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Chapter 4 Process design Shenval. Alamy
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Process design Process design Operations strategy
Improvement Planning and control Process design Supply network design Layout and flow Process technology People, jobs and organization Product/ service design Operations management
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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?
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Nature and purpose of the design activity
Products, services and the processes which produce them all have to be designed. Decisions taken during the design of a product or service will have an impact on the decisions taken during the design of the process which produces those products or services and vice versa.
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The design of products/services and processes are interrelated and should be treated together
Products and services should be designed in such a way that they can be created effectively. Product/service design has an impact on the process design and vice versa. Processes should be designed so they can create all products and services which the operation is likely to introduce.
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The overlap of activities is greater in service design
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.
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The Smart car uses environmentally friendly design principles
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Process mapping symbols
Delay (a wait, e.g. for materials) Operation (an activity that directly adds value) Inspection (a check of some sort) Transport (a movement of something) Storage (deliberate storage, as opposed to a delay) Process mapping symbols derived from ‘Scientific Management’ Decision (exercising discretion) Process mapping symbols derived from Systems Analysis Direction of flow Input or Output from the process Activity Beginning or end of process
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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.
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Manufacturing process types
Process tasks Process flow Diverse/ complex Repeated/ divided Intermittent Continuous Project High Jobbing Batch Variety Mass Contin-uous Low Low Volume High
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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.
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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.
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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.
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Mass (line) processes Higher volumes than batch
Standard, repeat products (‘runners’) Low and/or narrow skills No set-ups, or almost instantaneous ones.
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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.
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Service process types Process tasks Process flow High
Diverse/ complex Repeated/ divided Intermittent Continuous High Professional service Service shop Variety Mass service Low Low Volume High
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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.
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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.
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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.
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Deviating from the ‘natural’ diagonal on the product–process matrix has consequences for cost and flexibility Project Jobbing Batch Mass Continuous Manufacturing operations process types Variety Volume Professional service Service shop Mass Service operations process types The ‘natural’ line of fit of process to volume/variety characteristics None More process flexibility than is needed so high cost Less process flexibility than is needed so high cost None 9
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Deviating from the ‘natural’ diagonal on the product–process matrix has consequences for cost and flexibility (Continued) Variety Volume None The ‘natural’ line of fit of process to volume/variety characteristics Old process Old process new product New process new product 9
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Standard sandwich process
Customized sandwich – old process Raw materials Stored sandwiches Move to outlets Stored sandwiches Take payment Assembly Customer request Sell Standard sandwich process
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Customized sandwich – old process (Continued)
Raw materials Take payment Customer request Assembly
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Higher level process map
The outline process of making and selling customized sandwiches Prepare Assemble as required Take payment The operation of making and selling customized sandwiches Sandwich materials and customers Customers ‘assembled’ to sandwiches Bread and base filling Stored ‘bases’ Fillings Assemble whole sandwich Customer request Use standard ‘base’? Assemble from standard ‘base’ No Yes The detailed process of assembling customized sandwiches
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Customized sandwich - new process
Assemble whole sandwich Assembly of ‘sandwich bases’ Customer request Use standard ‘base’? No Yes Take payment Fillings Bread and base filling Stored ‘bases’ Assemble from standard ‘base’
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Flow process charts for processing expense
Send to accounts receivable Reports to batch control Reports filed Confirm payment Report arrives Stamp and date report Send cash to receipt desk Wait for processing Check expenses report Check employee record Check advance payment Send to account payable Attach payment voucher Collect retorts into batch Check against rules Batch control number Check payment voucher Log report Batch to audit desk Wait for batching Batch of reports logged Copy of reports to filing Description of activity Totals 8 1 2 4 5 6 7 9 10 3 18 11 12 14 15 16 17 19 20 13 26 22 23 24 25 21 Payment voucher to keying Before Reports to batch control Reports filed Payment voucher to keying Confirm payment Report arrives Stamp and date report Check expenses report Wait for processing Check reports and vouchers Attach payment voucher Collect retorts into batch Batch control number Batch to audit desk Wait for batching Copy of reports to filing Description of activity Totals 8 1 2 4 5 6 7 9 10 3 11 12 14 15 13 After
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Throughput (TH) = Work In Process (WIP) x Cycle Time (CT)
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
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Throughput (TH) = Work In Process (WIP) x Cycle Time (CT)
Little’s law (a really quite useful law) (Continued) 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 × 7 hours = 35 hours 35 hours = 500 scripts × Cycle times Cycle time = hours 500 scripts = 0.07 hours Number of markers = Work content = 1 hour = Cycle time 0.07
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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 × 100
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Arrival frequency (demand)
X 5–15 mins Arrival frequency (demand) Processing time Utilization = <100% % Q = >0 Throughput time and capacity utilisation Arrival frequency (demand) X Utilization = 100 % Q = infinity 9 mins X Utilization = 50 % Q = 0 20 mins X 10 mins Utilization = 100 % Q = 0 30 mins 10 mins Processing time Utilization = % Q = 0 High High utilization but long throughput times Low utilization but short throughput times Reduce process variability Process throughput time (or inventory) Average length of queue X X Low X 20% 40% 60% 80% 100% Capacity utilization
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Process utilization, waiting time and variability
High utilization but long waiting time Average number of units waiting to be processed Decreasing variability Average number of units waiting to be processed Reduction in process variability X Short waiting time but low utilization Z Y 10 20 30 40 50 60 70 80 90 100 10 20 30 40 50 60 70 80 90 100 Utilization Utilization (a) Decreasing variability allows higher utilization without long waiting times. (b) Managing process capacity and/or variability.
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