Mura

Mura, one of the three types of waste in the Toyota Production System, translates to "unevenness" or "inconsistency" in English. It refers to the irregularity in the flow of work, causing fluctuations in capacity and production. Identifying and removing Mura is essential for creating a steady work pace and optimizing resources.

One of the main causes of Mura is multitasking. When team members are constantly switching between tasks, they often lose focus and efficiency, leading to unevenness in the workflow. This results in longer lead times, increased inventory, and higher costs.

Another cause of Mura is overproduction. Producing more than what is needed, whether it's goods or services, creates an imbalance in the system and results in unnecessary inventory. This not only ties up valuable resources but also increases the risk of defects and rework.

To handle Mura, one must first understand the root cause of the unevenness. This can be done through value stream mapping, a tool that visually represents the flow of work and helps identify areas of waste. By analyzing the current state of the process, one can identify the steps that are causing Mura and implement solutions to eliminate them.

One effective solution is to implement a pull system, also known as "kanban" in Japanese. This system ensures that work is only produced when it is needed, eliminating overproduction and promoting a steady flow of work.

Another solution is to implement standard work. By standardizing the work process, team members are able to work consistently and efficiently, resulting in less Mura. This also helps in identifying and addressing any abnormalities that may occur in the process.

Additionally, involving the team members in problem-solving and continuous improvement activities can lead to increased ownership and accountability, leading to a reduction in Mura.

Implementing a pull system, standard work and involving team members in problem-solving and continuous improvement activities can help organizations to create a steady flow of work and optimize resources.

It's important to note that Mura is not a problem that can be solved once and for all. It's a continuous effort and requires constant monitoring and improvement. Regularly conducting value stream mapping and Gemba walks, where one goes to the place where the work is done to observe and understand the process, can help in identifying and addressing Mura.

In conclusion, Mura is a key concept in lean management and must be addressed to ensure a steady work pace and optimize resources. By understanding the root cause of Mura and implementing solutions such as pull systems, standard work, and involving team members in problem-solving and continuous improvement activities, organizations can achieve the goal of smooth and well-organized workflow.

Standard WIP (SWIP)

The minimum amount of material or product that must be in the process at all times to ensure smooth operation.

Standard Work is a little underrated concept in Lean Manufacturing. It is not simply standardization or work standards.

Standard Work is composed of three elements: Takt time, Work sequence and Standard Work in Process (SWIP). Takt Time is a fundamental concept of Lean Manufacturing, and Work Sequence is relatively intuitive. SWIP, however, is a bit more complex.

SWIP refers to the minimum necessary in-process inventory (work in process or WIP) to maintain Standard Work. It is not more or less than what is needed. To calculate the appropriate quantity for SWIP, one must ask a number of questions.

While a rough estimate of SWIP can be obtained by using the equation SWIP = Sum of Cycle Times / Takt Time, it is still necessary to determine where exactly this SWIP should be applied. The following steps provide a guide for determining the appropriate quantity of SWIP:

what’S the team size?

Standard Work is the most efficient combination of manpower, material, and machine, and is based on takt, work sequence, and Standard Work in Process (SWIP). By definition, it should include manual work. If a process is fully automated, it is not considered Standard Work. Instead, it is likely an NC program.

To determine the appropriate team size, the sum of manual cycle time is divided by Takt Time. Therefore, one piece of SWIP per person is required. The equation for manual SWIP would than be:

SWIP(manual) = Team member x (1 piece = person)

When determining the amount of SWIP, there should be no rounding, unless there is less than a full person. In that case, round up to the nearest whole number.

process steps as automatic one-piece cycle machines

Standard Work assumes the use of multiple processes or machines, and separates human and machine tasks as much as possible.

When using an automatic cycle, the worker will only be responsible for loading and unloading, and will not be present during the actual cycle. The automatic cycle time must also be shorter than the Takt Time, ensuring that there is always at least one piece in the machine during each cycle.

This is known as SWIP (single piece auto), and is calculated as the number of single-piece automatic cycle machines multiplied by one piece per machine. There is no rounding necessary as it is not possible to have less than a full machine. However, this only applies to single-piece automatic cycles, and calculations for batch processes or cycles with longer lead times may differ.

process steps as a single-piece non-machine automatic cycle

The term "non-machine automatic cycle" refers to process steps such as the drying time for paint, curing time for epoxy, and cooling time for hot parts.

These process steps may not involve machines, but they do require a certain amount of time for completion. The ratio of this time to the Takt Time is known as the Single-Piece Non-Machine Automatic (SWIP) cycle.

It is important to note that this value should always be rounded up to the nearest whole number. In some cases, equipment like turn tables or FIFO racks may be used to manage the curing process, ensuring that a finished product is available for each takt, and a new one is added for curing.

Process steps with a batch automatic cycle

Batch processes refer to situations in which equipment is designed to unload and load multiple pieces at a time, rather than one piece at a time.

A common example is heat treatment processes where a vacuum must be maintained and the door cannot be opened for hours. In such cases, a batch of parts is removed and then another batch is loaded. The cycle time per piece may be less than the Takt Time, but the overall automatic Cycle Time is greater than the Takt Time.

The Single-Piece Non-Machine Automatic (SWIP) cycle in this case is calculated as (Automatic time / Takt Time) x 2. The reason for this is that in batch processes, which do not allow for the addition or removal of individual pieces during the Takt, an extra quantity of complete parts is required. This concept can be compared to the idea of a pulley and bucket system used to retrieve water from a well, where one bucket is at the bottom of the well, full of water and another bucket is at the top, full of water, and during Takt, you empty out the bucket one by one and fill it back up one by one.

It's worth noting that in formulas 2, 3 and 4, manual cycle time is not included in the calculation because rule #1 takes care of that. This is because every manual Cycle Time must be within Takt by definition of Standard Work and since the unload/load time will involve one piece, there is no need to add manual time back into the calculation (in most of the cases).