MACHINE

LECTURE NOTES 8

Working principles grinding and superfinish machine , their mechanism

1 GRINDING MACHINE TOOLS

Grinding in generally considered a finishing operation. It removes metal comparatively in smaller volume. GRINDING MACHINE TOOLS

Grinding in generally considered a finishing operation. It removes metal comparatively in smaller volume. GRINDING MACHINE TOOLS

The material is removed in the form of small chips by mechanical action of particles bonded together in a .

• Producing smooth surface • Geometrically accurate surface • Dimensionally accurate MACHINE TOOLS Grinding Operations

(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 GRINDING MACHINE TOOLS Grinding Operations GRINDING MACHINE TOOLS Grinding Operations

Grinding operations are divided into two groups as surface grinding and cylindrical grinding according to the surface to be machined.

Cylindrical grinding operations are classified as and center-type grinding and also internal cylindrical grinding and external cylindrical grinding according to the applied surface. GRINDING MACHINE TOOLS Classification

Classification of Grinding Machine Tools

1. Surface Grinding Machine Tools 2. Cylindrical Grinding Machine Tools 3. Crank Grinding Machine Tools 4. Gear Grinding Machine Tools 5. Tool Cutter Grinding Machine Tools 6. Other Grinding Machine Tools 7. Utility Grinding Machine Tools GRINDING MACHINE TOOLS Classification

1. Surface Grinding Machine Tools

Surface grinding produces flat, angular, or contoured surfaces by feeding work in a horizontal plane beneath a rotating grinding wheel. Work is most often magnetically attached to the table, and may be ground by either a traversing or rotating movement of the table. Most surface grinding machines use a horizontal spindle which adjusts up and down allowing either the edge or the face of the wheel to contact the work. GRINDING MACHINE TOOLS Classification

1. Surface Grinding Machine Tools

In surface grinding, the spindle position is either horizontal or vertical, and the relative motion of the workpiece is achieved either by reciprocating the workpiece past the wheel or by rotating it. The possible combinations of spindle orientations and workpiece motions yield four types of surface grinding processes. GRINDING MACHINE TOOLS Classification

1. Surface Grinding Machine Tools

Four types of surface grinding with horizontal or vertical spindles, and with reciprocating linear motion or rotating motion of the workpiece. GRINDING MACHINE TOOLS Classification

1. Surface Grinding Machine Tools

a. Horizontal surface grinding machine tools b. Vertical surface grinding machine tools GRINDING MACHINE TOOLS Classification

1. Surface Grinding Machine Tools a. Horizontal surface grinding machine tools GRINDING MACHINE TOOLS Classification

1. Surface Grinding Machine Tools a. Horizontal surface grinding machine tools GRINDING MACHINE TOOLS Classification

1. Surface Grinding Machine Tools a. Horizontal surface grinding machine tools GRINDING MACHINE TOOLS Classification

1. Surface Grinding Machine Tools a. Horizontal surface grinding machine tools GRINDING MACHINE TOOLS Classification

1. Surface Grinding Machine Tools b. Vertical surface grinding machine tools GRINDING MACHINE TOOLS Classification

1. Surface Grinding Machine Tools b. Vertical surface grinding machine tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools Three types of feed motion are possible according to the direction of feed motion; 1. Traverse feed grinding (also through feed grinding, cross- feeding) in which the relative feed motion is parallel to the spindle axis of rotation, 2. Plunge grinding in which the grinding wheel is fed radially into the workpiece, and 3. A combination of traverse and plunge grinding in which the grinding wheel is fed at 45° to grind simultaneously the cylindrical part of the workpiece and the adjacent face. This methods provides a precise perpendicular mutual position of both surfaces. GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools

Traverse grinding: The wheel is positioned at a full thread depth, then the work is traversed past the wheel. The first thread form on the wheel removes the majority of metal and therefore is subjected to the most wear; the following threads affect the finishing. A single-rib wheel may be used for large threads. GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools

Plunge grinding: In this arrangement, the wheel is plunged into the WP to the full depth. The WP then makes one revolution, while the wheel traverses one pitch. This method gives a uniform wheel wear, but is used for short thread lengths. GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools a. External cylindrical grinding machine tools b. Internal cylindrical grinding machine tools c. Universal cylindrical grinding machine tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools a. External cylindrical grinding machine tools

In external cylindrical grinding, the workpiece rotates and reciprocates along its axis, although for large and long workpieces the grinding wheel reciprocates. GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools a. External cylindrical grinding machine tools i. Centerless external cylindrical grinding machine tools ii. Center-type external cylindrical grinding machine tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools a. External cylindrical grinding machine tools i. Centerless external cylindrical grinding machine tools Centerless grinding is a process for continuously grinding cylindrical surfaces in which the workpiece is supported not by centers or chucks but by a rest blade. The workpiece is ground between two wheels. The larger grinding wheel does grinding, while the smaller regulating wheel, which is tilted at an angle i, regulates the velocity Vf of the axial movement of the workpiece. GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools a. External cylindrical grinding machine tools i. Centerless external cylindrical grinding machine tools

Centerless grinding can also be external or internal, traverse feed or plunge grinding. The most common type of centerless grinding is the external traverse feed grinding GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools a. External cylindrical grinding machine tools i. Centerless external cylindrical grinding machine tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools a. External cylindrical grinding machine tools i. Centerless external cylindrical grinding machine tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools a. External cylindrical grinding machine tools i. Centerless external cylindrical grinding machine tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools a. External cylindrical grinding machine tools i. Centerless external cylindrical grinding machine tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools a. External cylindrical grinding machine tools ii. Center-type external cylindrical grinding machine tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools b. Internal cylindrical grinding machine tools

In internal cylindrical grinding, a small wheel grinds the inside diameter of the part. The workpiece is held in a rotating in the headstock and the wheel rotates at very high rotational speed. In this operation, the workpiece rotates and the grinding wheel reciprocates. GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools b. Internal cylindrical grinding machine tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools b. Internal cylindrical grinding machine tools i. Center-type internal cylindrical grinding machine tools ii. Centerless internal cylindrical grinding machine tools iii. Planet type internal cylindrical grinding machine tools GRINDING MACHINE TOOLS Classification

2. Cylindrical Grinding Machine Tools c. Universal cylindrical grinding machine tools

In universal cylindrical grinding, both the workpiece and the grinding wheel axis can be swivelled around a horizontal plane, permitting all these types of cylindrical grinding. GRINDING MACHINE TOOLS Classification

3. Crank Grinding Machine Tools GRINDING MACHINE TOOLS Classification

4. Gear Grinding Machine Tools GRINDING MACHINE TOOLS Classification

5. Tool Cutter Grinding Machine Tools a. Universal tool cutter grinding b. Special tool cutter grinding machine tool GRINDING MACHINE TOOLS Classification

6. Other Grinding Machine Tools a. Coordinate grinding machine tools b. Screw grinding machine tools c. Profile grinding machine tools d. Special grinding machine tools GRINDING MACHINE TOOLS Classification

7. Utility Grinding Machine Tools

The utility grinding machine is intended for offhand grinding where the workpiece is supported in the hand and brought to bear against the rotating grinding abrasive wheel. The accuracy of this type of grinding machine depends on the operator’s dexterity. skill, and knowledge of the machine’s capabilities and the nature of the work. The utility grinding machine consists of a horizontally mounted motor with a grinding abrasive wheel attached to each end of the motor shaft. GRINDING MACHINE TOOLS Classification

7. Utility Grinding Machine Tools

The typical floor-mounted utility grinding machine stands waist-high and is secured to the floor by bolts. GRINDING MACHINE TOOLS Classification

7. Utility Grinding Machine Tools

The bench-type grinding machine is intended for drill sharpening. The accuracy of this type of grinder is not dependent on the dexterity and skill of the operator because the drill is placed in a holding device. The holding device places the drill in the correct position for the clearance and included angle. GRINDING MACHINE TOOLS Classification

7. Utility Grinding Machine Tools GRINDING MACHINE TOOLS Workpiece Mounting

Mounting Workpiece for Cylindrical Grinding

Cylindrical grinding may be done with the workpiece setup between centers, held in the chuck and supported by a center rest, or clamped to the faceplate as in setups. GRINDING MACHINE TOOLS Workpiece Mounting

Mounting Workpiece for Surface Grinding

A workpiece for surface grinding is usually held to the reciprocating worktable by a magnetic chuck. It may also be held in a vise or clamped directly to the table. GRINDING MACHINE TOOLS Workpiece Mounting

Mounting Workpiece for Internal Grinding

Internal grinding is done with the universal with an internal grinding attachment. GRINDING MACHINE TOOLS Workpiece Mounting

Mounting Workpiece for Tool and Cutter Grinding

Listed below are methods for mounting workplaces when using the tool and cutter grinder:

• A workpiece for tool and cutter grinding is usually held between centers or on a clamped to the table.

• The workpiece is mounted in the same manner as for cylindrical grinding, except the if not used.

• When a fixture is used, the workpiece is placed in the fixture and the fixture is clamped to the table. HONING, , SUPER FINISHING, POLISHING

These are operations by which a product receives the final stage that applies for the service for which it is intended. These remove a very small amount of metal, and hence the surface finish obtained is specified in the ranges of microfinishes. These operations include honing, microhoning, lapping, and polishing. HONING MACHINE TOOLS

Honing is a controlled, low-speed sizing and surface- finishing process in which stock is abraded by the shearing action of a bonded abrasive honing stick.

Advantages of Honing • It is characterized by rapid and economical with a minimum of heat and distortion. • It generates round and straight holes by correcting form errors caused by previous operations. • It achieves high surface quality and accuracy. HONING MACHINE TOOLS

For the production of few parts, honing may be performed on drill presses or engine on which arrangements can be made for simultaneous rotating and reciprocating motions. HONING MACHINE TOOLS

The stroking can be done manually or powered depending on the equipment capabilities. On the other hand, the production honing is done with machines built for the purpose. HONING MACHINE TOOLS

These vertical machines are available in a wide range of sizes and designs.

Some horizontal machines operate by manual stroking.

In power stroking, the WP is usually held stationary in a rigid fixture, while the hone is rotated and hydraulically powered for stroking, which is considered beneficial for heavier workpieces. HONING MACHINE TOOLS HONING MACHINE TOOLS HONING MACHINE TOOLS

Machining Parameters

1. Rotation speed (Material being honed, Material hardness, Surface roughness, Number and width of sticks in the hone, Finish requirement) 2. Reciprocation speed 3. Control of cross-hatch angle 4. Honing pressure 5. Honing fluids MICROHONING MACHINE TOOLS

Microhoning is an abrading process that is used for external surface refining or cylindrical, flat, and spherical-shaped parts. It is not a dimension-changing process, but is mainly used for producing finished surfaces of superfine quality. Only a slight amount of stock is removed (2–30 μm), which represents the surface roughness. MICROHONING MACHINE TOOLS

The process of honing involves two main motions, whereas superfinishing requires three or more motions. As a result of these motions, the abrasive path is random and never repeats itself. MICROHONING MACHINE TOOLS MICROHONING MACHINE TOOLS

Machining Parameters

1. Abrasive stones [Al2O3 for carbon and alloy steels and SiC (more friable) for very soft and tough steels as well as for CI and most nonferrous metals]. (Grit size, Grade, Width, Number of stones, Stone length) 2. Work speed (Roughing. 12–15 m/min.; Finishing. 30–60 m/min) 3. Stroke length and speed of stone reciprocation 4. Stone pressure (For normal work, ph = 1.5–3.0 kg/cm2; For roughing, ph = 3.0–6.0 kg/cm2 ; For extra fine finishing, ph = 1.0–2.0 kg/cm2) LAPPING MACHINE TOOLS

The usual definition of lapping is the random rubbing of WP against a CI lapping plate (lap) using loose carried in an appropriate vehicle (oil) to improve fi t and finish. It is a low-speed, low-pressure abrading process. In general, the surface quality that can be obtained by lapping is not easily or economically obtained by other processes. Moreover, the life of the moving parts that are subjected to wear can be increased by eliminating hills and valleys that create a maximum percentage at bearing area. LAPPING MACHINE TOOLS

Lapping is a final machining operation that realizes the following major objectives:

• Extreme dimensional accuracies • Mirror-like surface quality • Correction of minor shape imperfections • Close fit between mating surfaces LAPPING MACHINE TOOLS

It does not require holding devices and consequently no WP distortion occurs. Also less heat is generated than in most of other finishing operations. Therefore, metallurgical changes are totally avoided. The temperature increase of the surface is only 1–2°C over ambient.

Lapping machines usually fall into one of the two categories: 1. Individual-piece lapping machines 2. Equalizing lapping machines LAPPING MACHINE TOOLS

(a) Schematic illustration of the lapping process (b) Production lapping on flat surfaces (c) Production lapping on cylindrical surfaces LAPPING MACHINE TOOLS LAPPING MACHINE TOOLS LAPPING MACHINE TOOLS

1. Individual-Piece Lapping

It is the most effective lapping method for hard metals and other hard materials. It is used to produce optically fl at surfaces and accurate surface plates. When both sides of a flat WP are lapped simultaneously, extreme parallelism is achieved. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping

Individual-piece lapping is performed using a lap that is softer than the WP so that the abrasives get embedded in the lap. The lap is usually made of close-grain soft CI that is free from porosity and defects. When CI is not suitable as a lap material, steel, brass, copper, or aluminum may be used. Wood is sometimes used for certain applications. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping

The vast majority of individual-piece lapping installations are of the following categories: a. Specialized single- or double-plate machines, such as ball or pin laps b. Single-sided flat or double-sided planetary laps c. A cup-lapping machine for lapping spherical surfaces LAPPING MACHINE TOOLS

1. Individual-Piece Lapping a. Double-plate lapping machines for cylindrical workpieces

Figure visualizes a typical vertical lapping machine used for lapping cylindrical surfaces in production quantities. The laps are two opposing CI circular plates that are held on vertical spindles of the machine. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping a. Double-plate lapping machines for cylindrical workpieces

The workpieces are retained between laps in a slotted- holder plate and rotate and slide in and out to break the pattern of motion by moving over the inside and outside edges of the laps that prevent grooving. The lower lap is usually rotated and drives the workpieces. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping a. Double-plate lapping machines for cylindrical workpieces

The upper one is held stationary but is free to float so that it can adjust to the variations in wokpiece size. The lower lap regulates the speed of rotation. To avoid damage of the surface being lapped, the holder plate or carrier is made of soft material (copper, laminate fabricate base, and so on). LAPPING MACHINE TOOLS

1. Individual-Piece Lapping a. Double-plate lapping machines for cylindrical workpieces

An alternative design of this machine is illustrated in below figure. Accordingly, the retainer is arranged eccentrically between the two laps and has a separate drive. In this design, both the upper and lower laps are rotating. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping a. Double-plate lapping machines for cylindrical workpieces

The abrasive with vehicle is provided to the laps before starting. Oil or kerosene is then added during the cycle to prevent drying of the vehicle, which could result in surface scratching. The best lapping practice is to load as many parts as possible to reduce the pressure applied on each part and slowdown the operation, which provides easier control on tolerances. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping a. Double-plate lapping machines for cylindrical workpieces

Achieved accuracy and surface finish

Fine surface finishes of 0.025 μm Ra and metal removal of 2.5–10 μm are feasible when CI laps are used. A diametric tolerance as low as ±0.5 μm, out-of-roundness of 0.13 μm, and taper less than 0.25 μm have been achieved. Such accuracies depend greatly on the accuracies achieved in prior machining operations. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping a. Double-plate lapping machines for cylindrical workpieces

Achieved accuracy and surface finish The abrasive with vehicle is provided to the laps before starting. Oil or kerosene is then added during the cycle to prevent drying of the vehicle, which could result in surface scratching. The best lapping practice is to load as many parts as possible to reduce the pressure applied on each part and slowdown the operation, which provides easier control on tolerances. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping a. Double-plate lapping machines for cylindrical workpieces

Applications Machine lapping between plates, as described earlier, is an economical and productive (100 parts/h) method of lapping cylindrical surfaces. The machine can be used for lapping parts such as plug gages, piston pins, hypodermic plungers, ceramic pins, small valve pistons, cylindrical valves, small engine pistons, roller and needle bearings, diesel injector valves, plungers, and miscellaneous cylindrical pins. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping a. Double-plate lapping machines for cylindrical workpieces

Applications

Either hard or soft materials can be lapped, provided that they are rigid enough to accept pressure of laps. Because the hardness slows the operation, soft materials lap more rapidly than hard ones. Additionally, hard materials provide easier control of tolerances. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping a. Double-plate lapping machines for cylindrical workpieces Limitations A part with diameter greater than its length is difficult or impossible to machine lap between plates. Parts with shoulders require special fixtures. Parts with keyways, flats, or interrupted surface are difficult to lap because the variations in lapping pressure that occur are likely to fall out of round. If the relief extends over the entire length of the part, this method of lapping cannot be used at all. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping b. Lapping of flat surfaces

Flat surfaces can be lapped by either i. manual or ii. mechanical methods.

Dual-face lapping machine using two bonded abrasive laps LAPPING MACHINE TOOLS

1. Individual-Piece Lapping b. Lapping of flat surfaces i. Manual Lapping

Manual lapping is used only for limited quantities, or when special requirements must be met. Hand rubbing of a fl at WP on a plate lap charged with an abrasive compound is the simplest method of flat lapping. The lap, usually made of iron, has regularly spaced grooves of about 1.6 mm depth to retain the lapping medium. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping b. Lapping of flat surfaces i. Manual Lapping

The workpiece is rubbed on the lap in a figure eight or a similar pattern that covers almost the entire lap surface. The lap remains flat for a considerable amount of work. This method of lapping is time-consuming and tedious, and requires a high degree of labor skill. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping b. Lapping of flat surfaces ii. Mechanical Lapping

Mechanical lapping is performed by flat lapping machines. The two general types are single and dual-face lapping machines. However, dual-face lapping machines are preferred due to their enhanced accuracy. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping c. Lapping machines for spherical surfaces

These are classified into two classes:

i. Single-piece lapping machine ii. Multiple-pieces lapping machines LAPPING MACHINE TOOLS

1. Individual-Piece Lapping c. Lapping machines for spherical surfaces

Lapping of spherical surfaces:

(a) single-spindle machine (b) two-spindle machine LAPPING MACHINE TOOLS

1. Individual-Piece Lapping c. Lapping machines for spherical surfaces i. A single-spindle machine with a vertical spindle that rotates the lap

Ferrous workpieces are held stationary by a magnetic chuck; those of nonferrous materials are clamped in a fixture. A crank is held by the chuck of a lathe, is provided by a ball-end crankpin that fits in a drilled hole in the back of the lap, rotates over the spherical surface of the workpiece. The workpiece is in line with the spindle of the lathe. The lap should be heavy enough to provide the required lapping pressure. LAPPING MACHINE TOOLS

1. Individual-Piece Lapping c. Lapping machines for spherical surfaces ii. A two-spindle machine

One spindle holds and rotates the WP, while the other holds the lap in a floating position and oscillates it through an angle large enough to lap the required area of the surface. LAPPING MACHINE TOOLS

2. Equalizing Lapping In this process, two WP surfaces are separated by a layer of abrasives mixed with a vehicle and rubbed against each other. Each piece drives the abrasive, so that the particles act on the opposing surface. Irregularities that prevent the two surfaces from fitting together precisely are thus lapped, and the surfaces are mated (equalized). SUPER FINISH MACHINE TOOLS SUPER FINISH MACHINE TOOLS

Super finish machine tool can super finish the rotating components with the help of the oscillating movement of the superfinishing stone. It is highly useful in improving the surface finish up to 0.02 µm on various shafts, piston rolls, hard chrome-copper plated/aluminum rolls, rotogravure rolls, and gear shaft needles. SUPER FINISH MACHINE TOOLS SUPER FINISH MACHINE TOOLS SUPER FINISH MACHINE TOOLS POLISHING MACHINE TOOLS

Smoothing the surface using abrasive and work wheel.

Abrasive materials are glued to the work wheel.

Polishing is often used to enhance the looks of the part, prevent contamination of part, remove oxidation, provide a reflective surface etc. POLISHING MACHINE TOOLS POLISHING MACHINE TOOLS