Precision die forging refers to the process of forging complex shape and high precision forgings on die forging equipment. For example, precision die forging bevel gears. The tooth profile can be forged directly without further cutting. The dimensional accuracy of die forgings can reach IT12~ITl5, and the surface roughness value Ra is 3.2~1.6 um.

Precision die forging process

①Draw forging drawing according to product parts drawing.

②Determine the die forging process and auxiliary process (including cutting the flash, deburring, etc.), determine the size of the process, determine the heating method and heating specifications.

③Determining the Method of Clearing Surface Defects of Billet.

④Determine the blank size, quality and allowable tolerance, and select the cutting method.

⑤Selection of precision die forging equipment.

⑥Determine blank lubrication and die lubrication and die cooling methods.

⑦Determine the cooling method and specification of forgings, and determine the heat treatment method of forgings.

⑧Technical requirements and inspection requirements of forgings are put forward.

Process Requirements for Precision Die Forging

The technological requirements of precision die forging are as follows:

①Billet preparation. Precision die forging has higher requirements for blanks, requiring small quality tolerance, small section collapse angle, flat end surface and perpendicular to the blank axis, blank surface should not have pits, cracks, pits, large scratches or bruises; and before forging, surface cleaning (grinding, polishing, pickling, etc.) must be carried out, and surface should be removed. Oil pollution, slag inclusion, bruising, depression, etc. At present, sawing and lathe cutting are mostly used in precision die forging of aluminium alloy, among which band saw cutting is more commonly used.

②Billet heating. The method of non-oxidation and less oxidation heating should be adopted, and the scale produced during heating should be minimized.

③Precision forging process and reduction. In precision die forging, crankshaft forging press and precision forging machine or other different equipment can be used for combined die forging. Repeated die forging, usually 2-3 times after ordinary die forging, can reach the accuracy of <0.2-0.3 mm, and the surface roughness value is below Ra6.3. In order to achieve higher precise size, the final cold precise pressing can be carried out on the precise press. Its accuracy can reach (+0.1 mm), and the surface roughness value can reach below Ra 0.80.

④Cleaning between processes. The next precision forging process can only be carried out by grinding or polishing the surface defects of the blank.

⑤Lubrication. Lubrication can make deformation uniform and increase metal fluidity. However, too thin or too thick lubrication will bring adverse consequences, lubrication must be moderate.

Process characteristics

Precision die forging is an advanced technology to improve the accuracy and surface quality of forgings. It can forge parts with complex shape and high dimensional accuracy, such as bevel gears and blades.

Its main technological characteristics are as follows:

1、It is necessary to calculate the size of the original blank accurately and cut the blank strictly according to the quality of the blank. Otherwise, the dimension tolerance of forgings will be increased and the accuracy will be reduced.

2、It is necessary to clean the surface of billet finely and remove oxide skin, decarbonization layer and other defects on the surface of billet.

3、In order to improve the dimensional accuracy and reduce the surface roughness of forgings, non-oxidation and less oxidation heating should be adopted to minimize the oxide scale formed on the surface of billets.

4、In order to minimize oxidation and improve the quality of forgings, the heating temperature of precision forging is lower. For carbon steel, the forging temperature is between 900 ~950 C, which is called warm die forging.

5、The precision of precision forging depends to a great extent on the precision of forging die. Therefore, the precision of precision forging die chamber must be very high. Generally, the accuracy of forgings is two levels higher than that of forgings. Precision forging die must have guide pillar guide sleeve structure to ensure accurate closing. In order to eliminate the gas in the die chamber, reduce the resistance of metal flow, and make the metal fill the die chamber better, there should be an exhaust orifice on the die.

6、Lubrication and cooling of the forging die should be carried out well in die forging.

7、Precision die forging is usually carried out on die forging equipment with high stiffness and accuracy, such as crank press, friction press or high-speed hammer.

Application of Precision Die Forging

Precision die forging is a new technology with little and no cutting developed on the basis of common dies. It is to forge directly or leave only a few grinding scenes on parts that used to require cutting to meet the accuracy requirements. Therefore, the adoption of precision die forging technology requires stricter technical requirements for the relevant links of die forging, such as: the most strict control over the quality of blank cutting and surface quality; the rational design of prefabricated blanks; the less and non-oxidizing heating of blanks; the control of heating and cooling standards; the control of die manufacturing and use accuracy; and the appropriate design of prefabricated blanks. Selection of lubrication and cooling conditions.

Precision die forging has the remarkable advantages of saving metal and reducing the working hours of cutting, but it will increase part of the cost because of strengthening the relevant links of die forging. Therefore, the choice of precision die forging process for specific products should be considered comprehensively according to the comprehensive economic index of finished parts and the special requirements of parts structure and performance.