Papers by Author: Luis Norberto López de Lacalle

Abstract: Coating of steel with aluminium alloy is needed for the execution of a functional layer for corrosion protection. Some experiments have been performed on square-section tubes (50 mm x 50 mm) of S235 steel, according to EN 10 025, to be coated with 1 mm thick sheets of EN AW 5754 aluminium alloy that have been previously bended as U shaped profiles. A new experimental model of specialized equipment has been used for certain experiments to make these functional layers of aluminium alloy on steel. Firstly, friction drilling and threading by form tapping, followed by screws-mounting without nuts have been used to make such joints. Several holes have been executed by a Ø4.3 friction drilling tool, then an M5 form tap was used for threading. For friction drilling, tools with 90% tungsten carbide content and 1 micron grain size were applied. By threading, TiN coated form taps have been used. Secondly, overlap friction stir welding (FSW) has been applied, to make a functional layer of aluminium alloy on a 50 mm x 50 mm S235 steel tube. The wings of the U profiles were overlapped. A quenched FSW tool, own-made of C 45 grade steel, EN 10083, has been used for these joining tests. The joining parameters are mentioned for each process. The run of each joining process is described and the joint test samples are presented. The appearance of the screw-mounted functional layers is appropriate. The metallographic analysis has revealed adequate form of the burr formed below the hole. The burr height is 2.5 – 3.2 mm. The pattern of the M5 thread is appropriate. No defects have been detected on the holes and threads. The appearance of the FSW functional layers is adequate. Metallographic analysis shows that FSW joints of the overlapped aluminium alloy sheets are adequate, because there is no gap between these sheets. There is only a narrow gap between the aluminium alloy bottom sheet and the wall of the steel tube, which proves an appropriate positioning of the two metals. No defects were detected, except for a weld flaw, as a small and isolated cavity, with a section less than 0.1 mm², considered within the acceptance limit, according to EN 25239-5. The U shaped sheets of aluminium alloy are firmly fixed on the square steel tube, for both coating types. The mentioned processes are proposed to increase productivity in industrial technologies for series production. The processes addressed in this paper are more rapid than conventional processes. Adequate preparation of the parts to be welded, mechanization and automation allow repeatability and quality. The target applications are coated structure elements for devices, appliances, tools, welded structures or automobiles. The involved industrial areas of the applications are: manufacturing, electro-technique, construction and automotive industries. The presented processes are ecological, because they do not need lubricants or other toxic substances and do not produce chips or harmfull substances.

Abstract: Gamma-TiAl intermetallic materials are the focus of all leading aerospace / gas turbine manufacturers, as a replacement for some nickel-based superalloy components in parts of the engine subject to temperatures < 900°C. Although applicable for only a relatively narrow range of applications, titanium intermetallic materials are likely to play a significant role in the production of future aeroengines. This work presents the results from grinding tests on two types of Gamma TiAl alloys.

Abstract: An accurate prediction of the dynamic stability of a cutting system involves the implementation of tool geometry and cutting conditions on any model used for such purpose. This study presents a dynamic cutting force model based on the collocation method by Chebyshev polynomials taking advantage from its ability to consider tool geometry and cutting parameters. In the paper, a simple 1DOF model is used to forecast chatter vibrations due to the workpiece and tool, which are distinguished in separate sections. The proposed model is verified positively against experimental dynamic tests.

Abstract: The work here exposed, is framed in the line of development of slight materials with good properties, used to reduction of weight in different components for the aviation and automotion where very high temperatures are the main factor. In these fields, several components must withstand high temperatures maintaining a high resistance. The superalloys of type Gamma TiAl is a attractive alternative to other titanium and nickel-based alloys, due to high relationship resistance/weigh and the resistance to the corrosion. This work presents the results from turning tests on three types of Gamma TiAl alloys. Coating tools of integral hard metal are used, with different advances and cut speeds.

Abstract: Boring operations of deep holes with a slender boring bar are often hindered by the precision because of their low static stiffness and high deformations. Because of that, it is not possible to remove much larger depths of cuts than the nose radius of the tool, unlike the case of turning and face milling operations, and consequently, the relationship between the cutting force distribution, tool geometry, feed rate and depth of cut becomes non-linear and complex. This problem gets worse when working with a rotating boring head where apart from the cutting forces and the variation of the inclination angle because of shape boring, the bar and head are affected by de centrifugal forces. The centrifugal forces, and therefore the centrifugal deflection, will vary as a function of the rotating speed, boring bar mass distribution and variable radial position of the bar in shape boring. Taking in to account all this effects, a load and deformation model was created. This model has been experimentally validated to use as a corrector factor of the radial position of the U axis in the boring head.

Abstract: Behavior of austenitic stainless steels is not well known and these materials are still considered as difficult to machining materials. Moreover, the continuous increment of cutting speeds and other cutting parameters derived from last technological advances in tool material makes it more difficult to understand the behavior of these materials in high performance machining. A mechanistic model is presented in this paper for cutting force prediction of austenitic stainless steels turned at very high cutting speeds (up to 750 m/min). The developed model allows the estimation of cutting forces in turning when the cutting action occurs on the side cutting edge and nose radius edge for general turning tools. A tool-part geometrical model is proposed and the cutting force coefficients have been calculated by means of characterization tests.

Abstract: In laser surface treatment the laser beam is used as energy source for surface modification improving aspects such as mechanical properties, tribology or surface texture. Modeling tools have special interest in processes with many variables, like laser surface processing, in order to minimize the tryout testing to find the optimal process parameters. The work presented here focuses on the prediction of the final topography in laser polishing process. By FFT analysis of the surface profile it is possible to get the different frequency components of the initial topography. On the other hand, thermal field simulation was carried out to evaluate the melt duration. Matching this with the spatial frequency damping during process, the reconstruction of the processed topography was obtained.

Abstract: Ever increasingly, universities have to face the demands of their students regarding tools and methods to complete their education in preparation for the industrial environment. On the other hand, the university has to meet a Research and Development function oriented to the improvement of the competitiveness of that environment. These are two different functions that the university must unite to offer an optimum service. Hence, the university needs tools that can meet this dual function: teaching and researching. This paper proposes the concept of a “Glass Machine” as a dual purpose approach based on the adaptation of machine tools to satisfy that dual function. This concept has been applied to a machine tool by means of two machines: a turn-milling centre and a feed-drive test bench, which have been used for practices in the subjects of 4th and 5th year of Industrial Engineering, allowing at the same time the usual research activity of the High Performance Machining Team. In short, this work is about the optimization of the available resources of the university, thus satisfying the needs of the students and the industrial environment.

Abstract: The European Higher Education Area has entailed some upheaval since it has involved deep changes in university education. Among the subjects taught in technical education such as Manufacturing Technologies, which involve strong experimental contents, the use of specific tools is helpful for better understanding of such subjects. This article highlights the need for the use of simulation tools in the field of manufacturing processes. The student may achieve optimal understanding and learning from them. They can understand, in a more visual way, complex phenomena that govern different processes and the influence of key variables. Applications related to sheet metal forming, forging and casting processes are presented. The main objective is to enable students to better understand the phenomena that govern the processes of moulding and forming, with the invaluable help of simulation software. The final aim is to ensure that the student reaches an optimum knowledge of moulding and forming processes using simulation software.

Abstract: A common problem in the aeronautical industry is the chatter vibration due to the lack of dynamic stiffness in the milling of thin walls and thin floors. The present work proposes a method for chatter avoidance in the milling of flexible thin floors with a bull nose end mill. It allows the calculation of the thickness previous to finish milling or the minimum dynamic stiffness that the floor must have to avoid the chatter vibration appearance. To obtain these values, the stability model algorithm has been inverted to estimate the thickness or the dynamic stiffness required in a floor to allow a stable milling. This methodology has been validated satisfactorily in several experimental tests.