Applied Mechanics and Materials Vol. 805

Abstract: Due to the use of rolling bearings instead of plain bearings friction and wear are drastically reduced in all kind of machines. However, despite the high technical standard of modern rolling bearings there is still a significant potential for optimization. Preliminary Studies show a reduction of the friction torque of up to 44 % compared to conventional rolling bearings because of the use of tribological coatings in certain applications. Based on the millionfold usage of rolling bearings in all industrial fields the reduced lost energy adds up to a remarkable potential for energy savings. If friction and wear are lowered sufficiently, the use of conventional lubricants based on mineral oil can be successively decreased or even completely avoided. In the latter case, the socalled dry running of the rolling bearing, the energy consumption of machines and systems can additionally be reduced significantly. For example, pumping stations or compressed air units, which would be necessary for transporting or spraying the lubricants, can then be saved.This paper presents first results of DLC-coated deep groove ball bearings, which are tested in a four-bearing-test-rig under purely radial load with respect to their friction and wear behaviour.

Abstract: The manufacturing of steel gears by cold forging can be realized by using the so called Samanta process. The present study focuses on the one hand on the FE based analysis of the forming of gears in forward extrusion and on the other hand on the modelling of a Samanta process, using the software Simufact.forming. Thereby the influence of different tool geometries and the tribological conditions on the forming are investigated. The aim is to obtain a basic understanding of the material flow and the filling of the tooth cavity depending on the geometry of the Samanta process. For the investigations the common heat-treatable steel 1.7131 (16MnCr5) was used. As an input parameter for the simulation the true stress-true strain curve of the material has been determined within compression tests. For the analysis of the forming the material flow into the cavities and the shape of the tooth flanks are evaluation criteria. Thus the influence of the different parameters on the distribution of equivalent plastic strain, the forming and the reachable accuracy have been investigated.

Abstract: The rising level of automation in the automotive industry also involves the use of more and more machines and with that an increase in power consumption. This requires the employment of more efficient production processes with higher efficiency. Laser beam welding offers the opportunity to substitute conventional laser sources like solid state lasers with ultra-high brightness direct-diode laser systems which have the advantage of less power consumption at a comparable beam quality. However, the absorption of laser radiation on metallic surfaces depends on the wavelength, thus the effect of the direct-diode laser wavelength on the welding process has to be investigated. In our research the effect of the laser wavelength on energy efficiency was studied by means of numerical simulations. Furthermore, experimental investigations were carried out to validate the numerical solutions. Different aluminum alloys and steel materials which are used in the automotive environment were investigated within the experiments. Due to the current lack of direct-diode laser systems with a laser power comparable to conventional laser systems, numerical simulations were also used to analyze these future systems. Thus we were able to assess the increase of efficiency in laser beam welding which will be achievable with future high-power direct-diode laser systems.

Abstract: Compared to steel, the required amount of energy for conventional welding of copper is higher, due to its higher thermal conductivity. This problem is mainly solved by preheating the work pieces or welding processes with high intensities such as laser beam welding. As the absorption of copper for infrared wavelengths, which are commonly used in industrial applications today, is typically low, the energy efficiency of the laser welding process is low. Besides this, if filler wires are used in order to increase the bridgeable width of joining gaps, the energy consumption of the process is further increased due to the additional amount of energy required to melt the filler material.As roughened surfaces of copper parts are known to increase absorption and consequently energy efficiency of laser beam welding without filler wires, this paper investigates the influence of surface structured filler wires on laser beam welding of copper alloys. Thus, the correlation between knurling geometries, absorption, molten volume and the welding result is investigated. For this reason, the welding result is evaluated by means of geometrical, electrical and mechanical weld seam properties e.g. seam width, weld reinforcement, area of cross-section, electrical resistance, tensile strength and strain.

Abstract: Due to the introduction of an energy management system, a lot of existing manufacturing plants were equipped with energy measurement systems. With sufficient sample rates those retrofitted energy measuring systems could provide additional information beside active power and energy consumption. Each production plant is characterized by a process and product specific power consumption with an associated power signal. In this paper a method to determine the information content in power signals of milling operations is discussed. By using the cross correlation function and hidden markov models (HMM) for operation recognition and automatic derivation of energy key performance indicators (EnPI) can be realized. In addition, further production related key performance indicators (KPI) can be derived with pattern recognition in load and current profiles.

Abstract: The electric base load of milling machine tools has a high share of the machine’s total energy consumption. An approach to decrease the energy demand per workpiece is to shorten the machining time by raising the material removal rate. The maximum feed depends on the tool’s wear resistance while the maximum depth of cut is often limited by the chatter stability of the machine. In this paper active damping is used to damp chatter vibrations, which leads to a higher depth of cut. To evaluate the decrease of energy consumption for any workpiece, a modeling methodology for the energy demand of machine tools was developed, which is presented in this paper. The methodology is able to estimate the energy requirements of the spindle during cutting, of the feed drives, of the auxiliary equipment and of the base load. The numerical results were experimentally validated by different 2.5D machining processes, with good agreement between the simulation model and the experimental results. Therefore, the proposed methodology can be used effectively for calculating the total energy required for the machining of any workpiece. In addition, the structural dynamics of the machine tool, the active damping system and the cutting process were modeled in order to simulate the chatter stability. This enables a straightforward determination of the optimum cutting parameters as well as a comparison of different milling part programs, both in terms of the energy demand. Furthermore, it is possible to evaluate the energy conservation by active damping and to point out for which cutting processes active damping is useful.

Abstract: In electronics production, the condensation based soldering technologies are known for reproducible solder profiles and efficient heat transfer methodology. The recent advancements in lead-free soldering and requirements for absolute void-free interconnections to increase the reliability and lifetime of the product needs optimization of the soldering process. The vacuum assisted vapor phase soldering process addresses the requirements with respect to mass production and parallelly resource efficient production which is also the motivation for the present work. This study is devoted to quantify the resource consumption and qualify this consumption through exergy flows in a vacuum vapor phase reflow soldering technology in electronics manufacturing.The analysis implies on the saving potential for energy consumption specifically during the vacuum process which also defines the void reduction quality of solder joints. Exergy efficiency analysis of a temperature profile depicts the influence of the materials used in the demonstrator. Shortening the production lead‑time, and increasing the production rate increase the efficiency of exergy and prevents wastage of usable energy. Furthermore, the set-up improvements for the temperature profiles processes are necessary, and the changes toward developing new, transformational technologies in pre-heating and vacuum zones are mandatory if a high efficiency of resources used is aimed.

Abstract: One important purchasing criterion for end customers is the resource consumption of products, which manufacturers aim to reduce through sustainable product designs and optimization of production processes. In order to quantify the resource consumption, in this study the demand of raw materials and operating materials of the selective laser melting process was quantified according to the methodology developed within the initiative Cooperative Effort on Process Emissions in Manufacturing (CO2PE!). The selective laser melting process was selected due to two reasons. First, the process enables lightweight constructions, which offers the potential to reduce the resource consumption during the product use phase. Second, few studies have been published about this process so far which also measure the demand of compressed air and shielding gas apart from the electric energy demand. It was found that the resource demand for the manufactured 0.5 cm³ cuboid part amounted to 3.6 kWh electric energy, 0.81 m³ compressed air and 0.31 m³ Argon. This corresponds to an energy demand of nearly 1000 kWh/kg, though such key performance indicators alone are not very representative for the selective laser melting process, as described below.

Abstract: Hybrid additive manufacturing technologies combine selective material deposition with a conventional milling process in one machine, enabling the production of complex metal parts and reducing the need for part specific tools. The hybrid technology offers technological advantages compared to more established additive fabrication processes, such as powder bed fusion. Compared to powder bed based additive processes, which are currently in a prevailing positon regarding AM adaption, hybrid additive technologies enable increased build rates, enhanced build volumes and a reduction of machine changes. In the Laser Metal Deposition (LMD) process, metal powder is deposited through a nozzle and melted by a laser on the surface of the part. By integrating the LMD process into a machining center, good surface roughness and low tolerances can be realized by means of e. g. milling without reclamping. In comparison to powder bed based processes, cost and resource input have not been investigated in detail. In this study, hybrid additive manufacturing technologies are analyzed regarding cost and resource input. A cost model for hybrid additive processes is introduced that enables the analysis of the manufacturing cost structure for a given part. Furthermore, the resource inputs for the operation of a hybrid production machine are estimated.

Abstract: In this paper, a modular dynamic model of an industrial robot (IR) for predicting and analyzing its energy consumption is developed. The model consists of control systems, which include a state-of-the-art feedback linearization controller, permanent magnet synchronous drives and the mechanical structure with Coulomb friction and linear damping. By using the developed model, a detailed analysis of the influence of different parameter sets on the energy consumption and loss energy of IRs is investigated. The investigation results show that the operating parameters, robot motor drives, and mechanical damping and elasticity of robot transmissions have a significant effect on the energy consumption and accuracy of IRs. However, these parameters are not independent, but rather interrelated. For example, a higher acceleration and velocity shortens IRs’ operating periods, but needs a greater motor current, tends to excite vibrations to a greater extent, and thus produces a higher amount of loss energy.