• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.117-120
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• 2003

A method for PID controller tuning based on process models for unstable processes was introduced. The optimal. proportional and derivative gains of the AMBs were determined by the tuning method and utilized for the chatter stability analysis in order to search for the chatter-free cutting region. The stability analysis results showed that the optimal gains give wider chatter-free cutting region, and as a result the proposed tuning method was confirmed to be an effective tuning method for determining the optimal gains of the AMBs.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2002.10a
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• pp.440-445
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• 2002

The characteristic equation for regenerative chatter loop including a delay element replaced by a rational function is presented by a linear differential-difference equation, accounting for the dynamics of the AMB controllers, the uncut chip thickness equation and the cutting process as well as the rigid spindle dynamics itself. The chatter stability analysis of a rigid milling spindle suspended by 5-axes active magnetic bearings(AMBs) is also performed to investigate the influences of the damping and stiffness coefficients of AMBs on the chatter free cutting conditions, as they are allowed to vary within the stable region formed by the AMB control gains. Several cutting tests varying the derivative gains of the AMB were performed to investigate the regenerative chatter vibrations, and it was concluded that the theoretical analysis results are in good consistency with the test results.

• Journal of the Korean Society for Precision Engineering
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• v.1 no.2
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• pp.33-40
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• 1984

Chatter is a relative vibration between workpiece and tool in machining of metals, and is an important limiting factor of production rate and surface quality, and also reduces the life of machine-tool itself and its tool. In this study, in order to suppress the machining chatter, the spring and the rubber damper are adopted to the tool post of a lathe. The results obtained in this experimental study are summarized as follows. 1. The spring and the damper employed in the tool post for the suppression of chatter increase the maximum chatter-free depth of cut and optimum values found for spring constant and compressive strain are 95kg/mm, 0.1954 respectively. 2. On the optimum condition resulting in this experimental study, the modified tool post increased 6 times in the maximum chatter-free depth of cut as compared with the conventional tool post.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2013.05a
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• pp.507-508
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• 2013

• Transactions of the Korean Society of Mechanical Engineers
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• v.13 no.5
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• pp.875-885
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• 1989

This work is concerned with the chatter suppression by inserting viscoelastic materials into tool clamping area. Chatter was observed with and without the viscoelastic materials during cutting tests, where the overhang of the tool was made long so that the tool may be a major cause for the chatter. Two viscoelastic materials were used and the effects of thickness and prestrain were investigated. impact tests were performed on the tool in cases where the tool post was set on the cross slide and was free from any boundary conditions. Material properties of the viscoelastic materials were also obtained from resonance test results. The effects on the chatter suppression by the type of the viscoelastic material and prestrain are discussed in relation with the measured material properties.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 1991.04a
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• pp.22-31
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• 1991

Machining with boring bars frequently induce chatter vibration because of the low stiffness and damping of cantilever shape of boring bars. To increase stiffness and damping, a carbon fiber epoxy composite boring bar was designed, manufactured and tested. The natural frequency of the carbon fiber epoxy composite boring bar in the free-free end condition was incerased more than 50% over that of the steel boring bar, and the damping of the carbon fiber epoxy composite boring bar was also increased 450%. The fundamental natural frequency of the carbon fiber epoxycomposite boring bar in the cantilever beam condition was found to be increased 20-30% over that of the steel boring bar in overhang length range 140-200mm. In machining S45C tapered workpieces, the limit of the overhang length of the steel boring bar was about 170mm in cutting speed 140m/min.

• Journal of the Korean Society for Precision Engineering
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• v.6 no.4
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• pp.126-135
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• 1989

In this study, in order to perform dynamic design of machine tools reasonably and effectively, a method was formulated to be applicable to the structures connected by joints having elasticity and damping by using substructure synthesis method. And to analyze chatter-free performance, a 3 dimensional cutting dynamics theory was used. Computer program package for the dynamic design of machine tools was developed by combining those and spplied to improvement of performance of NC lathe. Also, the optimization in the structural modifications of machine tool substructure was studied by evaluating the effects of the substructural modifications on total system performance.

• Proceedings of the Korean Society of Machine Tool Engineers Conference
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• 2004.04a
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• pp.404-409
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• 2004

To maximize the productivity in machining molds and dies, machine tools should operate at high speeds. During the high speed operation of moving frames or spindles, vibration problems are apt to occur if the machine tool structures are made of conventional steel materials with inferior damping characteristics. However, self-excited vibration or chatter is bound to occur during high speed machining when cutting speed exceeds the stability limit of machine tool. Chatter is undesirable because of its adverse effect on surface finish, machining accuracy, and tool life. Furthermore, chatter is a major cause of reducing production rate because, if no remedy can be found, metal removal rates have to be lowered until vibration-free performances is obtained. Also, the resonant vibration of machine tools frequently occurs when operating frequency approaches one of their natural frequencies because machine tools have several natural frequencies due to their many continuous structural elements. However, these vibration problems are closely related to damping characteristics of machine tool structures. The polymer concrete has high potential for machine tool bed due to its good damping characteristics with moderate stiffness. This paper presents the use of polymer concrete and sandwich structures to overcome vibration problems. Also, co-cure bonding method for functional part mounting was exhibited experimentally, by which manufacturing time and cost for polymer concrete bed will be remarkably reduced.

• Proceedings of the Korean Society of Precision Engineering Conference
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• 2003.06a
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• pp.113-116
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• 2003

To maximize the productivity in machining molds and dies, machine tools should operate at high speeds. During the high speed operation of moving frames or spindles, vibration problems are apt to occur if the machine tool structures are made of conventional steel materials with inferior damping characteristics. However, self-excited vibration or chatter is bound to occur during high speed machining when cutting speed exceeds the stability limit of machine tool. Chatter is undesirable because of its adverse effect on surface finish, machining accuracy, and tool lift. Furthermore, chatter is a major cause of reducing production rate because, if no remedy can be found, metal removal rates have to be lowered until vibration-free performances is obtained. Also, the resonant vibration of machine tools frequently occurs when operating frequency approaches one of their natural frequencies because machine tools have several natural frequencies due to their many continuous structural elements. However, these vibration problems are closely related to damping characteristics of machine tool structures. This paper presents the use of polymer concrete and sandwich structures to overcome vibration problems. The polymer concrete has high potential for machine tool bed due to its good damping characteristics with moderate stiffness. In this study, a polymer concrete bed combined with welded steel structure i.e., a hybrid structure was designed and manufactured for a high-speed gantry-type milling. Also. its dynamic characteristics were measured by modal tests.