A Complete Geometric Chip Breaking Method Based on Longitudinal-Torsional Composite Ultrasonic Vibration Drilling

Abstract

A complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling. The specific steps of the method are as follows: Step 1, construct a kinematic model of longitudinal-torsional composite ultrasonic vibration drilling; Step 2, construct the motion trajectory equations of two adjacent cutting edges on the tool during the machining process; Step 3, construct a mathematical model of the dynamic cutting thickness during the longitudinal-torsional composite ultrasonic vibration drilling process; Step 4, construct an expression for the minimum cutting thickness; Step 5, obtain the theoretical conditions for achieving complete geometric chip breaking; Step 6, conduct longitudinal-torsional composite ultrasonic vibration drilling experiments, collect chips under different machining parameter conditions and observe their morphologies; Step 7, organize the experimental results to obtain the process parameter matching criteria for achieving complete geometric chip breaking. The calculation process of the present invention is simple and has strong practicability, which is of great significance for improving machining quality and efficiency and reducing machining costs.

Description

Technical Field

[0001] The present invention belongs to the technical field of ultrasonic machining, and particularly relates to a complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling. Background Technique

[0002] In recent years, difficult-to-machine materials such as titanium alloys and superalloys have been widely used in strategic emerging industries such as aerospace, national defense military equipment, and rail transit. For these plastic difficult-to-machine materials, traditional drilling methods have problems such as difficult chip breaking and chip evacuation. The long chips wrapped around the tool are likely to scratch the inner surface of the hole and exacerbate tool damage, resulting in increased processing costs, reduced processing efficiency, and deteriorated processing quality, severely restricting the further application of these difficult-to-machine materials in the industrial field and making the chip breaking and chip evacuation problems of plastic difficult-to-machine materials an important research topic in the manufacturing industries of various countries.

[0003] Ultrasonic vibration drilling technology exhibits excellent process characteristics in the machining of difficult-to-machine materials and thus has broad application prospects. At the same time, as the main chip breaking method of ultrasonic vibration drilling, complete geometric chip breaking has been widely valued by the international academic community and the industry. However, the existing complete geometric chip breaking methods are only applicable to axial ultrasonic vibration drilling. A large number of literatures indicate that longitudinal-torsional composite ultrasonic vibration drilling has more advantages than axial ultrasonic vibration drilling in terms of improving machining quality and reducing tool wear. However, there is a more complex relative motion relationship between the tool and the workpiece during longitudinal-torsional composite ultrasonic vibration drilling, and the dynamic change law of the cutting thickness is also more complex. Therefore, the existing complete geometric chip breaking methods are not applicable to longitudinal-torsional composite ultrasonic vibration drilling, which severely restricts the further development and application of ultrasonic vibration drilling technology. Summary of the Invention

[0004] In order to overcome the above deficiencies, the present invention provides a complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling to solve the problems of difficult chip breaking and poor machining quality during the drilling of plastic difficult-to-machine materials.

[0005] In order to achieve the above object, the technical solution adopted by the present invention is as follows:

[0006] A complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling, and the specific steps of the method are as follows:

[0007] Step 1, according to the relative motion relationship between the tool and the workpiece during longitudinal-torsional composite ultrasonic vibration drilling, construct a basic motion model of longitudinal-torsional composite ultrasonic vibration drilling, and expand the ultrasonic vibration in three-dimensional space along the drill bit rotation direction into two-dimensional vibration in a plane, and then construct a motion model of longitudinal-torsional composite ultrasonic vibration drilling in the expanded plane;

[0008] Step 2: Based on the kinematic model of longitudinal-torsional composite ultrasonic vibration drilling established in Step 1, select any point on the cutting edge of the tool, construct its motion trajectory equation, and on the same tool, select another point at the same distance from the tool rotation axis on the adjacent cutting edge and construct its motion trajectory equation;

[0009] Step 3: Based on the motion trajectory equations of two adjacent cutting edges on the tool during longitudinal-torsional composite ultrasonic vibration drilling obtained in Step 2, calculate the displacement difference in the axial direction, and combine with the rotational displacement of the tool in the rotational direction to obtain the mathematical model of the dynamic cutting thickness during longitudinal-torsional composite ultrasonic vibration drilling;

[0010] Step 4: Based on the mathematical model of the dynamic cutting thickness during longitudinal-torsional composite ultrasonic vibration drilling obtained in Step 3, determine the relationship between the minimum cutting thickness and various process parameters, and construct the expression of the minimum cutting thickness during longitudinal-torsional composite ultrasonic vibration drilling;

[0011] Step 5: Based on the expression of the minimum cutting thickness obtained in Step 4, obtain the theoretical conditions for achieving complete geometric chip breaking during longitudinal-torsional composite ultrasonic vibration drilling;

[0012] Step 6: Select appropriate workpieces and tools, carry out longitudinal-torsional composite ultrasonic vibration drilling experiments with spindle speed, feed rate, and ultrasonic amplitude as processing parameters, collect chips under different processing parameter conditions, and observe their morphologies;

[0013] Step 7: Analyze and organize the experimental results to obtain the process parameter matching criteria for achieving complete geometric chip breaking.

[0014] For further optimization, the frequencies of the longitudinal ultrasonic vibration and the torsional ultrasonic vibration in Step 1 are the same, and the phase difference is 0.

[0015] For further optimization, the tool in Step 2 is a double-edge twist drill, and the motion trajectory equation is the motion trajectory equation in the plane unfolded along the tool rotation direction. The motion trajectory equations of two adjacent cutting edges on the tool are constructed as follows:

[0016]

[0017] In the formula, S(t) and Z(t), S'(t) and Z'(t) are the arc lengths and axial displacements rotated by the two cutting edges within a certain time respectively, A and B are the amplitudes of the longitudinal ultrasonic vibration and the torsional ultrasonic vibration respectively, n and f z are the spindle speed and feed rate respectively, r x is the perpendicular distance from this point to the drill bit axis, and f is the ultrasonic vibration frequency.

[0018] For further optimization, the mathematical model of the dynamic cutting thickness constructed in Step 3 is a parametric equation, as follows:

[0019]

[0020] In the formula, x is the rotational displacement of the tool within a certain period of time, and y is the difference in the axial displacements of two adjacent cutting edges of the tool within the same period of time. is the ultrasonic vibration phase difference between two cutting edges.

[0021] Further optimization: The expression for the minimum cutting thickness constructed in Step 4 is:

[0022]

[0023] In the formula, a cmin is the minimum cutting thickness, and i is the fractional part of the ratio of the ultrasonic vibration frequency to the spindle speed.

[0024] Further optimization: The condition for achieving complete geometric chip breaking in Step 5 is that the minimum cutting thickness is not greater than 0, that is:

[0025]

[0026] Further optimization: The material of the workpiece used in Step 6 is a plastic material, the tool is a double-edge twist drill bit, and the dry cutting method is used in this experiment.

[0027] The beneficial effects of the present invention are as follows:

[0028] 1. The present invention provides a complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling, which solves the problem of difficult chip breaking of plastic difficult-to-machine materials such as titanium alloy. At the same time, it provides a complete geometric chip breaking method applicable to longitudinal-torsional composite ultrasonic vibration drilling, promotes the further application of difficult-to-machine materials in the industrial field, and expands the application range of ultrasonic vibration drilling technology;

[0029] 2. Based on the kinematic model of longitudinal-torsional composite ultrasonic vibration drilling and the tool motion trajectory, the present invention constructs a dynamic cutting thickness mathematical model, which is accurate and reliable in analysis and has a profound theoretical basis, making the process parameter matching criterion for the finally obtained complete geometric chip breaking condition have high reliability and accuracy;

[0030] 3. The present invention comprehensively and fully considers various process parameters, and finally obtains a process parameter matching criterion that meets the complete geometric chip breaking condition. By reasonably setting process parameters using this criterion, the chip breaking effect can be effectively improved, thereby achieving the purpose of reducing processing costs, improving processing quality and processing efficiency. Description of the Drawings

[0031] Figure 1 is a flowchart of the specific implementation manner of the present invention;

[0032] Figure 2 It is the basic motion model diagram of longitudinal-torsional composite ultrasonic vibration drilling;

[0033] Figure 3 It is the motion model diagram of longitudinal-torsional composite ultrasonic vibration drilling unfolded along the drill bit rotation speed direction;

[0034] Figure 4 It is the motion trajectory diagram of two cutting edges of the drill bit in longitudinal-torsional composite ultrasonic vibration drilling;

[0035] Figure 5 It is the changing trend diagram of the cutting thickness in longitudinal-torsional composite ultrasonic vibration drilling;

[0036] Figure 6 It is the relationship diagram between the cutting thickness and the torsional amplitude;

[0037] Figure 7 It is the chip morphology under different machining parameters. Specific implementation manners

[0038] The present invention will be further described in detail below in conjunction with the accompanying drawings and specific embodiments.

[0039] In this embodiment, the experimental equipment used in the longitudinal-torsional composite ultrasonic vibration drilling experiment includes: GSK 980TDB numerical control lathe, drilling tool head, ultrasonic generator, horn, etc.; the tool is a double-edge straight shank twist drill bit made of M42 material with a diameter of 6 mm. The workpiece is made of Ti-6Al-4V titanium alloy material, and the workpiece is a bar with a diameter of 20 mm and a length of 10 mm. The experiment is carried out in a dry environment.

[0040] A complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling includes the following steps:

[0041] Step 1: Construct a kinematic model of longitudinal-torsional composite ultrasonic vibration drilling:

[0042] Longitudinal-torsional composite ultrasonic vibration drilling is based on traditional drilling, and two high-frequency and small-amplitude ultrasonic vibrations are respectively superimposed on the rotation direction and the feed direction of the drill bit. Therefore, the relative motion between the tool and the workpiece includes rotational motion, linear feed motion, longitudinal ultrasonic vibration and torsional ultrasonic vibration, and involves process parameters such as spindle speed, feed rate, longitudinal ultrasonic vibration frequency and torsional ultrasonic vibration frequency, longitudinal ultrasonic vibration amplitude and torsional ultrasonic vibration amplitude. According to the relative motion relationship between the tool and the workpiece, the ultrasonic vibration in the three-dimensional space can be unfolded along the drill bit rotation direction into two-dimensional vibration in the plane, and its kinematic model in the plane is as Figure 3 shown.

[0043] Step 2: Construct the motion trajectory equations of two adjacent cutting edges on the tool during the machining process:

[0044] Select an arbitrary point on the main cutting edge of the tool, and construct its motion trajectory equation in the plane developed along the tool rotation direction, as shown in Equation (1); then select a point at the same distance from the tool rotation axis on the adjacent cutting edge of the same tool. Since the tool is a double-edge twist drill, its two main cutting edges are symmetric, and the angle between them is 180°. Therefore, its motion trajectory equation can be constructed as shown in Equation (2).

[0045]

[0046]

[0047] In the formula, S(t) and Z(t), S'(t) and Z'(t) are the arc lengths and axial displacements rotated by the two cutting edges within a certain time respectively; A and B are the amplitudes of the longitudinal ultrasonic vibration and the torsional ultrasonic vibration respectively; n and f z are the spindle speed and the feed rate respectively; r x is the perpendicular distance from this point to the drill bit axis; f is the ultrasonic vibration frequency.

[0048] Using MATLAB software, the motion trajectories of the two cutting edges of the drill bit during the longitudinal-torsional composite ultrasonic vibration drilling process can be plotted, where the spindle speed n = 900 r / min, the feed rate fz = 0.04 mm / r, the axial amplitude A = 0.02 mm, the torsional amplitude B = 0.003 mm, and the ultrasonic frequency f = 20 KHz.

[0049] Step 3: Construct a mathematical model of the dynamic cutting thickness during the longitudinal-torsional composite ultrasonic vibration drilling process:

[0050] Define M as the number of times the tool vibrates during half a revolution of the drill bit rotation, then there is:

[0051]

[0052] where, K represents the integer part, and i represents the decimal part, then 0 < i < 1. Therefore, the phase difference of the ultrasonic vibration between the two main cutting edges of the drill bit can be expressed as:

[0053]

[0054] It can be seen from Formula (1) and Formula (2) that the axial displacement difference between the two cutting edges during the longitudinal-torsional composite ultrasonic vibration drilling process is:

[0055]

[0056] In longitudinal-torsional composite ultrasonic vibration drilling, the displacement of the drill bit in the rotational direction changes periodically with time, and the torsional ultrasonic vibration also has a great influence on the cutting thickness. It should be a function of the axial displacement between the two cutting edges of the drill bit with respect to the displacement in the rotational direction of the drill bit. Therefore, the cutting thickness of longitudinal-torsional composite ultrasonic vibration drilling is constructed as shown in Equation (6):

[0057]

[0058] In the formula, x is the rotational displacement of the tool within a certain time, y is the difference in axial displacement between two adjacent cutting edges of the tool within the same time, is the ultrasonic vibration phase difference between the two cutting edges. The change trend of the cutting thickness during longitudinal-torsional composite ultrasonic vibration drilling can be plotted using MATLAB software, as shown in the appendix Figure 5 shown.

[0059] Step Four: Construct the expression for the minimum cutting thickness:

[0060] According to Equation (6), the axial displacements of the two cutting edges of the drill bit change periodically and have a minimum value at certain moments, and at this time, there is a minimum cutting thickness. Since the displacement amounts of the two cutting edges of the drill bit in the rotational direction are always the same, the torsional amplitude has no influence on the minimum cutting thickness of longitudinal-torsional composite ultrasonic vibration drilling, as shown in the appendix Figure 6 shown. According to Equation (6), the expression for the minimum cutting thickness during longitudinal-torsional composite ultrasonic vibration drilling is constructed, as shown in Equation (7),

[0061]

[0062] In the formula, a cmin is the minimum cutting thickness.

[0063] Step Five: Obtain the theoretical conditions for achieving complete geometric chip breaking:

[0064] The condition for achieving complete geometric chip breaking is that the minimum cutting thickness is not greater than 0. Therefore, according to Equation (7), the theoretical conditions for satisfying complete geometric chip breaking are:

[0065]

[0066] Step Six: Conduct longitudinal-torsional composite ultrasonic vibration drilling experiments, collect chips under different machining parameter conditions, and observe their morphologies:

[0067] The experimental workpiece material is a Ti-6Al-4V titanium alloy material rod with a diameter of 20 mm and a length of 10 mm, and the cutting tool is a double-edged straight shank twist drill made of M42 material with a diameter of 6 mm. During the experiment, the chips obtained under different processing parameters were collected and processed, and then their macroscopic morphology was collected and analyzed using a camera. The experiment adopted a single-factor design method, and the processing parameters and chip morphology used are as Figure 7 shown.

[0068] Step 7: Organize the experimental results to obtain the process parameter matching criterion for achieving complete geometric chip breaking:

[0069] The experimental results show that traditional drilling is prone to produce long continuous chips when the ultrasonic amplitude A = 0, and the chip breaking effect is poor. Compared with traditional drilling, during the longitudinal-torsional composite ultrasonic vibration drilling process, by reasonably setting the process parameters to meet the conditions for complete geometric chip breaking, a good chip breaking effect can be obtained. Therefore, the process parameter matching criterion for achieving complete geometric chip breaking can be obtained, that is, the spindle speed, feed rate, and ultrasonic amplitude satisfy the following conditions:

[0070]

[0071] The experimental results show that the complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling proposed by the present invention is feasible. Using this method can effectively improve the chip breaking effect, thereby reducing the scratching of the hole wall by the chips and improving the processing quality.

[0072] The above shows and describes the main features, usage methods, basic principles, and advantages of the present invention. Those skilled in the art should understand that the present invention is not limited by the above embodiments. What is described in the above embodiments and the specification only illustrates the principle of the present invention. Without departing from the spirit and scope of the present invention, the present invention will also have various changes and improvements according to the actual situation, and these changes and improvements all fall within the scope of the present invention claimed. The scope of protection claimed by the present invention is defined by the appended claims and their equivalents.

Claims

1. A complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling, characterized in that, The specific steps of the method are as follows: Step 1: Based on the relative motion relationship between the tool and the workpiece during longitudinal-torsional composite ultrasonic vibration drilling, construct a basic motion model for longitudinal-torsional composite ultrasonic vibration drilling, and expand the ultrasonic vibration in three-dimensional space along the drill rotation direction into two-dimensional vibration in a plane, and then construct a motion model for longitudinal-torsional composite ultrasonic vibration drilling in the expanded plane; Step 2: Based on the kinematic model for longitudinal-torsional composite ultrasonic vibration drilling established in Step 1, select any point on the cutting edge of the tool and construct its motion trajectory equation. On the same tool, select another point at the same distance from the tool rotation axis on an adjacent cutting edge and construct its motion trajectory equation; Step 3: Based on the motion trajectory equations of two adjacent cutting edges on the tool during longitudinal-torsional composite ultrasonic vibration drilling obtained in Step 2, calculate the displacement difference in the axial direction, and combine it with the rotational displacement of the tool in the rotation direction to obtain a mathematical model for the dynamic cutting thickness during longitudinal-torsional composite ultrasonic vibration drilling; Step 4: Based on the mathematical model for the dynamic cutting thickness during longitudinal-torsional composite ultrasonic vibration drilling obtained in Step 3, determine the relationship between the minimum cutting thickness and various process parameters, and construct an expression for the minimum cutting thickness during longitudinal-torsional composite ultrasonic vibration drilling; Step 5: Based on the expression for the minimum cutting thickness obtained in Step 4, obtain the theoretical conditions for achieving complete geometric chip breaking during longitudinal-torsional composite ultrasonic vibration drilling; Step 6: Select appropriate workpieces and tools, and conduct longitudinal-torsional composite ultrasonic vibration drilling experiments with spindle speed, feed rate, and ultrasonic amplitude as machining parameters. Collect chips under different machining parameter conditions and observe their morphologies; Step 7: Analyze and organize the experimental results to obtain the process parameter matching criteria for achieving complete geometric chip breaking.

2. The complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling according to claim 1, characterized in that, In Step 1, the longitudinal ultrasonic vibration and the torsional ultrasonic vibration have the same frequency and a phase difference of 0.

3. A complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling as described in claim 1, characterized in that, In Step 2, the tool is a double-edge twist drill, and the motion trajectory equation is the motion trajectory equation in the plane expanded along the tool rotation direction. The motion trajectory equations of two adjacent cutting edges on the tool constructed are as follows: Wherein, S(t) and Z(t), S'(t) and Z'(t) are respectively the arc lengths and axial displacements rotated by two cutting edges within a certain period of time, A and B are respectively the amplitudes of longitudinal ultrasonic vibration and torsional ultrasonic vibration, n and f z are respectively the spindle speed and the feed rate, r x is the perpendicular distance from this point to the drill bit axis, and f is the ultrasonic vibration frequency.

4. A complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling as described in claim 1, characterized in that The mathematical model for the dynamic cutting thickness constructed in Step 3 is a parametric equation, as follows: Where x is the rotational displacement of the cutting tool within a certain period of time, and y is the axial displacement difference between two adjacent cutting edges of the cutting tool within the same period of time. is the ultrasonic vibration phase difference between the two cutting edges.

5. A complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling as claimed in claim 1, characterized in that, The expression for the minimum cutting thickness constructed in Step 4 is: where a cmin is the minimum cutting thickness, and i is the decimal part of the ratio of the ultrasonic vibration frequency to the spindle speed.

6. A complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling as described in claim 1, characterized in that The condition for achieving complete geometric chip breaking in Step 5 is that the minimum cutting thickness is not greater than 0, that is:

7. A complete geometric chip breaking method based on longitudinal-torsional composite ultrasonic vibration drilling as described in claim 1, characterized in that In Step 6, the material of the workpiece used is a plastic material, the tool is a double-edge twist drill, and the dry cutting method is used in this experiment.

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