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Cummins realises the benefits of using WITNESS simulation software in all Six Sigma projects to make significant savings in the Design of Experiments


When a change in fuel emission standards reduced demand for its N14 truck engine, Cummins used WITNESS simulation to take £185,000 of annual savings out of the engine’s post-assembly operation.

As important as it was to find these savings, however, Cummins made an even more valuable discovery through the simulation: the company learned that WITNESS could play a key role in its growing Six Sigma initiative. 

“The project opened the doors for using simulation in all our Six Sigma projects,” explains Maria Pasqualli, head simulation manager at Cummins. “It showed our master black belts that WITNESS could help them realise significant savings in the Design of Experiments phase of Six Sigma.”

Cummins manufactures electrical power generation systems, engines, and related technologies, including fuel systems, controls, air handling, filtration, and emissions solutions. Cummins engines can be found in pickups, recreational vehicles, trucks, busses, farm and construction equipment, tanks, boats and trains.

Headquartered in Columbus, Indiana, the company serves its customers through more than 500 company-owned and independent distributor locations in 131 countries and territories. With 24,900 employees worldwide, Cummins reported sales of £4 billion in 2001.

The origins of simulation and Six Sigma Cummins has been using WITNESS since 1991, simulating a wide range of processes including engine assembly, testing, post-assembly processes, supply chain and inventory. According to Pasqualli, Cummins chose WITNESS as its simulation system for three key reasons. 

“We needed a simulation package that was flexible enough to model a variety of different processes and products,” she says. “Plus, we wanted to make sure that we were using software that our biggest clients, DaimlerChrysler and Ford, also used. We were also looking for a solution that would meet our needs 10 years down the road. For flexibility, compatibility and stability, WITNESS was the best choice.”

Compared to simulation, Six Sigma is relatively new to Cummins. That’s the case for most of the manufacturers embracing the popular quality methodology. In fact, the first Six Sigma programs were implemented just seven years ago by GE, Motorola and AlliedSignal. What exactly is Six Sigma? Simply put, it’s a data-driven quality process for eliminating defects and delivering near-perfect products and services.

The word “Sigma” is a statistical term that measures how far a given process deviates from perfection. To achieve Six Sigma, a process must not produce more than 3.4 defects per million opportunities. The idea behind Six Sigma, then, is to measure how many "defects" there are in a process, then systematically figure out how to eliminate them to get as close to zero as possible. In the two years since Cummins started its Six Sigma initiative, the program has grown rapidly. Today, there are 20 master black belts, 200 black belts and 600 green belts working on Six Sigma at Cummins—and the numbers are growing. (These martial arts terms are simply titles to designate the hierarchy of responsibilities in a Six Sigma program.)

“Our program is getting bigger and bigger every year,” Pasqualli observes. “Each of our plants has a quality champion supervising projects and each different area has its own master black belt to train and assist black belts and green belts.”

"With the growth of Six Sigma at Cummins and the statistical, process-driven nature of simulation, it was only a matter of time." says Pasqualli, before the two methodologies leveraged each other’s value. “Six Sigma and WITNESS are a perfect fit for each other,” she explains. “WITNESS helps Six Sigma by providing an inexpensive way to conduct the Design of Experiments without disrupting production. And Six Sigma helps WITNESS by providing a wealth of accurate data. Building a simulation for a Six Sigma project takes me half the time that a normal simulation takes just because the data is all there.”

An aging engine brings WITNESS and Six Sigma together Despite the mutual advantages of simulation and Six Sigma, WITNESS didn’t catch the attention of Six Sigma experts until Pasqualli got involved in a project to modify the post-assembly process for a veteran truck engine. When emission regulations for heavy-duty trucks got changed, demand for Cummins’ N14 engine dropped drastically.

In the United States, the engine was effectively replaced by a higher-tech engine, but Cummins still needed to produce the engine for countries where the emission standards had yet to be changed. Overall, production of the N14 was scheduled to decrease by 50%. This presented a problem in the N14 post-assembly process—the stage of the operation where engines were washed, primed, painted and finished. With the PLC control logic geared for high volumes, there were large buffers between each of the stations. And since the process employed a “push” flow, engines wouldn’t get released until the buffers filled up. When the volume was reduced, fewer engines were running through the system, it took longer for those buffers to fill, and there were more delays in releasing engines at each station.

The result was a considerable drop in throughput and an increase in WIP. In fact, Cummins had more engines in WIP than they were producing each day. The lower volumes also created a problem with the overhead carriers, an expensive set of capital equipment. When the plant was producing 160 engines a day, it needed 92 overhead carriers to move them through the system. But with the decreased demand, post-assembly actually had more carriers in the operation than the number of engines that needed to be produced each day.

Six Sigma experts at the plant initiated a project to modify the post-assembly process to cope with decreased demand for the engine. In previous projects, they tried to conduct some of the Design of Experiments without simulation. As Pasqualli explains, this proved to be difficult for the workers and too disruptive to production. “One of the big issues was to figure out the right number of carriers to use,” she says. “Without simulation, we resorted to trial and error. The operators would have to take these carriers off, then put them back on to see what the optimal number should be. But these are heavy pieces of equipment. It was becoming time consuming and tiring work.”

When Kevin Aker, the black belt in charge, turned to Pasqualli and WITNESS for the Design of Experiments, production downtime was eliminated and the operators were a lot happier. Says Pasqualli: 

“With the simulation, we could show the team the way the system would behave with fewer carriers. So every time they took a carrier off, they knew they weren’t going to have to put it back on again. That was one of the important values of simulation—to create confidence that the changes we were making would work. The other important point was that we never had to stop the line to make a change.” Another benefit of simulation was that it enabled the Six Sigma team to evaluate months of performance for every scenario in a matter of minutes. This ability to conduct what Pasqualli calls “rifle-shot” what-if experiments gave the Six Sigma team a better understanding of the boundaries of what their potential changes could achieve. WITNESS points Six Sigma team toward big savings WITNESS showed the Six Sigma team that the best option for optimising throughput and reducing variation would be to modify the control logic and change the process to a “pull” flow employing 42 carriers.

The team also learned the system could handle up to 60 carriers with minimal impact on throughput time. Based on the findings from WITNESS, Cummins implemented several changes over a four-month period. The company reduced the buffers in the drying ovens, eliminated two workstations, and removed 27 carriers from the system. (The Six Sigma team kept some extra carriers in the system to handle any unexpected increase in demand.)


The results were dramatic. Throughput time was reduced 14%, WIP decreased 29%, and productivity improved 11%. Most importantly, the project realised nearly £185,000 in annual savings.

Another way the Six Sigma team quantified the value of the project was by showing what would’ve happened if their suggested improvements had not been implemented. “Without any changes, as the demand for the N14 dropped, throughput time would’ve been 93 minutes more than the 224 minutes we actually achieved, a 42 per cent increase,” notes Pasqualli.

From Six Sigma to “Sim” Sigma… As impressive as these results are, the biggest impact of the post-assembly project might be the precedent it set for using WITNESS in the Six Sigma Design of Experiments phase. Pasqualli explains: “We presented the final results of the project to a group of Master Black Belts, and they were so impressed with the savings and analysis simulation achieved in the DOE that we were invited to present our findings to the management committee.

Before this project, the master black belts were generally unaware of the extent to which simulation could help in Six Sigma.” One year after the project was finalised, WITNESS is playing a key role in several Six Sigma initiatives at Cummins. Most of the simulations that Pasqualli builds these days are related to a Six Sigma project. She’s currently working on a simulation to evaluate whether Cummins can increase throughput enough in its industrial engine test cells to eliminate a third shift. Pasqualli is pleased to see that the influence of WITNESS is growing within Cummins’ Six Sigma program. She’s also pleased that Lanner Group is responding to the newly discovered value of simulation by adding a suite of Six Sigma tools to its WITNESS release.

The feature she’s most excited about is the automatic link between WITNESS and MINITAB, the primary statistical analysis software used for Six Sigma. Currently, she takes her WITNESS output into Excel in order to export it to MINITAB. 

“The nice thing about WITNESS is that the output will go directly into MINITAB,” Pasqualli observes. “Without that link, it takes a few extra steps to get simulation output the way you need it for MINITAB analysis.”

The new Six Sigma toolkit in WITNESS is likely to spark more interest among Cummins Six Sigma experts for doing simulation. In fact, demand for Six Sigma simulations is already so great that black belts and green belts were recently trained in WITNESS at Lanner’s Detroit office. Cummins has also expanded the availability of WITNESS by adding six licenses to its network. Even with all the extra support, however, Pasqualli foresees that her involvement in Six Sigma projects will continue to grow. 

“Right now, I can’t keep up with all the Six Sigma requests for WITNESS work. Fortunately, many of the Six Sigma experts are familiar with simulation, and it takes me just a couple days to show them how to use WITNESS. “Still, the use of WITNESS in Six Sigma is becoming so popular that my involvement will be fairly constant,” Pasqualli adds. “If I’m not doing the simulation myself, I’ll be supervising it.”

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