[completed] 4과 material requirement planning

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4.material requirements planning

Introduction

material requitements planning(MRP) is the system used to avoid missing parts. it establishes a schedule(priority plan) showing the components required at each level of the assembly and based on lead tiems, calculates the time when these component will be needed.

• nature of demand
  • there are two type of demand : independent and dependent. independent demand is not related to the demand for any other product.it is essentially independent of any actions taken internally in the company. instead, it is dependent only on the external demand for the product.
  • master production schedule items are independent demand items.
  • the demand for the parts depends on the demand for the parent and these are dependent demand items.
  • since independent demand is not related to the demand for any other assemblies or products, it must be forecast.
  • however, since dependent demand is directly related to the demand for higher level assemblies or products, it can be calculated. material requitement planning is designed to do this calculation.
  • an item can have both a dependent and an independent demand.
  • dependency can be horizontal or vertical. the dependency of a component on its parent is vertical.
  • however, components also depend on each other. if one component is going to be a week late, then the final assembly is a week late. this is also a dependency and is called horizontal dependency.
• objective of MRP
  • material requirement planning has two major objectives: determine requirements and keep priorities current
    • determine requirements
      • to have the right materials in the right quantities available at the right tiem to meet the demand for the firm's products. 
      • the material requirements plan's objectives is to determine what components are needed to meet the master production schedule and  based on lead time, to calculate the periods when the components must be available.
      • it must determine the followings:
        • what to order
        • how much to order
        • when to order
        • when to schedule delivery
    • keep priorities current
      • changes daily.
      • be able to recognize priorities to kepp plans current. it must be able to add and delete, expedite, delay and change orders.
• Linkages to other manufacturing planning and control functions
  • the master production schedule drives the material requirements plan.
  • the mrp is a priority plan for the components neede to make the products in the MPS.
  • the plan is valid only if canpacity is available when neede to make the components, and the plan must be checked against capacity.
• MRP software
• Inputs to the material requirements planning system
  • there are three primary inputs to MRP systmes:
    • master production schedule
      • is a statement of which end item are to be produced, the quantity of each and the dates they are to be completed.
    • inventory records
      • a major inputs to the mrp system is inventory. whee a calculation is made to find out how many are needed, the quantities available must be considered.
      • there are two kind of information needed.
        • the first is called planning factors and includes information such as order quntities, leadtimes, safety stock and scrap. 
        • the second kind of information necessary is the status of each item. the mrp systme needs to know how much is available, how much is allocated, and how much is available for future demand.
        • this data is maintained in an inventory record, also called a part master or item master. each item has a record, and all the records together form a file or table.
    • bills of material
      • the bill of material is one of the most important documentas in a manufacturing company.

bills of material

as 'a listing of all the subassemblies, intermediates, parts, and raw materials that go into making the parent assembly showing the quantities of each required to make an assembly.

1. there are three important points around bills of material and part numbers:
2. the bill of material shows all the parts requited to make one of the item.
3. each part or item has only one part number. a part is defined by its form, fits or function. if any of these changes, then it is not the same part and it must have a different part number.

the bill of material shows the components that go into making the parent.

• bills of material structure
  • refer to the overall design for the arrangement of bills of material files.
    • product tree
    • parent-component relationship
    • mutilevel bill
    • multiple bill
    • single-level bill
    • indented bill
    • summarized parts list
    • planning bill
• where-used and pegging reports
  • where-used report
    • give the same information as bill of material, but the where- used report gives the parents for a component whereas the bill gives the components for a parent.
    • a listing of all the parents in which a component is used is called a where-used report
    • this has several uses, such as in implementing an enginering change or when materials are scarce or in costing a product.
• pegging report
  • is similar to a where-used report. however the pegging report shows only those parents for which there is an existing demand requirement, whereas the where-used report shows all parents for a component. the pegging report shows the paretns creating the demand for the components. pegging keeps track of the origin of the demand.
• uses for bills of material
  • some major uses are below
    • product definition : specifies the components needed to make the product
    • enginerring change control : changes must be recorded and controlled. the bill provides the method for doing so.
    • service parts: replacement parts needed to repait a broken component are determined from the bill of materials.
    • planning: defines what materials have to be scheduled to make the end product. they define what components have to be purchased or made to satisfy the master production schedule.
    • order entry : when a product has a vary large number of options, the order-entry system very often configures the end product bill of materials. the bill can also be used to price the product.
    • manufacturing : the bill provides a list of the parts needed to make or assemble a product.
    • costing : product const is usuallyy broken down into direct material, direct labor, and overhead. the bill provides not only a method of determining direct material but also a structure for recording direct labor and distributing overhead.

material requirements planning process

it is important to realize that planning and control take place for each component on the bill. raw material may go through several operations before it is processed and ready for assembly, or ther may be several assembly operations between components and parent. these operation are planned and controlled by production activity control, not material requirements planning.

the purpose of material requirements planning is to determine the components neede, quantities and due dates so item in the master production schedule are made on item.

• exploding and offsetting
  • leadtime 
    • is the span of time needed to perform a process. it includes time for order preperation, queuing, processing, moving, receiving and inspecting and any expected delay.
  • exploding the requirements
    • exploding is the process of multiplying the requirements by the usage quantity and recording the appropriate requirement throughtout the product tree.
  • offsetting
    •  is the process of placing the exploded requiretments in their proper periods based on lead time.
  • planned orders
    • noted that palnned order releases and planned order receipts are paired with each other. everytiem you have a palnned order receipts, it should generate a planned order release offset by the lead time. planned order release and receipts are assuemd to be orders for the item at the beginning of each period.
  • gross and net requirements
    • inventory is avaiable and must be included when calculation quantities to be produced. 
    • noted that the projected available inventory shows the quantity projected on hand for the end of period.
• releasing orders
  • since the objectives of the mrp is to have material available when it is needed and not before, orders for material should not be released until the planned order release date arrives.
  • releasing an order means that authorzation is given to purchasing to buy the necessary material or to manufacturing to make the component.
  • before a manufacturing order is released, component availabiltiry must be checked.
  • notice that scheduled receipts have been created, replacing the palnned order releases.
  • when a manufacturing order is released the computer will allocate the required quantities of a parent's components to that order. this means that the projected available quantity is reduced. the allocated quantity of components is still in inventory, but they are not available for other orders. they will stay in inventory until withdrawn for use.
• scheduled receipts
  • are orders placed on manufacturing or on a vendor and represent a commitment to make or buy.
• open orders
  • scheduled receipts on the mrp record are open orders on the factory or a vendor and are the responsibility of puchasing and of production activity control. these orders represent committed resources and are in process but not yet received. when goods are received into inventory and avaiable for use, the order is closed out. and the scheduled receipt disappear to become part of the on-hand inventory.
• net requirements
  • the calculation for net requirements can now be modified to include scheduled receipts.
    • net requitements= gross requirement - scheduled receipts - avaiable inventory
• basic MRP record
  • there are several points that are important
    • the current time is the beginning of the first period
    • the top row shows periods, called time buckets. these are often a week but can be any length of tiem convenent to the company. today's mrp applications typically use daily time buckets.
    • the number of periods in the record is called the planning horizon,  which shows the number of future periods for which plans are being made.
    • an item is considered available at the beginning of the time bucket in which it is required.
    • the quantity shown in the projected available row is the projected on-hand balance at the end of the period.
    • the immediate or most current period is called the action bucket. a quantity in the action bucket means tha tsome action is needed now to avoid a future problem.
    • a bucketless systme show only the time buckets that have MRP activity, ommiting the time periods with no activity.
• capacity requirements planning
  
  • low-level coding and netting
    • a component many reside on more than one level in a bill of materials. if this is the case, it is necessary to make sure that all gross requitements for that components have been recorded before netting takes place.
    • the low-level code is the lowest level on which a part reside in all bills of material. every parts has only one low-level code. 
• multiple bills of material
  • the material requirements planning system gathers the palnned order releases from all the parents and creates a schedule of gross requirements for the components.

using the material requirements plan

the material planner works with three types of orders: planned, released, firm.

planned order : automatically scheduled and controlled by the computer.

as gross requirements, projected available inventory and scheduled receipts change, the computer recalculates the timing and quantities of planned order releases.

released otders :the mrp program recommends to the planner the release of an order when the order enters the action bucket but does not release the order. when released, the order becomes an open order to the factory ot to purchaing and appears on the mrp record as a scheduled receipt. 

firm planned orders : the planner can tell the computer that the order is not to be changed unless the planner advises the computer to do so. the order is firmed or frozen against the logic of the computer

 

• exception messages
  • normally the system will work according to plan. however, it does print action or exception messages, suggesting that the palnner should act and what kind of action might be appropriate to keep the supplu and demand in balance. and mrp systmen generates exception messages to advise the planner when some event needs attion.
    • components for which palnner orders are in the action bucket and which should be considered for release.
    • open orders for which the timing or quantity of scheduled recipts does not satisfy the plan.
    • call for expediting to reduce the standard lead time.
• transaction message
  • means that some event has occured and must be reflected in the software in order to ensure the mrp records are updated.
• managing the material requirements plan
  •  the planner must evaluate this feedback and take corrective action if necessary. the planner must consider three important factors in managing the material requirements plan.
    • priority
      • refers to maintaining the correct due dates by constantly evaluating the true due date need for released orders and if necessary, expediting or de-expediting.
    • bottom-up replacing
      • action to respond for changed conditions should occur as low in the product structure as possible.
    • reducing systme nerwousness
      •  one method of reducing systme nervousness is firm planned order.

 

key term

action bucket

allocate

bill of material

bucketless system

component item

dependent demand

exception message

exploding

firm planned orders

independent demand

indented demand

indented bill

inventory record

lead time

llo-level code 100

master production schedule

material requirements planning (MRP)

multilevel bills

multiple bill

net requirements

offsetting

open order

parent

pegging report

planned orders

plaaned order receipt

planned order release

planning bills

planning factors

planning horizon

product tree

reducing systme nervousness

releasing an order

scheduled receipts

single - level bill

summarized parts list

time buckets

transactoin message

where-used report

 

 

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