Chapters 13, 14 and 15

Question 1

How to deal with demand fluctuations?

Answer 1

There are two types of options to deal:

1) Demand-based options:
- Reactive: Using inventory
- Proactive: Managing the yield
2) Capacity-based options: Means changing output to meet the demand, as doing over/undertime hours, hiring/firing or subcontracting workers

Question 2

Which aggregate plans are there?

Answer 2

1) Level aggregate plan:
- Maintains constant workforce
- Labor and equipment is based on AVERAGE demand
2) Chase aggregate plan:
- Produces the amount needed on each PERIOD
- Labor and equipment is based on periods
3) Hybrid: Essentialy combines both

Question 3

What are the 5 steps to develop an aggregate plan?

Answer 3

1. Choose the type of plan (Level, chase…)
2. Determinate the aggregate production rate (AVG demand or PERIOD)
3. Determinate the workforce size
4. Calculate all required info (inventory, employees)
5. Evaluate the plan’s peformance

Question 4

What happens with the aggregate plans when you have intangible goods?

Answer 4

Building up inventory is not possible for nontangible products
→chase aggregate plan: no impact
→level aggregate plan: capacity of labor and equipment must allow to meet
peak demand to avoid lost sales

Question 5

What the MRP’s (Material Requirements Planning) do? And MPS’s?

Answer 5

They are systems that translate an approved MPS* (Master Production Schedule) of final products into time-phased net requirements for subassembles* to be manufactured and raw materials to be purchased.

• MPS sets the nº of products to be manufactured in each period
• Subassembles = Subconjuntos

Question 6

What’s a closed-loop MRP?

Answer 6

Is a MRP that also includes CRP* (Capacity Requirements Planning).

CRP = They ENSURE that the schedule is FEASIBLE

Question 7

What are the independent and dependent demands’ functions?

Answer 7

1) Independent demand
* Concerns finished products sold to a customer
* Needs to be FORECASTED

2) Dependent demand
* Concerns materials needed to make finished products
* Calculated based on independent demand
* E.g., tops, bottoms, feet, doors, door magnets, door hinges, etc.

Question 8

What are the 3 lot-sizing rules?

Answer 8

1) Fixed-order quantity (FOQ)
- Order a fixed quantity or a multiple of this quantity whenever needed (PA < 0)
2) Lot-for-lot (L4L)
- Order exactly what is needed for this period.
3) Period-order quantity (POQ)
- Order exactly what is needed for n periods

Question 9

What are the priority rules to grant a job?

Answer 9

• First come first served (FCFS): the job that arrived first in the work center
• Last come first served (LCFS): the job that arrived last in the work center
• Earliest due date (EDD): the job with the earliest due date, minimizes job tardiness
• Shortest processing time (SPT): the job with the smallest processing time. minimizes mean job lateness, mean job flow time and number of jobs in the system
• Longest processing time (LPT): the job with the longest processing time
• Critical ratio (CR): the job with the smallest ratio of time remaining until due date to its processing time remaining
• Slack per remaining operation (S/RO): the job with the smallest ratio slack per remaining operations

Question 10

How to measure scheduling effectiveness?

Answer 10

• Job flow time = completion time – time job was first available
• Makespan* = completion time of the last job – starting time of the first job
  → measures total time to finish a batch of jobs (efficiency)
• Average number of jobs in the system = sum of individual job flow times / makespan
  → relates to the size of the queues, work-in-process inventory, etc.
• Job lateness = completion time – due date
  → measures whether a job is completed early, on time or too late
• Job tardiness = max(0, completion time – due date)
  → measures how many days after the deadline a job is completed (due date performance)

(Makespan = Tiempo de terminacion)

Question 11

What’s the Johnson’s rule?

Answer 11

Johnson’s rule: sequencing jobs through 2 subsequent work centers
* All jobs go through two successive operations, but have different durations
* Objective: minimize makespan

Question 12

OPT (Optimized Production Technology)?

Answer 12

Optimized Production Technology (OPT) ➔ Bottleneck activities determine the Performance of the system:
▪ Bottleneck resources must be used to their full capacity
▪ Non-bottleneck resources must be scheduled to support bottleneck resources

(R/ Maximum throughput of system is 6 units per hour).
(Bottleneck= 15min per unit vs 6,5,7…)