Did you know that a slow process can drag an entire production line below its actual capacity? In many factories, production lines may include dozens of different machines and processes operating continuously together. However, the overall efficiency of the entire line is not determined by the fastest machine but is often limited by the slowest process. An unstable machine, one that frequently stops or operates below its design speed, can affect the entire line downstream.

This is the bottleneck phenomenon, one of the common causes of reduced output, increased downtime, and a direct impact on the factory’s OEE.

I. What is a bottleneck? Why is the production line speed equal to the speed of the slowest process?

A bottleneck in production is a limiting factor in the overall capacity of a production line, occurring when one stage cannot process products at the same speed as the others. Simply put, the efficiency of a production line isn’t determined by the fastest machine, but is often limited by the slowest stage.

For example, a production line consists of the following stages: Machine A → Machine B → Machine C → Machine D

With production capacities:

• Machine A: 200 products/minute
• Machine B: 180 products/minute
• Machine C: 100 products/minute
• Machine D: 200 products/minute

Although Machines A, B, and D are capable of operating at higher speeds, the actual output of the entire line still only reaches a maximum of approximately 100 products/minute due to being limited by Machine C. In this case, Machine C is the bottleneck of the production line. When bottlenecks occur, businesses may encounter problems such as:

• Products accumulating before the bottleneck stage
• Lower machines having to wait due to a lack of input materials
• The entire line speed falling below design capacity
• End-of-shift output not meeting targets

Therefore, to improve production efficiency, businesses not only need to speed up individual machines but also need to accurately identify which stage is limiting the entire production line and focus on improving that specific bottleneck.

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► Read more: 6 big losses affecting OEE in manufacturing

II. Fixed Bottleneck and Shifting Bottleneck

Not all bottlenecks are fixed in one position. In manufacturing practice, bottlenecks are generally divided into two main types.

1. Static Bottleneck

A static bottleneck is a situation where a process frequently becomes a limiting factor in the overall production line. This is where the processing speed is lower than other processes and continuously impacts output. The causes of a static bottleneck often stem from several factors, including:

• Machines with lower design capacity than required by the production line;
• Old or degraded equipment reducing operational efficiency;
• Slower processing technology compared to other processes;
• Processes heavily reliant on manual operator actions.

For example: A packaging machine can only process 80 products/minute, while the processes ahead can produce 150 products/minute. Even with higher-capacity equipment, the final output of the production line is still limited by the speed of the packaging machine. The packaging machine now becomes a fixed bottleneck, preventing the production line from achieving its designed output unless this step is improved.

► Read more: Why do many factories still manage production using Excel?

2. Shifting Bottleneck

A shifting bottleneck is a bottleneck that is not fixed at one stage but can continuously shift between different machines or areas during the production process. Unlike a fixed bottleneck, a shifting bottleneck usually occurs due to operational fluctuations such as:

• Uneven micro-downtime between devices
• Machine speeds changing over time
• Repeated minor malfunctions at multiple stages
• Changes in product or operating conditions

Example:

In the morning, the filling machine frequently experiences micro-downtime due to bottle jams or equipment adjustments. This reduces processing speed and makes the filling machine the bottleneck of the line. However, by the afternoon, the filling machine operates stably again, but the packaging machine begins to slow down, causing the bottleneck to shift to the packaging stage.

This is a shifting bottleneck, one of the most difficult types of bottlenecks to detect because the problem is not fixed in one location. If businesses rely solely on manual observation or end-of-shift reports, it becomes very difficult to accurately determine which processes are actually limiting the efficiency of the production line at any given time.

► Read more: What is cycle time? 

III. Identifying Bottleneck Processes

A process may be experiencing a bottleneck if it exhibits the following signs:

1. Product Accumulation Before the Process

When a process slows down compared to the input speed, products will not be processed in time and will begin to accumulate in the area ahead. This is one of the typical signs that the process may be becoming a bottleneck in the production line.

Some common manifestations include:

• Goods or semi-finished products lined up waiting in front of the packaging machine.
• Pallets accumulating in the processing or transfer area.
• Buffers between processes are always full, while subsequent processes frequently lack products to operate.

If this situation occurs continuously, the business needs to immediately check the efficiency of the processing stage to identify the cause and take timely corrective measures.

2. Upstream Machines Frequently Waiting

Another sign of a bottleneck is that downstream processes frequently have to wait for incoming products before continuing operation. The cause is often not the process itself, but rather stems from the upstream process being slow or unstable.

Some easily recognizable signs include:

• Increased waiting time between processes.
• Machines operating intermittently instead of continuously.
• Reduced overall output compared to the plan.

If this situation occurs frequently, the business needs to analyze the performance of upstream processes to accurately identify the bottleneck and take timely corrective action.

3. An unusually high downtime for a single process

Small incidents occurring frequently during operation can also cause a process to become a bottleneck for the entire production line. Common situations include:

Product or packaging jams on the conveyor belt
Multiple machine resets required
Sensor malfunctions
Operators having to intervene frequently to resolve issues

Although each interruption may only last a few seconds or minutes, when repeated continuously throughout the production shift, they will reduce the processing speed of that process. As a result, products pile up ahead, processes behind have to wait, and the efficiency of the entire production line is affected.

4. Lower performance than other machines

Even if the machines do not malfunction or stop, operating at a speed lower than the design speed can still cause that process to become a bottleneck for the production line.

This type of loss often occurs silently and is difficult to detect through direct observation, because the production line continues to operate. However, a reduced processing speed will decrease actual output, leading to a decline in the overall efficiency of the entire line. This is also one of the common reasons why Performance and OEE scores are lower than expected, even without major machine downtimes.

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► Read more: How does downtime affect OEE?

IV. How to Identify Bottlenecks Using Data

In many factories, identifying bottlenecks still relies primarily on direct observation, operator experience, or reports compiled at the end of each shift. However, these methods often only partially reflect the operating conditions and are unlikely to yield accurate results, as the state of the production line can change continuously throughout the shift. In particular, micro-downtime, deceleration, or shifting bottlenecks are easily overlooked if only monitored manually.

To accurately identify the process limiting the efficiency of the production line, businesses need to analyze operational data for each machine and in real time. Monitoring metrics such as OEE, Performance, Availability, Cycle Time, and Downtime for each process will help quickly detect bottlenecks, assess their impact, and develop appropriate improvement solutions.

1. Comparing OEE for Each Process

Monitoring the OEE of each machine helps identify:

• Which machine has the lowest availability?
• Which machine has the most significant performance decrease?
• Which machine has the greatest impact on output?

2. Analyzing the Performance of Each Machine

The performance index indicates how well the machine is operating compared to its design or ideal speed.

Example:

• Machine A: Performance at 95%
• Machine B: Performance at 70%
• Machine C: Performance at 92%

In this case, Machine B has a significantly lower performance index than the others. This suggests that Machine B is likely operating slower than its design capacity and could become a bottleneck in the production line. Therefore, businesses should prioritize analyzing Machine B to identify the cause of the speed reduction, such as micro-downtime, recurring errors, equipment degradation, or suboptimal operating procedures.

3. Monitoring Downtime by Location

Monitoring downtime data helps businesses accurately answer crucial operational questions, such as:

• Which machines are down most frequently?
• How long does each downtime last?
• What are the causes of the downtime?
• Which errors are recurring frequently?

With this comprehensive data, businesses not only know where the production line is losing efficiency but also identify the root causes of the problem. From there, production and maintenance teams can prioritize improvements in the right areas, reduce downtime, eliminate bottlenecks, and improve the overall operational efficiency of the entire production line.

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► Read more: What is Data driven manufacturing?

V. Production Line Bottleneck Management Strategies

After identifying the bottleneck, businesses need to choose a suitable solution instead of investing in expanding the entire production line.

1. Improving Operational Processes

To eliminate bottlenecks and improve production line efficiency, businesses can start by improving operational processes. Some common solutions include:

• Reducing unnecessary manual operations to shorten processing time.
• Standardizing operational processes to minimize errors and ensure consistency across production shifts.
• Optimizing setup and changeover times to reduce downtime when switching products.
• Identifying and eliminating frequently recurring errors that disrupt or slow down operations.

These improvements not only help the bottleneck process operate more smoothly but also contribute to increased productivity, reduced downtime, and improved OEE (On-the-Earnings Effectiveness) of the entire production line.

2. Reduce Downtime at the Bottleneck Stage

One of the most effective ways to address a bottleneck is to reduce downtime at the stage that is limiting the line’s capacity. Businesses should prioritize analyzing and resolving the causes of frequent disruptions, such as:

• Frequent machine stoppages.
• Repeated micro-downtimes during a production shift.
• Operational errors due to operator handling.
• Incidents related to equipment, sensors, or control systems.

Focusing on improving the specific bottleneck stage can yield significant results without upgrading the entire production line. By simply reducing downtime and improving efficiency at the bottleneck point, businesses can increase output, improve OEE, and optimize the overall operational efficiency of the production system.

3. Balancing the Load Between Processes

Some cases can be addressed by:

• Adjusting line speed
• Changing personnel allocation
• Improving material flow
• Optimizing buffer

4. Selective Equipment Investment

Upgrading the entire production line isn’t always necessary. Bottleneck data helps businesses know exactly:

• Which machines to invest in
• Which processes yield the highest ROI.

VI. The Role of Machine-Specific OEE Dashboards in Early Bottleneck Detection

In modern production lines, bottlenecks are not always fixed but can change continuously between processes at any given time. Therefore, monitoring through direct observation, Excel spreadsheets, or end-of-shift reports is no longer sufficient to detect and address bottlenecks promptly.

Instead, a real-time OEE dashboard helps businesses comprehensively monitor the performance of each machine and process through indicators such as:

• OEE of each machine
• Availability
• Performance
• Downtime and causes of machine downtime
• Actual Cycle Time
• Output by process

When a process begins to slow down, experiences downtime, or shows signs of becoming a bottleneck, the system will immediately update the data on the dashboard. As a result, the operations and management team can quickly identify the cause, resolve issues promptly, and prevent the impact from spreading throughout the entire production line, contributing to maintaining OEE and optimizing production efficiency.

VII. View i-OEE Demo with i-Soft

Bottlenecks are one of the major reasons why production lines fail to reach their design capacity. A slow process can reduce the efficiency of the entire system, leading to decreased output, increased downtime, reduced performance, and impact on OEE (Output Effectiveness)…

Instead of making improvements based on intuition, businesses need to use real-time operational data to accurately identify the process limiting performance. Identifying and correctly addressing bottlenecks will help factories improve productivity, enhance OEE, and optimize operating costs. i-OEE helps businesses:

• Monitor OEE of each machine in the production line
• Detect bottlenecks in real time
• Analyze downtime and the causes of performance loss
• Optimize production efficiency based on real-time data

Contact i-Soft to experience our real-time production performance management solution.

i-Soft Joint Stock Company – specializing in providing factory digitalization software solutions

► Address: 115 N2 Road, Long Truong Ward, Ho Chi Minh City, Vietnam
► Hotline: 0989 739 488
► Email: info@i-soft.com.vn