Manual Assembly Corrado Poli Mechanical and Industrial Engineering UMass Amherst ©Fall 2001.
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Transcript of Manual Assembly Corrado Poli Mechanical and Industrial Engineering UMass Amherst ©Fall 2001.
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Manual Assembly
Corrado Poli Mechanical and Industrial Engineering
UMass Amherst©Fall 2001
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Two Phases of Assembly
• Handling
• Insertion
Can be done
• Manually
•Automatically
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Manual Handling(Affected primarily by geometry)
Bins
Workstation
Fixture
OperatorOperator
• Reaches into the bin
• Grasps the part
• Transports and orients the part
• Pre-positions it
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• Operator - places/fastens part onto a partially completed assembly/subassembly
BinsWorkstation
Fixture
Operator
(Affected by both the part geometry AND the part/parts to which it is placed/fastened/mated to.)
Manual Insertion
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Automatic Assembly(free transfer/non-synchronous system)
Buffer Stock
Workstations
BowlFeeder
WorkheadAssembly Machine -
Workcarrier Partially completed assembly transferring to next station
Gravity Feed Track
• Parts emptied into a bowl feeder which contain orienting devices.
• Parts exit feeder go down track in preparation for insertion.
BufferSpace
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Four Station Automatic AssemblySystem for Irrigation Mini-Drippers
(Rotary Indexing Machine)
Mini-dripper has a base, body, regulator and cover.
Schematic of assembly system
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Automatic Handling(From “Handbook of Feeding and Orienting Techniques for Small
Parts,” by Boothroyd, Poli and Murch)
Bowl Feeder Orienting system for cup shaped parts
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Cost of An Assembly
• Number of parts
• Ease with which the parts can be > Handled> Inserted
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Rule #1 - Eliminate Parts• Outright elimination of parts.
(screws, nuts, washers, etc.- use snap fits)
• Combining 2 or more distinct parts into a single molded, cast or stamped part.
9 parts 2 parts
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Eliminate Fasteners• If not possible, reduce the number or variety• Incorporate the fastening function with
another feature
4 screws1 screw
Snap
• Screws aren’t expensive - driving them is!
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Can Parts Be Combined?• Since there is no relative motion between the parts - and
• Since these parts can be made of the same material
•Why not combine them?
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Rule #2 -Design Parts
• So they can be easily handled and
• Inserted
BinsWorkstation
Fixture
Operator
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Factors Affecting Manual Handling Time (Cost)*
Part
• Symmetry> End-to-end> Rotational
• Size
• Thickness
• Mass
* Reference: G. Boothroyd, “Assembly Automation and Product Design,” Marcel Dekker, NY, 1992
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And
If the part is Easy to Grasp and Manipulate with One
Hand and No Tools
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Examples of Symmetry
• Parts with end-to-end symmetry
• Parts with no end-to-end symmetry
Dowel pin washer pin
nail bulbscrew disk
key
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Examples of Rotational Symmetry
• Parts with rotational symmetry.
• Parts with no rotational symmetry.
washer pinbulb
screw
diskkey
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Illustrations of Size and Thickness
size
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Illustrations of Light and Heavy Mass
Light Heavy
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Parts are Difficult to Grasp and Manipulate
•Nest or tangle(and degree of severity)
Slippery (ball bearings with oil)
Flexible - two hands to keep orientation prior to
insertion(belts, chains, gaskets)
Do not nest or tangle
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Parts are Difficult to Grasp and Manipulate - continued
•Need Grasping Tools(tweezers, magnets, snap rings, )
Due to part size/thicknessDue to obscured view/access
• Two hands
Heavy Large
• FragileComputer chipExpansion board
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Parts are Difficult to Grasp and Manipulate - continued
• Sharp/hot/ undesirable to touch
• Sticky
Grease on ball bearing Part with
adhesive
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Factors Affecting Manual Insertion*
* Reference: G. Boothroyd, “Assembly Automation and Product Design,” Marcel Dekker, NY, 1992
•Ease of alignment (provide feature to ease insertion)
No chamfers ChamfersDog point•Ease of insertion
(affected by clearance, jamming, wedging, pushing against a force)
Part jams on corners
Same clearance, no jamming
chamfers
Negative clearance (press fit) Push against a force
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Factors Affecting Manual Insertion - continued
•Obstructed view and/or obstructed access
Task: Place battery in shaver.View clear? Need to rely on tactile sensing?Access clear? Is there a feature that restricts access to the operator?
•Self-locating, no need to hold
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Additional Considerations
• Insert vertically from above (i.e. don’t fight gravity)
No Yes
•Provide features/obstructions to prevent incorrect assembly of the part.
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Additional Considerations
• Eliminate difficult to control operations -- welding, brazing, gluing, etc
• Eliminate extra operations such as special adjustments, torque adjustments etc.
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Additional Considerations• Design products into sub-assemblies that
can be assembled and tested separately.• ‘De-couple’ manual and machine
operations.• Group manual assembly operations to
optimize line balancing.
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Assembly Analysis
Three choices to analyze an assembly:
• Use an approximate approach during configuration stage of design?
Precision needed if you need to do
process planning.
Assembly Advisor Allow 7-9 sec/part
• Precise quantitative method - such as the Boothroyd approach*.
* Reference: G. Boothroyd, “Assembly Automation and Product Design,” Marcel Dekker, NY, 1992
(Fails to focus attention on characteristics that make
assembly difficult)
(Compromise approach)
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Assembly Advisor
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Combining Parts
Question: Is the design on the right, which contains fewer parts, less costly?
If Cdcx<5:
yes!