A processing method for drilling small-diameter deep holes by self-excited vibration

Abstract

The present invention discloses a method for self-excited vibration drilling of small-diameter deep holes. The method first constructs a dynamic drilling force model for the material and drill bit of the workpiece to be processed, then constructs a motion differential equation for the vibration component, and then performs a Lasik transformation on the differential equation. A frequency domain analytical method is used to obtain a relationship between the drill bit speed and the stiffness of a weak rigidity element, and a steady-state limit diagram for self-excited vibration drilling of small-diameter deep holes is drawn. The drill bit speed and the stiffness parameters of the weak rigidity element are then selected from the region in the steady-state limit diagram where self-excited vibration can be generated. The weak rigidity element of the selected stiffness is then set in a mechanical processing system, and finally the material is drilled into a small-diameter deep hole to achieve self-excited vibration drilling. The present invention only requires the installation of a weak rigidity element in the mechanical processing system, without the need for an additional excitation source device, to achieve the goal of converting continuous cutting into periodic and continuous vibration cutting, thereby improving chip breaking and chip removal capabilities and enhancing the precision and efficiency of drilling small-diameter deep holes.

Description

Technical Field

[0001] The invention belongs to the technical field of mechanical processing, and in particular relates to a processing method for self-excited vibration drilling of small-diameter deep holes. Background Art

[0002] Machining small-diameter deep holes in common metal materials presents a technical challenge in machining. Conventional drilling methods for small-diameter deep holes often suffer from low machining accuracy, poor hole surface quality, low machining efficiency, and susceptibility to drill breakage, due to limitations such as drill bit structural characteristics, chip breaking and evacuation, and cutting speed. Currently, a stepped feed drilling method is commonly used to improve chip evacuation, reduce chip scratching on the hole wall, and enhance surface quality. However, this increases the return stroke and re-feed idle stroke, further reducing machining efficiency. Low-frequency or ultrasonic vibration drilling of small-diameter deep holes can effectively improve chip breaking and evacuation, enhancing machining accuracy and hole surface quality. Low-frequency vibration drilling can also improve machining efficiency, but both methods require specialized external excitation equipment, limiting their application on general-purpose machine tools. Other specialized machining methods, such as electrochemical, laser, and electron beam drilling, are costly and unsuitable for machining small-diameter deep holes in common metal materials.

[0003] Therefore, there is an urgent need to develop a vibration drilling method that can not only improve processing efficiency but also be widely used on ordinary machine tools. Summary of the Invention

[0004] The purpose of the present invention is to solve the deficiencies of the prior art and to provide a method for self-excited vibration drilling of small-diameter deep holes, which has high machining accuracy, high drilling efficiency and low cost.

[0005] Technical Solution

[0006] The present invention installs a weak rigidity element in the machining process system. The rigidity of this weak rigidity element is less than the minimum rigidity of any component of the machining process system (machine tool, fixture, tool, and workpiece). Theoretically, it can be installed between the machine tool and fixture, between the machine tool and tool, or between the workpiece and fixture. During the drilling process, under the action of the drilling force, the weak rigidity element generates self-excited vibrations of a specific frequency and amplitude, causing the drill bit to produce periodic and continuous vibrations relative to the workpiece, thereby achieving vibration drilling of small-diameter deep holes in commonly used metal materials. The specific scheme is as follows:

[0007] A method for self-excited vibration drilling of small-diameter deep holes, comprising the following steps:

[0008] (1) Based on the empirical formula of drilling force, the dynamic drilling force expression during self-excited vibration drilling is constructed by replacing the theoretical cutting thickness with the instantaneous cutting thickness:

[0009] P(z)=k c ·z c ·d·h(t)

[0010] Where: k c is a coefficient determined by the drill geometry and the material of the workpiece to be machined, z c is the number of cutting edges of the drill bit, d is the diameter of the drill bit, and h(t) is the instantaneous cutting thickness of self-excited vibration drilling;

[0011] According to the regenerative chatter theory, the expression of the instantaneous cutting thickness h(t) in self-excited vibration drilling is: h(t) = h0-[z(t)-z(tT)]

[0012] Where h0 is the theoretical cutting thickness, is the feed per edge per revolution of the drill bit, [z(t)-z(tT)] is the dynamic cutting thickness generated by two adjacent cutting vibrations, t is a certain instant of drilling, and T is the period;

[0013] (2) Construct the differential equation of motion of the vibration component between the weak rigidity element of the machining process system and the workpiece to be machined during self-excited vibration cutting;

[0014] Specifically, the self-excited vibration cutting system is approximated as a typical single-degree-of-freedom system. The motion differential equation of the vibration component between the weak rigidity element of the machining process system and the workpiece to be machined (including the tool, tool rod, and other components that vibrate in the self-excited vibration cutting) can be described as:

[0015]

[0016] Where m is the mass of the vibrating component, z is the instantaneous axial displacement of the component, is the instantaneous axial velocity of the component, is the instantaneous axial acceleration of the component, F(z) is the reaction force of the dynamic drilling force P(z) constructed in step (1);

[0017] (3) Performing Laplace transformation on the dynamic drilling force expression during self-excited vibration drilling constructed in step (1) and the motion differential equation constructed in step (2), respectively, and drawing a system block diagram of the self-excited vibration drilling small-diameter deep hole system. From the system block diagram, the transfer function between the instantaneous cutting thickness and the theoretical cutting thickness in the Laplace domain can be obtained;

[0018] (4) Based on the transfer function obtained in step (3), the frequency domain analytical method is used to obtain the relationship between the drill bit speed and the stiffness of the weak rigid element;

[0019] (5) Based on the relationship obtained in step (4), a steady-state limit diagram is drawn when self-excited vibration drilling a small-diameter deep hole;

[0020] (6) According to the steady-state limit diagram drawn in step (5), the drill bit speed and the stiffness parameters of the weak rigid element are selected in the area where self-excited vibration can be generated in the diagram;

[0021] (7) setting the weak rigidity element in the machining process system according to the stiffness parameter of the weak rigidity element selected in step (6);

[0022] (8) The drill speed and theoretical feed rate selected in step (6) are used as cutting parameters, and a drill with predetermined parameters is used to drill a small-diameter deep hole in the workpiece to be processed.

[0023] Furthermore, in step (7), the rigidity of the weak rigidity element is less than the rigidity of the machine tool, fixture, tool and workpiece to be processed in the machining process system.

[0024] Furthermore, in step (7), when a weak rigidity element is provided in the machining process system, the weak rigidity element is provided between the machine tool and the tool, or between the workpiece and the fixture, or between the machine tool and the fixture.

[0025] Beneficial effects of the present invention:

[0026] 1. The present invention provides a method for self-excited vibration drilling of small-diameter deep holes. This method does not require an external excitation device to provide vibration energy, but only requires the addition of a weak rigidity element. The operation is simple and the cost is low.

[0027] 2. The present invention adopts self-excited vibration drilling to improve the chip breaking and chip removal capabilities of drilling. The drilling of small-diameter deep holes can be fed according to the cutting feed parameters for drilling general small-diameter holes. Compared with the graded feeding method, the chip removal return stroke and re-feed idle stroke are reduced. Compared with ultrasonic vibration drilling, the cutting feed speed can be increased, thereby improving the drilling efficiency.

[0028] 3. The weak rigidity element in the present invention can be set between the machine tool and the fixture, between the machine tool and the tool, and between the workpiece and the fixture. Therefore, self-excited vibration drilling can be widely implemented on ordinary machine tools, especially when the weak rigidity element is set between the machine tool and the tool.

[0029] 4. Apparently, when the method of the present invention is used, different drill diameters correspond to different steady-state limit diagrams, and the calculation and adjustment workload is large. However, in fact, the drill diameter is only a proportional coefficient of the relationship between the drill speed and the stiffness of the weak rigid element in step (4) of the present invention. The calculation workload can be reduced by superimposing the steady-state limit diagrams of the largest and smallest diameter drills and selecting a common area.

[0030] 5. The steady-state limit diagram generated using the present invention demonstrates that when the stiffness of the weakly rigid component exceeds a specific value, the machining system will not generate self-excited vibrations. Therefore, once the weakly rigid component is installed, the machining system can be made to generate self-excited vibrations by appropriately adjusting the rotational speed. This can meet the requirements for self-excited vibration drilling of small-diameter deep holes in one or more materials with similar properties, without the need for frequent adjustments to the stiffness of the weakly rigid component. BRIEF DESCRIPTION OF THE DRAWINGS

[0031] Figure 1 The process flow chart of the self-excited vibration drilling method for small diameter deep holes;

[0032] Figure 2 A machining process system for self-excited vibration drilling of small diameter deep holes;

[0033] In the figure, 1-machine tool; 2-weak rigidity component; 3-small diameter drill; 4-workpiece; 5-fixture;

[0034] Figure 3 This is a block diagram of a small-diameter deep-hole self-excited vibration drilling system;

[0035] Figure 4 This is the steady-state limit diagram of self-excited vibration drilling of small-diameter deep holes. DETAILED DESCRIPTION

[0036] The technical solution of the present invention is described in detail below through the accompanying drawings and specific embodiments, but the protection scope of the present invention is not limited to the embodiments.

[0037] Example 1

[0038] like Figure 1 As shown, a method for self-excited vibration drilling of small-diameter deep holes includes the following steps:

[0039] (1) According to the empirical formula of drilling force P(Z=k c ·z c ·d·f, by replacing the theoretical cutting thickness with the instantaneous cutting thickness, the dynamic drilling force expression during self-excited vibration drilling is constructed:

[0040] P(z)=k c ·z c ·d·h(t)

[0041] Where: k c is a coefficient determined by the drill geometry and the material of the workpiece to be machined, z c is the number of cutting edges of the drill bit, d is the diameter of the drill bit, and h(t) is the instantaneous cutting thickness of self-excited vibration drilling;

[0042] Note that the dynamic drilling force is not only related to the metal material properties, drill bit structural parameters and theoretical drilling parameters, but also to the instantaneous cutting thickness of drilling. According to the regenerative chatter theory, the expression of the instantaneous cutting thickness h(t) of self-excited vibration drilling is: h(t) = h0-[z(t)-z(tT)]

[0043] Where h0 is the theoretical cutting thickness, is the feed per edge per revolution of the drill bit, [z(t)-z(tT)] is the dynamic cutting thickness generated by two adjacent cutting vibrations, t is a certain instant of drilling, and T is the period;

[0044] (2) Construct the differential equation of motion of the vibration component between the weak rigidity element of the machining process system and the workpiece to be machined during self-excited vibration cutting;

[0045] Specifically, the self-excited vibration cutting system is approximated as a typical single-degree-of-freedom system. The motion differential equation of the vibration component between the weak rigidity element of the machining process system and the workpiece to be machined (including the tool, tool rod, and other components that vibrate in the self-excited vibration cutting) can be described as:

[0046]

[0047] Where m is the mass of the vibrating component, z is the instantaneous axial displacement of the component, is the instantaneous axial velocity of the component, is the instantaneous axial acceleration of the component, F(z) is the reaction force of the dynamic drilling force P(z) constructed in step (1);

[0048] (3) Perform pull-type transformation on the dynamic drilling force expression constructed in step (1) and the motion differential equation constructed in step (2), and draw the system block diagram of the self-excited vibration drilling small diameter deep hole system, as shown in Figure 2. Figure 3 As shown. From the system block diagram, the transfer function between the instantaneous cutting thickness and the theoretical cutting thickness in the Lagrangian domain can be obtained:

[0049]

[0050] Where, is the transfer function of the vibration component.

[0051] (4) Based on the transfer function obtained in step (3), the frequency domain analytical method is used to obtain the relationship between the drill bit speed and the stiffness of the weak rigid element:

[0052]

[0053] (5) According to the relationship obtained in step (4), the steady-state limit diagram of self-excited vibration drilling of small diameter deep holes is drawn, as shown in Figure 4As shown in the figure, the vertical axis is the flexibility of the weak rigid component, and the horizontal axis is the spindle speed.

[0054] (6) According to the steady-state limit diagram drawn in step (5), the drill bit speed and the stiffness parameters of the weak rigid element are selected in the area where self-excited vibration can be generated, such as Figure 4 ;

[0055] (7) According to the stiffness parameters of the weak rigidity element selected in step (6), the stiffness of the weak rigidity element is less than the stiffness of the machine tool, fixture, tool and workpiece to be processed in the machining process system; the weak rigidity element is set in the machining process system, and the structural diagram of the machining process system is as follows: Figure 2 As shown, the weak rigidity element is arranged between the machine tool and the tool;

[0056] (8) The drill speed and theoretical feed rate selected in step (6) are used as cutting parameters, and a drill with predetermined parameters is used to drill a small-diameter deep hole in the workpiece. During the drilling process, a continuous self-excited vibration drilling phenomenon can be generated.

[0057] As described above, although the present invention has been shown and described with reference to specific preferred embodiments, it should not be construed as limiting the present invention itself. Various changes may be made to it in form and detail without departing from the spirit and scope of the present invention as defined in the appended claims.

Claims

1. A method for self-excited vibration drilling of small diameter deep holes, characterized in that: The following steps are involved: (1) Based on the empirical formula of drilling force, the dynamic drilling force expression during self-excited vibration drilling is constructed by replacing the theoretical cutting thickness with the instantaneous cutting thickness: P(z)=k c ·z c ·d·h(t) Where: k c is a coefficient determined by the drill geometry and the material of the workpiece to be machined, z c is the number of cutting edges of the drill bit, d is the diameter of the drill bit, and h(t) is the instantaneous cutting thickness of self-excited vibration drilling; According to the regenerative chatter theory, the expression of the instantaneous cutting thickness h(t) of self-excited vibration drilling is: h(t) = h0-[z(t)-z(tT)] Where h0 is the theoretical cutting thickness, is the feed per edge per revolution of the drill bit, [z(t)-z(tT)] is the dynamic cutting thickness generated by two adjacent cutting vibrations, t is a certain instant of drilling, and T is the period; (2) Construct the motion differential equation of the vibration component between the weak rigidity element of the machining process system and the workpiece to be machined during self-excited vibration cutting: Where m is the mass of the vibrating component, z is the instantaneous axial displacement of the component, is the instantaneous axial velocity of the component, is the instantaneous axial acceleration of the component, F(z) is the dynamic drilling force reaction force constructed in step (1); (3) The dynamic drilling force expression during self-excited vibration drilling constructed in step (1) and the motion differential equation constructed in step (2) are respectively subjected to Laplace transformation, and the system block diagram of the self-excited vibration drilling small diameter deep hole system is drawn. The transfer function between the instantaneous cutting thickness and the theoretical cutting thickness in the Laplace domain is obtained: Where, is the transfer function of the vibration component; (4) Based on the transfer function obtained in step (3), the frequency domain analytical method is used to obtain the relationship between the drill bit speed and the stiffness of the weak rigid element: (5) Based on the relationship obtained in step (4), a steady-state limit diagram is drawn when self-excited vibration drilling a small-diameter deep hole; (6) According to the steady-state limit diagram drawn in step (5), the drill bit speed and the stiffness parameters of the weak rigid element are selected in the area where self-excited vibration can be generated in the diagram; (7) setting the weak rigidity element in the machining process system according to the stiffness parameter of the weak rigidity element selected in step (6); (8) The drill speed and theoretical feed rate selected in step (6) are used as cutting parameters, and a drill with predetermined parameters is used to drill a small-diameter deep hole in the workpiece to be processed.

2. The method for self-excited vibration drilling of small diameter deep holes according to claim 1, characterized in that: In step (7), the rigidity of the weak rigidity element is less than the rigidity of the machine tool, fixture, tool and workpiece to be processed in the machining process system.

3. The method for self-excited vibration drilling of small diameter deep holes according to claim 1 or 2, characterized in that: In step (7), when a weak rigidity element is provided in the machining process system, the weak rigidity element is provided between the machine tool and the tool, or between the workpiece and the fixture, or between the machine tool and the fixture.

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