Chapter 35: Surface Engineering DeGarmo’s Materials and Processes in Manufacturing

35.1 Introduction

Fatigue Strength as a Function of Finish FIGURE 35-1 Fatigue strength of Inconel 718 components after surface finishing by grinding or EDM. (Field and Kahles, 1971).

Surface Profiles FIGURE 35-2 Machining processes produce surface flaws, waviness, and roughness that can influence the performance of the component.

Machined Surfaces

Machined Surfaces FIGURE 35-3 (a) Terminology used in specifying and measuring surface quality; (b) symbols used on drawing by part designers, with definitions of symbols; (c) lay symbols; (d) lay symbols applied on drawings.

Surface Measurement FIGURE 35-4 (a) Schematic of stylus profile device for measuring surface roughness and surface profile with two readout devices shown: a meter for AA or rms values and a strip chart recorder for surface profile. (b) Profile enlarged. (c) Examples of surface profiles.

Surface Finish Measurement FIGURE 35-5 Typical machined steel surface as created by face milling and examined in the SEM. A micrograph (same magnification) of a 0.00005-in. stylus tip has been superimposed at the top.

SEM Micrograph FIGURE 35-6 (a) SEM micrograph of a U.S. dime, showing the S in the word TRUST after the region has been traced by a stylus-type machine. (b) Topographical map of the S region of the word TRUST from a U.S. dime [compare to part (a)].

Roughness FIGURE 35-7 Comparison of surface roughness produced by common production processes. (Courtesy of American Machinist.)

35.2 Mechanical Cleaning and Finishing Blast Cleaning

Finishing Barrel FIGURE 35-8 Schematic of the blow of material in tumbling or barrel finishing. The parts and media mass typically account for 50 to 60% of capacity.

Synthetic Media Geometry FIGURE 35-9 Synthetic abrasive media are available in a wide variety of sizes and shapes. Through proper selection, the media can be tailored to the product being cleaned

Vibration Finishing Tub FIGURE 35-10 Schematic diagram of a vibratory-finishing tub loaded with parts and media. The single eccentric shaft drive provides maximum motion at the bottom, which decreases as one moves upward. The dualshaft design produces more uniform motion of the tub and reduces processing time

Media to Part Ratio

Part Examples FIGURE 35-11 A variety of parts before and after barrel finishing with triangular-shaped media. (Courtesy of Norton Company.)

35.3 Chemical Cleaning

35.4 Coatings

Organic Finishes

Electroplating Processes FIGURE 35-12 Basic steps in the electrocoating process

Powder Coating

Powder Coating Systems FIGURE 35-13 A schematic of a powder coating system. The wheels on the color modules permit it to be exchanged with a spare module to obtain the next color.

Electroplating Circuitry FIGURE 35-14 Basic circuit for an electroplating operation, showing the anode, cathode (workpiece), and electrolyte (conductive solution).

Electroplating Design Recomendations FIGURE 35-15 Design recommendations for electroplating operations

Anodizing FIGURE 35-16 The anodizing process has many steps.

Nickel Carbide Plating FIGURE 35-17 (Left) Photomicrograph of nickel carbide plating produced by electroless deposition. Notice the uniform thickness coating on the irregularly shaped product. (Right) High-magnification cross section through the coating. (Courtesy of Electro-Coatings Inc.)

35.5 Vaporized Metal Coatings

35.6 Clad Materials

35.7 Textured Surfaces

35.8 Coil-Coated Sheets

35.9 Edge Finishing and Burrs

Burr Formation FIGURE 35-18 Schematic showing the formation of heavy burrs on the exit side of a milled slot. (From L. X. Gillespie, American Machinist, November 1985.)

Deburring Allowance

35.10 Surface Integrity

Burr Prevention FIGURE 35-19 Designing extra recesses and grooves into a part may eliminate the need to deburr. (From L.X. Gillespie, American Machinist, November 1985.)

Surface Deformation FIGURE 35-20 Plastic deformation in the surface layer after cutting. (B. W. Kruszynski and C. W. Cuttervelt, Advanced Manufacturing Engineering, Vol. 1, 1989.)

Shot Peening FIGURE 35-21 (a) Mechanism for formation of residual compressive stresses in surface by cold plastic deformation (shot peening). (b) Hardness increased in surface due to shot peening.

Surface Damage as a Function of Rake Angle FIGURE 35-22 The depth of damage to the surface of a machined part increases with decreasing rake angle of the cutting tool.

Surface Stress FIGURE 35-23 (Top) A cantilever-loaded (bent) rotating beam, showing the normal distribution of surface stresses (i.e., tension at the top and compression at the bottom). (Center) The residual stresses induced by roller burnishing or shot peening. (Bottom) Net stress pattern obtained when loading a surface-treated beam. The reduced magnitude of the tensile stresses contributes to increased fatigue life.

Fatigue Life with Surface Finish FIGURE 35-24 Fatigue life of rotating beam 2024-T4 aluminum specimens with a variety of surface-finishing operations. Note the enhanced performance that can be achieved by shot peening and roller burnishing.