Cellular manufacturing requires physical and mental shifts in how to create a specific process. Rather than produce multiple parts before sending them on to the next machine in the assembly process-economies of scale-the goal is to move products through the entire process one piece at a time, at a rate predicated on the flow of customers' orders.
At Lincoln Electric (Cleveland) a manufacturer of arc welding machines, cellular manufacturing has taken on the form of using carts to replace assembly lines. "We used to have three different products running on a line with six or eight assemblers," says Tom Soster, manufacturing engineering manager. "Because we could only run one type of product at a time, it seemed like no matter what we were making, it wasn't what we were selling."
Finding a solution
The problem was resolved by dropping the assembly line concept-and mentality-and replacing it with carts that permit each assembler to build an individual welder on a cart.
"We took some subassembly processes and created subassembly stations, for things like control panels," says Soster, "and put those subassemblies onto carts as well."
There are now three assembly stations, one for each of the company's product families. The station is large enough to accommodate two assemblers, each working on his own cart. "Finished welders are placed in a warehouse and orders for more welders are generated as units are sold," explains Soster.
One benefit of this new cellular manufacturing process is that its flexibility accommodates spikes in the ordering process. "It's easy to shift people over," says Soster. "And that has resulted in lower inventories in the warehouse as well as quicker response to customers' needs."
There is also an ergonomic benefit to building welders on the carts. Assemblers can move around the unit easier than working around units moving on a conveyor. "The parts for each welder are right where the operator can keep an eye on them and alert a supervisor if he's running short," he says.
Switching from an MRP planning system to a cellular manufacturing process has created a "pull" approach to building, says Soster. "When the assembler uses all the subassemblies on his cart, the cart returns to the subassembly station for refills. If nothing [meaning a specific product] is being built, we're not creating subassemblies, like case fronts, that we don't need." When the operator making case front subassemblies sees the empty cart, he knows assemblers are now working from subassemblies on the second cart, and that he should build replacement case fronts to fill the empty cart. It's a modified kanban system.
Customizing the product and process
Lincoln sells some of its products through home-improvement store retailers. It found that another benefit of its cellular manufacturing approach has been the ability to show each of its customers how units for specific businesses are assembled. One retailer might ask for some detail to be different on the welder, primarily for product differentiation. "We can tell that retailer we'll build welders to its specifications because we can easily create an assembly line dedicated to their product," says Soster.
Combining flow and cellular techniques is becoming a popular approach to manufacturing says Kevin Prouty, senior director of manufacturing solutions at Symbol Technologies (Holtsville, N.Y.). "We're seeing companies set up lines that look like a flow process with cell functions along that line," he says. If the work is highly repetitive, it skews more toward flow; if it's work that requires more machines than operators, cellular is a better approach.
"If the work involves highly skilled workers," says Prouty, "you have to look for the best asset utilization, and that usually means finding ways to cut the travel time of the operator."
A new facet of cellular manufacturing is mobile computing. "Having a computer in his hand gives the operator the ability to see what each machine in the cell is doing, without actually having to go over and look," says Prouty. Particularly in press operations and finishing processes, the idea is to maximize the uptime of the equipment and minimize the time of human input.
Spend money wisely
Prouty cautions that a company has to be careful with the human component of cellular manufacturing. A complex array of machinery purchased to establish manufacturing cells can create more maintenance issues than traditional material handling equipment might.
"The operator's vision into individual processes within the cell is critical," says Prouty. "If the operator is supposed to turn away from what he is doing, in favor of setting up something else, he must have visibility into how the job is running."
That kind of visibility can be achieved by making the cell small enough for him to easily watch the process, or by providing him with some kind of a device that allows him to view the process.
Cellular manufacturing should be thought of as an operational strategy, not as a solution to manufacturing woes. It can provide flexibility and allow a company to vary its product type in response to customer demands. Experts suggest thinking in terms of how to reduce the time it takes a single product to get through the manufacturing process, rather than thinking in terms of how many items can be produced in a given time frame.
More than manufacturing
Cellular manufacturing is now being viewed as potentially beneficial to the environment. According to the Environmental Protection Agency, because cellular manufacturing helps eliminate overproduction and reduce waste, it can have an impact.
Cellular manufacturing helps reduce waste by reducing defects that result from processing and product changeovers. Since products or components move through a cell one piece at a time, operators can quickly identify and address defects.
Allowing operators to stop production when defects occur (known as autonomation or jidoka in lean circles) prevents wasted material and time. Under a conventional batch-and-queue process, it is difficult to identify and respond to defects until the entire batch is produced or numerous pieces are processed. Reducing defects has several environmental benefits:
- Fewer defects decreases the number of products that must be scrapped;
- Fewer defects also means that the raw materials, energy, and resulting waste associated with the scrap are eliminated;
- Fewer defects decreases the amount of energy, raw material, and waste used or generated to fix defective products that can be re-worked.
Shifting to right-sized equipment means production equipment is sized to work best for the specific product mix being produced, as opposed to the equipment that would meet the largest possible projected production volume. Right-sized equipment is typically less material- and energy-intensive (per unit of production) than conventional, large-scale equipment.
Cellular production layouts typically require less floor space for equal levels of production. Reductions in square footage can reduce energy use for heating, air conditioning and lighting. Reduced square footage can also reduce the resource consumption and waste associated with maintaining the unneeded space (e.g., fluorescent bulbs, cleaning supplies). Even more significantly, reducing the spatial footprint of production can reduce the need to construct additional production facilities, as well as the associated environmental impacts resulting from construction material use, land use and construction wastes.
Cellular manufacturing layouts and autonomation can free workers to focus more closely on equipment maintenance and pollution prevention, reducing the likelihood of spills and accidents.