Wire Drawing All the wires that is available

Wire Drawing ØAll the wires that is available is produced by cold drawing through dies. ØIt 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). ØIn drawing the wire is pulled, rather than pushed, through the die. ØThis process requires very large forces in order to pull the metal through the die. ØDrawing 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. ØTo reduce the frictional force between the die and the metal the die is kept well lubricated 1

ØThe process of producing the wires of different diameters is accomplished by pulling a wire through a hardened die usually made up carbide. ØThe larger diameter oriented wire is first cleaned, pickled (H 2 SO 4), washed, coated with lime and then lubricated. ØCleaning is essentially done to remove any scale and rust present on the surface, which may severely affect the die. ØTo make for an easier entrance of wire into the die, the end of the stock is made pointed by hammering to facilitate the entry. ØA pointed or reduced diameter at the end of wire duly lubricated is pushed or introduced through the die which is water cooled also. ØIt 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. ØFor more reduction in diameter of the wire, various sets of dies can be used in line for subsequent reduction in diameter at each stage 2

ØThe reduction in each pass through the die range about 10% for steel and 40% for ductile materials such as copper. ØDies are severely affected because of high stresses and abrasion. ØDie materials are chilled cast iron, tool steels, tungsten carbide & diamond. ØThe cast iron dies are used for small runs. ØFor very large sizes, alloy steels are used in making the dies. ØThe tungsten carbide dies are used for medium size wires and large productions. ØSmaller diameter wires are drawn through a die made of diamond. 3

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Extrusion 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. ØExtrusion process is identical to the squeezing of tooth paste out of the tooth paste tube. ØThe cross-sections that can be produced vary from solid round, rectangular, to L shapes, T shapes. ØExtrusion may be continuous (theoretically producing indefinitely long material) or semi-continuous (producing many pieces). Extrusions can be done with the material hot or cold. ØCommonly extruded materials include metals, polymers, ceramics, and foodstuffs. 5

ØHot 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. ØThe extrusion setup consists of a cylinder container into which the heated billet or slug of metal is loaded. ØOn one end of the container, the die plate with the necessary opening is fixed. ØFrom 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. ØThe extruded metal is then carried by the metal handling system as it comes out of the die. 6

Direct or Forward Extrusion • • The heated metal billet is placed in to the die chamber and the pressure is applied through ram The metal is extruded through die opening in the forward direction, i. e. the same as that of the ram In this case, the problem of friction is prevalent because of the relative motion between the heated metal billet and the cylinder walls To reduce such friction, at lower temperatures, a mixture of oil and graphite is generally used as a lubricant. 7

Indirect Backward Extrusion • In 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 8

Tube Extrusion • This 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 Ø It is performed at temperatures significantly below the melting temperature of the alloy being deformed, and generally at room temperature. Ø The process can be used for most materials, provided that sufficiently robust machinery can be designed. Ø Products of cold extrusion include aluminium cans, collapsible tubes and gear blanks. 9

Shearing operations q Blanking q Punching q Piercing q Trimming 10

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 11

• • • Blankin g 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 plate The 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. 12

Punching and piercing • It 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. 13

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. 14

Stretch forming • In 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 15

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. ØThe position of neutral axis depends on the radius and angle of bend ØThe bend radius can not be made smaller than certain value. The minimum bend radius is expressed as 3 T, 5 T etc. 16

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. 17

Coining • • • Coining 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 18

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. 19

• For problems see the class notes or go through PN Rao Text book 1. Finding the die and blank sizes in blanking and piercing operations 2. Finding bending allowance, total length and bending force in bending operations 3. Drawing ratio and drawing force calculation 20

TYPES OF DIE q. Progressive die q. Compound die q. Combination die Progressive die §It perform two or more operation simultaneously in a single stroke of punch press. §Place where each operation is carried out is called station §Strip under goes operation in each station and while leaving at last station, finished component is obtained §Terms – advance distance, feed distance §Preferable sequence- piercing, blanking or cutoff operation §Choice of this die- mass production, medium size material 21

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Compound die §All the operations are carried out at a single station in single stroke of ram. §It contain compound die which consists of necessary set of punches and dies. §During stroke, piercing of hole is done and followed by blanking. §Blank is done opposite to the direction of piercing, so punch used for piercing becomes die. §Compound dies are slower and more accurate than the progressive die. §Components with small strips can also made easily. 24

Combination die §It is same as that of a compound die. §Here non cutting operations such as bending and forming also performed. 25