A picture is worth a thousand words, and in the world of lean management, a Yamazumi chart is the visual story of efficiency. This powerful tool provides a snapshot of the production process, breaking down tasks into manageable segments to pinpoint inefficiencies and streamline operations. In this blog post, we will explore what a Yamazumi chart is, how it functions as an essential component of lean management, and the benefits it offers in optimizing workflows and balancing workloads.
What exactly is a Yamazumi chart?
"Yamazumi" (山積み) is a Japanese term that translates to "to stack up," a name that perfectly describes the visual nature of this tool. Essentially, a Yamazumi chart is a type of stacked bar chart that teams use to illustrate the time taken for each process step.
Each bar on the chart typically represents a specific workstation or operator on a production line. Furthermore, the segments within each bar represent the individual tasks performed, while the height of each segment corresponds to the cycle time of that particular task.
At its core, the Yamazumi chart provides a visual representation of the distribution of work, making it an invaluable asset for identifying bottlenecks, uneven workloads, and, most importantly, opportunities to eliminate waste. In fact, this powerful visual tool offers a clear and immediate understanding of process performance, something that raw data in a spreadsheet can rarely convey.
The key components of a Yamazumi chart
To fully grasp the power of a Yamazumi chart, it's essential to understand its core components:
The X-axis and Y-axis
First, the x-axis shows the different workstations, operators, or distinct stages of the entire process. In conjunction with this, the y-axis shows the cycle time, typically measured in seconds or minutes. This fundamental structure allows for a quick comparison of the total time each operator or station is engaged in work.
Stacked bars
Next, each vertical bar is a stacked bar, representing the total workload of a single operator or workstation. The individual blocks that make up the stack, in turn, represent the different tasks performed.
Task categories and colour coding
The true genius of the Yamazumi chart lies in its categorization of tasks. Teams typically classify and color-code each task into one of three categories:
- Value-added (VA) tasks: These are the essential activities that directly contribute to the creation of the product or service in a way that meets customer demand. In other words, these are the tasks the customer is willing to pay for. (Often coded in Green)
- Non-value-added (NVA) tasks: On the other hand, these are pure waste. They consume resources and time but add no value from the customer's perspective. For this reason, the goal is to eliminate these activities. Examples include waiting, unnecessary motion, and defects. (Often coded in Red)
- Necessary non-value-added (NNVA) tasks: This category includes activities that don't directly add value but are unavoidable due to legal or operational reasons. For instance, teams must perform safety checks, essential machine setup, or regulatory compliance tasks. While necessary, the goal is still to minimize the time spent on these activities. (Often coded in Yellow or Orange)
Target cycle time (Takt time)
Another crucial element often depicted on a Yamazumi chart is a horizontal line representing the target cycle time, more commonly known as Takt time. Takt time is the rate at which a team needs to complete a product to meet customer demand. You can calculate it as:
Takt Time = Customer Demand / Available Production Time
Any workstation whose total cycle time exceeds the Takt time line immediately signals a bottleneck in the production line.
The benefits of embracing the Yamazumi chart
Adopting the Yamazumi chart is not just about creating a colourful graph; it's about unlocking plenty of benefits that can transform your operational landscape. For instance, here are some of the most significant advantages:
Visualizing and eliminating waste
First and foremost, the primary benefit of a Yamazumi chart is its ability to make waste visible. By categorizing tasks into value-added, non-value-added, and necessary non-value-added, it becomes obvious where the process wastes time and effort. As a result, this visual clarity serves as a powerful motivator for teams to focus on eliminating non-value-added activities.
Facilitating line balancing
An imbalanced production line, where some operators are overworked while others are idle, inevitably leads to bottlenecks and excess inventory. The Yamazumi chart provides a clear picture of the workload distribution, which consequently enables managers to perform effective line balancing. By redistributing tasks from overloaded to underloaded workstations, teams can achieve a smoother, more consistent workflow.
Driving process optimization
In addition, the chart serves as a roadmap for process optimization. It helps pinpoint which specific process tasks are taking the longest and which are ready for improvement. This data-driven approach to optimization is far more effective than relying on guesswork or anecdotal evidence.
Enhancing process efficiency
By systematically identifying and addressing waste and imbalances, the Yamazumi chart directly contributes to a significant boost in overall process efficiency. This, in turn, leads to reduced lead times, increased throughput, and lower operational costs.
Fostering a culture of continuous improvement
The Yamazumi chart is not a one-time fix. Instead, it's a dynamic tool that teams should use continuously to monitor process performance and drive continuous improvement. By making the chart visible to the entire team, it encourages a shared sense of ownership and a collective commitment to finding better ways of working. Both of which are the very essence of the Kaizen philosophy.
Improving workload balance and employee morale
An uneven workload balance can lead to stress, burnout, and decreased morale among employees. However, by using the Yamazumi chart to ensure a more equitable distribution of tasks, companies can create a fairer and more sustainable work environment.
How to create a Yamazumi chart
Creating a Yamazumi chart is a systematic process that requires careful observation and data collection. Here’s a detailed breakdown of the steps involved:
Step 1: Select the process to analyze
To begin, you must identify the specific process you want to improve. This could be a single production line, a particular work cell, or any workflow with a series of defined steps.
Step 2: Accurate data collection
This is the most critical phase. In fact, the accuracy of your Yamazumi chart depends entirely on the quality of your data.
- Observe the process: First, spend time on the shop floor or in the work area, observing the entire process from start to finish.
- Break down the tasks: Next, identify all the individual process tasks each operator performs or that occur at each workstation. Remember to be detailed in your breakdown.
- Time each task: Then, using a stopwatch, time how long each task takes. It’s important to observe multiple cycles and calculate an average cycle time to account for natural variations.
- Document everything: Finally, record your observations accurately. Be sure to note down the operator, the task, and the corresponding cycle time.
Step 3: Categorize the different tasks
Once you have your list of tasks and their cycle times, the next step involves categorizing each one. This requires a deep understanding of what adds value from the customer's perspective.
- Value-added (VA): Ask yourself, does this task change the form, fit, or function of the product in a way the customer is willing to pay for?
- Non-value-added (NVA): Conversely, is this task pure waste (e.g., waiting, rework, unnecessary movement)?
- Necessary non-value-added (NNVA): Lastly, is this task required for legal, safety, or operational reasons, even though it doesn't directly add value?
Step 4: Calculate the Takt time
To provide context to your Yamazumi chart, you need to determine the Takt time. As mentioned earlier, this represents the rhythm of your production, which customer demand dictates.
Step 5: Construct the stacked bar graph
Now it's time to bring your data to life in the form of a stacked bar graph. You can use a spreadsheet software like Microsoft Excel or a specialized lean manufacturing software for this purpose.
- Set up your axes: To start, the x-axis will represent the operators or workstations, and the y-axis will represent the cycle time.
- Create the stacked bars: Following that, for each operator, create a stacked bar where each segment represents a task. The height of the segment should be proportional to its cycle time.
- Apply colour coding: Then, use the predetermined colours to visually distinguish between VA, NVA, and NNVA tasks.
- Add the Takt time line: Finally, draw a horizontal line across the chart to indicate the target cycle time.
Step 6: Analyze and interpret the Yamazumi chart
With your completed Yamazumi chart, the analysis can begin. Specifically, look for:
- Bars exceeding the Takt time: These are your primary bottlenecks. The operators or workstations represented by these bars are clearly overloaded.
- Bars significantly below the Takt time: In contrast, these indicate under-utilized resources and an opportunity for workload distribution.
- Large red segments: A significant amount of red (NVA) in any bar is a clear signal for immediate waste elimination efforts.
- Large yellow segments: While necessary, you should still critically examine large yellow segments (NNVA). For example, ask if you can streamline or simplify these tasks.
Step 7: Take action and drive improvement
The final and most important step is to use the insights from your Yamazumi chart to make improvements.
- Redistribute tasks: To begin, move tasks from overloaded workstations to those with spare capacity. This is the essence of line balancing.
- Eliminate non-value-added activities: Subsequently, brainstorm with your team on how to eliminate the identified non-value-added tasks.
- Optimize necessary tasks: Even for necessary tasks, look for ways to reduce the process time. For instance, can you simplify a setup? Can a quality check be integrated into the main process?
- Implement and monitor: Lastly, implement the proposed changes and then create a new Yamazumi chart to measure the impact. This iterative process is the cornerstone of continuous improvement.
Real-world applications of the Yamazumi chart
You can best understand the power of the Yamazumi chart through its application in real-world scenarios.
The Toyota Production System
The Yamazumi chart has gained recognition as an essential tool in the Toyota Production System (TPS). In fact, Toyota uses these charts to meticulously analyze their assembly lines. Thereby, ensuring a balanced workflow and relentless elimination of waste. Unquestionably, this has been a significant contributor to their world-renowned efficiency and quality.
Beyond the assembly line
While its origins are in manufacturing, the principles of the Yamazumi chart are universally applicable. As a result, professionals have successfully adapted it for use in various sectors, including:
- Healthcare: To analyze and streamline patient admission processes, laboratory workflows, and even surgical procedures.
- Software development: To visualize and balance the workload of development teams in agile environments.
- Logistics and warehousing: To optimize order picking, packing, and shipping processes.
- Service industries: To analyze and improve customer service call flows and administrative processes.
