process analysis
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Process AnalysisProcess Analysis
““If you cannot describe what you are doing as aIf you cannot describe what you are doing as aprocess, you do not know what you are doing.process, you do not know what you are doing.””
W.E. DemingW.E. Deming
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What is a process?
A process is a series of independent tasks that transforms an input into output material of
higher value for the organization
Examples:
1. Honda transforms steel, rubber, and plastic into cars
2. McDonald’s transforms meat, potatoes, and sauces into packaged food
3. Dell transforms customer orders into PC’s
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Process Analysis
Let’s look at the “black box” in more detail…
Why do we need to analyze the process?- To identify inefficient tasks- To spot possible effectiveness improvement tasks- To understand where value can be added
How can we analyze a process? Map it!What are the relevant performance measures?
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Process Flow ChartsGraphical description of a process:
– Holding:• Raw Materials, RM• Work in Process, WIP• Finished Goods Inventory, FGI
– Flow of material or work
– Processing step
– Decision point
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Make-to-order vs. make-to-stock
Task 1 Task 2 FGI
Task 1 Task 2
Demand
If demand is satisfied by FGI then the system is make-to-stock, otherwise it is a make-to order system
Some examples…
What are the tradeoffs?
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• What is its capacity? How many units per unit time go through each task? The process as a whole?
• What is the bottleneck? Which production step limits the process capacity?
• What is the throughput time? How long does it take to get through the system?
Process Analysis: the performance measures
Assume a process is in place. What do we need to measure in order to understand how efficient it is?
Task 1 Task 2 Task 3
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How do we measure capacity?
Cycle Time: Average time for completion of a unit at a production step or process. Does not include waiting. Measured as time/unit
Throughput Rate: Average number of units processed over a time interval. Measured as units/time
1
Cycle TimeThroughput rate = Key
relationship
Capacity of a task is the physical limitation in terms of “how much can be processed at this task”
Capacity = throughput rate
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Computing Cycle Times
Processing a fixed amount of work
Cycle Time = Set-up Time + (Batch size) x (Time per unit)
Batch size
Example: Producing 100 cars. On average, production takes 5 hours per car. It takes 50 hours to set up the production line.
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Computing Cycle Times
Setup time:15 min
A B
Question: What is the cycle time between points A and B of the process, if we work in batches of 10?
Production Time:25min/unit
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What is a bottleneck?
Which task is the bottleneck?
3 units/hr 5 units/hr 2 units/hr
Bottleneck is theprocess stage with the
smallest throughput rate (longest cycle time)
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Capacity of a process
The capacity of the process is:
minimum throughput rate at any of the stages
What is the capacity of this process?
3 units/hr 5 units/hr 2 units/hr
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How do we measure throughput time?
Throughput Time: Average time that a unit takes to go through the entire process (including waiting time). Measured as time
Work in Process(WIP): Average number of units in system over a time interval. Measured as units
WIP
Throughput rateThroughput time =
Key relationship
(Little’s Law)
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How do we analyze a complex process…
1. Look at the process step by step
2. Determine throughput rate (i.e. capacity) of each step
3. Identify the process bottleneck (smallest processing rate, or largest cycle time).
4. The capacity of the process is equal to the capacity of the bottleneck
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Example : hammer production process
Description1. Work begins at the machining center. Here two lines form
the heads of the hammers and place them in a buffer.2. Handles are attached at the assembly step.3. Finished hammers are sent to the next stage, where they
are packed and shipped.
assemblypack and
ship
machining
machining
WIP WIP
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Process Data:• machining: Set up 80 min. 4 min per unit processing.
Batch size 200. Identical lines. • assembly: Manual by two workers (no set up). Each
hammer requires 40 min processing. 34 workers available.• pack and ship: 30 min set up, 2 min per unit processing.
Lot sizes of 100.
assemblypack and
ship
machining
machining
WIP WIP
Let’s analyze the hammer process…
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Step 1: Machining
• Look at one line. 200 units require:80 + 200 4 = 880 minutes/200 units
• The throughput rate is:200 / 880 = 0.227 units/minute
= 13.63 units/hour
• But we have two identical lines, so for the machining step capacity is 2 13.63 = 27.26 units/hour.
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Step 2: Assembly
• 1 unit requires 40 min processing time, so the throughput rate is:
1 unit / 40 min = 0.025 units/min = 1.5 units/hr
• 34 workers available, but 2 workers are required for each unit, so assembly capacity is:
17 1.5 = 25.5 units/hr
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Step 3: Pack and ship
• Similar to machining:30 + 100 2 = 230 min/100 units
• Pack & ship capacity is:
100 / 230 = 0.43 units/min
= 26.09 units /hr
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Hammer process: what is the capacity?
Process Step Capacity (units/hr)
Machining 27.26
Assembly 25.50
Pack & Ship 26.09
Assembly is the
bottleneck!
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Some vocabulary…Buffering: Keep some inventory between stages
0 11/2
Starving: Stoppage of activity because of lack of material
Blocking: Stoppage of flow because there is no storage place
1 00/2
1 12/2
1 1
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More Examples..
CT = 3s CT = 1s
FGITask 1 Task 2
Let’s study this make-to-stock system.
What is the capacity of the process?
What is the throughput time?
What is the average WIP?
Is any task starved or blocked?
Note: No buffer space between stations, so upstream station has to wait if downstream station is busy
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More Examples..
CT = 3s CT = 1s
FGITask 1 Task 2
Task 2 starved for 2s. each time.Throughput rate = 20 units/min at Task 1, 60 units/min at Task 2Capacity (throughput rate) of process = 20 units/minThroughput time = 4 seconds = 1/15 min
WIP = Throughput rate x Throughput time = 20 units/min x 1/15 min = 1.33 units
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More Examples..
CT = 1s CT = 3s
FGITask 1 Task 2
What is the capacity of the process?
What is the throughput time?
What is the average WIP?
Is any task starved or blocked?
Let’s study this make-to-stock system:
Note: No buffer space between stations, so upstream station has to wait if downstream station is busy
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More Examples..
CT = 1s CT = 3s
FGITask 1 Task 2
Task 1 blocked for 2s. each time.Throughput rate = 60 units/min at Task 1, 20units/min at Task 2Capacity of process = 20 units/minThroughput time = 6 seconds = 0.1 min
WIP = Throughput rate x Throughput time = 20 units/min x 0.1 min = 2 units
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More Examples..
CT = 3s CT = 3s
FGI
Task 1 Task 2
What is the capacity of the process?
Is any task starved or blocked?
Let’s study this make-to-stock assembly system:
Note: No buffer space between stations
CT = 4s
Task 3
CT = 2s
Task 4
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More Examples..
CT = 3s CT = 3s
FGI
Task 1 Task 2
CT = 4s
Task 3
CT = 2s
Task 4
Tasks 1 and 2 are blocked by Task 3 for 1 second per product.Task 4 is starved for 2 seconds per product.
The capacity of the process is 15 units/hour (limited by Task 3).