Process Selection�and �Facility Layout
1
2
Introduction
Make some components buy remaining
Introduction
3
Process selection refers to deciding on the way production of goods or services will be organized. It has major implications for capacity planning, layout of facilities, equipment, and design of work systems. Process selection occurs as a matter of course when new products or services are being planned. However, it also occurs periodically due to technological changes in products or equipment, as well as competitive pressures.
Process Selection and System Design
4
Forecasting
Product and�Service Design
Technological�Change
Capacity�Planning
Process�Selection
Facilities and�Equipment
Layout
Work�Design
Figure 6.1
5
Process Types
6
Questions Before Selecting A Process
and services
7
Job Shop
Batch
Repetitive
Continuous
Product – Process Matrix
8
Dimension | Job Shop | Batch | Repetitive | Continuous |
Job variety | Very High | Moderate | Low | Very low |
Process flexibility | Very High | Moderate | Low | Very low |
Unit cost | Very High | Moderate | Low | Very low |
Volume of output | Very low | Low | High | Very high |
Variety, Flexibility, & Volume
Product – Process Matrix
10
Process Type | High variety | | | Low variety |
Job Shop | Appliance repair�Emergency room | | | |
Batch | | Commercial�bakery��Classroom�Lecture | | |
Repetitive | | | Automotive�assembly��Automatic�carwash | |
Continuous�(flow) | | | | Oil refinery�Water purification |
11
Product-Process Matrix
Flexibility-Quality
Dependability-Cost
Continuous
Flow
Assembly
Line
Batch
Job
Shop
Low
Volume
One of a
Kind
Multiple
Products,
Low
Volume
Few
Major
Products,
Higher
Volume
High
Volume,
High
Standard-
ization
Book
Writing
Movie
Theaters
Automobile
Assembly
Sugar
Refinery
Flexibility-
Quality
Dependability-
Cost
12
Project. A project is used for work that is nonroutine, with a unique set of objectives to be accomplished in a limited time frame. Examples range from simple to complicated, including such things as putting on a play, consulting, making a motion picture, launching a new product or service, publishing a book, building a dam, and building a bridge. Equipment flexibility and worker skills can range from low to high
Process technology and information technology can have a major impact on costs, productivity, and competitiveness. Process technology includes methods, procedures, and equipment used to produce goods and provide services. This not only involves processes within an organization, it also extends to supply chain processes. Information technology (IT) is the science and use of computers and other electronic equipment to store, process, and send information. IT is heavily ingrained in today’s business operations. This includes electronic data processing, the use of barcodes and radio frequency tags to identify and track goods, devices used to obtain point-of-sale information, data transmission, the Internet, e-commerce, e-mail, and more.
Automation is machinery that has sensing and control devices that enable it to operate automatically. If a company decides to automate, the next question is how much. Automation can range from factories that are completely automated to a single automated operation
13
Flexible automation evolved from programmable automation. It uses equipment that is more customized than that of programmable automation. A key difference between the two is that flexible automation requires significantly less changeover time. This permits almost continuous operation of equipment and product variety without the need to produce in batches.
A flexible manufacturing system (FMS) is a group of machines that include supervisory computer control, automatic material handling, and robots or other automated processing equipment. Reprogrammable controllers enable these systems to produce a variety of similar products. Systems may range from three or four machines to more than a dozen. They are designed to handle intermittent processing requirements with some of the benefits of automation and some of the flexibility of individual, or stand-alone, machines (e.g., N/C machines).
Computer-integrated manufacturing (CIM) is a system that uses an integrating computer system to link a broad range of manufacturing activities, including engineering design, flexible manufacturing systems, purchasing, order processing, and production planning and control. Not all elements are absolutely necessary. For instance, CIM might be as simple as linking two or more FMSs by a host computer. More encompassing systems can link scheduling, purchasing, inventory control, shop control, and distribution.
Fixed automation: Low production cost and high volume but with minimal variety and high changes cost
Programmable automation: Economically producing a wide variety of low volume products in small batches
Flexible automation: Require less changeover time and allow continuous operation of equipment and product variety
14
Automation: Machinery that has sensing and control devices that enables it to operate
Robot
15
Show wafer_handler_web
Flexible Manufacturing System
reduce labor costs and more consistent quality
lower capital investment and higher flexibility than hard automation
relative quick changeover time
used for a family of products and require longer planning and development times
16
Computer-integrated manufacturing
rapid response to customer order and product change, reduce direct labor cost, high quality
17
18
Service Blueprint
Begin
Turn on laptop
Connect to LCD
A
A
View on
Yes
Lecture
No
Begin
19
Service Process Design
20
Layout
The Need for Layout Decisions
21
Inefficient operations
For Example:
High Cost
Bottlenecks
Changes in the design
of products or services
The introduction of new�products or services
Accidents
Safety hazards
The Need for Layout Design (Cont’d)
22
Changes in
environmental
or other legal
requirements
Changes in volume of
output or mix of
products
Changes in methods
and equipment
Morale problems
Basic Layout Types
23
A Flow Line for Production or Service
Flow Shop or Assembly Line Work Flow
24
Raw materials
or customer
Finished item
Station
2
Station
3
Station
4
Material
and/or labor
Station
1
Material
and/or labor
Material
and/or labor
Material
and/or labor
A U-Shaped Production Line
25
Advantage: more compact, increased communication facilitating team work, minimize the material handling
Process Layout
26
Dept. A
Dept. B
Dept. D
Dept. C
Dept. F
Dept. E
Used for Intermittent processing
Process Layout
(functional)
Process layouts (functional layouts) are designed to process items or provide services that involve a variety of processing requirements. The variety of jobs that are processed requires frequent adjustments to equipment. This causes a discontinuous workflow, which is referred to as intermittent processing. The layouts feature departments or other functional groupings in which similar kinds of activities are performed. A manufacturing example of a process layout is the machine shop, which has separate departments for milling, grinding, drilling, and so on. Items that require those operations are frequently moved in lots or batches to the departments in a sequence that varies from job to job. Consequently, variable-path material-handling equipment (forklift trucks, jeeps, tote boxes) is needed to handle the variety of routes and items. The use of general-purpose equipment provides the flexibility necessary to handle a wide range of processing requirements
Product Layout
27
Product Layout - work travels �to dedicated process centers
Milling
Assembly�& Test
Grinding
Drilling
Plating
Layout types: Product or Process Make your pick
28
A
B
A
B
Process vs Layout types
29
Match?
Product layout
Advantages
Disadvantages
30
Cellular Layouts
31
A Group of Parts
32
Similar manufacturing characters
Process vs. Cellular Layouts
33
Dimension | Process | Cellular |
Number of moves between departments | many | few |
Travel distances | longer | shorter |
Travel paths | variable | fixed |
Job waiting times | greater | shorter |
Amount of work in process | higher | lower |
Supervision difficulty | higher | lower |
Scheduling complexity | higher | lower |
Equipment utilization | Lower? | Higher? |
34
. To get a sense of the advantage of the cellular layout, trace the movement of an order in the traditional layout (6.7A) that is depicted by the path of the arrow. Begin on the bottom left at Shipping/Receiving, then follow the arrow to Warehouse, where a batch of raw material is released for production. Follow the path (shown by the arrows) that the batch takes as it moves through the system to Shipping/Receiving and then to the Customer. Now turn to Figure 6.7B . Note the simple path the order takes as it moves through the system.
Basic Layout Formats
Similar to cellular layout
35
Part Family W
Part Family X
Part Family Y
Part Family Z
Assemble Y,W
Assemble X,Z
Final Product
Fixed-Position and combination Layout
item being worked on remains stationary, and workers, materials and equipment are moved as needed.
Example: buildings, dams, power plants
combination of three pure types.
Example: hospital: process and fixed position.
36
Service Layouts
Issue: Frequency of orders
Issue: Traffic patterns and traffic flows
Issue: Information transfer, openness
37
Design Product Layouts: Line Balancing
38
Line balancing is the process of assigning tasks to workstations
in such a way that the workstations have approximately the same
processing time requirements. This results in the minimized idle time
along the line and high utilization of labor and equipment.
Cycle time is the maximum time allowed at each workstation
to complete its set of tasks on a single unit
What is the cycle time for the system above?
Worker 1
Worker 2
4 tasks
2 tasks
Each task takes 1 minutes, how to balance?
In the case of an automatic car wash, scrubbing and drying operations could not realistically be combined at the same workstation due to the need to rinse cars between the two operations.
Line balancing involves assigning tasks to workstations. Usually, each workstation has one worker who handles all of the tasks at that station, although an option is to have several workers at a single workstation.
39
Parallel Workstations
1 min.
2 min.
1 min.
1 min.
30/hr.
30/hr.
30/hr.
30/hr.
1 min.
2 min.
1 min.
1 min.
60/hr.
30/hr.
30/hr.
60/hr.
2 min.
30/hr.
30/hr.
Bottleneck
Parallel Workstations
The minimum cycle time is equal to the longest task time (1.0 minute), and the maximum cycle time is equal to the sum of the task times (0.1 + 0.7 + 1.0 + 0.5 + 0.2 = 2.5 minutes). The minimum cycle time would apply if there were five workstations. The maximum cycle time would apply if all tasks were performed at a single workstation.
Using parallel stations for the third task would result in a cycle time of 1 minute because the output rate at the parallel stations would be equal to that of a single station and allow an output rate for the line of 60 units per hour:
The obstacle
40
Cycle Time
41
Cycle time is the maximum time allowed at each workstation to complete its tasks on a unit.
The major determinant: cycle time
Minimum cycle time: longest task time by assigning each task to a workstation
Maximum cycle time: sum of the task time by assigning all tasks to a workstation
Determine Maximum Output�Cycle Time: Time to process 1 unit
42
Example: If a student can answer a multiple choice question in 2 minutes but gets a test with 30 questions and is given only 30 minutes then
OT=30 minutes; D=30
Desired cycle time=1 minute < 2 minutes = Cycle time from the process capability
Determine the Minimum Number of Workstations Required: Efficiency
43
Example: Students can answer a multiple choice question in 2 minutes but given a test with 30 questions and is given only 30 minutes. What is the minimum number of students to collaborate to answer all the questions in the exam?
Total operation (task) time = 60 minutes = 30 x 2 minutes
Operating time=30 minutes. 60/30=2 students must collaborate. This Nmin below.
Percent Idle Time
44
Efficiency = 1 – Percent idle time
Example 1: Precedence Diagram
45
Precedence diagram: Tool used in line balancing to display elemental tasks and sequence requirements
a
b
c
d
e
0.1 min.
0.7 min.
1.0 min.
0.5 min.
0.2 min.
It visually portrays the tasks that are to be performed along with the sequential requirements, that is, the order in which tasks must be performed. The diagram is read from left to right, so the initial task(s) are on the left and the final task is on the right. In terms of precedence requirements, we can see from the diagram, for example, that the only requirement to begin task b is that task a must be finished. However, in order to begin task d, tasks b and c must both be finished
Example 1: Assembly Line Balancing
Arrange the tasks shown in Figure 6.9 into three workstations. Use a cycle time of 1.0 minute. Assign tasks in order of the greatest number of followers.
The initial “time remaining” for each workstation is equal to the cycle time. For a task to be eligible, tasks preceding it must have been assigned, and the task’s time must not exceed the station’s remaining time.
Calculate Percent Idle Time
47
Efficiency=1-percent idle time=1-0.167=0.833=83.3%
48
In balancing an assembly line, tasks are assigned one at a time to the line, starting at the first workstation. At each step, the unassigned tasks are checked to determine which are eligible for assignment. Next, the eligible tasks are checked to see which of them will fit in the workstation being loaded. A heuristic is used to select one of the tasks that will fit, and the task is assigned. This process is repeated until there are no eligible tasks that will fit. Then the next workstation can be loaded. This continues until all tasks are assigned. The objective is to minimize the idle time for the line subject to technological and output constraints.
Technological constraints tell us which elemental tasks are eligible to be assigned at a particular position on the line. Technological constraints can result from the precedence or ordering relationships among the tasks. The precedence relationships require that certain tasks must be performed before others (and so, must be assigned to workstations before others)
Output constraints, on the other hand, determine the maximum amount of work that a manager can assign to each workstation, and this determines whether an eligible task will fit at a workstation. The desired output rate determines the cycle time, and the sum of the task times assigned to any workstation must not exceed the cycle time. If a task can be assigned to a workstation without exceeding the cycle time, then the task will fit. Once it is known which tasks are eligible and will fit, the manager can select the task to be assigned (if there is more than one to choose from). This is where the heuristic rules help us decide which task to assign from among those that are eligible and will fit. To clarify the terminology, following tasks are all tasks that you would encounter by following all paths from the task in question through the precedence diagram. Preceding tasks are all tasks you would encounter by tracing all paths backward from the task in question. In the precedence diagram below, tasks b, d, e, and f are followers of task a. Tasks a, b, and c are preceding tasks for e.
The positional weight for a task is the sum of the task times for itself and all its following tasks. Neither of the heuristics guarantees the best solution, or even a good solution to the linebalancing problem, but they do provide guidelines for developing a solution.
49
50
51
52
53
Companies use a number of other approaches to achieve a smooth flow of production. One approach is to use parallel workstations. These are beneficial for bottleneck operations which would otherwise disrupt the flow of product as it moves down the line. The bottlenecks may be the result of difficult or very long tasks. Parallel workstations increase the work flow and provide flexibility.
54
Designing Process Layouts
Another approach to achieving a balanced line is to cross-train workers so that they are able to perform more than one task. Then, when bottlenecks occur, the workers with temporarily increased idle time can assist other workers who are temporarily overburdened, thereby maintaining an even flow of work along the line. This is sometimes referred to as dynamic line balancing, and it is used most often in lean production systems. Still another approach is to design a line to handle more than one product on the same line. This is referred to as a mixed model line
55
At $1 per load meter, the cost for this plan is $7,600 per day. Even though it might appear that this arrangement yields the lowest transportation cost, you cannot be absolutely positive of that without actually computing the total cost for every alternative and comparing it to this one. Instead, rely on the choice of reasonable heuristic rules such as those demonstrated above to arrive at a satisfactory, if not optimal, solution.
Distance between locations (meters)
Interdepartmental work flow (loads per day)
Closeness Rating: multiple criteria
56
Muther Grid
57
58
Summary
Objective, Implication, types
Line balancing: procedures and measures
Information requirements, measures
From to chart and Muther grid
59