High-speed forging with active friction

Autor: L. V. Zubareva, A. N. Eliseev, V. N. Shcherba, S. V. Samusev, V. V. Ovechkin
Rok vydání: 1997
Předmět:
Zdroj: Metallurgist. 41:97-101
ISSN: 1573-8892
0026-0894
DOI: 10.1007/bf02767876
Popis: (HFAF) [I]. It is based on movement of the bottom die ahead of the top die. This makes it possible to speed the movement of the peripheral layers of the workpiece and delay the movement of the axial layers while creating a radial flow of metal along the surfaces of the top die and bottom die. These two interrelated flows create favorable conditions for developing the structure of the product and eliminating the formation of pulls, normal cracks, and other types of defects. Such a process was first used at the Moscow State Institute of Steel and Alloys (MSISA) for forging hard-to-deform aluminum alloys. It was realized on a special unit with hydraulic cylinders to move the top and bottom dies. The cylinders were initially mounted on the base of a P456 hydraulic press with a force of 2 M-N. A DB 2432A press with a force of 1.6 MN was used later. In both cases, the law governing the change in the velocity of the top die reflected the coaxial positioning of the top die and the head cylinder on the cross-arm. The unit also had a system that delivered a stable flow of hydraulic fluid, which was forced out of the cylinder through a choke. The data needed to develop essentially new designs of presses was obtained in the course of laboratory studies of patterns of change in the kinematic and force parameters of HFAF. As a result, specialized press PB8745-1, the first of its kind in the world, was designed and built in 1979 at the Kolomensk Heavy Machinery Plant. The 31.5-MN press has separate drives for the top and bottom dies and is intended for HFAF and impression-die forging. The unit was placed in operation in 1980 at the Stupinsk Metallurgical Combine. Use of the press has demonstrated the clear advantages of HFAF compared to traditional methods of closed-die and impression-die forging. However, the design of the press turned out to be nonoptimal, due to the difficulties encountered in making full use of its energy characteristics at all stages of the forging process. For example, the forces applied to the bottom and top dies were too low during the initial and final stages, respectively. The best results were obtained on a reconstructed P8546 press with a force of 35 MN. This press also had independent drives for the top and bottom dies. The forging press at the MSISA is similar to this press, differing from the original design in the presence of a system that stabilizes the downward velocity of the head cylinder. In this case, fluid is displaced from the latter into the cavities of two stabilizing cylinders whose pistons are connected to the cross-arm. This arrangement automatically ensures that the bottom die will remain "ahead of the top die by the necessary amount during the entire forging operation [2]. In 1989, the Kramatorsk Metallurgical Plant employed the same scheme as the basis for reconstruction of its 35-MN direct-acting P8546 press in order to make use of active friction during forging. The use of a compact configuration that enclosed the head cylinder and top die within the cross-arm made it possible to keep the dimensions of the press within the original limits. The movement of the bottom die is away from the cross-arm, while the top die moves apart from the head cylinder. The reconstruction involved location of the two cylinders and the stabilizing pistons above and below the cross-arm. The drive of the bottom die was modified due to the need to lengthen the travel of this die and free up space for the mechanisms that remove the press waste and return the bottom die to its initial position.
Databáze: OpenAIRE
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