08-16-2017, 09:47 PM
[attachment=2258]
[attachment=2259]
INTRODUCTION
As the world is advancing forth technically in the field of space research, missile and nuclear industry; very complicated and precise components having some special requirements are demanded by these industries. For meeting these challenges unconventional methods of machining have evolved. The unconventional methods of machining have several specific advantages over conventional methods of machining and these promise formidable tasks to be undertaken and set a new record in the manufacturing technology. These methods are not limited by hardness, toughness, and brittleness of materials and can produce any intricate shape on any workpiece material by suitable control over the various physical parameters of the processes.
These new processes can be classified into various groups according to (a) type of energy required to shape materials-mechanical, thermal and electrothermal, or chemical and electrochemical; (b) basic mechanism involved in the processes-erosion, ionic dissolution, vapourisation; © source of energy required for material removal-hydrostatic pressure, high current density, high voltage, ionised material; (d) medium for transfer of these energies-high velocity particles, electrolyte, electron, hot gases.
Laser Beam Machining (LBM) is one such method in which heat energy is concentrated on a small area of workpiece, to melt and vapourise the tiny bits of work material. Laser is an acronym for light amplification by stimulated emission of radiation. In this process, a narrow beam of coherent, monochromatic light is focused on workpiece by lens to give extremely high energy density to melt and vapourise any material.
There are two main types of lasers commonly used for material processing purposes: CO2 (carbon dioxide) and the Nd:YAG (neodymium-doped yttrium aluminium garnet). Another type of lasers used for manufacturing purposes is solid, liquid, gas and semiconductor. The main parts of a laser include a power supply, a lasing medium, and a pair of precisely aligned mirrors. Nd: YAG laser is a common solid-state laser which uses a single crystal of Yttrium Aluminium Garnet (YAG) doped with Neodymium as the lasing medium.
The laser machining system has great ability to machine very hard surfaces. A good number of fundamental research have already been made in the area of laser machining technology , further research is still needed for optimal parametric analysis for achieving high quality surface finish and dimensional accuracy during machining operation. For achieving the above mentioned things, the parameters affecting the process should be in the optimal state. There is at least, a worldwide recognition of the fact that pre-production experiments, properly designed and analysed, can significantly contribute to efforts towards the accurate characterisation and optimization of industrial processes, quality improvement of products, and reduction of costs and wastes.
Japanese industry, was the first to realize the potential of the statistical design of experiments (SDE) originally due to R. Fisher of Britain. One area of current development in manufacturing industry involves statistical experimentation as its main tool; in general terms, it is concerned with the application of modern off-line control techniques. In other words, eliminate the need for mass inspection by building quality into the product and process at the design stage.
Taguchi s method of robust design is one such method that uses experimental design methods for efficient characterisation of a product or process, combined with a statistical analysis of its variability. It is based on the concept of quality engineering. This approach allows quality considerations to be included at an early stage of any new venture: in the design and prototype phase for a product; during routine maintenance; or during installation and commissioning of a manufacturing process.
LASER PRINCIPLE
The laser beam is a very narrow, intense beam of coherent (united) light that can be controlled over a wide range of temperatures at the point of focus, from slightly warm to several times hotter than the surface of the sun. The general principle on which most lasers operate is as follows:
Electrons or molecules in a lasing medium, a gas or solid core are excited to higher energy levels by photons from another energy source. As they return to their original unexcited state, they release a burst of energy in the form of a photon. The energy source for solid-state lasers is a high intensity light; for gas lasers it is an electrical discharge.
When a photon passes near another excited particle in the same wavelength, that particle is stimulated to emit a photon. Each new photon is capable of initiating the release of other photons, thereby forming a chain reaction.
COMPONENTS OF LASERS
Three main components must be present to have a laser: active medium, excitation medium and feedback mechanism.
ACTIVE MEDIUM
Stimulated emission is a reaction that takes place when a photon of the proper wavelength comes near an excited atom creating another photon. This new photon and the original photon have the same wavelength, are coherent, and begin to travel in the same direction. The active medium, which can be solid, liquid or gas is the medium in which stimulated emission takes place. It can even be a semiconductor material. Some of more commonly used materials for the active medium component are ruby, glass, erbium, organic dyes, ionized argon, helium-neon, and CO2, gallium arsenide.
EXCITATION MECHANISM
The excitation mechanism is a device used to induce an excited state in an atom. Three different types of devices can be used as excitation mechanisms: electrical, chemical and optical. The excitation process involves pumping energy into the active medium. This process is sometimes called laser pumping.
Electrical devices are used as the excitation mechanism in lasers with an active medium that conducts electricity. Such active base materials as gallium arsenide, gallium antimonide, Indian arsenide, CO2, ionized krypton, helium-neon and ionized argon call for electrical excitation mechanisms.
Chemical devices are the least commonly used type of excitation mechanism. The primary application of lasers that use a chemical excitation device is in military uses.
Optical devices excite the active medium using light energy. Light energy of a predetermined wavelength from the sun, a flash lamp, or a variety of other sources is introduced into the active medium. Lasers with solid-state media, such as ruby, glass or erbium use optical devices as their excitation mechanisms.
FEEDBACK MECHANISM
The feedback mechanism uses mirrors to reflect light produced in the active medium back into the medium. By placing the mirrors properly, light can be reflected back and forth through the active medium. This continual reflecting of light waves back and forth through the medium keeps stimulated emission at a maximum. The more distance the light waves travel within the medium, the longer they stay with the medium and as a result the stronger is the amplification of light.
CLASSES OF LASERS
The laser is one of the most rapidly emerging technologies, but it can be dangerous. Because of this, lasers are placed in four categories according to their power and potential danger:
Class I lasers are the least powerful and the least dangerous.
Class II lasers can be hazardous, but only under certain conditions. Exposure of the eyes to class II lasers could theoretically result in damage. However, damage to eyes is not likely to occur in reality because of the eye s natural blinking reaction, which would absorb the laser beam sufficiently to prevent damage.
Class II lasers are powerful enough to damage the eyes even before the blinking reaction can prevent it.
Class IV lasers are the most powerful, and in turn, the most dangerous. They are strong enough to ignite any material that will burn
LASER BEAM MACHINING (LBM)
Laser beam machining is one of the main applications of the laser in manufacturing. The laser yields a power density sufficient to vapourise any known ferrous, nonferrous, non-metallic and diamond material, including wood, paper, and advanced composites. Not all the material is removed by evaporation. Laser machining is basically a high-speed ablation process.
THE PROCESS
The work piece is heated so that surface melting occurs. The evaporation of a very small portion of the liquid metal takes place so rapidly under the high intensities of a focused laser beam that a substantial impulse is transmitted to the liquid. Material leaves the not only through evaporation, but also in the liquid state at a relatively high velocity. It is common practice to enhance the cutting operation by introducing an assist gas such as oxygen, nitrogen, or compressed air to the point at which the laser beam is working. The type of laser gas used is dependent upon the type of material being cut. Machining a hole using a laser beam requires a short, high intensity pulse.
The machining by laser beam is possible when the power density of beam is greater than conduction, convection and radiation and further the radiation must penetrate and be absorbed into material.
The power density (P.D) of laser beam can be calculated from the relationship
P.D =4P pL2a2T
Where PD=power density of laser beam W/cm2
P=laser energy output, watts (W)
L=focal length of lens, cm
a=beam divergence, radian
T=pulse duration of laser, sec
The size of the spot (diameter d) produced by laser is given by diameter d=La
The cutting rate (mm/min.) can be expressed as =CP EAt
Where C=is a constant dependent upon the material and conversion efficiency of laser energy into the material
P=laser power incident on the surface
E=vaporization energy of material, W/mm3
A=area of laser beam at focal point, mm2
t=thickness of material, mm
The minimum thickness of the material to provide the required heat transfer to be welded is given by the relation
Thickness=(time duration of laser beam in sec diffusivity of metal in cm2/sec 0.38)0.5
The energy required to raise a given amount of metal to its melting temperature is given by the relation
E= ( [Cp (m-a) +L] 4.2) (1-R) joules
Where is the specific gravity, is the volume of the metal melted ,Cp is the specific heat, m is melting temperature, a is the ambient temperature,L is heat of fusion,R=reflectivity
ADVANTAGES
(1) There is no direct contact between tool and work piece. As such no tool wear problems are faced.Metal, non-metal irrespective of their brittleness and hardness, and even soft metals like plastics and rubber can be machined.
(2) Laser beam can be sent to longer distances, without diffraction. It can also be focused at one place thereby generating lot of heat. It is thus possible to weld, drill and cut areas not readily accessible.
(3) The advantage of laser welding are that heat treated and magnetic material can be welded without losing their properties all over the material except a small region of heat affection. Laser welding is possible in any environment through transparent materials and magnetic fields as well. Distortion is negligible and any two materials can be joined together. However it is important that the vaporization of the metal must be avoided.
(4) Micro sized holes can be laser drilled in difficult-to machine or refractory materials. Precision location is ensured by focusing of the beam. Deep holes of very short diameter can be drilled by using unidirectional multiple pulses.
(5) Beam configuration and size of exposed area can be easily controlled.
LIMITATIONS
LBM has the limitations of high initial cost, short life of flash lamp, safety procedures to be followed strictly, over all low efficiency(0.3%to 0.5%), very low material removal rate ,not able to drill too deep holes, machined holes not round and straight, and no possibility of matching some plastics which burn or char.
APPLICATIONS
(1) Used for making very small holes, difficult welding of non conductive and refractory materials, cutting complex profiles in thin and hard materials. Also used for partial cutting or graving.
(2) To project intense energy to a small area to illuminate, melt, weld, perforate or ignite.
(3) Can be used for mass micro machining production
(4) Can also be used for selective heat treatment of materials
(5) It is also some times used for dynamic balancing of rotating parts.
(6) It is very useful for producing very fine and minute holes.
(7) Micro-machining, micro-drilling, spectroseospic, metallographic sciences and photography have been developed.
CHARACTERISTICS OF LBM PROCESS
Material removal technique Heating, melting and
Vaporization
Tool Laser beams in wavelength range
of 0.4-0.6 m
Power density as high as 107W/mm2
Output energy of laser and 20 J, 1 milli second
Its pulse duration
Peak power 20 kW
Medium Normal atmosphere
Material removal rate 5mm3/min
Specific power consumption 1000W/mm3/min
Material of workpiece All materials except those with high
Thermal conductivity and high
Reflectivity
Applications Drilling micro holes (upto 250 m)
And cutting very narrow slots
Dimensional accuracy 0.025 mm
Efficiency 0.3-0.5%
Limitations Very large power consumption
LASER IN METAL CUTTING
A laser beam can be used for cutting metals, plastics, ceramics, textile, cloth and even glass, when its surface is coated with radiation absorbing material such as carbon. Usually laser cutting starts by drilling a hole through the workpiece, the4n moving along a pre-determined path of the shape to be cut. An argon laser however does not actually burn but ionizes the epoxy resin board in order to cut it. What actually occurs is the dissociation of chemical bonds and it leaves behind ash or charred remains. Carbon dioxide and YAG, on the other hand burn through the material. A jet of oxygen is used to obtain exothermic reaction with metals to produce a clean cut kerf and rapid rate of cutting or drilling. Of the industrial lasers, the CO2 laser has the highest depth to diameter ratio in most metals, using a gas-jet assist.
Cutting speeds depend on the material being cut, its thickness and physical characteristics and the output power of laser beam. Steel, titanium, nickel, certain refractory materials cut easily. Cutting aluminium metal and copper has been especially problematic, since these metals tend to absorb the applied heat. But recently YAG laser with enhanced focusing has been developed that can cut these metals. Besides speed-cutting the laser has an additional advantage in cutting complex shapes with sharp corners and slots. The advantage is that the heat affected zones are just 10-12 percent of kerf width and distortion is minimal.
LASER IN DRILLING
Not much precision can be attained in laser drilling in the sense of perfectly cylindrical holes; laser drilled holes tend to be conical. However, laser drilling is not suited for deep- hole drilling and for producing perfectly cylindrical holes. In industry, laser drilling is widely used for rough drilling, especially in watch jewels, diamond dies and other machine parts where a high level of precision is not demanded. The greatest advantage is its ability to make small and very small holes of shallow depth.
Laser machines now in use drill holes that are 75 micron in diameter. A drill bit would break if it is applied to such small holes. One application that is under proprietory wraps is the making of semi-conductor chips for computers and microprocessors, which benefits from the capability of a laser to etch lines at hair thickness. In aircraft-turbine industry laser drilling is used to make holes for air bleeds, air cooling or the passage of other fluids.
Other applications include making holes in hypodermic needles, automotive fuel plates, various lubrication devices, ceramic substrates for electronic circuits, holes in tungsten-carbide tool plates and so on.
LASER IN WELDING
Laser welding is essentially useful when it is essential to control the size of the heat affected zone, to reduce the roughness of the welded surface and to eliminate mechanical effects. Lasers are generally used for welding multilayer materials in which there are discontinuities in thermal properties at the interfaces where the layers come into contact.
There are two general kinds of laser welds: conduction-limited welds and deep-penetration welds. Former is normally used for joining thin components, the metal absorbs the laser beam at the work surface, and the area below the surface is heated by conduction. Latter requires greater power and CO2 laser is used for this purpose. In this case thermal conduction does not limit penetration, because the beam energy is delivered to the depth of weld. Neither type of weld requires any filler material
There are certain basic parameters for laser welding. The most important are: (a) the wavelength of the laser beam must be compatible with the material being welded, (b) the focus of the beam must be adjusted to the thickness of material;© a pulsed mode of operation is better than a continous wave;(d) a pulse shape of the laser beam must be controlled precisely from weld to weld; and (e) close contact with the surfaces of materials to be joined must be maintained.
The most important components of a laser system designed for welding consist of a source of alternating current, a step up transformer, a rectifying system, a pulse forming mechanism, a lasing element, a cooling system and an optical system for controlling the beam-profile projected to the specimen. To weld any two pieces of metal together, the temperature of the area must be raised to the melting point of metals. If both the metals are similar, then the problem is nominal. However, if two different metals need to be welded then a compromise of the laser energy must be made. In this case, the configuration of the joint, thermal conductivity, diffusivity, latent heat, etc. are also taken into consideration to determine the amount of laser energy required.
Laser welding has become popular for joining sheet metal or stock pieces of about 2.5mm thick or less. Besides eliminating the need for filler material, the extremely narrow continuous welds or spot welds can be made at fast speeds with very narrow heat-affected zones. It has become a viable alternative to electron beam welding in the case of productivity. With laser welding heat generation is least, weld quality excellent, weld speed moderate and ease of automation is excellent.
One of the main criteria for laser welding is the proper joint preparation. The two surfaces being welded must remain in close contact with each other. To establish an intimate contact, a pressure is applied. Alternatively, for sheet metal welds a transparent plastic is often used. Some of the most readily processed metals and alloys are: low carbon steels, stainless steel, titanium and titanium alloy, tantalum, zirconium, silicon, bronze and some nickel alloys. The least suitable are zinc, galvanized steel, brass, silver and gold.
LASER FOR SURFACE TREATMENT
By the preferential use of laser radiation, gears, saw teeth, valve wear pads and cylinder liners can be strengthened. The input heat is confined to a localized are and the mass of rest of the surrounding metal serves as the quench. The laser is used to deposit a thin layer of cobalt alloy on the turbine blade shroud-contact areas. Argon gas is used for shielding during deposition of the cobalt alloy and for cooling afterwards. It is possible to hard face the shroud wear pad of nickel-alloy turbine blades with a cobalt-base alloy. Therefore, the advantages are: the total input of heat to the blades has been considerably reduced, nickel dilution is minimal, the deposit is uniform, consumption of cobalt alloy is reduced by almost 50% and process time is reduced to one-tenth.
RECENT APPLICATIONS OF LASER
LASER CAVING
It makes it possible to machine cavities in work that is too hard to mill. Laser caving is especially effective in materials such as ceramics, composites, carbides, quartz glass and titanium based alloys. Running the cutting tool (laser) back and forth through the area to be machined, pockets are created. Because the laser cutter is very small, the material removal rates are relatively slow. Although the tool is small, it is possible to produce very accurate forms and sharper corners. This technology could be beneficial to die and mould makers who are constantly faced with producing and finishing intricate forms and shapes.
LASER HARDENING
The high-speed transformation hardening of carbon steels, over 0.2% carbon, is a major application of lasers. Before steel shafts are hardened, they must be stripped of any rust-protective coatings. Then a coating that improves the absorption of the laser radiation into the material is applied only to the requiring hardening. The heating process is immediately followed by a water or oil quench. The heating changes the carbon steel into austenite and the quenching transforms it to martensite.
LASER MARKING / BAR CODING
Laser marking is being used in many industries because of the drive for zero defects, inventory control, and the need to identify defects in the manufacturing process. Laser machining is able to mark identification codes on parts, particularly those of non-traditional materials or complex shapes.
Bar coding, one of the best data collection systems, can be used on anything that can be counted (taking inventory), packaged (supermarket labeling), and tracking (letters and packages in courier services). It can also be used for monitoring quality control on assembly lines and collecting information through multiple workstations. The most common application of bar coding is in the retail stores, where printed labels consisting of a series of black lines against a white background are used to code certain information about the product. The code could be used for pricing, tracking, and marketing and inventory purposes.
TAGUCHI S APPROACH TO EXPERIMENTAL DESIGN
The traditional approach to test products is to change the setting of only one factor while keeping every other fixed. A factor is a parameter, variable or any controllable source of variation. But this method is costly and unreliable in spite of being very popular in the West. In contrast SDE advocates the changing of many factors at the same time in a systematic way, ensuring the reliable and independent study of the factor s main and interaction effects. Once the factor effects have been adequately characterized, steps can then be taken towards their appropriate control during production, so that variability in the product s performance is minimized.
Full factorials (designs studying every possible combination of factor settings) are utilized when experimentation is easy or when the number of factors under study is small (3 or 4). Fractional factorials (designs consisting of only a certain number of combinations of factor settings out of all possible) are the most commonly used design as they provide a cost-effective way of studying many factors in an experiment, at the expense of ignoring some high-order interactions, which is considered a low-risk strategy since high-order interactions are usually insignificant and in any case difficult to interpret.
OBJECTIVE
The objective of Taguchi s efforts is process and product design improvement through the identification of easily controllable factors and their settings, which minimize the variations in product response while keeping the mean response on target. By setting those factors at their optimal levels, the product can be made robust to changes in operating and environmental conditions. Thus more stable and higher quality products can be obtained and this is achieved during Taguchi parameter design stage by removing the bad effect of the cause rather than the cause of the bad effect.
DIVISION OF FACTORS
There are two main aspects to the Taguchi technique. First the behavior of a product or process is characterized into two types:
1. Controllable factors- those whose values may be set or easily adjusted
by the designer or project engineer.
2. Uncontrollable factors, which are sources of variation often associated with the production or operational environment; overall performance should, ideally be insensitive to their variation.
PERFORMANCE MEASURES
The observations at each setting of the controllable factors provide means for the calculation of two performance measures.
1. The noise performance measures (NPM) ,reflecting the variation in the response at each setting; its analysis will determine the controllable factors which can affect this variation ; the optimal combined setting of these factors to minimize the variability will also be determined.
2. The target performance measure(TPM), reflecting the process average performance at each setting ;analysis of this will reveal those controllable factors ,which are not variability control factors, but have a large effect on the mean response . These can be manipulated to bring the mean response to the required target
Many measures for the NPM have been suggested. When there is a target value to be achieved for the response, the use of the signal to noise ratio (SNR) which estimates the ratio /s, with being the process mean and s the process standard deviation
SNR=10 log 10 (y2/s2)
Where y and s are respectively the sample mean and sample standard deviation of the n observations in each trial.
When the desired characteristics for the response is the smaller
=-10 log 10 {1/n y2}
Where as when the response is larger the better
=-10 log 10{1/ny-2 }
For the n observations y in each trial. The minus sign in n and is used by convention so that the NPM is always maximized.
INTERACTIONS
When the effect of one factor A (on the response) depends on the settings (levels) of another factor B, then an interaction effect (between A and B) is present (usually symbolized by AxB). Depending on the number of factors, orthogonal arrays exist which can also study interactions. Three cases arise:
1. Either the main effects of three factors (assigned on columns A, B and D) and all possible interactions between them.
2. Or the main effects of four factors (A, B, D, and G) and three interactions (A B, A D, B D).
3. Or the main effects of seven factors (A, B, C, D, E, F, and G) and no interactions.
Trial A B C
A B D
E
A D F
B D G
A B D
1 1 1 1 1 1 1 1
2 1 1 1 2 2 2 2
3 1 2 2 1 1 2 2
4 1 2 2 2 2 1 1
5 2 1 2 1 2 1 2
6 2 1 2 2 1 2 1
7 2 2 1 1 2 2 1
8 2 2 1 2 1 1 2
Case 1 corresponds to a full factorial whereas cases 2 and 3 are fractional factorials confounding main effects with certain interactions. Taguchi does not ignore interactions; in fact he suggests that a man who does not believe in the existence of non-linear effects is a man removed from reality.
MAIN POINTS OF TAGUCHI PHILOSOPHY
1. Change the timing of the application of quality control from on line to off line, so that you can cease to rely on inspection, can build quality into the product and the process and thus do it right first time .
2. Change the experimental procedures from varying one factor at a time, through statistical experimental design techniques.
3. Change the objectives of the experiments and the definition of quality from achieving conformance to specification to achieving the target and minimizing the variability .
4. Change the attitude for dealing with uncontrollable factors: remove the effect not the cause, by appropriately tuning the controllable factors.
MULTI-LEVEL COLUMN CREATION
Multi level factors can be studied by first creating the appropriate multilevel columns in two-level or three-level arrays. This is generally achieved by sacrificing 2 columns which are replaced by a new column whose levels directly correspond to every level-combination of the original 2 columns.
Combination Levels of new column
1, 1 1
1, 2 2
1, 3 3
1, 4 4
The only requirement for the creation of multilevel columns in this way is that an interaction column must exist for the sacrificed columns; this is also deleted.
TRIAL COLUMN COLUMN
1 2 3 4 5 6 7 ( 1 2 3 ) 4 5 6 7
1 1 1 1 1 1 1 1 1 1 1 1 1
2 1 1 1 2 2 2 2 1 2 2 2 2
3 1 2 2 1 1 2 2 2 1 1 2 2
4 1 2 2 2 2 1 1 2 2 2 1 1
5 2 1 2 1 2 1 2 3 1 2 1 2
6 2 1 2 2 1 2 1 3 2 1 2 1
7 2 2 1 1 2 2 1 4 1 2 2 1
8 2 2 1 2 1 1 2 4 2 1 1 2
In the first matrix given above column 3 is the interaction column for the factors associated with columns 1&2.The first three columns are therefore removed from the orthogonal array and in their place a new column at 4 levels is created.
GRAPHICAL REPRESENTATION
The effect of factors in an experiment can be presented on a graph using the following procedure.
1. Identify the largest and smallest average responses.
2. Draw a vertical scale to include all of these average values.
3. Draw a horizontal line at the grand average value.
4. For each factor plot the average response value at the high level and also at the low level. Plot one point directly over the other. One point will be above the grand average line and the other will be below. Also, they will be equidistant from grand average line.
5. Label the points and connect each pair of points by a vertical line.
CASE STUDY
In the case of profile generation using Nd:YAG laser beam machining an experiment was conducted to determine the effects of frequency of Q-switch(A), lamp current(B) and cutting speed©. The factors A, Band C were set at three levels as follows:
symbol Parameter Units Level 1 Level 2 Level 3
A Frequency of Q- switch kHz 5.5 5 4.5
B Lamp Current amp 20 21 22
C Cutting speed mm/s 8 10 12
The responses of interest were the surface roughness and angular deviation. Surface roughness was determined using a profilometer. In the present study only roughness will be analysed. The results are summarized in the table below:
Standard order trial no: Response Observed values (y) Frequency (A) (kHz)
A1 A2 A 3
Lamp current (B) (amp)
B1 B2 B3 Cutting speed © (mm/s)
C1 C2 C3
1 6.56 6.56 6.56 6.56
2 5.22 5.22 5.22 5.22
3 5.04 5.04 5.04 5.04
4 4.12 4.12 4.12 4.12
5 5.50 5.50 5.50 5.50
6 4.46 4.46 4.46 4.46
7 5.08 5.08 5.08 5.08
8 6.86 6.86 6.86 6.86
9 4.90 4.90 4.90 4.90
Total 47.74 16.82 14.08 16.84 15.76 17.58 14.4 17.88 14.24 15.62
Number of values 9 3 3 3 3 3 3 3 3 3
Average 5.304 5.60 4.69 5.61 5.25 5.86 4.8 5.96 4.74 5.20
RESULTS AND DISCUSSION
A). Effect of Operating Parameters on surface roughness.
Effect of frequency of Q-switch on surface roughness is 0.92
Effect of lamp current on surface roughness is 1.06
Effect of cutting speed on surface roughness is 1.22
B). The relative significance of the operating parameters on surface
roughness
Level of operating parameters for minimum surface roughness: [A2 B3 C2]
Frequency at level 2
Lamp current at level 3
Cutting speed at level 2
REFERENCES
HMT Production Technology, Tata Mcgraw Hill
R .K Jain ,Production Technology, Khanna Publishers
Steve Krar & Arthur Gill, Exploring Advanced Manufacturing Technology Industrial Press Inc.
International Journal The Machinist May-June 2003 ( pp 38-43)
N. Logothetis , Managing for Total Quality- From Deming to Taguchi & SPC Prentice Hall of India Private Limited