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A Hand power drill is a tool primarily used for making round holes or driving fasteners. It is fitted with a bit, either a drill or driver, depending on the application, secured by a chuck. Some of the hand-powered drills also include a hammer function.
Drills vary widely in speed, power, and size. They have characteristically corded electrically driven devices, with hand-operated types dramatically decreasing in popularity and cordless battery powered ones proliferating.
Drills are commonly used in woodworking, metalworking, machine tool fabrication, construction and utility projects. Specially designed drill versions are made for medicine, space, and miniature applications
Resistance is defined as the opposition offered by a substance to the flow of electric current.
where ρ is known as the resistivity of the material in ohm-meters.
It may be noted here that resistance is the electric friction offered by the substance and causes the 产品介绍ion of heat with the flow of electrical current. The moving electrons collide with atoms or molecules of the substance, each collision resulting in the liberation of a minute quantity of heat.
Unit of resistance. The practical unit of resistance is ohm and is represented by the symbol Ω. It is defined as under
A wire is said to have a resistance of 1 ohm if a p.d. of 1 volt across its ends causes 1 ampere to flow through it (See Fig.).
Another way of defining ohm.
A wire is said to have a resistance of 1 ohm (Ω) if it releases 1 joule (or develops 0.24 calorie of heat) when a current of 1 A flows through it for 1 second.
A little reflection shows that the second definition leads to the first definition. Thus 1 A current flowing for 1 second means that total charge flowing is Q = i × t = 1 × 1 = 1 coulomb. Now the charge flowing between A and B (See Fig.) is 1 coulomb and energy released is 1 joule (or 0.24 calorie).
Obviously, by definition, p.d. between A and B should be 1 volt.
since the current is the flow of free electrons, resistance is the opposition offered by the substance to the flow of free electrons. This opposition occurs because atoms and molecules of the substance obstruct the flow of these electrons. Certain substances (e.g. metals such as silver, copper, aluminum, etc.) offer very little opposition to the flow of electric current and are called conductors of electricity. On the other hand, those substances which offer high opposition to the flow of electric current (i.e. flow of free electrons) are called insulators e.g. glass, rubber, mica, dry wood, etc.
For establishing the relationship between measurable and actual forces Merchant’s circle will be used.
In machining operation there are four actual forces are acting. They are:
F = frictional force acting at the chip-tool interface.
N = force normal to the frictional force
Fs = Shear force acting along the shear plane.
Fsn = force normal to the frictional force.
But all the above four forces are acting in the dynamic environment, hence it is not possible to measure them and these forces are required for analysis of machining operation. Therefore each of the above actual forces can be resolved into two components of forces and the algebraic sum of forces can be taken as
Let, Fc = algebraic sum of vertical components of forces
FT = algebraic sum of horizontal components of forces
The above two forces can be measurable by using dynamometer or spring balance but these forces can’t be used in the analysis of machining. Hence to correlate the actual and measurable force the merchant’s circle will be used.
By using a dynamometer, the measurable forces can be measured and by using the merchant’s circle, the actual forces can be calculated. Using this actual force the machining can be analyzed.
From the above circle, it is found that there are three right-angled triangles are present and all will have common hypotenuse. Using this principle the forces can be related as
The resultant force, R = hypotenuse
using the above equations if the force Ft and Fc are known, the friction angle can be determined, the rake angle is already known from the tool designation and shear angle is known from the chip thickness so that the actual forces Fs, Fsn, F, N can be determined.
Whenever the tool is not performing a machining operation satisfactorily, it is assumed that the tool has been failed. Normally when the tool fails the tool will be re-grinded to re-sharpen the tool, but in case of throwaway type of the tools, the tool will be thrown away and new tool tip will be taken.
Although the supply of sharp or re-sharpened tools is usually available from the tool rooms, tool changing operations are time-consuming and inefficient. The need for a 更多 effective method has led to the development of inserts, which are individual cutting tools with several cutting points.
Inserts are usually clamped on the tool shank with various locking mechanisms. Inserts may also be brazed to the tool body but because of the difference in thermal expansion between the insert and the tool body, however, brazing must be carefully done to avoid warping or cracking.
Clamping is the preferred method of securing an insert because each insert has a number of cutting points and after one edge is worn, it is indexed to make it available another cutting tip. The strength of cutting the edge of an insert depends upon its shape. The smallest the included angle, the lower the strength of the edge. Most of the inserts are honed to a radius of 关于 0.025mm to strengthen the edge.
Generally, the cutting tools made by using powder metallurgy as the manufacturing process, the hardness of tool is very high and can’t be resharpened by grinding operation. But these very hard cutting tools made by the powder metallurgy process can be re-sharpened by using the electrochemical grinding (ECG) process and the cost of ECG is higher than the new cutting tool itself. Hence it is not preferable to due to the reduction in tool changing time the production rate can be increased.
Understanding the properties of fluids is essential to analyze their behavior in working conditions.
In this article, we have covered the fluid properties namely mass density, specific weight, specific volume, specific gravity, viscosity, vapor pressure, compressibility and surface tension.
Mass Density (ρ) is the property of a fluid that is the mass per unit volume.
Specific Weight (w) of a fluid is the weight per unit volume.
Specific Volume (v) of a fluid is the volume of the fluid per unit mass.
Specific Gravity (s) of a fluid is the ratio of the mass density of a fluid to the mass density of a standard fluid.
Viscosity is the property by virtue of which it offers resistance to the movement of one layer of fluid over the adjacent layer.
When a liquid is confined in a closed vessel, the ejected vapor molecules accumulated in the space between free liquid pressure and top of the vessel exert a partial pressure on the liquid surface. This pressure in the liquid is known as vapor pressure.
The normal compressive stress of any fluid element at rest is known as hydrostatic pressure which arises as a result of innumerable molecular collisions in the entire fluid. The degree of compressibility of a substance is characterized by bulk modulus of elasticity (B).
Surface tension is a measure of the fluid tendency to take a spherical shape, caused by the mutual attraction of the liquid molecules.
The failure of the tool is taking place in the following modes:
1. Failure through plastic deformation: During machining operation, when the temperature of the tip of the tool is greater than the hot hardness temperature of the tool material, the tool loses its hardness considerably and the tooltip will get deformed plastically called as plastic deformation failure. This is mainly due to the wrong selection of the process parameters or the wrong selection of the tool material. But this type of failure is considered as an abnormal failure of the tool.
2. Mechanical breakage failure of the tool: During machining operation suddenly the tool tip will get chipping away called as a mechanical failure of the tool. This is due to the impact loads acting on to the tool material, excessive plastic deformation, transient thermal stresses and localized cooling etc. The mechanical impact may be caused by intermittent cutting or due to the presence of blow holes or machining of hard inclusions etc. thermal stress are caused due to sharp temperature gradients within the tool and between the insert and the tool holder. Localized cooling may result from an incorrect application of the cutting fluid. This is also considered as an abnormal failure of the tool.
3. Failure through gradual wear: As the machining continues the tip of the tool will be wearing out slowly and when the wear becomes considerable, the tool can’t perform the machining satisfactorily called gradual wear failure of the tool. The gradual wear failure of the tool is taking place due to
a) Crater wear: The wear taking place on the rake face of a tool like a crater called the crater wear. The reason for crater wear are
b) Flank wear: The wear taking on the flank face is called flank wear. The reasons for flank wear are:
Laser technology is being used for a variety of industrial applications, including heat treatment, welding, measurement, as well as scribing, cutting, and drilling (described here). The term laser stands for light amplification by stimulated emission of radiation.A laser is an optical transducer that converts electrical energy into a highly coherent light beam. A laser light beam has several properties that distinguish it from other forms of light. It is monochromatic (theoretically, the light has a 单一 wavelength) and highly collimated (the light rays in the beam are almost perfectly parallel). These properties allow the light generated by a laser to be focused, using conventional optical lenses, onto a tiny spot with resulting high power densities. Depending on the amount of energy contained in the light beam, and its degree of concentration at the place, the various laser processes identified in the preceding can be accomplished.
Laser beam machining (LBM) uses light energy from a laser device for material removal by vaporization and ablation. The setup for LBM is illustrated in Figure 1. The types of lasers used in LBM are carbon dioxide gas lasers and solid-state lasers. In laser beam machining, the energy of the coherent light beam is concentrated not only optically but also regarding time. The light laser beam is pulsed so that the released energy results in an impulse against the work surface with the melted material evacuating the surface at a high velocity that produces a combination of evaporation and melting.
Laser Beam Machining (LBM) is used to perform various types of drilling, slitting, slotting, scribing, and marking operations. Drilling small diameter holes is possible—down to 0.025mm. For larger holes, above 0.50mm diameter, the laser beam is controlled to cut the outline of the hole. Laser Beam Machining (LBM) is not considered a mass production process, and it is used on thin stock. The range of work materials that can be machined by LBM is virtually unlimited. The ideal properties of the material for LBM include high light energy absorption, reduced reflectivity, low specific heat, low heat of fusion, excellent thermal conductivity, and low heat of vaporization. Of course, no material has this ideal combination of properties.
The actual list of work materials processed by LBM includes ceramics, glass and glass epoxy, plastics, rubber, cloth, wood, and metals with high hardness and strength, soft metals.
During motocross racing, riders will have to make many choices which side does he/she prefer to ride while crossing the opponent and making circular turns on the race track. To stand first in the racing competition, the rider has to choose the best lanes on the racing track. Many factors exist when deciding which lane to take through a corner.
Few of the factors that decide are Kinetic Energy, Newton’s First Law of Motion, Earth gravity, Inertia affect motocross rider when trying to take some tricky corners on the race track. Track design and conditions of the track such as corner filled with ruts or steep berms also need to be considered.
When taking a corner on a motocross racing track, there are several factors need to be considered while choosing a lane. They are:
Below visual infographic gives clear idea and helps the motocross riders to know how to choose the best lane in the racking, to be fast in motocross racing track and win the competition.
The post Science in Motocross Racing for Choosing Right Lane [资讯graphic] appeared first on ME Mechanical.
A more recent development in manufacturing is the concept of hybrid machining systems. Two or more machining processes are combined into one system to take advantage of the capabilities of each process, increasing production speed, and thus improving the efficiency of the operation. The system can handle a variety of materials, including metals, ceramics, polymers, and composites.
Examples of such systems include combinations and integration of the following processes:
The implementation of these concepts and the development of machinery and control systems present significant challenges. Essential considerations include factors such as
Ultrasonic machining (USM) is a non-traditional machining process in which abrasives contained in a slurry are driven at high velocity against the work by a tool vibrating at low amplitude and high frequency. The amplitudes are around 0.075 mm (0.003 in), and the frequencies are approximately 20,000 Hz. The tool oscillates in a direction perpendicular to the work surface and is fed slowly into the work so that the shape of the tool is formed in part. However, it is the action of the abrasives, impinging against the work surface, that performs the cutting. The general arrangement of the USM process is depicted in the below figure 1.
Common tool materials used in USM include soft steel and stainless steel. Abrasive materials in USM include boron nitride, boron carbide, aluminum oxide, silicon carbide, and diamond. Grit size ranges between 100 and 2000. The vibration amplitude should be set approximately equal to the grit size, and the gap size should be maintained at about two times grit size. To a significant degree, grit size determines the surface finish on the new work surface. In addition to surface finish, the material removal rate is an important performance variable in ultrasonic machining. For a given work material, the removal rate in USM increases with increasing frequency and amplitude of vibration.
The cutting action in USM operates on the tool as well as the work. As the abrasive particles erode the work surface, they also erode the tool, thus affecting its shape. It is, therefore, important to know the relative volumes of work material and tool material removed during the process similar to the grinding ratio. This ratio of stock removed to tool wear varies for different work materials, ranging from around 100:1 for cutting glass down to about 1:1 for cutting tool steel.
The slurry in USM consists of a mixture of water and abrasive particles. The concentration of abrasives in water ranges from 20% to 60%. The slurry must be continuously circulated to bring fresh grains into action at the tool work gap. It also washes away chips and worn grits created by the cutting process.
The development of ultrasonic machining was motivated by the need to machine hard, brittle work materials, such as ceramics, glass, and carbides. It is also successfully used on certain metals, such as stainless steel and titanium. Shapes obtained by USM include non-round holes, holes along a curved axis, and coining operations, in which an image pattern on the tool is imparted to a flat work surface.
A polymer is a compound formed of repeating structural units called mers, whose atoms share electrons to form huge molecules. Polymers usually consist of carbon plus one or more other elements, such as hydrogen, nitrogen, oxygen, and chlorine.
Polymers are divided into three categories:
Thermoplastic polymers can be subjected to multiple heating and cooling cycles without substantially altering the molecular structure of the polymer. Conventional thermoplastics include polyethylene, polystyrene, polyvinylchloride, and nylon.
Thermosetting polymers chemically transform (cure) into a rigid structure on cooling from a heated plastic condition, hence the name thermosetting. Members of this type include phenolics, amino resins, and epoxies.
Although the name thermosetting is used, some of these polymers cure by mechanisms other than heating.
Elastomers are polymers that exhibit significant elastic behavior; hence the name elastomer. They include natural rubber, neoprene, silicone, and polyurethane.
It utilizes a closed impression die to obtain the desired shape of the component. The shaping is done by the repeated hammering given to the material in the die cavity. The equipment used for producing the blows are called drop hammers. In general drop forging will be done in two halves of the dies. The bottom half of the die is fixed to the anvil of the machine but the upper half of the is fixed to the anvil of the machine but the upper half of the is fixed on the heated stock is kept in the bottom die and the top die or ram delivers few numbers of blows on the metal. Die impressions are machined in the cavity, hence some complex shapes can be produced. But too much complex shapes cannot be produced like cavities, deep pockets etc due to the limitation of withdrawal of finished forging. The products produced are crankshaft, crank, connecting rod, crane hook, wrench etc.
The process of producing the shape of the component sis similar to that of the drop forging but in press forging the required amount of force can be obtained continuously in the squeezing action. This squeezing is obtained by means of a hydraulic press or mechanical press. Because of continuous force application, the material gets uniformly deformed throughout the its depth.
The post Differences between Drop Forging and Press Forging appeared first on ME Mechanical.
Consider the moment of inertia IAA’ of an area A with respect to an axis AA’ (Fig.). Denoting by y the distance from an element of area dA to AA’, we write
Let us now draw through the centroid C of the area an axis BB’ parallel to AA’; this axis is called a centroidal axis. Denoting by y’
the distance from the element dA to BB’, we write y 5 y9 1 d, where d is the distance between the axes AA’ and BB’. Substituting for y in the above integral, we write
The first integral represents the moment of inertia IBB¿ of the area with respect to the centroidal axis BB9. The second integral represents the first moment of the area with respect to BB9; since the centroid C of the area is located on that axis, the second integral must be zero. Finally, we observe that the last integral is equal to the total area A. Therefore, we have
This formula expresses that the moment of inertia IAA9 of an area with respect to any given axis AA9 is equal to the moment of inertia IBB¿ of the area with respect to a centroidal axis BB9 parallel to AA9 plus the product of the area A and the square of the distance d between the two axes. This theorem is known as the parallel-axis
theorem. Substituting r2
AA9A for IAA9 and r
BB A for IBB, the theorem can also be expressed as
A similar theorem can be used to relate the polar moment of inertia JO of an area about a point O to the polar moment of inertia JC of the same area about its centroid C. Denoting by d the distance between O and C, we write
There are several operations related to drilling. Some of them are:
These are illustrated in Figure 1 and described in this section. Most of the operations follow the drilling process; a hole must be made first by drilling method, and then the hole is modified by one of the other operations related to drilling. Centering and spot facing operations are exceptions to this rule. All of the operations use rotating tools.