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

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.

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

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

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.

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

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.

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.

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

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.

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}

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.

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

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.

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

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

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.