China 
Africa 
Explore chapters and articles related to this topic
Machine Tools
Published in David A. Stephenson, John S. Agapiou, Metal Cutting Theory and Practice, 2018
David A. Stephenson, John S. Agapiou
The rotary seals at the front and rear of the spindle prevent dirt, coolant, and chips from entering the bearings and spindle housing. Seals are even more critical when through-the-spindle pressurized coolant is used because the coolant splashes against the front of the spindle with significant energy. Inadequate sealing has been found to be one of the major failure modes of spindles [171]. Spindles are usually easy to seal using lip seals, labyrinths, packing, face seals, and stuffing boxes. Some seals are designed dynamically so that they do not contact the shaft at running speeds, reducing heat generation. Other types of seals include noncontact types with air purging to prevent leakage. The mean time to failure for most seals is 500–1000 days [154]. The design of bearing seals is discussed in detail in [171, 188]. Rotary unions in machines with high pressure through-spindle coolant often require a minimum coolant pressure to seal; these unions must be changed if the machine is converted to minimum quantity lubrication (MQL) as discussed in Chapter 15.
Machine Tool Dynamics and Vibrations
Published in Osita D. I. Nwokah, Yildirim Hurmuzlu, The Mechanical Systems Design Handbook, 2017
In machine tools moving mechanisms are grouped into spindle and feed drives. The spindle drive provides sufficient angular speed, torque, and power to a rotating spindle shaft, which is held in the spindle housing with roller or magnetic bearings. Spindle shafts with a medium-speed range are connected to the electric motor via belts. There may be a single-step gear reducer and a clutch between the electric motor and spindle shaft. High-speed spindles have electric motors built into the spindle in order to reduce the inertia and friction produced by the motor-spindle shaft coupling. The feed drives carry the table or the carriage. In general, the table is connected to the nut, and the nut houses a lead screw. The screw is connected to the drive motor either directly or via a gear system depending on the feed speed, inertia, and torque reduction requirements. High-speed machine tools may employ linear direct motors and drives without the feed screw and nut, thus avoiding excessive inertia and friction contact elements. The rotating parts such as feed screws and spindles are usually made of steel alloys, which have high elasticity, a surface-hardening property, and resistance against fatigue and cracks under dynamic, cyclic loads.
Investigations into peck drilling process for large aspect ratio microholes in aluminum 6061-T6
Published in Materials and Manufacturing Processes, 2018
S. Ravisubramanian, M. S. Shunmugam
Microdrilling process differs from macrolevel drilling in many aspects. High speeds and stability are important requirements of microdrilling machine spindles. Microdrilling machines can work at high spindle speed because of the critical damping reduction with increase in spindle speed. The spindle speed is also important parameter in microdrilling. Drilling process is more economical when it utilizes high spindle speed for machining accurate microholes on different kinds of workpiece materials. The cutting forces in microdrilling are also influenced by edge radius. The radius on the edge of microtool affects the mechanics of cutting, as change in rake angle along with ploughing effect plays significant role.[15] The stresses induced in the microdrills are related to cutting forces on microdrill.[16] For good quality holes and improved drill life, drilling strategy followed is also an important factor apart from drilling parameters, namely, speed and feed of the spindle. By selecting proper drilling strategy and process parameters, large aspect ratio microholes can be produced. In general, deep-hole drilling refers to machining operation that produces holes having length to diameter ratio of greater than 5. In large aspect ratio or deep-hole drilling, the drill has to be repeatedly withdrawn from the workpiece for chip removal. During such action, the drill point is subjected to unequal forces that are practically inevitable. Special drill head involving BTA design is recommended to overcome the problem of force imbalance.[17] In different research works on microdrilling, it is seen that focus has been on selection of drilling parameters to produce quality holes with good surface finish. The typical work materials used are alumina ceramic, nickel-based super alloy, and austenitic stainless steel.[18,19]
Numerical and experimental analysis of vibration characteristics of spindle system under bearing assembly errors
Published in Mechanics Based Design of Structures and Machines, 2023
Pengfei Wang, Yang Yang, Baogang Wen, Hui Ma, Qingkai Han, Zhong Luo, Xiaopeng Li, Bangchun Wen
Bearings commonly used for machine tool spindles include deep groove ball bearings (DGBBs), angular contact ball bearings (ACBBs), cylindrical roller bearings, double-direction thrust angular contact ball bearings, tapered roller bearings, etc. However, due to the existence of nonlinear contact force, clearance, and variable stiffness excitation, rolling bearings are intrinsically nonlinear. Under the nonlinear support of bearings, the vibration of the spindle system exhibits obvious nonlinear characteristics. To clarify the nonlinear vibration characteristics and the influencing factors of the bearing-spindle system, Xu et al. (2020) and Miao et al. (2021) both discussed the influence of bearing parameters such as radial clearance and contact stiffness on spindle vibration response. Miao et al. (2022) proposed a mathematical expression for the forces of the ACBB installed in pairs and the dynamic cutting force of the ball-end milling cutter, which were coupled with the kinematic differential equations of the spindle system. Hao et al. (2023) proposed a generalized time-varying dynamic model of the motorized spindle, in which incentive factors such as unbalanced magnetic pull, nonlinear rolling bearing force and mass eccentric force were comprehensively considered. The influence of eccentricity, speed, motor and bearing parameters was analyzed. In addition, Liu et al. (2021) considered the influence of heat in the dynamic modeling of spindle-bearing of CNC lathe and established the quasi-static model of ACBB considering the thermal effect. They found that considering bearing thermal effect can reduce contact angle, contact load and stiffness, increase the system amplitude, and enrich the nonlinear characteristics. Alfares, Al-Daihani, and Baroon (2019) analyzed the effects of bearing inner raceway, outer raceway, and ball waviness on the working performance of the grinding machine spindle. They found that among the waviness of the three components, the inner raceway waviness had the greatest influence.