Short-Time Acceptance Test for Machine Tools Based on the Random Nature of the Cutting Forces

1972 ◽  
Vol 94 (4) ◽  
pp. 1020-1024 ◽  
Author(s):  
M. O. M. Osman ◽  
T. S. Sankar

A short-time dynamic acceptance test for machine tools based on a single measurement of a coefficient of dynamic stiffness (Kd) is proposed. A feature of this test is that it takes into account the random fluctuation of the cutting forces that will be experienced by the machine tool in actual operation. Kd is defined as the inverse of the standard deviation of the steady state translational dynamic response of the machine tool under these cutting forces and is a function of the static stiffness of the machine-tool-workpiece system, the damping in the machine, and the equivalent intensity coefficient of the random cutting forces. The analytical expression for the coefficient Kd is obtained from the stationary solution of the Fokker-Planck equation that describes the probabilistic response of the machine tool. The form of excitation considered in the final results is the equivalent “white-noise” spectral density of the ensemble of the cutting forces experienced by the particular machine over the range of feed rates and cutting speeds during operations such as roughing, finishing, etc.

2014 ◽  
Vol 657 ◽  
pp. 475-479
Author(s):  
Marius Pascu ◽  
Gheorghe Stan

A very important factor for the hydrostatic guideways is given by the presence of the restrictor on the supply circuit, whose hydraulic resistance may have important effects on the lubricant film behaviour and implicitly, on the static and dynamic stiffness of the system. This paper presents a new method of experimental research regarding the hydrostatic guideway stiffness, depending on the hydraulic resistances values which supply each pocket. During the experiments which approach the influence of the hydraulic resistances values of the restrictors on the hydrostatic guideway stiffness, a centered constant loads of 20, 50 and 100 [daN] was used. The experiments were carried out on an experimental setup composed of an open hydrostatic guideway, having the pocket dimensions of 150x88 [m, supplied with liquid under pressure through means of a pack of adjustable restrictors. The obtained experimental results are presented in both tabular and graphical form and constitute an experimental database which can be used by the machine tools designers and manufacturers. The paper contains recommendations regarding the usage of hydraulic resistances values depending on the machine tool type and size. Also, from the obtained results, recommendations can be made with regard to the type of restrictors to be used, so that the lubricant filtration grade is comprised between admissible values.


2019 ◽  
Vol 19 (3) ◽  
pp. 5-17
Author(s):  
Friedrich BLEICHER ◽  
Christoph REICHL ◽  
Felix LINHARDT ◽  
Peter WIMBERGER ◽  
Christoph HABERSOHN ◽  
...  

Machine tools are highly integrated mechatronic systems consisting of dedicated mechanic design and integrated electrical equipment - in particular drive systems and the CNC-control - to realize the complex relative motion of tool towards work piece. Beside the process related capabilities, like static and dynamic stiffness as well as accuracy behavior and deviation resistance against thermal influence, safety aspects are of major interest. The machine tool enclosure must fulfill multiple requirements like retention capabilities against the moving parts of broken tools, lose work pieces or clamping components. In regular use, the noise emission have to be inhibited at the greatest possible extent by the machine tool enclosure. Nevertheless, the loading door and the moving parts of the workspace envelope are interfaces where noise transmission is harder to be avoided and therefore local noise emissions increase. The aim of the objective investigation is to analyse the noise emission of machine tools to determine the local noise transmission of a machine tool enclosure by using arrays of microphones. By the use of this measuring method, outer surfaces at the front, the side and on the top of the enclosure have been scanned. The local transient acoustic pressures have been recorded using a standard noise source placed on the machine table. In addition, an exemplary manufacturing process has been performed to analyse the frequency dependent location resolved sound emissions.


Processes ◽  
2021 ◽  
Vol 9 (12) ◽  
pp. 2260
Author(s):  
Chunhui Li ◽  
Zhiqiang Song ◽  
Xianghua Huang ◽  
Hui Zhao ◽  
Xuchu Jiang ◽  
...  

Dynamic parameters are the intermediate information of the entirety of machine dynamics. The differences between components have not been combined with the structural vibration in the cutting process, so it is difficult to directly represent the dynamic characteristics of the whole machine related to spatial position. This paper presents a method to identify sensitive parts according to the dynamic stiffness-sensitivity algorithm, which represents the dynamic characteristics of the whole machine tool. In this study, two experiments were carried out, the simulation verification experiment (dynamic experiment with variable stiffness) and modal analysis experiment (vibration test of five-axis gantry milling machine). The key modes of sensitive parts obtained by this method can represent the position-related dynamic characteristics of the whole machine. The characteristic obtained is that the inherent properties of machine-tool structure are independent of excitation. The method proposed in this paper can accurately represent the dynamic characteristics of the whole machine tool.


Author(s):  
Necmettin Kaya ◽  
M. Onur Genç

Abstract In order to improve the dynamic behavior and cutting accuracy of an industrial laser cutting machine tool, a new beam structure was designed using topology optimization technique. Beams hold the cutting head and laser beam mirrors of laser cutting machine tools. Weight, static and dynamic stiffness of the beam affect the dynamic performance of the machine tool. High weight and low dynamic stiffness in high acceleration and deceleration will result in the vibration of the machine body. In this paper, a new beam is designed using topology optimization to reduce the weight of the beam structure. Static stiffness and natural frequencies were obtained by finite element analyses. The mass reduction obtained was 18%, the maximum displacement is reduced by 13% and the first natural frequency of beam is increased by 29 % in comparison to the original beam. Also the use of aluminum instead of steel was examined and the results are compared.


2015 ◽  
Vol 60 (2) ◽  
pp. 1023-1029 ◽  
Author(s):  
N. Kępczak ◽  
W. Pawłowski ◽  
Ł. Kaczmarek

Abstract Cast iron and mineral cast are the materials most often used in the machine structural elements design (bodies, housings, machine tools beds etc.). The materials significantly differ in physical and mechanical properties. The ability to suppress vibration is one of the most important factors determining the dynamic properties of the machine and has a significant impact on the machining capabilities of a machine tool. Recent research and development trends show that there is a clear tendency to move away from the traditional iron casting to the mineral casting, due to better dynamic properties of the latter. However mineral cast as a structural material for the whole machine tools bed turns out to be insufficient due to its poor mechanical strength properties. The best solution should benefit from the advantages of the cast iron and mineral cast materials while minimizing their drawbacks. The paper presents numerical modal analysis of two lathe beds: the first one made of gray cast iron and the second one made of hybrid connection of cast iron and mineral cast. The analysis was conducted in order to determine the dynamic properties of two bodies of similar shapes made in the traditional (cast iron) and innovative hybrid (cast iron and mineral cast) technology. In addition, an analysis of the static structure rigidity of the two beds was performed. During the simulation studies it was found a significant increase in dynamic stiffness and static rigidity of the machine tool body made of hybrid connection of cast iron and mineral cast. The results of numerical simulations have confirmed the desirability of using hybrid construction because the dynamic properties of such a body are more advantageous in comparison with the conventional body made of cast iron.


1980 ◽  
Vol 102 (1) ◽  
pp. 58-63 ◽  
Author(s):  
M. Samaha ◽  
T. S. Sankar

A nonlinear two-degree-of-freedom mathematical model of a general machine tool is considered for describing the responses in translational and rotational modes under the action of the actual randomly fluctuating metal cutting forces in a Gaussian, wide band form. The response process is determined by the Fokker-Planck technique for the simplified case and also by the statistical linearization method for the general case to establish accuracy of the results obtained. Based on the variances of the response derived and the system constants, a dynamic stiffness coefficient Kd is proposed for defining the degree of acceptance of a given machine tool under actual cutting conditions. Numerical results for specific examples are provided for purpose of illustration.


2012 ◽  
Vol 497 ◽  
pp. 68-72 ◽  
Author(s):  
Miki Shinagawa ◽  
Eiji Shamoto

The purpose of this study is to acquire design method of machine tools with higher dynamic stiffness and consequently higher chatter stability. This study focuses on stiffness of main structures and friction damping in guide of a machine tool, because stiffness and friction damping are considered to have major influence on the dynamic stiffness. A special testing machine with variable stiffness and friction was developed to clarify effects of the stiffness of main structures and the friction in guide on the dynamic stiffness and therefore the chatter stability. The stiffness of main structures and the friction in guide were changed experimentally, and it was clarified that the optimal friction force exists at every stiffness condition, and that higher stiffness does not always lead to higher stability.


Author(s):  
Petru A. Pop

The paper has presented a study of cutting forces about dynamic stability of milling machine tools. For that has required the analysis of dynamic machining system (DMS), represented by the interaction between elastic structure of machine tool and cutting process. The cutting force occurred during cutting process is dependent by a certain factors as thickness cut, physics-mechanics properties of workpiece, geometry of shaped edge tool, etc. An important factor, which has direct influenced about DMS, is present of vibration, in special at chatter frequency due to real perturbation and damages of DMS. The magnitude of cutting force depends largely on the tool-work engagement and depth of cut. The dynamic installation has used for study of milling cutting process assured the acquisition of vibration and cutting force on each three axes of milling machine tool. The calculus and interpretation of dynamic tests had done by MATLAB R14.v7.01 Program. Dynamic tests have been more that 150 recordings, by variation of cutting depth for each spindle speeds of machine until occurring chatter. It had used for testing four milling cutters with different geometric parameters and differential pitch of cutter. These dynamic tests are emphasizing the direct influences of cutting forces about dynamic machining system. Thus, by reducing, the magnitude of cutting forces due to suppressing the vibrations and implicit enhanced the dynamic stability of milling machine and quality of machining workpiece.


2021 ◽  
Vol 2021 (3) ◽  
pp. 4548-4555
Author(s):  
A. P. Kuznetsov ◽  
◽  
H. J. Koriath ◽  

Static and dynamic stiffness [N/m] determine the ability of solids to resist constant and variable loads. Both elastic characteristics of a machine tool effect their quality assessment. Thermal stiffness (comprising heat stiffness and temperature stiffness) [W/µm] is a key accuracy indicator of the machine tool's ability to resist temperature influences. The proposed method creates the thermo-physical structure of a machine tool, based on a set of homogeneous heat-active elements and quasi-thermostable links. Quasi-thermostable links retain constant properties when the thermal state of the heat-active elements changes within a given range, building and determining their spatial and temporal relative position. The structural formula is given: < S-thermal link > -<F-function of the thermal behavior of a heat-active element > - <S-thermal link>. When exposed to heat, heat-active elements change their temperature and thermoelastic properties change their temperature and thermoelastic properties with stress, strain, distortion. Thermal behavior F-functions characterize these changes over time. Thermal energy causes a heat exchange in the machine tool and leads to temperature differences, thermoelastic stresses and geometrical deformations. The material used in machine tools enables the thermal conduction, convection and radiation due to its dimensions, volume and surface area, thermal conductivity. Elasticity effects base on thermal linear expansion coefficient, modulus of elasticity, thermal energy storage due to its heat capacity. The analysis of the structural formula defines and describes generalized thermal stiffness indicators of a machine tool as a reaction to thermal effects when the heat sources are constantly active and when the heat source is absent, but only the ambient temperature changes. This paper presents relationships between the thermal stiffness and the thermo-physical property indicators of the machine tool. Examples of thermal stiffness are described for several machine tool types.


Author(s):  
Yong-Mo Moon ◽  
Sridhar Kota

Abstract In this paper, we present a systematic methodology for designing Reconfigurable Machine Tools (RMTs). The synthesis methodology takes as input a set of functional requirements — a set of process plans and outputs a set of kinematically-viable reconfigurable machine tools that meet the given design specifications. We present a mathematical framework for synthesis of machine tools using a library of building blocks. The framework is rooted in (a) graph theoretic methods of enumeration of alternate structural configurations and (b) screw theory that enables us to manipulate matrix representations of motions to identify appropriate kinematic building blocks. The methodology described in this paper provides a mathematical framework to address dynamic stiffness, and accuracy prediction of the kinematically-viable designs that are generated by the synthesis procedure. This methodology has been implemented in a program, called PREMADE (PRogram for REconfigurable MAchine tool DEsign), and the results are validated against commercial machine tool designs.


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