Continuous flow at its best

Adjust font size:

Magazine Article, Source : The Manufacturer US
Zone : World class manufacturing

Don’t stop till your customer says “Bravo.” For Signicast, John Harney learns, that customer was Volvo

“You have legitimate bragging rights,” said a Volvo representative at Signicast’s Hartford, WI, plant. “Word has spread fast that you are considered world class.”

Volvo representatives from both Sweden and the US toured the Hartford manufacturing plant in 2006 and, after a stringent review and audit, awarded Signicast a “World Class” rating for quality and efficiency. According to Volvo officials, the average plant audit receives review scores in the 50s and 60s. Signicast, on the other hand, received the exceptionally high rating of 87.

Signicast is an investment casting company that has achieved best-in-class results in its industry. Its best-in-class continuous flow practices, though, translate to any industry.

What’s known as “investment casting” is normally a labor-intensive, time-consuming foundry process of making metal parts from wax and ceramic castings. Usually people have to perform activities like pouring molten metal into molds on the shop floor and sanding metal castings after they’ve been broken from their molds. It’s also not a manufacturing process that lends itself to on-demand manufacturing. Typically metal parts made with this process are run through in batches and require significant backlogs between manufacturing operations as well as too much raw material in inventory and finished goods waiting to be shipped.

At least that’s the case with most investment casting manufacturers. Signicast is an exception. It manufacturers metal parts for companies like Harley-Davidson and Stanley Tools in all types of industries. It has mastered what it calls “continuous flow” manufacturing, which allows it to cast metal parts on demand with little raw material or finished goods inventory or backlogs between production line operations.

According to Signicast Executive Vice President Bob Schuemann, in investment casting the manufacturer first builds an aluminum mold for the part being made, then injects it with wax to form a wax replica of the final tool to be made. Actually, it does this with multiple molds arranged in a tree—or "runner”—pattern on one stem. Those replicas are then separated from the mold, cooled in water to harden them, then dipped in a ceramic mixture until a ceramic coating adheres to the wax pattern. The wax is then burnt out of the ceramic mold, and the ceramic is fire-strengthened in a furnace. When the ceramic molds come out of the furnace, metal is poured into them. The metal solidifies and cools, and then the ceramic is broken off the metal shape and the metal is detached from the runner. Typically, it then undergoes other treatments as well, such as sandblasting or machining.

Most job shop manufacturers use a batch system for this process. They run the whole batch out through one operation, such as wax injection, then move the batch to the next operation, where it waits its turn to be worked on. Schuemann explains that Signicast’s continuous flow process eliminates “the batching and the backlog between operations—if a backlog builds to more than four hours, we’ll shut down the upstream work center.” Instead, all work flows continuously through the system until the order is filled.

Thus, Signicast can produce parts much more cheaply and quickly than the competition. Schuemann says, “We’re doing castings in four and a half days, while our competition is doing them in four or five weeks.”

Also, Signicast has automated many of the previously manual operations in the casting process to improve efficiency and reduce labor costs. For instance, Signicast is the only company that automatically pours metal into the ceramic shells on the shop floor. Robots pick wax replicas out of the wax injection tool and place them in water for cooling, while other robots build up the shell around the wax tree and still others do finishing and sandblasting at the end of the process. What’s more, automatic storage and retrieval systems move parts between operations and deliver raw materials to operators as needed.

Signicast also manufactures on demand, if you will. Says Schuemann, “We start with the customer request date and plug that in as our due date; then we back-schedule to where it should be started; then we start the job on time.” So, he explains, “If we start on time and control our backlogs, we’ll ship on time.”

Usually, therefore, there are only one or two days’ worth of raw material inventory and finished goods because work-in-process flows through quickly. “Since we’re running at a continuous flow rate,” says Schuemann, “we know what that rate is and what the requirements are for raw material, so we bring raw material in just one or two days before we need it.”

If, on the other hand, a customer gives a due date that is not possible to hit using current processes, Signicast will speed up the processes in order to meet that customer’s desired due date. So both strategies are implemented with one thing in mind: satisfying the customer.

“Potential clients can’t believe it when they see how quickly we can ramp up and produce their parts within our zero-inventory plan,” says Todd McDonald, sales manager at Signicast. “But that’s the real beauty of continuous flow manufacturing.”