As a follow up to our 9-part “Ready for Change” article series, our next step down the “Lean” path is to introduce other tools and methods to reduce waste and time. The first in this new bi-monthly series focuses on SMED, Single Minute Exchange of Die, and how this process integrates with the 5S process.
In the distant past, a typical truss company fabricated 3 basic truss types. A common truss—depending on the load and span, a Queen, Fink, Warren, or Modified Queen—a gable end, and a scissor truss. These truss types typically possessed a standard heel, 24-0” overhang, and pitches of 4, 5, or 6/12. A skilled assembler (a layout man) using a tape, marker, and blocking would build a jig, define the span, set the location of the peak center, overall height, and tail length. In a given shift, 3 to 5 jigs might be set and the time it would take to construct the templates for a given truss could be as much as 20 to 60 minutes. After the jig was set, tens to hundreds of this truss were built. That was then—a high-volume, low mix market—however, today is very different.
At the Porsche plant in Stuttgart, Germany, robots assemble and weld the car frames, but the more intricate parts (i.e., engines and transmissions) are still fabricated by hand at a bench. All the pneumatic and air tools are suspended above the bench and within easy reach of the technicians. Hand tools are sorted and arranged, clipped to the bench in specific placement spots. All parts and materials are delivered to the bench by a robotic conveyor. Each piece is delivered in sequenced order and automatically arrives just-in-time based on the technician’s personal history of assembly time. At the bench, the operator has controls to speed up, pause, interrupt, and return defective parts, never having to walk away from the bench.
Today, the fabrication of roof trusses is a low-volume, high mix process. On average, 2 to 3+ trusses are built per jig and 30 to 70+ jig setups occur per shift.
Case Study:
If the truss station is setting up 32 jigs per shift at an average of 2 trusses per jig and 60 bd.’ per truss, that line is producing 3,840 bd.’ That equates to 4 setups per hour. How can a plant set up and build more per shift? The goal is to increase the number of setups to 40, reduce the time of each setup by 5 to 10 minutes, and enable 4,800 bd.’ of production.
Single-Minute Exchange of Die (SMED) is a lean method for reducing waste/time in the assembly process. It provides a rapid, efficient way of converting a manufacturing process from running the current product to the next. The action steps of this process are to convert as many changeover steps as possible to “external” (performed while the equipment is running), and to simplify and streamline all other steps.
For this example, a truss line has the latest in automated pucks to outline the perimeter of each new jig. Now, what steps take the most time in the setup of a truss? Based on this case study, each jig setup requires an average of 15 minutes to complete and start building the next truss type. If the automatic jigging pucks move into position within 2 minutes, how are the additional 13 minutes used and how can you reduce the time cycle? The sorting of cut parts, locating and pulling plates can easily account for the balance of this time. The “Lean” DMAIC method and applying SMED will lead you down the best path to cut this time.
Having a team member pulling plates in advance or, if your saw capacity exceeds production, having the saw team sort and move cut parts close to the jig site will greatly reduce time and allow 1 more jig setup per hour to 6 and increase production results.
The purpose of the 5S process is to Sort, Straighten, Shine, Standardize, and Sustain to improve efficiency by eliminating waste of motion, looking for tools and materials. The 5S process all alone is effective at reducing waste. 5S is a Lean method for implementing order in the workplace. But as illustrated in the Porsche example, integrating SMED with 5S is a powerful combination which can give your team context and a greater sense of purpose than 5S alone.
Next Article:
Implementing other Lean tools to improve productivity
A Certified Lean Practitioner, Keith Parker has helped companies define and implement practices that improve their businesses and their bottom lines. You may reach Keith at 612-239-1089 or email.