Cellular Processing is an approach in which equipment and workstations are arranged to facilitate small-lot, continuous-flow production. In a manufacturing "Cell," all operations necessary to produce a component or subassembly are performed in close proximity, thus allowing for quick feedback between operators when quality problems and other issues arise. Workers in a manufacturing cell typically are cross-trained and, therefore, able to perform multiple tasks as needed. Cells also work well in office functions.
Single-Piece-Flow can be described as an ideal state of efficient operations, where batch sizes and lot production are replaced by working on one piece at a time. It is a Lean Enterprise goal to achieve single-piece flow in every operation where possible.
The perfect process consists of a single object transitioning through a series of operations while constantly accumulating value that the customer is willing to pay for.
Typically, the methodology is applied within manufacturing operations but works equally if not better in administrative processes. The problem in administrative processes is that batches are often hidden electronically.
Batching is a natural human tendency for multiple reasons. It could be that a particular process step requires a significant amount of time to conduct a set-up or the task is onerous and people like to defer it to a later time. In the case of administrative instances, workers are constantly being interrupted by co-worker's phone calls, so they collect the most pertinent information and defer the final processing to a quieter time … whenever that may happen.
Achieving one-piece flow requires balancing the process steps to match Takt time. Takt time being available time divided by Customer demand. This means we can define the rate at which the customer can expect a product to be delivered.
WARNING!!! Be careful about balancing the process using only Takt time - you will be in trouble. Once you have calculated the Takt time you need to subtract losses (Quality, Personal Fatigue & Delay (PF&D) etc.) to define your processing time and then use this time to balance the process.
Achieving one-piece flow requires the elimination of waste. As a company reduces these wastes and strives for single-piece flow, many other benefits will follow. Some of these benefits include:
Improved quality and fewer defects
Less space required to build a product
Enhancement to overall manufacturing flexibility
Identification of future kaizen workshops
Ensures a safer work environment
Improves employee morale
We will review each of these benefits in more detail:
(1) Improved quality and fewer defects: When batching and lot production are eliminated, there is less opportunity to manufacture defects. Since the batch size will be just 1, there will not be mountains of inventory to count, move, store and pick.
Furthermore, single-piece flow ensures that if there is a quality problem, we know that the defect has affected only that single part. We do not need to dedicate hours isolating and testing other material in the same production run to determine if it meets quality standards.
Of course, if a defect is caught in a single piece flow environment, In this case, the manager or supervisor must determine if standard work was followed and if so, what changes need to be made to the standard in order to ensure that the problem will never resurface again. Kaizen!
(2) Reduced Inventory: Implementing single-piece flow will require each operation to only produce what is needed by the next operation (in Lean jargon, we call this individual the surgeon). When followed properly, the process will eliminate any opportunity to build ahead. Consequently, inventories will not be allowed to build up.
(3) Requires less space: As inventory levels are reduced, less space and manpower will be required to manage (receive, count, stock, store, pick and deliver) it. In addition, single-piece flow usually results in manufacturing cells that squeeze machines close together so that a single operator can oversee many pieces of equipment with the least amount of walking motion.
(4) Enhances overall manufacturing flexibility: We know from our value steam maps that the less inventory in a value steam, the shorter the lead-time will be from customer order to product delivery. In a single-piece flow environment, since we operate with less inventory, lead times will also drop, thereby giving us more time to react to customer orders (unless the strategic decision is made to pass off the lead-time gains to the customer in order to beat competitors!).
(5) Makes identifying future Kaizens simpler: We have already discussed that in a single-piece flow environment, defects and WIP inventories fall. As this happens, the shop floor will open up and it will become easier to see production problems. For example, if a particular process can not keep up with takt time and WIP is not allowed to be incurred, it will quickly become apparent to even the casual observer that something is wrong. In this case, it will be easy to decide where to focus the next improvement activity.
(6) Ensures a safer work environment: Less inventory means less clutter, more light in the darkest corners of the factory and the opportunity to better layout equipment and tools. Also, since manufacturing cells are occupied by a set number of employees who each know their repeating tasks (as defined by standard work), there is less opportunity for unexpected movements, which decreases the chances of accidents.
(7) Improves employee morale: Since single piece flow results in production problems being identified and (hopefully) solved right away. Team members will receive immediate feedback on their work. This in turn will give everybody more ownership in their production area. Also, provided they lead problem-solving efforts by focusing on processes and not individuals, more trust will be gained in managers.
These are just some of the benefits of single-piece flow. Of course, implementing such a production system is easy to write about or discuss in an academic context. Inside the plant, achieving single-piece flow will require years of work. At a minimum, waste must be continually sought, standards (via 5S for example) must be implemented and maintained, and a level loaded (heijunka) schedule must be developed. All this will require many hours of hard work and constantly challenging the current state.
You may have occasional work that interrupts the process. There is the roving operator defined as the Water Spider who flits around and between Cells acting as a line support function to handle relief work and recurring-but-not-every-cycle tasks, such as moving materials in, moving finished goods out, building another cardboard box when the previous one has been packed full of the finished product. When it is not practical to have a Water Spider, you can have Supervisors or team leaders help in these areas.
Cells and Single-Piece-Flow methodologies really seem counter-intuitive, but they work and your productivity will dramatically increase while your quality improves. However, you really need to stay committed during the development and compliance phases. Batch muscle memory is one of the hardest paradigms I have faced to kill in my career.