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Product specification Dimensioning and tolerancing

Product specification Dimensioning and tolerancing. It is impossible to make a perfect component so when we design a part we specify the acceptable range of features that make-up the part. Chapter 2 Suppliment DIMENSIONS, TOLERANCES, AND SURFACES.

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Product specification Dimensioning and tolerancing

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  1. Product specificationDimensioning and tolerancing It is impossible to make a perfect component so when we design a part we specify the acceptable range of features that make-up the part.

  2. Chapter 2 SupplimentDIMENSIONS, TOLERANCES, AND SURFACES • Dimensions, Tolerances, and Related Attributes • Surfaces • ASME Y14.5 Form Geometry • Effect of Manufacturing Processes IE 316 Manufacturing Engineering I - Processes

  3. THE DESIGN PROCESSProduct Engineering Design Process How can this be accomplished? 1. Clarification of the task 2. Conceptual design 3. Embodiment design 4. Detailed design 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

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

  5. A FREE-HAND SKETCHOrthographic Projection

  6. 0.9444" A FORMAL 3-VIEW DRAWING 4 holes 1/4" dia around 2" dia , first hole at 45° ± 2.000 0.001 A

  7. 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

  8. INTERPRETING A DRAWING

  9. 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

  10. 1.22 ' 0.98 ' 3.03 ' 1.72 ' 1.22 ' 3.03 ' DIMENSIONING Requirements 1. Unambiguous 2. Completeness 3. No redundancy Incomplete dimensioning 0.83 ' Redundant dimensioning 0.86 ' 0.83 ' Adequate dimensioning

  11. TOLERANCE Dimensional tolerance - conventional Geometric tolerance - modern 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 -

  12. 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

  13. 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

  14. 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

  15. TOLERANCE GRAPH d,t d,t d,t 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,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.

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

  17. 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?

  18. 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

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

  20. 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

  21. 3-D GEOMETRIC TOLERANCEPROBLEMS datum surface datum surface ± t Reference frame perpendicularity

  22. 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 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

  23. 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.

  24. 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)?

  25. 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.

  26. A RELATION BETWEENPRODUCT & PROCESSTOLERANCES • 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. ± 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

  27. 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

  28. 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

  29. 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

  30. 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 tolerance value symbol

  31. 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

  32. 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.

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

  34. 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

  35. Dimensions and Tolerances • In addition to mechanical and physical properties, other factors that determine the performance of a manufactured product include: • Dimensions - linear or angular sizes of a component specified on the part drawing • Tolerances- allowable variations from the specified part dimensions that are permitted in manufacturing IE 316 Manufacturing Engineering I - Processes

  36. Surfaces • Nominalsurface - intended surface contour of part, defined by lines in the engineering drawing • The nominal surfaces appear as absolutely straight lines, ideal circles, round holes, and other edges and surfaces that are geometrically perfect • Actual surfaces of a part are determined by the manufacturing processes used to make it • The variety of manufacturing processes result in wide variations in surface characteristics IE 316 Manufacturing Engineering I - Processes

  37. Why Surfaces are Important • Aesthetic reasons • Surfaces affect safety • Friction and wear depend on surface characteristics • Surfaces affect mechanical and physical properties • Assembly of parts is affected by their surfaces • Smooth surfaces make better electrical contacts IE 316 Manufacturing Engineering I - Processes

  38. Surface Technology • Concerned with: • Defining the characteristics of a surface • Surface texture • Surface integrity • Relationship between manufacturing processes and characteristics of resulting surface IE 316 Manufacturing Engineering I - Processes

  39. Figure 5.2 ‑ A magnified cross‑section of a typical metallic part surface IE 316 Manufacturing Engineering I - Processes

  40. Surface Texture The topography and geometric features of the surface • When highly magnified, the surface is anything but straight and smooth. It has roughness, waviness, and flaws • It also possesses a pattern and/or direction resulting from the mechanical process that produced it IE 316 Manufacturing Engineering I - Processes

  41. Surface Integrity Concerned with the definition, specification, and control of the surface layers of a material (most commonly metals) in manufacturing and subsequent performance in service • Manufacturing processes involve energy which alters the part surface • The altered layer may result from work hardening (mechanical energy), or heating (thermal energy), chemical treatment, or even electrical energy • Surface integrity includes surface texture as well as the altered layer beneath IE 316 Manufacturing Engineering I - Processes

  42. Surface Texture Repetitive and/or random deviations from the nominal surface of an object Figure 5.3 ‑ Surface texture features IE 316 Manufacturing Engineering I - Processes

  43. Four Elements of Surface Texture • Roughness - small, finely‑spaced deviations from nominal surface determined by material characteristics and process that formed the surface • Waviness - deviations of much larger spacing; they occur due to work deflection, vibration, heat treatment, and similar factors • Roughness is superimposed on waviness IE 316 Manufacturing Engineering I - Processes

  44. 3. Lay - predominant direction or pattern of the surface texture Figure 5.4 ‑ Possible lays of a surface IE 316 Manufacturing Engineering I - Processes

  45. 4. Flaws - irregularities that occur occasionally on the surface • Includes cracks, scratches, inclusions, and similar defects in the surface • Although some flaws relate to surface texture, they also affect surface integrity IE 316 Manufacturing Engineering I - Processes

  46. Surface Roughness and Surface Finish Surface roughness - a measurable characteristic based on roughness deviations Surface finish - a more subjective term denoting smoothness and general quality of a surface • In popular usage, surface finish is often used as a synonym for surface roughness • Both terms are within the scope of surface texture IE 316 Manufacturing Engineering I - Processes

  47. Surface Roughness Average of vertical deviations from nominal surface over a specified surface length Figure 5.5 ‑ Deviations from nominal surface used in the two definitions of surface roughness IE 316 Manufacturing Engineering I - Processes

  48. Surface Roughness Equation Arithmetic average (AA) is generally used, based on absolute values of deviations, and is referred to as average roughness where Ra = average roughness; y = vertical deviation from nominal surface (absolute value); and Lm = specified distance over which the surface deviations are measured IE 316 Manufacturing Engineering I - Processes

  49. An Alternative Surface Roughness Equation Approximation of previous equation is perhaps easier to comprehend: where Ra has the same meaning as above; yi = vertical deviations (absolute value) identified by subscript i; and n = number of deviations included in Lm IE 316 Manufacturing Engineering I - Processes

  50. Cutoff Length • A problem with the Ra computation is that waviness may get included • To deal with this problem, a parameter called the cutoff length is used as a filter to separate waviness from roughness deviations • Cutoff length is a sampling distance along the surface. A sampling distance shorter than the waviness width eliminates waviness deviations and only includes roughness deviations IE 316 Manufacturing Engineering I - Processes

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