METROLOGY

1. Manufacturing Processes METROLOGY Lecture 3 (Cont) Vu Anh Tuan

2. Outline • Geometric Dimensioning & Tolerance (GD&T) • Metrology

3. Goals • Provide students with definition of manufacturing accuracy • Describe possible errors in manufacturing processes • Introduce basic concepts with geometric tolerance of parts after machining • Equip students with the knowledge and ability to design and select proper measuring method to evaluate functions of machined parts

4. Outline • Geometric Dimensioning & Tolerance (GD&T) • Geometric tolerance • Metrology

5. Form errors • Does the pin show its proper functionality, even though size tolerance is fulfilled? • Form error is deviation between actual surface/profile and “ideal surface/profile” as design.

6. Form errors • Form error value is computed by an introduction of a datum. • The value of form errors are equal to the largest distance between actual geometry to datum geometry. • Datum geometries are included: datum line, datum circle and datum plane.

7. Datum definitions • Datum line is defined in such a way that the distance between a furthest point of actual geometry to this line is smallest. Linear datum

8. Datum definitions • Datum circle is defined in such a way that the distance between a furthest point of actual geometry to this circle is smallest.

9. Profile datum Actual profile Datum definitions • Datum cylinder is defined in such a way that the distance between a furthest point of actual geometry to this cylinder is smallest.

10. Plane datum Actual datum Datum definitions • Datum plane is defined in such a way that the distance between a furthest point of actual geometry to this plane is smallest.

11. DATUM FEATURE SIMULATOR (ADJUSTABLE GAUGE) DATUM FEATURE (ACTUAL SURFACE OF PART) DATUM FEATURE DATUM PLANE DATUM AXIS (CENTERLINE OF ADJUSTABLE GAUGE) SURFACE PLATE (DATUM FEATURE SIMULATOR) Datum Features vs. Datum Plane/Axis • Datum features are the features (surfaces…) on the part. The features are selected for datum based on their relationship to toleranced features. • Symbol for a datum is a capital letter in a box, for example: • Datum plane is a datum simulator such as a surface plate.

12. Meaning of datum features • Mating parts contact on their datum features. The clearance (gap) between two datum features within a fit is equal to 0. • In inspection process, datum feature of the measured part is equivalent to datum feature of measuring devices.

13. GD&T Symbols / Meanings

14. Example GD&T Symbols / Meanings

15. Datum line Planar form tolerance • Planar form tolerance is included: Straightness and Flatness • Symbols: straightness Flatness

16. Straightness • This form of tolerance specifies a tolerance zone for all the points on an element about a straight axis line • In the model shown above, it is required for the central axial line to be within a tolerance zone of 0.04 mm

17. Flatness /Evenness • This refers to a tolerance characterized by two parallel planes within which an elemental surface lies • In the model shown above, it is required that the surface has to be within a tolerance zone of 0.02 mm.

18. 0.03 tolerance zone Circular form tolerance • Circular form tolerance is included: Cylindricity & Roundness • Cylindricity:

19. Circular form tolerance • Circular form tolerance is included: Cylindricity & Roundness • Roundness: This refers to a tolerance zone bounded by two concentric circles within which each circular element of the surface must lie. • A circular tolerance zone of 0.25 mm is required in the model shown above.

20. Circular form tolerance • In special form, cylindricity can be in following forms:

21. Orientation tolerance - Parallelism

22. Datum Orientation tolerance - Parallelism

23. Datum plane Orientation tolerance - Perpendicularity

24. 0.05 tolerance zone 45.00° 45.00° Orientation tolerance - Angularity

25. Mutual datum axis Datum axis Tolerance of Location • Location tolerances are included: • Concentricity • Position • Symmetry

26. Run-out tolerance • Two types of run-out: • Circular Run-out • Total Run-out

27. Surface roughness • Product surface is not always smooth after machining; roughness is maintained on the finished surface after plastic deformation. • This occurrence is due to manufacturing errors. • Depending height and pitch of roughness, it is composed of: • Form deviation • Waviness • Roughness

28. Influences of roughness on product services • Stress concentration on the top of roughness  clearance increase, service-life time decrease • Avoid the appearance of lubricant in the space between two contact  increase friction, wear • Strength and endurance of products are reduced if they are induced dynamic and cyclic loads • Rusty and corrosion

29. Top line Depth line Mean line Profile roughness parameters • A roughness value can either be calculated on a profile or on a surface. The profile roughness parameter (Ra, Rz,...) are more common. The area roughness parameters (Sa, Sq,...) give more significant values.

30. Top line Depth line Mean line Profile roughness parameters • Ra parameter (most common) - arithmetic average of absolute values

31. Top line Depth line Mean line Profile roughness parameters • Rz parameter – average value based on five highest peaks and lowest valleys over the entire sample length.

32. Profile roughness parameters

33. Outline • Geometric Dimensioning & Tolerance (GD&T) • Metrology