[completed] 5과 Capacity Management

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Introduction

without the resource to achieve the priority plan, the plan will be unworkable. capacity management is concerned with supplying the necessary resources. this chapter looks more closely at the question of capacity: what it is, howmuch is available, how much is required, and how to balance priority and capacity.

Defination of Capacity

• capacity
  • is the amount of work that can be done in a specified time period. defines as 'the capability of a worker, machine, work center, plant or organization to produce output per time period.'capacity is  a rate of doing work, not the quantity of  work done.
  • there are two kinds of capacity - capacity available, capacity required
    • capacity available
      • is the capacity of a system of resource to product a quantity of output in agiven time period.
    • capacity required
      • is the capacity of a system or resource needed to produce a desired output in a given time period.
    • load 
      •  is the amout of released and planned work assigned to a facility for a particular time period. is the sum of all the required capacities.
• capacity management
  • is responsible for determining the capacity needed to achieve the priority plans as well as providing, monitoring and controlling that capacity so the priority plan can be met.
  • defines as 'the function of establishing, measuring, monitoring, and adjusting limits or levels of capacity in order to execute all manufacturing schedule.
• capacity planning
  • is the process of determining the resources requires to meet the priority plan and the methods needed to make that capacity available.
  • it takes place at each level of the priority palnning process.
  • capacity plannng links the various production priority schedules to manuufacturing resources.
• capacity control
  • is the process of monitoring production output, comparing it with capacity plan, and taking corrective action when needed.

Capacity Planning

involves calculating the capacity needed to achieve the priority plan and finding ways of making that capacity available.

the priority plan must then be translated into hours of work required and compared to the hours available.

the process of capacity planning is as follows:

• determine the capacity avalable at each work center in each time period
• determine the load at each work center in each time period
  • translate the priority plan into the hours of work requred at each work center in each time period
  • sum up the capacities required for each item on each work center to determine the load on each work center in each time period
• resolve diffrenced between available capacity and required capacity. if possible, adjust available capacity to match the load. otherwise, the priority plans must be changed to match the available capacity.

Capacity Requirements Planning

Resource plannng

• involves long-range capacity resource requirements and is directly linked to production planning.
• typically it involves translating monthly, quaterly, or annual product priorities form the production plan into some total measure of capacity ,such as gross labor hour.
• involves changes in staffing, capital equipment, product design or other facility changes that take a long tiem to acquire and eliminate.

Rough-cut capacity planning(RCCP)

• take capacity planning to the next level of detail.
• the master production schedule is the primary information source for RCCP.
• the purpose of rought- cut capacity planning is to check the feasibility of the MPS, provide warnings of any bottelenecks, ensure utilization of work centers, and advise vendors of capacity requirements.

Capacity requirements planning(CRP)

• is capacity planning at a more detailed level and is directly linked to the material requirements plan.
• is concerned with individual orders at individual work centers and calculates work center loads and labor requirements fpr each tiem period ar each work center.
• noted that although the upper levels of priority planning are input to lower level, the various capcity plans related only to their level in the priority plan, not to subsquent capacicty planning levels.

Capacity requirements planning(CRP)

occurs at the level of the material requirements plan(MRP)

It is the process of determining in detail the amount of labor and machine resources needed to achieve the required production.

planned order from the mrp and open shop order(scheduled receipts) are converted into demand for tiem in each work center in each time period.

this process takes into consideration the lead times for operations and offsets the operations ar wrok centers accordingly.

 

inputs 

the inputs needed for CRP  are open shop order(scheduled receipts), plaaned orders, routing, time standards, lead times, and work center capacities.

this information can be obtained from the following data:

• open orders
  • appears as a scheduled recieipt on the material requirements plan.
  • it is a released order for a quantity of a part to be manufactures and completed on a specific date.
  • shows all relevant information such as quantities, due date, and operations.
• planned order releases
  • are determined by the MRP logic based upon the gross requirements for a particular part.
  • they are inpurts to the CRP process in assessing the total capacity required in future time periods.
• routings
  • is the parth that work follows from worck center to work center as it is completed.
  • routing data should exist for every component manufactured and contain the following information:
    • operation to be performed
    • sequence of operations
    • work centers to be used
    • possible alternate work centers
    • tooling needed at each operation
    • standard times : set up times and run times per piece.
• work centers
  •  is comprised of a number of machines or workers capable fo ding the same work.
  • work center data contains information on the capacity and movem wait, and queue tiems associated with the center
    • move time
      • is the time normally taken to move materials from one work station to another
    • wait time
      • is the time a job is at a work center after completion and before being moved.
    • queue time
      • is the time a job waits at a work center before being processed.
    • lead time
      • is the sum of ques, setup, run,wait, and move times. 
• shop calendar
  • another piece of information needed is the number of working days available at a work center.

Capacity Available

is the capacity of a system or resource to produce a quantity of outpue in a given period. it is affected by the followings:

• product specifications
  • If the pdocut specification change, the process and time required to make the product may change, thus affecting the number of units that can be produced in a given time period.
• product mix
  • each products has its own set of processes and time requirements in what it takes to make the product. if the mix of products being produced changes, the total time, or capacity requited for the mix may change.
  • plant and equipment
    • relates to the methods used to make the product. if the method is changed, the rate of output may change
  • work effort
    • relateds to the spedd or pace at which the work is done.
• measuring capacity
  • units of output
    • if the variety of products produced at a work center or in a plant is not large, it is often possible to use a unit common to all products.
    • however, if a variety of peoducts is made, a good common unit may not exist. in this case, the unit common to all products to all products is time.
  • standard time
    • the work required to make a product is expressed as the time required to make the product using a given method of manufacture.
    • using time study techniques, the standard time ( = standard hours) for a job can be determined, that is the time it would take an average qualified operator working at a normal pace to do the job.
• levels of capacity
  • capacity is uaually measured on at least three levels:
    • machine or individual worker.
    • work center, production line of cell.
    • plant , which can be considered as a group of multiple work centers.
• determining capacity available - the factor of available time, utilization and efficiency are used to determine the three types of capacity(theoretical;calculated or rated; and demonstrated or measured)
  
  • available time
    • is the number of hours a work center can be used.
    • depends on the number of machines, the number of workers, and the hours of operation.
  • utilization
    • the available tiem is the maximum hours one can expect from the work center. but it is unlikey this will be attained all the time.
    • the percentage of time that the work center is active compared to the available tiem is called work center utilization
  • efficiency
    • it is possible for a work center to utilize 100 hours a week but not produce 100 standard hours of work.
    • efficiency measures the output as compared to the standard.
  • productivity
    • defines as the overall measure of the ability to produce a good or service. 
    • it compares the actual output of production to the actual input of all reqources, incorporating the utilization of the time available and the efficiency during that time.
    • theoretical capacity
      • is the maximum capacity available, with no regard for down time, utilization or efficiency.
  • rated capacity
    • the available capacity at a work center for a period of time, and accounnting for the average utilization and efficiency of that work center is known as calculated or rated capacity.
• demonstrated capacity
  • the historical output or capacity of a work center is known as demonstrated or measured capacity.
  • this type of capacity examines the previous production records and uses that information as the available capacity of the work center.
  • this is determined in part by the actual load input to the work center, and is not necessarily reflective of what the work center is capable of producing.
  • noted that demonstrated capacity is average, not maximum, output. 
  • it also depends on the utilization and efficiency of the work center, although these are not included in the calculation, as they would already have been taken into account in the production records used in the calculation
    • safety capacity
      • one other type of capacity
      • is available capacity that is planned to excedd capacity required.
      • also referred to as a capacity cushion, and can be used as an alternative to safety stock.

Capacity Required (Load)

determining the capacity required is a two-step process.

first, the time needed for each order at each work center is determined

second, the capacity required for individucal order to obtain the load is totaled.

• time needed for each order
  • is the sum of the setup time and  the run time.
  • the run time is equal to the run time per piece multiplied by the number of peces in the order.
• load
  • the load on a workcenter is the sum of the required times for all the planned and actual oreder to be run on the workcenter in specified period.
  • the steps in calculating load are as follows: 
    • determine the standard hours of operation time for each planned and released order for each work center by time period.
    • add all the standard hours together for each work center in each period
    • the result is the total required capacity(load) on that work center for each time period of the plan.
• work center load report
  • shows future capacity requirements based on released and planned orders for each time period of the plan.

Scheduling orders

most orders are processed across a number of work centers and it is necessary to calculate when orders must be started and completed on each work center so the final due date can be met.

this process is called scheduling.

defines a schedulas as 'timetalbe for planned occurrences'

back scheduling

the usual process is to start with the due date and using the elad times, to work back to find the start date for each operation. this process is called back schduling or backward scheduling.

to back schedule, the following must be known for each other. the back scheduling process starts with the last operation.

• quantity and due date
• sequence of operation and work centers needed.
• setup and runtimes for each operation
• queue, wait, and move times
• work center capacity available

the information needed is obtained from the followings:

• planned and open order : quantities and due dates
• routing : sequence of oeprations, work center needed, setup tiem, and runtime
• work center data: queue, move, and wait times and work center capacity

the process is as follows:

• for each work order, calculate the capacity required(time) at each work center.
• starting with the due date, schedule back to get the completion and start dates for each operatoin.

Making the plan

the next steps is to compare the load with available capacity to see if there are imbalances and if so, to find possible solutions.

there are two ways of balancing capacity available and load: alter the load or change the capacity available.

altering the load means shifting orders ahead or back so the load is leveled, which means that other components should be rescheduled and te master production schedule changed.

the result of capacity requirements planning should be a detailed workable plan that meets the priority objectives and provides the capacity to do so.

key term

Avaialbe Time

Back Scheduling

Backward Scheduling

Calculated capacity

capacity

capacity available

capacity control

capacity cushion

capacity management

capacity planning

capacity required

capacity requirements planning (CRP)

Demonstrated(measured) capacity

efficiency

lead time

load

load report

move time

open order

palnned orders

productivity

queue time

rated capacity

resource planning

rough-cut capacity planning (RCCP)

Routing

safety capcity

scheduling

shop calender

standard hours

srandard time

theoretical capacity

utilization

wait time

work center

 

Summary

capacity management occurs at all levels of the planning process.

capacity planning is concerned with translating the priority plan into the hours of capacity required in manufacturing to make the item in the priority plan and with methods of making that capacity abailable.

capacity available depends upon the number of workers and machines, their utilization, and efficiency.

capacity requirements planning occurs at the material requitements planning level. it takes open shop order and planned orders from the MRP and convers them to a load on each work center. it considers lead tiems and actual order quantities.