Chapter 6 Production Activity Control

 

NITIE, Mumbai Chap 6: Production Production Activity Control

Dipak Ramchandra utar

 

Chapter 6 Production Activity Control Introduction •

 

Production activity control (PAC) is responsible for executing the master production schedule and

the material requirements plan. At the same time, it must make good use of labor and machines, minimize work-in-process inventory, inventory, and maintain customer service.

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The material requirements plan authorizes A!" to release work orders to the shop for manufacturing, to take control of work orders and make sure they are completed on time, to be responsible for the immediate detailed planning of the flow of orders through manufacturing, and to manage day-to-day activity and provide the necessary support. support. The activities of the  A! A! system system can be classified into  planning, implementation, implementation, and control functions. functions.

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The flow of work through each work center must be planned. A A! ! must ensure that the required resources are available to manufacture the components as needed and develop a load profile for each work center to ensure the timely completion of orders by the scheduled date.

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 #ext we implement the plan. A! A! will gather the information needed by the shop floor to make the product and release orders to the shop floor as authorized by the material requirements plan (dispatching) .

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$onitor the process and determine the necessary corrective action. A! A! will rank the shop orders in desired priority sequence by work center cen ter and establish a dispatch list, track actual  performance to plan and take corrective action by replanning, rescheduling, or ad%usting capacity to meet delivery.

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&nderstand the characteristics and differences between flow, intermittent  and project  manufacturing.

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Data Reuirements •

 

To plan the processing of materials through manufacturing, A! must have the following information" 'hat 'hat and how much much to produce. 'hen parts are needed so the completion completion date can be met. 'hat operations are required to make the product and how long the operations operations will take. 'hat the available capacities of the various work centers are.

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A! A ! must have data, usually stored in databases, to drive the informatio information n systems. These database files are of two types, planning and control.

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The four planning files needed are the item master file, product structure fil e (!ill of material file), contains tains all of the pertinent pertinent data related to routing file and wor" center file. The item master file con each part number. The product structure or ()$ file contains single-level single-level ()$*s listing listing components and quantities quantities needed to assemble assemble a parent. +t forms a basis for a #pic" list$% A routing exists for each part number and consists of a series of operations and instructions required to make the item. The work center master master file collects relevant data data on a work center. center.

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The two control files are the shop order master file  and the shop order detail file. ach active manufacturing order has a record in the shop order master file to monitor production performance for each shop order. The shop order detail file contains the perform performance ance record for each operation.

&rder Preparation  

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)nce authorization to process an order has been received, A! A! is responsible for planning and  preparing its release to the the shop floor. The order should be reviewed to be sure that the the necessary resources are available. $aterial and capacity availability availability must must be checked. checked. !hecking capacity capacity availability is a two-step process. process. irst, the order must be scheduled to see when the capacity is needed, and second, the load on work centers must be checked in that period.

'cheduling •

 

The ob%ective of scheduling is to meet delivery dates and to make the best use of manufacturing resources. +t involves establishing establishing start and finish dates for each operation required to complete an

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item. To develop a reliable schedule, the planner must have inform information ation on routing, required and available capacity, capacity, competing %obs, and manufacturing lead times at each work center involved.

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anufacturing leadtime is the time normally required to produce an item in a typical lot quantity

and consists of five elements queue, setup, run and wait. The largest of the five elements is queue time. A! A! is responsible for managing the queue by regulating the flow of work into and out out of work  centers. A! A! must manage both the input of orders to the production process and the available available capacity to control queue and work-in-process.

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Cycle time (throughput time) is the length of time from when material enters a production facility

or operation until it exits.

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*orward scheduling assumes that material procurement and operation scheduling for a component

start when the order is received, whatever the due date, and that operations are scheduled forward from this date. The result is completion before the due date date,, which usually results in a buildup of inventory. •

 

+ac"ward scheduling schedules the last operation on the routing first and is scheduled for

completion at the due date. date. revious operations are scheduled back from the the last operation.

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Infinite loading assumes infinite capacity will be available.

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*inite loading assumes there is a defined limit to available capacity at any workstation.

 

 

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+n operation overlapping, the next operation is allowed to begin before the entire lot is completed on the previous operation. This reduces the total manufacturing manufacturing lead times because the second operation starts before the first operation finishes finishes all the parts in the order. +ncreased costs are  possible from move costs and the impact of queue and lead-time for other orders.

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&peration splitting is the process of splitting orders into two or more lots and run simultaneously on

two or more machines.

,oad ,eveling

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The load profile for a work center is constructed by calculating the standard hours of operation for each order in each time period and adding them together by time period.

'cheduling +ottlenec"s •

 

+ottlenec"s are overloaded workstations where the required capacity is greater than the available

capacity.. +t is a facility, function, capacity function, department, or resource whose capacity is equal to or less than the demand placed upon it.

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through a facility. facility. (ottlenecks control the -hroughput is the total volume of production passing through throughput of all products.

-heory of Constraints and Drum+ufferRope •

 

The fundamental concept behind -heory of Constraints, developed by .liyahu % /oldratt, is that every operation producing producing a product or service is a series of linked process processes. es. ach process has a specific capacity to produce the given defined output for the operation, and that in virtually every case, there is one process that limits or constrains bottleneck/ the throughput from the entire operation. ocus on balancing balancing the flow through the shop. shop. The time lost at a nonconstraint nonconstraint is a mirage, and transfer batches do not have to be the same size as process batches.

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)nce constraint has been identified, there is a five-step process that is recommended to help improve the performance of the operation. The five steps are" 0/ identify the constrain constraint, t, 1/ exploit the constraint, 2/ subordinate everything to the constraint, 3/ elevate the constraint, 4/ once the constraint is a constraint no longer, find the new one and repeat the steps.

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The scheduling system for Theory of !onstraints is described as Drum+ufferRope. The drum of the system refers to the 5drumbeat6 5drumbeat6 or pace of production production.. +t represents the master master schedule for the operation, which is focused around the pace of throughput throughput as defined by the constraint. 7ince it is so important that the constraint never be 5starved6 for needed inventory, a 5time6 buffer is often established in front of the constraint. +t is called a time buffer because it represents the amount of time that the inventory in the buffer protects the constraint constraint from disruption. The analogy is that the rope 5pulls6 production production to the constraint for necessary processing. processing. The primary focus of the

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scheduling system is on effective management of the organization*s constrain constraintt to throughput and sales.

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)rders that do not have all of the necessary resources, tooling, material, and capacity, should not be released because they only cause excess work-in-process inventory and may interrupt work on orders that can be completed.

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A shop pac"et accompanies a shop order order release to manufacturing. This packet m may ay include the shop order, engineering drawings, bills of material, routing r outing sheets, materials issue tickets or pick list, tool requisitions, %ob tickets for each operation to be performed, and move tickets that authorize movement of work between operations.

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)nce work orders have been issued to manufacturing, manufacturing, their progress has to be controlled. To control  progress, performance has to be measured measured and compared to what is planned. +f what is actually happening what is measured/ varies significantly from what was planned, either the plans have to be changed or corrective action must be taken to bring performance back to plan.

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A! A ! must balance the flow of work to and from different work centers. This is to ensure queue, work-in-process, and lead times are controlled. The input0output control system is designed to  balance the input rate in hours hours with the output output rate. The input rate is controlled controlled by the release release of orders to the shop floor. The output rate is controlled by in increasing creasing or decreasing the capacity of a work center.

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To control control input and output, a plan must be devised along with a method for comparing what actually occurs against what was was planned. This information information is shown on an input0output report% Cumulative variance is the difference between the total planned for a given period and the actual

total for that period (Cumulative variance 1 previous cumulative variance 2 actual 3 planned)%   lanned and actual inputs monitor the flow of work coming coming to the work center. lanned and actual outputs monitor the performance performance of the work center. lanned and actual backlogs monito monitorr the queue and lead-time performance.

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&peration seuencing is a technique for short-term planning of actual %obs to be run in each work

center based on capacity and priorities. priorities. !ontrol of priorities is exercised through dispatching. dispatching. Dispatching is the function of selecting and sequencing available %obs to be run at individual work

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centers. The dispatch list is the instrument of priority control. +t*s a list listing ing by operation of all the  %obs available to be run at a work center with the %o %ob b listed in priority sequence.

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The ranking of %obs for for the dispatch list is created created through the appl application ication of priority ru rules. les. 7ome commonly used rules are" 0/ first come, first served !7/, 1/ earliest %ob due date 88/, 2/ earliest operation due date )88/, 3/ shortest process time 7T/, and 4/ critical ratio !9 : due date ; present date/ < lead time remaining/.

Reference •

4% Introduction Introduction to aterial management5 management5 ifth dition =. 9. Tony Arnold, 7tephen #.

!hapman, !hapma n,

9.>. 9amakrishnan 9amakri shnan

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