Flow is a key element in lean manufacturing. Manufacturers want to minimize inventory waste, motion, product, resources and time by smoothing out the flow of raw resources into the finished product. However, as a company works to enhance flow, it most likely will encounter some problems. To improve productivity while working toward the ideal of "continuous flow," a firm may need to have some buffer inventories or buffer stock of essential components.
Despite good intentions, however, maintaining buffer inventory can run amok. For example, a ground beef processor I have been working with had a buffer stock problem resulting in expensive setbacks. The processor needed large amounts of boxes. The size and number, however, had not been worked out to optimize continuous flow. The facility had made sure enough boxes were available, so it did not slow down the line and always had plenty of buffer stock.
The down side of this buffer system is boxes are gravity fed to the pack. Visualize 10 lines perpendicular to one packaging line. Two case erectors are located above the packing line. Starting at the platform, boxes come down two conveyors to the packing line. The box maker is on the upper platform running the two different case erectors. And despite being older models, both case erectors work rather well.
The box maker’s job is to maintain box blank inventory; stack cardboard box blanks, feed the blanks into the machines, fold, glue and distribute the box onto the gravity-fed conveyor system. He maintains inventory, keeps the machines running and ensures the glue is warm and tacky. Once the lines are filled, this particular box maker stands out on the steps overlooking the packers. This is where problems arise.
Unfortunately, the box maker has not demonstrated an appreciation for the lean manufacturing concept of continuous flow.
More specifically, he does not grasp the nuance of buffer stock, which helps keep the lines running smoothly. He makes about 15 boxes more than needed, puts them on the feed chute and takes a break. He is aware of the fine line between continuous flow and too much buffer stock, but he does not see continuous flow as part of his job.
Meanwhile, packers are pulling boxes from a line at shoulder height. When extra boxes are on the line, gravity and extra weight make pulling boxes off the feed line difficult. Moreover, boxes tend to jam and often fall off the feed line onto the wet and sometimes bloody floor, and these boxes become waste. If each box costs 30 cents and at least 40 boxes are wasted each day, the daily cost can reach $12 just for materials.
While this cost may not be significant, it is counter to continuous flow. Other labor for cleanup and material costs such as processing cardboard scrap and wasted glue increase the cost associated with this problem.
Additionally, there is a substantial potential cost, which is difficult to predict in dollars but, nevertheless, is guaranteed to be expensive for the company and damaging to employees. This potential cost is injury.
Every time a worker pulls extra hard to dislodge a box, there is an injury risk. Sometimes the effect is immediate and a packer may need to rest or treat sore muscles. More insidious is carpal tunnel syndrome. From my consulting viewpoint, a carpal tunnel injury is brewing in the extra buffer stock situation.
Just one case of carpal tunnel can have major financial impact on a company. While the injured worker goes on disability and only gets paid partial wages, production is eliminated and another packer must be hired to replace the disabled one. Additionally, insurance rates most likely will increase 1 percent to 5 percent. Meanwhile, the box maker in question could still be making extra boxes each run, and the waste and costs accumulate.
Something had to be done about this buffer stock situation. First, the plant canceled the work request for a shutoff switch to regulate the number of boxes on the chute using an electronic eye. The idea of the switch was to shut down the case erectors once the boxes reached a certain height on the conveyor. It probably would have worked, but it was fairly expensive and would take time from routine and preventive maintenance.
Boxes did not bind up at the packer level if they did not exceed a certain height on the chutes. The ideal height lined up with the conveyor chute hangers — the hangers for the gravity feed line were at the correct spot. The box maker was informed that when the boxes lined up to the hanger supports to stop making more boxes.
If box production was stopped at that point, packers could pull boxes with ease. However, the box maker’s behavior did not change. He worked fast, made extra boxes lined up to the case erector platform. Again, he was reprimanded and continued working ahead to facilitate his break. There was no understanding of the value of continuous flow and buffer stock. So the team leaders, safety representative and I used our imagination again. This time, the box maker was given a floor clean up job, and he is now picking up waste. We are hopeful he will learn the value of minimizing waste. The company has lowered box waste and has surely precluded costs and concerns related to injured personnel.
While not every processor has the same equipment or manufacturing system, the concepts of continuous flow, buffer stock and elimination of waste are universal. Team leaders should take time to walk through their plants looking for waste. Waste elimination can be applied to countless applications. By spotting waste and eliminating it, savings continue. The traditional thinking vs. lean thinking graphic on Page 56 demonstrates how a company can have a better price point, while still generating the same profit. The elimination of waste is like a tax credit. If a plant eliminates a dollar of waste, it is converted to a dollar in profits.