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Abstract

The article presents an analysis of the multi-operation hot die forging process, performed on a press, of producing a lever forging used in the motorcycles of a renowned producer by means of numerical simulations. The investigations were carried out in order to improve (perfect) the currently applied production technology, mainly due to the presence of forging defects during the industrial production process. The defects result mainly from the complicated shape of the forging (bent main axis, deep and thin protrusions, high surface diversity in the cross section along the length of the detail), which, during the filling of the die by the deformed material, causes the presence of laps, wraps and underfills on the forging. Through the determination of the key parameters/quantities during the forging process, which are difficult to establish directly during the industrial process or experimentally, a detailed and complex analysis was performed with the use of FEM as well as through microstructure examinations. The results of the performed numerical modelling made it possible to determine: the manner of the material flow and the correctness of the impression filling, as well as the distributions of temperature fields and plastic deformations in the forging, and also to detect the forging defects often observed in the industrial process. On this basis, changes into the process were introduced, making it possible to improve the currently realized technology and obtain forgings of the proper quality as well as shape and dimensions.
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Abstract

The study presents a durability analysis of dies used in the first operation of producing a valve-type forging from high nickel steel assigned to be applied in motor truck engines. The analyzed process of producing exhaust valves is realized in the forward extrusion technology and next through forging in closed dies. It is difficult to master, mainly due to the increased adhesion of the charge material (high nickel steel) to the tool’s substrate. The mean durability of tools made of tool steel W360, subjected to thermal treatment and nitriding, equals about 1000 forgings. In order to perform a thorough analysis, complex investigations were carried out, which included: a macroscopic analysis combined with laser scanning, numerical modelling by FEM, microstructural tests on a scanning electron microscopy and light microscopy (metallographic), as well as hardness tests. The preliminary results showed the presence of traces of abrasive wear, fatigue cracks as well as traces of adhesive wear and plastic deformation on the surface of the dies. Also, the effect of the forging material being stuck to the tool surface was observed, caused by the excessive friction in the forging’s contact with the tool and the presence of intermetallic phases in the nickel-chromium steel. The obtained results demonstrated numerous tool cracks, excessive friction, especially in the area of sectional reduction, as well as sticking of the forging material, which, with insufficient control of the tribological conditions, may be the cause of premature wear of the dies.
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