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Adding Conveyors to the Lean Manufacturing Mix

Wed, 12/02/2009 - 4:26am
Kevin Gingerich
Moving to a lean system can be of great benefit to most medical device manufacturers. Unfortunately, not all of them are familiar with the tools and strategies that need to be put in place to maximize the return on this investment. This article focuses on conveyors and illustrates how they can further optimize an existing lean set-up or move a company more towards achieving a lean system.


Kevin Gingerich has worked in the area of assembly technologies at Bosch Rexroth for 18 years and has written extensively on assembly technologies and techniques during that time. He is the co-author of Rexroth's guidebook "Lean Manufacturing: Principles, Tools and Methods." Gingerich can be reached at kevin.gingerich@boschrexroth-us.com.

Automated assembly conveyors are usually not the first thing that lean manufacturing planners think of when developing their company's lean strategy.

Using conveyors in a lean manufacturing strategy is more than just moving things from one place to another; it's about eliminating unproductive waiting time by delivering things to meet customer or station demand.
That's because lean, in its most basic form, is generally associated with manual production systems that offer great flexibility. Not only can the workstations or lean cells be structured to match the value-added steps precisely, but workers can be shuffled into and out of the cell as production volumes change. Additionally, lean teaches companies to value its human workforce. A company's associates are both its most flexible work asset and its best source of new ideas for continuous improvement. And finally, it's often extremely helpful to prove out a strategy first before making an investment in new equipment, so many companies will dip their toes in lean by simply re-arranging existing workstations. All of this makes tremendous sense.

Where do Conveyors Fit in a Lean Strategy?
Curved conveyor sections can go around obstacles in the plant and take advantage of tight space limitations in the overall floorplan.
One of the common misconceptions about conveyors is that the only function they perform is to move things from one place to another. It's very common for people to view conveyors as unsophisticated, non-value-adding parts movers. In this line of thinking, conveyors represent unnecessary "transportation"–one of the seven classic forms of waste that lean companies should strive to eliminate. But today's modular, flexible conveyor systems go far beyond the simple transport of products. Using sophisticated aluminum bending technology, conveyor suppliers can create curved sections that can go around obstacles in a medical assembly plant, provide steep uphill or downhill transport, create tight-radius storage and buffering systems in small amounts of space, or build a sophisticated highway-like product routing, assembly, handling, and packaging system. With contemporary modular designs and hundreds of positioning, orientation, and handling accessories, the conveyor of today is nothing like the long, flat, endless belt of products many people still picture when they hear the word "conveyor." Years of innovation have created a generation of modular conveyors that put the right part in the right place at the right time to ensure maximum productive output.

Conveyors Help Eliminate Waste
In a power-and-free system, the part is placed on a workpiece carrier or pallet, which is then placed on the transport belt. Parts can be routed to balance the flow of work.
If circumstances are right to consider the use of conveyors (i.e., production volumes are high enough), they can help eliminate waste in any lean strategy. One of the most important contributions is to help eliminate unproductive time ("waiting time"–another of the seven classic forms of waste.) A well-designed conveyor system should deliver parts or subassemblies to stations at the pace necessary to meet customer or station demand. In other words, any assembly and production that's done using conveyor systems should be tied to customer "Takt" time, just as processes using manual work cells would be.

Today's modular conveyor systems let assembly system designers do just that through the use of "power-and-free" technology. In a power-and-free system, the part is placed on a workpiece carrier or pallet, which itself is then placed on the transport belt or chain. This enables one pallet (or several) to be stopped, while the belt or chain continues to run and other parts continue to travel through the system. Once the necessary work is performed, the part is released to the next step, and the next part arrives at this station. If one process takes more time than another, parts can be routed onto one or more cycle-independent spurs to balance the flow of work. Accessory modules, such as various types of stops, sensors, curves, lifts, positioning units, and right-angle transfer stations make it easy to put a part exactly where it's needed when it's needed there. Waiting time is eliminated, because new work arrives as completed work leaves.

Conveyors make it easy to put a part exactly where it's needed when it's needed there, eliminating waiting time because new work arrives as completed work leaves.
Modular conveyor systems can also help eliminate wasted motion. The use of T-slotted aluminum as the main framing system lets users order as much or as little conveyor as they need and lay it out in the most efficient manner for a given production environment. The work height can be set to minimize worker reaching and bending, and the T-slotted frame allows for the attachment of work instructions, tool balancers, vision systems, and other necessary tools anywhere along the conveyor. The modular design also allows manufacturers to take full advantage of three-dimensional space by using vertical and horizontal curves, and vertical pallet transfer units to keep the conveyor footprint as tight as needed. Additionally, since the system can employ bolt-together technology, the line can be taken apart and moved, reconfigured, or expanded as the lean manufacturing concept changes.

For medical manufacturers, quality control is extremely critical, and modular conveyors can help to eliminate another kind of waste–correction and re-work. By transporting a product on a workpiece carrier and stopping it precisely in a station, flexible assembly conveyors ensure that the product is positioned exactly as needed for careful work to occur, either manually or in an automated station. It's also possible to build a mini cleanroom environment around a single process or route a section of the conveyor through a cleanroom. Integration with vision systems can verify that work has occurred properly or that no contamination has occurred to any sensitive components.

Conclusion
Today's modular conveyors make it easy to develop curved sections that can go around obstacles in a plant, provide steep uphill or downhill transport, and create tight-radius buffering systems in small amounts of space.
In today's highly customized assembly and handling environments, the use of lean manufacturing techniques plays a critical role in eliminating waste. Modular assembly conveyors, when used in a lean environment, can make a big contribution to waste reduction by minimizing unproductive time, wasted motion, correction, and re-work. The ability to design and install a system that can change easily to keep up with the evolution of a lean strategy over time gives medical manufacturers an important tool in laying out that strategy. Conveyors are here to stay, and they're better than ever at meeting the demands of today's sophisticated manufacturing planners.

Online
For additional information on the technologies, techniques, and products discussed in this article, see MDT online at www.mdtmag.com or Bosch Rexroth at www.boschrexroth-us.com/lean.
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