Toplu üretim planlama'dan ana üretim programlamaya geçiş ve bilgisayar destekli bir uygulama

Abstract

Kıt kaynakların en etkin kullanımını hedefleyen üretim planlamanın amacı, birimleri kendi baslarına en iyilemek değil isletmenin tüm birimleri için genel bir optimizasyon sağlamaktır. İsletmelerde birimlerin koordinasyonsuz çalışması genel anlamda verimliliğin azalmasına ve toplu hedeflerden sapmalara yol açmaktadır. Orta dönem kararları uygulama aracı olan Toplu üretim Planlarının islerlik kazanması daha ayrıntılı bir yapı arzeden Ana üretim Programları ile sağlanmaktadır. Bu aşamada planlamacılar etkin bir kaynak planlama ve kaba kapasite planlama çalışmalarına dayandırılmış veri tabanına ihtiyaç duyarlar. Böylece Ana üretim Programlarının oluşturulması aşamasına gelinir. Malzeme ve kapasite ihtiyaç planlama çalışmalarındaki bilgisayar destekli hızlı gelismeler Ana üretim Programlarını daha -fonksiyonel hale getirmektedir. Ana üretim Programı, isletmedeki tüm modüller arasında koordinasyonu sağlayan temel bir unsur olarak nitelendirilebilir.

Aggregate Production Planning, is the production portion of the business plan and addresses the demand side o-F the -Firm's activities by showing the outputs it will produce, expressed in numbers o-F units o-F its product groups may be produced at diverse plants, -Facilities or divisions each of them needs its own production plan. The divisions aggregate production plan covers the coming 6 to 18 months on a weekly or monthly basis. Planning at this level ignores such details as how many o-F each individual product, style or model to produce. The plan recognizes the divisions existing fixed capacity and the company's overall policies -For maintaining inventories and backlogs, employment stability and subcontracting. A statement o-F desired output is useful only if it is -feasible. This is the role of aggregate capacity planning to keep capacity utilisation at desired levels and to test the feasibility of planned output against existing capacity. Thus it addresses the suply side of the firm's ability to meet the demand. As for aggregate output plans, each plant, facility or division requires its own aggregate capacity plan. Capacity and output must be in balance. A capacity plan translates an output plan into input terms, approximating how much of the divisions capacity will be consumed. A product group, for example, usually consumes predictable amounts of capacity such as labor hours of assembly or machine hours for fabrication. Although these basic capacities are fixed, management can manipulate the short and capacities by the ways they deplay their work force, by subcontracting or by using multiple work shifts to adjust the timing of overall outputs. As a result, the aggregate planning process balances output levels, capacity constraints and temporary capacity adjustment to meet demand and utilize capacity at desired levels during the coming months. All these explanations arE placed in Chapter 1. The resulting plan sets limits on the Master Production Schedule. Vi The purpose of master production scheduling (MPS) is to meet the demand for individual products in the product group» This more detailed level o-f planning disaggregate the product groups into individual products and indicates when they will be produced. The Master Production Scheduling is an important link between marketing and production. It shows when incoming sales orders can be scheduled into production and when each shipment can be scheduled for delivery. It also takes into account current backlogs so that production and delivery schedules are realistic. An effective Master Production Schedule is the heart - or at least the pacemaker - g-F many operations. The -First of the tools deals with assessing how much capacity exists -For the process at any period of time. The discussion continues with coverage o-F the ways the schedule (either the master schedule) can be -Filled. This discussion begins in terms o-F Master Sceduling but get more precise and mathematical with the material under "Scheduling Techniques". As demand -Firms up, the broad outlines o-F the production schedule, as determined by the aggregate plan, can be -Filled in with greater detail. Broad product line demand -Forecasts are replaced with more detailed -Forecasts o-F specific products and eventually, with specific product variations material supply capabilities and lead times are known with more certainty. More specifics ere known about actual labor and machine availabilities. The aggregate planning stage gives way to successive stages of more detailed scheduling, generally termed Master Production Scheduling (MPS). The production schedule starts to reflect orders actually booked as well as those expected. The schedule begins to become firm, but it generally cannot be completely set until days or weeks before actual production. Thus, some day-to-day or week-to-week leeway is permitted in the schedule, it is the job of the production schedule to use this leeway in devising a detailed production schedule (sometimes termed a final assembly schedule) that places as balanced a demand on the process as possible. This means that the scheduler must be thoroughly aware of the capacities of each segment of the process and where any bottlenecks are likely to show up. This kind of knowledge often leads a scheduler to conduct rules of thumb that help develop a schedule that is feasible, balanced and reasonably low cost. The MPS must also reflect material availability. In the interest of clarity and order on the factory floor itself, it is often unwise to release an order whose component parts have not yet arrived or to vi i released just to "get it moving" through the process. In both o-F these situations, work-in process inventories built up, excessive work-in process is too often disruptive and time consuming to manage» Often companies are better o-f-F it they risk some idling workers temporarily because of no work than they would be purposely littering the -floor with work- in process. The hidden costs of work-in process induced inefficiencies are frequently greater than the highly visible costs of idle labor. As the foregoing discussion has made clear the scheduling process requires increasing refinement about capacities, demand and material availability. The details of Master Production Schedule are placed in Chapter 4. Capacities, materials requirements and knowledges of product structure are examined in Chapter 3. The Master Production Schedule is the driving first for material requirements planning. As discussed in Chapter 3, MRP shows the time phased requirements for releasing material and receiving materials that enable the Master Production Schedule to be implemented. A typical MPS system involves planning for raw materials, components, subassemblies and assemblies or final products. A company would purchased some of these and fabricated assemble others. Aircraft, automobiles, toys, household appliances and industrial machinery are some of the examples of industries using MRP systems. In addition to the demand for final products, an MRP system also has to fulfil customer demands for components and subassemblies to be used as spare parts. In fact, for some industries supply of spare parts constitutes a more profitable business segment. Several firms compete in fulfilling customer demands for end-products but there may be little or no competition in supplying the spare parts for specific products. Rough-cut capacity planning (sometimes called resource requirements planning) is done in conjunction with the tentative master production schedule to test its feasibility in terms of capacity before the MPS is finally settled. This step ensures that a purposed MPS does not inadvertently overload any key department, work center or machine making the MPS unworkable. Although the check can apply to all work centers, it is typically applied only to the critical ones that are most likely to be bottlenecks. It is a quick and inexpensive way to find and correct gross discrepancies between the capacity requirements (in direct labor- hours, for example) of the MPS and available capacity. vi 1 1 This is a manual, graphical technique -For planninq, schedul ing and monitoring progress o-F simple to complex projects. These may be products assembled over a moderate time period against a -Firm schedule, a development program -For a complex assembly or a research and engineering project. The project is represented by a network showing the relationship in time among the various milestones that make up the project. The discipline required to set up the chart can help to ensure thorough planning. The schedule of critical activities can be developed accurately and the actual progress monitored. The technique permits showing the -Following simultaneously on one charts - Source o-F each component element (purchase, manufacture, assembly? test,etc), - sequence o-F assembly, including subassembly, testing, inspection, packaging, shipping and related activities, - Comparison o-F scheduled versus actual -Finished product deliveries, - Comparison o-F scheduled versus actual component element completions, showing present and potential shortages or delays. The technique is expensive to set up, increasingly so as the number of components and control points increases. It is in-Fiexibie and expensive to revise in terms o-F schedule changes, variations in elements or revisions in elemental lead times. Analysis o-F project status requires accumulating data on all elements simultaneously. LOB has been most -Frequently applied to complex assemblies built -For the US Navy, whose contracts have required using the chart to report status to government inspectors. Commercial and industrial applications o-F LOB as an operating technique are extremely rare. Its major application is in planning, scheduling and controlling the production o-F complex, assembled products. An LOB chart consists o-F three sections; the production plan, the objective chart and the progress chart. The lower hal-F is the production plan; inaccuracies in it will be re-Fleeted throughout the LOB chart. It is a key components product treewith time represented on the horizontal axis» The length o-f each product tree bar denotes the lead time required the produce one batch o-f that component or assembly; the overall product structure length is the total product lead time. For example, purchased part 1 requires 12 working days lead time and the total product lead time is 24 days. To construct a production plan, -first select those components or events whose timely completion is important to poject. Relatively unimportant components are lumped together. Second, obtain or estimate the lead times for each batch of the selected key components; these should be the most likely time, inclusive o-f processing, movement and waiting time. Third, draw the chart by starting from the right with the completion day, week or month as zero and working to the left, "branching out" as assemblies become subassemblies, and subassemblies become components. Fourth, connect all component horizontal lead time bars with a vertical line where subassembly or assembly occur, forming an interconnected network. Select a time scale in units suitable for effective monitoring. Fifth, mark the start of each key component or event line with a control point number, commencing from the top left and moving to the bottom right. Intermediate events should be given a number only if they are to be monitored. Always number the completion of the project. Symbols indicating the type of component (raw material, purchased part, manufactured part, subassembly, etc.) are helpful and color coding increases the ease of interpretation. Descriptions of components or events can be shown on the chart. The selection of key components and events, the assignment of control point numbers and the use of descriptions must be dictated by the economics of over-or undercontrolling the project's progress. The completed production plan could be used like a Gantt chart for monitoring one project by assigning specific dates to the horizontal time scale and recording actual progress on individual progress on individual bars of the chart where few or no partial lots of the total order are expected at any control point. Where individual lots are scheduled over several periods, the Gantt chart is difficult to adapt and the LOB progress chart makes it possible to record the control point completion status against the schedule.