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Posted by Sadia Waseem
One piece flow also known as single-piece flow is the concept of producing one good at a time as it flows between different processes. It is a part of the lean manufacturing concept that ultimately increases the efficiency of a process by reducing waste. The concept originated from the Toyota Production System (TPS) and is an important part of Just In Time (JIT) manufacturing, a technique that produces products only when needed.
The effectiveness of single-piece flow can be judged from the case study by Procedia Manufacturing, which shows that implementing single-piece flow in an automotive industry increased productivity by 6% and significantly decreased the scrap rate.
There are numerous benefits of single piece flow. However, before we move on to those, let’s understand the concept of single-piece flow. It is a quite broad concept, associated with many other tools and techniques. In this article, we will dive into every aspect and show you the best way to implement it.
The concept of one-piece flow is based on some principles to ensure an efficient production system. Here, we will explore how these principles are interconnected to determine the foundation of the one-piece flow methodology.
1.Minimize Work-in-Process (WIP) Inventory
One of the most important principles of single piece flow is that it targets Work-In-Process inventory, which refers to the goods that are unfinished and waiting to be sold. For example, in a textile factory, fabric that is cut and waiting to be sewed is an example of WIP inventory. It is important to reduce WIP inventory since it does not add value to the process, increases costs and takes up space. One piece flow eliminates large batches between each stage waiting to be processed, which ultimately minimizes WIP inventory and associated costs.
Effectiveness: A study in the International Journal of Computer Integrated Manufacturing showed that by implementing a one-piece flow in the production system, a company was able to eliminate WIP inventory completely which previously added 216 minutes of non-valued time to the process.
2.Continuous Flow of Units
This principle involves moving units continuously through each production stage without waiting in between, which not only leads to smoother operations, but quick detection of defects and rapid remedial action. When units are produced in batches, defect rates are quite high because they are inspected after one batch is completed. Continuous flow of units ensures shorter lead time and low cost, with quick adaption to flexibility according to changes in demand.
Effectiveness: One of the books about Just In Time (JIT) manufacturing by Pearson discussed the reduction of cost in an example after the implementation of continuous flow. It is stated that after the implementation of continuous flow, indirect expenses reduced from $200,000 to $180,000 as it cut down direct labor cost.
3.Cellular Manufacturing Layout
Cellular manufacturing layout is another fundamental principle of one-piece flow. It involves the arrangement of equipment and workstations in a logical and sequential order to minimize transportation and waiting. In a cellular manufacturing layout, machines are placed close to each other, and the layout follows the process steps. This arrangement enhances communication between workers and the changeover is also quick between stations.
Effectiveness: Mohd. Norzaimi conducted a study about the effectiveness of a one-piece flow system in which he stated that a one-piece flow 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.
4. Kanban Board for Pull Production System:
A pull production system is essential to implement single-piece flow. In this production system units are only processed when there is a demand rather than producing large quantities of units beforehand and storing them as an inventory. The best way to use a pull production system is through a kanban board, which uses a card, or an electronic equipment to signal when material is needed and ensures smooth flow of material through visual representation.
Effectiveness: John Miltenburg researched about implementing a single-piece manufacturing flow on a production line he used a Kanban board for the pull production system. As per the study, the Kanban board not only helped to implement the pull production system but also identified problem areas that could hinder the effective implementation of one-piece flow.
Successful implementation is possible through careful planning and adequate preparation. Here are the pre-requisites and detailed steps to successfully implement one-piece flow:
Pre-requisites for One-Piece Flow Implementation:
• Stable Demand Patterns
For an effective implementation of one-piece flow, the demand for products should be stable. Stable demand can be predicted without variation which helps to prepare beforehand for the process. High variation in demand for the product can challenge the system’s efficiency.
• Standardization of Work Process
The basis of one-piece flow is standardization, so make sure that your process is well-defined before you implement one-piece flow. You can use a worksheet to standardize your process. The worksheet can document the movements and time required for each task.
• Skilled and Adaptable Workforce
The workforce should be skillful to perform efficient work. Moreover, make sure they can adapt well to any changes in the production system that took place after the implementation of single-piece flow.
• Analyzing the Current State
The first step to implementing a one-piece flow is analyzing the current state of the production process. You can analyze it through developing Value Stream Mapping (VSM) of the process. VSM is a visual tool in which all the manufacturing steps are mentioned along with their cycle time. It helps to identify value-added and non-value-added time and activities. The visual map of the process helps to identify inefficiencies and bottlenecks
• Design a one-piece flow layout
After analyzing the current state of the process, it is necessary to rearrange the workstations and machines according to the flow of material. The goal is to develop a layout that minimizes material and man movement along with less lead time and maximum efficiency.
• Standardize cycle time
Once you have modified the layout, you can conduct a time study to calculate the cycle time for each of the steps to ensure the workload is balanced across the station. Ensure that cycle times are consistent to maintain flow. You can use AI-powered software such as Kaizen Copilot to automatically balance your lines and ensure that work is distributed evenly across workstations.
• Kanban system for material control
Once you have standardized your work process, develop a Kanban system to visually analyze and control the flow of material. The Kanban system shows backlog in process, along with the ongoing material movement. With the kanban system, you can easily identify, any inventory that has been stuck between processes for a long time, so you can quickly take decision about these items. To use the Kanban system effectively, keep an eye on your work-in-progress inventory and reduce it to a minimum.
• Employee training
Make sure your employees are familiar with new work procedures and one-piece flow principles. Ensure they are adequately trained through practical demonstrations. You can do this effectively by using software like Assembly Copilot. Assembly Copilot gives process instructions in real time to workers and alerts them when they are about to make a mistake, which makes the transition easier from batch to one-piece flow.
• Monitoring and Review
Monitor the process regularly to ensure that the one-piece flow is implemented efficiently. Workers tend to start working in batches when no one’s watching, which defeats the purpose of implementing one-piece flow and reduces quality and throughput. You can use Assembly Copilot can help to enforce that worker keep performing single-piece flow and don’t start working in batches.
While one-piece flow has numerous benefits, it does come with its own limitations and challenges such as:
• Product variety and complexity
One-piece flow can be quite difficult to implement when you are dealing with a high variety of products. For example: a guitar manufacturer who custom builds guitars according to customer specifications may struggle with one-piece flow.
Consideration: Hybrid systems or cellular manufacturing may be more appropriate for high-variety environments.
• Cultural shift and resistance to change
The transition from traditional batch processing to one-piece flow often requires a major change in working practices and mindset. Employees are used to of their traditional work environment and may resist change to a one-piece flow.
Solution: Comprehensive training programs and clear communication about the benefits of one-piece flow is essential.
• Initial investment in layout changes
Changing whole layout of the factory to accommodate one-piece require initial investment for the arrangement of machines. For instance, you might need to invest in the set-up of U-shaped cells or to rearrange some equipment so that flow can be continuous.
Recommendation: Do a comprehensive cost benefit analysis before making the investment.
• Maintaining flow during disruptions
In most cases, one-piece flow system cannot handle disruptions like equipment breakdown or material shortages. A single point of failure can shut down the whole assembly line.
Solution: Implement preventive maintenance programs and rapid-response protocols for handling disruptions.
Despite the limitations and challenges, many organizations successfully implement and profit from this technique. However, it requires thoughtful planning and continued dedication to continual improvement along with appropriate technologies that help in transitioning into a one-piece flow.
Many organizations still follow the batch flow technique, in which an entire batch is made first before it is moved to the next station. Is batch flow better than single-piece flow? There isn’t a simple “better” answer between single-piece flow and batch flow. The ideal approach depends on several factors specific to your manufacturing environment. Here’s a breakdown to help you decide:
|
One-Piece Flow |
Batch Flow |
|
Production Method |
|
|
The units are produced one at a time, with no waiting between stations |
Large quantities of units are processed at each workstation before moving to the next stage |
|
Quality Control |
|
|
One-piece flow allows immediate detection of defects, resulting in high-quality products |
Batch processing can lead to a large number of defective products before the defects are identified and rectified |
|
Productivity |
|
|
There is no setup time involved, which reduces processing time and increases productivity |
It requires longer setup and processing time, leading to low productivity |
|
Lead Time |
|
|
The lead time is quite low comparatively as the processing time is shorter and shipment can also be made in smaller quantities |
The lead time is high in batch flow since there is waiting involved between stations and a large quantity is required for shipment |
|
Inventory levels |
|
|
Minimal Work-in-Process (WIP) inventory levels as a single unit is moving through the entire process |
High Work-in-Process (WIP) inventory is accumulated while batch flow |
Ultimately, the best approach might involve a hybrid combining elements of both methods. Analyze your specific needs, resources, and production environment to determine the optimal workflow for your business.
It may take long to realize the benefits of implementing one-piece flow and it might seem difficult as well initially. However, there is no doubt that the long-term benefits often outweigh these hurdles. Nowadays, it has become easier with AI-based software like Kaizen Copilot and Assembly Copilot. You can use Kaizen Copilot to set up and optimize a process quickly and then use Assembly Copilot to train workers and ensure compliance. Want to try out AI Copilots for your manufacturing processes? Get a free demo today!
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