Chapter 5. Process design

Transcription

1 Chapter 5 Process design

2 Slack et al s model of operations management Direct Product and service design Design Operations Management Deliver Develop Process design Location, layout and flow

3 Key operations questions In Chapter 5 Process design Slack et. al. identify the following key questions. What is process design? How does volume and variety affect process design? How are processes designed in detail? What are the human implications of process design

4 Process mapping symbols Process mapping symbols derived from Scientific Management Operation (an activity that directly adds value) Inspection (a check of some sort) Transport (a movement of some thing) Process mapping symbols derived from Systems Analysis Beginning or end of process Activity Input or Output from the process Delay (a wait, e.g. For materials) Storage ( deliberate storage, as opposed to a delay) Direction of flow Decision (exercising discretion)

5 Designing processes There are different process types Process types are defined by the volume and variety of items they process Process types go by different names depending on whether they produce products or services

6 Manufacturing process types Process tasks Process flow Diverse/ complex Intermittent High Project Jobbing Variety Batch Mass Repeated/ divided Continuous Low Low Volume Continuous High

7 Project Processes One-off, complex, large scale, high work content products Specially-made, every one customized Defined start and finish: time, quality and cost objectives Many different skills have to be coordinated

8 Jobbing Processes Very small quantities: one-offs, or only a few required Specially-made. High variety, low repetition. Strangers every one customized Skill requirements are usually very broad Skilled jobber, or team, complete whole product

9 Batch Processes Higher volumes and lower variety than for jobbing Standard products, repeating demand. But can make specials Specialized, narrower skills Set-ups (changeovers) at each stage of production

10 Mass (Line) Processes Higher volumes than batch Standard, repeat products ( runners ) Low and/or narrow skills No set-ups, or almost instantaneous ones

11 Continuous Processes Extremely high volumes and low variety: often single product Standard, repeat products ( runners ) Highly capital-intensive and automated Few changeovers required Difficult and expensive to start and stop the process

12 Service process types Process tasks Process flow Diverse/ complex Repeated/ divided Intermittent Continuous Low Variety High Professional service Service shop Mass service Low Volume High

13 Professional service High levels of customer (client) contact Clients spend a considerable time in the service process High levels of customization with service processes being highly adaptable Contact staff are given high levels of discretion in servicing customers. People-based rather than equipment-based

14 Service shops Medium levels of volumes of customers Medium, or mixed, levels of customer contact Medium, or mixed, levels of customization Medium, or mixed, levels of staff discretion

15 Mass service High levels of volumes of customers Low to medium levels of customer contact Low, or mixed, levels of customization Low, or mixed, levels of staff discretion

16 Deviating from the natural diagonal on the productprocess matrix has consequences for cost and flexibility Manufacturing operations process types Volume Variety Service operations process types Project Jobbing Batch Mass Continuous None Less process flexibility than is needed so high cost None More process flexibility than is needed so high cost Professional service Service Shop Mass service The natural line of fit of process to volume/variety characteristics

17 Deviating from the natural diagonal on the productprocess matrix has consequences for cost and flexibility Volume Variety Old process None Old process new product New process new product None The natural line of fit of process to volume/variety characteristics

18 Customized sandwich - old process Raw Materials Assembly Stored Sandwiches Move to Outlets Stored Sandwiches Sell Take Payment Standard sandwich process Customer Request

19 Customized sandwich - old process Raw Materials Assembly Take Payment Customer Request

20 Higher level process map The operation of making and selling customised sandwiches Sandwich materials and customers Prepare Assemble as required Take payment Customers assembled to sandwiches Use standard base? Customer Request Bread and Base filling No Yes Stored Bases Assemble whole sandwich Fillings Assemble from standard base The outline process of making and selling customised sandwiches The detailed process of assembling customised sandwiches

21 Customized sandwich - new process Assemble whole sandwich Assembly of sandwich bases Use standard base? No Take payment Fillings Bread and base filling Customer Request Yes Stored Bases Assemble from standard base

22 Flow process charts for processing expenses Description of activity Report arrives Wait for processing Check expenses report Stamp and date report Send cash to receipt desk Wait for processing 7 Check advance payment 8 9 Send to accounts receivable Wait for processing 10 Check employee record 11 Send to account payable 12 Attach payment voucher 13 Log report 14 Check against rules 15 Wait for batching 16 Collect retorts into batch 17 Batch to audit desk 18 Wait for processing 19 Batch of reports logged 20 Check payment voucher Reports to batch control Batch control number 23 Copy of reports to filing 24 Reports filed 25 Payment voucher to keying 26 Confirm payment Before Description of activity Report arrives Stamp and date report Check expenses report Attach payment voucher Wait for batching Collect retorts into batch Batch to audit desk Wait for processing Check reports and vouchers Reports to batch control Batch control number Copy of reports to filing Reports filed Payment voucher to keying Confirm payment After Totals Totals

23 Little s law (a really quite useful law) Throughput (TH) = Work In Process (WIP) x Cycle Time (CT) Cycle time = 2 mins WIP = 10 Throughput time =? Throughput time = 10 x 2 mins Throughput time = 20 mins

24 Little s law (a really quite useful law) Throughput (TH) = Work In Process (WIP) x Cycle Time (CT) Need to mark 500 exam scripts in 5 days (working 7 hours a day). Takes 1 hour to mark a script. How many markers are needed? Throughput time = 5 days x 7 hours = 35 hours 35 hours = 500 scripts x Cycle times Cycle time = 35 hours 500 scripts = 0.07 hours Number of markers = Work content = 1 hour = Cycle time 0.07

25 Throughput efficiency Throughput efficiency is the work content of whatever is being processed as a percentage of its throughput time Throughput efficiency = Work content Throughput time X 100

26 Balancing loss is that proportion of the time invested in processing the product or service which is not used productively An ideal balance where work is allocated equally between the stages Cycle time = 2.5 mins Work allocated to stage Load Stage

27 Balancing loss is that proportion of the time invested in processing the product or service which is not used productively But if work is not equally allocated, the cycle time will increase and balancing losses will occur Cycle time = 3.0 mins Work allocated to stage Idle time Load Stage

28 Long & thin versus short & fat arrangements A 60 minute task with a required cycle time of 15 minutes every 15 minutes every 15 minutes every 15 minutes 60

29 Arrival frequency (demand) mins mins Processing mins mins time time Utilization Utilization = <100% % %% Q = 0infinity 0>0 X High Process Average throughput length of queue time (or inventory) Low Low utilization but short throughput times High utilization but long throughput times X X X Reduce process variability X 0 20% 40% 60% 80% 100% Capacity Utilization X X

30 Process utilization, waiting time and variability Average number of units waiting to be processed Decreasing variability Average number of units waiting to be processed Short waiting time but low utilization Y High utilization but long waiting time Reduction in process variability Z X Utilization Utilization (a) Decreasing variability allows higher utilization without long waiting times (b) Managing process capacity and/or variability.