12:25 AM
Chapter 2
Production Planning System
Introduction
- A good planning system must answer four questions of priority and capacity: What are we going to make? What does it take to make it? What do we have? What do we need?
- Priority, as established by the marketplace, relates to what products are needed, how many are needed, and when they are needed.
- Capacity is the capability of manufacturing to produce goods and services (deliverables). It depends on company resources and the availability of material from suppliers.
Manufacturing Planning and Control System
- The five major levels in the manufacturing planning and control system are: strategic business plan, production plan (sales and operations plan), master production schedule, material requirements plan, and purchasing and production activity control. Each level varies in purpose, time span (planning horizon), level of detail, and planning cycle (frequency). At each level, three questions must be answered:
What are the priorities --- how much of what is to be produced and when?
What is the available capacity --- what resources do we have?
- Strategic Business Plan – It is senior management’s statement of the broad direction of the firm, major goals and objectives the company expects to achieve over the next two to ten years or more. It is based on long-range forecasts and provides a framework that sets the goals and objectives for further planning by marketing, finance, engineering and production/operations. The level of detail is not high. It is concerned with general market and production requirements. It is often stated in dollars rather than units.
- Production Plan – Given the objectives set by the strategic business plan, production management is concerned with the quantities of each product group or family that must be produced in each period, the desired inventory levels, the resources of equipment, labor, and material needed in each period, and the availability of the resources needed. For effective planning, there must be a balance between priority and capacity. The planning horizon is usually six to 18 months and is reviewed perhaps each month or quarter.
- Master Production Schedule (MPS) – is a plan for the production of individual end items. It breaks down the production plan to show, for each period, the quantity of each end item to be made. Inputs to the MPS are the production plan, the forecast for individual end items, sales orders, inventories, and existing capacity. The level of detail for the MPS is higher than for the production plan. The planning horizon usually extends from three to 18 months but primarily depends on the purchasing and manufacturing lead times. Master scheduling describes the process of developing a master production schedule; the term master production schedule is the end result of the process. Plans are reviewed and changed weekly or monthly.
- Material Requirements Plan (MRP) – is a plan for the production and purchase of the components and/or services used in making the items in the MPS. The MRP establishes when the components and services are needed to make each end item. The level of detail is high. The planning horizon is similar to MPS, extending from 3 to 18 months.
- Purchasing and Production Activity Control (PAC) – represents the implementation and control phase (execution phase). Purchasing is responsible for establishing and controlling the flow of raw materials into the factory. PAC is responsible for planning and controlling the flow of work through the factory. The planning horizon is very short and the level of detail is high.
- Capacity Management – At each level in the manufacturing planning and control system, the priority plan must be tested against the available resources and capacity of the manufacturing system. The basic process is one of calculating the capacity needed to manufacture the priority plan and of finding methods to make that capacity available. If the capacity cannot be made available when needed then the plans must be changed.
- Sales and Operations Planning (SOP) – is a process for continually revising the strategic business plan and coordinating plans of the various departments. SOP is a cross-functional business plan that involves sales and marketing, product development, operations, and senior management. Operations represents supply, marketing represents demand. The SOP is the forum in which the production plan is developed and a dynamic process in which the company plans are updated on a regular basis, at least monthly. (See figure 2.5 and the benefits listed above.)
- Manufacturing Resource Planning (MRP II) – The manufacturing planning and control system described here, is a master game plan for all departments in the company and works from the top down with feedback from the bottom up (see figure 2.6). This fully integrated planning and control system is called a manufacturing resource planning, or MRP II, system. The phrase “MRP II” is used to distinguish the “manufacturing resource plan” (MRP II) from the “materials requirement plan” (MRP).
- Enterprise Resource Planning (ERP) – is an accounting oriented information system for identifying and planning the enterprise---wide resources needed to make, ship, and account for customer orders. ERP encompasses the total company and MRP II is manufacturing.
Making the Production Plan
· Based on the market plan and available resources, the production plan sets the limits or levels of manufacturing activity for some time in the future. The production plan sets the general levels of production and inventories over the planning horizon. Its prime purpose is to establish production rates that will accomplish the objective of the strategic business plan, including inventory levels, backlogs (unfilled customer orders), market demand, customer service, low-cost plant operation, labor relations, and so on. The plan must extend far enough in the future to plan for the labor, equipment, facilities, and material needed to accomplish it.
· For planning purposes, a common unit or small number of product groups based on similarity of manufacturing processes is what is needed. Manufacturing is concerned more with the demand for the specific kinds of capacity needed to make the products than with the demand for the product.
· Capacity is the ability to produce goods and services. It means having the resources available to satisfy demand. Capacity can be expressed as the time available or as the number of units or dollars produced in a given period. The demand for goods must be translated into the demand for capacity. This requires identifying product groups, or families, of individual products based on the similarity of manufacturing process. Usually the following can be varied to adjust capacity:
People can be hired and laid off, overtime and short time can be worked, and shifts can be added or removed.
Inventory can be built up in slack periods and sold or consumed during high demand.
Work can be subcontracted or extra equipment leased.
Manufacturing management is responsible for determining the least-cost alternative consistent with the goals and objectives of the business.
· Three or four basic strategies can be used in developing a production plan:
Chase (demand matching) strategy – producing the amount demanded at any given time (see figure2.8). Inventory levels remain stable while production varies to meet demand.
Production leveling – continually producing an amount equal to the average demand. Companies calculate their total demand over the time span of the plan and, on the average, produce enough to meet it. Production leveling means the company will use its resources at a level rate and produce the same amount each day it is operating. The advantage is that it results in a smooth level of operation that avoids the costs of changing production levels. The disadvantage is that inventory build up during periods of low demand (see figure 2.9).
Subcontracting – means producing at the level of minimum demand and meeting any additional demand through subcontracting. Costs associated with excess capacity are avoided, and because production is leveled, there are no costs associated with changing production levels. The main disadvantage is that the cost of purchasing may be greater than if the item were made in the plant (see figure 2.10).
Hybrid strategy – is a combination of the other three strategies. Production management is responsible for finding the combination of strategies that minimizes the sum of all costs involved, providing the level of service required, and meeting the objectives of the finance and marketing plans.
· The objective in developing a production plan is to minimize the costs of carrying inventory, changing production levels, and stocking out (not supplying the customer what is wanted when it is wanted). The information needed to make a production plan is as follows: forecast by period for the planning horizon, opening inventory, desired ending inventory, and any past-due customer orders (back orders).
· Make-to-Stock Production Plan – Products are made and put into inventory before an order is received. Sale and delivery are made from inventory. Make to stock when demand is fairly constant and predictable, there are few product options, delivery times demanded by the marketplace are much shorter than the time needed to make the product, and product has a long shelf life.
· Level production plan – The general procedure for developing a plan for level production is total the forecast demand for the planning horizon, determine the opening inventory and the desired ending inventory, calculate the total production required (Total Production = total forecast + back orders + ending inventory – opening inventory), calculate the production required each period by dividing the total production by the number of periods, and calculate the ending inventory for each period.
· Chase strategy .
· Make-to-Order Production Plan – Wait until an order is received from a customer before starting to make the goods. Make to order environment has backlog of unfilled customer orders instead of an inventory of finished goods. The backlog will be for delivery in the future and does not represent orders that are late or past due. Firms make to order when: goods are produced to customer specification, the customer is willing to wait while the order is being made, the product is expensive to make and to store, and several product options are offered.
· Assemble to order – Where several product options exist and where the customer is not willing to wait until the product is made, manufacturers produce and stock standard component parts. When an order is received, they assemble the component parts from inventory. Since the components are stocked, the firm needs only time to assemble before delivering the product. Assemble to order is a subset of make to order. To make a production plan, one will need a forecast by period for the planning horizon, an opening backlog of customer orders and desired ending backlog.
· To develop a level production plan, total forecast demand for the planning horizon, determine the opening backlog and the desired ending backlog, calculate total production required (Total production = total forecast + opening backlog – ending backlog), calculate the production required each period, and spread the existing backlog over the planning horizon according to due date per period.
· Resource Planning – Once the preliminary production plan is established, it must be compared to the existing resources of the company. If enough capacity to meet the production plan cannot be made available, the plan must be changed.
· Resource bill shows the quantity of critical resources (materials, labor, and “bottleneck” operations) needed to make one average unit of the product group.