Conquering Waste Through One Piece Flow. A Lean Approach

One piece flow, also known as single piece flow, is a lean manufacturing concept that allows products to smoothly flow through production processes one piece at a time. 

It is a pull production system where downstream processes signal their needs to upstream processes, which then produce just what is needed by the next step.

Key Highlights

• One piece flow is a lean production method that allows workpieces to move through production processes one piece at a time
• It minimizes work-in-progress, reduces lead times, improves flexibility, and promotes continuous improvement
• Its implementation involves steps like calculating takt time, designing process layouts, applying pull, and standardizing work
• Challenges include change management, training requirements, and initial investment costs
• Benefits like improved quality, safety, machine utilization, and waste reduction can outweigh implementation barriers

Introduction to One Piece Flow

Unlike batch production where components are grouped, one piece flow emphasizes continuous production flow with each unit going through assembly processes consecutively. 

This methodology helps eliminate many forms of muda or waste associated with traditional production systems. 

When implemented correctly, it can significantly improve productivity, and reduce lead times and costs, while promoting better quality and flexibility.

In this article, we will cover the fundamentals of one piece flow including its definition, benefits, implementation steps, associated lean tools, some real-world examples, challenges faced, and overall best practices. 

By the end, you will have a clear understanding of how to transition from batch-and-queue to smooth-flow production.

What is One Piece Flow?

One piece flow, also known as single-piece flow, is a lean production concept where parts and products move through a manufacturing process one unit at a time. 

This is in contrast to batch production, where parts are produced in large lots and units have to wait before moving to the next operation.  

It means that a single part or product moves from one workstation directly to the next with no wait time in between. 

This creates a smooth, continuous passage through the production line. As one piece exits a process step, the next enters right behind it.

The goal of implementing one piece flow is to align production pace with actual customer demand. Parts are made according to the pull of customer orders rather than pushing large batches through each process. 

This lean technique helps reduce lead times, lower work-in-progress inventory, prevent overproduction, and improve quality.

Overall, one piece flow creates a streamlined, flexible production system that produces finished goods just as they are needed by enhancing the connection between workstations. 

It is a key enabler for reducing waste and meeting customer demands in a lean manufacturing environment.

Benefits of One Piece Flow

One piece flow offers numerous benefits that lead to improved efficiency, quality, and flexibility in manufacturing processes. 

Understanding these benefits can help motivate organizations to implement it. 

Some of the major benefits include:

Reduced Lead Times

One of the biggest advantages of one piece flow is that it dramatically reduces lead times. 

By limiting work-in-progress and producing goods just as they are needed, products traverse smoothly from one workstation to the next without any waiting time in between steps. 

This allows organizations to respond to customer orders much faster. Lead times can be reduced by 50-90%.

Lower Work-in-Progress Inventory  

In traditional production systems, large batches lead to piles of unfinished goods stacking up between workstations. 

One piece flow limits the amount of work-in-progress by producing goods just as they are needed. 

This frees up significant space on the production floor and reduces the need for storage. Lower inventory levels also reduce costs associated with storage, handling, damage, and obsolescence.  

Improved Process Flexibility

With small batch sizes and standardized work, one piece flow allows companies to switch production lines over to new products very quickly. 

This gives companies the flexibility to respond to changes in customer demand. The streamlined production passage also makes it easier to identify and resolve bottlenecks or quality issues.

Better Workplace Safety 

The organization and visual controls implemented for one piece flow create a cleaner, more ergonomic working environment. 

Also, by balancing workloads across processes, issues like workplace fatigue and injury can be minimized. This leads to safer working conditions.

Higher Quality and Fewer Defects

In one piece flow, defects can be identified and resolved in real-time as they occur. This prevents defects from stacking up across large batches. 

The root causes of quality issues also become more visible. With greater quality control, scrap and rework costs are minimized.

Implementing One Piece Flow

Implementing one piece flow requires careful planning and execution across four key areas:

Calculating Takt Time

• Takt time calculates the rate at which products must be produced to meet customer demand. It is calculated by dividing the available production time by the customer demand.
• Accurately calculating takt time ensures production is aligned with actual demand instead of forecasting. It sets the pace of production under one piece flow.
• As takt time fluctuates based on demand, production capacity, and pace must remain flexible in this system.

Designing Process Layout

• The process layout should follow the sequence of production from raw material to finished goods based on the requirements of one piece flow.
• Workstations are arranged adjacent to each other in a linear sequence to facilitate smooth material and information passage.
• Distance between workstations is minimized to reduce transport waste and enable continuous flow.
• Workstation capacity, number of operators, inventory buffers, etc. are designed based on takt time.

Applying Pull System 

• One piece flow relies on a pull system where downstream processes signal their material requirements from upstream processes.
• Pull authorizes production based on consumption rather than forecast. It prevents overproduction and excess inventory.
• Kanban cards or signals can facilitate pull by regulating inventory buffers between processes. 
• Consumption-based pull aligns closely with the one piece flow’s objective of single-unit processing.

Standardizing Work

• Instructions are created, optimized, and standardized for each workstation. 
• Standardization minimizes inconsistencies and creates predictable output.
• As each unit follows the same work sequence, standardized work enables smooth, continuous flow.
• Standard work forms the baseline for kaizen or continuous improvement efforts.

The foundation of implementing one piece flow is understanding actual demand through takt time. 

Pull-based production, optimized process layout, and standardized work can then deliver enhanced flow efficiency.

Lean Tools for One Piece Flow

Implementing a one piece flow requires the use of various lean tools and techniques to analyze current processes, design future state value streams, standardize work, and drive continuous improvement. 

Some of the most important lean tools for enabling one piece flow include:

Value Stream Mapping

• Value stream mapping visually documents the traversal of materials and information required to bring a product or service to the customer
• It captures data on cycle times, inventory levels, material flows, and information flows to identify waste and opportunities
• This enables smarter redesign of future state with one piece flow in mind  

Kaizen and Continuous Improvement

• Kaizen is focused on continuous improvement through small, incremental changes rather than radical transformation
• Facilitating regular kaizen events focused on flow and waste elimination engages staff and uncovers further one piece flow improvements   
• Kaizen promotes sustained progression towards optimal traversal by repeatedly asking “Why?” and challenging the status quo

Visual Management Boards 

• Visual boards make deviations from standard visible so that issues can be addressed immediately
• Common boards used are production schedules, Kanban cards, inventory levels, quality metrics, etc.
• These provide staff with real-time visibility into flow disruptions as they occur

Standard Work Instructions

• Standard work documents the current best practice for performing a process
• It breaks down job tasks, work sequences, cycle times, and inventory buffers
• Having stable, repeatable standards is crucial before optimizing the stream

By combining these various lean tools into a systemic approach, significant gains can be realized on the journey toward one piece flow. 

They are complementary and mutually reinforcing when implemented together correctly.

Case Studies and Examples

Toyota Production System

The Toyota Production System (TPS) is well-known for effectively implementing one piece flow to reduce waste and optimize efficiency. 

At Toyota, one piece flow is enabled through several elements:

• Standardized work instructions that balance cycle times and workloads
• Pull system that links processes so parts are only made when needed downstream 
• Quick changeovers so machines can switch between products rapidly
• Error-proofing (poka-yoke) and quality control at each process
• Continuous improvement (kaizen) events to further optimize flow

This allows Toyota to produce vehicles with minimal work-in-progress and inventories. It has become a model framework for lean manufacturing across industries.

Other Manufacturing Success Stories

Beyond automotive, the one piece flow has delivered major improvements in industries like:

Electronics – Increased productivity by over 50% and reduced lead times from days to hours

Machining – Cut average queue and wait times by 80% by linking processes in a U-shaped cell

Furniture – Decreased physical distance between processes from 1 mile to 75 feet

Food Production – Improved line efficiency from 60% to over 90% 

In these cases, one piece flow increased focus on waste reduction and process stability. Implementing smaller transfer batch sizes and quality controls at each stage enabled smoother flow. 

Despite high upfront costs, the long-term benefits were substantial across quality, cost and delivery time.

The key is to map out current processes, analyze bottlenecks, and steadily implement standardized one piece flow procedures. 

While it takes commitment, it consistently enables leaps in manufacturing performance.

Challenges and Pitfalls

Implementing one piece flow can deliver tremendous benefits, but it also poses some challenges that organizations need to be aware of.

Change Management

Transitioning to one piece flow requires changing ingrained habits and processes. 

This can cause resistance from staff who are used to batch production. Strong leadership and communication are vital.

There may be pushback from managers who are reluctant to empower frontline workers or decentralize decision-making. Carefully presenting its benefits can help obtain buy-in.

Training Requirements

Workers need training in standardized work, quality control, machine operation, and maintenance. This represents an upfront time and monetary investment.

Multi-skilling workers so they are flexible across tasks require substantial training. But it enables smooth flow when bottlenecks occur.

Initial Investment Costs

Alterations to layout, new equipment like small conveyors, visual controls, and software to synchronize flow don’t come for free. Leadership must consider ROI.

Space may be reallocated to streamline process stream. This space optimization can lead to significant one-time costs.

While transitioning to one piece flow is hugely impactful, the challenges shouldn’t be underestimated. 

Careful change management, worker training, and calculating the ROI of investments can set up the initiative for long-term success. 

Leadership must have patience, as it takes time for one piece flow to be fully embedded into an organization’s culture.

Conclusion

Implementing one piece flow can lead to tremendous improvements in efficiency, quality, and flexibility for a lean production system. 

However, it requires careful planning, analysis, and change management.

One piece flow means producing and moving one item at a time through a series of processes, instead of batch production. 

This leads to faster lead times, lower WIP, and exposing problems sooner.

• Calculating takt time and designing optimal process layouts are essential first steps.
• Workstations should be arranged in process sequence and balanced for cycle times.
• Applying pull systems, visual controls, and standard work creates the framework for continuous one piece flow. 
• As problems surface, continuous improvement through kaizen events can further optimize the workflow.

Although the transition requires upfront investment and training, the long-term benefits of improved quality, reduced costs, and flexible operations outweigh the efforts

For companies starting their lean journey, here are some next steps to consider for implementing one piece flow:

• Conduct value stream mapping for the current and future states to analyze improvement opportunities. 
•  Run production trials of one piece flow on a pilot line and quantify operational metrics before and after. 
• Train employees from top to bottom on lean principles and standard work procedures.
• Invest in flexible equipment and tooling to enable quick changeovers between product variants.
• Focus on small incremental workflow improvements through regular kaizen activities. 

With strong leadership commitment and a culture of continuous improvement, transitioning to one piece flow can transform manufacturing operations to be more efficient and responsive to customer demands.