What is Machine Forging ?
Machine forging is the process of forging in a forging machine (upsetter), in which the metal is moved into the die impression by the pressure applied in a horizontal direction by the moving die in the ram.
Machine forging, also known as upset forging, involves the upsetting operation. Though drop and press forging are also done by machines, only upset forging has historically been referred to as machine forging. Horizontal forging machines are used for machine forging.
Originally developed for bolt heads, machine forging is now widely used to produce a wide range of shapes.
Example of Upset or Forging Machine
It is used to make gear blanks, shafts, axles, rods with flanges, and similar parts. Figure below shows some parts produced by machine or upset forging.
Forging of the ring and rod types with all kinds of heads and shoulders, such as bolts, nuts, washers, and collars, pinion-gear blanks, etc. can be conveniently produced in forging machine.
Machine Forging Construction
Generally, Upset machines have horizontal axis. The machine consists of a two part a.) die and b.) corresponding punch. In the given figure, The die may have several impressions and corresponding punches or heading tool. The die is composed of two parts; one is fixed to the machine frame while another is movable along with the die slide.
A length of rolled stock is cut, heated in a suitable heating unit, and automatically fed into the machine. The hot work part is then held in place by a stationary die grip. The heading tool then advances against the stock, causing it to be upset in order to completely fill the die cavity. When the upsetting is finished, the heading tool or punch returns to its original position. Finally, the component is released by moving the movable gripper die forward.
Number of Passes and Die Impressions in Machine Forging Process
In machine forging, similar to drop forging, it is not possible for obtaining the desired finished shape in a single pass or stroke.
So,a number of passes are required to finish the component, which varies depending on the complexity of the shape, material type, and number of die impressions. In addition, depending on the geometry of the shape required, a part can be forged in one or more die impressions.
The die cavities required for the various operations are all provided vertically on the gripper dies. The metal stock is circulated step by step after completion of each operation.
As shown in Fig. 5.27, the corresponding heading tools are also provided along their respective cavities.
Machine Forging Working and Sequence of Operations
Machine forging consists of applying lengthwise pressure to a hot bar held between grooved dies to enlarge some section or sections, usually the end. Not only bulging, but piercing can also be done by the machine forging method. In this method the metal is displaced from the interior and made to flow around the outside, for the full length of the blank when necessary. Careful gathering of a large volume of metal on the end results in controlled grain structure, with dense fiber for maximum length.
Mostly a through-bore is drilled longitudinally through the die for the feeding of bar stock. Further, the die is split up to into halves which form two jaws; one of them is fixed, whereas the other one can be opened to admit the blank. Mostly, these jaws also serve for clamping the workpiece to be upset.
A forging sequence for a horizontal machine is illustrated in Fig. 8.22. The heated end of the bar stock is inserted into the stationary die upto the stop. At this time, the punch is in its left-hand position (Fig. 8.22a). Next the movable die grips the bar stock and, at the same time, an impression is formed in the closed dies for shaping the projecting stock; the stop is automatically retraced to its idle position (Fig. 8.22b).
Then the punch advances to upset the bar and forms the finished forging (Fig. 8.22c) and finally, the movable die and the punch are withdrawn to their initial position (Fig. 8.22d). The rod and forging are shifted to the next pass where the forging is cut off.
Horizontal forging operate at a high rate. They have an output of from 400 to 600 forgings per hour and develop a forging force of from 100 to 3000 tonnes.
Types of Machine Forging
1. Drop Forging Machine
It produce complex shapes by dropping heated metal into a punch and die that gradually compresses the part. The ram of the punch causes this malleable metal to conform to the shape of the punch and die cavities. Drop forging equipment, also known as power hammers or drop hammers, can be powered by pneumatic, hydraulic, or electrical means. The dies and punches can be flat or V-shaped, and the striking force can range from 11,000 to 425,000 pounds (lbs). Because only one ram is required to form the part, flash is produced and must be trimmed.
2. Open Die Forging Machine
Open die forging machines work with ingots, billets, bars, and preforms. They deform the workpiece between flat or shaped dies without completely restricting metal flow. This causes the workpiece to lengthen while decreasing its cross-section. Using multiple impacts, lengthening and upsetting can be accomplished. Metal parts can range in length from a few centimeters (cm) to 30 meters (m) and weight from several to several hundred thousand kilograms (kg). Open die forging machines can produce fairly complex shapes, but they are typically used to produce simple solids or hollows that require significant machining to achieve their final shape.
3. Closed Forging Machine
This machines do not require the formation of flash to ensure that the die is completely filled. The metal is deformed in a cavity that does not allow excess material to escape, putting greater emphasis on proper die design.
4. Isothermal Forging Machine
Isothermal forging machines heat materials and dies to the same temperature. To avoid oxidation, it is usually performed on super alloys in a vacuum with a tightly controlled atmosphere.
Advantages of Machine Forging
1. Very High production rate up to 4500 parts per hour.
2. The process can be completely automated.
3. Elimination of the forging draft and flash.
4. High efficiency of material utilization, as the process produces little or no waste.
We have tried to cover all the details regarding the Machine Forging in this article including definitions, types, process, and advantages. Hope you liked the article and please give your feedback in the comment section below.