Papers by Author: Jon Larrañaga

Abstract: The general trend in the field of machine tools is to increase the speed of feed axes with the aim of reducing manufacturing times, high speed machining is a significant example of such increase. Ball screws have proven their ability to fulfill requirements of workpiece positioning accuracy, nevertheless, the heat generated in the screw-nut interaction increases proportionally with the speed of the axes. As a result, an increase in temperature takes place, which causes thermal expansion of the ball screw, producing positioning errors and decreasing the service life of the ball screws, therefore it is important to have effective methods for predict the temperature.The main objective of the present work is to predict the heat generated in the screw-nut contact based on analytical models in order to estimate the temperature distribution in the nut. For this purpose a heat transfer FE model of a preloaded high speed ball screw nut has been developed. Additionally, experimental heating tests have been performed to validate the FE numerical model. In this way, the temperature predictions obtained at different working conditions have less than 6% of deviation comparing with the experimental results.

Abstract: Bending in a V-die has been used to indicate the outcome of bending in cold roll forming, although little direct correlation has been performed. In this work direct comparison of the springback in both processes was performed using six samples of automotive steels in a conventional roll forming line where the transverse springback is measured. A bend of similar radius was formed in a V-die and the springback determined. In general, the springback in V-die forming was greater than in roll forming, in some cases by a factor of 2. The theoretical springback angle was determined for all steels using a simple and approximate analytical equation and compared to the experimental roll forming and bending results. While for the roll forming process good agreement was achieved the theoretical values significantly underestimated springback in the V-bending process.

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.