How does your product flow? How will it flow after you implement lean manufacturing? These questions must be addressed. Products must move from one workstation or one process to another. As I've mentioned, this physical movement is wasted motion and you must apply careful consideration when deciding product flow. What works well for one manufacturer may not be the best solution for another. I will present a few options and then discuss the pros and cons of each.
Conveyor Belts
Conveyor belts are very common. Automated or manual, a conveyor belt allows the product to move along the line with very little effort, thereby reducing physical strain. In my opinion, this is a conveyor belt's only positive attribute. Automated conveyor belts are typically controlled by foot pedal at either the beginning or the end of the line. If the operator at the beginning of the line controls the foot pedal, it can create an early push. Once an operator has completed her work, the unit is pushed to the next worker. Ready or not, here it comes! The remaining workers are then forced to work while the product is in motion. On the other hand, if the last operator is in control, there could be an early pull, and although a pull system is the ideal condition, a pull signal can be initiated improperly.
Again, operators are working with a moving product. From an ergonomic perspective, operators are confined to one specified height that is set for the team as a whole.
If you choose to use conveyor belts, you will need to deal with culture change early in the process. The best approach is to ensure that operators flex within the workstations, a practice that allows all operators on the line to perform work within the specified task time. When each worker has completed his work, the foot pedal can be pressed to move the belt for the team and not the individual.
Conveyor Rollers
Conveyor rollers are very similar in use to conveyor belts; both move product. However, belts control all the workstations on a line, whereas rollers physically divide the workers and do not move the entire line. Automated conveyor rolling systems can be implemented, and they are essentially like belts. My focus is on manual roller systems.
Roller systems are built to a predetermined height. However, the rollers can be modified to fit individual workstations or lift tables. Operators pull units into their workstations as needed. But, as with belt systems, an early push or pull can be forced. Use of roller systems requires training and then control to ensure that products are not forced onto other workers. Conveyor rollers work well when used in conjunction with other workstation items, such as benches and lift tables.
Lift Tables
Lift tables are one of my favorite choices if the target process or assembly line can use them effectively. Operators are not confined to a predetermined height and can adjust and maneuver the unit to a height that is suitable to their personal working requirements. I call this "climbing in the product." Lift tables come with a foot pedal that is used to raise or lower the table to the desired height. Lift tables come in a variety of sizes, so there is one to fit every type of line.
As I've mentioned, adding conveyor rollers to a lift table provides more options in product flow. Production workers can place the unit at a productive height and also can easily pull units into their workstations. When you balance the line, be sure to account for the time associated with up and down motions of the lift table. Although it may take only a few seconds, when multiplied over numerous workstations throughout the day, this time can add up. Of course, movement time is wasted motion, but I consider it low priority because it is a valuable addition to the process.
Workbenches
If you are opting to use workbenches in a manufacturing line, make sure you analyze the need for them. From a materials and tools presentation perspective, workbenches are great because parts and tools can be placed directly in front of the worker. Adjustable workbenches are available that have a lever that can be turned to raise or lower the table.
When you analyze the need for workbenches, take into account that they often attract chairs or stools. I have never been a fan of chairs and stools on the production floor, because they take too much space and can place operators in poor sitting positions, causing back and neck strain. Does the work warrant the need for chairs? Small products require intricate work, perhaps with a magnifying glass, so these production lines may be good candidates for chair use.
On most other lines, production workers should be standing in front of product at all times. Standing encourages attentiveness and increased productivity, whereas chairs and stools may cause operators to become complacent or to slow down. If the workbenches are set at waist level in the station, you can avoid the use of chairs altogether. However, it is important to remember that workers may be standing for eight hours at a time. I discuss operator fatigue later in this chapter.
Mobile Lines
Assembly lines that can be moved easily, or rolled around the factory floor, are very handy. I once worked for a company that used mobile lines. They allowed flexibility, because the company could maneuver the processes as needed. Some products are heavy and bulky, requiring a mobile approach for efficient product flow.
Pallet jacks, pallets, carts, and so on are only a few types of mobile units that can be used on a line based on product requirements. For example, if your products require thick steel casings, as do safes or ATMs, placing them on pallets and moving them with pallet jacks is the recommended solution. Although there is some manual movement required within the process, you greatly reduce the
possibility of injured workers or the product falling and becoming damaged.
I assisted a company that removed an old conveyor roller system that had been used to build medium- sized engines. The roller system was replaced with customized carts, each with a small platform on which the engine was secured during assembly and transportation. These mobile carts were height adjustable and moved through the assembly line like a train. The wheels were also lockable to avoid uncontrolled rolling of the carts. When the engine was lifted off the cart into the next process for installation, the empty cart was returned to the beginning of the line. The materials and tools racks were also on wheels, so the entire line could quickly be rolled out of the way for cleanup or inventory counts.