Theory Of Constraints
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Theory of Constraints
Eliyahu Goldratt • Philosophy : The Goal. • Management concept : Theory of Constraints. (TOC). • Technical Component : Optimized Production Technology (OPT).
The Goal : เป้าหมายขององค์กร Make money in the present as well as in the future.
Measuring the goal • Net profit • Cash • Return on Investment (ROI) For a manufacturing enterprise, the goal can also be measured by • Throughput • Inventory • Operating expenses
Definitions • Throughput: The rate at which the system generates money through sales. – Note that the money is generated through sales and not production because if you produce something and don’t sell it, you have not really had throughput. (You’ve just put it into inventory). – Unsold Product is not throughput.
Definitions • Inventory : money that system has invested in purchasing thing it intends to sell, it measures inventory in term of material cost only . • Operational Expense: All the money the system spends in order to turn inventory into throughput.
to accomplish the Goal, the company must simultaneously
• Increase throughput. • Reduce inventory. • Cut operating expenses.
ข้อจำากัด (Constraint) • Anything that limits a system from achieving higher performance in attaining its goal. • Two types of constraints – Bottleneck – Capacity constrained resource
Constraint • Bottleneck – The resource’ s capacity is less than or equal to the market demand
• Capacity constrained resource – Resource that has become a bottleneck as a result of inefficient utilization
• For simplicity, we will only use the term bottleneck
Constraint
Cutting 1,300/day
Machining 800/day 1:1
Pressing 1,000/day
Welding 900/day
Assembly 1,100/day
Customer Demand 850/day
OPT Rules • Balance flow , not capacity. • Constraints determine nonbottleneck utilization. • Utilization and activation of a resource are not synonymous. • An hour lost at a bottleneck is an hour lost for the total system. • An hour saved at a nonbottleneck is a mirage.
OPT Rules • Bottleneck govern both throughput and inventory in the system. • The transfer batch may not, and many times should not, be equal to the process batch. • The process batch should be variable, not fixed. • Schedules should be established by looking at all of the constraints. Lead time are the result of a schedule and cannot be predetermined.
Example A 2 min/unit
Drill
C(2) 4 min/unit
D(2) 3 min/unit
B 4 min/unit D(1) Lathe 3 min/unit
Assembly
Lathe
Assembly
E(2) Mill 10 min/unit
Two Product Demand A : 300/day B : 50/day Production 2 Drills m/c 1 Lathe m/c 1 Milling m/c three shift per day (1440 minutes)
Machine Load Units Unit required Processing per Time assembly
2*1*300
Total Processing Time
Avail Utiliz able ation
A
B
A
B
A
B
Total
Assembly
2
4
1
1
600
200
800
1440
55.7%
Drill
4
0
2
0
2400
0
2400
2880
88.3%
Lathe
3
3
2
1
1800
150
1950
1440
10*2*50
135.4%
Mill
0
10
0
2
0
1000
1000
1440
69.4%
Example • • • •
The Lathe is the bottleneck resource. Daily demand cannot met. Lathe utilization will be 100%. Utilization of the other machines will decrease. (activation of the resources can be at different utilization levels. • Operate the nonbottleneck operations more efficiently will not contribute anything to throughput.
The transfer batch / the process batch. Operation 3 Process
Transfer 10
Operation 2 Process batch = 10 Transfer Batch = 10
Transfer 10
Operation 1 10
20
30
time
The transfer batch / the process batch.
Process
Operation 3 Transfer 5
Operation 2 Process batch = 10 Transfer Batch = 5
Transfer 5
Operation 1 10
20
30
Process Batch/Transfer Batch
Transfer Batch = 50
ส่งครั้งละ 50 Process 1
ผลิตครัง้ ละ 200 Process batch =200
50
Process 2
Theory of Constraints (TOC) • System’s output are determined by its constraints. • Broad categories of constraints – Internal Resource Constraint : machine ,worker ,tool. – Market Constraint :The market demand is less than production capacity – Policy constraint: A policy dictate the rule of production
Performance Measure • TOC focuses on the role constraints play in systems in order to improve system performance toward the GOAL. • Two type of performance measures – Financial Measures : net profit , ROI , cash flow – Operational Measures • Throughput • Inventory • Operating Expenses
• Efficiency measure,such as resource utilization,are not part of the operational measures.
Five step of TOC • • • • •
Identify the Constraint (The Drum). Exploit the Constraint (Buffer the Drum) Subordinate Everything Else (Rope) Elevate the Constraint If the Constraint Moves, Start Over
DBR Technique • Drum-Buffer-Rope (DBR) is a production control technique to implement the step of TOC. • Drum – Bottleneck, beating to set the pace of production for the rest of the system
• Buffer – Inventory, placed in front of the bottleneck to ensure it is always kept busy – Determines output or throughput of the system
• Rope – Communication signal, tells processes upstream when they should begin production
DBR Technique Raw material dispatching point Raw Material
1
2 Rope
… m
Drum … Buffer
n
Customer
Buffer • มีไว้เพื่อรองรับความไม่แน่นอนของกระบวนการต้นนำ้าที่ทำาหน้าที่สง่ ชิน้ ส่วนให้กับ Bottleneck • ขนาดของ Buffer คิดจากเวลามาตรฐานที่ Bottleneck จะใช้ชิ้นส่วนใน Buffer จนหมด • แนะนำาให้ขนาด Buffer เป็น หนึ่งในสีข่ อง Lead Time ของระบบ • เช่น ถ้าชิน้ ส่วนเดินทางจากต้นทางถึงจบกระบวนการเป็นสินค้าใช้เวลา 8 ชั่วโมง ขนาดของ Buffer คือ 2 ชัว่ โมง
มี 4 Work Center แต่ละ WC มีกำาลังผลิต 2400 นาทีตอ่ สัปดาห์
ตัวอย่าง สินค้า P อุปสงค์ 100/สัปดาห์ ราคา 90
สินค้า Q อุปสงค์ 50/สัปดาห์ ราคา 100
Purchased Part 5/pcs
D 10 นาที
D 5 นาที
C 10 นาที
C 5 นาที
B 15 นาที
A 15 นาที
B 15 นาที
A 10 นาที
RM 1 20/pcs
RM 2 20/pcs
RM 3 20/pcs
ใช้ตัวแบบ LP หา Bottleneck
• สินค้า P ราคา 90 บาท หักวัตถุดิบและชิ้นส่วนออก 45 บาท เหลือรายได้ = 45 บาท • สินค้า Q ราคา 100 บาท หักวัตถุดิบและชิ้นส่วนออก 40 บาท เหลือรายได้ = 60 บาท • นัน้ คือ Objective Function Z = 45P+60Q
ข้อจำากัด • • • • • •
15P+10Q <= 2400 15P+30Q <= 2400 15P+5Q <= 2400 10P+5Q <= 2400 P <= 100 Q <= 50
Work Center A Work Center B Work Center C Work Center D Demand P Demand Q
Linear Programming Model • Max Z = 45P+60Q Subject to • 15P+10Q <= 2400 • 15P+30Q <= 2400 • 15P+5Q <= 2400 • 10P+5Q <= 2400 • P <= 100 • Q <= 50 P,Q >= 0
Work Center A Work Center B Work Center C Work Center D Demand P Demand Q
นำาไปหาคำาตอบจะได้ Slack ของข้อจำากัด WC B=0 แสดงว่า WC B เป็น Bottleneck
Resource
min/Week P
min/week Q
Process Load per Week
Available time per week
Percentage Load per week
A
1500
500
2000
2400
83
B
1500
1500
3000
2400
125
C
1500
250
1750
2400
73
D
1000
250
1250
2400
52
Purchased Part 5/pcs
D C
A RM 3
RM 1
Buffer
B RM 2 Buffer
Drum
Eliyahu Goldratt • Philosophy : The Goal. • Management concept : Theory of Constraints. (TOC). • Technical Component : Optimized Production Technology (OPT).
The Goal : เป้าหมายขององค์กร Make money in the present as well as in the future.
Measuring the goal • Net profit • Cash • Return on Investment (ROI) For a manufacturing enterprise, the goal can also be measured by • Throughput • Inventory • Operating expenses
Definitions • Throughput: The rate at which the system generates money through sales. – Note that the money is generated through sales and not production because if you produce something and don’t sell it, you have not really had throughput. (You’ve just put it into inventory). – Unsold Product is not throughput.
Definitions • Inventory : money that system has invested in purchasing thing it intends to sell, it measures inventory in term of material cost only . • Operational Expense: All the money the system spends in order to turn inventory into throughput.
to accomplish the Goal, the company must simultaneously
• Increase throughput. • Reduce inventory. • Cut operating expenses.
ข้อจำากัด (Constraint) • Anything that limits a system from achieving higher performance in attaining its goal. • Two types of constraints – Bottleneck – Capacity constrained resource
Constraint • Bottleneck – The resource’ s capacity is less than or equal to the market demand
• Capacity constrained resource – Resource that has become a bottleneck as a result of inefficient utilization
• For simplicity, we will only use the term bottleneck
Constraint
Cutting 1,300/day
Machining 800/day 1:1
Pressing 1,000/day
Welding 900/day
Assembly 1,100/day
Customer Demand 850/day
OPT Rules • Balance flow , not capacity. • Constraints determine nonbottleneck utilization. • Utilization and activation of a resource are not synonymous. • An hour lost at a bottleneck is an hour lost for the total system. • An hour saved at a nonbottleneck is a mirage.
OPT Rules • Bottleneck govern both throughput and inventory in the system. • The transfer batch may not, and many times should not, be equal to the process batch. • The process batch should be variable, not fixed. • Schedules should be established by looking at all of the constraints. Lead time are the result of a schedule and cannot be predetermined.
Example A 2 min/unit
Drill
C(2) 4 min/unit
D(2) 3 min/unit
B 4 min/unit D(1) Lathe 3 min/unit
Assembly
Lathe
Assembly
E(2) Mill 10 min/unit
Two Product Demand A : 300/day B : 50/day Production 2 Drills m/c 1 Lathe m/c 1 Milling m/c three shift per day (1440 minutes)
Machine Load Units Unit required Processing per Time assembly
2*1*300
Total Processing Time
Avail Utiliz able ation
A
B
A
B
A
B
Total
Assembly
2
4
1
1
600
200
800
1440
55.7%
Drill
4
0
2
0
2400
0
2400
2880
88.3%
Lathe
3
3
2
1
1800
150
1950
1440
10*2*50
135.4%
Mill
0
10
0
2
0
1000
1000
1440
69.4%
Example • • • •
The Lathe is the bottleneck resource. Daily demand cannot met. Lathe utilization will be 100%. Utilization of the other machines will decrease. (activation of the resources can be at different utilization levels. • Operate the nonbottleneck operations more efficiently will not contribute anything to throughput.
The transfer batch / the process batch. Operation 3 Process
Transfer 10
Operation 2 Process batch = 10 Transfer Batch = 10
Transfer 10
Operation 1 10
20
30
time
The transfer batch / the process batch.
Process
Operation 3 Transfer 5
Operation 2 Process batch = 10 Transfer Batch = 5
Transfer 5
Operation 1 10
20
30
Process Batch/Transfer Batch
Transfer Batch = 50
ส่งครั้งละ 50 Process 1
ผลิตครัง้ ละ 200 Process batch =200
50
Process 2
Theory of Constraints (TOC) • System’s output are determined by its constraints. • Broad categories of constraints – Internal Resource Constraint : machine ,worker ,tool. – Market Constraint :The market demand is less than production capacity – Policy constraint: A policy dictate the rule of production
Performance Measure • TOC focuses on the role constraints play in systems in order to improve system performance toward the GOAL. • Two type of performance measures – Financial Measures : net profit , ROI , cash flow – Operational Measures • Throughput • Inventory • Operating Expenses
• Efficiency measure,such as resource utilization,are not part of the operational measures.
Five step of TOC • • • • •
Identify the Constraint (The Drum). Exploit the Constraint (Buffer the Drum) Subordinate Everything Else (Rope) Elevate the Constraint If the Constraint Moves, Start Over
DBR Technique • Drum-Buffer-Rope (DBR) is a production control technique to implement the step of TOC. • Drum – Bottleneck, beating to set the pace of production for the rest of the system
• Buffer – Inventory, placed in front of the bottleneck to ensure it is always kept busy – Determines output or throughput of the system
• Rope – Communication signal, tells processes upstream when they should begin production
DBR Technique Raw material dispatching point Raw Material
1
2 Rope
… m
Drum … Buffer
n
Customer
Buffer • มีไว้เพื่อรองรับความไม่แน่นอนของกระบวนการต้นนำ้าที่ทำาหน้าที่สง่ ชิน้ ส่วนให้กับ Bottleneck • ขนาดของ Buffer คิดจากเวลามาตรฐานที่ Bottleneck จะใช้ชิ้นส่วนใน Buffer จนหมด • แนะนำาให้ขนาด Buffer เป็น หนึ่งในสีข่ อง Lead Time ของระบบ • เช่น ถ้าชิน้ ส่วนเดินทางจากต้นทางถึงจบกระบวนการเป็นสินค้าใช้เวลา 8 ชั่วโมง ขนาดของ Buffer คือ 2 ชัว่ โมง
มี 4 Work Center แต่ละ WC มีกำาลังผลิต 2400 นาทีตอ่ สัปดาห์
ตัวอย่าง สินค้า P อุปสงค์ 100/สัปดาห์ ราคา 90
สินค้า Q อุปสงค์ 50/สัปดาห์ ราคา 100
Purchased Part 5/pcs
D 10 นาที
D 5 นาที
C 10 นาที
C 5 นาที
B 15 นาที
A 15 นาที
B 15 นาที
A 10 นาที
RM 1 20/pcs
RM 2 20/pcs
RM 3 20/pcs
ใช้ตัวแบบ LP หา Bottleneck
• สินค้า P ราคา 90 บาท หักวัตถุดิบและชิ้นส่วนออก 45 บาท เหลือรายได้ = 45 บาท • สินค้า Q ราคา 100 บาท หักวัตถุดิบและชิ้นส่วนออก 40 บาท เหลือรายได้ = 60 บาท • นัน้ คือ Objective Function Z = 45P+60Q
ข้อจำากัด • • • • • •
15P+10Q <= 2400 15P+30Q <= 2400 15P+5Q <= 2400 10P+5Q <= 2400 P <= 100 Q <= 50
Work Center A Work Center B Work Center C Work Center D Demand P Demand Q
Linear Programming Model • Max Z = 45P+60Q Subject to • 15P+10Q <= 2400 • 15P+30Q <= 2400 • 15P+5Q <= 2400 • 10P+5Q <= 2400 • P <= 100 • Q <= 50 P,Q >= 0
Work Center A Work Center B Work Center C Work Center D Demand P Demand Q
นำาไปหาคำาตอบจะได้ Slack ของข้อจำากัด WC B=0 แสดงว่า WC B เป็น Bottleneck
Resource
min/Week P
min/week Q
Process Load per Week
Available time per week
Percentage Load per week
A
1500
500
2000
2400
83
B
1500
1500
3000
2400
125
C
1500
250
1750
2400
73
D
1000
250
1250
2400
52
Purchased Part 5/pcs
D C
A RM 3
RM 1
Buffer
B RM 2 Buffer
Drum
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