Contact Pressure Measurement System in Cross Wedge Rolling

In the cross wedge rolling process (CWR), plastic deformation is geared by a driving torque transmitted by friction on die surface. Friction plays a role which has to be further identified in this metal forming process. The local contact pressure between a cylindrical billet and flat dies seems to be a relevant parameter to characterize the severe contact conditions during the rolling. This paper deals with an experimental measurement technology, which has been designed and implemented on a semi-industrial CWR test bench with plate configuration. This measurement system using pin and piezoelectric sensor is presented, with an analysis of the system operation and design detail. Characterization of systematic error and calibration tests are then explained. Additional tests performed on hot steel preforms allow to check the ability of the contact pressure measurement system to resist under severe operating conditions. Realistic results for varying temperatures are then discussed

Cobalt-based superalloy layers deposited on X38CrMoV5 steel base metal by explosion cladding process

This work is the fruit of a collaboration between CETIM (CEntre Technique de l'Industrie de la Mécanique) and ENSAM. Authors are obliged of the “Commission Forge Du CETIM” for its financial support. Authors also acknowledge the support of AFF (“Association Française de Forge”), DNC Nobelclad and ThyssenKruppVDM.A grade 25 cobalt-based superalloy in the form of a sheet 5 mm in thickness and a steel substrate of type X38CrMoV5 are joined by explosion cladding. The macrostructure and microstructure of the interface and of the co-based superalloy layers are studied. The interface presents the form of wavelets with a period of 1000 µm and an amplitude of 250 µm. The superalloy grains are deformed during the cladding process with several slip systems appearing. Near to the interface, the superalloy grains elongate and tend to follow the geometry of the interface. Observation with a scanning electron microscope (SEM) reveals zones of localised fusion at the interface. The EDS analysis shows that these fusion zones are the result of mixing between the base and cladding plates. Radiocrystallographic analysis by X-ray diffraction reveals the presence of the f.c.c cobalt in the cobalt-based superalloy layer. Thus cobalt retains its crystallographic structure (f.c.c) after cladding process. Hardness is evaluated with reference to microstructure. Near the interface, the hardness of the superalloy is of the order of 600 HV1 kg. In the remainder of the thickness, hardness is of the order of 500 HV1 kg, being greater than that of the unplated superalloy (270 HV1 kg). The track obtained by an indentation test at the interface under a load of 100 kg exhibits no cracking. This tends to prove the good metallurgical bond at the interface

Role of Surface Texture on Workpiece Angular Deformation in Cross Wedge Rolling

The cross wedge rolling process is commonly used for the manufacturing of shaft or for preforms, being used for preliminary operation of forming cycle. The presence of angular deformation produced during the rolling process is analyzed in this paper. This work shows some experimental results obtained on parts made of steel in semi-industrial condition. Visioplasticity technique is used to measure the angular displacement occurring in some sections with reference to the adjacent ones. Thus the test samples are prepared to include surface grooves filled up with quite similar steel grade. After rolling process, angular deformations are highlighted by observations and external deformation profile. Influence of surface texture of the forming area is experimentally demonstrated. Moreover, the numerical simulation with the software FORGE is used to verify the adequacy between the observed phenomena and forecasts which can be obtained today.Conclusions about the relative influence of friction factors on the internal stresses creation are finally presented to better identify potential occurrence of these phenomena. Strain diagrams are used to bring out the magnitude of angular variations depending on local plastic strain on parts. Possible consequences for process optimization are raised

Hot Forging of a Cladded Component by Automated GMAW Process

Weld cladding is employed to improve the service life of engineering components by increasing corrosion and wear resistance and reducing the cost. The acceptable multi-bead cladding layer depends on single bead geometry. Hence, in first step, the relationship between input process parameters and the single bead geometry is studied and in second step a comprehensive study on multi bead clad layer deposition is carried out. This paper highlights an experimental study carried out to get single layer cladding deposited by automated GMAW process and to find the possibility of hot forming of the cladded work piece to get the final hot formed improved structure. The experiments for single bead were conducted by varying the three main process parameters wire feed rate, arc voltage and welding speed while keeping other parameters like nozzle to work distance, shielding gas and its flow rate and torch angle constant. The effect of bead spacing and torch orientation on the cladding quality of single layer from the results of single bead deposition was studied. A hot bending test at different temperatures of cladded plates with different dilution and nominal energy carried out

Thermal exchange effects on steel thixoforming processes

Steel thixoforging is an innovative semi-solid forming process. It allows the manufacturing of complex parts and minimises the forming load. This work aims to identify and characterise the main feature zones of a thixoforging part. The material flow and the forging load are dependent on the thixoforging speed, the tool temperature and the initial temperature of the slug. The data are obtained for C38 thixoforging steel. A specific extrusion tool was designed that integrates the heating of the tool and the slug. This tool was set up on a high-speed hydraulic press. This work highlights the effects of heat exchange on the microstructure, the internal flow and the mechanical characteristics of thixoforging material. These heat exchanges depend primarily on the working speed and tool temperature. The internal flow is composed of three distinct zones. Among them, only semisolid zone is observed during working. The microstructures of thixoforming C38 steel consist of ferrite, pearlite and bainite

Consideration of residual stress and geometry during heat treatment to decrease shaft bending

In automotive industry, heat treatment of components is implicitly related to distortion. This phenomenon is particularly obvious in the case of gearbox parts because of their typical geometry and precise requirements. Even if distortion can be anticipated to an extent by experience, it remains complex to comprehend. Scientific literature and industrial experience show that the whole manufacturing process chain has an influence on final heat treatment distortions. This paper presents an approach to estimate the influence of some factors on the distortion, based on the idea of a distortion potential taking into account not only geometry but also the manufacturing process history. Then the idea is developed through experiments on an industrial manufacturing process to understand the impact of residual stress due to machining on shaft bending and teeth distortion during heat treatment. Instead of being measured, residual stress is being neutralized. By comparing lots between each other, connections between gear teeth geometry and manufacturing steps before heat treatment are obtained. As a consequence, geometrical nonconformities roots can be determined more easily thanks to this diagnosis tool, and corrective actions can be applied. Secondly, the influence of product geometry on bending is experimentally considered. Moreover, metallurgical observations enable to explain the influence of workpieces geometry on shaft bending. Thanks to the obtained results, process and product recommendations to decrease shafts bending are proposed

Effects of Vibrations on Metal Forming Process: Analytical Approach and Finite Element Simulations

Vibration assisted forming is one of the most recent and beneficial technique used to improve forming process. Effects of vibration on metal forming processes can be attributed to two causes. First, the volume effect links lowering of yield stress with the influence of vibration on the dislocation movement. Second, the surface effect explains lowering of the effective coefficient of friction by periodic reduction contact area. This work is related to vibration assisted forming process in viscoplastic domain. Impact of change in vibration waveform has been analyzed. For this purpose, two analytical models have been developed for two different types of vibration waveforms (sinusoidal and triangular). These models were developed on the basis of Slice method that is used to find out the required forming force for the process. Final relationships show that application of triangular waveform in forming process is more beneficial as compare to sinusoidal vibrations in terms of reduced forming force. Finite Element Method (FEM) based simulations were performed using Forge2008®and these confirmed the results of analytical models. The ratio of vibration speed to upper die speed is a critical factor in the reduction of the forming force.ENSA

Overview of the mean of production used for FSW

The Friction Stir welding process is now introduced in production plants. More and more applications are developed and the most part of the work is now centered on the mean of production to be used. Institut de Soudure and Arts et Métiers ParisTech are working on this subject since mid of 2005. The results of this work is a recognize knowledge on the methodology for qualifying a Friction Stir Welding Equipment [1]. In the same time, and based on this work, Institut de Soudure has bought a new kind of Friction Stir Welding machine based on a KUKA Robot

Experimental investigation of the influence of the FSW plunge processing parameters on the maximum generated force and torque

The paper presents the results of an experimental investigation, done on the friction stir welding (FSW) plunging stage. Previous research works showed that the axial force and torque generated during this stage were characteristic for a static qualification of a FSW machine. Therefore, the investigation objectives are to better understand the relation between the processing parameters and the forces and torque generated. One of the goals is to find a way to reduce the maximum axial force and torque occurring at the end of the plunging stage in order to allow the use of a flexible FSW machine. Thus, the influence of the main plunge processing parameters on the maximum axial force and torque are analysed. In fact, forces and torque responses can be influenced by the processing parameter. At the end, a diagram presenting the maximum axial force and torque according to the processing parameters is presented. It is an interesting way to present the experimental results. This kind of representation can be useful for the processing parameters choice. They can be chosen according to the force and torque responses and consequently to the FSW machine capacities

Microstructure Evolution and Material Flow of Steel in Semi-solid Forming Process

The present study aims to identify and characterize the development of microstructure and deformation characteristics of steel grades in semi-solid state which is affected by the change in morphologies of microstructure at high temperature. Thixoextrusion tests with different combinations of forming temperature and forming speed were performed. It was identified that several process parameters, such as initial billet and die temperatures or forming speed, affect thermal exchanges thereby influencing the microstructure evolution and material flow. Furthermore, 2D and 3D microstructure characterization was performed on the same sample which was partial remelted and quenched. Reconstructed 3D images were compared with the ones obtained with a Scanning Electron Microscope and an Energy Dispersive Spectrometry system. The good agreement between 2D SEM observations and 3D X-ray microtomography results makes these two techniques efficient to characterize steels in the semi-solid state