Carleton manufacturing, quality, and process engineers have sized support cells using operator balance charts. The engineering staff continually works to improve the total work content required to build a micro climate cooling unit to improve the capacity of the Carlton operation. Team members employ a variety of Lean Manufacturing and Six Sigma techniques to minimize and eliminate muda, mura, and muri.
In summary, Carleton applies a variety of Lean Six Sigma tools and techniques to continually improve our MCU value stream to provide the best quality, delivery, cost and service to our customers and their clients.
