1. Centreless Grinding (New) (Finishing)
Among cylindrical grinding techniques, cemreless methods have an exceptional position with respect to their process structure and area of application. Centreless grinding's main area of use is in large batch and mass production. While the workpiece is led during grinding between centres in its rotation axis, its position in centreless grinding is determined by a three-point positioning be-tween the grinding wheel, control wheel and workrest plate. The component is si-multaneously conveyed to its peripheral area and machined. Since the material removal process corresponds to that of other cylindrical grinding methods, we concentrate in the following on only method-specific fea-tures. Like grinding between centres, centreless grinding is also subdivided ac-cording to the orientation of the main feed direction. In centreless plunge grinding (external cylindrical peripheral plunge grinding), the grinding wheel is moved radially towards the workpiece. With these technique kinematics, rotation-symmetrical parts can be produced. for example. bearing car-riers of camshafts, valve tappets. jet needles, rotor axes and ball studs. In centreless through feed grinding (external cylindrical peripheral longitudinal grinding), the workpiece is moved in the direction of the grinding wheel rotation axis. This technique is a typical mass production process of components with cy-lindrical, conical or spherical working surfaces. Working examples are bars, bolts, axles and roller bearing elements. The grinding and control wheels as well as the workrest plate can he arranged horizontally, vertically or angularly, whereby the horizontal design is the most common (Fig. 6-46)
The new one is better.
2. Creep feed grinding (old)Creep feed grinding is a new form of grinding operation different from the conventional grinding proc-ess. In creep feed grinding the entire depth of cut is completed in one pass only using very small in teed rates. As shown in Fig. 9.16. this process is characterised by high depth of cut of the order of Ito 30 mm with low work speeds of the order of I to 0.025 m/min. The actual material removal rates calculated from these process parameters are generally in the same range as that of conventional grinding. How-ever, the idle time (stopping and wheel/table reversal) gets reduced since the grinding operation is com-pleted in one pass.
(Rao P. N., Manufacturing technology: metal cutting and machine tools, p. 235)
Creep feed grinding (new) (Finishing)
Creep feed grinding is a new form of grinding operation different from the conventional grinding proc-ess. In creep feed grinding the entire depth of cut is completed in one pass only using very small in teed rates. As shown in Fig. 9.16. this process is characterised by high depth of cut of the order of Ito 30 mm with low work speeds of the order of I to 0.025 m/min. The actual material removal rates calculated from these process parameters are generally in the same range as that of conventional grinding. How-ever, the idle time (stopping and wheel/table reversal) gets reduced since the grinding operation is com-pleted in one pass.
The cutting forces and consequently the power required increases in the case of creep fccd grinding. but has a favourable G-ratio. It is necessary to continuously dress the grinding wheel (to reduce the wheel dullness) fcr efficient operation. This however causes wheel wear and makes it necessary to adjust the wheel head. Soft and open wheels are used to take care of the wheel dressing and accommodate large volume of chips generated in the process. The grinding wheel speeds used are also low of the order of IS rri/s compared to the 30 m/s used in conventional grinding operations. Thc inked rates used arc low, of the order of 0.005 mm/pass. The grinding fluids used are oil based in view of the low grinding speeds employed. However, the volume of grinding fluid is much more compared to conventional grinding in view of the high heats generated in the process.
(Posinasetti Nageswara Rao,Manufacturing Technology: Metal Cutting and Machine Tools,page 235)
Creep-feed grinding is characterized by the use of slow (creep) work-piece velocities and extremely large depths of cut which are hundreds or even thousands of times greater than those in regular grinding applications. With this process, it may he possible to grind complex profiles or deep slots in only a few or even a single pass. Applications of creep-feed grinding include the machining of drill flutes and the profiling of turbine blade roots for jet engines 155-571. Because of the heavy wheel depths of cut in creep-feed grinding, which typically range from 1 to 10 min. the wheel-work contact lengths and grinding zone areas are also very big. Therefore, we should expect much bigger specific energies than in regular grinding owing to much bigger sliding forces (Eq. (5-11)). An example of this behavior in Figure 5-19 illustrates the sensitivity of the specific grinding energy to the wear-flat area for straight creep-feed grinding of a nickel-base alloy with a high-porosity aluminum oxide wheel 158.591. Whereas our grinding model predicts a linear relationship between specific energy and wear-flat area. these results suggests a discontinuous curve with two slopes. This discontinuity at a specific energy approaching 200 Jimml may he associ-ated with burn-out of the grinding fluid (see Chapter 7). The intercept at about 25 Enin0 in Figure 5-19 is comparable to that expected for the combined chip-formation and plowing energy' components. and the very large specific grinding energies can be attributed to sliding of the wear flats against the workpiece.
(Malkin S., Guo C., Grinding technology: theory and applications of machining with abrasives, p.141)
The new one is better.
3. Excimer Laser (Old)(manufacturing)
An excimer laser belongs to a famşly of gas lasers
that produce nanosecond-long powerfull pulses at wavelenghts near of in the
ultraviolent portion of the electromagnetic spectrum. These lasers use the
mixures of gases. The bulk of the gas mixture is a gas such as helium or neon
that aids in energy trasnfer . A rare gas is source of laser actiın and usually
makes up only one half the 12 percent of the total mixture. The important
excimer laser gases are krypton flouride, xenon flouride, argon flouride and
xenon chloride. An exicemr laser can generate pulses of over one bilion watts of
power.
(Charlene W Billings, Lasers: New Technology Of Light. P. 25 )
Excimer Lasers (New)
Excimer lasers are important because they were the first lasers capable of producing high-power, ultraviolet (UV) output with good electrical efficiency. Remember that UV photons contain more energy than visible or infrared photons. so UV photons can often do things that less-energetic photons cannot. 'fins fact makes excimer lasers useful in a wide range of applications. Though solid-state lasers have experienced significant improvement in power capability with the onset of less-expensive diode pump arrays, the conversion of a solid-state laser's near-infrared output to the ultraviolet requires nonlinear optical frequency shifting a step that limits achievable power. In practice then. if one needs an average output power greater than about 5 W in the UV. or to access wavelengths where nonlinear materials severely limit the UV power. the excimer is the laser of choice.
(C. Breck Hitz,J. J. Ewing,Jeff Hecht, Introduction to Laser Technology, page 116)
The new one is better.
4. Self Centering Chuck(Old)Chucks are designed to move all jaws equally and simultaneously to center the part
in the chuck.Self centering chucks normally have higher gripping forces and are more
accurate than other chuck types.These chucks are recommended for bar stock, forgings,
castings, or turned parts that are located from gripping diameter.Some Self centering
power chucks are equipped with centrifugal force counter balance that maintain the
gripping force at high speeds.
(Stephen F. Krar,Arthur Gill,Exploring advanced manufacturing technologies,p. 4-1-6)
Self Centering Chuck(New) (Tool)
Self-centering chucks Self-centering chucks have 3 jaws that clamp the workpiece and centre it automati-cally during clamping. Chucks with 2 or 4 jaws are also available. In the case of the self-centering chucks, all 3 jaws are adjusted simultaneously by
a) a spiral (spiral chuck) (Figure 7.16)
b) spiral ring chucks, in which the chuck has adjustable jaws (Figure 7.17)
c) wedge rods (wedge rod chuck. Figure 7.18)
by means of a socket wrench.
The spiral chuck acconling to DIN 6150 uses an Arclumedean spiral as the adjusting clement In this spiral the jaws. which are also ground. grip with hardened and ground thread Flanks At the bottom side. this spiral ring is designed as a nng gear Pinions that are situated at 3 positions along the circumference or the chuck, engage into this ring gear With the square wrench. we can twist each pinion and, given this connec-tion. the spiral ring. Thus, the radial chucking motion or the jaws is generated In the wedge chuck, a tangentially located screw shills a wedge bar, which, in turn. rotates a driving ring Turning the driving ring simultaneously thins the two other wedge rods, with which the matt jaws of the chuck engage. In its basic sinecure. the spiral ring chuck with adjustable jaws corresponds to thc viral chuck 11cm. however, the intnnsic jaws, which can be adjusted using a spindle. am put on a master jaw The matir jaws are moved by the piral ring - as in the spiral chuck.
(Heinz Tschätsch, Applied Machining Technology, page 60-61)
The new one is better.
5. Radiographic Testing (old) (Testing)
Radiographic testing (RT) uses X rays or
gamma (g) rays that are passed through the weld and expose a photographic film
on the opposite side of the joint. X rays are produced by high voltage
generators, while g rays are produced by atomic disintegration of radioactive
isotopes.
Whenever radiography is used, precautions must be taken to protect workers from exposure to excessive radiation. Safety measures dictated by the Occupational Safety and Health Administration (OSHA), the National Electrical Manufacturer’s Association (NEMA), the Nuclear Regulatory Commission (NRC), the American Society of Nondestructive Testing (ASNT), and other agencies should be carefully followed when radiographic inspection is conducted. Radiographic testing relies on the ability of the material to pass some of the radiation through, while absorbing part of this energy within the material. Different materials have different absorption rates. Thin materials will absorb less radiation than thick materials. The higher the density of the material, the greater the absorption rate. As different levels of radiation are passed through the materials, portions of the film are exposed to a greater or lesser degree than the rest. When this film is developed, the resulting radiograph will bear the image of the cross section of the part. A radiograph is actually a negative. The darkest regions are those that were most exposed when the material being inspected absorbed the least amount of radiation. Thin parts will be darkest on the radiograph. Porosity will be revealed as small, dark, round circles. Slag is also generally dark, and will look similar to porosity, but will be irregular in its shape. Cracks appear as dark lines. Lack of fusion or underfill will show up as dark spots. Excessive reinforcement on the weld will result in a light region.
Radiographic testing is most effective for detecting volumetric discontinuities: slag and porosity. When cracks are oriented perpendicular to the direction of the radiation source, they may be missed with the RT method. Tight cracks that are parallel to the radiation path have also been overlookedwith RT.
Radiographic testing has the advantage of generating a permanent record for future reference. With a “picture” to look at, many people are more confident that the interpretation of weld quality is meaningful. However, reading a radiograph and interpreting the results requires stringent training, so the veracity of a radiograph depends to a great degree on the skill of the technician.
(Manufacturing Engineering Handbook, H. Geng, p. 21.40)
Whenever radiography is used, precautions must be taken to protect workers from exposure to excessive radiation. Safety measures dictated by the Occupational Safety and Health Administration (OSHA), the National Electrical Manufacturer’s Association (NEMA), the Nuclear Regulatory Commission (NRC), the American Society of Nondestructive Testing (ASNT), and other agencies should be carefully followed when radiographic inspection is conducted. Radiographic testing relies on the ability of the material to pass some of the radiation through, while absorbing part of this energy within the material. Different materials have different absorption rates. Thin materials will absorb less radiation than thick materials. The higher the density of the material, the greater the absorption rate. As different levels of radiation are passed through the materials, portions of the film are exposed to a greater or lesser degree than the rest. When this film is developed, the resulting radiograph will bear the image of the cross section of the part. A radiograph is actually a negative. The darkest regions are those that were most exposed when the material being inspected absorbed the least amount of radiation. Thin parts will be darkest on the radiograph. Porosity will be revealed as small, dark, round circles. Slag is also generally dark, and will look similar to porosity, but will be irregular in its shape. Cracks appear as dark lines. Lack of fusion or underfill will show up as dark spots. Excessive reinforcement on the weld will result in a light region.
Radiographic testing is most effective for detecting volumetric discontinuities: slag and porosity. When cracks are oriented perpendicular to the direction of the radiation source, they may be missed with the RT method. Tight cracks that are parallel to the radiation path have also been overlookedwith RT.
Radiographic testing has the advantage of generating a permanent record for future reference. With a “picture” to look at, many people are more confident that the interpretation of weld quality is meaningful. However, reading a radiograph and interpreting the results requires stringent training, so the veracity of a radiograph depends to a great degree on the skill of the technician.
(Manufacturing Engineering Handbook, H. Geng, p. 21.40)
Radiographic Testing (new)
In radiographic testing (RT) a source of X-rays or gamma-rays (from radioactive elements such as Iridium 192. or Cobalt 60) is placed on one side of the specimen or pipe wall, and a film or a fluoroscope (for real time examination) is placed on the opposite face, as close as possible to the wall. There are many ways of placing source and film, as illustrated in Figure 16-3. Whether X-rays or gamma rays are used, the radiation energy and radiographic techniques must achieve a specified quality of resolution. Current developments are in the area of filmless radiography (instant radiographic imaging) where the radiographic image is captured on a phosphor screen then stored on a digital file for immediate viewing and filing. Radiographic testing equipment is calibrated using a penetrameter with a thickness of about T=2% t where t is the thickness of the weld to be examined, and with holes with diameter IT. 21 and 41. For example a -2-2T- penetrameter has a thickness of T=2% t and a 21 hole. Real-time non-film radiography has a sensitivity in the order of 2%-2T.
(G. A. Antaki,Marcel Dekker (Firma comercial, Piping and Pipeline Engineering: Design Construction, Maintenance, Integrity ..., page 312)
The new is better.
The new is better.
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