• Proceedings of the Korean Society of Tribologists and Lubrication Engineers Conference
• /
• 2002.10b
• /
• pp.115-116
• /
• 2002

This study was carried out as one of efforts to overcome difficulties in air bearing design due to low stiffness and low damping. Hydrodynamic effects on hydrodynamic stiffness of a fluid film in a high speed air bearing with tow-row air sources are investigated. The hydrodynamic effects by the high speed over DN 1,000,000 and eccentricity of a proceeding which are not considered in conventional design of an air bearing need to be reconsidered. The hydrodynamic effects, which dominantly influence on the load capacity of air bearing, are caused mainly by proceeding speed, eccentricity, and the source positions. The two-row source arrangement in the air bearing produces quite unique hydrodynamic effects with respect to pressure distribution of the air film. Optimal arrangement of the two-row sources improves performance of an air bearing in film reaction force and loading capacity of high speed spindles. This study compares the pressure distribution by numerical simulation as a function of eccentricity of proceeding and the source positions. The air source position 1/7L form one end of an air bearing was found to be superior to source position of 1/4L. The dynamic stiffness were obtained using a two-dimensional cutting method which can directly measure the cutting reaction forces and the displacements of the spindle in two directions using a tool dynamometer and transducer sensors. Heat generation in the air film can not be negligible over the speed of DN 2,000,000. In order to analysis effects of heat generation on the characteristics of air bearing, high cooling bearing spindle and low cooling bearing spindle were tested and compared. Characteristics of the frequency response of shaft and motion of run out errors were different for the spindle. The test results show that, in the case of low cooling bearing spindle, the stiffness became smaller due to heat generation. The results, which were obtained for high speed region, may be used as a design information for spindle which can be applied to precision devices such as ultra precision grinding and ultra high speed milling.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2000.05a
• /
• pp.922-925
• /
• 2000

Generally, the machining accuracy in ball end milling directly depends on the rotational accuracy affected by the spindle speeds. The effects of spindle speeds for rotational accuracy in the high speed regions are more dominant than those in the low speed regions. This paper will investigate effects that the Increased speed affects on the rotational error according to the increase of a rotational speed and machining characteristics of the high speed ball-end milling in various rotational speeds and on various materials by using the high speed air-bearing spindle.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.19 no.3
• /
• pp.334-339
• /
• 2010

The development of high-speed spindle have been studied extensively for micro machining in advanced industrial countries. The research of miniaturized high-speed air spindle is important part which needs for the micro machining process of high quality. So, This study was to carry out results about design characteristics of miniaturized high-speed air spindle. We had designed 4type turbines and shaft. They were simulated in use the computer simulation programs. We made them as products. They measured RPM (revolutions per minute). As a result of experiments, there was a contrast among 4type Turbines. it reached 384,000rpm in 4.5bar of air pressure. And, We tried to compare the results of measurement whit the results of computer simulation.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.20 no.1
• /
• pp.96-100
• /
• 2011

The hydrostatic bearings have a relatively small run-out comparing to its shape error by fluid film effect in hydrostatic state as like pneumatic bearing and have a high stiffness, load capacity and damping characteristics. As there is no maintenance and semipermanent in these bearing type, it has been usually adopted as main spindle bearing for grinding machine. In this thesis, to develop hydrostatic bearing for high speed spindle, the cooler setting temperature, bearing clearance and nozzle pressure of belt-driven hydrostatic bearing are investigated. The bearing temperature is decreased, as the cooler setting temperature is lower, nozzle pressure is higher and bearing clearance is wider. The front temperature of bearing is nearly $8^{\circ}C$ higher than the rear one up to 13,000 rpm of spindle revolution. The thermal deflection of X-axis is ${\pm}16\;{\mu}m$ in range of 12,000 rpm-13,000 rpm. Therefore, it is conformed that the built-in motor hydrostatic bearing can be used to high speed spindle.

• Journal of the Korean Society of Manufacturing Process Engineers
• /
• v.8 no.1
• /
• pp.10-17
• /
• 2009

Spindle design is very important for the improvement of the competitive power in production cost of high quality machine tools. The important factor in spindle design is not only to improve the natural frequency of spindle but also to reduce displacement of spindle end. In this paper, parameters those influence on static and dynamic stiffness of high-speed spindle have selected form preceding studies. And those selected parameters are applied to Taguchi Method. To perform FEM analysis, bearing conditions are selected with optimized condition. To know how to improve static and dynamic stiffness of machine tool spindle, natural frequency and displacement of spindle end are obtained by FEM analysis. The Taguchi Method was used to draw optimized condition of bearing position and it's stiffness. From these results, amplitude of vibration is enough good less than $3{\mu}m$ pk-pk of the spindle of 40,000rpm manufactured in this work by the optimal design.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2005.06a
• /
• pp.1640-1643
• /
• 2005

This paper presents analysis of dynamic characteristics of a high-speed milling spindle with a drawbar and a built-in motor. The spindle system with a built-in motor can be used to simplify the structure of machine tools, to improve the machining flexibility of machine tools, and to perform the high speed machining. In this system the shaft is usually assumed as a rigid rotor. In this paper, the modal characteristics of drawbar in high-speed milling spindle system due to supporting stiffness between drawbar and shaft and considering the mass and stiffness effects of the built-in motor's rotor are analyzed by numerical method. The result shows enough stiff supports must be provided between shaft and drawbar to prevent occurring drawbar vibration lower than the natural frequency of 1st bending mode of spindle. And considering the mass and stiffness of built-in motor's rotor is important thing to derive more accurate results.

• Journal of the Korean Society of Manufacturing Technology Engineers
• /
• v.5 no.4
• /
• pp.90-97
• /
• 1996

The thermal deformation of a machine tool spindle influences the performance of the manufacturing systems for precision products. In this research, thermal analysis of a high speed machine tool spindle with the rolling bearing and the built-in motor is carried out by using Finite Difference Method. The thermal boundary conditions describing the heat generation in the bearing and built-in motor are considered in the simulation. And various convective boundary conditions are assumed with the empirical formula in the references. From the simulation results, the characteristics of each element affecting the dynamic thermal behaviour of the machine tool spindle system have been clarified. Therefore, this model can be well applied to the future development of the high speed spindle systems.

• Proceedings of the Korean Society for Noise and Vibration Engineering Conference
• /
• 2008.11a
• /
• pp.184-185
• /
• 2008

Modal analysis is an important and essential process in design of a high speed machining center. Generally, modal analysis of a built-in spindle system has not taken the work piece's shape and dimension into consideration. Since small and long work pieces influence greatly the natural frequency of the entire system, the high speed spindle system which continuously makes small machine parts by long work pieces for improvement of machining time has to consider the machining work pieces. Therefore frequency characteristics of the spindle system with long work pieces are studied in this paper.

• Transactions of the Korean Society for Noise and Vibration Engineering
• /
• v.15 no.3 s.96
• /
• pp.297-305
• /
• 2005

A high-speed spindle can be very sensitive to rotating mass unbalance which has harmful effect on many machine tools. Therefore, the balancing procedure to reducevibration in rotating system is certainly needed for all high-speed spindles. An active balancing program using influence coefficient method and an active balancing device of an electro-magnetic type have been applied to the developed high-speed spindle system in this study. A reliable gain-scheduling control using influence coefficients of the reference model although system characteristics are changed is applied. The stability of reference influence coefficients is verified by frequency response functions. The active balancing experiment for the developed high-speed spindle during operation is well performed with an active balancing program and device. As a result, controlled unbalance responses are below the vibration limit at all rotating speed ranges with critical speed.

• Proceedings of the Korean Society of Precision Engineering Conference
• /
• 2000.05a
• /
• pp.1021-1026
• /
• 2000

The thermal characteristics of high-speed air spindle system with built-in motor are studied. Experiment and finite element method analysis obtain temperature rise and temperature distribution of housing. For the analysis three-dimensional model is built and temperature rise and distribution in thermal steady state are computed for each rotational frequency. Generally. It is said that the heat generation of air bearing is negligible. But it is certain that the heat generation of air bearing can not be negligible especially in high-speed conditions Frequency response test for air spindle system is executed. In case that the heat generation of air spindle system is high, natural frequency of the system becomes lower when it reaches thermal steady-state and it means that the stiffness of air hearing becomes smaller due to the change of bearing clearance. It is shown that the temperature rise of all spindle system causes thermal expansion md induces the variation of hearing clearance. In consequence the st illness of air bearing becomes smaller.