1. Chapter 2 – Manufacturing Operations
INSY Manufacturing Systems Design
2/27/2019
Chapter 2 – Manufacturing Operations
John L. Evans, Ph.D.
INSY 4700
2/27/2019
Assembly Systems
AU - Industrial and Systems Engineering

2. Introduction to Assembly Systems
INSY Manufacturing Systems Design
2/27/2019
Introduction to Assembly Systems
Definition of the term assembly
The aggregation of all processes by which various parts and sub-assemblies are built together to form a complete, geometrically designed assembly or product either by an individual, batch, or continuous process.
Assembly of manufactured goods accounts for:
over 50% of total production time,
20% of the total unit production cost, and
33%-50% of labor costs
2/27/2019
Assembly Systems
AU - Industrial and Systems Engineering

3. Types of Manufacturing Industries
Aerospace Apparel Automotive
Basic Metals Beverages Building Materials
Chemicals Computers Construction
Appliances Electronics Equipment
Fab Metals Food Glass
Machinery Paper Petroleum
Pharmaceuticals Plastics Power Utilities
Publishing Textiles Tire and Rubber
Wood Furniture
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Assembly Systems

4. Processing and Assembly Operations
Solidification Processes
Casting and Molding
Particulate Processing
Pressing Powers and Sintering
Deformation Processes
Forging, Extrusion, Rolling, Drawing, Forming, Bending
Material Removal
Turning, Drilling, Milling, Gringing
Material Finishing
Heat Treatment, Cleaning, Surface Treatment
Assembly Operations
Welding, Brazing, Soldering, Adhesive, Rivets, Press, Threaded Fastners
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Assembly Systems

5. Product Assembly
Virtually all end products go through some assembly process.
Approaches
Craftsman approach l
Output = l parts/unit time
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Assembly Systems

6. Product Assembly
Virtually all end products go through some assembly process.
Approaches
Craftsman approach l l l
Output = 3l parts/unit time
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Assembly Systems

7. Product Assembly
Virtually all end products go through some assembly process.
Approaches
Craftsman approach
Assembly line 3l l l l
Output = 3l parts/unit time
Output = 3l parts/unit time
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Assembly Systems

8. INSY 4700 - Manufacturing Systems Design
2/27/2019
Example 3l l n1 m1 m2 m3
l = 2 parts/hour
3l = 6 parts/hour (each)
n = 1/3l = 1/6 hour n2
l = 2 part/hour (each)
3l = 6 parts/hour
m = 1/l = 1/2 hour n3
Craftsman approach:
Craftsman  very little control over the cycletime.
Need a skilled craftsman for each additional station (increase in demand)
Line approach:
Relies on the principles of interchangeability and division of labor
Must be able to partition tasks – assumption here that n1=n2=n3
Assume m1=m2=m3=m
Assume n1=n2=n3=n
2/27/2019
Assembly Systems
AU - Industrial and Systems Engineering

9. INSY 4700 - Manufacturing Systems Design
2/27/2019
Assembly Line
Each part moves sequentially down the line, visiting each workstation.
Assembly (or inspection) tasks are performed at each station. 2 4 6 1 3 5
Tc is defined as the cycle time. At steady state, one unit is produced every Tc time units (i.e., TC = 1/required number of assemblies per unit time).
Paced lines vs. unpaced lines
Single product vs. mixed lines
Flexible flow lines
The line does not necessarily have to be straight – U-shaped or serpentine.
How do we determine the cycle time? The pace of the slowest station dictates.
General problems:
Partitioning of tasks
Assignment of tasks to stations
Buffer allocation (if we consider variability)
Part sequencing (for mixed lines)
2/27/2019
Assembly Systems
AU - Industrial and Systems Engineering

10. Assembly Line Balancing
INSY Manufacturing Systems Design
2/27/2019
Assembly Line Balancing
Assembly line balancing problems:
ALB-1 - Assign tasks to the minimum number of stations such that the workload assigned to each station does not exceed the cycle time, TC.
ALB-2 - Assign tasks to a fixed number of stations such that the cycle time, TC, is minimized.
An assembly consists of a set of tasks.
Task precedence relationships
Precedence relationships are described by a graph G = (N, A) where njÎN represents task j, and aijÎA indicates that task i is an immediate predecessor of task j.
For ALB-1, the required cycle time can be determined base on the demand. For example,
Weekly demand: 3000 units
5 days, 1 shift/day, 8 hrs/shift  40 hrs/week
40 hrs/week / 3000 units/week = hrs/unit = 48 seconds/unit
 Cycletime <= 48 seconds
ALB-2 – assume that you already have a line configured or that you have a fixed number of stations.
2/27/2019
Assembly Systems
AU - Industrial and Systems Engineering

11. Production Concepts and Models
Production Rates
TC= TO + Th + Tth
Where TC = Operation Cycle Time
TO = Time of Actual Processing
Th = Handling Time
Tth = Tool Handling Time
For total batch processing time
Tb = Tsu + QTc
Where Q = Batch Quantity
Tsu = Total Setup Time
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Assembly Systems

12. Production Concepts and Models (2)
The Average Production Time for a Part (Batch)
Tp = Tb/Q
The Average Production Rate (pc/hr)
Rp = 60/Tp
For Job Shop Production
Tp= Tsu + Tc
For Mass Production – Q is very large making
Rp ~ = Rc = 60/Tc
Where Rc =Operation Rate of the Machine
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Assembly Systems

13. Production Concepts and Models (3)
For Multiple Stations Dividing work evenly is not realistic
Bottleneck Station is the “Gating” or limiting operation
Tc = Tr + Max To
Where Tr = time to transfer work between stations
Max To = operation time at bottleneck operation
Therefore the theoretical production rate is approximately
Rc = 60/Tc
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Assembly Systems

14. Production Concepts and Models (4)
Production Capacity is defined as
PC = nSHRp
Where n = number of work stations
S = number of shifts per period
H = hr/shift
Rp= hourly production rate of each center
Utilization is defined as
U = Q/PC
Availability is defined as
A = (MTBF – MTTR)/MTBF
Where MTBF is mean time between failure (hr)
MTTR is mean time to repair (hr)
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Assembly Systems

15. Manufacturing Lead Time
The Lead Time for Manufacturing a Product Through the Entire Operation is defined as
MLTj = Sum of (Tsuij + QiTcji + Tnoji) i = 1 to oj
Where Tsuji = Setup Time for Operation i
Qj = Quantity of product j
Tcji = Operation cycle time for operation i
Tnoji = Nonoperation time with operation i
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Assembly Systems

16. Manufacturing Lead Time
Lead Time for Job Shop – Q = 1
MLT = no(Tsu + Tc + Tno)
Lead Time in Mass Production
MLT = no(Tr + Max To) = noTc
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Assembly Systems

17. Work-in-Process
Work-in-Process is the quantity of products currently in the process of production
WIP = [ AU(PC)(MLT)] / SH
Where A is Availability
U is Utilization
PC is Production Capacity
MLT is Manufacturing Lead Time
S is number of Shifts per Week
H is the number of Hours per Shift
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Assembly Systems

18. Costs of Manufacturing
Fixed and Variable Costs
TC = FC + VC (Q)
Where TC is the Total Cost
FC is the Total Fixed Cost
VC is the Variable Cost per unit
Q is the Quantity
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Assembly Systems

19. Manufacturing Analysis
Evaluate or Optimize
Minimize Throughput Time
Minimize Labor
Minimize Capital Investment
Maximize Capacity
Minimize Operational Cost
Minimize Cost Per Unit
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Assembly Systems

20. Types of Analysis Problems
Capacity of Process Time
Analyze Lead Time to Production
“Optimize” Process Steps or Sequence
Evaluate WIP
Evaluate Cost of Operation
“Optimize” Capital Investment
Minimize Travel Time
Minimize Floorspace
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Assembly Systems

21. Example Problem a b c d e
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Assembly Systems

22. Assembly Line Balancing
INSY Manufacturing Systems Design
2/27/2019
Assembly Line Balancing
Problem (ALB-1): Assign tasks to workstations
Objective: Minimize assembly cost
f(labor cost while performing tasks, idle time cost)
Constraints:
Total time for all tasks assigned to a workstation can not exceed C.
Precedence constraints between individual tasks.
Zoning constraints
Same workstation
Different workstation
Zoning constraints:
Same workstations – specialized equipment, timing considerations, raw material usage, etc.
Different workstations – safety, equipment conflicts, personnel (skill) concerns, etc.
2/27/2019
Assembly Systems
AU - Industrial and Systems Engineering

23. Parameters / Inputs Parameters / Inputs P parts/unit time are required
m parallel lines are to be designed (usually 1)
C = m/P is the required cycle time
ti is the assembly time required by task i, i = 1,…,N
IP = {(u,v) | task u must precede task v}
ZS = {(u,v) | tasks u and v must be assigned to the same workstation}
ZD = {(u,v) | tasks u and v can not be assigned to the same workstation}
S(i) is the set of successors for task i.
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Assembly Systems

24. Parameters / Decision Variables (cont.)
k is the number of workstations required (unknown).
cik is a set of cost coefficients such that:
cik is the cost of assigning task i to station k
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Assembly Systems

25. Problem Formulation
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Assembly Systems

26. Solving the Problem Very difficult to solve optimally
Integer variables
Non-linear constraints
Heuristic Solutions
COMSOAL
Ranked positional weight
Enumeration Methods
Tree Generation
Niave approach
Fathoming rules
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Assembly Systems

27. Example Problem 10 1 2 3 9 7 5 4 6 8 11
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Assembly Systems

28. Example Problem (cont.)10 1 2 3 9 7 5 4 6 8 11
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Assembly Systems

29. Ranked Positional Weight Example
C = 72
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Assembly Systems