mt-i additional course material

7/27/2019 MT-I Additional Course Material

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Introduction to Stir Casting:

Metallic parts produced by casting are comparatively inexpensive, but are often subject to metallurgical

flaws like porosity and micro structural defects. Friction stir processing can be used to introduce a

wrought microstructure into a cast component and eliminate many of the defects. By vigorously stirring

a cast metal part to homogenize it and reduce the grain size, the ductility and strength are increased.

Sand Reclamation:

Most sand foundries recover a significant proportion of the waste sand for internal reuse. This

significantly reduces the quantity of sand that must be purchased and disposed of. Most sand is

reclaimed mechanically; cores and large metal lumps are removed by vibrating screens and the binders

are removed by attrition (i.e. by the sand particles rubbing together). Fine sand and binders are

removed by extraction and collected in a baghouse. In some systems metals are removed using magnets

or other separation techniques. For operations using mechanical reclamation, the recycle rate is often

limited to around 70%. This is due to the need to maintain a minimum sand quality. For large iron

foundries, where sand quality requirements are less stringent, over 90% reclamation can be achieved by

mechanical means. For many processes, mechanically reclaimed sand is not of sufficiently high quality tobe used for core production.

Thermal reclamation is becoming more widely used. This process heats the sand to the point where

organic materials, including the binders, are driven off. This process can return the sand to an as new

state, allowing it to be used for core making. Thermal reclamation is more expensive than mechanical

systems.


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Sand can also be reclaimed using wet washing and scrubbing techniques. These methods produce sand

of a high quality but are not commonly used because they generate a significant liquid waste stream and

require additional energy input for sand drying.

The amount of internal reuse depends on the type of technology used and the quality requirements of

the casting process. Reclamation processes, particularly mechanical ones, break down the sand particles

and this can affect the quality of some metals. Also, for mechanical reclamation techniques, impurities

may build up in the sand over time, requiring a proportion of the material to be wasted. Large iron

foundries do not require a high sand quality so typically achieve the highest rate of reuse in the industry.

Often sand cycles through the operation until it is ground down to a fine dust and removed by

baghouses.

Friction stir welding:

Friction Stir Welding is a solid-state process, which means that the objects are joined without reaching

melting point. In FSW, a cylindrical shouldered tool with a profiled pin is rotated and plunged into the

joint area between two pieces of sheet or plate material. The parts have to be securely clamped to

prevent the joint faces from being forced apart. Frictional heat between the wear resistant welding tool

and the workpieces causes the latter to soften without reaching melting point, allowing the tool to

traverse along the weld line. The plasticised material transferred to the trailing edge of the tool pin, is

forged through intimate contact with the tool shoulder and pin profile. On cooling, a solid phase bond is

created between the workpieces

Friction Stir Welding can be used to join aluminium sheets and plates without filler wire or shielding gas.

Material thicknesses ranging from 0.5 to 65 mm can be welded from one side at full penetration,

without porosity or internal voids.


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Explosive Cladding:

A plate of cladding material is accelerated under the influence of a detonation to impinge obliquely onto

a base plate. This is illustrated by the figure below. A jet of metal (from both plates) in the form of a

spray is ejected ahead of the collision point, cleaning the weld surfaces of any oxide films or surface

impurities. Pressure at the collision point is well in excess of the yield strength of any metal, resulting in

inter-atomic bonding between the contacting surfaces.

Schematic representation of explosive cladding

This method can clad a wide range of metals to almost any base material. The main applications are in

flat plate cladding or cladding of cylindrical geometries. The main industrial sectors include the food and

chemical process industries. Explosive cladding can also be used to produce microwelds between metal

foils as thin as 11m. An example of this is the coating of titanium sheets with platinum.

Acoustic Emission Technology:

Acoustic Emission (AE) testing is a powerful method for examining the behavior of materials deformingunder stress. Acoustic Emission may be defined as a transient elastic wave generated by the rapid

release of energy within a material. Materials "talk" when they are in trouble: with Acoustic Emission

equipment you can "listen" to the sounds of cracks growing, fibers breaking and many other modes of

active damage in the stressed material.

Small-scale damage is detectable long before failure, so AE can be used as a non-destructive technique

to find defects during structural proof tests and plant operation. AE also offers unique capabilities for

materials research and development in the laboratory. Finally, AE equipment is adaptable to many

forms of production QC testing, including weld monitoring and leak detection.


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Basic Weld Symbol:

The weld symbol always includes

1. An arrow line2. A reference line3. A dashed line4. A symbol

Note: Weld symbols on the full reference line relates to welds on the near side of the plate beingwelded. Weld symbols on the dashed line relates to weld on the far side of the plate. If the welds are

symmetrical on both sides of the plate the dashed line is omitted. If the dashed line is above the full line

then the symbol for the nearside weld is drawn below the reference line and the symbol for the far side

weld is above the dashed line. For example see sketch below Supplementary symbols below.

More Detailed Symbolic Representation of Weld


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Table of Weld Symbols

Supplementary Symbols

The weld symbols below are used in addition to the primary weld symbols as shown above. They are

not used on their own.

Below is an example of the application of one of these symbol illustrating the identification of the

location of the weld relative to the symbol.


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Hardenability:

The hardenability of a metal alloy is the depth up to which a material is hardened after putting through

a heat treatment process. The unit of hardenability is the same as of length. It is an indication of how

deep into the material a certain hardness can be achieved.

Extrusion:

Extrusion is a process used to create objects of a fixed, cross-sectional profile. A material is pushed or

drawn through a die of the desired cross-section. The two main advantages of this process over other

manufacturing processes are its ability to create very complex cross-sections and work materials that

are brittle, because the material only encounters compressive and shear stresses. It also forms finished

parts with an excellent surface finish.

Extrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous

(producing many pieces). The extrusion process can be done with the material hot or cold.

Commonly extruded materials include metals, polymers, ceramics, concrete, play dough, and foodstuffs.

Hot extrusion is a hot working process, which means it is done above the material's recrystallization

temperature to keep the material from work hardening and to make it easier to push the material

through the die.

Wire drawing:

Wire drawing is a metalworking process used to reduce the cross-section of a wire by pulling the wire

through a single, or series of, drawing die(s). There are many applications for wire drawing, includingelectrical wiring, cables, tension-loaded structural components, springs, paper clips, spokes for wheels,

and stringed musical instruments. Although similar in process, drawing is different from extrusion,

because in drawing the wire is pulled, rather than pushed, through the die. Drawing is usually performed

at room temperature, thus classified as a cold working process, but it may be performed at elevated

temperatures for large wires to reduce forces.


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Copying Lathe:

A machine used for the reproduction of plane and curved surfaces from a master (template, pattern,

model, or blueprint) on products made of various materials. Copying lathes are made for plane, contour,

three-dimensional, and combined profiling with a mechanical, hydraulic, electric, or photoelectric

servomechanism or without a servomechanism.

The main assembly of a copying lathe is a duplicating device. Copying milling machines are widely usedin metalworking; lathes and milling machines are used in woodworking. Many all-purpose lathes (such

as turning lathes) are also equipped with a duplicating device. Copying lathes are used in series and

mass production of patterned furniture pieces, complex casting patterns, profiled cams, eccentrics,

templates, and matrices.

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