The Principles of the Toyota Production System
The Toyota Production System is 80 percent waste elimination (Industrial Engineering), 15 percent production system and only 5 percent kanban communication.
Some Commonly Used Terms in TPS
Waste of Overproduction
There are two types of overproduction:
* Making more than required quantity for a delivery period.
* Making a product before it is needed.
Many systems are happy to produce an item before its delivery date and feel comfortable. But Toyota system does not want both types of overproduction.
Just-in-time
JIT also means just-on-time. An item should be made available when it is required not before or after the required time.
Separation of Worker from the Machine
The whole productivity movement of Toyota was based on the fact that per worker production of cars in America was 10 times that of Toyota company. Toyota wanted to improve their productivity and therefore concentrated on reducing the time spent by a worker on the machine. Machines must work without the assistance of the worker as much as possible. Jidoka or autonomation is the name given to this activity. Along with JIT or stockless production, separation of worker from the machine forms the two pillars of Toyota Production System.
Low Utilization Rates
Toyota's machine-output ratio is two to three times that of similar companies. This could be due to flow production systems or due to planned extra machine capacity to take care of extra demand. But one must always remember that Toyota's main goal is cost reduction and every decision in Toyota is subjected to engineering economic evaluation.
Multi-machine Handling
In 1955, 700 workers were handling 3500 machines. Hence sometimes machines are idle because worker is busy with other machines and cannot load the machines. Toyota permits machine idle times but it does not permit man idle time. The reason is that a machine costs $500 per month but a man costs twice or thrice more.
Equipment Planning and Low Operating Rates
As low operating rate is expected, Toyota buys less expensive machines. But it improves the machines to suit its requirements continuously. Because in normal times machines have excess capacity or low operating rates, peak demand can be handled by hiring temporary workers.
Perform Operation and Remove the Defective Part
Whenever a problem appears, Toyota insists on proper diagnosis of the root cause and demands that an operation is done to remove the replace the defective part of the process. It is not content with the temporary cure of rework on the defective workpiece.
Fundamentals of Toyota Production System
Adopting a Non-Cost Principle
Elimination of Waste
Eliminating waste through fundamental process improvements
Processing purpose evaluation and rationalization
Inspection purpose evaluation and rationalization
Transport purpose evaluation and rationalization
Delay reason evaluation and rationalization
Storage purpose evaluation and rationalization
Eliminating waste through fundamental operation improvement
Setup improvement
Auxiliary improvement
Job allowance improvement
Workshop allowance improvement
Improving processing and essential operations
Ask the "five W's and one H" and "Why?" Five Times
What - What is being produced - Is it required - Value engineering
Who - Men, machines, tools and jigs used for the production
When - Time - Production planning also comes here.
Where - Space (Layout)
Why - rational for the use of everything used in production. Because it provides opportunities for improvement.
How - The methods - motion used by man, speed and feeds used by machines
At Toyota specially, 5 Whys are used to identify root causes for defects and appearance of problems.
Mass Production and Large Lot Production are not same
Mass production is beneficial. Large lot production has extra cost. It can be reduced with SMED.
Order-based Production
Characteristics of Order-based Production
To take care of fluctuations in the orders, Toyota sets basic productions capacity at minimum demand level and handles increases through overtime and the use of excess machine capacity and temporary workers.
Overtime: There are four hour breaks between the two shifts and overtime can be given in either shift as needed.
Excess capacity: During the minimum load, many workers manage ten machines but up to 50% capacity only. As demand increases, temporary workers are hired and machines can work at 100% capacity. But machine work has to be simplified and standardized so that temporary workers can be trained in three days and they operate the machines.
Strong Market Research
Toyota does spend on market research to know market requirements. Twice in a year 60,000 people are surveyed. Five or six additional surveys are done in a year.
Production Planning
Long term planning is done.
Annual planning is done.
Monthly planning is done.
Daily planning is done. Daily planning based on actual orders. The actual orders are informed to the first stage of assembly section and they draw the components as required from component supply stages.
Toyota's Supermarket System
In the supermarket system of Toyota, stocking is triggered by actual demand for the components for a daily requirement.
Differences between Ford and Toyota Systems
Large lot versus small lot production
Mixed model assembly in Toyota system
More consistent one piece flow in Toyota system
Chapter 6 Improving the Process - Mechanics of the Toyota Production System
Improving the Process
Toyota makes efforts and reduces production cycle.
Seven Principles for Shortening the Production Cycle
Reduce process delays
Reduce lot delays
Reducing production time
Employ layout, line forming, and the full work control system
Synchronize operations and absorb deviations
Establishing tact time
Ensure product flow between processes
Adopting SMED
Elimination of Defects
Inspection to prevent defects must be practiced.
100% inspection must be adopted.
Poka-Yoke has to be used as a means for zero defects.
Eliminating Machine Breakdowns
It is also process improvement in TPS. Workers are asked to stop a machine if there is some trouble. Supervisors are given training and are urged to try to keep machines running. When a trouble appears, a visual indication is given and all try to take care of the problem. Preventing recurrence is the motto of TPS.
Chapter 7 Improving Process - Multi Product Assembly Lines - Daily Leveling of Assembly Production and the Nagara System (Mechanics of the TPS)
Improving Process - Multi Product Assembly Lines and Daily Leveling and the Nagara SystemMulti Product Assembly Lines
Toyota developed multi product assembly line on which multiple models can be assembled. The assembly line has tools required to assemble multiple models, operators are trained to assembly any model required as needed and the system and procedures are developed and sufficient training is given to operators, supervisors, engineers and managers to operate the system efficiently and produce the finished car at the target cost.
What is Daily Leveling?
Leveling is a method of balancing load and capacity in a way different from the traditional way.
For example if load on car assembly plant is 300,000 sets of model A, 600,000 sets of model B and 900,000 units of model C and capacity is 1,800,000 units, the traditional solution is to make 300,000 sets of model A and 300,000 sets of model B in the first 10 days, 300,000 sets of model B and 300,000 sets of model c and in the next 10 days, and 600,000 units of model C in the last 10 days. The load is balanced at the month level, but it gives rise to inventories of various models and even shortages of some models.
But Toyota followed a different way because it has as its aim prevention and reduction of over production. In the first 10 days, production of 100,000 units of model A, 200,000 units of model B and 300,000 units of model C are produced. We can see now that inventory will come down. It the 10 day planning/production period can be further reduced, all models are produced in much smaller periods the over production can further be reduced. Toyota uses this approaches and reduces the planning period in which all models are made further and further. This is called "mixed production" and on assembly line it is called "mixed model assembly."
Segmented Production
Making production plans for half a month(H), ten days (T), week (W) and Day (D) are segmented production plans.
Mixed Production and Tact Time
Toyota combines product A with 30 Seconds and product B with 25 seconds and specifies 55 seconds as tact time for A+B.
Nagara System
In this system operator works on multiple unrelated machines laid out as per process sequence.
The nagara system facilitates one piece flow by laying out machines in the sequence of operations by transcending the earlier shop divisions and training and facilitating operators to operate multiple unrelated machines in sequence.
Smooth production flow, ideally one piece at a time, characterized by synchronization (balancing) of production processes and maximum use of available time; includes overlapping of operations where practical. A nagara production system is one in which seemingly unrelated tasks can be produced simultaneously by the same operator.
Nagara is multi-machine handling in a process or flow system. The operator works with two or more different machines.
The example given in the body refers to a spot welding operation, followed by a press operation and then a welding operation that attached the pressed part to a body.
Chapter 8 Improving Operations
Improving Operations
Operations concern the flow of equipment and operators in time and space. Improvements in operations have long been emphasized in the Toyota Production system.
Components of Operations
1. Preparation and after-adjustment
2. Principal operations
3. Marginal allowances
Preparation and After-Adjustment
Reduce them through SMED
Margin Allowances
Personal allowances - For fatigue and personal needs
Non-personal allowances -
Operational allowances: Oiling, clearing away chips etc.
Workplace related: parts arriving late and machine breakdowns
Standard Operation and Standard Operation Sheets
Standard operation implies optimization of work conditions by analyzing
What is produced
Who - persons, machines, tools,and jigs
How - Method - machine speeds and feeds, man's movements
Where - Layout of the equipment and man - Work Station Design
When - Standard time, and Schedule
Present
There has to be a standard operation sheet by the side of the machine using which new workers are trained.
Future:
The Toyota system demands that all work is done within standard time and supervisor is charged with the responsibility. He has to train the worker. Also supervisor is responsible for improvements.
Types of Standard Operating Charts
Capacity charts by part
Standard task combination
Task manual
Task instruction manual
Standard operating sheet
The topic of standard operations is discussed in more detail in
Standard Operation and Standard Operation Sheets in Toyota Production System
Improving Methods of Operation
The operation, which is a man-machine combination can be improved through:1. Improvements in human motions
2. Improvement in machine movements - increasing machine cutting speeds, reducing time through simultaneous cutting on multiaxis machines, and using multiple turret heads to shorten tool replacements.
3. Mechanizing human motions.
Improving human motions
Motion study can be used to reduce the operation time or the operator time. Motion study improves the movements or motions made by the operator and also improves the arrangement of materials and tools. 5S movement of Japanese industry is basically the offshoot of principles of motion economy.
Items must be arranged neatly, they must be easily accessible and they must be uniformly aligned.
Improvements in Machine Movements
Examples include raising output by increasing machine cutting speeds, reducing time through simultaneous cutting on multi-axis machines, and using multiple turret heads to shorten tool replacement time. This could involve using faster cutting processes like milling in the place of slower process like shaping.
Mechanizing Human Motions
In Toyota, first the human motions are optimized and then mechanization is attempted. Whenever mechanization is thought of its economics are thoroughly investigated. Toyota insists on kaizen - good change.
Machine Layout and Worker Efficiency
Workers are stationed with in a U layout so that they can easily help one another in case of need. Toyota encourages workers to assist each other in case of need or necessity. It discourages island mentality. The system requires each worker to learn the operations performed at the two processes adjacent to his or her own and help the others when needed.
Multiple Machine Handling Operations
In 1955 itself, Toyota operated 3,500 machines with only 700 workers. So one worker operates five machines on an average. In recent years (1981), Toyota managers started advocating multi-process handling. In multiple machine handling, the worker may handling the same type of machines. But in multi-process handling, the worker will handling multiple machines in accordance with the flow of operations or process. The capability of multi-process handling by a worker improves the flow of the process and also improves productivity.
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