PART DESIGN SPECIFICATION Spring 2011 Dr. R. A. Wysk

Agenda Go over engineering specifications Functional requirements Form, fit and function Dimensioning Tolerancing Engineering drawings datum

Materials Read Chapter 2 and 3 from Computer Aided manufacturing (3rd Edition) Overview of engineering design Mechanical design representations Engineering drawing Geometric dimensioning and tolerancing AMSE Y14.5

THE DESIGN PROCESS Product Engineering Off-road bicycle that ... 1. Conceptualization 2. Synthesis 3. Analysis 4. Evaluation 5. Representation Design Process How can this be accomplished? 1. Clarification of the task 2. Conceptual design 3. Embodiment design 4. Detailed design Functional requirement -> Design Steps 1 & 2 Select material and properties, begin geometric modeling (needs creativity, sketch is sufficient) 3 mathematical, engineering analysis 4 simulation, cost, physical model 5 formal drawing or modeling

DESIGN REPRESENTATION Engineering Representation Manufac- turing • Verbal • Sketch • Multi-view orthographic drawing (drafting) • CAD drafting • CAD 3D & surface model • Solid model • Feature based design Requirement of the representation method • precisely convey the design concept • easy to use

A FREE-HAND SKETCH Orthographic Projection

A FORMAL 3-VIEW DRAWING 0.9444" A 4 holes 1/4" dia around 2" dia , first hole at 45° ± 2.000 0.001 A

DESIGN DRAFTING Third angle projection Drafting in the third angle Y P z o n t a l Z I X I I V F r o n t a l p l a n e Third angle projection Drafting in the third angle

INTERPRETING A DRAWING

DESIGN DRAFTING Partial view Cut off view and auxiliary view 2 . ± 1 Partial view A - A Cut off view and auxiliary view Provide more local details

DIMENSIONING Requirements 1. Unambiguous 2. Completeness 3. No redundancy Incomplete dimensioning 0.98 ' 1.22 ' 1.72 ' 0.83 ' 3.03 ' Redundant dimensioning 0.86 ' 1.22 ' 0.83 ' 3.03 ' Adequate dimensioning

TOLERANCE Dimensional tolerance - conventional Geometric tolerance - modern nominal dimension + 1.00 0.05 - means a range 0.95 - 1.05 tolerance + 0.10 - 0.00 + 0.00 - 0.10 unilateral bilateral 0.95 1.05 1.00 0.05 + -

TOLERANCE STACKING 1. Check that the tolerance & dimension specifications are reasonable - for assembly. 2. Check there is no over or under specification. "TOLERANCE IS ALWAYS ADDITIVE" why? 1.20 ' ±0.01 0.80 ' ±0.01 1.00 ' ±0.01 ? What is the expected dimension and tolerances? d = 0.80 +1.00 + 1.20 = 3.00 t = ± (0.01 + 0.01 + 0.01) = ± 0.03

TOLERANCE STACKING (ii) ? 0.80 ' ±0.01 1.20 ' ±0.01 3.00 ' ±0.01 What is the expected dimension and tolerances? d = 3.00 - 0.80 - 1.20 = 1.00 t = ± (0.01 + 0.01 + 0.01) = ± 0.03

TOLERANCE STACKING (iii) x 1.20 ' ±0.01 ? 0.80 ' ±0.01 3.00 ' ±0.01 Maximum x length = 3.01 - 0.79 - 1.19 = 1.03 Minimum x length = 2.99 - 0.81 - 1.21 = 0.97 Therefore x = 1.00 ± 0.03

TOLERANCE GRAPH A B C D E G(N,d,t) N: a set of reference lines, sequenced nodes d: a set of dimensions, arcs t: a set of tolerances, arcs d : dimension between references i & j t : tolerance between references i & j ij ij Reference i is in front of reference j in the sequence.

EXAMPLE TOLERANCE GRAPH d,t d,t d,t A B C D E d,t different properties between d & t

OVER SPECIFICATION If one or more cycles can be detected in the graph, we say that the dimension and tolerance are over specified. d1 d2 A B C d1,t1 d2,t2 d3 Redundant dimension d3,t3 A B C t1 t2 A B C t3 Over constraining tolerance (impossible to satisfy) why?

UNDER SPECIFICATION When one or more nodes are disconnected from the graph, the dimension or tolerance is under specified. d1 d2 A B C D E d3 A B C D E C D is disconnected from the rest of the graph. No way to find

PROPERLY TOLERANCED A B C D E d,t d,t d,t A B C D E d,t

TOLERANCE ANALYSIS For two or three dimensional tolerance analysis: i. Only dimensional tolerance Do one dimension at a time. Decompose into X,Y,Z, three one dimensional problems. ii. with geometric tolerance ? Don't have a good solution yet. Use simulation? d i a m e t e r & t o l e r a n c e A circular tolerance zone, the size is influenced by the diameter of the hole. The shape of the hole is also defined by a geometric tolerance. t r u e p o s i t i o n

3-D GEOMETRIC TOLERANCE PROBLEMS datum surface datum surface ± t Reference frame perpendicularity

TOLERANCE ASSIGNMENT Tolerance is money • Specify as large a tolerance as possible as long as functional and assembly requirements can be satisfied. (ref. Tuguchi, ElSayed, Hsiang, Quality Engineering in Production Systems, McGraw Hill, 1989.) Q u a l i t y function C o s t cost + t - t d ( n o m i n a l d i m e n s i o n ) Tolerance value Quality cost

REASON OF HAVING TOLERANCE • No manufacturing process is perfect. • Nominal dimension (the "d" value) can not be achieved exactly. • Without tolerance we lose the control and as a consequence cause functional or assembly failure.

EFFECTS OF TOLERANCE (I) 1. Functional constraints e.g. flow rate d ± t Diameter of the tube affects the flow. What is the allowed flow rate variation (tolerance)?

EFFECTS OF TOLERANCE (II) 2. Assembly constraints e.g. peg-in-a-hole dp How to maintain the clearance? dh Compound fitting The dimension of each segment affects others.

RELATION BETWEEN PRODUCT & PROCESS TOLERANCES Machine uses the locators as the reference. The distances from the machine coordinate system to the locators are known. The machining tolerance is measured from the locators. • In order to achieve the 0.01 tolerances, the process tolerance must be 0.005 or better. • When multiple setups are used, the setup error need to be taken into consideration. A ± . 1 t o l e r a n c e s Design specifications S e t u p l o c a t o r s ± . 5 ± . 5 ± . 5 Process tolerance

TOLERANCE CHARTING A method to allocate process tolerance and verify that the process sequence and machine selection can satisfy the design tolerance. Not shown are process tolerance assignment and balance blue print Operation sequence produced tolerances: process tol of 10 + process tol of 12 process tol of 20 + process tol 22 process tol of 22 + setup tol

SURFACE FINISH w a v i n e s s r o u g h n e s s r o u g h n e s s w i d t h w a v i n e s s w i d t h Usually simplified: waviness height waviness width 63 roughness height 0.002 - 2 (m inch) 63 0.010 0.005 roughness width cutoff default is 0.03" (ANSI Y14.36-1978) roughness width Lay (inch)

PROBLEMS WITH DIMENSIONAL TOLERANCE ALONE As designed: 1 . ± . 1 6 . ± . 1 As manufactured: 1 . 1 Will you accept the part at right? Problem is the control of straightness. How to eliminate the ambiguity? 1 . 1 1 . 1 6 .

GEOMETRIC TOLERANCES ANSI Y14.5M-1977 GD&T (ISO 1101, geometric tolerancing; ISO 5458 positional tolerancing; ISO 5459 datums; and others), ASME Y14.5 - 1994 FORM straightness flatness Circularity cylindricity ORIENTATION perpendicularity angularity parallelism Squareness roundness LOCATION concentricity true position symmetry RUNOUT circular runout total runout PROFILE profile profile of a line

DATUM & FEATURE CONTROL FRAME Datum: a reference plane, point, line, axis where usually a plane where you can base your measurement. Symbol: Even a hole pattern can be used as datum. Feature: specific component portions of a part and may include one or more surfaces such as holes, faces, screw threads, profiles, or slots. Feature Control Frame: A datum // 0.005 M A modifier symbol tolerance value

MODIFIERS Maximum material condition MMC assembly Regardless of feature size RFS (implied unless specified) Least material condition LMC less frequently used Projected tolerance zone Diametrical tolerance zone T Tangent plane F Free state maintain critical wall thickness or critical location of features. MMC, RFS, LMC MMC, RFS RFS

SOME TERMS MMC : Maximum Material Condition Smallest hole or largest peg (more material left on the part) LMC : Least Material Condition Largest hole or smallest peg (less material left on the part) Virtual condition: Collective effect of all tolerances specified on a feature. Datum target points: Specify on the drawing exactly where the datum contact points should be located. Three for primary datum, two for secondary datum and one or tertiary datum.

DATUM REFERENCE FRAME . Three perfect planes used to locate the imperfect part. a. Three point contact on the primary plane b. two point contact on the secondary plane c. one point contact on the tertiary plane P r i m a r y T e r t i a r y S e c o n d a r y Secondary O 0.001 M A B C primary Tertiary C B A

STRAIGHTNESS Tolerance zone between two straightness lines. . 1 Value must be smaller than the size tolerance. 1.000 ' ±0.002 M e a s u r e d e r r o r Š . 1 . 1 1.000 ' ±0.002 . 1 Design Meaning

FLATNESS Tolerance zone defined by two parallel planes. . 1 1.000 ' . 1 1.000 ' ±0.002 p a r a l l e l p l a n e s . 1

CIRCULARITY (ROUNDNESS) a. Circle as a result of the intersection by any plane perpendicular to a common axis. b. On a sphere, any plane passes through a common center. Tolerance zone bounded by two concentric circles. . 1 1.00 ' ±0.05 . 1 T o l e r a n c e z o n e At any section along the cylinder

CYLINDRICITY Tolerance zone bounded by two concentric cylinders within which the cylinder must lie. . 1 1.00 ' ±0.05 Rotate in a V . 1 Rotate between points

PERPENDICULARITY A surface, median plane, or axis at a right angle to the datum plane or axis. . 2 T A . 2 A . 2 1.000 ' ±0.005 t o l e r a n c e z o n e p e r p e n d i c u l a r t o t h e d a t u m p l a n e 0.500 ' ±0.005 A 2.000 ' ±0.005 A . 2 d i a m e t e r t o l z o n e i s p e r p e n d i c u l a r O 1 . ± . 1 t o t h e d a t u m p l a n e . 2 A

ANGULARITY A surface or axis at a specified angle (orther than 90°) from a datum plane or axis. Can have more than one datum. . 5 A 1 . 5 ± . 5 4 ° 3.500 ' ±0.005 A

PARALLELISM The condition of a surface equidistant at all points from a datum plane, or an axis equidistant along its length to a datum axis. . 1 A 1.000 " ±0.005 2.000 " ±0.005 A . 1

PROFILE A uniform boundary along the true profile within whcih the elements of the surface must lie. . 5 A B B A . 1

RUNOUT A composite tolerance used to control the functional relationship of one or more features of a part to a datum axis. Circular runout controls the circular elements of a surface. As the part rotates 360° about the datum axis, the error must be within the tolerance limit. 1.500 " ±0.005 A 0.361 " ±0.002 . 5 A D e v i a t i o n o n e a c h c i r c u l a r c h e c k r i n g i s l e s s t h a n t h e D a t u m t o l e r a n c e . a x i s

TOTAL RUNOUT 1.500 " ±0.005 A 0.361 " ±0.002 . 5 A D e v i a t i o n o . 5 A D e v i a t i o n o n t h e t o t a l s w e p t w h e n t h e p a r t i s r o t a t i n g D a t u m i s l e s s t h a n t h e a x i s t o l e r a n c e .

TRUE POSITION Dimensional tolerance Hole center tolerance zone . 2 2 1 . ± . 1 1 . 2 ± . 1 O . 8 ± . 2 Hole center tolerance zone O . 1 M A B True position tolerance T o l e r a n c e z o n e . 1 d i a 1 . B A 1 . 2

HOLE TOLERANCE ZONE Tolerance zone for dimensional toleranced hole is not a circle. This causes some assembly problems. For a hole using true position tolerance the tolerance zone is a circular zone.

TOLERANCE VALUE MODIFICATION 1 . ± . 2 O . 1 M A B Produced True Pos tol hole size 0.97 out of diametric tolerance 0.98 0.01 0.05 0.01 0.99 0.02 0.04 0.01 1.00 0.03 0.03 0.01 1.01 0.04 0.02 0.01 1.02 0.05 0.01 0.01 1.03 out of diametric tolerance 1 . M L S B 1 . 2 MMC LMC A The default modifier for true position is MMC. For M the allowable tolerance = specified tolerance + (produced hole size - MMC hole size)

MMC HOLE , Given the same peg (MMC peg), when the produced hole size is greater than the MMC hole, the hole axis true position tolerance zone can be enlarged by the amount of difference between the produced hole size and the MMC hole size.

PROJECTED TOLERANCE ZONE Applied for threaded holes or press fit holes to ensure interchangeability between parts. The height of the projected tolerance zone is the thickness of the mating part. . 3 7 5 - 1 6 U N C - 2 B O . 1 M A B C . 2 5 p

SOME NUMBERS Krulikowski, A., GD&T Challenges the Fast Draw, MFG ENG, Feb 1994. GD&T drawings are more expansive to make, however, saves revision cost. Drawing revision costs $500 - $2000 on the paper work How much does it cost to “put a part number” onto a part? Estimates range from $1,000 -$10,000.