4.1. Chapter 4. Process design 4.1

Transcription

1 4.1 Chapter 4 Process design 4.1

2 4.2 Key operations questions In Chapter 4 Process design Slack et al. identify the following key questions: What is process design? What objectives should process design have? How does volume and variety affect process design? How are processes designed in detail? 4.2

3 4.3 To design: design (v.) 1540s, from Latin designare "mark out, devise, choose, designate, appoint" from de- "out" (see de-) + signare "to mark," from signum "a mark, sign". Originally in English with the meaning attached to designate; many modern uses of design are metaphoric extensions. to form or conceive in the mind; to invent, to work out the structure or form of (something), as by making a sketch, outline, or pattern for a specific purpose; to mark out or designate the boundaries and functions of the system 4.3

4 4.4 Nature and purpose of the design activity Products, services and the processes which produce them all have to be designed. In manufacturing operations overlapping the activities of product and process design is beneficial. In most service operations the overlap between service and process design is implicit in the nature of service. Product/service design has an impact on the process design and vice versa. 4.4

5 4.5 The design of products/services and processes are interrelated and should be treated together The design of your operations is the mould where your planning is going to be based Products and services should be designed in such a way that they can be created effectively and efficiently. Effective = doing the right things (goals) Efficient = doing the right things in the right way (performance) 4.5

6 4.6 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 something) 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) 4.6

7 4.7 Designing processes A production process transforms resources into products/services (including the customer!) 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 in different volume and variety. 4.7

8 4.8 Process design Volume-variety and design The four V s of operations were volume, variety, variation and visibility. The first two usually go together (high variety usually means low volume, high volume normally means low variety). Volume and variety determine the way we design performance objectives - quality, speed, dependability, flexibility and cost X X X X 4.8

9 Low Variety High 4.9 Manufacturing process types Process tasks Process flow Diverse/ complex Intermittent Project Jobbing Batch Mass Repeated/ divided Continuous Low Volume Continuous High 4.9

10 4.10 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. 4.10

11 4.11 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. 4.11

12 4.12 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. 4.12

13 4.13 Mass (line) processes Higher volumes than batch Standard, repeat products ( runners ) Low and/or narrow skills No set-ups, or almost instantaneous ones. 4.13

14 4.14 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. 4.14

15 Low Variety High 4.15 Service process types Process tasks Process flow Diverse/ complex Intermittent Professional service Service shop Repeated/ divided Continuous Low Volume Mass service High 4.15

16 4.16 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. 4.16

17 4.17 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. 4.17

18 4.18 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. 4.18

19 4.19 Deviating from the natural diagonal on the product process 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 4.19

20 4.20 Customized sandwich old process Raw materials Assembly Stored sandwiches Move to outlets Stored sandwiches Sell Take payment Standard sandwich process Customer request 4.20

21 4.21 Higher level process map The operation of making and selling customized 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 customized sandwiches The detailed process of assembling customized sandwiches 4.21

22 4.22 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 4.22

23 4.23 Flow process charts for processing expense Description of activity Report arrives Wait for processing Check expenses report Stamp and date report Send cash to receipt desk Wait for processing Check advance payment Send to accounts receivable Wait for processing Check employee record Send to account payable Attach payment voucher Log report Check against rules Wait for batching Collect retorts into batch Batch to audit desk Wait for processing Batch of reports logged Check payment voucher Reports to batch control Batch control number 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

24 4.24 Performance objectives What do these mean for different products and services i.e. architects vs electricity company architects, the final aesthetic appearance of the building and the appropriateness of its detailed design. electricity supply company, quality is exclusively concerned with error-free service electricity must be constantly available in the correct form (in terms of voltage, frequency, etc.) Architects: Low economies of scale and high product variability make product more expensive to produce Electricity: High economies of scale and cost variability makes it less expensive to produce Quality Cost Speed For architects means negotiating a completion date with each client, based on the client s needs and the architects estimates of how much work is involved in each project. Speed in the electricity utility means literally instant delivery. No electricity company could ask its customers to wait for their delivery of electricity Flexibility Dependability For architects means keeping to each individually negotiated delivery date. In continuous operations, dependability often means the availability of the service. A dependable electricity supply is one which is always there. For architects means the ability to design many different kinds of buildings according to its clients various requirements. With the electricity company s process, the need for product flexibility has disappeared entirely but the ability to meet almost instantaneous demand changes through volume flexibility is vital.

25 4.25 Performance objectives Quality The meaning of quality has shifted from being concerned primarily with the performance and specification of the product or service towards conformity to a predefined standard, as we move from low volume-high variety operations through to high volume-low variety operations. Speed Speed means an individually negotiated delivery time in low volume-high variety operations, but moves towards meaning instant delivery in some high volume-low variety operations. Dependability Dependability has moved from meaning on-time delivery in low volume-high variety operations to availability in high volume-low variety operations. Flexibility Flexibility has moved from meaning product flexibility in low volume-high variety operations to volume flexibility in high volume-low variety operations. Cost Cost, in terms of the unit cost per product or service, varies with both the volume of output of the operation and the variety of products or services it produces. When variety of products or services in low-volume operations is relatively high, running the operation will be expensive because of the flexible and high skill levels employed. Further, because the volume of output is relatively low, a few products or services are bearing the operation s high cost base. Also, and more significantly for the operation, the cost of each product or service is different. At the other end of the scale, high-volume operations usually produce similar products or services, output is high, so that whatever the base cost of the operation, it is shared among a high number of products or services. Cost per unit of output is therefore usually low for operations such as the electricity utility but, more significantly, the cost of producing one second of electricity is the same as the next second. Cost is relatively constant. 4.25

26 4.26 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 2 mins Throughput time = 20 mins 4.26

27 4.27 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

28 Process Average throughput length of queue time (or inventory) 4.28 Throughput time and capacity utilisation Arrival frequency Processing (demand) mins mins mins mins time time Utilization Utilization = <100% % %% Q = 0 infinity 0 >0 X High High utilization but long throughput times X Low Low utilization but short throughput times X X Reduce process variability 4.28 X X 0 20% 40% 60% 80% 100% Capacity utilization X

29 Average number of units waiting to be processed Average number of units waiting to be processed 4.29 Process utilization, waiting time and variability Decreasing variability 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. 4.29