A significant part of the energy in forging is used to break the interfacial junctions due to friction between the tool and the workpiece. The life of hot-forging tools is usually limited by complex interactive mechanisms under cyclic loading such as abrasive, adhesive and scaling wear, thermal and mechanical fatigue, and plastic deformation. This contribution deals with the wear mechanisms of the tempered martensitic X38CrMoV5 steel (AISI H11) under high-temperature and dry-sliding wear. The investigations are carried out with high-temperature pin-on-disc tests. The pin is cut from bars of X38CrMoV5 steel treated at 42 and 47 HRC. The disc is made of common steel (AISI 1018, XC18). Temperature of the disc ranges from 20 to 950 • C. Before the test starts, the disc is first pre-heated for 1 h. The experiments are performed under constant load and velocity. The friction coefficient decreases quasi-linearly with the rising disc temperature up to 800 • C. Over this temperature, it decreases drastically for the 42 HRC steel but remains linear for the 47 HRC steel. Scanning electron microscopy (SEM) and energy dispersive spectrometry (EDS) investigations have revealed that wear is essentially due to abrasion, plastic deformation and fatigue. Set of cracks due to contact rolling fatigue is observed on the pin and the disc. Those cracks are located on the transferred scale on the pin and on the oxide scale of the disc wear track. The cross-section observations of the pin have revealed a plastically deformed zone beneath the surface. In this sub-surface layer, the tempered martensitic microstructure seems to be more aligned due to friction and the plastic deformation.
The wear rate of sliding materials seems impossible to predict. It is clearly a function of substrate material, but we are learning that many surface events are also important. In particular, studies on the last 20 years have shown that substances develop between two sliding bodies have a strong influence on both friction and wear. These substances had become known as "third bodies". Whereas third bodies have been proven to be important, they have not been completely characterized. The third bodies have been studied, but it appears that the geometries of the sliding pairs are also important. This paper describes some experiments in which the composition of third-body materials are controlled by temperatures and in which the durability of third-body films are influenced by the geometry of contact between sliding bodies.
a b s t r a c tGiven the specific micro-structure of some steel grades, under tribological conditions the sub-surface material or sub-layers of sliding bodies are prone to cumulative cyclic plastic deformation, leading to the formation and emission of wear debris.In the present paper, a new wear model based on a cyclic ratchetting-type plastic deformation of subsurface material is proposed. It is considered that the debris is formed and the wear-loss occurs when the accumulated plastic deformation at sub-surface exceeds "a critical strain" or "rupture limit". The model takes into account the number of cycles or test duration, a characteristic thickness of the sub-layer dependent on tribological conditions and material properties, the shear rupture ductility and an average plastic strain increment. The average plastic strain increment is estimated by numerical simulation of pinon-disc friction. A very close correlation is found between the predicted and experimental wear heights versus time and/or versus the number of cycles.The wear investigations were carried out on a high-temperature pin-on-disc tribometer under dry friction conditions. Experiments were performed under constant load, speed and disc temperature for different durations. The steel grade involved was a tempered martensitic tool steel X38CrMoV5 (AISI H11). Wear mechanisms were investigated by Scanning Electron Microscopy (SEM) observations in surface and cross-section.
The rear part of the APF A380 has a deep drawn shape. In order to develop the forming by SPF process of this part, numerical simulation by finite elements has been performed. Several configurations for 2D and 3D modeling were studied to determine an efficient forming strategy. A double-action solution was chosen. It ensures a satisfactory thickness distribution. This article will deal with the modeling assumptions, the results of individual cases of calculation and comparison with parts obtained at the Airbus plant.
To save costs of superplastic forming, an economic way to raise the temperature of the blank is described. The use of infra-red lamps cuts the tool heating time to a few minutes instead of 24hours. The tool core is not completely heated anymore, leading to greater efficiencies. Numerical simulations have been used as a predicting tool of the infra-red lamps power to ensure a homogeneous temperature in the blank during the superplastic forming. Thermomechanical simulations are needed. The infra-red emitter have been tested on a superplastic press. Successful results are presented in the field of forming TA6V sheets. A special attention is carried on the effect of heating on the TA6V microstructure.
With its experience in the SPF simulation and tool manufacturing, Aurock completes its offer in the titanium SPF field with the part forming and brings a global support from the conception up to the manufacturing. Aurock proposes tool design, forming strategy and simulation, rapid tool manufacturing made of refractory castable reinforced with metallic fibre and now titanium superplastic forming. To improve its offer, Aurock started from a blank page and developed a specific SPF press to test and assess new heating solutions. One major innovation permits to reduce the heating time using a direct sheet heating. The process becomes anisothermal. This approach avoid time to heat up to 900°C large toolings. The completed offer for titanium SPF parts and successful results on the heating solutions are presented.
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