Die forging is a forging method that making metal billet to produce a plastic deformation in a die and be full of a cavity to obtain the shape and size as required under the effect of external force. Most metals are forged in hot state, so die forging is also called hot die forging.
Compared with free forging, die forging can forge parts more complex in shape and more accurate in size. The production efficiency of die forging is high, it can produce forging parts with the same shape and size, which facilitates using automatic machine tools and automatic production lines in the subsequent cutting process. After die forging, a directional fiber structure formed inside forging parts which was called as streamline.
Select reasonable die forging process and dies, to let the stream line distribution in consistent with the parts shape, which can significantly improve the forging parts mechanical properties. But die forging needs special dies. The dies must be made of high quality alloy tool steel. The dies cavity is complex, high precision, the die need comply with large quantity processing, long production cycle, so the price is expensive. Therefore, die forging is generally suitable for mass production with high requirements for forging parts shape and performance.
Hammer forging
The hammer forging is widely used in the production.
Forging dies include two pieces: upper die and lower die, which are fixed on the head and anvil block of hammer respectively. For forging parts, the upper die of the hammer head strikes to the lower die on the anvil block (if no anvil block hammer, the up and lower anvil beating each other). The blank usually passes through a number of forging processes, so there are correspondingly multiple die cavities on the forging die. When forging, the blank is heated to the forging beginning temperature first (see theCommon Sense Of Steel Forging Temperature.), then is transferred to the corresponding mold manually, and is strike by the forging hammer in turn and finally formed in the finish die cavity. Typical hammer forging has 6 processes as Pic1 (No upsetting process in this die)
1) Upsetting: It is used to reduce the blank height and increase the cross-sectional area.
2) Drawing out: It is used to reduce the blank local section and extend the blank length by turning the blank around the axis and draw out along the axis.
3) Rolling press: While operating, just reverse the blank without the input, which can reduce the blank local section and increase the blank length, making the whole blank surface round and smooth.
4) Bending: It is used to change the shape of the billet along the central axis.
5) Pre-forging: To improve the forming condition of forging part and reduce the wear of finish forging die cavity.
6) Finish forging: To make the parts to final shape and determine the parts shape and precision. There is a trimming groove around this forging die cavity.
The forging hammer has a fast strike speed and high impact energy, and the striking weight can be controlled by the operator freely, so it has good adaption for forging parts, and the forging parts can be forged from 1 kg to 200 kg of complex shapes, such as the engine connecting rod, crankshaft, automobile universal joint, front beam and various gear. The hammer forging is of high productivity, low equipment investment, but its disadvantage is too much vibration and noise, difficult to operate, poor working conditions and strong labor intensity. In addition, the forging hammer generally has no ejection device, the forging parts needs a larger die forging slope, so the machining allowance is larger in next process, the die life is less.
² Hot die forging press die forging
The hot die forging press is generally a crank type mechanical press. It's vibration and noise are smaller than that of hammer, and the operating of hot die forging is easy, the productivity is high and easy to match with manipulator to realize automatic production. The hot die forging press has good rigidity, high guiding accuracy of the slide block, also has ejection device, so the forging part with a smaller die forging slope. The stroke of hot die forging press is fixed, can neither replace the roll forging machine or other equipment to complete the corresponding blank making operation, nor use the impact inertia to form the forging parts like forging hammer. In order to make the forging parts full of die cavity, it is often necessary to increase the pre-forging times, let the blank is gradually approaching the shape of the forging parts in several die cavities, so its die structure is more complex. Die forging of hot die forging press is suitable for mass production.
² Screw press die forging
The screw press has a large forming energy, and good mechanical press guide. It has ejection device and doesn’t need steam power. It is a more versatile die forging equipment. It only produces a small amount of trimming for the draft angle is very small. After forging, the forging part is ejected out by the ejector pin. For small and medium sized forging parts, the effect of single die cavity forging is very good, especially for upsetting the head of rod parts like valve and bolt. Complex shape parts can be pre-blanked on other equipment, then forged on the screw press. Please refer
What Are The Characteristics Of Electric Screw Presses and How to Choose Between Electric Screw Press and CNC Hydraulic Hammer for more information.
Hydraulic press die forging
The hydraulic press has the characteristics of low speed, large stroke, high pressure, adjustable pressure and ejection device. It can give pressure in several directions if need (in multi direction hydraulic press). The pressure of giant hydraulic press reaches tens of thousands KN, and the working platform tens square meters. It is suitable for forging large steel, titanium alloy, aluminum alloy and magnesium alloy forging parts, especially large aviation forging parts, such as aircraft frames and landing gear beams. Multi direction hydraulic press is suitable for forging all kinds of multi cavities complex forgings, such as high pressure casing, valve body and three fork, four fork pipe joint, etc. (Pic2: multi direction forging sketch).
Horizontal forging machine die forging
The horizontal forging machine is a crank press with its working part to do horizontal reciprocating motion. So the horizontal forging machine has the characteristics of the hot die forging press, such as the large rigidity, the fixed stroke, the good dimension stability of the forgings in the direction of the length (the direction of being hit). The forming of the forging by static pressure during the work, so the vibration is small and no need for a huge foundation. It has high productivity and is a universal die forging equipment widely used in mass production.
According to the location of the parting surface of the female die, the forging press can be divided into two types: vertical parting and horizontal parting. The horizontal die forging machine with horizontal parting has good operation conditions and is easy to realize automation, but the structure is rather complicated.
Horizontal forging process features:
Pic4 Horizontal forging die and its movement
When working as above sample, the movable die is moved to clamp the heated bar at the end, then upsetting by a multi-position punch fixed on the main slider to fill the cavity of the die. If the length of the bar's deformation part is more than 3 times of the rod diameter, the end of the rod must be accumulated one or several times before the pre-forging and finish forging, so as to avoid the bending or folding of the rod during upsetting. When forging through hole, first forge parts with blind holes, then separate the parts from the rods when male die is piercing. The horizontal forgings usually don’t produce trimming or only produce small trimming, so the material usage is high, but it is still necessary to clamp the rod to be forged, so the diameter tolerance of blank is small.
Besides the continuous improvement of the traditional die forging methods in these year, there are also many new precise, high speed die forging technology and new equipment with technology development. For example, the precisely forge turbine blade by hydraulic screw press, just leave a small grinding allowance on the blade; the precisely die forging gear by SSET automatic line the gear teeth don’t need machining any more, our Red punching machine is a multiple positions automatic hot upsetting machine which heated the blank and then formed the forging in 3-4 working position, is economical and has high efficiency.
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