Chapter 4 Surfaces, Tribology, Dimensional Characteristics, Inspection and Product Quality Assurance

Transcription

1 Chapter 4 Surfaces, Tribology, Dimensional Characteristics, Inspection and Product Quality Assurance

2 Cross-Section of Metal Surface FIGURE 4.1 Schematic illustration of the cross-section of the surface structure of metals. The thickness of the individual layers depends on processing conditions and the environment. Source: After E. Rabinowicz and B. Bhushan.

3 Surface Finish FIGURE 4.2 (a) standard terminology and symbols used to describe surface finish. The quantities are given in µ in. (b) Common surface-lay symbols.

4 Coordinates For Measurement of Surface Roughness FIGURE 4.3 Coordinates used for measurement of surface roughness, using Eqs. (4.2) and (4.2).

5 Measuring Surface Roughness FIGURE 4.4 (a) Measuring surface roughness with a stylus. The rider supports the stylus and guards against damage. (b) Path of the stylus in measurements of surface roughness (broken line) compared with the actual roughness profile. Note that the profile of the stylus s path is smoother than the actual surface profile source; D. H. Buckley. Typical surface profiles produced by (c) lapping, (d) finish grinding, (e) rough grinding, and (f) turning processes. Note the difference between the vertical and horizontal scales. Source: D. B. Dallas (ed.), Tool and Manufacturing Engineers Handbook, 3d. Ed. Copyright 1976, McGraw-Hill Publishing Company. Used with Permission.

6 Exercise and Home Work From a surface measurement made by surface profilometer, the following point values were obtained (the scale factor is 0.6 micro meter) There are 10 points: 438, 461, 458, 460, 452, 477, 449, 477, 467, and 478. Try to find Ra, Rq and Rt values and the ratio Ra/Rq. Home Work problem: 1. Same as above but change the 10 points as: 516, 534, 518, 533, 518, 530, 520, 526, 521, and Calculate the Ra and Rq values for a sine wave surface, and find the ratio of Ra/Rq.

7 Real Area of Contact FIGURE 4.5 (a) Schematic illustration of the interface of two contacting surfaces, showing the real areas of contact. (b) Sketch illustration the proportion of the apparent area to the real area of contact. The ration of the areas can be as high as four to five orders of magnitude.

8 Friction Force vs. Normal Force FIGURE 4.6 Schematic illustration of the relation between friction force F and normal force N. Note that as the real area of contact approaches the apparent area, the friction force reaches a maximum and stabilizes. Most machine components operate in the first region. The second and third regions are encountered in metalworking operations, because of the high contact pressures involved between sliding surfaces, i.e., die and workpiece.

9 Coefficient of Friction in Metalworking PROCESS Rolling Forging Drawing Sheet-metal f orming Machining COEFFICIENT OF FRICTION (µ) COLD HOT Table 4.1 Coefficient of friction in metalworking processes.

10 Changes In Surface Profiles After Wear FIGURE 4.9 Changes in originally (a) wire-brushed and (b) ground-surface profiles after wear. Source: E. Wild and K. J. Mack.

11 Adhesive Wear FIGURE 4.10 Schematic illustration of (a) two asperities contacting, (b) adhesion between two asperities, and (c) the formation of a wear particle. Abrasive Wear FIGURE 4.11 Schematic illustration of abrasive wear in sliding. Longitudinal scratches on a surface usually indicate abrasive wear.

12 Wear Coefficient UNLUBRICATED k LUBRICATED k Mild steel on mild steel brass on hardened tool 10-2 to steel on steel 10-7 to steel Aluminum bronze on 10-8 Hardened tool steel on 10-4 hardened steel hardened tool steel Hardened steel on 10-9 Polytetrafluoroethylene (PTFE) on tool steel Tungsten carbide on mild steel 10-5 hardened steel 10-6 Table 4.2 Approximate order of magnitude for wear coefficient k in air

13 Regimes of Lubrication FIGURE 4.13 Types of lubrication generally occurring in metalworking operations. Source: After W. R. D. Wilson.

14 An ISO System of Tolerances FIGURE 4.19 (a) Basic size, deviation, and tolerance on a shaft, according to the ISO system. (b)-(d) Various methods of assigning tolerances on a shaft. Source: L. E. Doyle.