Manajemen Persediaan. MRP Lot For Lot. Modul ke: Fakultas FEB. Program Studi Manajemen

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Cameron Wright
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1 Modul ke: 10 Manajemen Persediaan MRP Lot For Lot Fakultas FEB Program Studi Manajemen

2 Learning Objectives Describe the conditions under which MRP is most appropriate. Describe the inputs, outputs, and nature of MRP processing. Explain how requirements in a master production schedule are translated into material requirements for lower-level items. Discuss the benefits and requirements of MRP.

3 Learning Objectives Explain how an MRP system is useful in capacity requirements planning. Outline the potential benefits and some of the difficulties users have encountered with MRP. Describe MRP II and its benefits. Describe ERP, what it provides, and its hidden costs.

4 MRP Material requirements planning (MRP): Computer-based information system that translates master schedule requirements for end items into time-phased requirements for subassemblies, components, and raw materials. End products MRP Time-phase based Subassemblies Components Raw materials

5 Independent and Dependent Demand Independent Demand A Dependent Demand B(4) C(2) D(2) E(1) D(3) F(2) Independent demand is uncertain. Dependent demand is certain.

6 Dependant Demand Dependent demand: Demand for items that are subassemblies or component parts to be used in production of finished goods. Once the independent demand is known, the dependent demand can be determined.

7 Amount on hand Amount on hand Demand Demand Demand Stable demand Lumpy demand Time Time Safety stock Time Time

8 Overview of MRP MRP Inputs MRP Processing MRP Outputs Master schedule Bill of materials MRP computer programs Primary reports Secondary reports Changes Order releases Planned-order schedules Exception reports Planning reports Performancecontrol reports Inventory records Inventory transaction

9 MPR Inputs Master Production Schedule Time-phased plan specifying timing and quantity of production for each end item. Material Requirement Planning Process

10 Master Schedule Master schedule: One of three primary inputs in MRP; states which end items are to be produced, when these are needed, and in what quantities. Cumulative lead time: The sum of the lead times that sequential phases of a process require, from ordering of parts or raw materials to completion of final assembly.

11 Planning Horizon Assembly Subassembly Procurement Fabrication Time Period (weeks)

12 Bill-of-Materials Bill of materials (BOM): One of the three primary inputs of MRP; a listing of all of the raw materials, parts, subassemblies, and assemblies needed to produce one unit of a product. Product structure tree: Visual depiction of the requirements in a bill of materials, where all components are listed by levels. Low-level coding: Restructuring the bill of materials so that multiple occurrences of a component all coincide with the lowest level the component occurs

13 Level 0 Product Structure Tree Chair 1 Leg Assembly Seat Back Assembly 2 Legs (2) Cross bar Side Rails (2) Cross bar Back Supports (3) Level 0 X X 1 B (2) C B (2) C 2 D (3) E E (2) F (2) D (3) E E (2) F (2) 3 E (4) E (4) E E (2)

14 Inventory Records One of the three primary inputs in MRP Includes information on the status of each item by time period Gross requirements Scheduled receipts Amount on hand Lead times Lot sizes And more

15 Inventory Requirements Net requirements: Net Requirements = Gross Requirements Available Inventory Available Inventory: Available Inventory = Projected on hand Safety stock Inventory allocated to other items

16 Assembly Time Chart Procurement of raw material D Procurement of raw material F Fabrication of part E Procurement of part C Procurement of part H Subassembly A Subassembly B Final assembly and inspection Procurement of raw material I Fabrication of part G

17 Time-Phased Product Structure Start production of D Must have D and E completed here so production can begin on B Lead time 2 weeks 1 week G (1) D (2) 2 weeks 1 week 3 weeks 2 weeks D (2) E (2) 2 weeks to produce E (2) 1 week F (2) B (2) 1 week C (3) Time in weeks A A B C D E F G weeks weeks weeks weeks weeks weeks weeks

18 Gross Requirements Plan Week Lead Time A. Required date 50 Order release date 50 1 week B. Required date 100 Order release date weeks C. Required date 150 Order release date week E. Required date Order release date week F. Required date 300 Order release date weeks D. Required date Order release date week G. Required date 300 Order release date week

19 MRP Structure Data Files BOM Lead times (Item master file) Master production schedule Output Reports MRP by period report MRP by date report Planned order report Inventory data Purchasing data Material requirement planning programs (computer and software) Purchase advice Exception reports Order early or late or not needed Figure 14.5 Order quantity too small or too large

20 Determining Gross Requirements Starts with a production schedule for the end item 50 units of Item A in week 8 Using the lead time for the item, determine the week in which the order should be released a 1 week lead time means the order for 50 units should be released in week 7 This step is often called lead time offset or time phasing

21 Determining Gross Requirements From the BOM, every Item A requires 2 Item Bs 100 Item Bs are required in week 7 to satisfy the order release for Item A The lead time for the Item B is 2 weeks release an order for 100 units of Item B in week 5 The timing and quantity for component requirements are determined by the order release of the parent(s)

22 Determining Gross Requirements The process continues through the entire BOM one level at a time often called explosion By processing the BOM by level, items with multiple parents are only processed once, saving time and resources and reducing confusion Low-level coding ensures that each item appears at only one level in the BOM

23 Net Requirements Plan

24 Net Requirements Plan

25 MRP Processing Gross requirements Schedule receipts Projected on hand Net requirements Planned-order receipts Planned-order releases

26 MPR Processing Gross requirements Total expected demand Scheduled receipts Open orders scheduled to arrive Projected on hand Expected inventory on hand at the beginning of each time period

27 MPR Processing Net requirements Actual amount needed in each time period Planned-order receipts Quantity expected to be received at the beginning of the period Offset by lead time Planned-order releases Planned amount to order in each time period

28 Lot-Sizing Techniques Lot-for-lot techniques order just what is required for production based on net requirements May not always be feasible If setup costs are high, costs may be high as well Economic order quantity (EOQ) EOQ expects a known constant demand and MRP systems often deal with unknown and variable demand

29 Lot-Sizing Techniques Part Period Balancing (PPB) looks at future orders to determine most economic lot size EPP = setup cost / holding cost Programming technique Assumes a finite time horizon Effective, but computationally burdensome

30 Lot-for-Lot Example Week Gross requirements Scheduled receipts Projected on hand Net requirements Planned order receipts Planned order releases Holding cost = $1/week; Setup cost = $100/times; Lead time = 1 week

31 Gross requirements Scheduled receipts Projected on hand Lot-for-Lot Example No on-hand inventory is carried through the system Total holding cost = $0 Net requirements Planned order receipts There are seven setups for this item in this plan Total setup cost = 7 x $100 = $700 Planned order releases Holding cost = $1/week; Setup cost = $100/times; Lead time = 1 week

32 EOQ Lot Size Example Week Gross requirements Scheduled receipts Projected on hand Net requirements Planned order receipts Planned order releases Holding cost = $1/week; Setup cost = $100/times; Lead time = 1 week Average weekly gross requirements = 27; EOQ = 73 units

33 Scheduled receipts Projected on hand Planned order receipts Planned order releases EOQ Lot Size Example Annual demand = 1,404 Total cost = setup cost + holding cost Total cost = (1,404/73) x $100 + (73/2) x ($1 x 52 weeks) Total Gross cost = $3,798 /year requirements Cost for 10 weeks = $3,798 x (10/52) = $730 Or Total Net cost = setup cost + holding cost requirements Total cost = 4 x $ x ($1 /weeks) Total cost = $ Holding cost = $1/week; Setup cost = $100/times; Lead time = 1 week Average weekly gross requirements = 27; EOQ = 73 units

34 PPB Example Gross requirements Scheduled receipts Projected on hand Net requirements Planned order receipts Planned order releases Holding cost = $1/week; Setup cost = $100; Lead time = 1 week ; EPP = 100 units

35 Gross requirements Scheduled receipts Projected on hand Net requirements Planned order receipts Planned order releases PPB Example Trial Lot Size Periods (cumulative net Costs Combined requirements) Part Periods Setup Holding Total , = 340 x , 3, = 40 x , 3, 4, = 50 x x = 170 2, 3, 4, 5, = 90 x x x 1 Combine periods 2-5 as this results in the Part Period closest to 35 the EPP , = 30 x 1 6, 7, = 30 x 1 6, 7, 8, = 60 x x = 220 Combine periods 6-9 as this results in the Part Period closest to the EPP = 100 Total cost = 490 Holding cost = $1/week; Setup cost = $100; EPP = 100 units

36 Lot-Sizing Summary For these three examples Lot-for-lot $700 EOQ $730 PPB $490 Wagner-Whitin would have yielded a plan with a total cost of $455 for this example

37 Example Gross requirements Scheduled receipts Projected on hand Net requirements Planned order receipts Planned order releases Holding cost = $1/week; Setup cost = $100; Lead time = 1 week ; EPP = 100 units

38 Lot-Sizing Summary In theory, lot sizes should be recomputed whenever there is a lot size or order quantity change In practice, this results in system nervousness and instability Lot-for-lot should be used whenever economical Lot sizes can be modified to allow for scrap, process constraints, and purchase lots

39 Lot-Sizing Summary Use lot-sizing with care as it can cause considerable distortion of requirements at lower levels of the BOM When setup costs are significant and demand is reasonably smooth, PPB, Wagner-Whitin, or EOQ should give reasonable results

40 Updating the System Regenerative system Updates MRP records periodically Net-change system Updates MPR records continuously

41 MRP Primary Reports Planned orders - schedule indicating the amount and timing of future orders. Order releases - Authorization for the execution of planned orders. Changes - revisions of due dates or order quantities, or cancellations of orders.

42 MRP Secondary Reports Performance-control reports system evaluation, deviation, late delivery, stockouts Planning reports useful for forecasting future inventory, assess future material requirement Exception reports late or overdue orders, excessive scrap rate, requirement of nonexisting parts

43 Material Checking & Balancing Use for monitoring of amount of part and product during processes Needs information to balance materials Accumulative production planning or target plan BOM or Assembly diagram Normally periodic checked

44 Accumulative production Material Checking & Balancing B C G Assembly diagram D A E H I J K F Target Plan Week Balancing chart J F M A M J J A S O N D A B C D E F G H I J K

45 Standard labor hours Standard labor hours Resource Requirements Profile 200 Capacity exceeded in periods 4 & Lot 6 split Lot 11 moved Lot 1 Lot 2 Lot 3 Lot 4 Lot 5 Lot 6 Lot 7 Lot 8 Lot 11 Lot 9 Lot 12 Lot 10 Lot 13 Available capacity Lot 15 Lot 14 Lot Period (a) Lot 1 Lot 2 Lot 3 Lot 4 Lot 5 Lot 6 Lot 7 Lot 8 Lot 9 Lot 12 Lot 10 Lot 13 Available capacity Lot 11 Lot 15 Lot 14 Lot Period (b)

46 Smoothing Tactics 1. Overlapping Sends part of the work to following operations before the entire lot is complete Reduces lead time 2. Operations splitting Sends the lot to two different machines for the same operation Shorter throughput time but increased setup costs 3. Lot splitting Breaking up the order into smaller lots and running part ahead of schedule

47 Other Considerations Safety Stock Lot sizing Lot-for-lot ordering Economic order quantity Fixed-period ordering

48 MRP in Services Food catering service End item => catered food Dependent demand => ingredients for each recipe, i.e. bill of materials

49 Benefits of MRP Low levels of in-process inventories Ability to track material requirements Ability to evaluate capacity requirements Means of allocating production time Ability to easily determine inventory usage by backflushing Backflushing: Exploding an end item s bill of materials to determine the quantities of the components that were used to make the item.

50 Requirements of MRP Computer and necessary software Accurate and up-to-date Master schedules Bills of materials Inventory records Integrity of data

51 MRP II Expanded MRP with emphasis placed on integration Financial planning Marketing Engineering Purchasing Manufacturing

52 Adjust master schedule MRP II Finance Market Demand Manufacturing Master production schedule Marketing Production plan MRP Adjust production plan Rough-cut capacity planning Capacity planning Yes No Requirements No Yes Problems? Problems? schedules

53 ERP Enterprise resource planning (ERP): Next step in an evolution that began with MPR and evolved into MRPII Integration of financial, manufacturing, and human resources on a single computer system.

54 ERP Software ERP software provides a system to capture and make data available in real time to decision makers and other users in the organization Provides tools for planning and monitoring various business processes Includes Production planning and scheduling Inventory management Product costing Distribution

55 MRP in Services Service applications such as: Professional services Postal services Retail Banking Healthcare Higher education Engineering Logistical services Real estate

56 ERP Strategy Considerations High initial cost High cost to maintain Future upgrades Training

BPFE, Yogyakarta Siswanto, (2005), Riset Operasi, Erlangga, Jakarta M.

57 Daftar Pustaka Richardus Eko Indrajit, (2005), Manajemen Persediaan, Grasindo, Jakarta Heizer Jay, B.Rander, (206), Manajemen Operasi, Salemba Empat, Jakarta Hani handoko, (2002), Manajemen Produksi dan Operasi, BPFE, Yogyakarta Siswanto, (2005), Riset Operasi, Erlangga, Jakarta M. Syamsul Ma arif, (2003), Manajemen Operasi, Grasindo, Jakarta Sofyan Assauri, (2001), Manajemen Operasi, BPFE, Jakarta Martinich, (2003), Operation Manaement, Prenice hall, New Yory

58 Terima Kasih

Net Requirements Plan. The logic of net requirements. MRP Planning Sheet. Gross Requirements Schedule

Net Requirements Plan. The logic of net requirements. MRP Planning Sheet. Gross Requirements Schedule Net Requirements Plan The logic of net requirements Gross Requirements Schedule MRP Planning Sheet Safety Stock BOMs, inventory records, purchase and production quantities may not be perfect Consideration