AOD for LGO 1 © Daniel E Whitney 9/15/2015 Assembly-Oriented Design Dan Whitney April 5, 2002

AOD for LGO 2 © Daniel E Whitney 9/15/2015 Poll 1.We design assemblies explicitly as part of our product development process 2.Our suppliers design our assemblies 3.We design things and our manufacturing engineers try to get us to change them 4.We design parts using the best CAD system in the world and then we wonder why we have trouble assembling them 5.We don’t have any assembly problems

AOD for LGO 3 © Daniel E Whitney 9/15/2015 Scope of “Assembly” Assembly spans the entire range from point processes to business strategy Assemblies are things that do something –Attributes –Architecture –Families, platforms… Assembly is a process of putting things together –On the factory floor –Operations –Equipment –Ergonomics

AOD for LGO 4 © Daniel E Whitney 9/15/2015 Scope of Assembly - 2 Design for assembly –Part handling and mating –Part consolidation Integral architecture favors performance Modular architecture favors business issues Design of assemblies - technical and business issues –Design intent –CAD representation –Key Characteristics –Math models, constraint, tolerances –Architectures, families, delayed commitment, flexibility

AOD for LGO 5 © Daniel E Whitney 9/15/2015 Conventional DFA Addresses local issues Is applied too late in the process Addresses some of the things that factory MEs worry about Favors integrated designs Any attempt to broaden its reach requires a great deal of additional knowledge –Business tradeoffs –Supply chain management during design and production –Ergonomics

AOD for LGO 6 © Daniel E Whitney 9/15/2015 Sony Does DFA During Concept Design

AOD for LGO 7 © Daniel E Whitney 9/15/2015 Things an Assembly Theory Must Do Represent top-level goals for the assembly Link these goals to requirements on the assembly and the parts Represent nominal and varied location of parts in space Provide for declaration of mutual constraint between parts Merge design of assembly and of assembly processes, including adjustments and fixtures Support a design process for assemblies that can be added to CAD

AOD for LGO 8 © Daniel E Whitney 9/15/2015 This Theory of Assembly... Focuses on “Kinematic Assemblies” Emphasizes Delivery of Key Characteristics (KCs) Documents KC Delivery and Constraint with the Datum Flow Chain (DFC) Achieves Constraint with Assembly Features Achieves DFC Robustness via Tolerance Analysis Exploits Underconstrained Assemblies to Achieve Adjustments

AOD for LGO 9 © Daniel E Whitney 9/15/2015 What Happens During Assembly People think assembly is fastening Assembly is really the chaining together of coordinate frames These chains of frames “deliver” certain parts or features on parts to desired places in space relative to other parts or features on them within tolerances Complete chains describe Key Characteristics of the assembly This theory of assembly generates a design process for assemblies based on creating these chains

AOD for LGO 10 © Daniel E Whitney 9/15/2015 “Chain of Delivery” of Quality No single part “delivers” the KC. Closure Panel Check Fixture: Fixture Vendor G Organizational Boundary LIF RIF RS LOFROF H KC KC BF G Liaison Diagram:

AOD for LGO 11 © Daniel E Whitney 9/15/2015 Maintaining Oversight on KCs To design the chains that deliver the KCs, we have developed the Datum Flow Chain (DFC) A DFC is an assembly-level statement of design intent that- –documents the chain that delivers the KC –identifies the parts that make up the chain –provides a skeleton for the strategy by which the parts will be located in space as links in the chain Each step in the assembly process adds links to the chain and each subassembly is kinematically constrained

AOD for LGO 12 © Daniel E Whitney 9/15/2015 Office Stapler Liaison Diagram

AOD for LGO 13 © Daniel E Whitney 9/15/2015 Datum Flow Chains in the Stapler The datum flow chain is a chain of constraining mates from one end of the KC to the other.

AOD for LGO 14 © Daniel E Whitney 9/15/2015 Mates, Contacts, and KC Delivery MateContact Mates give location. Contacts reinforce location. Variation travels from part to part along the chain of mates.

AOD for LGO 15 © Daniel E Whitney 9/15/2015 Coordinate Frames..

AOD for LGO 16 © Daniel E Whitney 9/15/2015 Chains of Frames = Assembly.

AOD for LGO 17 © Daniel E Whitney 9/15/2015 Dash L. Fender R. Fender L. Body Side R. Body side L. Door R. Door Underbody R. Apron L. Apron L. I. Shot. R. I. Shot. L. O. Shot. R. O. Shot. L. O. Rail R. O. Rail Hood L. HingeR. Hinge Bolster Hood Latch L. Lamp R. Lamp Fascia L. I. Rail R.I. Rail y, z F1 L. Bracket x,  x,  y,  z y,  z x, z,  x,  y,  z y xx y y z,  y x,  x 6 6 x, z,  x,  y,  z x,  x,  y,  z 66 Hood fixture FF F F F F F x, z,  x,  y x, z  x,  y 6 F F F F 6 z,  x  y F x,  x y, z,  y,  z z,  y y x, y,  z x  y,  z x, y,  z F F Datum Flow Chain for Car Front End Drawn by Gennadiy Goldenshteyn, MIT Student

AOD for LGO 18 © Daniel E Whitney 9/15/2015 DFC for Aircraft Circumference

AOD for LGO 19 © Daniel E Whitney 9/15/2015 DFC Carries Design Intent Designer declares how KCs will be delivered Intent is expressible in CAD terms Intent expressed this way is independent of CAD vendor DFCs can be bookshelved for future use

AOD for LGO 20 © Daniel E Whitney 9/15/2015 Connective Assembly Model Parts A and B are joined by two features The nominal location of part B can be calculated from the nominal location of part A using 4x4 transform math T T T AF FB AB A B T AF A T FB B

AOD for LGO 21 © Daniel E Whitney 9/15/2015 Varied Part Location Due to Variation T T T AF FB' AB' A B' T BB' The varied location of Part B can be calculated from the nominal location of Part A. This process can be chained to Part C, etc., including errors on Part B. It uses the same math as the nominal model.

AOD for LGO 22 © Daniel E Whitney 9/15/2015 Stapler Variations. CARRIER STAPLE ANVIL RIVETCRIMPER X ERROR ANVIL RIVET CRIMPER CARRIER STAPLES  Y ERROR

AOD for LGO 23 © Daniel E Whitney 9/15/2015 When Parts are Joined, Degrees of Freedom are Fixed Parts join at places called assembly features Different features constrain different numbers and kinds of degrees of freedom of the respective parts (symmetrically) Parts may join by –one pair of features –multiple features –several parts working together, each with its own features When parts mate to fixtures, dofs are constrained

AOD for LGO 24 © Daniel E Whitney 9/15/2015 Overconstrained and “Properly” Constrained Assemblies Assemblies that function by geometric compatibility and force/moment equilibrium are called –statically determinate –“properly” constrained –“kinematic” or “semi-kinematic” Assemblies that require the other principle of statics (stress-strain relations) are called –statically indeterminate –“over-constrained” Constraint is a property of the nominal design

AOD for LGO 25 © Daniel E Whitney 9/15/2015 Car Seat Mounting Original Design: 25mm ± 0.5 mm 4 Holes Final Design 25mm ± 0.5mm 25mm x 40mm 40mm As the vehicle moved into launch, the model continued to be updated to reflect locator changes, assembly sequence changes and actual production dimensional control levels. The seat installation process was having difficulty achieving consistent clearance to trim panels. The model demonstrated that the see was over located by four sized holes and operator dependent for installation. Be increasing the size of two mounting holes and elongating a slot on the third stanchion, the remaining sized hole became the 4-way locator. The operator was instructed to start with this hole. Surprisingly, consistent installation was achieved, by increasing the tolerances for the three holes.

AOD for LGO 26 © Daniel E Whitney 9/15/2015 Summary of Assembly Theory - Nominal Design An assembly is a set of parts that deliver their quality, defined by the KCs, as a result of the geometric relationships between the parts (and fixtures) Designing an assembly means designing these relationships in terms of one DFC per KC –The DFC documents the nominal relationships in terms of constraint –The DFC passes from part to part via mates The nominal design is a constraint structure Assembly features create the constraint relationships at each mate

AOD for LGO 27 © Daniel E Whitney 9/15/2015 Summary of Assembly Theory - Variation Design Tolerances should assure the robustness of the DFC KC delivery is verified by a tolerance analysis of each DFC Tolerances on parts derive from tolerances on the KCs Part tolerances are sublinks of the DFC Type-1 assembly-level tolerances come from part tolerances Type-2 assembly-level tolerances can be altered by adjustments to the assembly process

AOD for LGO 28 © Daniel E Whitney 9/15/2015 Assembly Course Topics Assembly in the small: –Physics of part mating Assembly in the large: –Key characteristics –Constraint –Tolerances –DFA –Product architecture, customization A class project on these topics lasts all term

AOD for LGO 29 © Daniel E Whitney 9/15/2015 Poll 1.We design assemblies explicitly as part of our product development process 2.Our suppliers design our assemblies 3.We design things and our manufacturing engineers try to get us to change them 4.We design parts using the best CAD system in the world and then we wonder why we have trouble assembling them 5.We don’t have any assembly problems

AOD for LGO 30 © Daniel E Whitney 9/15/2015 Questions and Answers