Classifications

• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
  • B23Q17/00—Arrangements for observing, indicating or measuring on machine tools
  • B23Q17/12—Arrangements for observing, indicating or measuring on machine tools for indicating or measuring vibration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23B—TURNING; BORING
  • B23B31/00—Chucks; Expansion mandrels; Adaptations thereof for remote control
  • B23B31/02—Chucks
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23C—MILLING
  • B23C5/00—Milling-cutters
  • B23C5/003—Milling-cutters with vibration suppressing means
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23Q—DETAILS, COMPONENTS, OR ACCESSORIES FOR MACHINE TOOLS, e.g. ARRANGEMENTS FOR COPYING OR CONTROLLING; MACHINE TOOLS IN GENERAL CHARACTERISED BY THE CONSTRUCTION OF PARTICULAR DETAILS OR COMPONENTS; COMBINATIONS OR ASSOCIATIONS OF METAL-WORKING MACHINES, NOT DIRECTED TO A PARTICULAR RESULT
  • B23Q11/00—Accessories fitted to machine tools for keeping tools or parts of the machine in good working condition or for cooling work; Safety devices specially combined with or arranged in, or specially adapted for use in connection with, machine tools
  • B23Q11/0032—Arrangements for preventing or isolating vibrations in parts of the machine
  • B23Q11/0039—Arrangements for preventing or isolating vibrations in parts of the machine by changing the natural frequency of the system or by continuously changing the frequency of the force which causes the vibration
• • B—PERFORMING OPERATIONS; TRANSPORTING
  • B23—MACHINE TOOLS; METAL-WORKING NOT OTHERWISE PROVIDED FOR
  • B23B—TURNING; BORING
  • B23B2250/00—Compensating adverse effects during turning, boring or drilling
  • B23B2250/16—Damping of vibrations

Definitions

• the present invention is related to a method and a product developed to solve the chatter problem in milling processes in machining centers.
• Schmitz [4] has achieved modal interaction in spindle-tool holder-tool (MTT) systems, adjusted the tool length and reduced the tool tip vibrations in order to provide a solution for the chatter problem.
• Schmitz has empirically matched the fundamental natural frequency of the tool to a natural frequency of the spindle-tool holder (MT) substructure by using a "trial/error" approach.
• FFF Frequency Response Function
• Mohammadi et al. [6] with the aim of maximizing dynamic stiffness in machining centers, have optimized the tool overhang length by means of a systematic method that is based on an analytical solution.
• Optimal tool holder selection has been carried out by using the same method as well.
• tool length adjustment is the least common method used for eliminating chatter vibrations. Furthermore, reducing tool tip vibrations is not possible by optimizing the overhang length of the tool in some cases.
• tool holders exist as ready-made parts and it may not be possible to create tuned mass damper effect in some machining centers by using tool holder designs available.
• an optimized system prevents the machine and other elements from sustaining damage due to chatter vibrations of high magnitude.
• spindle bearings of machining centers sustain damage due to being exposed to chatter for extended periods of time and hence, they require replacement. Consequently, this implies bringing the machine to a halt in addition to costs incur from repairs and may result in critical disruptions in the production at facilities of mass production.
• fretting wear on tool holder surfaces which are exposed to chatter for extended periods, and which come into contact with the spindle, shortens the physical life of these elements which cannot be repaired in terms of both precision and contact rigidity in many cases.
• the present invention with the aim of overcoming all the disadvantages mentioned above and of introducing further advantages into the relevant technical field, is related to a method and product developed to solve the chatter problem in milling processes in machining centers.
• the present invention changes the dynamics of the system and provides a solution that reduces the vibration problem.
• the object of the present invention is to ensure that milling processes are carried out with a material removal rate (MRR) that features further depth and higher stability (chatter-free) by increasing the stability of the process against chattering.
• MRR material removal rate
• Another object of the present invention is to provide a system and a method that enable improving the dynamic stiffness of the system by using extensions in milling tools.
• Figure 1 illustrates a typical stability lobe diagram (Stable region and unstable region are shown, biim unit is mm, n is rpm).
• Figure 2 illustrates the MTUT system.
• Figure 3 illustrates (a) the FRF of the tool tip with 40 mm tool holder extension length and with 50 mm tool overhang length in the MTUT system, and (b) FRF of the tool tip in the same system (In graphs, units of are m/N, and the frequency unit is Hz).
• Figure 4 illustrates the FRF of the tool tip with 24 mm tool holder extension length and with 50 mm tool overhang length (The MTUT system with UT subsystem, optimal tool holder extension length and arbitrary tool length is shown.
• unit is m/N, and the frequency unit is Hz).
• Figure 5 illustrates the FRF of the tool point with 47 mm tool holder extension length and with 39 mm tool overhang length (The MTUT system with UT subsystem, optimal tool holder extension length and arbitrary tool length is shown.
• unit is m/N, and the frequency unit is Hz).
• Figure 6 illustrates the FRFs of the tool tip (In the graph,
• Figure 7 illustrates the stability diagrams (biim unit is mm, n is rpm).
• Figure 8 illustrates the view in which the Tool Holder, Front Bearing, Rear Bearing, and Spindle are shown together.
• Figure 9 illustrates the tool holder extension.
• Figure 10 illustrates the tool element number 3.
• Figure 11 illustrates the view in which the tool Holder Extension, Tool and Tool Holder, Front Bearing, Rear Bearing, and the Spindle are shown together.
• Figure 12 illustrates the flowchart of the optimization methodology that enables improving the dynamic stiffness in milling tools. Description of the Elements and Parts that Constitute the Invention
• the present invention is proposed with the aim of solving the chatter problem in milling processes in machining centers.
• the method and the product proposed herein change the dynamics of the system and provides a solution that reduces the vibration problem.
• the stability of the process against the chattering is increased, thereby substantially improving the stable (chatter-free) material removal rate (MRR) and the efficiency of the operation.
• Tool holder extensions are used instead of long milling tools in order to reduce the costs in milling operations that require reaching areas far from the tool holder point.
• the conception implying that such extensions increase the flexibility of the system, and therefore the vibrations produced during the milling process is a widespread belief.
• studies conducted in line with the present invention demonstrated that such extensions, once design parameters thereof are optimized, can produce tuned mass damper effect, and further can improve the dynamic stiffness of the milling system.
• the length of the cutting tool was also considered as a variable in the optimization problem in addition to the design parameters of tool holder extensions.
• significant improvement was achieved on the stability limit of a process, i.e., the highest vibration-free milling depth per spindle revolution speed and accordingly, the manufacturing efficiency.
• the method proposed in the present invention seeks to enable designing a product unique to a machining center and to provide a solution for the chatter problem in machining centers.
• the eigenvalue A of the dynamic cutting system can be expressed as follows ao and ai are parameters expanded below the formula. These are shown as such in order to abbreviate the formula.
• Stability limits are related to the FRF of the tool tip as indicated in the equation. Thus, the stability limit of the process can be increased by decreasing the maximum amplitude of the tool tip FRF.
• the tool tip dynamics of the MTUT system may be analytically modelled by using Receptance Coupling Substructure Analysis.
• FRFs of every component may be calculated by using Timoshenko Beam Theory, and subsequently, tool tip dynamics of the combined MTUT system may be obtained by considering the interface dynamics between the components.
• FRF matrices of Timoshenko Beam with free-free boundary conditions may be formulated as indicated below [2] :
• H, L, N, P correspond to receptance functions expressed by the equations given below [2]: Here and respectively denote the transverse and rotational displacement on the f coordinate; respectively denote the force and the moment applied on the j coordinate.
• Figure 2 illustrates the components and the coupling points of the MTUT system.
• MT subsystem indicates the spindle-tool holder subsystem, while U indicates the tool holder extension and T indicates the tool.
• the MT subsystem comprises of spindle, tool holder, front bearings, and the rear bearings.
• Numbers 1 2 2 1 shown in Figure 2 correspond to the coordinates required for the modelling of the system by using Receptance Coupling Substructure Analysis.
• the FRF matrix of the tool holder extension tip may be written as follows by using Receptance Coupling Substructure Analysis method.
• [MT ⁇ ] denotes the FRF matrix of the spindle-tool holder tip, and denote the direct and the cross FRFs of the tool holder extension. denotes the interface dynamics between the tool holder and the tool holder extension. may be calculated by means of the inverse Receptance Coupling Substructure Analysis as follows. corresponds to the cross FRF matrix of the tool holder extension.
• FRF matrix at the tool tip is calculated as follows.
• the aim here is to produce a tuned mass damper effect by creating a modal interaction between the subsystems of a machining center and to decrease the maximum amplitude of the tool tip FRF, i.e., to increase the dynamic stiffness of the system.
• Various methods have been proposed in the literature in order to determine the optimal parameters of tuned mass dampers. In this study, optimal parameters are determined by using the minimax approach.
• the aim behind the minimax approach is to determine design parameters that minimizes the maximum amplitude of the tool tip FRF, which is a complex function, within a given frequency range [3]. Optimization problem and the objective function thereof may be formulated as follows.
• x denotes the design parameters to be optimized.
• the optimization problem may be univariate or multivariate.
• the FRF matrix has a magnitude of 2*2 as it can be understood from equation (5).
• the expanded form of the tool tip FRF matrix is as follows. used in the plotting of the stability lobe diagram is the direct frequency response function of the tool tip of the MTUT system.
• Tool tip FRF of the modelled MTUT system is plotted in Figure 3a, and a dominant mode was observed at 1700 Hz.
• FRF of the MT subsystem is plotted in Figure 3b and modes at 1100 Hz, 1930 Hz, and 3620 Hz that may be used to produce tuned mass damper effect by creating modal interaction were observed.
• optimization problem is formulated as follows:
• the length of the optimal tool holder extension was sought in a range between 20 mm and 50 mm.
• the length of the tool holder extension that minimizes the maximum amplitude of the tool tip FRF was determined to be 24 mm.
• FRF of the modified tool tip is plotted in Figure 4.
• the same graph further shows the FRF of cantilevered tool holder extension and tool (UT) subsystem coupled to the wall with interface dynamics As is seen, a mode of the TU subsystem was moved to 1930 Hz, and a modal interaction was created between the MT and UT subsystems.
• l 7 denotes the overhang length of the tool.
• Optimal tool holder extension length and tool overhang length were determined as 47 mm and 39 mm, respectively.
• the modified tool tip FRF of the MTUT system is plotted in Figure 5. As it can be observed, while the peak of the FRF magnitude was with the optimization of the tool holder extension length only, it decreased to with the simultaneous optimization of both the tool holder extension length and the tool overhang length.
• the optimal tool overhang length was determined to be 55,5 mm.
• FRF of the tool tip optimized for the MTT system is plotted in Figure 6. Modified tool tip FRFs were compared for MTT and MTUT systems in the same graph. As it can be seen from the FRF obtained by optimizing the overhang length of the tool in the MTT system, positioning a piece with the optimized dimensions between the tool holder and the tool increased the tuned mass damper effect despite the increase in the effective length in milling.
• Tool point dynamics can be changed as desired and in a practical manner by optimizing the design parameters of tool holder extensions. Moreover, when compared to previously proposed methods, substantially better results can be achieved in certain machining centers by means of the simultaneous optimization of geometric parameters of both the tool holder extension and the cutter tool itself.
• the method proposed herein allows for producing tuned mass damper effects through multivariate optimization of complex mechanical systems.
• the FRF of the system can be changed as desired without using any additional devices.
• the design of optomechanical systems, where vibration problems have significance can be optimized according to the proposed method in order to dampen vibrations. It may be possible to create subcomponents in sample designs and to produce tuned mass damper effects in the system by ensuring modal interaction among them.
• Multivariate optimization proposed herein can be used for frequency matching between the components.
• the present invention is a system that aims to solve chatter problem in milling processes carried out in machining centers, wherein said system possesses the characteristics given below:
• the present invention eliminates chatter vibrations in milling processes by determining the characteristics of system components in a proper and optimal manner, and without the need for an additional damping device. This has the potential of increasing the efficiency of milling processes, which are widely used in various industries, substantially, and thus, making significant savings in terms of both costs and time. Moreover, it is known for a fact that eliminating chatter vibrations significantly improves the physical life of tools, which in turn, will provide substantial cost savings for a plurality of industries [7].
• extension elements and milling tools are manufactured through mass production and used in machines and spindles with different dynamic characteristics. Considering the fact that dominant frequencies of several types of machines and spindles used in the industry vary drastically, the importance of having a wide effective frequency range can be understood more clearly.
• a system that enables improving the dynamic stiffness in milling tools, characterized in that it comprises a tool holder extension (U) (2) that is attached to the tip of a spindle-tool holder (MT) and that is positioned between the spindle-tool holder (MT) and the tool (T) (3) in order to solve the chatter problem in milling processes in machining centers.
• U tool holder extension
• MT spindle-tool holder
• T tool
• a method for operating the system that enables improving the dynamic stiffness by using extensions in milling tools in the method developed with the present invention, characterized in that, said method comprises the process steps of;
• MTUT system that consists of a tool holder extension with an arbitrary geometry and a tool with an arbitrary overhang length by applying the hammer impact test

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• Engineering & Computer Science (AREA)
• Mechanical Engineering (AREA)
• Numerical Control (AREA)
• Auxiliary Devices For Machine Tools (AREA)
• Milling Processes (AREA)
• Automatic Control Of Machine Tools (AREA)

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Publications (2)

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• 2020
  • 2020-12-25 TR TR2020/21810A patent/TR202021810A1/tr unknown
• 2021
  • 2021-11-19 WO PCT/TR2021/051242 patent/WO2022139738A1/en not_active Ceased
  • 2021-11-19 EP EP21911718.1A patent/EP4263124A4/de active Pending

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