Chapter 6: Designing Lean Systems Lean System and JIT Process - - PDF document

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Chapter 6: Designing Lean Systems

 Lean System and JIT  Process Considerations  The Kanban System  Supply Chain Considerations

What is a Lean System?

Operations systems that maximize the value added by each of a company’s activities by removing waste and delays from them. Just‐in‐time

 A highly coordinated production system in which materials

are moved through the system with precise timing, just as they are needed.

 JIT system  lean system  JIT (pull) ← → MRP (push)

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 Toyota switched from automated looms to

military trucks just prior to WWII.

History of Toyota

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 Secondhand equipment and high unit

costs forced Toyota to reduce waste and improve quality whenever possible.

Eight Types of Waste (Muda)

 Overproduction 庫存過多、沒有改善品質的壓力  Inappropriate Processing 殺雞焉用牛刀  Waiting 人員或產品的等待過程不會創造價值  Transportation 物料搬運不會創造價值且易造成損壞  Motion 不必要的動作或行走不會創造價值且容易勞累  Inventory 庫存會隱藏問題、占空間、造成等待  Defects 增加檢查成本、時間與材料的浪費  Underutilization of Employees 浪費員工的時間與腦力

Waste can be eliminated by cutting unnecessary capacity or inventory and removing non‐value‐added activities in operations.

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Process Considerations in Lean Systems

Kaizen: continuous improvement (改善) Pull Method of Work Flow: supplying material based on demand using Kanban (看板) Quality at the Source: Jidoka: automatic detection (自働化) Poka‐yoke: fool‐proofing to reduce errors Uniform Work loads: Heijunka (平準化) Flexible Workforce: cross training, work rotation (兩小時換場制) 5S: 整理SEIRI、整頓SEITON、清掃SEISO、清潔SEIKETSU、素養SHITSUKE Total Preventive Maintenance 全面預防保養

Kaizen: Continuous Improvement

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水位高度相當於產能或庫存，暗礁代表生產線各種問題 生產線必須面對並解決各種問題 進一步降低庫存 降低庫存

4 Single Minute Exchange of Dies = Single Digit Setup

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faster set up  smaller lot sizes  smaller inventory

internal setup external setup 事先調整定位、簡 易拆卸、預熱模具

F1 Pit Stops 1950 vs 2013_ Quick Changeover

Quality at the Source

 Jidoka

Automatically stopping the process when something is wrong and then fixing the problems on the line itself as they occur.

 Poka‐Yoke

Mistake‐proofing methods aimed at designing fail‐safe systems that minimize human error.

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Heijunka leveling of production load

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根據實際需求安排生產計劃，使生產量與生產內容平準化

當月計劃生產 800A、 600B、 400C 每週生產 200A、 150B、 100C 每天生產 40A、 30B、 20C 實際現場排程 AAAABBBCC AAAABBBCC mixed model assembly

Process Considerations in Lean Systems

Flexible Workforce

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Workers can be trained to perform more than one job.

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A benefit is the ability to shift workers among workstations to help relieve

• bottlenecks. At some firms, workers may switch jobs every 2 hours.

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An environment to foster cooperation and mutual trust between workforce and management.

Total Preventative Maintenance

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Maintenance is done on a schedule that balances the cost of the preventive maintenance program against the risks and costs of machine failure.

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Data can be collected for establishing trends in failure pattern of machines, which can subsequently be analyzed to establish better standards and procedures for preventive maintenance.

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5S

整理 整頓 清掃 清潔 素養 Separate needed items from unneeded items (including tools, parts, materials, and paperwork. Neatly arrange what is

• left. Organize the work

area so that it is easy to find what is needed. Clean and wash the work area and make it shine. Establish schedules and methods of performing the cleaning and sorting. Implement mechanisms to sustain the gains by involving people and recognizing them.

House of Toyota

Needs close cooperation between companies and their suppliers to improve efficiency and reduce inventories.

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Kanban

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由下游往上游拉(pull)的物料控制方式，看板提供的 相關資訊，包括時間、規格、數量、運送地點等

Operating Rules for Single-Kanban Systems

• 1. Each container in the process must have a Kanban card. (授權)
• 2. The assembly line (下游) always withdraws materials from the

fabrication cell (上游主動權). The fabrication cell never pushes parts to the assembly line.

• 3. Containers of parts must never be removed from a storage area

without a Kanban first being posted on the receiving post. (時機)

• 4. The containers must always contain the same number of good parts.
• 5. Only nondefective parts should be passed along to the assembly line

(下游) to make the best use of materials and worker’s time. (品質)

• 6. Total production should not exceed the total amount authorized on

the Kanbans in the system. (總量管制)

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The Single Kanban System 1/4

Storage area Full containers Receiving post Kanban card for product 1 Kanban card for product 2

Fabrication cell

O1 O2 O3 O2

Assembly line 1 Assembly line 2

The Single Kanban System 2/4

Storage area Full containers Receiving post Kanban card for product 1 Kanban card for product 2

Fabrication cell

O1 O2 O3 O2

Assembly line 1 Assembly line 2

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The Single Kanban System 3/4

Storage area Full containers Receiving post

Fabrication cell

O1 O2 O3 O2

Kanban card for product 1 Kanban card for product 2

Assembly line 1 Assembly line 2

The Single Kanban System 4/4

Storage area Full containers Receiving post

Fabrication cell

O1 O2 O3 O2

Kanban card for product 1 Kanban card for product 2

Assembly line 1 Assembly line 2

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Determining the Number of Kanbans

 Too many kanbans  excessive inventory  Too few kanbans  not enough supply to the next station.  Two determinations:

 Number of units to be held by each container  Number of kanbans (containers) between two stations

 Little’s Law

Work‐in‐process L = W  = demand rate W= average time a container spends in the process Supplies must be shipped frequently, have short lead times, arrive

• n schedule, and be of high quality. In US, such arrangements may

prove difficult because of the geographic dispersion of suppliers.

Example 6.2

 A container of parts spends 0.02 day in processing and 0.08 day

in materials handling and waiting

 Daily demand for the part is 2,000 units  Safety stock equivalent of 10 percent of inventory

If each container has 22 parts, how many kanbans are needed? Suppose that a proposal would cut materials handling and waiting time per container to 0.06 day. How many kanbans are needed?

k = 2,000(0.08 + 0.02)(1.10) 22 = = 10 containers 220 22 k = 2,000(0.06 + 0.02)(1.10) 22 = = 8 containers 176 22