1. Manufacturing planning & control : Integration of MRP & JIT Prepared by: Ankit P. Sarvaiya (09CAD14)

2. Introduction In simplest form, 'the manufacturing process' is a composition of the material flows. Both Material requirements Planning (MRP) and Just-in-Time (JIT) are designed to manage the flow of materials, components, tools, and associated information. The entire manufacturing systems from purchasing to shop floor management can be controlled based on either MRP or JIT systems. Therefore, MRP and JIT systems are powerful management tools to determine success or failure of the manufacturing system. Considers general, discrete, multi-stage, production inventory system (MS-PIS) with multiple machines at each stage that manufacture multiple products. The MS-PIS is very important because it is by far the most common type of manufacturing systems.

3. Introduction In the MS-PIS, each product or part requires one or more operations to be processed at some designated machines or work centers. Different machines can be used to perform the same operation; however, they may possess different setup times and per unit processing times, as well as different per unit time costs.

4. Introduction A typical example of this type of manufacturing environment can be illustrated as follows. Suppose that a firm manufactures two products, P1 and P2. The BOM for the two products are shown in Fig.1. According to the figure, product P1 is made up of one unit of part B and one unit of part C, and part B is composed of one unit of part D and two units of part E, while product P2 consisted of one unit of part C and one unit of part F. Fig. 1.

5. Introduction Fig. 2.

6. Introduction Fig.2. shows the operations required to process each part and product. For example, part B requires two operations: the first operation can only be processed by machine 2 (M2); while the second operation can be processed by Ml or M5. Diagrams shown in Fig. 2 as Bill of operations, since they illustrate the operations and their precedent relationships required to produce a part or product. The demand for products P1 and P2, and parts B, C, D, E and F come at some specific times for some specific quantities. This manufacturing environment is an example of the MS-PIS since it involves multiple products (Fig. 1) and multiple machines (Fig.2). Also, each product or part may require one or more operations (Fig.2).

7. MRP vs. JIT 'MRP' is used interchangeably for either Material requirement Planning (MRP) or Manufacturing Resource Planning (MRP II). the basic mechanism of the MRP and MRP II systems, the time- phased closed-loop material or resource preparation process, remains the same. 'JIT' is defined as 'the basis of Toyota production system on which the right parts are needed in assembly line at the time they are needed and only in the amount needed' to achieve 'the absolute elimination of waste’. The scope of JIT system reaches every function such as product and process design, human resource management, MPC, and physical distribution

8. MRP and MRP II MRP was to manage the inventory waste for dependent demand items. Objective:- MRP system is to generate accurate inventory information in order to determine the right order quantities at the right time. MRP argue that MRP is just an information software package, which only determines the prospective material flow and has nothing to do with running production systems.

9. MRP and MRP II Master production schedule MRP system Purchasing Scheduling Receiving Loading Receiving inspection Dispatching Stores Shop floor control MRP planning and execution system

10. Just-In- Time Production JIT is manufacturing philosophy to minimize waste, and the JIT production system is a subsystem controlled by Kanban. The Kanban controlled JIT production system has been erected based on the premise of minimizing work-in process inventories (waste) by reducing or eliminating discrete batches. The reduced lot sizes not only contribute to production efficiency and product quality, but also reduce the overall costs associated with production in the JIT manufacturing environment. Kanban controlled production system is supported by smoothing of production, standardization of jobs, reduction of setup times, improvement of activities, design of machine lay out, and automation of processes.

11. Just-In- Time Production Success of the JIT production system must be explained in conjunction with Continuous Improvement and Total Quality Management. The JIT production system is often called 'lean production system' because it uses less of every resource compared with the conventional mass production system.

12. JIT pull and MRP push? There are two principles that initiate material flow in the MPC system, push and pull logic. Three ways to define push and pull systems in general:- 1)Differences in terms of the order release = pull system, removing an end item (or a fixed lot of end items) triggers the order release, by which the flow of materials or components is initiated. push systems allow for the production or material flow in anticipation of future demand. 2)Examine the structure of the information flow = pull system, the physical flow of materials is triggered by the local demand from the next server. pull system is a decentralized control strategy in which the ultimate goal of meeting demand is disregarded in the local servers.

13. JIT pull and MRP push? 3) Practical approach associated with WIP level on the shop floor = a push system is considered an open queuing network with infinite queue space, and a pull system is a closed queuing network. Above three viewpoints,it can be concluded that if materials flow is initiated by the central planning system without controlling WIP level. In a pure push system the parts or component will proceed based on the predetermined schedule regardless of whether the next server is busy or idle. In a pure pull system the subsequent process will withdraw (i.e., pull) the parts from the preceding process using local information and controlling WIP inventory level.

14. Major problems of MRP MRP is a computerized information system for managing dependent-demand inventory and scheduling stock replenishment orders. 1) how should one determine the planned lead time? = lead time is composed of processing time, setup time, waiting time in queue and a certain fixed idle time, such as the time needed to cool down a part. lead time is very much determined by how long it takes to obtain the required capacity. Therefore, setting optimal planned lead times for MRP is not a simple task.

15. Major problems of MRP 2 ) how to decide the order quantity? = This is generally called the lot-sizing decision. the average MRP system offers about three or four methods. The most common techniques are lot for lot (LFL),, fixed order quantity (FOQ), fixed period quantity (FPQ), and period order quantity (POQ). The third major issue of MRP is that it does not produce a workable schedule for the shop-floor. The planned order release and the planned order receipt specify the start date and finish date of an order. So, MRP cannot determine the exact time period and workstation for processing each operation.

16. Major problems of MRP The last major problem of MRP is capacity planning. When MRP is employed to perform capacity requirements planning, it assumes that the resource capacity is utilized at the period that a job is released or at the middle period between planned order release and planned order receipt dates.

17. Major problems of JIT JIT approach requires the production of precisely the necessary parts in the necessary quantity at the right time. The main objective is to achieve zero inventories. One of the major requirements for JIT production is a stable environment so as to obtain a level schedule.

18. Proposed integrated MRP – JIT approach MRP is an ideal mechanism for planning and control propose, while JIT is the best tool for reducing cost and lead times. By taking advantage of the two, one can obtain the best of both. The proposed integrated system is a pull system in both materials planning and operations scheduling levels. Integrated system in the following order. First, we discuss the logic of the integrated system. Second, we describe the major inputs and outputs of the integrated MRP and JIT system. Third, we discuss the performance criteria used to evaluate the goodness of a schedule.

19. Proposed integrated MRP – JIT approach the following example to illustrate how the proposed integrated framework captures the pull element through its operations scheduling process.

20. Proposed integrated MRP – JIT approach Suppose that there are 10 and 25 units of demand for product P1 in periods 8 and 10, respectively, and that there are 20 and 5 units of demand for product P2 in periods 6 and 7, respectively. Furthermore, above Table gives the machine or resource routing information, for example, it shows that the second operation of part B can be performed by either machine 1 or machine 5 and that the setup time and unit processing time for both machines are 6 and 0.2 h, respectively. Also, a capacity of 40 h is assumed for each machine in each period. It should be noted that the example routing file assumes, without the loss of generality, that the same setup time and unit processing time are used for those routing with multiple machines, and that the machine cost per unit for each machine is identical.

21. Proposed integrated MRP – JIT approach propose forward and backward heuristics to implement the proposed framework. We will use a forward heuristic…. The earliest demand in the planning horizon is 20 units of P2 in period 6, so the integrated system first finds the last operation of P2, P2 requires only one operation, this system can scheduled the operation at m/c 2 in period 6. The forward heuristic employs an objective, such as least unit total cost (LUTC), to determine the operations scheduling. To demonstrate the principle of the proposed framework, we assume that the heuristic schedules the operation in period 6 at machine 2, as shown in machine 2 of below Table. This triggers or pulls the production of parts C and F.

22. now schedule the second operation of part C and the first operation of part F in period 5 or earlier., no consecutive operations of a part can be scheduled in the same period schedules operation 2 of part C and operation 1 of part F in period 5 at machines 2 and 3, respectively (see in Table). This triggers the need to schedule operation 1 of part C in period 4 or earlier and signals that the material requirements of part F should arrive by period 5. Table indicates the scheduling of operation 1 of part C in period 4 at machine 1. Now, the integrated framework schedules the operations derived from the 5 units of demand of P2 in period 7, and this process continues until all demands are covered. Proposed integrated MRP – JIT approach

24. there are a number of differences between MRP & proposed sys.. 1) MRP does not provide a daily production schedule. However, the integrated system gives the detailed day-to-day schedule. 2) The lead time is fixed and pre-determined in MRP, the lead time of the integrated system can be varied, and it is derived from the schedule. 3) A period defined in the integrated system, usually a shift or a day, is generally shorter than that of MRP. 4) The integrated system determines the TPC as part of its output. In contrast, MRP does not consider the total cost, since it essentially specifies the planned order releases and receipts dates. Proposed integrated MRP – JIT approach

25. The integrated system is similar to JIT because its operations scheduling process is driven by the pull from downstream operations. However, JIT does not provide a pre-determined daily formal schedule. Also, JIT production follows a more rigid scheduling of products since it requires more or less level production, which is more suitable to repetitive mfg. environment. On the other hand, the integrated system does not require a level production, hence, it can be employed in both repetitive or batch manufacturing environments. Furthermore, the integrated system employs heuristics to construct schedules to minimize the TPC, while JIT production does not. Proposed integrated MRP – JIT approach

26. five major inputs of the integrated system are: MPS, BOM, inventory records file, bill of operations and standard time database. MPS specifies the independent demand by period for each part. BOM provides the parts and their quantities. Inventory records file provides the on-hand inventory and the portion of fixed lead time for each part. Bill of operations gives the NOP and their processing precedent relationships. Standard time database provides information, machine capacity, unit machine time cost, and operation unit processing time and setup time information.

27. Basic structure of integrated system

28. Conclusions An integrated MRP and JIT framework is proposed to solve the MS-PIS. First of all, efficient heuristics need to be developed to solve the MS-PIS problem under the proposed framework. Moreover, it is interesting to determine the factors, such as the length of planning horizon and the size of a time period, that have significant impacts on the performance of heuristics.