Learning Objectives:
Producing a product made of multiple components
requires significant coordination to ensure that component parts are available
when they are required for production. This segment examines how MRP can
accomplish this coordination.
Contents:
Translating an Aggregate Plan into a Production and
Ordering Schedule
Aggregate Plan (3-12 months
ahead)
Master Production Schedule (1-3
months)
Material Requirements Plan (0-3 months)
- A detailed plan that states how many END ITEMS
(the final product sold to the customer) will be available for sale or
distribution during specific periods
- Short time frame: 1-3 months
Purposes of the Master Production Schedule:
- to
set due dates for the availability of end items
- to
provide information regarding resources and materials required to support
the aggregate plan
- as
an input to Materials Requirements Planning, which will set specific
production schedules for parts and components used in end items
What the Master Production Schedule is NOT:
- a
sales forecast (MPS summarizes production to meet sales forecasts)
- a
manufacturing schedule (MPS tells when end items are available for sale,
but not when the end items or their component parts will be manufactured)
Inputs To Mps
- Market
requirements
- Production
Plan from Aggregate Planning
- Resources
available
Constraints
- Quantities
of individual items must equal aggregate quantities from the Production
Plan
- Demand
which must be met
� Capacity available
Output
An MPS showing end items available every month (or
period) that is feasible with respect to demand and capacity.
At this point we know when we need units available
so we can plan when to produce or order using MRP.
A
computerized system for managing dependent-demand inventory, scheduling
replenishment orders, and meeting demand for end items as given in the Master
Production Schedule.
Two basic characteristics of MRP:
- MRP
derives demand for components, subassemblies, materials, etc., from demand
for and production schedules of parent items.
- MRP
offsets replenishment orders (purchase orders or production schedules)
relative to the date when replenishment is needed.
|
Information
Needed for MRP
|
Information
Obtained from MRP
|
|
|
MRP Inputs
1. Master Production
Schedule
- Product Structure
- Inventory Levels
Lot Sizing Choices in MRP
Lot sizing:
Determining
the lot size (order quantity or production quantity) of an item
Static lot sizing rule:
- A
decision rule that orders the same quantity each time an order is placed.
- Tend
to generate higher average on-hand inventory because they create inventory
remnants.
- Can
provide extra safety stock.
Dynamic lot sizing rule:
- A
decision rule that changes the order quantity with each order, typically
so that each order is just large enough to prevent shortages over a specified
time period.
- Tend
to cause instability by tying lot-size to gross requirements.
- Lower-level
components may not be able to respond sufficiently fast to changes in
requirements.
Static Lot-sizing Rules
1. Fixed order quantity (FOQ)
- Order
(or produce) a fixed quantity, or a multiple of that fixed quantity.
2. Economic Order Quantity (EOQ)
- Order
(or produce) the economic order quantity, plus any additional items needed
to replenish safety stock if it has fallen below its desired level.
- Yields
minimum total setup/ordering plus holding costs.
- Assumes
relatively constant demand.
Dynamic Lot-sizing Rules
1. Lot-for-Lot (L4L)
- Order
(or produce) exactly the quantity required in each period to satisfy gross
requirements and to maintain safety stock at its required level.
- Simple
to use, and agrees with Just-In-Time philosophy of ordering/producing only
when required.
- Lot
size can be modified easily for purchase discounts or restrictions, scrap
allowances, process constraints, etc.
- Minimizes
on-hand inventory, but maximizes number of orders placed (so can be
expensive if setup/ordering costs are significant).
2. Periodic Order Quantity (POQ)
- Order/produce
a quantity equal to the gross requirements for P periods minus any
items in on-hand inventory plus any additional items
needed to replenish safety stock if it has fallen below its desired level.
- Restores
safety stock and covers exactly P periods of gross requirements.
- Reduces
on-hand inventory by attempting to match the quantity ordered to the
quantity required.
Completing MRP Tables
Objective:
The
purpose of MRP is to schedule orders for end
items and the components of those end
items. We wish to determine when to release orders and how
much to order.
Step 1
Begin with the end items. Complete one table at a
time.
- Schedule
the gross requirements, GR.
- Enter
records for any scheduled receipts, SR.
- Consider
GR, SR and inventory, I, to determine timing and size of orders we will
plan to receive, PR. These are orders which we must receive to meet demand.
PRt = It-1 + SRt -
GRt - It
- Use
the lead time to schedule the planned order releases, POR, so that the
orders are received when they are needed.
Time of POR = Time of PR - L
- A
POR for an end item in week t becomes a GR in week t for every component part
of the end item.
Step 2
Schedule the components. If a component occurs at
more than one level it is scheduled at the deepest level so that you will know
all demand for parents of the component before you try to schedule the
component.
Level 1 components:
The POR's for end items are scheduled as GR's for
level 1 components. Any spare parts orders are scheduled as GR's also.
- Complete
the table as discussed in step 1.
Repeat the process for all components.
For each component the gross requirements come from
planned order releases for all direct parents of the component and from any
orders for spare parts.
The final result will be planned orders (quantity
and timing) for end products and all of their component which must be made in
order to meet demand.
Example 2
Favourable environments for MRP:
- batch
manufacturing environment
- stable
demand
- limited
number of products
- large
number of bill-of-materials levels
- large
lot sizes
Some conditions which are less favourable for MRP
Process-focused environments:
- many
customized products
- small
production volumes
- small
number of bill-of-materials levels
Just-In-Time environments:
- small
batch sizes
- demand
pulls parts and components through the system
Closed-loop MRP:
MRP
system that provides feedback to other stages of the production plan, such as
the aggregate production plan, capacity plan, and Master Production Schedule.
Manufacturing Resource Planning (MRP II):
A
planning system that uses all outputs of a MRP system to integrate production,
marketing, and financial plans.
Distribution Resource Planning (DRP):
A
time-phased stock replenishment technique for distribution networks based on
MRP procedures and logic.
Industry Week - View selected industry related
articles in the Industry Week magazine by clicking on the magazines or by
searching for a topic.
ITEM:
|
Week
|
1
|
2
|
3
|
4
|
5
|
6
|
7
|
8
|
|
Gross Requirements
|
|
|
|
|
|
|
|
|
|
Scheduled Receipts
|
|
|
|
|
|
|
|
|
|
Projected on hand
|
|
|
|
|
|
|
|
|
|
|
Planned Receipts
|
|
|
|
|
|
|
|
|
|
Planned
order releases
|
|
|
|
|
|
|
|
|
Tidak ada komentar:
Posting Komentar