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PART DESIGN SPECIFICATION

PART DESIGN SPECIFICATION. Fall 2008 Dr. R. A. Wysk. Go over engineering specifications Functional requirements Form, fit and function Dimensioning Tolerancing Engineering drawings datum. Agenda. Read Chapter 2 and 3 from Computer Aided manufacturing (3 rd Edition)

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PART DESIGN SPECIFICATION

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  1. PART DESIGN SPECIFICATION Fall 2008 Dr. R. A. Wysk

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

  3. 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 Materials

  4. Design Process How can this be accomplished? 1. Clarification of the task 2. Conceptual design 3. Embodiment design 4. Detailed design THE DESIGN PROCESSProduct Engineering Design Process Off-road bicycle that ... 1. Conceptualization 2. Synthesis 3. Analysis 4. Evaluation 5. Representation 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

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

  6. A FREE-HAND SKETCHOrthographic Projection

  7. 0.9444" A FORMAL 3-VIEW DRAWING 4 holes 1/4" dia around 2" dia , first hole at 45° ± 2.000 0.001 A

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

  9. INTERPRETING A DRAWING

  10. A A ± 2 . 0 0 0 0 . 0 0 1 A DESIGN DRAFTING Partial view A - A Cut off view and auxiliary view Provide more local details

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

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

  13. 1.20 ' ±0.01 1.00 ' ±0.01 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? 0.80 ' ±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

  14. 3.00 ' ±0.01 TOLERANCE STACKING (ii) ? 0.80 ' ±0.01 1.20 ' ±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

  15. 1.20 ' ±0.01 3.00 ' ±0.01 TOLERANCE STACKING (iii) x ? 0.80 ' ±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

  16. G(N,d,t) N: a set of reference lines, sequenced nodes d: a set of dimensions, arcs t: a set of tolerances, arcs TOLERANCE GRAPH d,t d,t d,t A B C D E d,t 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.

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

  18. If one or more cycles can be detected in the graph, we say that the dimension and tolerance are over specified. OVER SPECIFICATION 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?

  19. UNDER SPECIFICATION When one or more nodes are disconnected from the graph, the dimension or tolerance is under specified. d2 d1 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

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

  21. 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? TOLERANCE ANALYSIS 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

  22. 3-D GEOMETRIC TOLERANCEPROBLEMS datum surface datum surface ± t Reference frame perpendicularity

  23. 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.) TOLERANCE ASSIGNMENT Q u a l i t y C o s t function cost + t - t d ( n o m i n a l d i m e n s i o n ) Tolerance value Quality cost

  24. • 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. REASON OF HAVING TOLERANCE

  25. 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)?

  26. 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.

  27. 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 RELATION BETWEENPRODUCT & PROCESSTOLERANCES ± 0 . 0 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 ± 0 . 0 0 5 ± 0 . 0 0 5 ± 0 . 0 0 5 Process tolerance

  28. A method to allocate process tolerance and verify that the process sequence and machine selection can satisfy the design tolerance. TOLERANCE CHARTING 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

  29. 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 63 waviness width roughness height 0.002 - 2 63 roughness width cutoff default is 0.03" (ANSI Y14.36-1978) 0.010 0.005 (m inch) roughness width (inch) Lay

  30. PROBLEMS WITH DIMENSIONALTOLERANCE ALONE As designed: 1 . 0 0 ± 0 . 0 0 1 6 . 0 0 ± 0 . 0 0 1 As manufactured: 1 . 0 0 1 1 . 0 0 1 Will you accept the part at right? Problem is the control of straightness. How to eliminate the ambiguity? 1 . 0 0 1 6 . 0 0

  31. FORM straightness flatness Circularity cylindricity 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 ORIENTATION perpendicularity angularity parallelism Squareness roundness LOCATION concentricity true position symmetry RUNOUT circular runout total runout PROFILE profile profile of a line

  32. 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: DATUM & FEATURE CONTROL FRAME A datum // 0.005 M A modifier tolerance value symbol

  33. 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 MODIFIERS maintain critical wall thickness or critical location of features. MMC, RFS, LMC MMC, RFS RFS

  34. 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. SOME TERMS

  35. 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 primary Tertiary O 0.001 M A B C DATUM REFERENCE FRAME . P r i m a r y T e a y r r t i S e c o n d a r y Secondary C B A

  36. 1.000 ' ±0.002 1.000 ' ±0.002 STRAIGHTNESS Tolerance zone between two straightness lines. Value must be smaller than the size tolerance. 0 . 0 0 1 M e a s u r e d e r r o r Š 0 . 0 0 1 0 . 0 0 1 0 . 0 0 1 Design Meaning

  37. 1.000 ' ±0.002 FLATNESS Tolerance zone defined by two parallel planes. 0 . 0 0 1 p a r a l l e l p l a n e s 0 . 0 0 1

  38. 1.00 ' ±0.05 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. 0 . 0 1 0 . 0 1 T o l e r a n c e z o n e At any section along the cylinder

  39. 1.00 ' ±0.05 CYLINDRICITY Tolerance zone bounded by two concentric cylinders within which the cylinder must lie. 0 . 0 1 Rotate in a V 0 . 0 1 Rotate between points

  40. A . 0 0 2 T 1.000 ' ±0.005 0.500 ' ±0.005 2.000 ' ±0.005 PERPENDICULARITY A surface, median plane, or axis at a right angle to the datum plane or axis. . 0 0 2 A 0 . 0 0 2 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 A A 0 . 0 0 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 . 0 0 ± 0 . 0 1 t o t h e d a t u m p l a n e . 0 0 2 A

  41. 3.500 ' ±0.005 ANGULARITY A surface or axis at a specified angle (orther than 90°) from a datum plane or axis. Can have more than one datum. 0 . 0 0 5 A 1 . 5 0 0 ± 0 . 0 0 5 4 0 ° A

  42. 1.000 " ±0.005 2.000 " ±0.005 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. . 0 0 1 A A 0 . 0 0 1

  43. B PROFILE A uniform boundary along the true profile within whcih the elements of the surface must lie. 0 . 0 0 5 A B 0 . 0 0 1 A

  44. 1.500 " ±0.005 0.361 " ±0.002 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. A 0 . 0 0 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

  45. 1.500 " ±0.005 0.361 " ±0.002 TOTAL RUNOUT A 0 . 0 0 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 .

  46. TRUE POSITION T o l e r a n c e z o n e 2 Dimensional tolerance 0 . 0 2 1 . 0 0 ± 0 . 0 1 1 . 2 0 ± 0 . 0 1 O . 8 0 ± 0 . 0 2 Hole center tolerance zone O 0 . 0 1 M A B True position tolerance T o l e r a n c e z o n e 0 . 0 1 d i a 1 . 0 0 B 1 . 2 0 A

  47. 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.

  48. 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 TOLERANCE VALUE MODIFICATION O 1 . 0 0 ± 0 . 0 2 O 0 . 0 1 M A B 1 . 0 0 M L S B 1 . 2 0 MMC LMC A The default modifier for true position is MMC. For M the allowable tolerance = specified tolerance + (produced hole size - MMC hole size)

  49. 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. MMC HOLE ,

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