scholarly journals Numerical and experimental modal analysis of machine tool spindles accounting for system decay and its application to chatter avoidance.

2021 ◽  
Author(s):  
Omar Gaber
Keyword(s):  
Natural Frequency ◽  
Surface Finish ◽  
Dynamic Stiffness ◽  
System Change ◽  
Cutting Parameters ◽  
Production Constraints ◽  
Vibrational Characteristics ◽  
The Stability ◽  
Cutting System ◽  
Relevant Boundary Condition

Cycle time, which is the time it takes to machine a certain part, has undergone a great deal of scrutiny as it is directly related to a company's profitability. When trying to machine a part as quickly as possible, selecting the wrong cutting parameters will cause chatter. Tight surface finish and thickness tolerances are usually required by customers. Money lost due to rework and scrap from the destructive nature of chatter has driven a significant number of research studies. It is well established that chatter is directly linked to the natural frequency of the cutting system. As the spindle ages, the vibrational characteristics of the system change. The wear in the spindle bearings causes the system stiffness to decline which results in the changing of natural frequency changing. This change causes the stability lobes to shift. This shift could render a usually stable cut unstable, causing poor surface finish. Excessive chatter can also damage the spindle and shorten its usable life. The objective of this study is to predict the vibrational behaviour of a spindle as it ages. This will be done for spindles utilized under different production constraints. A model of the spindle is also developed by exploiting its Dynamic Stiffness Matrix (DSM) and applying the proper boundary conditions. These results will then be compared to the experimental results obtained from tap testing different spindles to validate and tune the model. Once the static (non-spinning) results are confirmed and the spindle model tuned to represent the real system, the DSM formulation will then be extended to include varying rotational speeds and relevant boundary condition for further modelling purposes. Ultimately, the goal of this research is to develop a procedure to be able to select the correct cutting parameters over the life cycle of the spindle while minimizing the number of tap tests done on the spindle.

scholarly journals Numerical and experimental modal analysis of machine tool spindles accounting for system decay and its application to chatter avoidance.

2021 ◽  
Author(s):  
Omar Gaber
Keyword(s):  
Natural Frequency ◽  
Surface Finish ◽  
Dynamic Stiffness ◽  
System Change ◽  
Cutting Parameters ◽  
Production Constraints ◽  
Vibrational Characteristics ◽  
The Stability ◽  
Cutting System ◽  
Relevant Boundary Condition

Cycle time, which is the time it takes to machine a certain part, has undergone a great deal of scrutiny as it is directly related to a company's profitability. When trying to machine a part as quickly as possible, selecting the wrong cutting parameters will cause chatter. Tight surface finish and thickness tolerances are usually required by customers. Money lost due to rework and scrap from the destructive nature of chatter has driven a significant number of research studies. It is well established that chatter is directly linked to the natural frequency of the cutting system. As the spindle ages, the vibrational characteristics of the system change. The wear in the spindle bearings causes the system stiffness to decline which results in the changing of natural frequency changing. This change causes the stability lobes to shift. This shift could render a usually stable cut unstable, causing poor surface finish. Excessive chatter can also damage the spindle and shorten its usable life. The objective of this study is to predict the vibrational behaviour of a spindle as it ages. This will be done for spindles utilized under different production constraints. A model of the spindle is also developed by exploiting its Dynamic Stiffness Matrix (DSM) and applying the proper boundary conditions. These results will then be compared to the experimental results obtained from tap testing different spindles to validate and tune the model. Once the static (non-spinning) results are confirmed and the spindle model tuned to represent the real system, the DSM formulation will then be extended to include varying rotational speeds and relevant boundary condition for further modelling purposes. Ultimately, the goal of this research is to develop a procedure to be able to select the correct cutting parameters over the life cycle of the spindle while minimizing the number of tap tests done on the spindle.

scholarly journals Effects of Machine Tool Spindle Decay on the Stability Lobe Diagram: An Analytical-Experimental Study

2021 ◽  
Author(s):  
Omar Gaber ◽  
Seyed M. Hashemi
Keyword(s):  
Machine Tool ◽  
Natural Frequency ◽  
Dynamic Stiffness ◽  
Significant Shift ◽  
Stability Lobe Diagram ◽  
Element Analysis ◽  
Stability Lobe ◽  
Machine Tool Spindle ◽  
Linear Spring ◽  
The Stability

An analytical-experimental investigation of machine tool spindle decay and its effects of the system’s stability lobe diagram (SLD) is presented. A dynamic stiffness matrix (DSM)model for the vibration analysis of the OKADA VM500 machine spindle is developed and is validated against Finite Element Analysis (FEA).The model is then refined to incorporate flexibility of the system’s bearings, originally modeled as simply supported boundary conditions, where the bearings are modeled as linear spring elements.The system fundamental frequency obtained from the modal analysis carried on an experimental setup is then used to calibrate the DSM model by tuning the springs’ constants. The resulting natural frequency is also used to determine the 2D stability lobes diagram (SLD) for said spindle. Exploiting the presented approach and calibrated DSM model it is shown that a hypothetical 10% change in the natural frequency would result in a significant shift in the SLD of the spindle system, which should be taken into consideration to ensure chatter-free machining over the spindle’s life cycle.

scholarly journals Optimization in Milling of Polymer Materials for High Quality Surfaces

2021 ◽  
Vol 15 (4) ◽  
pp. 512-520
Author(s):  
Ryota Uchiyama ◽  
Yuki Inoue ◽  
Fumihiro Uchiyama ◽  
Takashi Matsumura ◽  
◽  
...  
Keyword(s):  
Neural Network ◽  
Surface Quality ◽  
Surface Finish ◽  
Cutting Parameters ◽  
Polymer Materials ◽  
Optimization Approach ◽  
High Quality ◽  
Gradient Information ◽  
Surface Finishes ◽  
The Stability

High quality surfaces with transparency are required for manufacturing of plastic products. In cutting of polymer materials, surface quality is sometimes deteriorated by tarnish and/or unequal spaces of area on a surface. The cutting parameters should be determined through understanding of surface finish characteristics. This paper presents an optimization approach in milling of polycarbonate with polycrystal diamond tools in terms of the surface finish. Surfaces are finished with changing the feed rate and the clearance angle of the tool. The surface finishes, then, were observed to classify the deterioration type into welding, adhesion, and the unequal space of cutter marks with measurement of the surface profiles. The measured surface roughnesses are decomposed into the theoretical/geometrical term and the irregular term induced by the thermal and the dynamic effects. A map is presented to characterize the irregular term for the feed rates and the clearance angles. Because the surface roughnesses are measured at discrete sets of the cutting parameters in the actual cutting tests, the process design cannot be conducted to optimize the operation parameters. Therefore, a neural network is applied to associate the cutting parameters with the irregular term in the map. An approach is presented to determine the number of hidden nodes/units in the design of the neural network. Three prominent areas of welding, adhesion, and unequal spaces of the cutter marks, appear in the map of irregular roughness. The map of the surface roughness is made to optimize the cutting process. The applicable feed rates and clearance angles are determined for the tolerable surface roughnesses. The gradient information in the map is used to evaluate the stability/robustness of the surface quality for changing the parameters. The optimum parameters were determined to minimize the gradient information in the applicable feed rates and clearance angles.

scholarly journals Modal analysis of spindles while accounting for system decay and its application to machine tool chatter prevention

2021 ◽  
Author(s):  
Seyed M. Hashemi ◽  
Omar Gaber
Keyword(s):  
Life Span ◽  
Natural Frequencies ◽  
Dynamic Stiffness ◽  
Advanced Manufacturing ◽  
Machining Parameters ◽  
Fundamental Frequencies ◽  
Stability Lobes ◽  
Machine Tool Chatter ◽  
Vibrational Characteristics ◽  
The Stability

This paper investigates the vibrational characteristics of a machining spindle over its life span. The experimental investigation was carried out using tap testing, where the fundamental frequencies of the spindle system were recorded for different spindle categories, namely, ‘production’ and ‘prove-out’ spindles. Focussing on production spindles, the system ageing translated through a reduction in the system’s natural frequency is modelled as changes in the bearings’ stiffness. The experimentally evaluated natural frequencies were then used to calculate the equivalent bearings’ stiffness within the spindle by means of a calibrated dynamic stiffness method (CDSM) at various stages of spindle’s life. A comparison between the stability lobes generated for two different instances in time, in a full slotting cuts process, shows that over the life span of a spindle, the stability lobes would shift sufficiently to cause chatter after initially being stable. Therefore, as the spindle ages, the presented methodology can be exploited to predict the updated machining parameters necessary to avoid unstable chatter conditions.<div><br></div><div>This is a post-peer-review, pre-copyedit version of an article published in The International Journal of Advanced Manufacturing Technology. The final authenticated version is available online at: https://doi.org/10.1007/s00170-015-6979-4 <br></div>

scholarly journals Stability Analysis of Multispan Pipeline Embedded in Temperature-Dependent Matrix

2021 ◽  
Vol 2021 ◽  
pp. 1-12
Author(s):  
Nan Wu ◽  
Yongshou Liu ◽  
Guojun Tong ◽  
Jiayin Dai
Keyword(s):  
Natural Frequency ◽  
Critical Velocity ◽  
Critical Pressure ◽  
Dynamic Stiffness ◽  
Second Order ◽  
Temperature Dependent ◽  
Temperature Changes ◽  
First Order ◽  
The Stability ◽  
Increasing Temperature

In this paper, dynamic stiffness method is used to study the stability of multispan pipelines in temperature-dependent matrix. The effects of temperature changes and different span combinations on the natural frequency, critical velocity, and critical pressure of pipelines are discussed. The main conclusions are obtained and shown as follows. The increase of temperature will lead to the decrease of the first three order natural frequencies. The first two order critical velocities and critical pressure of the system will also decrease with increasing temperature. The change of span combination has no influence on the first-order critical velocity and first-order critical pressure of the system, but it has influence on the second order. The influence of the change of span combination on the first-order natural frequency is regular, but that on the second-order and third-order is not. The increase of the velocity will change the instability form of systems with different span combinations, while the change of the pressure inside the tube will not change the instability form of the system.

scholarly journals Effects of Machine Tool Spindle Decay on the Stability Lobe Diagram: An Analytical-Experimental Study

2021 ◽  
Author(s):  
Omar Gaber ◽  
Seyed M. Hashemi
Keyword(s):  
Machine Tool ◽  
Natural Frequency ◽  
Dynamic Stiffness ◽  
Significant Shift ◽  
Stability Lobe Diagram ◽  
Element Analysis ◽  
Stability Lobe ◽  
Machine Tool Spindle ◽  
Linear Spring ◽  
The Stability

An analytical-experimental investigation of machine tool spindle decay and its effects of the system’s stability lobe diagram (SLD) is presented. A dynamic stiffness matrix (DSM)model for the vibration analysis of the OKADA VM500 machine spindle is developed and is validated against Finite Element Analysis (FEA).The model is then refined to incorporate flexibility of the system’s bearings, originally modeled as simply supported boundary conditions, where the bearings are modeled as linear spring elements.The system fundamental frequency obtained from the modal analysis carried on an experimental setup is then used to calibrate the DSM model by tuning the springs’ constants. The resulting natural frequency is also used to determine the 2D stability lobes diagram (SLD) for said spindle. Exploiting the presented approach and calibrated DSM model it is shown that a hypothetical 10% change in the natural frequency would result in a significant shift in the SLD of the spindle system, which should be taken into consideration to ensure chatter-free machining over the spindle’s life cycle.

scholarly journals Modal analysis of spindles while accounting for system decay and its application to machine tool chatter prevention

2021 ◽  
Author(s):  
Seyed M. Hashemi ◽  
Omar Gaber
Keyword(s):  
Life Span ◽  
Natural Frequencies ◽  
Dynamic Stiffness ◽  
Advanced Manufacturing ◽  
Machining Parameters ◽  
Fundamental Frequencies ◽  
Stability Lobes ◽  
Machine Tool Chatter ◽  
Vibrational Characteristics ◽  
The Stability

This paper investigates the vibrational characteristics of a machining spindle over its life span. The experimental investigation was carried out using tap testing, where the fundamental frequencies of the spindle system were recorded for different spindle categories, namely, ‘production’ and ‘prove-out’ spindles. Focussing on production spindles, the system ageing translated through a reduction in the system’s natural frequency is modelled as changes in the bearings’ stiffness. The experimentally evaluated natural frequencies were then used to calculate the equivalent bearings’ stiffness within the spindle by means of a calibrated dynamic stiffness method (CDSM) at various stages of spindle’s life. A comparison between the stability lobes generated for two different instances in time, in a full slotting cuts process, shows that over the life span of a spindle, the stability lobes would shift sufficiently to cause chatter after initially being stable. Therefore, as the spindle ages, the presented methodology can be exploited to predict the updated machining parameters necessary to avoid unstable chatter conditions.<div><br></div><div>This is a post-peer-review, pre-copyedit version of an article published in The International Journal of Advanced Manufacturing Technology. The final authenticated version is available online at: https://doi.org/10.1007/s00170-015-6979-4 <br></div>

Stability analysis of a two-segment constructed nanotube embedded in an elastic matrix

2019 ◽  
Vol 26 (3-4) ◽  
pp. 241-252
Author(s):  
Guo-jun Tong ◽  
Yong-shou Liu ◽  
Qian Cheng ◽  
Jia-yin Dai
Keyword(s):  
Elastic Modulus ◽  
Natural Frequency ◽  
Critical Velocity ◽  
Dynamic Stiffness ◽  
Elastic Matrix ◽  
Length Ratio ◽  
Mass Ratio ◽  
Modulus Ratio ◽  
Elastic Coefficient ◽  
The Stability

In this paper, the dynamic stiffness method is used to study the stability of a two-segment constructed nanotube embedded in an elastic matrix. The influences of the length ratio, elastic modulus ratio, mass ratio, and elastic coefficient on the stability of the nanotube are investigated. It can be concluded that a change in the elastic coefficient, length ratio, and elastic modulus ratio has no effect on the form of instability of the two-segment constructed nanotube, but a change in the mass ratio has a significant influence on the form of instability of the nanotube. The elastic coefficient of the elastic matrix mainly affects the natural frequency and the critical velocity of the nanotube of the first mode. The change in the length ratio and elastic modulus ratio mainly affects the natural frequency and the critical velocity of the second mode. The mass change in the two materials mainly affects the natural frequency of the nanotube and has no effect on the critical velocity.

Chatter Vibration in Drilling

1988 ◽  
Vol 110 (4) ◽  
pp. 309-314 ◽  
Author(s):  
S. Ema ◽  
H. Fujii ◽  
E. Marui
Keyword(s):  
Natural Frequency ◽  
Cutting Parameters ◽  
Experimental Results ◽  
Chatter Vibration ◽  
Additional Mass ◽  
Regenerative Chatter ◽  
Drill Point ◽  
The Stability

Chatter vibration of long drills has been investigated using several drills with different overhang lengths and special drills with different pieces of additional mass. The frequency, amplitude, initiation boundary, and unstable range of chatter vibration were measured at various cutting parameters. The experimental results showed that the vibration is a regenerative chatter and its frequency is equal to the bending natural frequency of the drill when the drill point is supported in a machined hole. Based upon the experimental results, the stability of chatter vibration was discussed. It was clarified that unstable ranges appear only when the chatter frequency in one workpiece rotation is an odd number.

scholarly journals An Ultra-Low Frequency Two DOFs’ Vibration Isolator Using Positive and Negative Stiffness in Parallel

2016 ◽  
Vol 2016 ◽  
pp. 1-15 ◽  
Author(s):  
Min Wang ◽  
Xuedong Chen ◽  
Xiaoqing Li
Keyword(s):  
Natural Frequency ◽  
Vibration Isolation ◽  
Dynamic Stiffness ◽  
Low Frequency ◽  
Vertical Direction ◽  
Negative Stiffness ◽  
Effective Bandwidth ◽  
Vibration Isolator ◽  
Analysis System ◽  
The Stability

With the improvement of performance in the ultra-precision manufacturing engineering, the requirements for vibration isolation have become increasingly stringent. In order to get wider effective bandwidth and higher performance of vibration isolation in multiple DOFs system, an ultra-low frequency two DOFs’ vibration isolator with positive and negative stiffness in parallel (PNSP) is proposed. The two DOFs’ isolator which combines a positive stiffness (PS) air spring with a negative stiffness (NS) magnetic spring in parallel and combines a PS flat spring with an NS inverted pendulum in parallel is designed to reduce the natural frequency and broaden the effective bandwidth in horizontal and vertical direction. Based on this structure, stiffness models of different components in different directions are established. Compared with a PS isolator, it possesses the characteristic of high-static-low-dynamic stiffness. The simulation curves also provide strong evidence. Last, a real-time active control system and a spectrum testing and analysis system are used for the contrast experiment between the mentioned PNSP structure and PS only. The experimental results demonstrate that the isolator with PNSP can obviously reduce the natural frequency to 1 Hz and simultaneously maintain the stability of the system and consequently verify the validity and superiority of the mentioned structure.

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