Lecture 4 and 5: Forecasting and Scheduling

Question 1

Explain the manufacturing to order techniques

Answer 1

Engineer to order: product designed and built to customer order

Make to order: material ordered and product made only after order is recieved

Assemble to order: producer holds components to assemble an order required by customer

Make to stock: typical of commodities and continuous processing

Question 2

What are the different types of mass customisation?

Answer 2

Modular product design

Modular process design

Agile supply networks

Question 3

What are the different approaches to mass customisation?

Answer 3

• Collaborative: works with customers
• Adaptive: point of use
• Cosmetic: different presentation same product
• Transparent: customised without being aware

Question 4

What are the different forecasting methods?

Answer 4

• Qualitative (long term, years)
  
  • market surveys
  • problems: bias, ignorance
• Quantitative (short to medium term)
  
  • Extrinsic (based on external patterns)
    
    • Problem: will miss unual events
  • Intrinsic (based on patterns of data at first level)
    
    • Moving average, exponential smoothing
    • Problem: based exclusively on historical data

Question 5

Summary of ES

Answer 5

• It copes OK with step changes in demand
• Does not cope well with linear trends
• An adaption of simple ES can cope: double ES

Question 6

What are the general rules for forecasting accuracy?

Answer 6

1. The forecast is always wrong
2. The longer the horizon, the worse the forecast
3. The less aggregated, the worse the forecast

Question 7

What are the different objectives we might face in scheduling? What are their algorithms or heuristics?

Answer 7

• Minimising average completion time
  
  • put jobs with Shortest Processing Time earlier
• Minimising the maximum lateness
  
  • Put jobs in order of Earliest Due Date
• Minimise the average tardiness
  
  • Modified Due Date
• Minimise the number of Tardy Jobs
  
  • Moores Algorithm
• Minimise the makespan of 2 machines
  
  • Johnsons Rule

Question 8

What is an assembly line?

Answer 8

Consists of a sequence of operations such as fitting of components, assembling two parts together

Question 9

What is the takt time?

Answer 9

Available time per period / demand per period

Every X seconds a product is finished

Question 10

What is assembly line balancing?

Why important?

Answer 10

Technique of assigning work to individual stations so the variability across all stations in an assembly line is minimised

Minimise overload, waste (inventory, time), variation in output

Question 11

What are the two heuristic methods for assembly line balancing?

Answer 11

Longest sequential chain of followers

Total number of followers

Question 12

What is the Balancing loss?

Answer 12

Question 13

Explain “push” scheduling

Answer 13

• In a push system, the orders are planned and issued centrally
• Upon completion, the order is moved forward, until the next process is issued with the order to start processing it
• Hence, the longest time process sees the new order first
• This is called backward scheduling

Push systems schedule and issue orders centrally. MRP systems are computerised systems to support push scheduling

Question 14

Explain pull scheduling

Answer 14

• In a pull system, processes are triggered by a replenishment signal
• Upon withdrawal of material from inventory, the preceding process is authorised to start processing, and only then!
• Hence, the final process sees the new order first
• This is called forward scheduling

In a pull system, processes are triggered by a replenishment signal, such as the kanban cards in JIT scheduling