Basic of Supply Chain Management
Session 3: Master Planning 主生产计划
In Session 2, Demand Management, we addressed the role of marketing and customer relationship management and demand planning in determining customer demand.
This session examines the phase of MPC called master planning. Master planning includes sales and operations planning (S&OP), which produces the production plan, and master scheduling, which produces the MPS. The latter is a priority plan consisting of due dates for the production of end items. It then becomes a major input to material requirements planning (MRP), which takes priority planning down to the component level.
Learning Objectives 学习目标
Purpose and Scope of Master Planning 主排程的目的和范围
Explain the elements and importance of the priority plan.
Differentiate between the planning horizons and levels of detail of business planning, S&OP, and master scheduling.
Sales and Operations Planning and Production Planning 销售运营计划和生产计划
Describe the purpose of, and key inputs to, S&OP.
Explain the advantages of production planning at the product family level.
List four production strategies and their differences with respect to inventory.
Calculate a level production plan and ending inventories for all periods.
Master Scheduling and the Master Production Schedule 主排程和主生产计划
Differentiate between the production plan and the master production schedule (MPS).
Explain the significance of the MPS planning horizon, time fences, and zones.
Calculate the projected available balance and the MPS in a master schedule.
Describe the purpose of the final assembly schedule.
Resource Planning and Rough-Cut Capacity Planning
Differentiate between resource planning and rough-cut capacity planning (RCCP).
Describe the differences in the bill of resources data requirements between resource planning and RCCP.
Master Production Schedule and Sales 主生产计划和销售
Explain the use of the MPS in available-to-promise (ATP).
Perform a simple ATP calculation.
Purpose and Scope of Master Planning 主排程的目的和范围
In the previous session, we addressed demand management's role in shaping and recognizing independent demand. The role of MPC is to synchronize and translate independent demand into dependent demand.
Two of the MPC processes, as shown in Visual 3-6, are S&OP and master scheduling. These are known collectively as master planning. Note that they also are known as priority planning activities.
Priority Planning 优先计划
In conventional manufacturing, planning the material transformation process requires a sequence of due dates for the start and finish of the purchasing and subassembly operations, some of which might be parallel, leading up to the final product.
due date -- The date when purchased material or production material is due to be available for use. -- APICS Dictionary 交期 —— 采购材料或生产材料的到期日。
"Available for use" means that the material or component has been completed and is ready for use by the next operation, or is available as an end item to be delivered or stocked.
The setting and maintaining of time-phased due dates is called priority planning. Priority planning of due dates for end items is the domain of master planning:
S&OP develops plans for products at the family level.
Master scheduling develops due dates and quantities at the end-item level.
Once end-item due dates are established by the master schedule, MRP determines the priority plan and due dates for purchased and manufactured components.
priority planning -- The function of determining what material is needed and when. Master scheduling and MRP are the elements used for the planning and replanning process to maintain proper due dates on required materials.
-- APICS Dictionary
优先计划 —— 决定什么时候需要什么材料的功能。主调度和MRP是计划和重新计划过程中用于在所需材料上维护适当交期的元素。
The focus of this session is on master planning's role in priority planning.
Planning Horizon and Level of Detail 计划的范围和详细程度
In Session 2, we pointed out the importance of how forecasts support the three different levels of planning. A visual from Session 2 is repeated here in Visual 3-8 to emphasize the differences in the planning horizons for the planning processes within MPC, including the business plan. We will discuss the role of master planning in translating the business plan into an MPS shortly. Note the differences in time horizons and the priority planning activities' level of detail. This reflects the top-down approach to translating aggregate business-level plans into plans for products at the family level (S&OP), the end-item level (master schedule), and the component level (MRP).
S&OP and Production Planning 销售运营和生产计划
Sales and Operations Planning 销售和运营计划
S&OP translates the strategic business plan into production rates that meet company financial, customer service, and other business goals. Properly performed S&OP is characterized by the following:
- Continual updating of the operations, sales, and finance plans in order to meet annual strategic business plan objectives based on the latest market conditions and company capabilities
- A formal process for obtaining inputs from and updating the plans of various functions within the organization, especially sales, operations, product development, and finance
A regular schedule for meeting with senior executives to review the updated plans, usually monthly but as often as weekly in some companies
A check to see if resources will be adequate, leading to realistic and coordinated sales, operations, and finance plans
Better management of the production rate, sales activities, inventory, and backlog
Production Planning 生产计划
Purpose and Scope 目的和范围
The production plan is a major output of S&OP and should reflect the resolution of decisions and tradeoffs made during the S&OP process. It is a major input to the end-item priority planning that takes place in master scheduling.
production planning -- A process to develop tactical plans based on setting the overall level of manufacturing output and other activities to best satisfy the current planned levels of sales, while meeting general business objectives of profitability, productivity .. and so on, as expressed in the overall business plan. 生产计划——一种制定战术计划的过程，该计划的基础是制定总体水平的生产产出和其他活动，以最好地满足当前计划的销售水平，同时满足盈利能力和生产率的一般业务目标。等等，就像整个商业计划所表达的那样。 -- APICS Dictionary
Production planning is concerned with the following:
The quantities demanded of each product family or product line in each period -- Because not much detail is needed, planning is done by product families.
Desired inventory levels -- Inventory usually is a major asset, and companies will want to control inventory levels. If an item is already in stock, the company does not need the resources to make it.
The resources of equipment, labor, and material needed in each period -- The purpose of the production plan is to be able to meet demand; to do so, manufacturing must find out what resources are needed.
The availability of needed resources -- Once the required resources are decided, the next step is to compare required resources with available resources.
Typical Production Planning Situation 典型的生产计划情况
Production planning faces the following typical situation:
The time horizon may be more or less than 12 months and even up to 36 months depending on the manufacturing cycle.
The plan usually is stated as a monthly rate.
Demand fluctuates or is seasonal for many products.
A plan is made for product families or groups.
Plant and equipment usually are fixed within the time horizon.
Management will have a variety of objectives.
Production Strategies 生产策略
Four different strategies can be used to develop a production plan.
Chase, or demand matching, strategy: Production level matches the quantity demanded by period.
Level production strategy, or production leveling: Production level is equal to the average demand.
Subcontracting: Production level is equal to the level of the minimum demand and the rest is fulfilled through subcontracting.
Hybrid, or combination, strategy: In addition to the above individual strategies, a hybrid strategy may be used to balance customer service, inventory, and stable labor force objectives.
Chase (demand matching) strategy 追赶（需求匹配）策略
The goal of the chase strategy is to produce the quantity demanded at any time. Because the inventory level is stable, the cost of the inventory will not vary significantly from period to period. Production is adjusted to match sales requirements. However, this strategy also has disadvantages:
As production increases, workers must be hired and trained. Extra shifts may be needed, and overtime may be necessary. These requirements all increase cost.
As production decreases, people are laid off and employee morale suffers.
When production starts to increase again, the best workers may have other jobs and their skills will not be available.
Manufacturing must have enough plant capacity to produce at the highest capacity level needed, but that capacity might be underutilized during periods of low demand.
Level Strategy 均衡策略
The basic approach of the level strategy is to make an accurate forecast of average demand for a period, such as one year, and then set a level production rate to match the average. As seen in Visual 3-16, this shows a buildup of inventory during the first part of the year, followed by a drawdown to match demand during the latter half.
The advantages are 优势是
level production avoids the costs of workforce and capacity adjustments of the chase strategy
level production avoids changeover costs and enables long runs that reduce per-item production costs.
The disadvantages are
a buildup of inventory and inventory carrying costs
it requires a more accurate forecast.
Another approach is to level production at a rate equal to the minimum demand level and to meet all additional demand through subcontracting.
Its advantages are as follows:
It prevents the buildup of inventory that occurs in the level production strategy.
In a repetitive flow environment, this strategy avoids excess capacity costs and reduces the costs of changeovers and workforce adjustments.
It can be a means of quickly acquiring additional capacity.
Its disadvantages are as follows:
Companies do not want to subcontract items for which they have developed propriety production methods that provide a competitive advantage.
The costs of subcontracting might exceed the cost of in-house production.
Hybrid strategy 混合策略
Anold et al., in Introduction to Materials Management, 7th ed. chap.2, refers to chase, level, and subcontracting as pure production strategies. They have their own sets of cost characteristics and tradeoffs.
The hybrid strategy as shown in Visual 3-19 attempts to combine the above elements to balance inventory and production costs by minimizing changeovers during the planning cycle in order to satisfy customers. The diagram shows two changeovers during the cycle, and the production rate tracks fairly closely with demand.
The characteristics of the hybrid strategy are as follows:
Production is at or close to full capacity for at least part of the planning cycle.
Production is at a lower rate during the other part of the cycle.
Production is level during both parts of the cycle.
Workforce adjustment costs are less than they are in a chase strategy.
Inventory buildup is less than it is in a level strategy.
Hybrid strategy requires a more accurate forecast as in the level strategy.
As with the level strategy, an accurate forecast is a big advantage. For example, if the forecasted average demand during the low demand period is too low, the buildup of inventory during this period might not suffice during the period of high demand.
Note the example of the hybrid strategy is a simplified one. There are numerous variations of such strategies, each with its own costs and benefits. It is management's job to find the best strategy.
Developing a Make-to-Stock Production Plan 制定一个生产计划
In MTS production, finished goods are put into and sold from inventory. It is used when
demand is fairly constant and predictable
only a few product options exist
the required delivery times are shorter than the manufacturing lead time.
Information needed for a MTS production plan includes
- a forecast by time period for the planning horizon
- opening inventory
- desired ending inventory.
Resource Planning 资源计划
We mentioned earlier that the production plan is a major output of S&OP and that its validity is not just a concern for the manufacturing function but also for the following functions:
Finance: Revenue projections only are as good as sales.
Sales and marketing: Sales only are as good as production schedules.
Operations: Production schedules only are as good as the availability of resources.
The production plan must be compared with the availability of resources. Two questions must be answered:
- Are the required resources available when needed? The resources of concern at this point are critical resources such as materials, labor, and other operations constraints and especially those that take a long time to acquire.
- If not, how will the difference between planned load and available resources be reconciled? Choices are changing resources or altering load.
Bill of Resources 资源清单
At this stage in the MPC process, resource planning is driven by the production plan and the bill of resources. An example of a bill of resources, sometimes called a resource bill, is shown in Visual 3-32. It lists the resources required to make one average unit in each of three product families for cycles: unicycle, bicycle, and tricycle.
在MPC过程的这个阶段，资源计划是由生产计划和资源清单驱动的。bill of resources子，有时也被叫作resource bill。这里有个例子如图3-32所示。它列出了在三个产品系列中制造一个平均单位所需的资源:独轮车、自行车和三轮车。
Note the following characteristics and implications of the bill of resources shown.
The three product families, which all are types of cycles, share the same manufacturing resources, such as the plant facility.
The resource requirements shown for each of the three product families are based on the average unit of each type.
The product families require two critical resources: steel tons and assembly time labor hours.
In multiplying the planned production quantities by the amount of steel and assembly hours needed for each item, total resources required by the three product families can be calculated and then campared with available resources.
Master Scheduling and Master Production Schedule 主排程与主生产计划
In the S&OP process, the production plan determines a feasible rate of production at the product family level over a planning horizon of one to three years. The development of the master schedule is the next step of master planning. It has the following purposes:
- Link, or disaggregate, production planning at the product family level (in this case, unicycles, bicycles, and tricycles) to the end-item level (specific models of each family).
Create the priority plan, including due dates and quantities, for end item manufacturing.
Provide end-item due dates and quantities used for calculating the rough-cut capacity plan.
Drive the material requirements plan, which takes the priority plan to the component due date and quantity level.
Master planning seeks to plan and control the impact of independent demand on material and capacity. The master schedule is a vital link between sales and production.
It makes valid order promises possible.
It represents an agreed-upon plan between sales and production.
The objectives of master scheduling are to
- maintain the desired level of customer service 维持客户服务的理想水平
- make the best use of resources 充分利用资源
- keep inventories at the desired level. 保持所需的库存水平。
Inputs to the master scheduling process include
- the production plan 生产计划
- forecasts for individual end items 单个成品的预测
- orders from customers 客户订单
- additional independent demand 额外的独立需求
- inventory levels 库存水平
- capacity constraints 产能约束
Relationship to the Production Plan 生产计划关系
Visual 3-39 is a simplified example of the use of input data from the production plan and data from the item forecast to develop a master schedule.
The production plan data is aggregate data for product family W by month.
The MPS data have been disaggregated on a weekly basis to the end-item level by forecasts for products X and Y, which are in product family W.
Production plans usually are started in months, and the master schedule usually is stated in weeks.
Why, if this is a level production plan, does the production plan vary from 19,000 to 23,000 units per months?
Developing a Master Schedule 制订主排程
The steps in developing a master schedule are as follows:
Create a preliminary master schedule for each end item with demand.
Aggregate the master schedule for all end items if the products use the same resources and take the same amount of time.
Resolve differences and publish the MPS.
Master Schedule Versus MPS 主排程与MPS
The master schedule is represented by a time-phased planning chart that includes the forecast, customer orders, projected available balance of inventory, available-to-promise (ATP), and a line called the MPS. It is this line that we refer to when we develop an MPS. Note that customer orders and ATP are not included in the simplified example of the master schedule shown in Visual 3-41.
Projected Available Balance (PAB) 预计可用库存
The projected available balance in any period tells you if you need to schedule an MPS. Visual 3-41 shows a forecast and projected available balance at the beginning of a six-period master schedule. If the balance is high enough to cover forecasted demand during all six periods, no MPS receipts are necessary.
At first glance, it appears that the projected available balance at the beginning of the six-period schedule is not enough to cover the forecasted demand for the entire schedule.
Visual 3-42 shows the calculation of the PAB at the end of period 1. The PAB for period 2 is 10 units while the forecast for period 2 is 30 units. There is a projected shortfall of 20 units of inventory in period 2.
When you encounter negative PAB numbers, what should be done?
Preliminary MPS 初步的MPS
The first step in creating a master schedule and MPS, or the bottom row in the master scheduling grid in this case, is to develop a preliminary MPS for all end items during the six-period master schedule.
The procedure for calculating the MPS receipt for a single period is as follows:
Determine if the projected end of period PAB is negative or positive:
Ending PAB = beginning PAB + scheduled MPS receipt - forecast
If it's negative, schedule the MPS receipt according to lot-size policy.
Recalculate the PAB for the period using the formula above.
Planning Horizon 计划展望期
Visual 3-48 illustrates the product structure of end item A. It shows the lead time in weeks for each step of the assembly process, plus the time required to acquire and receive purchase components.
What is the longest cumulative lead time in weeks in this example?
The number of weeks in the cumulative lead time represents the time required to place and order for and receive the lowest-level component, E, assemble D, and assemble the end item,A. The longest cumulative lead time in the product structure is important because it determines the minimum planning horizon for the item's MPS.
Note, however, that by convention, the receipt of a component or end item is due at the very beginning of the period after the end of the lead time period. In other words, "due" means being available for the next operation or for delivery to the customer on the first day of the next period.
In this example, what is the minimum planning horizon in weeks?
Actually, companies will add one or more periods to the planning horizon on top of the cumulative lead time. This gives better visibility in their application software to demand and supply issues just beyond the cumulative lead time that might affect the validity of the MPS.
Final Assembly Schedule 总装计划
The example of the planning horizon above applies mainly to MTS production environments that we introduced in Session 1. The MPS is for the end time that is sold to customers.
In a typical assemble-to-order environment, however, separate MPSs are developed and maintained for the MTS components. A final assembly schedule is used for the assembly or configuration of the end item -- of which there might be numerous options -- when the customer order arrives.
An example would be coverings, or paints, which consist of a base color -- of which there are several -- in different volumes or container sizes to which various tints are added to achieve the final color. All of these are made to stock and sit on the paint store shelf until final assembly, when base and tints are mixed to complete the actual customer order. This model also could apply in a factory where large custom orders from distributors and commercial contractors are fulfilled.
Time Fences and Zones 时栅和区域
Time fences and zones are used to manage the master schedule and to deal with changes that occur in customer demand and internal priorities, and problems that arise from supplier delays, machine breakdowns, or higher-than-expected scrap rates. A detailed discussion of time fences and zones would go beyond the basics of master scheduling taught in this course. Here are some important points to consider.
Liquid zone: Beyond the planning time fence, changes to the MPS for the manufacture or purchase of components are easy to make as long as they are consistent with the production plan. Demand at this time usually consists mainly of forecasts and not actual orders. Planning software often will make routine changes. The planning horizon for master scheduling must extend beyond the planning time fence.
Slushy zone: Between the demand time fence and the planning time fence, priorities are not as easy to change as in the liquid zone. Demand consists of orders and forecasts, so tradeoffs are possible -- unlike in the frozen zone. Materials have been ordered and some capacity might have been allocated to the assembly of low-level components. Planning software will not make the changes.
Frozen zone: Inside the demand time fence, demand is based on customer orders, and capacity and materials have been committed to specific orders. Changes would have ripple effects and cause other orders to be late. Approval to change requires senior management approval. Extra costs will be incurred to reroute, reschedule, and perform additional setups.
Aggregating the Master Schedules 聚合主排程
We mentioned earlier that the there are four steps in developing a master schedule. We have reviewed the first step, creating a preliminary master schedule for individual end items.
The second step requires the aggregation of MPSs -- as in the six-week planning period shown in Visual 3-51. Aggregation is needed only if the products use the same resources and take the same amount of time. This provides the total order quantity for all items in each week. This information then can be used in RCCP to determine if production resources will be adequate during the planning period.
Rough-Cut Capacity Planning 粗能力计划
RCCP is the third step in the master scheduling process. It is the second check on the availability of critical resources in the MPC process. The first check is called resource planning, which should have validated the production plan at an earlier date. Resource planning was covered earlier in this session.
The major differences between resource planning and RCCP can be summarized as follows:
|Resource Planning||Rough-cut capacity planning|
|Validates and plans resource availability for the production plan and for the business plan
|Validates resource availability for the MPS
|Based on the quantity of a resource required to make one average unit of a product family
|Based on the quantity of a resource required to make one unit of the specific models or types of end items in a product family
Resolving Differences and Publishing the MPS 解决差异并发布MPS
The fourth step in developing an MPS is to resolve any differences between the end-item priority plan and available capacity. Available capacity must be equal to or greater than required capacity.
If required capacity exceeds available capacity
- the capacity must be increased, or 必须增加产能，或
- the plan must be altered. 计划必须修改。
Once capacity issues are resolved, the MPS summary establishes the gross requirements for MRP of component, which we will cover in Session 4.
How can capacity be increased or demand be decreased?
Master Scheduling and Sales 主排程与销售
It is important to understand the relationship between manufacturing, sales, and the MPS. Here are some important points to consider:
The MPS is manufacturing's anticipated build schedule for end items.
It is based on end-item demand forecasts and customer orders provided by sales.
The master scheduler relies on the production plan to make sure that the priority plan -- including end-item quantities and due dates -- established by the MPS is realistic and achievable, and that materials and operational resources will be available and sufficient.
Manufacturing does not build directly to the forecast; the MPS factors in available inventory and safety stock requirements.
The master schedule, of which the MPS is a major component, must be flexible enough to accommodate changes in demand, production delays, and material shortages.
MPS and Delivery Promises MPS和交付承诺
In the management of real customer orders, the interests of manufacturing and sales again intersect in the master schedule. Customers are placing orders for both
items that are in stock 库存商品
items that are in production or are planned. 正在生产或计划的商品。
The MPS is the basis for making delivery promises.
In this short section, we will address the basics of the ATP process.
available-to-promise (ATP) -- The uncommitted portion of a company's inventory and planned production, maintained in the master schedule to support customer order promising. The ATP quantity is the uncommitted inventory balance in the first period and is normally calculated for each period in which an MPS receipt is scheduled.
-- APICS Dictionary
Sales, customer service, and distribution use the master schedule to determine the ATP.
Visual 3-57 demonstrates a basic approach to ATP for a specific end item.
It is period 1, at the start of business on the fist day.
Customer orders on hand are as shown in the Visual 3-57.
MPS receipts have been scheduled by the master scheduler.
Use inventory on hand (200 units) to determine what is uncommitted or ATP in the current plan period of period 1.
Calculate ATP for each period in which an MPS receipt has been scheduled.
Assume in your calculation that the entire ATP will be sold before the next scheduled receipt.
When calculating ATP, subtract all orders until the next scheduled receipt.
ATP for period 1 = On hand + MPS scheduled receipt in period 1 - customer orders due before next MPS scheduled receipt
1期的ATP = 在手库存 + 1期的MPS计划接收 - 客户订单在下一个MPS计划接收之前到期
ATP for period 2, 4, and 6 (periods with MPS scheduled receipts) = MPS scheduled receipt - customer orders due before next MPS scheduled receipt
第2、4和6期的ATP(有MPS计划接收的时期) = MPS计划接收 - 客户订单在下一个MPS计划接收之前到期
With the instructor, work through the solution.
How many uncommitted units are expected to be promised to orders in week 1, and later in weeks 4 and 5?