1. Assembly Lines – Reliable Serial Systems
Active Learning
Module 1
Dr. César O. Malavé
Texas A&M University

2. Background Material
Modeling and Analysis of Manufacturing Systems by Ronald G. Askin , Charles R. Standridge, John Wiley & Sons, 1993, Chapter 2.
Manufacturing Systems Engineering by Stanley B. Gershwin, Prentice – Hall,1994, Chapter 2.
Any good manufacturing systems textbook which has detailed explanation on reliable serial systems.

3. Lecture Objectives
At the end of this module, the students should be able to
Explain the fundamentals of assembly lines.
Explain the basics of problem formulation of
line – balancing problems.
Formulate the problem and solve them

4. Time Management 3 Assignment 15 Problem Formulation 5 Team Exercise
50 Mins
Total Time
Spot Exercise 12
Assembly Lines - Introduction
Readiness Assessment Test (RAT)
Introduction

5. Readiness Assessment Test (RAT)
Assume that there is a proposal for developing new car. Enumerate the various and basic stages in the development of this new product.
At the end, each team should turn in the solutions and the instructor may ask a group to discuss with the class.

6. RAT – Solution Customers Product Features Functions Product Design
Part
Design
Process
Planning
Fabricate
Assemble

7. Introduction
Assembly Line – Set of sequential workstations, connected by a continuous material handling system.
Each Assembly activity divided into productive work elements, adds value to product.
Group of such elements are assigned to each workstation.
Assembly Lines rely on Principle of Interchangeability and Division of Labor.
Principle of Interchangeability – Individual Components that make up the final product must be interchangeable
Division of Labor – Work Simplification, Standardization and Specialization.

8. Introduction – Cont… Advantages of Assembly Lines
Ability to keep direct labor or machines busy doing work
Minimal setup requirements as products are repeated.
Less space required, lower inventory costs and shorter throughput time.
Many items don’t justify assembly lines. So Mixed lines are used.
Mixed Lines – Several products on the line in different workstations at the same time.
Single or Multiple Assembly Lines depends on various factors like economics, labor psychology etc.

9. Spot Exercise
Discuss the advantages & disadvantages of multiple parallel lines
Advantages
Disadvantages
Easier to balance work load between stations
Higher setup costs
Increased scheduling flexibility
Higher equipment costs
Job enrichment
Higher skill requirements
Work Independence
Slower Learning
Increased accountability
More complex supervision

10. Introduction – Cont…
Use of buffers increase productivity and flexibility.
Buffers provide the “Cushion Effect” in production.
Paced Lines – Each workstation given same amount of time to operate on each unit of product.
Unpaced Lines – Each workstation removes a new unit from the material handling system as soon as it completes the previous unit.
Flexible Flow Lines – Product units routed thru workstations based on task requirements & input buffers. Also facilitates job enrichment & cycle time balancing.

11. Problem Formulation Objective is to minimize unit assembly cost.
Assembly Cost = Labor Cost + Idle Time Cost.
Assume
P  Production rate
M  Number of Parallel Lines
Cycle Time = m/p
No worker assigned with tasks exceeding the cycle time.
Set IP shows the ordering constraints
IP = {(u, v): task u must precede v}

12. Problem Formulation – Cont…
Zoning Restrictions – Which tasks must be and must not be assigned to the same workstation.
ZS  Set of tasks to be assigned
ZD  Set of tasks not to be assigned
Binary indicators used as decision variables
To minimize idle time, we try to force tasks into the lowest numbered stations.
Unused stations will be discarded.

13. Problem Formulation – Cont…
The formulation becomes
Constraint ensures that the sum of task times for the set of tasks assigned to each workstation doesn’t exceed the cycle time.
Constraint ensures that the task is assigned to exactly one station
Constraint forces the adherence to precedence restrictions
Zoning Constraint : Marriage Type
Zoning Constraint : Divorce Type

14. Problem Formulation – Cont…
Objective Function – Advantageous to fill up lower numbered stations before opening new station.
Let K*  Number of station (workers) required by the solution.
Balance Delay D, measure for comparing solutions, proportion of idle time.
Objective function fails to recognize a secondary objective of allocating the idle time equally to all the workstations.

15. Immediate Predecessor
Team Exercise
Develop a complete binary integer programming formulation for the line balancing problem. Let C = 100.
Task
Time
Immediate Predecessor a 40 - b 75 c 50 d 35 e 80

16. Team Exercise – Solution
Ci1 = 1; Ci2 = 20;
Ci3 = 400; Ci4 = 8000
We Choose K = 4 as a start since
 ti / C = 2.8
k = 1,…,4
Likewise for (a, c), (c, d) and (d, e)
All Xik 0 or 1

17. Assignment
A manufacturer of communications equipment is constructing a line to assemble several similar models of speaker phones. An industrial engineer had divided assembly of each model in to elemental tasks. Phones require about 30 operations. Task times vary from 5 to 36 seconds. Determine the appropriate cycle time if demand requires producing 750 phones per shift. Each shift has 8 productive hours.