Two Phases of Assembly Handling Insertion Can be done Manually Automatically
Manual Handling (Affected primarily by geometry) Bins Workstation Fixture Operator 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 Bins Workstation 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 Bowl Feeder Workhead Assembly 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. Buffer Space
Four Station Automatic Assembly System 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 screws 1 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 Bins Workstation 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 bulb screw disk key
Examples of Rotational Symmetry Parts with rotational symmetry. Parts with no rotational symmetry. washer pin bulb screw disk key
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/thickness Due to obscured view/access Two hands Heavy Large Fragile Computer chip Expansion 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 chamfersChamfers Dog 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 AdvisorAllow 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)
Combining Parts Question: Is the design on the right, which contains fewer parts, less costly? If C dcx <5: yes !