Lecture 2 (3)

Question 1

Assembly line balancing

Answer 1

1. Specify the sequential relationships among tasks using a precedence diagram
2. Determine the required workstation cycle time

C = Production time per day/required outper per day (in units)

3. Determine the theoretical minimum number of workstations

Nt = Sum of task times (T)/ Cycle time (C)

4. Select a primary rule to assign task to workstations and a secondary rule to break ties
5. Assing tasks (one at a time) to the first workstation unitil no more tasks can be added (due to cycle time or sequencing constraints) Repeat for all subsequent workstations until all tasks are assigned
6. Evaluate the efficiency of the balance

Efficiency = Sum of task times (T)/ Actual number of workstations (Na) * Workstation cycle time (C)

7. If efficiency is unsatisfactory, rebalance using a different rule

Question 2

Workstation cycle time formula

Answer 2

C = production time per day/required output per day

The maximum duration a job takes for completion at each workstation

Question 3

Theoretical number of workstations Nt

Answer 3

Nt = sum of task times (T)/cycle time (C)

Question 4

Efficiency of the balance formula (assembly line balancing)

Answer 4

Efficiency = Sum of task times (T)/Actual number of workstations (Na) * WOrkstation cycle time (C)

Question 5

Primary rule of prioritizing tasks

Answer 5

Prioritize tasks based on the largest number of following tasks

Secondary rule: Prioritize tasks in order of longest task time

Question 6

Break-even analysis

Answer 6

A standard approach to choosing among alternative processes or equipment is a break even analysis

A break-even chart visually presents alternative profits and losses due to number of units produced or sold

The method is most suitable when processes and equipment entail a large initial investment and fixed cost, and when variable production costs are reasonably proportional to the number of units produced

Question 7

Break even analysis example

Answer 7

• A manufacturer is considering three options for obtaining a machined
  part
• Buy the part from a supplier for $200 per unit (no fixed cost)
• Purchase Cost = $200 × Demand
• Make the part on a semi-automatic lathe for $75 per unit
  (fixed costs of $80,000)
• Produce-using-lathe cost = $80,000 + $75 × Demand
• Make the part with a machining center for $15 per unit
  (fixed costs of $200,000)
• Produce-using-machining-center cost = $200,000 + $15 × Demand

Break even point A: Set totla cost for option 2 equal to total cost for option 3

Break point B: Set total cost for option 1 equal to total cost for option 2 and solve for D

Chart alternatives with break points: for this example: at break point A machine center becomes efficient

At break point B semiautomatic lathe becomes efficient