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OIDD midterm review good luck

This is a draft cheat sheet. It is a work in progress and is not finished yet.

Lecture 2

Flow Rate
Min between demand and capacity
Utiliz­ation = R/Capacity
fraction of time spent working
Cycle Time = 1/ Flow Rate
Time between when units exit process
Flow Time = I/R
Time unit spends in process
Cost of Direct Labor
=(wages per unit of time x #of workers) / Flow Rate
Labor Content
sum of processing times involving labor (don't multiply by #of workers)
Labor Utiliz­ation
= R / Labor Capacity
Labor Capacity
= N (# of workers) / Labor content
Takt Time =1/ Demand Rate
Time between when flow units are demanded
Target Manpower = Labor Content/ Takt Time
= Labor Content/ Takt Time
Goal of Line Balancing
Find min cycle time

Process Flows (Lecture 1)

Little's Law: I = R x T
I= Inventory, R= Flow Rate, T= Flow Time
Days of Supply = I/R = 1/Turns
The "­T" in Little's Law (add def)
Inventory Turns = 1/T = R/I = COGS/ I
COGS = R, the flow rate
Gross Margin % = (Price - Cost) / Price

Decision trees

Maximin Decision
Find the minimums of each branch, then choose the max of the mins
Maximax Decision
Find the max of each branch, then choose the max of the maxes
Expected value of Perfect info
= (expected value of decision w/ perfect info) - (expected value of decision w/o perfect info)

Baye's Rule

Queues

Length of queue at time T = T x (Demand - Capacity)
Time to serve Qth person in queue = Q/Capacity
Time to serve customer arriving at time T = T x (Deman­d/C­apa­city-1)
Avg time to serve customers in the queue = 1/2 x T x (Deman­d/C­apacity -1)
Variables to know
a= inter arrival time, m= # of worker­s/k­iosks, p = avg processing time
Demand = 1/a
Capacity= m x (1/p)
Utiliz­ation = P / ( a x m)
m = P /( a x utiliz­ation)
Time spent in system = Time in queue + Time in processing
Inventory = Inventory in queue + Inventory in service
Inventory in queue = Time in queue/ a
Inventory in service = p/a
CVa= Standard deviation inter arrival time / avg inter arrival time
CVp= Standard deviation processing time/ avg processing time
Time in queue increases dramat­ically as utiliz­ation approaches 100%
 

Yield and Capacity of Process

Yield = Flow Rate goof output/ Flow rate bad output
Yield of Process = Product of resource yields
Implied Utiliz­ation = Demand/ Capacity
Can be over 100% , bottleneck has highest IU
Capacity = 1/Proc­essing Time
Processing Time = 1/Capacity
Demand (in min of work) = Processing time x Demand
Required input = Desired output/ Process yield
Required resource capacity = Resource's demand with required input
Required resource capacity = Resource's demand with required input
Finding capacity of process
Find capacity of each step and find the bottleneck

Solving Questions

What the question is asking
Approach to take
Inventory costs are what percent of purchasing costs?
Find Flow Time. Then multiply annual inventory cost percentage by flow time in years and by individual unit cost
Cost to hold inventory for a year
Cost of individual unit x annual holding cost percentage
What is the avg time...
Find flow time
Total time to process 20 customers
Time to process 1st customer (sum of processing times) + time to process other customers ( 19 x Cycle Time)
Total ordering costs
(K x R) / Q
Total holding costs
1/2 x Qh
How many individual units should they produce in each batch
Use desired capacity to find full batch size. Then multiply batch size by ratio of individual demand­/ca­pacity over total demand­/ca­pacity
If company ordered a specific number of cases at a time, what would be their holding and ordering costs
Find C(Q)
If company ordered a specific number of cases, what would be holding and ordering cost per case
Find C(Q)/ R
Quantity of cases per order
Find EOQ
How long will you wait if you are nth in line
Find the time to serve the number of people in front of you.

Avg Inventory

  

Setup Times and Batching

Capacity = Number of units produced/ Time to Produce units
Utiliz­ation (with a setup time) = Flow rate x Processing Time

Capacity

EOQ and Quantity Discounts

Inventory Variables
Q= quantity in each order, R=Flow Rate, h = inventory holding cost per unit time, K= fixed vost per order
Time between shipments = Q/R
Avg inventory = Q/2
Number of orders placed per unit of time = R/Q
Capacity (in min of work/hr) = #of workers x 60

Quantity minimizing ordering and holding costs

Batch Size

Ordering plus inventory holding cost per unit time

Time in Queue