manual assembly corrado poli mechanical and industrial engineering umass amherst ©fall 2001
TRANSCRIPT
Manual Assembly
Corrado Poli Mechanical and Industrial Engineering
UMass Amherst©Fall 2001
Two Phases of Assembly
• Handling
• Insertion
Can be done
• Manually
•Automatically
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
• 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
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
Four Station Automatic AssemblySystem for Irrigation Mini-Drippers
(Rotary Indexing Machine)
Mini-dripper has a base, body, regulator and cover.
Schematic of assembly system
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
Cost of An Assembly
• Number of parts
• Ease with which the parts can be > Handled> Inserted
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
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!
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?
Rule #2 -Design Parts
• So they can be easily handled and
• Inserted
BinsWorkstation
Fixture
Operator
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
And
If the part is Easy to Grasp and Manipulate with One
Hand and No Tools
Examples of Symmetry
• Parts with end-to-end symmetry
• Parts with no end-to-end symmetry
Dowel pin washer pin
nail bulbscrew disk
key
Examples of Rotational Symmetry
• Parts with rotational symmetry.
• Parts with no rotational symmetry.
washer pinbulb
screw
diskkey
Illustrations of Size and Thickness
size
Illustrations of Light and Heavy Mass
Light Heavy
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
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
Parts are Difficult to Grasp and Manipulate - continued
• Sharp/hot/ undesirable to touch
• Sticky
Grease on ball bearing Part with
adhesive
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
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
Additional Considerations
• Insert vertically from above (i.e. don’t fight gravity)
No Yes
•Provide features/obstructions to prevent incorrect assembly of the part.
Additional Considerations
• Eliminate difficult to control operations -- welding, brazing, gluing, etc
• Eliminate extra operations such as special adjustments, torque adjustments etc.
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.
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)
Assembly Advisor
Combining Parts
Question: Is the design on the right, which contains fewer parts, less costly?
If Cdcx<5:
yes!