Mes assignment solutions
1 Forging temperatures are found out using fiberoptic dual or multiwave light sensors
2. A chisel is a tool with a characteristically shaped cutting edge (such that wood chisels have lent part of their name to a particular grind) of blade on its end, for carving or cutting a hard material such as wood, stone, or metal. The handle and blade of some types of chisel are made of metal or wood with a sharp edge in it.
A hot chisel is used to cut metal that has been heated in a forge to soften the metal. One type of hot chisel is the hardy chisel, which is used in an anvil hardy hole with the cutting edge oriented up. The hot workpiece cut is then placed over the chisel and struck with a hammer. The hammer drives the workpiece into the chisel, which allows it to be snapped off with a pair of tongs.
Flat Cold Chisel
A cold chisel is a tool made of tempered steel used for cutting ‘cold’ metals, meaning that they are not used in conjunction with heating torches, forges, etc. Cold chisels are used to remove waste metal when a very smooth finish is not required or when the work cannot be done easily with other tools, such as a hacksaw, file, bench shears or power tools.
The name cold chisel comes from its use by blacksmiths to cut metal while it was cold as compared to other tools they used to cut hot metal. This tool is also commonly referred to by the misnomer coal chisel. Because cold chisels are used to form metal, they have a less-acute angle to the sharp portion of the blade than a woodworking chisel. This gives the cutting edge greater strength at the expense of sharpness.
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Press forging works slowly by applying continuous pressure or force, which differs from the near-instantaneous impact of drop-hammer forging. The amount of time the dies are in contact with the workpiece is measured in seconds (as compared to the milliseconds of drop-hammer forges).
The press forging operation can be done either cold or hot.
The main advantage of press forging, as compared to drop-hammer forging, is its ability to deform the complete workpiece. Drop-hammer forging usually only deforms the surfaces of the workpiece in contact with the hammer and anvil; the interior of the workpiece will stay relatively undeformed. Another advantage to the process includes the knowledge of the new part’s strain rate. We specifically know what kind of strain can be put on the part, because the compression rate of the press forging operation is controlled. There are a few disadvantages to this process, most stemming from the workpiece being in contact with the dies for such an extended period of time. The operation is a time consuming process due to the amount of steps and how long each of them take. The workpiece will cool faster because the dies are in contact with workpiece; the dies facilitate drastically more heat transfer than the surrounding atmosphere. As the workpiece cools it becomes stronger and less ductile, which may induce cracking if deformation continues. Therefore heated dies are usually used to reduce heat loss, promote surface flow, and enable the production of finer details and closer tolerances. The workpiece may also need to be reheated. When done in high productivity, press forging is more economical than hammer forging. The operation also creates closer tolerances. In hammer forging a lot of the work is absorbed by the machinery, when in press forging, the greater percentage of work is used in the work piece. Another advantage is that the operation can be used to create any size part because there is no limit to the size of the press forging machine. New press forging techniques have been able to create a higher degree of mechanical and orientation integrity.
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Open-die drop forging
Open-die forging is also known as smith forging. In open-die forging, a hammer strikes and deforms the workpiece, which is placed on a stationary anvil. Open-die forging gets its name from the fact that the dies (the surfaces that are in contact with the workpiece) do not enclose the workpiece, allowing it to flow except where contacted by the dies. Therefore the operator needs to orient and position the workpiece to get the desired shape. The dies are usually flat in shape, but some have a specially shaped surface for specialized operations. For example, a die may have a round, concave, or convex surface or be a tool to form holes or be a cut-off tool.
Open-die forging lends itself to short runs and is appropriate for art smithing and custom work. In some cases, open-die forging may be employed to rough-shape ingots to prepare them for subsequent operations. Open-die forging may also orient the grain to increase strength in the required direction.
Cogging is successive deformation of a bar along its length using an open-die drop forge. It is commonly used to work a piece of raw material to the proper thickness. Once the proper thickness is achieved the proper width is achieved via edging.
Edging is the process of concentrating material using an concave shaped open die. The process is called edging, because it is usually carried out on the ends of the workpiece. Fullering is a similar process that thins out sections of the forging using a convex shaped die. These processes prepare the workpieces for further forging processes.
3. Grain Flow Comparison
Forged Bar: Directional alignment through the forging process has been deliberately oriented in a direction requiring maximum strength. This also yields ductility and resistance to impact and fatigue.
Machined Bar: Unidirectional grain flow has been cut when changing contour, exposing grain ends. This renders the material more liable to fatigue and more sensitive to stress corrosion cracking.
Cast Bar: No grain flow or directional strength is achieved through the casting process.
4. Figure 8-5.—The ac welding cycle.Figure 8-4.—Effects of polarity on the weld.also turn the main welding current on and off at the sametime. This not only allows the operator to start and stopwithout leaving the work but also to adjust the currentwhile welding.Most of these welding machines can produce bothac and dc current. The choice of ac or dc depends on thewelding characteristics required.DIRECT CURRENT.— As you learned in chapter7, a direct-current welding circuit maybe either straightor reverse polarity. When the machine is set on straightpolarity, the electrons flow from the electrode to theplate, concentrating most of the heat on the work Withreverse polarity, the flow of electrons is from the plateto the electrode, thus causing a greater concentration ofheat at the electrode. Because of this intense heat, theelectrode tends to melt off; therefore, direct-currentreverse polarity (DCRP) requires a larger diameter elec-trode than direct-current straight polarity (DCSP).The effects of polarity on the weld are shown infigure 8-4. Notice that DCSP produces a narrow, deepweld. Since the heat is concentrated on the work, thewelding process is more rapid and there is less distortionof the base metal.
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Overall, straight polarity is preferredover reverse polarity because you can achieve betterwelds.DCRP forms a wide and shallow weld and is rarelyused in the GTAW process. The exception to this is whenit is used to weld sections of aluminum or magnesium.DCRP has excellent cleaning power that results from theFigure 8-6.—ACHF combines the desired cleaning action ofDCRP with the good penetration of DCSP.action of positive-charged gas ions. When these gas ionsstrike the metal, they pierce the oxide film and form apath for the welding current to follow. This same clean-ing action occurs in the reverse polarity half of analternating-current welding cycle.ALTERNATING CURRENT.— AS shown in fig-ure 8-5, ac welding is actually a combination of DCSPand DCRP; however, the electrical characteristics of theoxides on the metal often prevent the current fromflowing smoothly in the reverse polarity half of thecycle. This partial or complete stoppage of current flow(rectification) causes the arc to be unstable and some-times go out. Ac welding machines were developed witha high-frequency current flow unit to prevent this recti-fication. The high-frequency current pierces the oxidefilm and forms a path for the welding current to follow.The effects of alternating current high-frequency(ACHF) are shown in figure 8-6. Notice that ACHFoffers both the advantages of DCRP and DCSP. ACHF
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5. BACKGEAR As its name implies, “backgear” is a gear mounted at the back of the headstock (although in practice it is often located in other positions) that allows the chuck to rotate slowly with greatly-increased turning power. For a novice the ability to run a workpiece slowly might seem unnecessary, but a large-diameter casting, fastened to the faceplate and run at 200 r.p.m. (around the bottom speed commonly found on a lathe without backgear) would have a linear speed at its outer edge beyond the turning capacity of a small lathe. By engaging backgear, and so reducing r.p.m. but increasing torque, even the largest faceplate-mounted jobs can be turned successfully. Screwcutting also requires slow speeds, typically between 25 and 50 r.p.m. – especially if the operator is a beginner, or the job tricky. A bottom speed in excess of those figures (as found on most Far Eastern and some European “Continental” machines) means that screwcutting – especially internally, into blind holes – is, in effect, impossible. These lathes are advertised as “screwcutting” but what that really means is just power sliding – a power feed along the bed.
With these machines even if you go to the trouble of making up a complex pulley system to reduce the spindle speed (like the early Atlas 9-inch) you will find the torque required when turning large diameters at slow speeds causes the belts to slip. The only solution is a gear-driven low speed – and so a properly-engineered small lathe, with a backgear fitted, not only becomes capable of cutting threads but can also tackle heavy-duty drilling, big-hole boring and large-diameter turning and facing; in other words, it is possible to use it to the very limits of its capacity and strength. To show how important backgear has always been considered examine the small English-made metal turning lathes made from the mid 19th century onwards: nearly every one was so equipped. For a further explanation of the desirable features required in a small lathe,
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6. Factors on which feed rate depends on
The feed rate used on milling depends upon several factors, such as:
a.The depth and width of the cut.
b.The design or type of the cutter.
c.The sharpness of the cutter.
d.The workpiece material.
e.The strength and uniformity of the workpiece
The most common fuel used in welding is acetylene, which has a two-stage reaction. The primary chemical reaction involves the acetylene disassociating in the presence of oxygen to produce heat, carbon monoxide, and hydrogen gas: C2H2 + O2 → 2CO + H2. A secondary reaction follows where the carbon monoxide and hydrogen combine with more oxygen to produce carbon dioxide and water vapor. When the secondary reaction does not burn all of the reactants from the primary reaction, the welding processes produces large amounts of carbon monoxide, and it often does. Carbon monoxide is also the byproduct of many other incomplete fuel reactions.
Oxy-fuel welding (commonly called oxyacetylene welding, oxy welding, or gas welding in the U.S.) and oxy-fuel cutting are processes that use fuel gases and oxygen to weld and cut metals, respectively. French engineers Edmond Fouché and Charles Picard became the first to develop an oxygen-acetylene welding set-up in 1903. Pure oxygen, instead of air (20% oxygen/80% nitrogen), is used to increase the flame temperature to allow localized melting of the workpiece material (e.g. steel) in a room environment. A common propane/air flame burns at about 2,000 °C (3,630 °F), a propane/oxygen flame burns at about 2,500 °C (4,530 °F), and an acetylene/oxygen flame burns at about 3,500 °C (6,330 °F).
Welding processes such as Gas Metal Arc Welding and Gas Tungsten Arc Welding are commonly used for welding copper and its alloys, since high localized heat input is important when welding materials with high thermal conductivity. Manual Metal Arc Welding of Copper and Copper alloys may be used although the quality is not as good as that obtained with the gas shielded welding processes. The weldability of copper varies among the pure copper grades (a) (b) and (c).
The high oxygen content in tough pitch copper can lead to embitterment in the heat affected zone and weld metal porosity. Phosphorus deoxidized copper is more weldable, with porosity being avoided by using filler wires containing deoxidants (Al, Mn, Si, P and Ti).
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Thin sections can be welded without preheat although thicker sections require preheats up to 60°C. Copper alloys, in contrast to copper, seldom require preheating before welding. The weldability varies considerably amongst the different copper alloys and care must be taken to ensure the correct welding procedures are carried out for each particular alloy to reduce the risks of welding defects.
Weld quality is the overall quality of the finished welded product
The following weld defects are
Cracking , incorrect edge preparation,crters, undercutting, unequal legs, porous weld, over welding.
Brazing is a metal joining process which uses a non-ferrous filler metal with a melting
point below that of the base metals but above 800 degrees F. The filler metal wets the base
metal when molten in a manner similar to that of a solder and its base metal. There is a
slight diffusion of the filler metal into the hot, solid base metal or a surface alloying of the
base and filler metal. The molten metal flows between the close-fitting metals because of
In the case of brazing operations not contained within an inert or reducing atmosphere environment (i.e. a furnace), flux is required to prevent oxides from forming while the metal is heated. The flux also serves the purpose of cleaning any contamination left on the brazing surfaces. Flux can be applied in any number of forms including flux paste, liquid, powder or pre-made brazing pastes that combine flux with filler metal powder. Flux can also be applied using brazing rods with a coating of flux, or a flux core. In either case, the flux flows into the joint when applied to the heated joint and is displaced by the molten filler metal entering the joint. Excess flux should be removed when the cycle is completed because flux left in the joint can lead to corrosion, impede joint inspection, and prevent further surface finishing operations. Phosphorus-containing brazing alloys can be self-fluxing when joining copper to copper. Fluxes are generally selected based on their performance on particular base metals. To be effective, the flux must be chemically compatible with both the base metal and the filler metal being used. Self-fluxing phosphorus filler alloys produce brittle phosphides if used on iron or nickel. As a general rule, longer brazing cycles should use less active fluxes than short brazing operations.
Rake angles come in two varieties, positive and negative
If the leading edge of the blade is ahead of the perpendicular, the angle is, by definition, negative.
Examples of negative rake instruments are reamers, K-files, K-Flex files, diamond burs, most NiTi-files, and burnishing burs or regular burs run backwards.
If the leading edge of the blade is behind the perpendicular, the angle is by definition, positive.
Examples of positive rake instruments are my Fine-Cut files, hedstrom files, Dynatrak files and most dental burs (when run normally)
Precision cutting requires high amount of care and accuracy. Increasing the cutting speed results in a rough cut and increases the chances of having a defect in the work piece which may cause a delay in the entire assembly line.
Cutting fluid is a type of coolant and lubricant designed specifically for metalworking and machining processes. There are various kinds of cutting fluids, which include oils, oil-water emulsions, pastes, gels, and mists. They may be made from petroleum distillates, animal fats, plant oils, or other raw ingredients. Depending on context and on which type of cutting fluid is being considered, it may be referred to as cutting fluid, cutting oil, cutting compound, coolant, or lubricant.
Cutting fluids have been associated with skin rashes, dermatitis, esophagitis, lung disease, and cancer. These problems result from either toxicity or bacterial or fungal contamination.
Metalworking fluids often contain substances such as biocides, corrosion inhibitors, metal fines, tramp oils, and biological contaminants. Inhalation of cutting fluid aerosols may cause irritation of the throat, nose, and lungs and has been associated with chronic bronchitis, asthma, hypersensitivity pneumonitis (HP), and worsening of pre-existing respiratory problems. Skin exposure may result from touching contaminated surfaces, handling parts and equipment, splashing fluids, and aerosol mist settling on the skin. Skin contact with cutting fluids may cause allergic contact dermatitis, irritant contact dermatitis, and occupational (“oil”) acne.
Safer formulations provide a natural resistance to tramp oils allowing improved filtration separation without removing the base additive package. Ventilation, splash guards on machines, and personal protective equipment can mitigate hazards related to cutting fluids.
Bacterial growth is predominant in semi-synthetic and synthetic fluids. Tramp oil along with human hair or skin oil are some of the debris during cutting which accumulates and forms a layer on the top of the liquid, anaerobic bacteria proliferate due to a number of factors. An early sign of the need for replacement is the “Monday-morning smell” (due to lack of usage from Friday to Monday). Antisepticsare sometimes added to the fluid to kill bacteria. Such use must be balanced against whether the antiseptics will harm the cutting performance, workers’ health, or the environment. Maintaining as low a fluid temperature as practical will slow the growth of microorganisms.
Heat treatment is done basically to achive a stress relived product also to get uniformly cooled product and to make sure that the finished product complies to a set standard.
SPECIAL OPERATIONS ON DRILLING MACHINES
COUNTERSINKING: Countersinking is the tapering or beveling of the end of a hole with a conical cutter called a machine countersink. Often a hole is slightly countersunk to guide pins which are to be, driven into the workpiece; but more commonly, countersinking is used to form recesses for flathead screws and is similar to counterboring
Proper alignment of the countersink and the hole to be recessed are important. Failure to align the tool and spindle
with the axis of the hole, or failure to center the hole, will result in an eccentric or out-of-round recess.
COUNTERBORING AND SPOT FACING
Counterboring is the process of using a counterbore to enlarge the upper end of a hole to a predetermined depth and
machine a square shoulder at that depth (Figure 4-40).
Spot facing is the smoothing off and squaring of a rough or
curved surface around a hole to permit level seating of washers, nuts, or bolt heads (Figure 4-40).
are primarily used to recess socket head cap screws and similar bolt heads slightly below the surface. Both
counterboring and spotfacing can be accomplished with standard counterbore cutters.
Spot Facing Spot facing is basically the same as counterboring, using the same tool, speed, feed, and lubricant. The operation of spot facing is slightly different in that the spot facing is usually done above a surface or on a curved surface. Rough surfaces,
castings, and curved surfaces are not at right angles the cutting tool causing great strain on the pilot and counterbore which can lead to broken tools. Care must be taken when starting the spot facing cut to avoid too much feed. If the tool grabs the
workpiece because of too much feed, the cutter may break or the workpiece may be damaged. Ensure securely mounted and that all backlash drilling machine spindle.
Tapping is cutting a thread in a drilled hole. Tapping is accomplished on the drilling machine by selecting and drilling
the tap drill size (see Table 4-5 in Appendix A), then using the drilling machine chuck to hold and align the tap while it is
turned by hand. The drilling machine is not a tapping machine, so it should not be used to power tap. To avoid
breaking taps, ensure the tap aligns with the center axis of the hole, keep tap flutes clean to avoid jamming, and clean chips
out of the bottom of the hole before attempting to tap.