# Railways NTPC (Technical Ability) Metal Forming, Casting and Cutting Metal Cutting

Metal Cutting

Category : Railways

Metal Cutting

• Metalworking is the process of working with metals to create individual parts, assemblies, or large-scale structures. The term covers a wide range of work from large ships and bridges to precise engine parts and delicate jewelry. It therefore includes a correspondingly wide range of skills, processes, and tools.
• Metalworking is a science, art, hobby, industry and trade. Its historical roots span cultures, civilizations, and millennia. Metalworking has evolved from the discovery of smelting various ores, producing malleable and ductile metal useful for tools and adornments.
• Modem metalworking processes, though diverse and specialized, can be categorized as forming, cutting, or joining processes. Today's machine shop includes a number of machine tools capable of creating a precise, useful work piece.
• The oldest archaeological evidence of copper mining and working was the discovery of a copper pendant in northern Iraq from 8,700 BC. The earliest substantiated and dated evidence of metalworking in North America was the processing of copper.
• Copper was hammered until brittle then heated so it could be worked some more. This technology is dated to about 4000-5000 BC. The oldest gold artifacts in the world come from the Bulgarian Varna Necropolis and date from 4450 BC.
• Not all metal required fire to obtain it or work it. Isaac Asimov speculated that gold was the "first metal." His reasoning is that gold by its chemistry is found in nature as nuggets of pure gold.
• In other words, gold, as rare as it is, is always found in nature as the metal that it is. There are a few other metals that sometimes occur natively, and as a result of meteors. Almost all other metals are found in ores, a mineral bearing rock, that require heat or some other process to liberate the metal.
• Another feature of gold is that it is workable as it is found, meaning that no technology beyond eyes to find a nugget and a hammer and an anvil to work the metal is needed. Stone hammer and stone anvil will suffice for technology.
• This is the result of gold's properties of malleability and ductility. The earliest tools were stone, bone, wood, and sinew. They sufficed to work gold.
• At some unknown point the connection between heat and the liberation of metals from rock became clear, rocks rich in copper, tin, and lead came into demand. These ores were mined wherever they were recognized. Remnants of such ancient mines have been found all over what is today the Middle East.
• Metalworking was being carried out by the South Asian inhabitants of Mehrgarh between 7000$-$3300 BC. The end of the beginning of metalworking occurs sometime around 6000 BC when copper smelting became common in the Middle East.
• The oxidation potential is important because it is one indicator of how tightly bound to the ore the metal is likely to be. As can be seen, iron is significantly higher than the other six metals while gold is dramatically lower than the six above it.
• Gold's low oxidation is one of the main reasons that gold is found in nuggets. These nuggets are relatively pure gold and are workable as they are found.
• Copper ore, being relatively abundant, and tin of became the next important players in the story of metalworking. Using heat to smelt copper from ore, a great deal of copper was produced. It was used for both jewelry and simple tools. However, copper by itself was too soft for tools requiring edges and stiffness.
• At some point tin was added into the molten copper and bronze was born. Bronze is an alloy of copper and tin Bronze was an important advance because it had the edge-durability and stiffness that pure copper lacked.
• Looking beyond the Middle East, these same advance and materials were being discovered and used the word around. China and Britain jumped into the use of bronze with little time being devoted to copper.
• Japan began the use of bronze and iron almost simultaneously. In the Americas things were different. Although the peoples of the Americas knew of metals, it wasn't until the arrival of Europeans that metal for tools and weapons took off.
• Jewelry and art were the principal uses of metals in the Americas prior to European influence.
• Around the date 2700 BC, production of bronze was common in locales where the necessary materials could be assembled for smelting, heating, and working the metal. Iron was beginning to be smelted. Iron began its emergence as an important metal for tools and weapons. The Iron Age was dawning.
• Metalworking generally is divided into the following categories, forming, cutting, and Joining. Each of these categories contain various processes.
• Prior to most operations, the metal must be marked and/or measured, depending on the desired finished product.
• Marking out is the process of transferring a design or pattern to a work piece and is the first step in the handcraft of metalworking. It is performed in many industries or hobbies, although in the repetition industries the need to mark out every individual piece is eliminated.
• In the metal trades area, marking out consists of transferring the engineer's plan to the work piece in preparation for the next step, machining or manufacture.
• Calipers are hand tools designed to precisely measure the distance between two points. Most calipers have two sets of flat, parallel edges used for inner or outer diameter measurements.
• These calipers can be accurate to within one-thousandth of an inch. Different types of calipers have different mechanisms for displaying the distance measured. Where larger objects need to be measured with less precision, a tape measure is often used.
• Plastic deformation involves using heat or pressure to make a work piece more conductive to mechanical force. Historically, this and casting were done by blacksmiths, though today the process has been industrialized.
• Cutting is a collection of processes wherein material is brought to a specified geometry by removing excess material using various kinds of tooling to leave a finished part that meets specifications.
• The net result of cutting is two products, the waste or excess material, and the finished part. If this were a discussion of woodworking, the waste would be sawdust and excess wood. In cutting metals the waste is chips or swarf and excess metal.
• Chip producing processes most commonly known as machining
• Burning, a set of processes wherein the metal is cut by oxidizing a kerf to separate pieces of metal
• Miscellaneous specialty process, not falling easily into either of the above categories
• Drilling a hole in a metal part is the most common example of a chip producing process. Using an oxy-fuel cutting torch to separate a plate of steel into smaller pieces is an example of burning.
• Chemical milling is an example of a specialty process that removes excess material by the use of etching chemicals and masking chemicals.
• There are many technologies available to cut metal, including:

$-$Manual technologies: saw, chisel, shear or snips

$-$Machine technologies: turning, milling, drilling, grinding, sawing

$-$Welding/burning technologies: burning by laser, oxy-fuel burning, and plasma

$-$Erosion technologies: by water jet, electric discharge, or abrasive flow machining.

$-$Chemical technologies: Photochemical machining

• Cutting fluid or coolant is used where there is significant friction and heat at the cutting interface between a cutter such as a drill or an end mill and the work piece.
• Coolant is generally introduced by a spray across the face of the tool and workpiece to decrease friction and temperature at the cutting tool/workpiece interface to prevent excessive tool wear. In practice there are many methods of delivering coolant.
• Milling is the complex shaping of metal or other materials by removing material to form the final shape. It is generally done on a milling machine, a power-driven machine that in its basic form consists of a milling cutter that rotates about the spindle axis and a worktable that can move in multiple directions.
• Turning is a metal cutting process for producing a cylindrical surface with a single point tool. The workpiece is rotated on a spindle and the cutting tool is fed into it radially, axially or both. Producing surfaces perpendicular to the workpiece axis is called facing. Producing surfaces using both radial and axial feeds is called profiling
• Grinding uses an abrasive process to remove material from the workpiece.
• A grinding machine is a machine tool used for producing very fine finishes, making very light cuts, or high precision forms using an abrasive wheel as the cutting device. This wheel can be made up of various sizes and types of stones, diamonds or inorganic materials.
• Filing is combination of grinding and saw tooth cutting using a file. Prior to the development of modern machining equipment it provided a relatively accurate means for the production of small parts, especially those with flat surfaces.
• Broaching is a machining operation used to cut keyways into shafts. Electron beam machining (EBM) is a machining process where high-velocity electrons are directed toward a work piece, creating heat and vaporizing the material. Ultrasonic machining uses ultrasonic vibrations to machine very hard or brittle materials.

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##### Notes - Metal Cutting

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