Chapter 26 Abrasive Machining and Finishing Operations Manufacturing

Chapter 26 Abrasive Machining and Finishing Operations Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

ABRASIVE It is a small hard particle having sharp edges and an irregular shape e. g. sand paper and grinding wheels are used to sharpen knives, tools and give good dimensional accuracy and surface finish to products Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 1 Typical abrasive grains; note the angular shape with sharp edges. (a) A single, 80 -mesh Al 2 O 3 grit in a freshly dressed grinding wheel; (b) An 80/100 mesh diamond grit; diamond and cubic boron nitride grains can be manufactured in various geometries, including the “blocky” shape shown. Source: Courtesy of J. Badger. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 2 A variety of bonded abrasives used in abrasive-machining processes. Source: Courtesy of Norton Company. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 3 The types of workpieces and operations typical of grinding: (a) cylindrical surfaces; (b) conical surfaces; (c) fillets on a shaft; (d) helical profiles; (e) concave shape; (f) cutting off or slotting with thin wheels; and (g) internal grinding. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

Abrasives are harder than cutting tool materials TYPES OF ABRASIVES 1. conventional abrasives: Aluminum oxide (for carbon steel and ferrous alloys)and Silicon carbide (non ferrous metals, glass and marble) 2. super abrasives: diamond (ceramics and hardeneded steel) and cubic boron nitride (steels and cast iron) friability: ability of abrasive grains to fracture into smaller pieces. This gives abrasives their self sharpening characteristics essential in maintaining their sharpness during use Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

GRINDING WHEELS The abrasives grains are held together by a bonding material in order to achieve high material removal rates Marking of bonded abrasives 51 A 36 L 5 V 23 A: abrasive type AL 36 : grain size L grade from A (soft) till Z (hard) 5: dense from 1 -…. V: bond type (R: rubber, S: silicate, V: vitrified 51 and 23: manufacturer Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 4 Schematic illustration of a physical model of a grinding wheel, showing its structure and its wear and fracture patterns. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 5 Common types of grinding wheels made with conventional abrasives; note that each wheel has a specific grinding face; grinding on other surfaces is improper and unsafe. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 6 Examples of superabrasive wheel configurations; the annular regions (rims) are superabrasive grinding surfaces, and the wheel itself (core) generally is made of metal or composites. The bonding materials for the superabrasives are (a), (d), and (e) resinoid, metal, or vitrified; (b) metal; (c) vitrified; and (f) resinoid. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

THE GRINDING PROCESS Difference between action of an abrasive grain and that of a single-point cutting tool 1. Grains have irregular shapes 2. The radial position of a grain on the surface of the wheel varies, so not all grains are active during grinding 3. Surface speed of grinding wheels are higher Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 11 Schematic illustration of the surface-grinding process, showing various process variables; the figure depicts conventional (up) grinding. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 13 Chip formation and plowing of the workpiece surface by an abrasive grain. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

GRINDING OPERATIONS AND MACHINES Selection of a grinding process depends upon: 1. Shape of work piece 2. Its size 3. Ease of fixturing 4. Production rate required Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

TABLE 26. 4 General Characteristics of Abrasive Machining Processes and Machines Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

SURFACE GRINDING work piece is flat grinding wheel is mounted on a horizontal spindle work piece is mounted on work table the table reciprocates longitudinally and is fed laterallyin the direction of the spindle axis Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 15 Schematic illustrations of various surface-grinding operations. (a) Traverse grinding with a horizontal-spindle surface grinder. (b) Plunge grinding with a horizontal-spindle surface grinder, producing a groove in the workpiece. (c) A vertical-spindle rotary-table grinder (also known as the Blanchard type). Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 16 Schematic illustration of a horizontal-spindle surface grinder. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

CYLINDRICAL GRINDING the work piece rotates and reciprocates along its axis in roll grinders, the grinding wheel reciprocates Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 18 Examples of various cylindrical-grinding operations: (a) traverse grinding; (b) plunge grinding; and (c) profile grinding. Source: Courtesy of Okuma Corporation. Printed with permission. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 19 shape. Plunge grinding of a workpiece on a cylindrical grinder with the wheel dressed to a stepped Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 20 Schematic illustration of grinding a noncylindrical part on a cylindrical grinder with computer controls to produce the shape. The part rotation and the distance x between centers are varied and synchronized to grind the particular workpiece shape. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 21 Thread grinding by (a) traverse and (b) plunge grinding. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

INTERNAL GRINDING a small wheel is used in grinding the inside diameter of a part the work piece is held in a rotating chuck the wheel rotates at a high speed(higher than 30000 r. p. m Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 23 Schematic illustrations of internal grinding operations: (a) traverse grinding; (b) plunge grinding; and (c) profile grinding. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FINISHING OPERATIONS Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 27 Schematic illustration of the structure of a coated abrasive; sandpaper (developed in the 16 th century) and emery cloth are common examples of coated abrasives. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

BELT GRINDING Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 28 Turbine nozzle vane considered in Example 26. 5. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

WIRE BRUSHING work piece is held against a circular wire brush that rotates the tips of the wire produce longitudinal scatches on the surface of the work piece Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

HONING Used to improve the surface finish of holes The honing tool consists of aluminum oxide or silicon carbide bonded abrasive sticks called stones The stones can be adjusted radially to suit different hole sizes The tool has a reciprocating motion Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 29 holes. Schematic illustration of a honing tool used to improve the surface finish of bored or ground Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

LAPPING Used for finishing cylindrical, flat or curved surfaces The lap is relatively soft and porous, made of cast iron, leather or cloth Lapping is done under pressures depending upon the type and hardness of the work piece Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 31 (a) Schematic illustration of the lapping process. (b) Production lapping on flat surfaces. (c) Production lapping on cylindrical surfaces. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

POLISHING Produces a smooth , lustrous surface finish Softening and smearing of surface layers occur by frictional heating developed during polishing, and by very fine scale abrasive removal from work piece surface Polishing is done with discs or belts made of fabric or leather, coated with fine powders of aluminum oxide or diamond Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

DEBURRING OPERATIONS Burrs are thin edges that develop along edges of a work piece due to machining operations or shearing metal sheets Burrs can be detected with a finger, toothpick or cotton swab DISADVANTAGES OF BURRS 1. Interfere with the mechanical assembly of parts 2. Unsafe to personnel handling the parts 3. May reduce fatigue life of parts 4. May cause low bendability if the burr is on the tensile size Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.

FIGURE 26. 37 Increase in the cost of machining and finishing a part as a function of the surface finish required; this is the main reason that the surface finish specified on parts should not be any finer than is necessary for the part to function properly. Manufacturing Engineering and Technology , Seventh Edition Serope Kalpakjian | Steven R. Schmid Copyright © 2014 by Pearson Education, Inc. All rights reserved.