Sliding bearings have good damping properties and a high stiffness. However, stiction and poor sliding friction characteristics limit their use in applications, where high requirements are defined on ...the smoothness of motion. By inducing ultrasonic oscillations into the sliding contact it is possible to actively control the friction. The adjustable friction bearing uses this principle. This leads to a new bearing type that has the stiffness and damping properties of a sliding bearing, while at the same time, offering a linear friction characteristic without stiction. This paper presents basic principles for the design of ultrasonic bearings along with experimental results of a friction-adjustable machine table.
Controlled heating of metal billets into the semi-solid state for thixoforming is a challenging task, mainly due to the difficulties in measuring the liquid fraction of the billet during heating. ...Past research primarily focused on methods measuring the liquid fraction during heating of low-melting aluminium alloys. One of these methods is time constant measurement, a contactless measurement method that uses the heating coil as a sensor. The current through the coil is used to determine the electrical time constant of the heating circuit, which itself is influenced by the specific resistance of the billet inside the coil. While previous works focused on the suitability of this method for industrial applications using aluminum alloys, this paper extends this research to the high-melting titanium alloy Ti6Al4V. This alloys shows high strength, low density and excellent corrosion resistance. It is therefore used to produce light-weight and durable components for medical and aerospace applications. Ti6Al4V is an expensive and difficult to machine alloy. Thus, it is an interesting alloy for thixoforging. However, heating of the billet into a homogeneous state of defined liquid fraction is difficult due to the poor thermal conductivity of Ti6Al4V. This paper analyses the potential of using time constant measurement for controlled heating of Ti6Al4V into the semi-solid state.
Ball screws are robust and economic linear positioning systems that are widely employed in high speed and high precision machines. Due to precision and stability requirements, the preload force has ...been considered one of the main parameters in order to define the axial rigidity and the maximum axial load capacity of ball screw feed drives. In high speed motions, thermal effects are also considerably relevant regarding positioning precision and dynamic stability of the machine. The temperature increase and the thermal gradient between the screw, the balls and the nuts led to a variation in the contact geometry and consequently in the preload force. This paper presents an experimental analysis of the preload variation due to the temperature increase. The study has been performed for several initial preload forces and linear speeds in a preloaded double nut ball screw. The heating of the system results in a decrease of the preload force, where a maximum decrease of 60 % has been observed for a temperature increase of 28 K in the test bed of the study. Regarding the consequences of the loss of rigidity, the first eigenvalue decreased by only 5 % for a preload drop of 33 %.
This paper presents an efficient and industry-ready system architecture that enables both the control of machining operations and the high-frequency acquisition of controller data and external sensor ...signals. Using the recorded data, a dexel-based mechanistic cutting force model, which enables the estimation of cutting forces for complex tool geometries in arbitrary machining operations, is parameterized via an instantaneous cutting force identification method. In the introduced identification method, Bayesian Optimization and Dynamic Time Warping are combined to avoid time-consuming and error-prone synchronization of measurement and simulation. The suitability of this approach was demonstrated by performing cutting experiments at various radial depths of cut and feed rates per tooth. Thereby, a good agreement between simulation and measurement could be observed.
State of the art machine tool controllers offer several Internet-of-Things (IoT) interfaces for machine data acquisition using industrial or edge computers. However, the available data exchange rates ...for these communication platforms are limited to a few hundred Hertz. As the data is not available in high frequency resolution, such a network communication is not suitable for monitoring and optimizing highly dynamic machining processes. This paper describes an efficient system architecture, which enables the acquisition of internal machine data as well as the high frequency sampling of external sensors. Based on this data, an Operational Modal Analysis (OMA) approach can be used to determine the tool tip dynamics during the machining process. Identification of tool tip frequency response requires the reconstruction of the excitation of the machine tool structure, i.e. the occurring machining forces. For this purpose, an approach relying on monitoring the commanded motor currents is applied.
In many sectors such as the aerospace industry, the manufacturing of rotating components is based on multi-stage production systems to achieve the complex requirements of high quality products. Even ...in the presence of Industry 4.0 and the increasing connectivity, these systems are very prone to failure due to the high level of potential influences of both the system and the products, ultimately leading to defects. The project "ForZDM", funded by the EU under Horizon2020, envisions reducing scrap rate by avoiding and compensating defects at an early stage thus guaranteeing a high quality product. This paper presents an approach using an existing manufacturing line to compensate the dimensional deviations of an inner contour of a turbine shaft at an early stage. Based on measurements of the inner contour, a new rotation axis for the subsequent manufacturing processes is calculated in order to avoid unbalances at the end-of-line control. Different algorithms are developed and integrated in a web-based application to find an optimal rotation axis under consideration of the to-be-manufactured outer contour in an operator-friendly usage on the shop floor. The application is connected with the measurement system and the subsequent CNC machine which enables automatic execution and data transfer.
Open control systems: state of the art Brecher, C.; Verl, A.; Lechler, A. ...
Production engineering (Berlin, Germany),
05/2010, Letnik:
4, Številka:
2-3
Journal Article
Recenzirano
Within the European initiative OSACA (Open System Architecture for Controls with Automation Systems) a company-spanning open control architecture has been developed as of 1992. Since then the ...development of open control systems has continued until today. In 2008 a study was carried out with the objective to verify the results of 15 years of work for open control systems in Europe. It ought to identify especially the state of the art in the polled companies as well as their wishes and goals for the future. This article contains the most important results.
This paper presents a method for reducing non-productive times in the planning and interpolation of lift movements during 2.5D machining. At the moment, this mostly vertical lift movement is executed ...separately from the position changing in the operating plane. This sequential processing of motions increases the non-productive time in processes with frequent changes of operating height, such as laser cutting. The reduction is realized by superimposing the planar path movements with lift motion. An asynchronous axis interpolation is applied to make use of the maximum machine dynamics. In addition, known obstacles can be taken into account by further parameters in the planning.
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