This paper presents two triaxial finite element (FE) models: a “full model” and a “quarter model”, representing the contact between the specimen’s rough surface and the ideally smooth and flat surface of the punch. Models have a contact zone that represents the topography of the real surface and has elastoplastic properties close to those of the real contact. The contact zone was entirely modelled on the basis of roughness measurements performed on a real milled specimen made of 5083 aluminium alloy. The developmentof the FE models, the stages in their refinement and the interlinking of the contact zone with the material of the specimen are described. The results of the computed deformations occurring during the specimen contact loading with the punch were compared with the experimental results. The possible causes of the observed deviations of the computer simulation results from the experimental ones were discussed. The models were used to analyse the effect of the specimen’s material properties, i.e. Young’s modulus, yield strength, compressive strength and material hardening, on the deformations in the contact. On this basis a procedure for predicting the parameters describing the contact characteristic in cases of changes in the properties of the subsurface zone is proposed.
Hereby paper shows the structure of mutually connected thermal interactions in a machine tool, a tool and a workpiece, which finally leave their traces on a machined workpiece in form of machining errors. Thermal interactions of a machine tool and the environment on own and workpiece errors were discussed. Thermal interaction cases were considered, connected with the varying environment and the main drive operation, as well as total influence of the varying environment, main drive and two drives of controllable axes. The interactions of the cutting process itself were discussed, assuming three basic mechanisms: thermal, physically-mechanical and tribological. On the example of turning it was proven that the character of changes in total influences between the tool and workpiece has the shape of a temperature curve.
This article shows the aspects of precise modelling of precise High-speed Machining Centres for High-Speed Cutting (HSC) of parts used in the aerospace industry. The main focus was made on the thermal errors having a dominant influence on the precision of machining. Main assumptions for a hybrid thermal model of a centre thermal behaviour have been stated, taking into account the characteristics of heat sources. On the example of a 3-axis machining centre, measured runs of heating up and heat displacements have been shown, compared to these determined with the use of simulations of a behaviour in assumed working conditions. A special attention was drawn to the phenomena taking place in motorspindles, as well as to the displacements of a spindle face during high rotational speeds of spindles and step changes of rotational speeds. The significance and influence of the bearing preload and centrifugal forces on the spindle axial displacements was shown, which is decisive on the precision of part machining. Additionally, it was shown that the important component of a machining error is an error of spindle position identification by means of a linear encoder, resulting from the thermal deformation of a centre body, to which a quartz linear encoder is fixed.
The assurance of high precision alignment of workpieces with low stiffness requires thorough knowledge about the phenomena taking place in the contact area under the influence of forces exerted by actuators. It is indispensable to utilise the model of a contact and deformations taking place in it. In order to solve the problem of contact, the contact geometry was modelled by means of a flat and rough surface model based on stereometric measurements, as well as by means of the finite element method (FEM). In a FEM method, a spherical structure of the surface layer was assumed and only one zone was taken into consideration, i.e. 0.4.Rt (maximum surface roughness). Zone structure allows easy changing of mechanical properties of material during the introduction of data defined by a strengthening curve in the plastic region. The possibility of expanding the model by consecutive zones allows taking into consideration the physical properties in complex analyses of the surface layer. This paper presents the problem of contact related to the alignment and fixing process, a model of contact deformations between a flat and a rough surface, as well as the algorithm for determining the model of a surface profile according to the bearing ratio curve.
In order to improve the process of designing mechatronic devices, an approach, based on a mechatronic model, is proposed. The structure of such model is presented, consisting of partial models of single elements in a system. Methods of creating these models and integrating them into one mechatronic model are discussed. In order to illustrate the approach, a case study is shown, consisting of a mechatronic alignment and fixing device for high-precision machine tools. A test bed of such device is under construction, which will allow experimental verifying partial models of components, as well as the entire system's mechatronic model. An extended set of monitoring sensors will provide accurate system behaviour data useful for such process.
In this paper, a method of hybrid modelling of machine's mechanic structure together with mechatronic cooling system of its body is presented. In this method, a FEM model, traditionally used for thermal analyses of machine's thermal behaviour, has been integrated with mechatronic model of cooling system, implemented in MATLAB. In such way, a hybrid model has been created, allowing to simulate the control of machine body cooling process. Applied simulation of cooling the region of body, adjacent to the guide, illustrates the possibility of controlling the temperature in chosen points of the machine tool, in transient state, which would ensure minimal body deformations, small enough not to require compensation, which is generally hard and of limited precision. Thermal model of machine tool has been built with the use of SATO system [1]. In this work, time-domain temperature changes with and without the use of regulation by means of PID regulator have been compared. Results of the simulation show the usefulness of presented hybrid modelling method for the improvement of machine tool thermal behaviour.
Simulating of workpiece and fixture behaviour is commonly done with the use of Finite Element Analyses. In the most, if not all, cases researchers usually use traditional implicit integration scheme FEM codes (e.g. ANSYS, ABAQUS/Standard, NASTRAN, FEAP). In this paper a different approach is proposed. FEM code of ABAQUS/Explicit, based on explicit integration of equations of the motion is used to predict workpiece behaviour during alignment and fixing process in quasistatic state. Comparison of results obtained using both implicit and explicit techniques is also presented, results and differences are discussed.
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