Toyota Production System Implementation of lean manufacturing tools

Traditionally operated garment industries are facing problems like low productivity,
longer production lead time, high rework and rejection, poor line balancing, low
flexibility of style changeover etc. These problems were addressed in this study by the
implementation of lean tools like cellular manufacturing, single piece flow, work
standardization, just in time production etc.

2.1 Toyota Production System

It is a manufacturing system developed by Toyota in Japan after World War II, which aims to increase production efficiency by the elimination of waste. The Toyota production system was invented and made to work, by Taiichi Ohno. While analyzing the problems inside the manufacturing environment; Ohno came to conclude that different kinds of wastes (non value added works) are the main cause of inefficiency and low productivity. Ohno identified waste in a number of forms, including overproduction, waiting time, transportation problems, inefficient processing, inventory, and defective products.

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Figure 1 shows the Toyota Production System in detail. From this figure it can be seen that TPS is not only a set of different tools but it is the philosophy and integration of different tools and systems to achieve a common goal of waste reduction and efficiency improvement. Each element of this house is critical, but more important is the way the elements reinforce each other. Just In Time (JIT) means removing the inventory used to buffer operations against problems that may arise in production. The ideal of one-piece flow is to make one unit at a time at the rate of customer demand or Takt time. Using smaller buffers (removing the “safety net”) means that problems like quality defects become immediately visible. This reinforces Jidoka, which halts the production process. This means workers must resolve the problems immediately and urgently to resume production.

FIGURE 1: Toyota Production System1

Stability is at the foundation of the house. While working with little inventory and stopping production when there is a problem causes instability and a sense of urgency among workers. In mass production, when a machine goes down, there is no sense of urgency because the maintenance department is scheduled to fix it while the inventory keeps the operations running. By contrast, in lean production, when an operator shuts down equipment to fix a problem, other operations will also stop immediately due to no inventory creating a crisis. So there is always a sense of urgency for everyone in production to fix problems together to get the machine in working condition and to run the production as soon as possible.

If the same problem occurs repeatedly, management will quickly conclude that this is a critical situation and it should be cracked without any delay. People are at the center of the house, because it is only through continuous improvement that the operation can ever attain this needed stability. People must be trained to see waste and solve problems at the root cause by repeatedly asking why the problem really occurs. Problem solving should be on the actual site of the problem where everything is visible and practical also; this technique of problem solving is called Genchi Genbutsu. In general TPS is not a toolkit. It is not just a set of lean tools like just-in-time, cells, 5S (sort, stabilize, shine, standardize, sustain), Kanban, etc. It is a sophisticated system of production in which all parts contribute to a whole. On the whole, its focus is on supporting and encouraging people to continually improve the processes they work on.

2.2 Kind of Wastes

According to David Magee, (Magee, 2007, p. 67) different kinds of wastes in a process can be categorized in following categories. These wastes reduce production efficiency, quality of work as well as increase production lead time.

1. Overproduction – Producing items more than required at given point of time i.e. producing items without actual orders creating the excess of inventories which needs excess staffs, storage area as well as transportation etc.

2. Waiting – Workers waiting for raw material, the machine or information etc. is known as waiting and is the waste of productive time. The waiting can occur in various ways for example; due to unmatched worker/machine performance, machine breakdowns, lack of work knowledge, stock outs etc.

3. Unnecessary Transport – Carrying of work in process (WIP) a long distance, insufficient transport, moving material from one place to another place is known as the unnecessary transport.

4. Over processing – Working on a product more than the actual requirements is termed as over processing. The over processing may be due to improper tools orimproper procedures etc. The over processing is the waste of time and machines which does not add any value to the final product.

5. Excess Raw Material - This includes excess raw material, WIP, or finished goods causing longer lead times, obsolescence, damaged goods, transportation and storage costs, and delay. Also, the extra inventory hides problems such as production imbalances, late deliveries from suppliers, defects, equipment downtime, and long setup times.

6. Unnecessary Movement – Any wasted motion that the workers have to perform during their work is termed as unnecessary movement. For example movement during searching for tools, shifting WIP etc.

7. Defects – Defects in the processed parts is termed as waste. Repairing defective parts or producing defective parts or replacing the parts due to poor quality etc. is the waste of time and effort.

8. Unused Employee Creativity – Loosing of getting better ideas, improvement, skills and learning opportunities by avoiding the presence of employee is termed as unused employee creativity (Liker, 2003, p. 29).

2.3 Lean Manufacturing Tools and Techniques

 
There are numbers of lean manufacturing tools which, when used in proper ways will give the best results. Once the source of the waste is identified it is easier to use the suitable lean tool to reduce or eliminate them and try to make waste free systems. Some of these tools are discussed in this chapter.

2.3.1 Cellular Manufacturing

 
A cell is a combination of people, equipment and workstations organized in the order of process to flow, to manufacture all or part of a production unit (Wilson, 2009, p. 214-215). Following are the characteristics of effective cellular manufacturing practice.

1. Should have one-piece or very small lot of flow.

2. The equipment should be right-sized and very specific for the cell operations.
 

3. Is usually arranged in a C or U shape so the incoming raw materials and outgoing finished goods are easily monitored.

4. Should have cross-trained people within the cell for flexibility of operation.

5. Generally, the cell is arranged in C or U shape and covers less space than the long assembly lines.

There are lots of benefits of cellular manufacturing over long assembly lines. Some of them are as follows (Heizer and Render, 2000, p. 345-346).

 
1. Reduced work in process inventory because the work cell is set up to provide a balanced flow from machine to machine.

2. Reduced direct labor cost because of improved communication between employees, better material flow, and improved scheduling.

3. High employee participation is achieved due to added responsibility of product quality monitored by themselves rather than separate quality persons.

4. Increased use of equipment and machinery, because of better scheduling and faster material flow.

5. Allows the company higher degrees of flexibility to accommodate changes in customer demand.

6. Promotes continuous improvement as problems are exposed to surface due to low WIP and better communication.

7. Reduces throughput time and increases velocity for customer orders from order receipt through production and shipment.

8. Enhances the employee’s productive capability through multi-skilled multimachine operators.

Apart from these tangible benefits, there is the very important advantage of cellular manufacturing over the linear flow model. Due to the closed loop arrangement of machines, the operators inside the cell are familiar with each other’s operations and they understand each other better. This improves the relation between the operators and helps to improve productivity. Whereas in long assembly line one operator knows only two operators (before and after his operation in the line) it seems that operators are working independently in the line.

2.3.2 Continuous Improvement

 
According to (Gersten and Riss, 2002, p. 41) Continuous improvement (CI) can be defined as the planned, organized and systematic process of ongoing, incremental and company-wide change of existing practices aimed at improving company performance. Activities and behaviors that facilitate and enable the development of CI include problem-solving, plan-do-check-act (PDCA) and other CI tools, policy deployment, cross-functional teams, a formal CI planning and management group, and formal systems for evaluating CI activities. Successful CI implementation involves not only the training and development of employees in the use of tools and processes, but also the establishment of a learning environment conducive to future continuous learning.

The short description of PDCA cycle is given below

 
Plan: Identify an opportunity and plan for change.

Do: Implement the change on a small scale.

Check: Use data to analyze the results of the change and determine whether it made a difference.

Act: If the change was successful, implement it on a wider scale and continuously assess the results. If the change did not work, begin the cycle again. Thus continuous improvement is an ongoing and never ending process; it measures only the achievements gained from the application of one process over the existing. So while selecting the continuous improvement plan one should concentrate on the area which needs more attention and which adds more value to our products. There are seven different kinds of continuous improvement tools (Larson, 2003, p. 46) they can be described as follows. The use of these tools varies from case to case depending on the requirement of the process to be monitored. Pareto Diagram: The Pareto diagram is a graphical overview of the process problems,in ranking order from the most frequent, down to the least frequent, in descending order from left to right. Thus, the Pareto diagram illustrates the frequency of fault types. Using a Pareto, one can decide which fault is the most serious or most frequent offender.

Fishbone Diagram: A framework used to identify potential root causes leading to poor quality.

Check Sheet: A check sheet is a structured, prepared form for collecting and analyzing data. This is a generic tool that can be adapted for a wide variety of purposes.

Histogram: A graph of variable data providing a pictorial view of the distribution of data around a desired target value.

Stratification: A method of sorting data to identify whether defects are the result of a special cause, such as an individual employee or specific machine.

Scatter Diagram: A graph used to display the effect of changes in one input variable on the output of an operation. 

Charting: A graph that tracks the performance of an operation over time, usually used to monitor the effectiveness of  improvement programs.

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By,

MD Shakhawat Hossain

B.sc in Textile Engineer

Executive of Marketing

Facebook : shakhawat.rasel

Skype : shrtex

E-Mail : shrtex@gmail.com