DRILLING MACHINE

Drilling is an operation of making a circular hole by removing a volume of metal from the job by cutting tool called drill.

CONSTRUCTION OF DRILLING MACHINE

In drilling machine the drill is rotated and fed along its axis of rotation in the stationary workpiece. Different parts of a drilling machine are shown in Fig. 1 and are discussed below: (i) The head containing electric motor, V-pulleys and V-belt which transmit rotary motion to the drill spindle at a number of speeds. (ii) Spindle is made up of alloy steel. It rotates as well as moves up and down in a sleeve. A pinion engages a rack fixed onto the sleeve to provide vertical up and down motion of the spindle and hence the drill so that the same can be fed into the workpiece or withdrawn from it while drilling. Spindle speed or the drill speed is changed with the help of V-belt and V-step-pulleys. Larger drilling machines are having gear boxes for the said purpose. (iii) Drill chuck is held at the end of the drill spindle and in turn it holds the drill bit. (iv) Adjustable work piece table is supported on the column of the drilling machine. It can be moved both vertically and horizontally. Tables are generally having slots so that the vise or the workpiece can be securely held on it. (v) Base table is a heavy casting and it supports the drill press structure. The base supports the column, which in turn, supports the table, head etc. (vi) Column is a vertical round or box section which rests on the base and supports the head and the table. The round column may have rack teeth cut on it so that the table can be raised or lowered depending upon the workpiece requirements. This machine consists of following parts

1. Base
2. Pillar
3. Main drive
4. Drill spindle
5. Feed handle
6. Work table

 

Fig. 1 Construction of drilling machine

METTAL CUTTING

In metal cutting operation, the position of cutting edge of the cutting tool is important based on which the cutting operation is classified as orthogonal cutting and oblique cutting. Orthogonal cutting (Fig. 1) is also known as two dimensional metal cutting in which the cutting edge is normal to the work piece. In orthogonal cutting no force exists in direction perpendicular to relative motion between tool and work piece. Oblique cutting (Fig. 2)is the common type of three dimensional cutting used in various metal cutting operationsin which the cutting action is inclined with the job by a certain angle called the inclination angle.

Fig. 1 Orthogonal cutting

Fig. 2 Oblique cutting

POWDER METALLURGY

POWDER METALLURGY PROCESS
The powder metallurgy process consists of the following basic steps:
1. Formation of metallic powders.
2. Mixing or blending of the metallic powders in required proportions.
3. Compressing and compacting the powders into desired shapes and sizes in form of articles.
4. Sintering the compacted articles in a controlled furnace atmosphere.
5. Subjecting the sintered articles to secondary processing if needed so.

Production of Metal Powders

Metallic powders possessing different properties can be produced easily. The most commonly used powders are copper-base and iron-base materials. But titanium, chromium, nickel, and stainless steel metal powders are also used. In the majority of powders, the size of the particle varies from several microns to 0.5 mm. The most common particle size of powders falls into a range of 10 to 40 microns. The chemical and physical properties of metalsdepend upon the size and shape of the powder particles. There are various methods of manufacturing powders.The commonly used powder making processes are given as under.

MILLING

A milling machine is a machine tool that removes metal as the work is fed against a rotating multipoint cutter. The milling cutter rotates at high speed and it removes metal at a very fast rate with the help of multiple cutting edges. One or more number of cutters can be mounted simultaneously on the arbor of milling machine.

Milling machine is used for machining flat

surfaces, contoured surfaces, surfaces of revolution, external and internal threads, and helical surfaces of various cross-sections. Typical components produced by a milling are given in Figure 1. In many applications, due to its higher production rate and accuracy, milling machine has even replaced shapers and slotters.

Figure 1 Job surfaces generated by milling machine

MATERIALS FOR HEAT EXCHANGER

Heat exchangers take heat from one fluid and pass it to a second (Figure 1). The fire-tube array of a steam engine is a heat exchanger, taking heat from the hot combustion gases of the firebox and transmitting it to the water in the boiler. The network of finned tubes in an air conditioner is a heat exchanger, taking heat from the air of the room and dumping it into the working fluid of the conditioner. A key element in all heat exchangers is the tube wall or membrane that separates the two fluids. It is required to transmit heat, and there is frequently a pressure difference across it, which can be large.

Figure 1 A heat exchanger. There is a pressure difference Δp and a temperature difference ΔT across the tube wall that also must resist attack by chloride ions.

MATERIALS FOR FLYWHEELS

Flywheels store energy. Small ones—the sort found in children’s toys—are made of lead. Old steam engines have flywheels; they are made of cast iron. Cars have them too (though you cannot see them) to smooth power-transmission. More recently flywheels have been proposed for power storage and regenerative braking systems for vehicles; a few have been built, some of high strength steel, some of composites. Lead, cast iron, steel, composites—there is a strange diversity here.

An efficient flywheel stores as much energy per unit weight as possible. As the flywheel is spun up, increasing its angular velocity, ω, it stores more energy. The limit is set by failure caused by centrifugal loading: if the centrifugal stress exceeds the tensile strength (or fatigue strength), the flywheel flies apart. One constraint, clearly, is that this should not occur. The flywheel of a child’s toy is not efficient in this sense. Its velocity is limited by the pulling-power of the child, and never remotely approaches the burst velocity. In this case, and for the flywheel of an automobile engine—we wish to maximize the energy stored per unit volume at a constant (specified) angular velocity. There is also a constraint on the outer radius, R, of the flywheel so that it will fit into a confined space. The answer therefore depends on the application. The strategy for optimizing
flywheels for efficient energy-storing systems differs from that for children’s toys. The two alternative sets of design requirements are listed in Table 1(a) and (b).

MATERIALS FOR SPRINGS

Springs come in many shapes (Figure 1 and Table 1) and have many purposes: think of axial springs (e.g. a rubber band), leaf springs, helical springs, spiral springs, torsion bars. Regardless of their shape or use, the best material for a spring of minimum volume is that with the greatest

Figure 1 Springs store energy. The best material for any spring, regardless of its shape or the way in which it is loaded, is that with the highest value of σf²/E, or, if weight is important, σf²/Eρ.

Table 1 Design requirements for springs

Function	Elastic spring
Constraints	No failure, meaning σ<σ­f throughout the spring
Objective	- Maximum stored elastic energy per unit volume, or - Maximum stored elastic energy per unit weight
Free variables	Choice of material

value of σf²/E, and for minimum weight it is that with the greatest value of σf²/ρE (derived below). We use them as a way of introducing two of the most useful of the charts: Young’s modulus E plotted against strength σf, and specific modulus E/ρ plotted against specific strength σf/ρ.

The model

The primary function of a spring is to store elastic energy and— when required—release it again. The elastic energy stored per unit volume in a block of material stressed uniformly to a stress σ is

where E is Young’s modulus. We wish to maximize Wv. The spring will be damaged if the stress σ exceeds the yield stress or failure stress σf; the constraint is σ<σf. Thus the maximum energy density is

Torsion bars and leaf springs are less efficient than axial springs because much of the material is not fully loaded: the material at the neutral axis, for instance, is not loaded at all. For leaf springs

and for torsion bars

But—as these results show—this has no influence on the choice of material. The best stuff for a spring regardless of its shape is that with the biggest value of

If weight, rather than volume, matters, we must divide this by the density ρ (giving energy stored per unit weight), and seek materials with high values of

The selection. The choice of materials for springs of minimum volume is shown in Figure 2(a). A family lines of slope 2 link materials with equal values of M1 = σf²/E; those with the highest values of M1 lie towards the bottom right. The heavy line is one of the family; it is positioned so that a subset of materials is left exposed. The best choices are a high-strength steel lying near the top end of the line. Other materials are suggested too: CFRP (now used for truck springs), titanium alloys (good but expensive), and nylon (children’s toys often have nylon springs), and, of course, elastomers. Note how the procedure has identified a candidate from almost every class of materials: metals, polymers, elastomers and composites. They are listed, with commentary, in Table 2(a). Materials selection for light springs is shown in Figure 2(b). A family of
lines of slope 2 link materials with equal values of

Figure 2(a) Materials for small springs. high strength (‘‘spring’’) steel is good. Glass, CFRP and GFRP all, under the right circumstances, make good springs. Elastomers are excellent. Ceramics are eliminated by their low tensile strength.

Figure 2(b) Materials for light springs. Metals are disadvantaged by their high densities. Composites are good; so is wood. Elastomers are excellent.

Table 2(a) Materials for efficient small springs

Material	M1=σf2/E (MJ/m3)	Comment
Ti alloys	4–12	Expensive, corrosion-resistant
CFRP	6–10	Comparable in performance with steel; expensive
Spring steel	3–7	The traditional choice: easily formed and heat treated
Nylon	1.5–2.5	Cheap and easily shaped, but high loss factor
Rubber	20–50	Better than spring steel; but high loss factor

Table 2(b) Materials for efficient light springs

Material	M1 = σf2/ρE (MJ/m3)	Comment
Ti alloys	0.9–2.6	Better than steel; corrosion-resistant; expensive
CFRP	3.9–6.5	Better than steel; expensive
GFRP	1.0–1.8	Better than spring steel; less expensive than CFRP
Spring steel	0.4 –0.9	Poor, because of high density
Wood	0.3–0.7	On a weight basis, wood makes good springs
Nylon	1.3–2.1	As good as steel, but with a high loss factor
Rubber	18–45	Outstanding; 20 times better than spring steel; but with high loss factor