Wire Drawing Shearing Processes Final

*Wire DrawingAll the wires that is available is produced by cold drawing through dies.

It 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).

In drawing the wire is pulled, rather than pushed, through the die.

This process requires very large forces in order to pull the metal 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.

To reduce the frictional force between the die and the metal the die is kept well lubricated

*The process of producing the wires of different diameters is accomplished by pulling a wire through a hardened die usually made up carbide.

The larger diameter oriented wire is first cleaned, pickled (H2SO4), washed, coated with lime and then lubricated.

Cleaning is essentially done to remove any scale and rust present on the surface, which may severely affect the die.

To make for an easier entrance of wire into the die, the end of the stock is made pointed by hammering to facilitate the entry.

A pointed or reduced diameter at the end of wire duly lubricated is pushed or introduced through the die which is water cooled also.

It is then gripped and pulled for attaching it to a power driven reel then wire diameter is reduced in die because of the ductility property.

For more reduction in diameter of the wire, various sets of dies can be used in line for subsequent reduction in diameter at each stage

*The reduction in each pass through the die range about 10% for steel and 40% for ductile materials such as copper.

Dies are severely affected because of high stresses and abrasion.

Die materials are chilled cast iron, tool steels, tungsten carbide & diamond.

The cast iron dies are used for small runs.

For very large sizes, alloy steels are used in making the dies.

The tungsten carbide dies are used for medium size wires and large productions.

Smaller diameter wires are drawn through a die made of diamond.

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*It is the process of enclosing the heated billet or slug of metal in a closed cavity and then pushing it to flow from only one die opening so that the metal will take the shape of the opening.

ExtrusionExtrusion process is identical to the squeezing of tooth paste out of the tooth paste tube.

The cross-sections that can be produced vary from solid round, rectangular, to L shapes, T shapes.

Extrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous (producing many pieces). Extrusions can be done with the material hot or cold.

Commonly extruded materials include metals, polymers, ceramics, and foodstuffs.

*The extrusion setup consists of a cylinder container into which the heated billet or slug of metal is loaded. From the other end, a plunger or ram with help of dummy block compresses the metal billet against the container walls and the die plate, thus forcing it to flow through the die opening, acquiring the shape of the opening.

The extruded metal is then carried by the metal handling system as it comes out of the die.Hot extrusion is done at an elevated temperature to keep the material from work hardening and to make it easier to push the material through the die.

On one end of the container, the die plate with the necessary opening is fixed.

The heated metal billet is placed in to the die chamber and the pressure is applied through ramThe metal is extruded through die opening in the forward direction, i.e. the same as that of the ramIn this case, the problem of friction is prevalent because of the relative motion between the heated metal billet and the cylinder wallsTo reduce such friction, at lower temperatures, a mixture of oil and graphite is generally used as a lubricant.*Direct or Forward Extrusion

Indirect Backward ExtrusionIn indirect extrusion, the billet remains stationary while the die moves into the billet by the hollow ram (or punch), through which the backward extrusion take place.

Since, there is no friction force between the billet and the container wall, therefore, less force is required by this method

This process is not widely used because of the difficulty occurred in providing support for the extruded part*

Tube ExtrusionThis process is an extension of direct extrusion process where additional mandrel is needed to restrict flow of metal for production of seamless tubes.*Cold Extrusion

It is performed at temperatures significantly below the melting temperature of the alloy being deformed, and generally at room temperature.

The process can be used for most materials, provided that sufficiently robust machinery can be designed.

Products of cold extrusion include aluminium cans, collapsible tubes and gear blanks.

Shearing operationsBlanking PunchingPiercingTrimming *

Shearing It is separation of metal by two blades

In shearing a narrow strip of metal is severely plastically deformed to the point where it fracture at the surface in contact with the blades

The fracture then propagate inward to provide complete separation

The depth through which the punch must penetrate depends on the ductility of the metal

Insufficient clearance distortion of edges and power required is high*

Blanking A typical die and punch set used for blanking operation The sheet metal used is called strip or stock. The punch which is held in the punch holder is bolted to the press ram while die is bolted on the press table. During the working stroke, the punch penetrates the strip, and on the return stroke of the press ram the strip is lifted with the punch, but it is removed from the punch by the stripper plateThe clearance angle provided on the die depends on the material of stock, as well as its thickness.

*For thicker and softer materials generally higher angular clearance is given. In most cases, 2 degree of angular clearance is sufficient.

Punching and piercingIt is the operation of producing circular holes on a sheet metal by a punch and die.

It is a process by which a hole is cut (or torn) in metal. It is different from punching piercing does not generate a slug. Instead, the metal is pushed back to form a jagged flange on the back side of the hole. A pierced hole looks somewhat like a bullet hole in a sheet of metal. Piercing operations are frequently (but not always)defined as forming a hole in sheetmetal with a pointed punch with no metal fallout (slug). In this case, a significant burr or deformed sharp edge is created on the bottom side of the material being pierced. This is not to say the punched material will not have a burr, but the pierced holes will have a significantly more pronounced burr*

Trimming When parts are produced by die casting or drop forging, a small amount of extra metal gets spread out at the parting plane. This extra metal, called flash, is cut off before the part is used, by an operation called trimming. The operation is very similar to blanking and the dies used are also similar to blanking dies. The presses used for trimming have, however, relatively larger table.

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Stretch formingIn this forming tensile force is applied on the metal which is placed over the die

Due to tensile stress large deformation for ductile metal can be achieved only by this process

Sheet is first wrapped around the block and the tensile load is increased through jaws until sheet is plastically deformed to final shape

Spring back effect is eliminated

Used in air craft industries for producing larger curvature*

Bending It is a operation by which straight length is converted to curved like drums,channels.As a sheet metal is bent its fibres experience a distortion such that those nearer its outside, convex surface are forced to stretch and come in tension, while the inner fibres come in compression.Somewhere, in the cross section, there is a plane which separates the tension and compression zones. This plane is parallel to the surface around which the sheet is bending, and is called neutral axis.

*The position of neutral axis depends on the radius and angle of bend

The bend radius can not be made smaller than certain value. The minimum bend radius is expressed as 3T,5T etc.

Embossing Embossing is an operation in which sheet metal is drawn to shallow depths with male and female matching dies.

The operation is carried out mostly for the purpose of stiffening flat panels.

The operation is also sometimes used for making decoration items like number plates or name plates, jewellery, etc.

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CoiningCoining is a severe metal squeezing operation in which the flow of metal occurs only at the top layers of the material and not throughout the values. It is mainly used for production of important articles such as medals, coins, tickers and other similar articles, which possess shallow configurations on their surfaces.The blank is kept in the die cavity and pressures as high as five to six times the strength of material are applied

*The difference between coining and embossing is that the same design is created on both sides of the work piece in embossing (one side depressed and the other raised) whereas in coining operation, a different design is created on each side of work piece.

Force required for coining process is more than embossing process

Drawing*It is a process of making cups, shells an similar articles from metal blank

Shaping of materials where the heated or normal blank is placed over the die opening the punch forces the blank through the die opening to form a cup or shell.

The multiple dies are also used to accomplish the stages in drawing process.

Kitchen utensils and components of food processing industries are manufactured by this process.

V.Thulasikanth, Asst Prof, Mech Engg Dept, SRM UNIVERSITY*V.Thulasikanth, Asst Prof, Mech Engg Dept, SRM UNIVERSITY