Layout StrategiesDetermine the cost of this layout
Try to improve the layout
Prepare a detailed plan
*
30 50 10 0
Assembly (1)
Painting (2)
*
*
+ $30 + $50 + $10
+ $40 + $100 + $50
= $570
+ $60 + $50 + $10
+ $40 + $100 + $50
= $480
*
Medium Production Quantities
Batch production – A batch of a given product is produced, and then the facility is changed over to produce another product
Changeover takes time – setup time
Typical layout – process layout
Cellular manufacturing – A mixture of products is made without significant changeover time between products
Typical layout – cellular layout
Work Cells
Reorganizes people and machines into groups to focus on single products or product groups
Group technology identifies products that have similar characteristics for particular cells
Volume must justify cells
*
Reduced direct labor
Increased use of equipment and machinery
Reduced investment in machinery and equipment
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Improving Layouts Using Work Cells
Current layout - workers in small closed areas. Cannot increase output without a third worker and third set of equipment.
Improved layout - cross-trained workers can assist each other. May be able to add a third worker as additional output is needed.
Figure 10 (a)
Improving Layouts Using Work Cells
Current layout - straight lines make it hard to balance tasks because work may not be divided evenly
Improved layout - in U shape, workers have better access. Four cross-trained workers were reduced.
Figure 10 (b)
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A high level of training, flexibility and empowerment of employees
Being self-contained, with its own equipment and resources
Test (poka-yoke) at each station in the cell
*
Total work time available
*
Mirror production scheduled for 8 hours per day
From a work balance chart
total operation time
Mirror production scheduled for 8 hours per day
From a work balance chart
total operation time
= .8 mins = 48 seconds
Total operation time required
Can help identify bottleneck operations
Flexible, cross-trained employees can help address labor bottlenecks
Machine bottlenecks may require other approaches
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High Production
Quantity production – Equipment is dedicated to the manufacture of one product
Standard machines tooled for high production (e.g., stamping presses, molding machines)
Typical layout – process layout
Product requires multiple processing or assembly steps
Product layout is most common
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Volume is adequate for high equipment utilization
Product demand is stable enough to justify high investment in specialized equipment
Product is standardized or approaching a phase of life cycle that justifies investment
Supplies of raw materials and components are adequate and of uniform quality
Organized around products or families of similar high-volume, low-variety products
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Machine-paced
Assembly line
Paced by work tasks
Balanced by moving tasks
*
Low material handling costs
Work stoppage at any point ties up the whole operation
Lack of flexibility in product or production rates
Disadvantages
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Product variety
Soft product variety = differences between models of products
Product and part complexity
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Total number of product units Qf = PQ
Total number of parts produced npf = PQnp
Total number of operations nof = PQnpno
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Manufacturing capability - the technical and physical limitations of a manufacturing firm and each of its plants
Three dimensions of manufacturing capability:
Technological processing capability - the available set of manufacturing processes
Physical size and weight of product
Production capacity (plant capacity) - production quantity that can be made in a given time
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Computer programs are available to solve bigger problems
Computer Packages are in two domain
Construction Programs
Inputs
CRAFT Algorithm
Start with an initial layout with all departments made up of individual square grids (Note: each grid represents the same amount of space)
Estimate the best two-way department exchange assuming department centroids exchange exactly
Departments i and j exchange
New centroid i = centroid j
New centroid j = centroid i
Only consider exchanging adjacent departments
Execute the exchange if the estimated cost of the best exchange in (2) is lower than the best cost found so far
The actual result of the exchange is problem-dependent
If the estimated cost of the best exchange in (2) is higher than the best cost found so far, stop
Else, go to 1
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1 A A A A B B
2 A A A A B B
3 D D D D D D
4 C C D D D D
5 F F F F F D
6 E E E E E D
PATTERN
1 D D D D B B
2 D D D D B B
3 D D D E E E
4 C C D E E F
5 A A A A A F
6 A A A F F F
PATTERN
1 A A A A B B
2 A A A A B B
3 D D D D D D
4 C C D D D D
5 F F F F F D
6 E E E E E D
PATTERN
1 D D D D B B
2 D D D D B B
3 D D D E E E
4 C C D E E F
5 A A A A A F
6 A A A F F F
PATTERN
handling,
efficiency,
Flexible Manufacturing System
A Flexible manufacturing system is a system that is able to respond to changed conditions.
Where to Apply FMS Technology
The plant presently either:
Produces parts in batches or
Uses manned GT cells and management wants to automate the cells
It must be possible to group a portion of the parts made in the plant into part families
The part similarities allow them to be processed on the FMS workstations
Parts and products are in the mid-volume, mid-variety production range
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Flexible Manufacturing System - Defined
A highly automated GT machine cell, consisting of a group of processing stations (usually CNC machine tools), interconnected by an automated material handling and storage system, and controlled by an integrated computer system
The FMS relies on the principles of GT
No manufacturing system can produce an unlimited range of products
An FMS is capable of producing a single part family or a limited range of part families
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Flexibility Tests in an Automated Manufacturing System
To qualify as being flexible, a manufacturing system should satisfy the following criteria (“yes” answer for each question):
Can it process different part styles in a nonbatch mode?
Can it accept changes in production schedule?
Can it respond gracefully to equipment malfunctions and breakdowns?
Can it accommodate introduction of new part designs?
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9 – *
Automated manufacturing cell with two machine tools and robot. Is it a flexible cell?
Automated Manufacturing Cell
Part variety test
Can it machine different part configurations in a mix rather than in batches?
Schedule change test
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Error recovery test
Can it operate if one machine breaks down?
Example: while repairs are being made on the broken machine, can its work be temporarily reassigned to the other machine?
New part test
As new part designs are developed, can NC part programs be written offline and then downloaded to the system for execution?
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Number of machines (workstations):
Flexible manufacturing cell (n = 2 or 3)
Flexible manufacturing system (n = 4 or more)
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Designed to produce a limited variety of part styles
The complete universe of parts to be made on the system is known in advance
Part family likely based on product commonality rather than geometric similarity
Random-order FMS
New part designs will be introduced
Production schedule is subject to daily changes
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Computer control system
Manual or automated
Includes communication interface with worker to specify parts to load, fixtures needed, etc.
CNC machine tools in a machining type system
CNC machining centers
Milling machine modules
Capability to handle a variety of part styles
Standard pallet fixture base
Temporary storage
Compatibility with computer control
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Secondary handling system - functions:
Transfers work from primary handling system to workstations
Position and locate part with sufficient accuracy and repeatability for the operation
Reorient part to present correct surface for processing
Buffer storage to maximize machine utilization
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Five Types of FMS Layouts
The layout of the FMS is established by the material handling system
Five basic types of FMS layouts
Inline
FMS In-Line Layout
Straight line flow, well-defined processing sequence similar for all work units
Work flow is from left to right through the same workstations
No secondary handling system
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FMS In-Line Layout
Linear transfer system with secondary parts handling system at each workstation to facilitate flow in two directions
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FMS Loop Layout
One direction flow, but variations in processing sequence possible for different part types
Secondary handling system at each workstation
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FMS Rectangular Layout
Rectangular layout allows recirculation of pallets back to the first station in the sequence after unloading at the final station
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Loop with rungs to allow greater variation in processing sequence
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Suited to the handling of rotational parts and turning operations
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Central intelligence required to coordinate processing at individual stations
Production control
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Traffic control
Management of the primary handling system to move parts between workstations
Shuttle control
Workpiece monitoring
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Tool life monitoring
Monitoring usage of each cutting tool and determining when to replace worn tools
Performance monitoring and reporting
Diagnostics
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Loading and unloading parts from the system
Changing and setting cutting tools
Maintenance and repair of equipment
NC part programming
Overall management of the system
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Assembly
Inspection
Forging
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Automatic tool changing
Queues of parts at stations to maximize utilization
Dynamic scheduling of production to account for changes in demand
Fewer machines required
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Lower manufacturing lead times
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Part family considerations
Based on part similarity
Based on product commonality
Physical characteristics of workparts
Size and weight determine size of processing equipment and material handling equipment
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Production volume
Types of workstations
Machine loading
Part routing
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Which parts should be on the system at one time
Tool management
When to change tools
Pallet and fixture allocation
Limits on fixture types may limit part types that can be processed
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Just-In-Time Production
Production and delivery of exactly the required number of each component to the downstream operation in the manufacturing sequence just at the moment when the component is needed
Minimizes:
Work-in-process
Setup time reduction for smaller batch sizes
Stable and reliable production operations
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Pull System of Production Control
A system in which the order to make and deliver parts at each workstation in the production sequence comes from the downstream station that uses those parts
JIT is based on a pull system of production control
Alternative is a push system in which parts are produced at each station irrespective of the immediate need for those parts at the downstream station
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Setup Time Reduction
Starting point in setup time reduction is recognition that the work elements in setup are of two types:
Internal elements – can only be done while the production machine is stopped
External elements – do not require the machine to be stopped
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Strategy:
Design the setup tooling and plan the changeover procedure to permit as much of the setup as possible to consist of external elements
Examples:
Assemble tools for next job
Reprogram machine for next job
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Internal Work Elements
Use time & motion study and methods improvement to minimize the sum of the internal work element times
Use two workers rather than one to accomplish the changeover
Eliminate adjustments in the setup
Use quick-acting fasteners rather than bolts and nuts
Use U-shaped washers instead of O-shaped washers
Design modular fixtures consisting of a base plus insert tooling that can be quickly changed for each new part style
Base part remains attached to production machine
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Production Operations
Production leveling - distribute changes in product mix and quantity as evenly as possible over time
On-time delivery of components
Defect-free components and materials
Dependable supplier base
Quality at Source
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Automotive
Assembly-Line Balancing
Objective is to minimize the imbalance between machines or personnel while meeting required output
Starts with the precedence relationships
Determine cycle time
Wing Component Example
This means that tasks B and E cannot be done until task A has been completed
Performance Task Must Follow
40 units required
Units required per day
2. Most following tasks
Choose the available task with the largest number of following tasks
3. Ranked positional weight
Choose the available task for which the sum of following task times is the longest
4. Shortest task time
5. Least number of following tasks
Choose the available task with the least number of following tasks
I
G
F
C
D
H
B
E
A
10
11
12
5
4
3
7
11
3
40 units required
40 units required
40 units required
Efficiency =
= 91.7%