INFLUENCE OF LINEAR FEED DRIVE CONTROLLER SETTING IN CNC TURNING LATHE ON THE STABILITY OF MACHINING

The paper deals with the influence of linear feed drive controller setting of a CNC turning lathe on the stability of machining. A coupled simulation model of feed drive control and ball screw drive mechanics with a transmission belt was created and validated by the feed drive diagnostic measurements. The influence of drive control on the overall dynamic compliance at the TCP and the limits of stable depth of cut was examined. Impact of the feed drive actual kinematics configuration on the stability limits was studied as well

Integrated force interaction simulation model for milling strategy optimization of thin-walled Blisk blade machining

Complex shaped thin-walled blades that are extensively used in jet engines or stream turbines are very difficult to machine due to low rigidity of the blades, typically limited space between the blades and strict requirements on the surface quality and accuracy. The paper focuses on multi-axis machining of thin-walled and complex shaped Blisk blades made of aluminium alloys. The resulting surface quality and accuracy is mainly affected by the risk of elevated vibration occurrence, both forced and self-excited, and static deflections between the compliant tool and workpiece. An innovative integration of the transformed FE model of the blade into virtual machining simulation has been proposed, allowing to effectively solve the complex optimization task considering both the criterion of stable machining condition and static deflections as well. When choosing a machining strategy and cutting conditions, there are many variables that fundamentally affect the process. These variables are not easy to choose correctly the first time, so it is advisable to choose to use a simulation model in production preparation. The proposed simulation model allowed to effectively optimize the process parameters to keep the machining process stable and the static deformation of tool and workpiece under a defined level. The proposed model and optimization strategy was validated on a thin-walled blade machining. At the top part of the blade, the surface roughness decreased from 1.6 Ra to 0.84 Ra, and the maximum deviations from the reference model were reduced from 0.18 mm to 0.08 mm

Coordinate-free formulation of the cutting process

This work was supported by the Grant Agency of the Czech Technical University in Prague, grant No. SGS16/220/OHK2/3T/12.Machining processes are invaluable in many industrial branches. Calculation of the cutting forces is important for quality prediction of the machined surface. The cutting forces are usually expressed and manipulated in a certain coordinate system. So long the geometry of the cutting process is simple, the approach works well, however dynamics of more general operations like 5-axis milling are often difficult to describe without some additional simplifications

Coupled Model of the Spindle and Machine Tool Frame

Influence of the machine frame on the dynamic properties of spindle and tool is investigated using an example of a real machine tool. Model of the whole mechanical system is created as a coupled system of the tool, spindle and machine frame single submodels. Experimental verification of the model has shown a good match of the system critical frequencies and compliances. It has been proved that properties of the machine frame limit the dynamic properties at the tool tip especially in the case, if a compact tool is used

Coupled modelling for machine tool structural optimization

Effective machine tool design needs to take into account various kinematic configurations and possible combinations of structural parts, which meet the requirements of both the structural properties on one hand and technology and cost limitation on the other hand. Prior to a detailed developing a certain machine tool structure, an expert based decision on the machine tool conception needs to be performed. A high number of design variants should be explored in a short time. Fulfilling those demands leads to developing a machine tool modular models, enabling easy changing the kinematic configuration or various structural parts. In the paper the techniques for effective component coupling and model order reduction using mode truncation or Krylov subspace based technique for creating the machine tool coupled models are introduced. Case studies considering real machine tool structures are given. High quality of Krylov subspace reduction technique in connection with multipoint constraint surface coupling is shown both in terms of dynamic properties of the reduced multibody model and a very low time demands at the same time

Virtual Evaluation of Machine Tool Cover Passive Forces Using a Cover Complex Model

The passive forces acting against the drive force are phenomena that influence dynamical properties and precision of linear axes equipped with feed drives. Covers are one of important sources of passive forces in machine tools. The paper describes virtual evaluation of cover passive forces using the cover complex model. The model is able to compute interaction between flexible cover segments and sealing wiper. The result is deformation of cover segments and wipers which is used together with measured friction coefficient for computation of cover total passive force. This resulting passive force is dependent on cover position. Comparison of computational results and measurement on the real cover is presented in the paper

Comparison of Two Model Coupling Methods for Joint Identication

An experimental identification of joint dynamic properties requires accurate models of the joined bodies and an appropriate model coupling method. The bodies to be coupled can be described by their mass, stiffness and damping matrices (M, K, C) or by receptance matrices. Each approach has its advantages and disadvantages. The receptance matrix method requires a high number of measurements. However the measured data can be used directly and no model identification is needed. The experimental identification of the M, K, C matrices feasible for creating precise coupled models is difficult. Therefore, an approach based on a verified FE model can be employed. The two methods of model identification and coupling are discussed using a case study of two bolted beams. Several ways of the receptance matrices measurement simplification and their influence on the accuracy of the results are studied. The effect of noise, measured FRF peak accuracy and data filtering on the resulting coupled receptance matrix is studied as well. The results obtained by the receptance matrix method are compared to the results obtained by the method of coupling the verified FE models. It has been found that the method based on coupling the verified M, K, C matrices proves to be a more reliable approach, which will allow a more precise joint dynamic model identification in the next step

Aerodynamische Eigenschaften der Kogel-Auflieger und ihre Optimierung -Ergebnisse aus den Windkanal-Modellmessungen.

Pressure distribution on the outer surfaces of a scaled trailer unit model was measured with respect to various shape-modifications of the trailer. A new method for flow control in the wake behind the trailer was examined. Pressure measurements are supported by flow visualisation.Available from STL Prague, CZ / NTK - National Technical LibrarySIGLECZCzech Republi