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Presented By
Niaz Ahmed CSCM, MBA in MIS (DU), B.Sc in ME (MIST)
Material And Inventory Management
Welcome to Day Long Training on
Material Management • It is concerned with Planning, organizing, and controlling the flow of materials from the
initial purchase thru internal operation to the service point thru distribution
• Material Management is a scientific technique concerned with Planning, Organizing and control of flow of materials from the initial phase to destination.
• Aim of Material Management:
To Get
The Right Quality
Right Supplier
Right Quantity
Right Time
Right Place
Right Cost
What is Logistics? Movement of Goods
Three Things Flow During any Business:
Information
Fund
Material
Characteristics of Forecasts
• All forecasts are wrong (rarely correct). The best we can hope for is to reduce the amount of error. Forecasts should include expected value and measure of error.
• Long-term forecasts are less accurate than short-term forecasts (forecast horizon is important)
• Aggregate forecasts are more accurate than disaggregate forecasts
Forecasting is the process of projecting the values of one or more variables into the future.
Forecasts reduce the uncertainty in our decision making. Forecasts aid us in planning. They allow us to plan for contingencies.
Benefits of Forecasts
Types of Forecasts by Time Horizon
• Short-range forecast
– Usually < 3 months • Job scheduling, worker assignments
• Medium-range forecast
– 3 months to 2 years • Sales/production planning
• Long-range forecast
– > 2 years • New product planning
Design of system
Detailed use of system
Quantitative methods
Qualitative Methods
• Causal
• Judgment
• Causal
• Judgment
• Time series
• Causal
• Judgment
Forecasting
Technique
• Facility location
• Capacity planning
• Process
management
• Staff planning
• Production
planning
• Aggregate Prod.
scheduling
• Purchasing
• Distribution
• Inventory Mgt.
• Final assembly
scheduling
• Workforce
scheduling
• Master Prod.
scheduling
Decision
Area
• Total sales • Total sales
• Groups of products
or services
• Individual
products or
services
Forecast
Focus
Long Term
(over 2 years)
Medium Term
(3 months–2 yrs)
Short Term
(0–3 months)
Application
Time Horizon
Demand Forecasting Summary
Time Series Analysis
• Time series forecasting models try to predict the future based on past data
• One can pick models based on:
1. Time horizon to forecast
2. Data availability
3. Accuracy required
4. Size of forecasting budget
5. Availability of qualified personnel
Basic Time-Series Patterns There are five basic patterns of most time series.
a. Horizontal: Over time the data fluctuates around a constant
mean.
b. Trend: The systematic increase (or decrease) in the data over
time.
c. Seasonal: A repeatable pattern of increases and decreases in
demand that relates to a specific period, such as the time of day,
week, month, or season.
d. Cyclical: Less predictable, gradual increases and decreases over
longer periods of time (years or decades), such as the business
cycle. No consistent time frame.
e. Random: A variation in demand that has no pattern.
The data cannot be used for forecasting.
TIME-SERIES METHODS
• NAÏVE FORECASTING: A time-series method whereby the forecast
for the next period is the known demand for the current period.
– It takes the most recent known period value and projects it to
the first forecast period.
• SIMPLE MOVING AVERAGES is a time-series method that averages
demand over a specified period “n” of time.
– It computes the average for the last “n” periods and uses that as
the forecast for the next period.
– By averaging, it removes the effects of random fluctuations, and
it is most useful when demand has no pronounced trend or
seasonal influences.
Simple Moving Averages
22 becomes the forecast for week #5 23.25 becomes the
forecast for week #6.
This is a 4-period moving average.
The moving average method involves the use of as many periods
of past demand as desired or deemed appropriate. The stability of
the demand series generally determines how many periods.
WEEK DEMAND AVERAGE
1 20
2 23
3 21
4 24 22
5 25 23.25
6 ?
Simple Moving Average Formula
• The simple moving average model assumes an average is a good estimator of future behavior
• The formula for the simple moving average is:
F = A + A + A +...+A
nt
t-1 t-2 t-3 t-n
Ft = Forecast for the coming period
N = Number of periods to be averaged
A t-1 = Actual occurrence in the past period for
up to “n” periods
Comparison of 3- and 6-Week Moving Average Forecasts
Week
Pati
en
t A
rriv
als
Actual Data Historic Data
3-week moving
average forecast 6-week moving
average forecast
A longer averaging period soothes the fluctuations.
Simple Moving Average Problem (1)
Question: What are the 3-week and 6-week moving average forecasts for demand?
Assume you only have 3 weeks and 6 weeks of actual demand data for the respective forecasts
Week Demand
1 650
2 678
3 720
4 785
5 859
6 920
7 850
8 758
9 892
10 920
11 789
12 844
F = A + A + A +...+A
nt
t-1 t-2 t-3 t-n
Week Demand 3-Week 6-Week
1 650
2 678
3 720
4 785 682.67
5 859 727.67
6 920 788.00
7 850 854.67 768.67
8 758 876.33 802.00
9 892 842.67 815.33
10 920 833.33 844.00
11 789 856.67 866.50
12 844 867.00 854.83
F4=(650+678+720)/3
=682.67
F7=(650+678+720
+785+859+920)/6
=768.67
Calculating the moving averages gives us:
©The McGraw-Hill Companies, Inc., 2004
500550600650700750800850900950
1 2 3 4 5 6 7 8 9 10 11 12
De
man
d
Week
Demand 3-Week 6-Week
Plotting the moving averages and comparing them shows how
the lines smooth out to reveal the overall upward trend in this
example
Note how the 3-
Week is
smoother than
the Demand, and
6-Week is even
smoother
Simple Moving Average Problem (2) Data
Question: What is the 3 week moving average forecast for this data?
Assume you only have 3 weeks and 5 weeks of actual demand data for the respective forecasts
Week Demand
1 820
2 775
3 680
4 655
5 620
6 600
7 575
Simple Moving Average Problem (2) Solution
Week Demand 3-Week 5-Week
1 820
2 775
3 680
4 655 758.33
5 620 703.33
6 600 651.67 710.00
7 575 625.00 666.00
F4=(820+775+680)/3
=758.33
F6=(820+775+680
+655+620)/5
=710.00
WEEK DEMAND SINGLE DOUBLE
AVG AVG
1 20
2 25
3 34
4 19 25
5 22 25
6 12 22
7 36 22 23
8 14 21 23
9 19 20 21
10 24 23 22
11 22 20 21
12 18 21 21
13 27 23 22
Double Moving Averages (Averaging the averages)
n= 4 periods for the average
Averages are rounded to the nearest whole numbers.
WEEK DEMAND Wt. Wt. AVERAGE
1 20 .1
2 23 .2
3 21 .3
4 24 .4 22.5
WEIGHTED MOVING AVERAGES
Weighted moving average method: A time-series method in which
each historical data point can have its own weight. (The sum of the weights
equals 1.0)
It allows the forecaster to give more weight to the more recent data or the
more relevant data.
Important in trend or cyclical data
(20*0.1)+(23*0.2)+(21*0.3)+(24*0.4)=22.5
Weighted Moving Average Formula
F = w A + w A + w A +...+w At 1 t-1 2 t-2 3 t-3 n t- n
w = 1ii=1
n
While the moving average formula implies an equal weight being placed on each value that is being averaged, the weighted moving average permits an unequal weighting on prior time periods
wt = weight given to time period “t”
occurrence (weights must add to one)
The formula for the moving average is:
Weighted Moving Average Problem (1) Data
Weights:
t-1 .5
t-2 .3
t-3 .2
Week Demand
1 650
2 678
3 720
4
Question: Given the weekly demand and weights, what is the forecast
for the 4th period or Week 4?
Note that the weights place more emphasis on the most recent
data, that is time period “t-1”
Weighted Moving Average Problem (1) Solution
Week Demand Forecast
1 650
2 678
3 720
4 693.4
F4 = 0.5(720)+0.3(678)+0.2(650)=693.4
Weighted Moving Average Problem (2) Data
Weights:
t-1 .7
t-2 .2
t-3 .1
Week Demand
1 820
2 775
3 680
4 655
Question: Given the weekly demand information and
weights, what is the weighted moving average
forecast of the 5th period or week?
Weighted Moving Average Problem (2) Solution
Week Demand Forecast
1 820
2 775
3 680
4 655
5 672
F5 = (0.1)(755)+(0.2)(680)+(0.7)(655)= 672
JUDGMENT METHODS
• Sales force estimates: Forecasts are made by a company’s sales-force
members who have first-hand interaction with customers.
• Executive opinion (Executive intuition): The opinions, experience, and technical knowledge of experienced managers are summarized to
arrive at a single forecast.
• Market research: A systematic approach to determining consumer interest in a service or product through data-gathering surveys.
(Quantitative methods are often applied to this data.)
• Delphi method: A process of gaining consensus from a group of experts, usually external to the organization, while maintaining
individual anonymity. (Survey-feedback-survey method)
– Experts are drawn from across the industry, government, public and
private organizations.
Material Requirements Planning
• Materials requirements planning (MRP) is a means for determining the number of parts, components, and materials needed to produce a product.
• MRP provides time scheduling information specifying when each of the materials, parts, and components should be ordered or produced
• Dependent demand drives MRP
There are two types of demand.
• Independent Demand – Is the demand for finished products
– Does not depend on the demand of other products
– Needs to be forecasted
• Dependent Demand – Is the demand derived from finished products
– Is the demand for component parts based on the number of end items being produced and is managed by the MRP system
34
Firm orders
from known
customers
Forecasts
of demand
from random
customers
Aggregate
product
plan
Bill of
material
file
Product
design
changes
Inventory
record file
Inventory
transactions
Master production
Schedule (MPS)
Primary reports Secondary reports
Planned orders
Order release notices
Changes in due dates of open orders
Cancellations or suspensions of open orders
Inventory status data
Exception reports
Planning reports
Reports for performance control
Material
Requirement
Planning
(MRP)
MRP inputs and outputs
BOM Example
B(2) C(3) 1
E(2) E(2) F(2) 2
D(2) D(2) G(1) 3
Product structure for Finished Product (A)
A
Level
0
• Gross requirements
– Total expected demand
• Scheduled receipts
– Open orders scheduled to arrive
• Projected available balance
– Expected inventory on hand at the beginning of each time period
• Net requirements
– Actual amount needed in each time period
• Planned-order receipts
– Quantity expected to received at the beginning of the period
– Offset by lead time
• Planned-order releases
– Planned amount to order in each time period
Additional MRP Scheduling Terminology
MRP Logic with Example
A(2) B(1)
D(5) C(2)
X
C(3)
Item On-Hand Lead Time (Days)
X 50 2
A 75 3
B 25 1
C 10 2
D 20 2
Requirements include 95 units (80 firm orders and 15 forecast) of X
in day 10
MRP Example 1 Day: 1 2 3 4 5 6 7 8 9 10
X Gross requirements
LT=2 Scheduled receipts
Proj. avail. balance
On- Net requirements
hand Planned order receipt
50 Planner order release
A Gross requirements
LT=3 Scheduled receipts
Proj. avail. balance
On- Net requirements
hand Planned order receipt
75 Planner order release
B Gross requirements
LT=1 Scheduled receipts
Proj. avail. balance
On- Net requirements
hand Planned order receipt
25 Planner order release
C Gross requirements
LT=2 Scheduled receipts
Proj. avail. balance
On- Net requirements
hand Planned order receipt
10 Planner order release
D Gross requirements
LT=2 Scheduled receipts
Proj. avail. balance
On- Net requirements
hand Planned order receipt
20 Planner order release
Item On-Hand Lead Time (Days)
X 50 2
A 75 3
B 25 1
C 10 2
D 20 2
Gross
requirement of X
is 95 units on
day 10
A(2) B(1)
D(5) C(2)
X
C(3)
MRP Example Day: 1 2 3 4 5 6 7 8 9 10
X Gross requirements 95
LT=2 Scheduled receipts
Proj. avail. balance 50 50 50 50 50 50 50 50 50 50
On- Net requirements 45
hand Planned order receipt 45
50 Planner order release 45
A Gross requirements 90
LT=3 Scheduled receipts
Proj. avail. balance 75 75 75 75 75 75 75 75
On- Net requirements 15
hand Planned order receipt 15
75 Planner order release 15
B Gross requirements 45
LT=1 Scheduled receipts
Proj. avail. balance 25 25 25 25 25 25 25 25
On- Net requirements 20
hand Planned order receipt 20
25 Planner order release 20
C Gross requirements 45 40
LT=2 Scheduled receipts
Proj. avail. balance 10 10 10 10 10
On- Net requirements 35 40
hand Planned order receipt 35 40
10 Planner order release 35 40
D Gross requirements 100
LT=2 Scheduled receipts
Proj. avail. balance 20 20 20 20 20 20 20
On- Net requirements 80
hand Planned order receipt 80
20 Planner order release 80
X
It takes
2 A’s for
each X
A(2)
MRP Example Day: 1 2 3 4 5 6 7 8 9 10
X Gross requirements 95
LT=2 Scheduled receipts
Proj. avail. balance 50 50 50 50 50 50 50 50 50 50
On- Net requirements 45
hand Planned order receipt 45
50 Planner order release 45
A Gross requirements 90
LT=3 Scheduled receipts
Proj. avail. balance 75 75 75 75 75 75 75 75
On- Net requirements 15
hand Planned order receipt 15
75 Planner order release 15
B Gross requirements 45
LT=1 Scheduled receipts
Proj. avail. balance 25 25 25 25 25 25 25 25
On- Net requirements 20
hand Planned order receipt 20
25 Planner order release 20
C Gross requirements 45 40
LT=2 Scheduled receipts
Proj. avail. balance 10 10 10 10 10
On- Net requirements 35 40
hand Planned order receipt 35 40
10 Planner order release 35 40
D Gross requirements 100
LT=2 Scheduled receipts
Proj. avail. balance 20 20 20 20 20 20 20
On- Net requirements 80
hand Planned order receipt 80
20 Planner order release 80
X
It takes
1 B for
each X
A(2) B(1)
MRP Example Day: 1 2 3 4 5 6 7 8 9 10
X Gross requirements 95
LT=2 Scheduled receipts
Proj. avail. balance 50 50 50 50 50 50 50 50 50 50
On- Net requirements 45
hand Planned order receipt 45
50 Planner order release 45
A Gross requirements 90
LT=3 Scheduled receipts
Proj. avail. balance 75 75 75 75 75 75 75 75
On- Net requirements 15
hand Planned order receipt 15
75 Planner order release 15
B Gross requirements 45
LT=1 Scheduled receipts
Proj. avail. balance 25 25 25 25 25 25 25 25
On- Net requirements 20
hand Planned order receipt 20
25 Planner order release 20
C Gross requirements 45 40
LT=2 Scheduled receipts
Proj. avail. balance 10 10 10 10 10
On- Net requirements 35 40
hand Planned order receipt 35 40
10 Planner order release 35 40
D Gross requirements 100
LT=2 Scheduled receipts
Proj. avail. balance 20 20 20 20 20 20 20
On- Net requirements 80
hand Planned order receipt 80
20 Planner order release 80
X
It takes
3 C’s for
each A
A(2) B(1)
C(3)
MRP Example Day: 1 2 3 4 5 6 7 8 9 10
X Gross requirements 95
LT=2 Scheduled receipts
Proj. avail. balance 50 50 50 50 50 50 50 50 50 50
On- Net requirements 45
hand Planned order receipt 45
50 Planner order release 45
A Gross requirements 90
LT=3 Scheduled receipts
Proj. avail. balance 75 75 75 75 75 75 75 75
On- Net requirements 15
hand Planned order receipt 15
75 Planner order release 15
B Gross requirements 45
LT=1 Scheduled receipts
Proj. avail. balance 25 25 25 25 25 25 25 25
On- Net requirements 20
hand Planned order receipt 20
25 Planner order release 20
C Gross requirements 45 40
LT=2 Scheduled receipts
Proj. avail. balance 10 10 10 10 10
On- Net requirements 35 40
hand Planned order receipt 35 40
10 Planner order release 35 40
D Gross requirements 100
LT=2 Scheduled receipts
Proj. avail. balance 20 20 20 20 20 20 20
On- Net requirements 80
hand Planned order receipt 80
20 Planner order release 80
X
It takes
2 C’s for
each B
A(2) B(1)
C(3) C(2)
MRP Example Day: 1 2 3 4 5 6 7 8 9 10
X Gross requirements 95
LT=2 Scheduled receipts
Proj. avail. balance 50 50 50 50 50 50 50 50 50 50
On- Net requirements 45
hand Planned order receipt 45
50 Planner order release 45
A Gross requirements 90
LT=3 Scheduled receipts
Proj. avail. balance 75 75 75 75 75 75 75 75
On- Net requirements 15
hand Planned order receipt 15
75 Planner order release 15
B Gross requirements 45
LT=1 Scheduled receipts
Proj. avail. balance 25 25 25 25 25 25 25 25
On- Net requirements 20
hand Planned order receipt 20
25 Planner order release 20
C Gross requirements 45 40
LT=2 Scheduled receipts
Proj. avail. balance 10 10 10 10 10
On- Net requirements 35 40
hand Planned order receipt 35 40
10 Planner order release 35 40
D Gross requirements 100
LT=2 Scheduled receipts
Proj. avail. balance 20 20 20 20 20 20 20
On- Net requirements 80
hand Planned order receipt 80
20 Planner order release 80
X
It takes
5 D’s for
each B
A(2) B(1)
C(3) C(2) D(5)
Lot Sizing in MRP Programs
Lot-for-lot (L4L)
Economic order quantity (EOQ)
Periodic Order Quantity (POQ)
Least total cost (LTC)
Least unit cost (LUC)
Which one to use? — The one that is least costly!
Lot-for-Lot Example WEEK 1 2 3 4 5 6 7 8 9 10
Gross requirements
35 30 40 0 10 40 30 0 30 55
Scheduled receipts
Projected on hand 35 35 0 0 0 0 0 0 0 0 0
Net requirements 0 30 40 0 10 40 30 0 30 55
Planned order receipts
30 40 10 40 30 30 55
Planned order releases
30 40 10 40 30 30 55
Holding cost = $1/week; Setup cost = $100; Lead time = 1 week
Lot-for-Lot Example
WEEK 1 2 3 4 5 6 7 8 9 10
Gross requirements
35 30 40 0 10 40 30 0 30 55
Scheduled receipts
Projected on hand 35 35 0 0 0 0 0 0 0 0 0
Net requirements 0 30 40 0 10 40 30 0 30 55
Planned order receipts
30 40 10 40 30 30 55
Planned order releases
30 40 10 40 30 30 55
Holding cost = $1/week; Setup cost = $100; Lead time = 1 week
No on-hand inventory is carried through the system
Total holding cost = $0
There are seven setups for this item in this plan
Total ordering cost = 7 x $100 = $700
EOQ Lot Size Example WEEK 1 2 3 4 5 6 7 8 9 10
Gross requirements
35 30 40 0 10 40 30 0 30 55
Scheduled receipts
Projected on hand 35 35 0 43 3 3 66 26 69 69 39
Net requirements 0 30 0 0 7 0 4 0 0 16
Planned order receipts
73 73 73 73
Planned order releases
73 73 73 73
Holding cost = $1/week; Setup cost = $100; Lead time = 1 week
Average weekly gross requirements = 27; EOQ = 73 units
EOQ Lot Size Example
WEEK 1 2 3 4 5 6 7 8 9 10
Gross requirements
35 30 40 0 10 40 30 0 30 55
Scheduled receipts
Projected on hand 35 35 0 43 3 3 66 26 69 69 39
Net requirements 0 30 0 0 7 0 4 0 0 16
Planned order receipts
73 73 73 73
Planned order releases
73 73 73 73
Annual demand D = 1,404 (27 x 52)
Holding cost = 375 units x $1 (including 57 units on
hand at end of week 10) (43+3+3+66+26+69+69+39+57)
Ordering cost = 4 x $100 = $400
Total cost = $375 + $400 = $775
Holding cost = $1/week; Setup cost = $100; Lead time = 1 week
Average weekly gross requirements = 27; EOQ = 73 units
POQ Lot Size Example WEEK 1 2 3 4 5 6 7 8 9 10
Gross requirements
35 30 40 0 10 40 30 0 30 55
Scheduled receipts
Projected on hand 35 35 0 40 0 0 70 30 0 0 55
Net requirements 0 30 0 0 10 0 0 0 30 0
Planned order receipts
70 80 85 0
Planned order releases
70 80 85
EOQ = 73 units; Average weekly gross requirements = 27;
POQ interval = 73/27 ≅ 3 weeks
POQ Lot Size Example
WEEK 1 2 3 4 5 6 7 8 9 10
Gross requirements
35 30 40 0 10 40 30 0 30 55
Scheduled receipts
Projected on hand 35 35 0 40 0 0 70 30 0 0 55
Net requirements 0 30 0 0 10 0 0 0 55 0
Planned order receipts
70 80 85
Planned order releases
70 80 85
Setups = 3 x $100 = $300
Holding cost = (40 + 70 + 30 + 55) units x $1 = $195
Total cost = $300 + $195 = $495
EOQ = 73 units; Average weekly gross requirements = 27;
POQ interval = 73/27 ≅ 3 weeks
Lot-Sizing Summary For these three examples
COSTS
SETUP HOLDING TOTAL
Lot-for-lot $700 $0 $700
EOQ $400 $375 $775
POQ $300 $195 $495
1.Spot Contract
2.Regular Contract
3.Call Off Contract
4.Fixed Contract
5.Partnership
6.Joint Ventures
Different Types of Contract
10 Rules of Negotiation 1.Do Not Negotiate
2.Do Not Negotiate with yourself
3.Never Ever Ever Ever Ever Ever Accept the first Offer
4.Never make the first offer if you can avoid it
5.Use 80/20 Rules, 80% listen and watch and 20% Talk
6.Never give anyone a free gift
7.Watch out for the “Salami” effect (Break Down)
8.Avoid the Rookies Regret
9.Always avoid the Quick Deal
10.Never Disclose the Bottom line
Inventory System Defined • Inventory is the stock of any item or resource used in an
organization and can include: raw materials, finished products,
component parts, supplies, and work-in-process
• An inventory system is the set of policies and controls that
monitor levels of inventory and determines what levels should be
maintained, when stock should be replenished, and how large
orders should be Inventory Costs
• Holding (or carrying) costs – Costs for storage, handling, insurance, etc
• Setup (or production change) costs – Costs for arranging specific equipment setups, etc
• Ordering costs – Costs of someone placing an order, etc
• Shortage costs – Costs of canceling an order, etc
Types of Inventory • 1. Cycle Inventory
• Anticipation Inventory
• Safety Inventory
• In Transit Inventory
ABC Analysis
How to Reduce Supply Lead Time and Lead Time Uncertainty
Line of Balance (LOB) Supplier Monitoring
Vendor Management Inventory (VMI)
Customer Managed Inventory (CMI)
Electronic Data Interchange (EDI)
Business Process Re-engineering (BPR)
Effective Customer Response (ECR)
SKU (Stock Keeping Unit):
Different Types of Distribution Network:
1. Manufacturing Storage with Direct Shipping
2. Manufacturing Storage with Direct Shipping and In Transit
Merge
3. Distributor Storage with Carrier delivery
4. Distributor Storage With Last Mile Delivery
5. Manufacturer or Distributor Storage with Consumer Pickup
6. Retail Storage with Consumer Pickup
Cost Minimization Goal
Ordering Costs
Holding
Costs
Order Quantity (Q)
C O S T
Annual Cost of
Items (DC)
Total Cost
QOPT
By adding the item, holding, and ordering costs
together, we determine the total cost curve, which in
turn is used to find the Qopt inventory order point that
minimizes total costs
Basic Fixed-Order Quantity (EOQ) Model Formula
H 2
Q + S
Q
D + DC = TC
Total
Annual =
Cost
Annual
Purchase
Cost
Annual
Ordering
Cost
Annual
Holding
Cost + +
TC=Total annual
cost
D =Demand
C =Cost per unit
Q =Order quantity
S =Cost of placing
an order or setup
cost
R =Reorder point
L =Lead time
H=Annual holding
and storage cost
per unit of inventory
Deriving the EOQ Using calculus, we take the first derivative of the
total cost function with respect to Q, and set the derivative (slope) equal to zero, solving for the optimized (cost minimized) value of Qopt
Q = 2DS
H =
2(Annual Demand)(Order or Setup Cost)
Annual Holding CostOPT
R eorder point, R = d L_
d = average daily demand (constant)
L = Lead time (constant)
_
We also need a
reorder point to
tell us when to
place an order
EOQ Example (1) Problem Data
Annual Demand = 1,000 units
Days per year considered in average
daily demand = 365
Cost to place an order = $10
Holding cost per unit per year = $2.50
Lead time = 7 days
Cost per unit = $15
Given the information below, what are the EOQ and
reorder point?
EOQ Example (1) Solution
units 90or units 89.443 = 2.50
)(10) 2(1,000 =
H
2DS = QOPT
d = 1,000 units / year
365 days / year = 2.74 units / day
Reorder point, R = d L = 2.74units / day (7days) = 19.18 or _
20 units
In summary, you place an optimal order of 90 units. In
the course of using the units to meet demand, when
you only have 20 units left, place the next order of 90
units.
EOQ Example (2) Problem Data
Annual Demand = 10,000 units
Days per year considered in average daily
demand = 365
Cost to place an order = $10
Holding cost per unit per year = 10% of cost per
unit
Lead time = 10 days
Cost per unit = $15
Determine the economic order quantity
and the reorder point given the following…
EOQ Example (2) Solution
Q =2D S
H=
2(10,000 )(10)
1.50= 365.148 units, or O PT 366 units
d =10,000 units / year
365 days / year= 27.397 units / day
R = d L = 27.397 units / day (10 days) = 273.97 or _
274 units
Place an order for 366 units. When in the course of
using the inventory you are left with only 274 units,
place the next order of 366 units.
Price-Break Model Formula
Cost Holding Annual
Cost) Setupor der Demand)(Or 2(Annual =
iC
2DS = QOPT
Based on the same assumptions as the EOQ model,
the price-break model has a similar Qopt formula:
i = percentage of unit cost attributed to carrying inventory
C = cost per unit
Since “C” changes for each price-break, the formula
above will have to be used with each price-break cost
value
Price-Break Example Problem Data (Part 1)
A company has a chance to reduce their inventory
ordering costs by placing larger quantity orders using
the price-break order quantity schedule below. What
should their optimal order quantity be if this company
purchases this single inventory item with an e-mail
ordering cost of $4, a carrying cost rate of 2% of the
inventory cost of the item, and an annual demand of
10,000 units?
Order Quantity(units) Price/unit($)
0 to 2,499 $1.20
2,500 to 3,999 1.00
4,000 or more .98
Price-Break Example Solution (Part 2)
units 1,826 = 0.02(1.20)
4)2(10,000)( =
iC
2DS = QOPT
Annual Demand (D)= 10,000 units
Cost to place an order (S)= $4
First, plug data into formula for each price-break value of “C”
units 2,000 = 0.02(1.00)
4)2(10,000)( =
iC
2DS = QOPT
units 2,020 = 0.02(0.98)
4)2(10,000)( =
iC
2DS = QOPT
Carrying cost % of total cost (i)= 2%
Cost per unit (C) = $1.20, $1.00, $0.98
Interval from 0 to 2499, the
Qopt value is feasible
Interval from 2500-3999, the
Qopt value is not feasible
Interval from 4000 & more, the
Qopt value is not feasible
Next, determine if the computed Qopt values are feasible or not
Price-Break Example Solution (Part 3) Since the feasible solution occurred in the first price-
break, it means that all the other true Qopt values occur
at the beginnings of each price-break interval. Why?
0 1826 2500 4000 Order Quantity
Total
annual
costs So the candidates
for the price-
breaks are 1826,
2500, and 4000
units
Because the total annual cost function is
a “u” shaped function
Price-Break Example Solution (Part 4)
iC 2
Q + S
Q
D + DC = TC
Next, we plug the true Qopt values into the total cost
annual cost function to determine the total cost under
each price-break
TC(0-2499)=(10000*1.20)+(10000/1826)*4+(1826/2)(0.02*1.20)
= $12,043.82
TC(2500-3999)= $10,041
TC(4000&more)= $9,949.20
Finally, we select the least costly Qopt, which is this
problem occurs in the 4000 & more interval. In summary,
our optimal order quantity is 4000 units
JIT/Lean Operations Good production systems require that managers
address three issues that are pervasive and fundamental to operations management: eliminate waste, remove variability, and improve throughput
Waste is anything that does not add value from the customer point of view
Storage, inspection, delay, waiting in queues, and defective products do not add value and are 100% waste
1. Eliminate Waste
Ohno’s Seven Wastes
Overproduction
Queues
Transportation
Inventory
Motion
Overprocessing
Defective products
The 5 Ss
• Sort/segregate – when in doubt, throw it out • Simplify/straighten – methods analysis tools • Shine/sweep – clean daily • Standardize – remove variations from processes • Sustain/self-discipline – review work and recognize
progress
Two additional Ss
Safety – build in good practices
Support/maintenance – reduce variability and unplanned downtime
2. Remove Variability JIT systems require managers to reduce variability caused by both
internal and external factors
Variability is any deviation from the optimum process
Inventory hides variability
Less variability results in less waste
3. Improve Throughput The time it takes to move an order from receipt to delivery
The time between the arrival of raw materials and the shipping of the finished order is called manufacturing cycle time
A pull system increases throughput
By pulling material in small lots, inventory cushions are removed, exposing problems and emphasizing continual improvement
Manufacturing cycle time is reduced
Push systems dump orders on the downstream stations regardless of the need
Why Six Sigma?
Visible costs •Scrap
•Rework
•Warranty
Hidden Costs
• Conversion efficiency of materials
• Inadequate resource utilization
• Excessive use of material
• Cost of redesign and re-inspection
• Cost of resolving customer problems
• Lost customers / Goodwill
• High inventory
Cost of quality at various levels of Sigma
Sigma Defect rate(PPM) Cost of quality Competitive level
3.4 <10%
233 10-15%
6210 15-20%
66807 20-30%
308537 30-40%
6,90000 >40%
World
Class
Industry
Average
Non
Competitive
6
5
4
3
2
1
DMAIC: Define, Measure, Analyze, Improve, Control
Define: Project Charter,
SIPOC (Supplier, Input, Process, Output, Customers)
Value Stream Map
Measure: Process Observation
Time Value Map
Pareto Chart
Time Series Plots
Analyze: Cause and Effect Diagram
Scatter Plots
Improve: PICK Chart
Four Step Rapid Setup
Control: Control Charts
Six Sigma Tools
Six Sigma Toolbox Green Belt tools • Benchmarking • Brainstorming • Cause- Effect diagrams • Critical to Customer Tree • Data Collection Plan • FMEA( Failure modes and effect) • Improvement strategy • Interviews/ Precision
questioning • Prioritization matrices • Project Charter • Project plan template • Process flow • Surveys • Workflow mapping
Black Belt tools • Activity analysis • Affinity diagram • Data Presentation
– Control Charts – Pareto Chart – Bar Graphs
• Design of experiments – Full factorial – Reduced fractions – Screening designs
• Hypothesis tests – t- test – Paired t-test – ANOVA – Chi Square
• Process sigma • Kano modeling • Quality Functional Deployment(QFD) • Regression • Sampling