Implementing One Piece Flow with U shaped manufacturing cells is a great way to eliminate waste in most manufacturing environments with moderate amounts of variability in production size and product mix. One piece flow will have a tremendous impact on manufacturing lead times, production delays, inventory levels, and warehousing space requirements. Some of the key concepts to understand when transitioning to a manufacturing cell are: one piece flow, line balancing, right sizing, ergonomics, and quality control.

One Piece Flow, the opposite of batch processing, is the movement of a single product through the manufacturing process. One piece flow redirects the workforce away from non value added activities (waste) and to to focus on the manufacturing process. With batch processing, large amounts of wastes exist in waiting, transporting, and storage of inventory. Workers maximize their output at the expense of downstream processes and increased work in process.

With one piece flow, the work in progress (WIP) is drastically reduced, which minimizes exposure to defects in the manufacturing process and allows for quicker reaction to fluctuating customer demands.

One piece flow creates a smoother production process, with steady workloads and shorter lead times. It’s important the units of work performed in each position have equivalent cycle times in order to keep the process smooth. This technique is called “Line Balancing.”

Equipment

Batch processing relies on large machinery, which processes in 1,000-piece lots. Each process is dependent on the output of the last process as its input, so we must wait for the first process to end before the next begins. There is typically some storage and transportation delay between machinery. To calculate the total process time for up to 1,000 units, multiply each process by 1,000 (4s x 1,000 / 1s x 1,000 / 3s x 1,000) and add the values to the delay between processes. (900s + 1,500s). This example is optimized for the batch size (best case scenario), but note that producing 1, 25, 800 or 1,000 pieces takes the same total cycle time and creates excess inventory.

Right sizing machinery to meet customer demand, instead of minimizing part cost, is essential to the success of cellular manufacturing. Placing smaller and slower equipment in close proximity to other equipment and processes helps eliminate wasted space, walking, inventory build-up and lower initial cost. Cellular manufacturing is a system to transfer products between stations (i.e. U, J, or L shaped cell), a method to feed parts into the stations (flow racks, bins, or carts), and a means by which to flow finished goods and packaging out of the system.

Set Up Tips
* Always flow product in the same direction, counterclockwise.
* Cross train employees to be able to perform all or most functions within the cell to increase responsibility, quality, and traceability.
* Use a U shaped cell when possible to minimize the distance between the beginning and the end of the process.
* Use First In First Out to shorten lead times, reduce errors, and improve order accuracy.
* Position workstations as close together as possible to eliminate wasted space but not so close as to hinder maintenance or create discomfort for employees.
* Create a system for flowing sub parts into the system in an optimal manner, considering ergonomic principles.
* Keep the path of flow within the cell clear and unhindered.

The benefits of implementing cellular manufacturing in the appropriate environments can have a positive impact on a business. Reconfiguring machinery into cells reduces material handling and warehouse footprint. When properly executed, a company will simultaneously shorten their lead times and dramatically reduce work in process inventory. Having a cross trained workforce gives a factory increased flexibility to meet variations in demand and a better understanding of a quality product.

For more information, contact UNEX Manufacturing at 800-695-7726 or lean@unex.com.