J. Coello

Electrical Evaluation Of Welding Machines Based On The Arc Properties. Application To SMAW, GMAW And GTAW Processes

In this work, a methodology to obtain the electrical behavior of arc welding equipments is presented. The method is based on the electrical arc fundamentals and it is applied to Shielding Metal Arc Welding and to Gas Metal Arc Welding processes. For the first one, different arc points are achieved by practicing several arc lengths. For MIG process, different arc lengths are made by changing the feel wire velocity. Arc current and voltage are measured for the different arc length in both cases. Finally, a Gas Tungsten Arc Welding equipment has been used to obtain the electrical arc characteristics as a function of arc length. Different considerations about the thermal and electrical principles related to the arc behavior have been made.

A Proposal for Bending Process of TRIP Steel Sheets Based on the Springback Behavior

TRIP steels, or Transformed Induced Plasticity steels, have excellent mechanical properties if compared with conventional steels. The highlighted characteristic of these steels is that they modify the microstructure with the deformation process as part of the austenite transforms to martensite, with the consequent change of the material properties. One of the main problems of TRIP steels is strong elastic recovery, or springback, after forming. In this work, the springback phenomenon is evaluated by bending tests and the influence of the variables involved in it is determined. Experimental bending forces do not agree with theoretical predictions that are proposed in the literature. In spite of the bending radius having been considered an influence factor in the process, this work demonstrates that the aforementioned factor has a minor influence, at least for TRIP 800. The factor found to affect material recovery the most was the bending angle.

Learning Chip Type Strategies in Turning Processes by Viewing with High-Speed Video Cameras

This work develops a methodology that allowed students to associate the effect of some cutting variables with chip type. For that, turning processes were carried out on two different materials since their physical and mechanical properties have a relevant influence on the chip formation. Cutting tests were run by varying the feed rate, while cutting speed and depth of cut had fixed values. These cutting conditions led to different chip geometries being obtained. Thus, it was possible to establish a chip type classification in turning operations. The methodology herein presented is based on new technologies, which raised great expectations among students, who positively considered this experience. The effect of other variables, apart from feed rate, must be theoretically analyzed in order to improve the comprenhension of the process herein involved.

Proposal of an Educational Methodology to Analyze Cutting Temperature in Turning Operations by Infrared Themography

The present work develops a learning methododology based on experiments related to the cutting temperature concept in turning processes. This proposal allows students to measure the temperature actually reached during a typical turning operation with a semi-automatic lathe. Temperature data are collected by a thermographic camera, which implies acquiring competences in this technique. The different tests involved in the practical experiment are defined for various cutting speeds and feed rates, and for a constant depth of cut. Two different materials are considered to point out the influence of turning parameters on cutting temperature.

INFLUENCE OF TURNING PARAMETERS ON CUTTING TEMPERATURE BY APPLYING THE DESIGN OF EXPERIMENTS WITH THE DEFINITION OF THE WORKPIECE MATERIAL BEHAVIOR

This paper evaluates the behavior of cutting temperature under the influence of specific cutting parameters by applying both Factorial Design and the Surface Response Methodology. Cutting speed, the feed rate and type of material were selected as input parameters to perform this study. As type of material is a non quantitative factor, it is necessary to establish a particular index to define it. Although different properties were analyzed, the average stress between the yield and strength stresses was demonstrated as the most representative property to describe material. The experimental values of temperatures during the turning process were obtained with an infrared thermography camera and experiments were designed to run the statistical analysis with commercial software. Both the Factorial Design and Surface Response methodologies showed the influence that specific values of the input parameters had on cutting temperatures. Factorial Design allowed more accurate results, but more experiments had to be carried out, while the Surface Response Methodology provided suitable information with fewer tests. A comparison was made between the experimental and some analytical results, for example those obtained by Cook, and showed a good agreement.

A Procedure Based on Magnetic Induction to Evaluate the Effect of Plastic Deformation by Multiaxial Stresses on TRIP Steels

As it is well-known, TRIP 800 steels modify their structure with the deformation grade. So, part of the retained austenite turns into martensite by plastic deformation. The usual techniques tried out to evaluate this transformation whether do not lead to obtain good results or the experimentation with them is very complex. In this work, a magnetic induction method is experimented and developed in order to determine the evolution of a TRIP 800 steel microstructure with the strain grade. The variables that can have influence on this kind of analysis methodology have been studied and their effects evaluated. This method has been applied to determine the induced martensite by deformation under conditions of pure shear deformation. Results point that this method allows to state that the microstructure evolution taking place in TRIP 800 steels is not proportional to the strain applied.

Learning Strategies for Deep-Drawing Processes in the European Higher Education Area Context

A traditional educational strategy for teaching sheet stamping processes consists in theoretical planning. Having experimental media available to conduct stamping processes in university teaching laboratories is not that usual. In this work Problem Based Learning is carried out. Students must evaluate some data from deep-drawing experiences that have been previously done by the teaching team. The innovation proposal starts with deep-drawing experimental demonstrations performed by an experimental device that has been designed in the laboratory for researching and teaching aims. Processing the information that students acquire helps them to analyse the main deep-drawing technological fundamentals.

An Educational Proposal: A Soldering Practice For Mechanical Engineering Students

In the present work, an educational proposal for soldering practice in the University Education System is presented. Therefore, the content and development of this proposal must be focused on the main factors that take place in this kind of process. The idea of the multidisciplinary educational process must be taken into account and a suitable amount of engineering contents are involved. This way, the students have to achieve a professional specific training. The fundamentals of the process and the mechanical behavior of solder joints must be analyzed in an adequate way. Moreover, different solders and joints have been experimentally tested and the results have been evaluated. The correlation between them has been carried out by strength materials principles. At the same time, some details about the process have also been described. The authors agree with the results obtained and claim their important consequences.