Japanese were rational shoppers for production technology and management methods from USA and other countries. Taiichi Ohno and Shigeo Shingo combination improved the production line technique pioneered by Henry Ford in to a very high productive system. There is a book written during Henry Ford's time itself describing the full process of Ford system (Hartley W. Barclay "Ford Production Methods," Harper & Brothers, New York, 1936.). MIT faculty, Richard Muther published a book in 1944 describing the planning, optimizing, and operating the production line system. He also wrote essays in Maynard's Handbook on Industrial Engineering on the topic.
We can see that quality and maintenance were given stress by Muther. Ohno and Shingo developed methods and tools to squeeze out further waste from the production line system due to extra setup time, poor quality and maintenance problems.
Muther's Description
Line production is a method of manufacture or an arrangement of work areas where the material moves continuously and at a uniform rate through a sequence of balanced operations which permit of simultaneous performance throughout, the work progressing toward completion along a reasonably direct path. Actually, the complete refinements of line production are seldom attained.
Principles of Production Flow Line
1. The principle of minimum distance moved.
2. The principle of flow of work.
3. The principle of division of labor
4. The principle of simultation or simultaneous operation
5. The principle of unit operation
6. The principle of fixed routing
7. The principle of minimum time or material in process
8. The principle of interachangeability
Enforcement of Operation Study.
Muther gives this point as an advantage of Production Flow Line.
It is especially important that adequate operation-analysis and methods study go into the job before it starts into production.
When a production line is installed, it works as a unit. Recognition of this necessity causes a critical examination of every phase of the job. This demand for thorough analysis of all details leads to many improvements in operations which might otherwise never have been noticed. Thus efficient performance of the work follows.
Line production and the motion study
In line production the work of motion study should be conducted along with the design of the tools. The chief objective is to build the quality and cost of the job and the skill required into the tools. The ease of operation is highly desirable. Thought should be given to the motions of the operator of the tool before it goes into the line. Building the line as a piecemeal activity with work simplification
appearing after the job is under way is not only wasteful, but it leads to unbalancing the line
Motion economy rules to guide tool designers and process men.
1. Make the necessary movements as short as possible without crowding the operator.
2. Replace hand movement by automatic machine movement where practical.
3. Replace hand movement by foot movement.
4. Eliminate the passing of work from one hand to the other.
5. Provide hand levers, etc., with multiple functions.
6. Use mechanical ejectors.
7. Arrange so that finished work will drop from fixture into discharge chutes. Use drop discharge chutes and the pushthrough idea.
8. When drop discharge cannot be used, arrangement for disposal directly in front of operator, over top of machine, is often a good solution.
9. Arrange for getting new work from hopper or chute as close as possible to loading point or from location close to discharge point so as to overlap movements.
10. Provide mechanical holders to eliminate the use of the operator's hand as a holding device.
11. When possible keep hand movements within radius of forearm pivoted from elbow. In all events keep within radius of full arm without body bend or twist and without necessity for stepping to reach point desired.
12. Eliminate barriers so that movements can follow shortest path.
13. Keep both hands busy with useful work and avoid waiting of one hand.
14. Provide double station fixtures; one for each hand.
15. Centralize all control levers and starting buttons within the normal work area.
16. Aid locating by means of slides, guides, flanges, stops, bell mouth holes and bullet-nosed pins.
17. Separate scrap from good parts by simple mechanical means.
18. Eliminate all unnecessary use of the eyes. Keep necessary eye use within small space (about six-inch circle if possible).
19. Avoid necessity for operator to assume uncomfortable position. Most of the work should be at elbow level when seated and 6" below elbow level when standing.
20. Build controls of proper size, shape, and weight, and build to operate without undue effort.
Perquisites for Feasibility for Establishing Production Flow Line
1. Quantity
2. Balance
3. Continuity
Methods and Equipment
It is especially important that adequate operation-analysis and methods study go into the job before it starts into production.
Also it is adequate many times to supply a line with equipment that is slower instead of the fastest one available in the market. The machine must serve the needs of the line speed to do its role in the line.
Line Balance
The desired rate of production is converted into a time for work station. This time is called station time or cycle time. If every operator and every equipment is busy for this cycle time,the line has perfect balance. But this perfect balance is rarely achieved. Operators with idle time can be assigned material handling, taking routine care of the machine etc.
Mechanics of Balancing
Adjust operations by combining or dividing operations to get a total time that is equal to the station time.
Layout
Make sure:
1. adequate space for maintenance and repair.
2. space for material handling
3. adequate storage space for materials
4. provision of inspection points
Manning the Line
The number of operators required equals the total time (in standard hours allowed) required to perform all operations on one unit mutliplied by the rate of production scheduled divided by the length of the shift or period worked in hours per man. This number is based on no idle time to balance.
Assuring Continuity of Manpower
If a line has to work all operators have to be on the line as per planned. No doubt line can be operated at lower rates of output with lesser number of operators. But this is once again planned before hand. Hence the number of operators has to be assessed before the start of the line and actions are to be taken to see that planned number of operators are there.
Incentives
Some companies give incentives and operators as a group have to the freedom to operate the line at the speed they desire and also vary it as they want.
Assuring Continuity of Material
To keep a line running, adequate materials and components must flow into the line at various work stations as per plan. Quantity, quality and location have to right. Material and component planning must synchronize and schedule the work so that everything flows together as needed.
To assure the material, advance plans are required and these plans are refined as actual production period approaches. Muther described that a company makes five different types of plans.
1. Broad plan for the year.
2. Tentative 90-day schedule
3. Definite program for 30 days
4. Shipping schedules for 10 days
5. Daily schedule with complete specificationi
Purchasing
In line production, the ability of the vendor to supply the correct parts when they are needed is very important. The supplier has to be reliable in both quantity and quality.
Material Control
Storage of material along the line
1. Store material at the point of use.
2. Predetermine and identify all storage places along the line.
3. Replenish material along line every night.
4. Have adequate communication system for material control men.
5. Make material control people conscious of not wasting material and components due to faulty handling.
Quality
Muther has listed the factors that may aid quality in line production. Similarly he highlighted some factors that give rise to quality problems.
He gave the following directions to improve quality.
1. Test all sample parts for quality check.
2. Check all tools, dies, and fixtures to make sure that they produce quality output.
3. In stead of depending on individuals, put confidence in tooling, inspection gauges, and fixtures (This point needs thinking. Is Muther hinting at Poka Yoke?)
4. Plan for the inspection group to be busier than usual during pilot-lot or trial run period.
5. Assign inspectors along the line:
6. Maintain clean-up touch up stations at the end of the line to care for minor defects.
7. Stop production line and move operators to the end of the line to correct units when large number of mistakes occur.
Maintenance
Machines should not break down during the time line is running. All maintenance activities have to be undertaken to ensure that all machines are available during the planned run of time of line.
The recommended steps:
1. Sound preventive maintenance program involving periodic inspectioni, repair, or replacement of tools, equipment, and handling devices.
2. Rapid communication system or automatic signaling devices to indicate a breakdown and where it has occurred.
3. Ample use of fuses, overload switches, shear pin on conveyor drives, electric-cye or limit switch controls to stop overrunning.
4. Pay group incentive based on freedom from downtime on the line.
5. Stand-by equipment
6. Guards and protective devices to avoid machine or conveyor jamming.
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