S. K. Loh

Bio: S. K. Loh is an academic researcher from International Islamic University Malaysia. The author has contributed to research in topics: Modal analysis & Modal testing. The author has an hindex of 3, co-authored 4 publications receiving 31 citations.

Dynamic Modal Analysis of Vertical Machining Centre Components

Abstract: The paper presents a systematic procedure and details of the use of experimental and analytical modal analysis technique for structural dynamic evaluation processes of a vertical machining centre. The main results deal with assessment of the mode shape of the different components of the vertical machining centre. The simplified experimental modal analysis of different components of milling machine was carried out. This model of the different machine tool's structure is made by design software and analyzed by finite element simulation using ABAQUS software to extract the different theoretical mode shape of the components. The model is evaluated and corrected with experimental results by modal testing of the machine components in which the natural frequencies and the shape of vibration modes are analyzed. The analysis resulted in determination of the direction of the maximal compliance of a particular machine component.

Finite element and experimental analysis of dynamic behaviour of Vertical Machining Centre Components by Modal Analysis

Abstract: The paper presents a systematic procedure and details of the use of experimental and analytical modal analysis technique for structural dynamic evaluation processes of a vertical machining centre. The main results deal with assessment of the mode shape of the different components of the vertical machining centre. The simplified experimental modal analysis of different components of milling machine was carried out. This model of the different machine tool's structure is made by design software and analyzed by finite element simulation using ABAQUS software to extract the different theoretical mode shape of the components. The model is evaluated and corrected with experimental results by modal testing of the machine components in which the natural frequencies and the shape of vibration modes are analyzed. The analysis resulted in determination of the direction of the maximal compliance of a particular machine component.

Characterisation of dynamic behaviour of vertical machining centre components: experimental and simulation approaches

Abstract: The paper presents a systematic procedure and details of the use of experimental and analytical modal analysis technique for structural dynamic evaluation processes of a vertical machining centre. The main results deal with assessment of the mode shape of the different components of the vertical machining centre. The simplified experimental modal analysis of different components of milling machine was carried out. This model of the different machine tool's structure is made by design software and analysed by finite element simulation using ABAQUS software to extract the different theoretical mode shape of the components. The model is evaluated and corrected with experimental results by modal testing of the machine components in which the natural frequencies and the shape of vibration modes are analysed. The analysis resulted in determination of the direction of the maximal compliance of a particular machine component.

Dynamic characteristics optimization for a whole vertical machining center based on the configuration of joint stiffness

Abstract: Joint stiffness often has a significant effect on the dynamic characteristics of the whole machine tool. In this paper, a joint stiffness configuration method is developed to optimize the dynamic characteristics of a whole vertical machining center, in which the premise is considering the joint characteristics to create the accurate finite element model (FEM) of the whole machine tool. Identifying the joints parameters including the contact stiffness and damping of the linear guides, bolts, ball screws, and bearings is conducted. Vibration test and finite element simulation are implemented to verify the accuracy of the FEM which is created based on the identified joints parameters by comparing the tested and simulated frequency-response functions (FRFs). With these tested and simulated results, taking the dynamic flexibility at the spindle nose to measure the dynamic characteristics of the whole machine tool, vibration modes, and joints related to a higher modal flexibility and elastic energy distribution ratio can be determined to be the weak modes and joints respectively. Optimization aiming to decrease the modal flexibility is conducted by adopting the orthogonal experiment method to instruct the simulations to predict how stiffness of the weak joints affected the dynamic characteristics of the whole vertical machining center. Thus, an optimal joint stiffness configuration can be obtained by using the range analysis and fuzzy similar preference ratio method to analyze the simulated results. Redoing the simulation with the optimal configuration, results indicate that modal flexibility of each weak mode is decreased obviously. The decreased modal flexibilities and dynamic responses verify that the optimal configuration method is feasible to provide a way for improving the dynamic characteristics of the whole machine tool.

Modal Analysis of the Milling Machine Structure through FEM and Experimental Test

Abstract: Machine tool vibrations have great impact on machining process. In this paper the dynamic behavior and modal parameters of milling machine is presented. For this purpose, the CAD model of the milling machine structure is provided in CATIA and then Natural frequencies and mode shapes of the machine tool structure are carried out through FEM modal analysis under ANSYS Workbench. The model is evaluated and corrected with experimental results by modal testing on FP4M milling machine. Finally, the natural frequencies and mode shapes obtained by both experimental and FEM modal analysis are compared. The results of two methods are in widely agreement.

Influence of Chip Serration Frequency on Chatter Formation During End Milling of Ti6Al4V

Abstract: This paper includes the findings of an experimental study on instabilities of the chip formation process during end milling of Ti6Al4V alloy and the influence of these instabilities on chatter formation. It has been identified that the chip formation process has a discrete nature, associated with the periodic shearing process during machining. The chip formed during machining of titanium alloy Ti6Al4V is found to be mainly with primary serrated teeth appearing in the main body of the chip. Secondary serrated teeth resulting from the coagulation of a certain number of primary serrated teeth also happen to appear at the free or constrained edge of the chip, especially when the system enters into chatter. In order to identify the interaction of these chip instabilities with the prominent natural vibration of the machine tools system components, the different mode frequencies of the vibrating components of the system have been identified using experimental and finite element modal analyses, and vibration responses during actual cutting have also been recorded using an online vibration monitoring system. The vibration signals in frequency domain (fast Fourier transform) have been analyzed to identify the chatter frequencies and the peak amplitude values. Chatter was found to occur at two dominant mode frequencies of the spindle. These mode frequencies at which chatter occurred have been compared with the chip serration frequencies in a wide cutting speed range for different conditions of cutting. It has been concluded from these findings that chatter occurs during end milling due to the resonance of the machine tools system component when the frequency of primary serrated teeth formation is approximately equal to the "prominent natural frequency" modes of the system components, which are the two mode frequencies of the VMC machine spindle in this particular case.

Modal analysis of the vertical moving table of 4-DOF parallel machine tool by FEM and experimental test

Abstract: The vibration of the machine tool has important effect on machining quality of parts. So, in this paper, the dynamic behavior and modal parameters of the vertical moving table of the 4-DOF parallel machine tool are studied using the FEM and experimental methods. The prepared model of the vertical moving table in Solidworks is exported to ANSYS environment. Then, its natural frequencies and mode shapes are extracted using the modal analysis. Then having the FEM results, the exact modal data of the vertical moving table is obtained by the experimental tests. The exciting conditions of the machine tool table are obtained through modeling of machining operations. Finally, the resonance situations of the table are found using the modal data of the table and the cutting parameters of the machine tool. The results of this research can help the machine tool operator to avoid the vibration condition through correct selection of the cutting parameters.