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December 06, 2007

Metalworking

Metalworking is the craft and practice of working with metals to create structures or machine parts. The term covers a wide range of work, from large ships, bridges and oil refineries to delicate jewellery and instruments. Consequently, this craft covers a wide range of skills and entails the use of many types of tools.

History

Metalworking is an art, hobby, industry, and trade. It relates to metallurgy, a science, jewelery making, an art-and-craft, and as a trade and industry with ancient roots spanning all cultures and civilizations. Metalworking had its beginnings millennia in the past. Early humans, we speculate, realized different stones had different properties. These were freed metal ores on the earth's surfaces. We can further speculate that some indigenous groups attributed magical and spiritual significance to them. At some imprecise point humankind discovered that these lustrous rocks were meltable, and ductile and able to be formed into various articles for tools, adornment and practical uses. Humans over the millennia learned to work raw metals into objects of art, adornment, trade and practicality.

By the historical periods of the Pharohs in Egypt, the Vedic Kings in India, and the Tribes of Israel, and Mayan Civilization in North America among other ancient populations, precious metals began to have value attached to them, and in some cases rules for ownership, distribution, and trade were created, enforced and agreed upon by respective peoples. By the above periods skills at creating objects of adornment, religious artifacts, and trade instruments of precious metals (non-ferrous), as well as weaponry usually of ferrous metals and/or alloys were finely honed and flawlessly executed skills and techniques practised by artisans, blacksmiths, atharvavedic practitioners, alchemists, and other categories of metalworkers around the globe. For example, the ancient technique of granulation is found spontaneously around the world in numerous ancient cultures before the historic record shows people travelled seas or overland to far regions of the earth to share this process still being used, and attempted by metalsmiths today.

As time progressed metal objects became more common, and ever more complex. The need to further acquire and work metals grew in importance. Skills related to extracting metal ores from the earth began to evolve, and metalsmiths became more knowledgable. Metalsmiths became important members of society. Fates and economies of entire civilizations were greatly affected by the availability of metals and metalsmiths. Today modern mining practices are more efficient, and conversely more damaging to the earth, and the workers that are engaged in the industry. Those that finance the operations are driven by profits per ounce of extracted precious metals and today's gold market which as of the date of this editing, are at a 25 year high. The metalworker though depends on the extraction of precious metals to make jewelery, build more efficient electronics, and for industrial and technological applications from construction to shipping containers to rail, and air transport. Without metals, goods and services would cease to move around the globe on the scale we know today. More individuals then ever before are learning metalworking as a creative outlet in the forms of jewelery making, hobby restoration of aircraft and cars, blacksmithing, tinsmithing, tinkering, and in other art and craft pursuits. Trade schools continue to teach welding in all of its forms, and there is a proliferation of schools of Lapidary and Jewelers arts and sciences at this- the beginning of the 21st. Century a.c.e./a.d.

Processes

Shape modifying by material removal processes

Milling

Main article: Milling machine

Milling is the complex shaping of metal (or possibly other materials) parts, by removing unneeded material to form the final shape. It is generally done on a milling machine, a power-driven machine that in its basic form is comprised of a milling cutter that rotates about the spindle axis (like a drill), and a worktable that can move in multiple directions (usually three dimensions [x,y,z axis] relative to the workpiece, whereas a drill can only move in one dimension [z axis] while cutting). The motion across the surface of the workpiece is usually accomplished by moving the table on which the workpiece is mounted, in the x and y directions. Milling machines may be operated manually or under computer numerical control (CNC), and can perform a vast number of complex operations, such as slot cutting, planing, drilling and threading, rabbeting, routing, etc. Two common types of millers are the horizontal miller and vertical miller.

Turning

Main article: Lathe (metal)
Conventional metalworking lathe
Conventional metalworking lathe

A lathe is a machine tool which spins a block of material so that when abrasive, cutting, or deformation tools are applied to the workpiece, it can be shaped to produce an object which has rotational symmetry about an axis of rotation, called Solids of Revolution. Examples of objects that can be produced on a lathe include candlestick holders, table legs, bowls, baseball bats, crankshafts or camshafts.

The material may be held in place by a chuck or worked between one or two centers of which at least one can be moved horizontally to accommodate varying material lengths. In a metalworking lathe, metal is removed from the workpiece using a hardened cutting tool which is usually fixed to a solid moveable mounting called the "toolpost", this arrangement is then moved around the workpiece using handwheels and/or computer controlled motors. The main difference between the Milling Machine and the Lathe is that in the Milling Machine the tool is moving but in the Lathe, the work is moving. Modern CNC lathes can do secondary operations like milling in X,Y,Z direction by using driven tools also called live tools. When driven tools are used the work piece stops rotating and the driven tool executes the machining operation with a rotating cutting tool. Driven tools increase machining performance as all operations can be made in one set up in the CNC lathe.

Cutting

There are many technologies available to cut metal. Sawing, chisel, shearing, burning by Laser, gas jet and plasma, erosion by water jet or electric discharge, and hand cutting. Cutting fluid or coolant are introduced by a spray across the face of the tool and piece to decrease the temperature caused by friction and to prevent tool point weld.

Drilling and threading

Three different types and sizes of taps
Three different types and sizes of taps

Drilling is the process of using a drill bit in a drill to produce holes. Under normal usage, swarf is carried up and away from the tip of the drill bit by the fluting. The continued production of chips from the cutting edges pushes the older chips outwards from the hole. This continues until the chips pack too tightly, either because of deeper than normal holes or insufficient backing off (removing the drill slightly [breaking the chip] or totally from the hole [clearing the bit] while drilling). Lubricants (or coolants) (i.e. cutting fluid) are sometimes used to ease this problem and to prolong the tool's life by cooling, lubricating the tip and improving chip flow.

Taps and dies are tools commonly used for the cutting of screw threads in metal parts. A tap is used to cut a female thread on the inside surface of a predrilled hole, while a die cuts a male thread on a preformed cylindrical rod.

Grinding

Main article: Grinding machine
Flick grinder with magnetic chuck
Flick grinder with magnetic chuck

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 a abrasive wheel as the cutting device. This wheel can be made up of various sizes and types of stones, diamonds or inorganic materials.

The simplest grinder is a bench grinder or a hand-held angle grinder, for deburring parts or cutting metal with a zip-disc.

Grinders have increased in size and complexity with advances in time and technology. From the old days of a manual toolroom grinder sharpening endmills for a production shop, to today's 30000rpm CNC auto-loading manufacturing cell producing jet turbines, grinding processes vary greatly.

Grinders need to be very rigid machines to produce the required finish. Some grinders are even used to produce glass scales for positioning CNC machine axis. the common rule is the machines used to produce scales be 10 times more accurate than the machines the parts are produced for.

In the past grinders were used for finishing operations only because of limitations of tooling. Modern grinding wheel materials and the use of industrial diamonds or other made-made coatings (cubic boron nitride) on wheel forms have allowed grinders to achieve excellent results in production environments instead of being relegated to the back of the shop.

Modern technology has advanced grinding operations to include CNC controls, high material removal rates with high precision, lending itself well to aerospace applications and high volume production runs of precision components.

Shape modifying with material retention processes

These processes modify the shape of the object being formed, without removing any material.

Casting

Plastic deforming

Powder forming

Sheet metal forming

Joining processes

Welding

Main article: Welding
Arc welding
Arc welding

Welding is a fabrication process that joins materials, usually metals or thermoplastics, by causing coalescence. This is often done by melting the workpieces and adding a filler material to form a pool of molten material that cools to become a strong joint, but sometimes pressure is used in conjunction with heat, or by itself, to produce the weld.

Many different energy sources can be used for welding, including a gas flame, an electric arc, a laser, an electron beam, friction, and ultrasound. While often an industrial process, welding can be done in many different environments, including open air, underwater and in space. Regardless of location, however, welding remains dangerous, and precautions must be taken to avoid burns, electric shock, poisonous fumes, and overexposure to ultraviolet light.

Brazing

Main article: Brazing

Brazing is a joining process in which a filler metal is melted and drawn into a capillary formed by the assembly of two or more work pieces. The filler metal reacts metallurgically with the workpiece(s) and solidifies in the capillary, forming a strong joint. Unlike welding, the work piece is not melted. Brazing is similar to soldering, but occurs at temperature higher than 800F. Brazing has the advantage of producing less thermal stresses than welding, and brazed assemblies tend to be more ductile than weldments because alloying elements can not segregate and precipitate.

Brazing techniques include, flame brazing, resistance brazing, furnace brazing, diffusion brazing, and inductive brazing.

Soldering

Main article: Soldering

Soldering is a joining process that occurs in the temperature ranges of 1100F to 1600F. It is similar to brazing in the fact that a filler is melted and drawn into a capillary to form a join. However, in soldering, the metallurgical reaction between filler and work piece is minimal, resulting in a weaker joint.

Hand fabrication

Three different engineering hand scrapers
Three different engineering hand scrapers

A wide variety of hand and small power tools are often used for metalworking, and an experienced machinist can fabricate almost any part using only hand tools, although it may require more time than with advanced machinery. Many types of hand tools are used, including cutting and scraping tools to remove metal, impact tools to reshape metal, and a wide variety of tools for marking, positioning, or otherwise assisting the fabrication process.

Ball-peen hammerC-clampClampCombination squareDie grinderDrift pinF-clampFileFile cardHacksawHammerHand scraperMachinist squareMagnetic basePliersPower toolPunchRotary toolSaw piercingScriberTap and dieThroatless shearTongsTube and pipe bendersViseWorkbenchWrench

Preparation and validation

Marking out

Main article: Marking out
A combination square used for transferring designs.
A combination square used for transferring designs.

Marking out (also known as layout) is the process of transferring a design or pattern to a workpiece 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 workpiece in preparation for the next step, machining or manufacture.


2 comments:

Heard of Zebras said...

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