Assembly Handbook: Integrated Workstations Streamline Assembly Flow
But all of that changed when Branson developed its new Bransonic Series family of benchtop ultrasonic cleaners, for use in cleaning medical instruments and jewelry. In a break from the past, Branson involved its manufacturing engineering department in the project from its inception. Ease of assembly was included in the product design criteria, along with factors such as parts count reduction, and total quality procedures. A team headed by Walt Kohler, Branson’s manager of advanced manufacturing process development, was given a clean slate for creating a Just-In-Time (JIT) assembly cell to replace the traditional batch assembly line system. The goal was development of a world class manufacturing operation.
Branson’s specific objectives included a reduction of work-in-process (WIP) by at least 50%. The team also aimed to increase throughput via the adoption of a one-piece flow system that would include on-line testing and packaging. A significant reduction in non-productive labor, elimination of excessive lifting, and improved ergonomics were also on the list.
The Branson team decided to develop its assembly cell using modular, FlexiMate Integrated Workstations supplied by Worksmart Systems, Inc. (Burlington, MA). The workstations are a hybrid of a workstation and a free conveyor, and are constructed with high-strength, anodized aluminum tubing. Glass-filled polycarbonate fittings join the frame together.
Branson engineers joined together five of the workstations to create a flexible assembly line. The flexibility afforded by the modular approach was of particular benefit, allowing Branson to move and improve the cell three Arial during the first six months.
In the Branson plant, each workstation is joined together with tracks that have carts riding on them. The ultrasonic cleaners are transported on the carts during the entire assembly process. The carts replace the traditional workbenches, which required the assemblers to pass a unit from station to station.
The new approach has produced a number of benefits, Branson officials report. Because the transport track only allows one cart to be staged between assemblers, for example, the new system minimizes the amount of work-in-process. Under the old system, assemblers batch-built subassemblies, and then stored many partially-built units on the floor around the line. These multiple units, in various stages of completion, created WIP carrying costs that were unacceptably high, says Kohler. They also made it tough to gage productivity levels. "At break time, when the assemblers left the line, we had difficulty figuring out how many units were completed, nearly completed, or half completed," Kohler observes. "Now with one unit per cart, our production is accountable."
The one-piece flow design also significantly reduced non-value adding labor, points out Jane Schaeffer, Branson’s senior manufacturing engineer. Because the old benches stockpiled units, assemblers were required to collect parts and components each time they began work on a new unit. "Assemblers spent a great deal of time moving around gathering parts," says Schaeffer. The new workstation system eliminates that problem, enabling parts for each model type to be stored at the station.
Branson stores a week’s worth of supplies in each station. As part of a continuous improvement program, the company is constantly moving closer to JIT operation. Currently, manufacturing moves most parts straight to the cells from the stock room, with vendors held responsible for quality assurance and on-time delivery. Parts are maintained in a two-bin Kan Ban system. When one of the bins is empty, the assembler simply allows the second bin to slide forward and puts the empty one on a shelf. A full-time stock handler replenishes the bins as necessary throughout the day from a small, nearby stock room.
Under the previous batch system, assemblers stacked completed units on the floor awaiting inspection and testing. When 30 to 40 units had been produced, the units were carried to quality control, where they underwent a 2-hour wet test on benches. This approach required excessive handling and work-in-process. Further, the test was timed by a clock on the wall, a procedure prone to error.
With the new cell assembly system, however, Branson was able to revamp its wet test procedure. Instead of a batch test, units are now tested on-line, with a trolley duct providing power. Working with Branson, the workstation vendor also designed and installed an automated timing mechanism that, combined with the trolley duct used for power, has eliminated the tester’s reliance on the wall clock. The result is a smooth flow of products through the 2-hour run-in cycle, and on to the packaging department. By keeping the test on-line, Branson has also significantly reduced unit handling requirements.
Under the new system, Branson’s assemblers are trained to work "one-up/one-down," which eliminates line imbalances. Because the transport track only allows one cart staged between assemblers, an assembler cannot advance-build more than two units. Assemblers take a team approach; if an assembler builds up two units at his or her own station, that worker moves to the next station to help out. "With the cell we designed with Worksmart, one unit is now built beginning to end, and it’s continuous flow," observes Schaeffer. "The JIT cell keeps exact control of how many units go in and out."
Branson officials have been pleased with the improvements made with the new assembly approach. During the first run on the new benchtop cleaner product, the one-piece flow cell increased throughput by 32% compared to the old system. As part of its commitment to implement a world class manufacturing operation, employees are encouraged to make suggestions on how the assembly process can be continuously improved.
"We put a lot of energy into this product launch, and our new Bransonic family of benchtop ultrasonic cleaners was a success right out of the gate, with orders far exceeding our forecast," says Kohler. "It was critical to meet this market acceptance with quality product. We would have been hard pressed to achieve this degree of control without the new workstation cell and techniques that we put in place with Worksmart Systems."