1. IE 368: FACILITY DESIGN AND OPERATIONS MANAGEMENT
Lecture Notes #2
Production System Design
Part #1

2. Production System Design
Abstraction of production systems for system design purposes
General concepts/definitions that may be used to represent many different systems
High level qualitative analysis for the selection of a general system flow concept

3. Production System Design (cont.)
Part #1
Calculations for estimating resource requirements
Equipment fraction calculations
Extensions
Machine assignment
Part #2
Calculations for evaluating system performance
Review of relevant probability/statistics concepts
Application of queuing models

4. Production System Design (cont.)
Part #3
Generalizations of queuing model
Generalizations of utilization formula
Multiple linked workstations
Automated systems
Batched arrivals and departures

5. Production system Workstation
Generalization/Abstraction of Production Systems for IE Design/Analysis
Production system
A collection of workstations that perform operations such as manufacturing, assembly, inspection, finishing, testing, etc. to create products
Workstation
A collection of machines/operators that perform the same operation for the same set of products
A machine/operator may be:
An automated machine
A machine operated by a human
A human operator performing a manual operation
* Terminology in this area is not standardized

6. Generalization/Abstraction of Production Systems for IE Design/Analysis (cont.)
The production systems to be addressed are discrete part production systems
Each part produced is a distinct entity
Vehicle, computer, hamburger, etc.
This is in contrast to continuous goods production such as fluids, powders, etc.
Often in the domain of chemical process engineers
Thus, the product being produced will be referred to generically as a part or job

7. Production System Design
The general arrangement of workstations, dictating the pattern of flow of the products, and the resource requirements at each workstation
WS1
WS5
WS4
WS3
WS2

8. Production System Performance Characterization
At the level of abstraction presented, the performance of the production system is evaluated by determining the following:
How fast
Throughput (e.g., jobs/hour, parts/minute)
How long
Time-In-System (TIS)
Flow Time
Cycle Time (we will not use this term)
How much
Work-In-Progress (WIP)

9. Examples of Production Systems
Simulation models
Truck assembly
FMS
Distribution center
Questions
What constitutes a job?
What are the workstations?
Why are jobs flowing as they are?

10. Production System Design – Different Perspectives
Manufacturing engineer
Designs/selects the processes and operations required to produce the product
e.g., fixturing, tooling, feed rates, cutting speeds, etc.
Human factors engineer
Design of the individual human operated workstation
e.g., bench heights, lifting angles, placement of tools, presentation of visual information, etc.

11. Production System Design – Different Perspectives (cont.)
Higher level IE analysis/business operations
Supply chain design
The number, level, and location of suppliers
Delivery, ordering, inventory policies
The number of distributors and their locations …

12. General Production System Flow
Examine product volume versus variety
Typically cannot have both
Automation
Hard Systems
Special Purpose Machines
Volume of
Production
General Purpose Equipment
Flexible Systems
Skilled labor
Variety of Products or Parts

13. Basic Types of Production System Flow
Example
Job Shop
Batch Processing
Production Line
Continuous Flow

14. Job Shop Characteristics
Many products; low volume
General purpose machinery
Operators work at only one department and are highly skilled in that operation
Process Layout
Equipment of the same type is located in the same department
Unorganized material flow
High material handling
High cycle time
High flexibility

15. Job Shop Characteristics (cont.)

16. Production Line Characteristics
Few products; high volume (mass production)
Highly standard parts
Somewhat similar to continuous production
Special purpose machinery
Low skill labor
Equipment is arranged into a line almost in the same order of required production operations
Low material handling
Short cycle time
Well organized material flow

17. Production Line Characteristics (cont.)

18. Group Technology/Batch Processing Characteristics
Fewer products than Job Shop; higher production volume
Products are produced in batches satisfying a few days up to few months of demand
Less general purpose machinery than job shop
Process layout & cellular layout; machines to produce family of products are located in the same cell
Large batches have organized material flow
High to moderate material handling
Moderate cycle time
High flexibility

19. Group Technology/Batch Processing Characteristics (cont.)
Group Technology Cell

20. Group Technology/Batch Processing Characteristics (cont.)
Batch processing layout

21. Product Volume versus Variety
Product Volume versus Product Variety in Production System Design
Volume of
Production
Variety of Products or Parts

22. Variety-Volume-Flexibility
Product Variety
High
Moderate
Low
Vey Low
Equipment Flexibility
Volume
Moderate Volume
High Volume
Very High Volume

23. Quiz
For the following situations, would you suggest a production line, job shop, or hybrid facility? Why?
The assembly of vehicle bodies for a popular sport utility vehicle
Fabrication and assembly of custom sheet metal parts
Fabrication of computer boxes for a line of desktop PC’s plus custom sheet metal parts
Assembly of three distinct families of electronic card assemblies for high end printers
Production of high end office furniture

24. Determining Resource Requirements
Assume you are running a manufacturing facility. What information would you need to determine how many machines/people are required at each workstation?
* Text reading – Chapter 2 pp , 56-63

25. Example 2.5
A machined part has a standard machining time of 2.8 min per part on a milling machine
During an 8-hour shift, 200 units are to be produced
Of the 480 min available for production, the machine will be operational 80% of the time
During that time the machine is operational, parts are produced at a rate equal to 95% of the standard rate
How many milling machines are required?

26. Example 2.5 – “Common Sense” Solution

27. Determining Resource Requirements
Equipment Fraction
Number of “machines” required at a workstation
Where
F = Number of machines required per “shift”
S = Standard time per job
Q = # of jobs to produce over a fixed time period
E = Actual performance expressed as a percentage of standard time
H = Amount of time available per machine
R = Reliability of a machine, expressed as a percent of uptime

28. Determining Resource Requirements (cont.)
Other considerations
If shifts are used
In how many shifts a machine can be used
Setup times
Takes away available production time

29. Important Observations
The equipment fraction as presented is helpful
It is more important to understand the fundamentals behind the formula because, as is, it is not applicable in all situations
A specified quantity must be produced in some time period and each machine can produce a certain amount in that time period
Efficiency, availability and reliability can be expressed in different ways and all these factors affect machine capability
Units must be consistent

30. Incorporating the Production of Scrap in the Equipment Fraction
Material waste that is generated in the manufacturing process
Affects the number of times an operation must be performed to get a specific number of good jobs
Typically due to geometric or quality considerations

31. Incorporating the Production of Scrap in the Equipment Fraction (cont
Nomenclature

32. Incorporating the Production of Scrap in the Equipment Fraction (cont
WS1
WS2
…….
WSn

33. Example 2.1
97,000 good parts are required. Three operations are used to produce the part with scrap percentages of d1=0.04, d2=0.01, d3=0.03. What are the required inputs to each operation?

34. Incorporating the Production of Scrap in the Equipment Fraction (cont
Calculations with rework
WS2
WS1
WS3
Rework
station

35. In-Class Exercise Part X requires machining on a milling machine
Operations A and B are required
Assume the company will be operating 5 days/week, 18 hours/day
The following information is known:
The milling machine requires 30 minutes for tool changes and preventive maintenance after every 400 parts
Assume that operation A is first and that both operations A and B are completed before the next part is started
Find the number of machines required to produce 2,500 parts per week
Operation
Standard Time
Efficiency
Reliability
Scrap A
2 min
95% 2% B
4 min
90% 5%

36. In-Class Exercise – Solution

37. In-Class Exercise – Solution

38. Modifications to the Equipment Fraction Equation
The equipment fraction equation is applicable to machines which can be human operators, a single operator running a single machine, and also automated machines
For automated machines, data is often not expressed as in the equipment fraction equation
In some cases a single operator runs >1 machine in which case the machines are not producing at their maximum rates (the opposite can occur also)

39. Modification for Automated Machines
Automated Workstation
A workstation where the movement of jobs in and out of the workstation, and the processing of jobs is performed by machines
While the workstation is operating, the move times and processing times are predictable

40. Modification for Automated Machines (cont.)
Cycle time
Represented as C
Total time required to produce a single job on a workstation when it is operating
Normally C = Process time + Move time
Move time
The time to move a job into and/or out of the workstation
Does the movement of a job into a workstation occur at the same time as the movement of a job out of the workstation?

41. Modification for Automated Machines (cont.)
Mean (Operating) Time Between Failures (MTBF)
The average time between unplanned failures of the machine
Excludes scheduled down time or non-operating time
Mean Time To Repair (MTTR)
The average time to bring the machine back to operating status after a failure occurs

42. Modification for Automated Machines (cont.)
Equipment Fraction
S = standard time per job
Q = # of jobs to produce over a fixed time period
E = actual performance expressed as a percentage of standard time
H = amount of time available per machine
R = Reliability of a machine, expressed as a percent of uptime

43. Modification for Automated Machines (cont.)
Referred to as
Stand Alone Availability

44. Modification for Automated Machines (cont.)
Example
An automated machine has a move time = 10 sec/job and a processing time of 1 min/job. The machine will be used for a single 8 hr shift and has a MTBF = 75 min and a MTTR = 5 min. What is the number of machines required to produce 1,000 jobs per shift?

45. In-Class Exercise Part X requires machining on a CNC milling machine
Operations A and B are required
Assume the machine will be operating 5 days/week, 18 hours/day
The following information is known:
The milling machine requires tool changes and preventive maintenance after every 400 parts. This takes 30 minutes.
Assume that operation A is first and that both operations A and B are completed before the next part is started
Move times in and out of the machine occur at the same time
Find the number of machines required to produce 2,500 parts per week
Operation
Process Time
Move Time
MTBF
MTTR
Scrap A
5 min
0.5 min
500 min
20 min 2% B
7 min
700 min
30 min 5%

46. In-Class Exercise – Solution

47. Rates and Times in Calculations
No general rules
Assess the general quantity being calculated, then use common sense
Test calculations in extreme cases
Example 1 – Calculate Average Speed of Vehicle
10 mph
40 mph
5 miles
5 miles

48. Rates and Times in Calculations (cont.)
Example 2 – Calculate Average Job Interarrival Time
Example 3 – Calculate Average Job Processing Rate of M1
10 min* M1
5 min
6 min
* Time between job arrivals
Jobs
…CBACBA M1 ?
M1 processing rates:
A – 20 JPH
B – 30 JPH
C – 60 JPH

49. Rates and Times in Calculations (cont.)

50. Machine Assignment
There are many cases where multiple machines are run by a single operator
The number of machines running may be limited by the number of operators or the number of machines may determine how busy the operator is

51. Model for the Number of Machines to Assign to an Operator
Assumptions
All machines are identical and perform the same task
All times are known and constant
Use this model as a starting point or approximation

52. Model for the Number of Machines to Assign to an Operator (cont.)
Figure 2.19 from Tompkins

53. Model for the Number of Machines to Assign to an Operator (cont.)
Notation for machine assignment

54. Model for the Number of Machines to Assign to an Operator (cont.)
L = Load UL = Unload
T = Transport I&P = Inspect & Pack 11 11
Figure 2.18 Multiple activity chart

55. Model for the Number of Machines to Assign to an Operator (cont.)
A machine uses (a + t) minutes (use min for clarity) per job
An operator devotes (a + b) minutes to each machine per job

56. Model for the Number of Machines to Assign to an Operator (cont.)
Since m must be an integer
See Figure 2.18 (slide #53)

57. Model for the Number of Machines to Assign to an Operator (cont.)
See Figure 2.18
Idle time per machine in steady state = 1 minute
Im = m(a+b) - (a+t) = 3(2+1) – (2+6) = 1 minute

58. Model for the Number of Machines to Assign to an Operator (cont.)
For the example in Figure 2.18
3 parts are produced every 9 minutes  20 jobs/hour
Not 22.5 jobs/hour with no idle time
Examine the operation of a single machine
For a single machine, 1 part is produced every
6 minutes + 1 minute + 1 minute + 1 minute = 9 minutes
(Machining + load unload idle )

59. Machine Assignment Impact on Cost Per Job
Machine assignment decisions affect the cost per job produced

60. Machine Assignment Impact on Cost Per Job (cont.)

61. Machine Assignment Impact on Cost Per Job (cont.)
Let then either TC(n) or TC(n+1) will minimize cost per job
It is straightforward to show that

62. Example
Problem 2.38
Suppose 5 identical machines are to be used to produce two different products
The operating parameters for the two products are as follows: a1 = 2 min, a2 = 2.5 min, b1 = 1 min, b2 = 1.5 min, t1 = 6 min, and t2 = 8 min
The cost parameters are the same for each operator-machine combination: Co = $15/hr and Cm = $50/hr
Determine the method of assigning operators to machines that minimizes the cost per unit produced

63. Example

64. Example

65. In-Class Exercise
Semiautomatic mixers are used in a paint plant. It takes 6 min for an operator to load the appropriate pigments and paint base into a mixer. Mixers run automatically and then automatically dispense paint into 50-gallon drums. Mixing and unloading take 30 min. Mixers are cleaned automatically between batches; it takes 4 min to clean a mixer. Between batches, an operator places empty drums in a magazine to position them for filling. It takes 6 min to load the drums into the magazine. Filled drums are transported automatically by conveyor to a test area before being stored. Mixers are located close enough for travel between mixers to be negligible.
What is the maximum number of mixers that can be assigned to an operator without mixer idle time?
If Co =$12/hr and Cm=$25/hr, what assignment of mixers to operators will minimize cost per batch?

66. In-Class Exercise – Solution