One-piece flow, also known as continuous flow or single-piece flow, is a manufacturing process that involves producing products one at a time, without interruption.
This process can help minimize inventory levels, waiting times, and defects, while also maximizing utilization of talent and space.
One piece flow, sometimes referred to as “continuous flow” or “single-piece flow,” is a discrete production method used in lean manufacturing that is closely associated with the Just-in-Time system—a key concept within the Toyota Production System. One piece flow is also one of the most important factors to consider when it comes to developing a lean environment.
It is closely associated with the Just-in-Time system because manufactured goods go through a continuous flow of steps with no Work-in-Process (WIP) or downtime. In a one piece flow setup, workstations are arranged in a way where production can flow continuously—one at a time through each step of the process—from setup until completion.
One-piece flow, also called continuous flow, refers to the way products move from one step in the process to the next—moving them efficiently by planning workflow based on the product and its needs, instead of the organization or equipment.
One Piece Flow and How it Reduces Waste and Increases Productivity
One-piece flow is a manufacturing process in which units are processed one at a time and move through the process independently from other units. This type of flow minimizes inventory levels, waiting times, and defects while maximizing utilization of talent and space. However, one-piece flow can be more expensive to set.
One piece flow, sometimes referred to as “continuous flow” or “single-piece flow,” is a discrete production method used in lean manufacturing that is closely associated with the Just-in-Time system—a key concept within the Toyota Production System. One piece flow is also one of the most important factors to consider when it comes to developing a lean environment.
It is closely associated with the Just-in-Time system because manufactured goods go through a continuous flow of steps with no Work-in-Process (WIP) or downtime. In a one piece flow setup, workstations are arranged in a way where production can flow continuously—one at a time through each step of the process—from setup until completion.
one-piece flow is a key concept within the Toyota Production System. Achieving one-piece flow helps manufacturers achieve true just-in-time manufacturing. That is, the right parts can be made available when they are needed in the quantity they are needed.
In the simplest of terms, one-piece flow means that parts are moved through operations from step to step with no work-in-process (WIP) in between either one piece at a time or a small batch at a time. This system works best in combination with a cellular layout in which all necessary equipment is located within a cell in the sequence in which it is used.
While many are familiar with the terminology, there is still a significant amount of confusion regarding what one-piece flow means and, more importantly, how to achieve it.
Functional Layout
Let us begin by stepping back and attempting to understand the concept of “connected flow.” Achieving connected flow means implementing a means of connecting each process step within a value stream. In a typical MRP batch-and-queue manufacturing environment as illustrated above, parts move from functional area to functional area in batches, and each processing step or set of processing steps is controlled independently by a schedule. There is little relationship between each manufacturing step and the steps immediately upstream or downstream. This results in:
Large amounts of scrap when a defect is found because of large batches of WIP
Long manufacturing lead time
Poor on-time delivery and/or lots of finished goods inventory to compensate
Large amounts of WIP
When we achieve connected flow, there is a relationship between processing steps: That relationship is either a pull system such as a supermarket or FIFO lane or a direct link (one-piece flow). As illustrated below, one-piece flow is the ideal method for creating connected flow because product is moved from step to step with essentially no waiting (zero WIP).
One Piece Flow Cellular Layout
Why would we not always create one-piece flow for every set of processes within a value stream? To be good candidates for one-piece flow, we must have the following conditions:
Processes must be able to consistently produce good product. If there are many quality issues, one-piece flow is impossible.
Process times must be repeatable as well. If there is much variation, one-piece flow is impossible.
Equipment must have very high (near 100 percent) uptime. Equipment must always be available to run. If equipment within a manufacturing cell is plagued with downtime, one-piece flow will be impossible.
Processes must be able to be scaled to takt time, or the rate of customer demand. For example, if takt time is 10 minutes, processes should be able to scaled to run at one unit every 10 minutes.
Without the above conditions in place, some other form of connecting flow must be used. This means that there will be a buffer of inventory typically in the form of a supermarket or FIFO lane between processes; the goal would be to eventually achieve one-piece flow (no buffer) by improving the processes.
If a set of processes is determined to a candidate for one-piece flow, then the next step is to begin implementation of a one-piece flow cell.
The first step in implementing a one-piece flow cell is to decide which products or product families will go into the cells, and determine the type of cell: Product-focused or mixed model. For product focused cells to work correctly, demand needs to be high enough for an individual product. For mixed model cells to work, changeover times must be kept short; a general rule of thumb is that changeover time must be less than one takt time.
The next step is to calculate takt time for the set of products that will go into the cell. Takt time is a measure of customer demand expressed in units of time and is calculated as follows:
Takt time = Available work-time per shift / Customer demand per shift
Next, determine the work elements and time required for making one piece. In much detail, list each step and its associated time. Time each step separately several times and use the lowest repeatable time.
Then, determine if the equipment to be used within the cell can meet takt time. Considerations here include changeover times, load and unload times, and downtime.
The next step is to create a lean layout. Using the principles of 5-S (eliminating those items that are not needed and locating all items/equipment/materials that are needed at their points of use in the proper sequence), design a layout. Space between processes within a one-piece flow cell must be limited to eliminate motion waste and to prevent unwanted WIP accumulation. U-shaped cells are generally best; however, if this is impossible due to factory floor limitations, other shapes will do. For example, I have implemented S-shaped cells in areas were a large U-shape is physically impossible.
Finally, balance the cell and create standardized work for each operator within the cell. Determine how many operators are needed to meet takt time and then split the work between operators. Use the following equation:
Number of operators = Total work content / Takt time
In most cases, an “inconvenient” remainder term will result (e.g., you will end up with Number of Operators = 4.4 or 2.3 or 3.6 instead of 2.0, 3.0, or 4.0). If there is a remainder term, it may be necessary to kaizen the process and reduce the work content. Other possibilities include moving operations to the supplying process to balance the line. For example, one of my clients moved simple assembly operations from their assembly line to their injection molding operation to reduce work content and balance the line.
After implementation is complete, one-piece flow must be sustained through regular auditing of standardized work.
One-piece flow is one of the key concepts within lean manufacturing; in most cases, a piece of a value stream can be transformed into a one-piece flow operation. While one-piece flow is not always achievable for an entire door-to-door value stream, manufacturers must continually improve their processes in an attempt to get closer and closer to true one piece flow. This will reduce inventory levels, reduce manufacturing lead time, and improve customer service levels.
How does One Piece Flow work – a quick overview –
In a one-piece flow, a product is completed before the next one is started. The name refers to the maximum number of products between operations, workstations, processes. That’s why it’s also called “single-piece flow”, as everything is constantly progressing and only one item is in any given queue at a time.
One Piece Flow Definition it can be defined as a manufacturing process that involves producing products in a continuous flow, one piece at a time. The process involves moving a single unit of product through each stage of production, from start to finish, without interruption.
One-piece flow can have the following advantages:
Eliminates overproduction
Reduces inventory
Maximizes floor space utilization
Makes it easier to identify and segregate defects
Creates a safer environment
Reduces lead times
Here are some steps you can take to implement one-piece flow:
Assess your current production process, Invest in the right equipment and resources, Train your workers, Implement changes slowly, and Monitor and adjust as needed.
One-piece flow can be more expensive to set up than other methods, such as batch production.
Batch production involves producing goods by batch, in bulk, or en masse. The goods in batch production have to be finished first before it can be moved to another step.
This can result in longer lead times due to the time required to produce a large volume of products before they can be shipped.
Achieving connected flow means implementing a means of connecting each process step within a value stream. In a typical MRP batch-and-queue manufacturing environment as illustrated above, parts move from functional area to functional area in batches, and each processing step or set of processing steps is controlled independently by a schedule. There is little relationship between each manufacturing step and the steps immediately upstream or downstream. This results in:
Large amounts of scrap when a defect is found because of large batches of WIP
Long manufacturing lead time
Poor on-time delivery and/or lots of finished goods inventory to compensate
Large amounts of WIP
When we achieve connected flow, there is a relationship between processing steps: That relationship is either a pull system such as a supermarket or FIFO lane or a direct link (one-piece flow). As illustrated below, one-piece flow is the ideal method for creating connected flow because product is moved from step to step with essentially no waiting (zero WIP).
Advantages
One piece flow has a number of major advantages compared to batch production flow, particularly in terms of waste reduction, manufacturing time reduction, and better process efficiencies. More about its advantages are listed below:
Shorter production time—it reduces the time needed for completion because there is reduced WIP and no downtime. When there is a shorter processing time, expenses required for production are automatically reduced. Additionally, when the production time is reduced, manufacturing companies can be more flexible in responding to demands or changes required by customers.
Less inventory—it reduces the need for floor space or warehouse space for stocks because companies are only producing what is needed or ordered from them.
Faster detection of errors or defects—it is easier to spot defects in the one piece flow system because manufacturing is focused on one product at a time. If a problem is detected, the only affected product will be the one in the current process. Whereas, defects in a batch production can affect the entire batch or more before they are noticed. When detection is faster, corrective action can be taken quickly to ensure the problem won’t reoccur and affect the other items.
Improved lead times—it helps in getting the products reach your customers faster, boosting customer satisfaction.
Better product quality—it becomes much easier for a manufacturer to make quality products. This is because each operator doubles up as a quality control inspector and can fix problems they encounter at their work station before moving the item to the next step in production.
Reduced waste—it minimizes the occurrence of deadly waste because one piece flow prevents overproduction, whereas all unsaleable items from batch production contribute to a myriad of waste—inventory waste, waste in labor, waste in capital, and time wasted.
Safer work environment—it makes the workplace safer because clutter is lessened when one piece flow is implemented, minimizing the risk of work-related injuries.
Improved workers’ morale—it encourages employee engagement and involvement in problem-solving, making the workplace conducive to proactively catching issues.