Hollow shapes, including rounds, polygons and splines are also forward extruded. The process differs from forward extrusion in that the workpiece is in tension, whereas forward extrusion places the workpiece in compression. Upon separation of split die, the heated bar is moved from one cavity to the next. Aluminum and magnesium alloys are more suitable although steel can also be precision — forged. Seven common process combinations are shown in Figure 5-25.
Process Sequence In almost all cases, cold forgings are made in several forming strokes. The operator obtains the desired shape of forging by manipulating the work material between blows. The process uses split dies with one or several cavities in the die. Two types of lateral extrusion are shown in Figure 5-20. Radial forging can also be used to make solid parts, such as axles.
With the rotation of rolls through half a revolution, the bar is progressively squeezed and shaped. Hollow parts, such as gun barrels, can be axially forged using a mandrel. Using open-die forging operation, a solid cylindrical piece of 304 stainless steel having 100 mm dia x 72 mm height is reduced in the height to 60 mm at room temperature. The forces required for forging are high. Most impression — die sets contain several cavities. Dies are generally heated during press forging to reduce heat loss, promote more uniform metal flow and production of finer details. Process Sequence In almost all cases, cold forgings are made in several forming strokes.
Backward extrusion is used to produce circular inside and outside diameters, squares with rounded corners, multiple outside diameters and multiple inside diameters. . Figure 5-19 shows three types of backward extrusion. The workpiece is formed either in the cavity formed between the punch and die, or in the cavity of the punch. Therefore, the term forging usually implies hot forging carried out at temperatures which are above the recrystallization temperature of the material.
The force is applied to the bottom of the preform by a relatively long punch. The application of surface coatings between processes may be necessary for some materials. Forging is an effective method of producing many useful shapes. Nosing Nosing is used to reduce the end of a backward extrusion, or its radius. Backward extrusion is used to produce circular inside and outside diameters, squares with rounded corners, multiple outside diameters and multiple inside diameters.
The shape of the cavities cause the metal to flow in desired direction, thereby imparting desired fibre structure to the component. Parts can be upset — forged from bars or rods upto 200 mm in diameter in both hot and cold condition. Press forgings generally need smaller draft than drop forgings and have greater dimensional accuracy. Hollow shapes, including rounds, polygons and splines are also forward extruded. This process is most often used to make near — final shape of the part so that some further operation done on the job produces the final shape. The forged parts have good strength and toughness; they can be used reliably for highly stressed and critical applications.
The split dies are then forced together to grip the and a heading tool or ram advances axially against the bar, upsetting it to completely fill the die cavity. It is the simplest forging process which is quite flexible but not suitable for large scale production. The process is carried out on a rolling mill that has two semi — cylindrical rolls that are slightly eccentric to the axis of rotation. Radial Forging In this process, tools moving radially forge the workpiece to the desired shape, as shown in Figure 5-24. Let the coefficient of friction be 0.
Process sequences for two cold forgings are shown in Figures 5-26 and 5-27. Three types of upsetting operations are shown in Figure 5-21. It is used to produce solid shapes such as rounds, thread blanks, squares, rectangles, triangles, polygons and splines. Radial Forging In this process, tools moving radially forge the workpiece to the desired shape, as shown in Figure 5-24. The process is shown in Figure 5-23. Ironing In this process, the wall thickness of hollow cans or tubes is reduced, as shown in Figure 5-22.
When the rolls are in open position, the heated bar stock is placed between the rolls. Seven common process combinations are shown in Figure 5-25. Upsetting machines, called upsetters, are generally horizontal acting. A variety of forging processes have been developed that can be used for either producing a single piece or mass — produce hundreds of identical parts. Therefore, the impressions obtained in press forging are more clean.
The force is applied to the bottom of the preform by a relatively long punch. The metal is deformed in cavity so that no flash is formed and the final dimensions are very close to the desired component dimensions. Examples of products produced by this process include leaf springs, axles, and levers. Nosing Nosing is used to reduce the end of a backward extrusion, or its radius. The force is applied to the bottom of the preform by a relatively long punch. Roll Forging This process is used to reduce the thickness of round or flat bar with the corresponding increase in length.