Key Engineering Materials Vols. 504-506

Abstract: Friction Modified Processing (FMP) is a novel solid state processing technique which can be used for microstructural modification of surface layers in metallic materials. The paper deals with the investigation of the influence of process parameters on the microstructure in the surface layer of a cast aluminum alloy. The FMP was conducted on a constructed welding machine equipped with appropriate devices (LOWSTIR and TermSTIR). The measurements of temperature in the stir zone were compared with a numerical model. Another model was developed to determine the quantitative relationships between mass of modified material and processing speeds over a wide experimental range. An exponential formula has been found to describe the relationship between mass of modified material and rotational speed. The evaluation of the traveling speed affecting the mass of the modified material was successfully approximated by linear functions.

Abstract: In this paper technological and economical capabilities of manufacturing titanium- and nickel-based alloys via unpulsed Electrochemical Machining (ECM) are presented. A standardized test to receive typical workpiece material removal properties according to its electrochemical machinability is introduced. First of all the experimental setup of this test is described in detail. The test results for the materials Ti-6Al-4V and Inconel 718 are presented and discussed. Here the feed rate – current density- and surface roughness – current density curves are in focus. With help of these two functions as an example out of many possible applications the capability of blisk manufacturing by electrochemical machining is quantified. Therefore the theoretical machining times for both materials of substituted blisk geometry are calculated. Finally on this basis an economical comparison between ECM and milling as rough estimation is executed.

Abstract: A scraper was developed and attached to the single roll caster in order to improve the free solidified surface of as-cast strip cast. Semisolid metal on the free solidified surface was flattened by the scraper and the surface became flat. The AA5182 aluminum alloy could be cast at speeds up to 40m/min. Thickness was about 3mm. Pressure of the unit width of the scraper was ranging from 0.1N/mm to 1.0N/mm, and these pressure was enough to make the free solidified surface flat. Center line segregation did not occur as the strip was solidified from single side at the strip cast by the single roll caster. Roll-cast strip could be cold rolled down to 1mm. There was not difference between the roll contact surface and the free solidified surface of the strip after cold rolling judging by a visual examination. Result of tension test of the roll cast and cold rolled strip was as same as that of D.C. cast and rolled strip. Deep drawing test was operated at the conditions both of the roll contact surface and the free solidified surface were outer side. LDR (limited drawing ratio) was same at both conditions and they were 1.8. Thickness of the strip was controlled by the roll speed, solidification length (length of the melt pool) and pressure of the scraper. The single roll caster is simpler than a twin roll caster. Rigidity for rolling was not required for the single roll caster. Cost of the roll is half comparing a twin roll caster. The equipment cost of the single roll caster is more economy than that of the twin roll caster.

Abstract: The roll forming process is a very interesting process for the production of profile shaped parts because of its high production rate, low investment and efficient use of the material. However, as in most of the manufacturing processes, the set up of the machine is very important for the quality of the profiles to be manufactured being the traditionally used trial and error method high time and scrap consuming. Within the set up, one of the most important variables to be defined is the right gap or distance between the upper and the lower roll at each station. This gap can lead to, or avoid, the appearance of geometrical errors such as differences in springback effect or longitudinal bow of the final profile. Furthermore, to find the correct gap between the rolls,a traditional tedious and costly work must be made based on a trial and error methodology. Different sensor based methodologies have already been implemented successfully in other forming processes. The present work aims at evaluating if force and torque measurements are a viable solution to decrease the roll forming process set-up time. This way, the effect of the gap for three different materials, a DC01, DP600 and MS1200 steel, has been analyzed. For this purpose, force and torque measurement together with final geometry measurements have been made at different gap configurations. A correlation between the profile quality and the process variables has been carried out in order to identify the influence of the gap at the setting up of the machine.

Abstract: Rubber forming is an ideal process for the manufacture of a wide variety of flanged parts in small products series, and is attractive for industries like the aircraft industry. The flanges of a formed part are straight, stretch or shrink flanges, each type having its own limits. The forming limits for the straight and stretch flanges are dominated by the formability of the material and the applied strains, which are related to the (local) geometry of the flange. The prediction of the limits for the shrink flanges is much more complicated, since both plastic flow and instability play a role. In recent years, a number of authors developed methods for the prediction of wrinkle formation in metal sheets in different applications. This paper focuses on an alternative approach for the prediction of failure limits of shrink flanges. Shrink flanges wrinkle right from the start of forming process. At first the deformations are elastic, but for the creation of flanges the material has to become plastic. The geometry of the cross-section of the wrinkles can be approximated by sinusoidal shapes having a length and amplitude. During processing the values of both parameters decrease, although the ratio of the two is even more important and should decrease in order to obtain a wrinkle-free part. In the paper the topic is addressed using experimental data, showing the influence of the most important variables like materials properties, strain values, and variables like thickness. Subsequently the parameters are used to provide relations between the different variables, which are used for numerical simulations.

Abstract: Biomass materials such as wood are attracting renewed attention as alternative fuels in order to help resolve environmental resources caused by the use of fossil fuels. In this study, the possibility of products being processed from wood bulk was investigated by means of boss forming using open-die forging. Additionally, the difference in formability and deformation behavior during forging was investigated by changing the experimental conditions, such as the moisture content of the wood billets used, the forming pressure, and the forming temperature. The experimental results showed that wood had enough liquidity to be forged, and that two sudden and large increases in displacement occur during forging. Finally, the conditions governing these displacements were summarized from these results

Abstract: Micro-milling with a cutting tool is a manufacturing technique that allows production of parts ranging from several millimeters to several micrometers. The technique is based on a downscaling of macroscopic milling process. Micro-milling is one of the most effective process to produce complex three-dimensional micro-parts, including sharp edges and with a good surface quality. Reducing the dimensions of the cutter and the cutting conditions requires taking into account physical phenomena that can be neglected in macro-milling. These phenomena include a size effect (nonlinear rising of specific cutting force when chip thickness decreases), the minimum chip thickness (under a given dimension, no chip can be machined) and the heterogeneity of the material (the size of the grains composing the material is significant as compared to the dimension of the chip). The aim of this paper is to introduce some phenomena, appearing in micromilling, in the mechanistic dynamic simulation software ‘dystamill’ developed for macro-milling. The software is able to simulate the cutting forces, the dynamic behavior of the tool and the workpiece and the kinematic surface finish in 2D1/2 milling operation (slotting, face milling, shoulder milling,…). It can be used to predict chatter-free cutting condition for example. The mechanistic model of the cutting forces is deduced from the local FEM simulation of orthogonal cutting. This FEM model uses the commercial software ABAQUS and is able to simulate chip formation and cutting forces in an orthogonal cutting test. This model is able to reproduce physical phenomena in macro cutting conditions (including segmented chip) as well as specific phenomena in micro cutting conditions (minimum chip thickness and size effect). The minimum chip thickness is also taken into account by the global model. The results of simulation for the machining of titanium alloy Ti6Al4V under macro and micro milling condition with the mechanistic model are presented discussed. This approach connects together local machining simulation and global models.

Abstract: Hobbing is one of the most productive methods for manufacturing external gears. According to the requirements of green manufacturing, the lubrication in gear hobbing has to be reduced with the final aim of dry machining. Influences due to thermal aspects during machining have to be considered, especially in hobbing of large modules or ring gears, because in this case, hobbing could be the last step in the process chain. Within the priority program (SPP) “Modeling, Simulation and Compensation of Thermal Effects for Complex Machining Processes”, founded by the DFG, special emphasis is laid on the thermally caused geometrical deviation in dry cutting. To predict the heat flux, which leads to thermal expansions and geometrical deviations of the gear, a validated model for forces and temperatures is necessary. The validation of single generation positions and chips is focused in this paper.

Abstract: Machining is a complex process during which the material undergoes large deformations at high strain-rates with large variations in temperatures. One of the difficulties faced during the simulation of machining is that of determining appropriate material parameters which are valid for such large ranges of strains, strain-rates and temperatures. An inverse method of material parameter identification from machining simulations is proposed in this paper. An error function is defined that takes into account the chip overlap error and the cutting force difference at different frames of observation. The two components are suitably weighted so that the contribution of each is rendered almost equally. A two stage optimisation process is employed for the minimisation of the error function where the Levenberg-Marquardt algorithm is used in the first stage for faster convergence and the Downhill Simplex algorithm in the second stage in order to navigate through the noisy error landscape. A wide range of cutting conditions is used and the method is shown to work also for non-adiabatic simulations. However, the converged parameter sets are found to be non-unique.

Abstract: The phenomenological models for material flow stress and fracture, typically used in the Finite Element simulations of Inconel 718 alloy during machining processes, are often deemed to represent only certain metallurgical material states. In contrast, these models are not suitable to describe the constitutive behaviour of the workpiece for different metallurgical states (i.e., annealed, aged, etc.) and, consequently, different hardness values. Since the description of the material behaviour requires correct formulation of the constitutive law, new flow stress models which include also the hardness effect should be developed and, accordingly used, for computer simulation of machining Inconel alloy. This paper describes the development of a hardness-based flow stress and fracture models for machining Inconel 718 alloy, which can be applied for a wide range of work material hardness. These models have been implemented in a non-isothermal viscoplastic numerical model to simulate the influence of work material hardness on the chip formation process. The predicted results are being validated with experimental results available in literature. They are found to satisfactory predict the cutting forces, the temperature, the shear angle and the chip morphology from continuous to segmented chip as the hardness values change.