RU2412023C2 - Method of vibration drilling with fine crushing of chips - Google Patents

Abstract

FIELD: process engineering.

SUBSTANCE: invention relates to machining methods, namely, to drilling of bores with application of vibrations on drilling tools. Constant and variable magnetic fields are use to affect spindle assembly with shaft, flexible elements and appliance to make tool reciprocate. Tool is vibrated and fed. Tool reciprocation is effected at vibration frequency of 500 to 2000 Hz. Note here that vibration amplitude is set equal to A₁≤0.5S_F, where S_F is tool feed.

EFFECT: better bore shaping and bore surface quality, higher efficiency of machining and longer life of tool.

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Description

The invention relates to the processing of materials by cutting with the imposition of external vibrational vibrations on the tool when drilling holes.

A known method of processing metal by cutting, characterized in that the tool along with the main rotational movement is informed by an additional oscillatory movement relative to the workpiece, it is called - vibration cutting. Such cutting is used for crushing chips in the processing of difficult materials (stainless and heat-resistant steels), author D. Kumabe (Kumabe D. Vibration cutting / D. Kumabe, trans. From Japanese S.L. Maslennikova // Ed. I.I. . Portnova, VV Belova. - M.: Mechanical Engineering, 1985. - 424 p., See s.31-43) - [1].

Closest to the claimed solution is the method presented in the works of the domestic author V.N. Poduraev (V. Poduraev, Cutting with vibrations. - M.: Mechanical Engineering, 1970. - 350 p.) [2].

The known method comprises a tool on which low-frequency (up to 150-200 Hz) vibrational vibrations are applied, which are axial (in the direction of the longitudinal feed of the tool; radial (in the direction of the transverse feed of the tool) or tangential (directed tangentially to the surface of the workpiece).

The disadvantage of the prototype method is the inability to control the relationship between the frequency and amplitude of the oscillations, as well as their dependence on the processed material, tool and cutting conditions, which ultimately does not provide the ability to conduct a high-performance process with fine crushing of chips.

The technical result of the invention is aimed at increasing the intensification of the chip crushing process, bringing it to fine crushing, which allows forcing the drilling process and improving the quality of processing.

This is achieved by the fact that there is a connection in a single process in the range from 500 to 2000 Hz (which were not previously studied and not used) with the process discontinuity - tool feed and phase angle of rotation of the spindle shaft, providing fine crushing of the chips.

Thus, to solve the problem, a method is proposed for intensifying crushing of chips from drain to fine by increasing the discreteness of cutting with combined high-frequency vibration cutting.

The essence of the method is illustrated by the drawings. Figure 1 shows the construction of the sweep of the machined surface obtained during cutting with axial vibrations at the amplitude and processing modes that provide frequent interruption of the cutting process, which ensures the formation of small chips in the contact zone between the drill and the workpiece) [1].

Figure 2 shows a diagram of a developed device that implements the proposed method of processing combined drilling.

The method is as follows. The tool system with an elastic spindle shaft, in which the drill bit (tool) is held, is given harmonic vibrations in the high-frequency range (500 ... 2000 Hz) and can withstand a strictly defined discontinuity of the vibration drilling process, determined by the ratio of the process parameters in the form of a specific function of the form A _h = f (S _p , τ ₀ ), where the frequency of vibration impacts (A _h ) is interconnected with the tool feed S _p and the phase angle of rotation of the shaft τ ₀ .

Thus, in order to implement the method, it is necessary to carry out at least three consecutive actions (operations):

1) to give the instrument forced high-frequency oscillations in the range of 500 ... 2000 Hz;

2) to establish the technological modes of processing according to the amplitude of the oscillations, having endured the relationship of the form of the function A ₁ = f (S _p ), i.e., the amplitude of the oscillations with the feed rate of the tool.

This operation is guaranteed to provide fine crushing chips. Moreover, the combination of high-frequency vibration drilling with the use of additional forced interruption of the drilling process during the processing phases with a step-by-step scheme for removing allowance along the depth of the hole in total provides a high-performance and high-quality treatment of holes in metals, including corrosion-resistant steels.

Justification of the method by confirming calculations. Based on the calculation of the cutting length l _T = v / f in one cycle of vibrational vibration cutting, it was found that in order to increase the cutting speed and productivity, it is necessary to increase the vibration frequency to the maximum possible level. Therefore, it is advisable to create dynamic oscillatory systems of the instrument having high oscillation frequencies (over 500 Hz) and sufficient power.

At a constant oscillation frequency of the cutting wedge (cutting element of the drill), the length l _T decreases as the cutting speed decreases. If the cutting speed is kept constant, then an increase in the oscillation frequency leads to a decrease in l _T.

Figure 1 shows a graphical construction of the scan-machined surface obtained by cutting with axial vibrations and amplitude, providing sufficient interruption of the cutting process [1]. Accepted designations: f - frequency of oscillations (instrument); T = l / f is the period of oscillation of the cutter; ω is the circular oscillation frequency; y - moving the cutter; v _b is the vibration velocity of the tool; v is the cutting speed; v _c is the critical velocity; S _p - axial feed.

On the surface, thin lines show the cutting edges of the tool after a quarter of the oscillation period. The dashed lines indicate the traces of the tool tip during uniform cutting, i.e. when cutting with constant feed. Here, cross sections of the sheared layer are shaded after a quarter of the oscillation period. The trajectories of the tool tip during cutting with vibrations are shown by solid lines; the intersection lines of surfaces formed by the movement of the main cutting edge of the cutter (to the right of the line) and the auxiliary cutting edge at the next revolution of the part (to the left of the line) are also shown. During the construction, the tool vibrations were accepted harmonic.

The circumference describing the machined surface is significantly longer than the tool feed per part revolution, i.e. πD _d > S _p (figure 1) [1]. Therefore, the paths of the tip of the cutting edge at two adjacent revolutions do not differ much from sinusoids with the same frequency and amplitude, shifted relative to each other along the x _p axis by the feed amount and along the z _p axis by the phase angle τ ₀ . This angle characterizes the length of the part of the wave of oscillations that did not fit perfectly on one revolution of the unfolded surface of the hole in the part, and can be determined as follows.

The phase angle τ ₀ is determined by the ratio between the circular oscillation frequency ω and the angular velocity ω _d :

можно представить как сумму его целой части k, являющейся числом волн колебаний, откладывающихся нацело на одном обороте режущей кромки по поверхности, и дробной q:Attitude

can be represented as the sum of its integer part k, which is the number of oscillation waves deposited entirely on one revolution of the cutting edge over the surface, and fractional q:

поэтомуObviously, the relative position of the sinusoids is determined only by the fractional part of the relation

so

We indicate an addition to the condition, due to which the chips are crushed. We derive a formula that will show how many parts the chip is crushed in one revolution of the drill for given values of the spindle speed n and the oscillation frequency of the drill f, i.e. we get

where k is the number of separated parts of the chips formed during one revolution of the drill, pcs;

f is the oscillation frequency of the drill from an external source of oscillation, Hz;

n is the rotational speed of the drill, rpm

With a constant speed of rotation of the drill (n = const) and an increasing frequency of oscillation of the drill, the chips will be split into a larger number of parts in one revolution of the drill. Provided that the volume of detachable chips for one revolution of the drill is the same at any frequency of oscillation of the drill, it can be assumed that the higher the oscillation frequency of the drill, the smaller the chip. It was established empirically that the optimal vibration frequency of the drill is in the range 500 ... 2000 Hz.

In the work (Poduraev V.N. Physical features of the vibration drilling process / V.N. Poduraev, V.I. Valikov // Cutting of hard-to-work materials. MDNTP. 1969. S.95-101 - [3]) it is noted that with vibration When drilling, the ratio of the axial oscillation frequency of the drill f to the spindle speed n is important:

where K is the number of complete periods of axial vibrations of the drill during its half-revolution;

i is the correct fraction, numerically equal to the remainder of the oscillation period that occurs during the same half-turn of the drill.

When cutting with axial vibrations, the distance a is the current value of the chip thickness when axial harmonious vibrations are superimposed. It depends on the feed, the amplitude of the oscillations A _h , the phase angle τ = ω · t and the phase angle and is equal to:

The value of a determines the height of the microroughness h ₁ and the cross-sectional area of the cut layer F ₁ , therefore, we have

The microroughness h _{1 is} proportional to a , the area F _{1 is} almost proportional to a . When τ ₀ = π (i = 0.5), the amplitude of vibrations that ensures crushing of the chips is the smallest: A _h = 0.5 · S _p .

If A ₁ is the maximum value of the periodic oscillation strength, then F ₁ (t) = A ₁ sin (ωt). The possibilities of crushing chips and the quality of the processed surface are largely determined by the values of a _min and a _max . When a = a _min, the cross-sectional area of the cut layer is the smallest and, accordingly, the most likely chip break. When a = a _{max, the} height of the microroughness is greatest, its value determines the roughness of the formed surface. The values of a _min and a _{max are} found as a result of studying the function at the extremum:

where from

Reducing the cross-sectional area of the cut layer to F ₁ = F ₁ min is a prerequisite for fracture chips. Machining with axial vibrations due to instant interruption of the cutting process ensures guaranteed chip crushing regardless of the processing conditions, i.e. by reducing F ₁ min to zero. From the second expression of system (9) we have

Expression (10) is a condition for reliable fine crushing of chips during processing of any materials and specified parameters of the technological process. In a generalized form, we have the representation of formula (10) as a function of A _h = f (S _p , τ ₀ ), where A _h is the oscillation frequency, S _p is the tool feed, and τ ₀ is the phase angle of rotation of the shaft.

не должно быть целым числом. Практически целесообразным представляется следующее ограничение:It can be seen from expression (10) that the amplitude guaranteeing chip crushing depends on the feed S _p and also on the angle τ _0. As a result, we have the following: for τ ₀ = 0 (q = 0) we get that A ₁ → ∞. To obtain a limited amount of chips by expression (2), the ratio

should not be an integer. The following limitation seems practical:

Then follows 0.16≤q≤0.833, i.e. the range of q satisfying condition (11) is quite large. When τ ₀ = π (q = 0.5), the smallest amplitude of oscillations providing fine crushing of the chip is

Thus, the relationship between the necessary conditions is indicated in order to implement the proposed method - the actions under paragraph two.

The practical implementation of the proposed method is tested on typical modes of vibration drilling holes. So, when using a drill with a diameter of 1.5 mm and drilling steel 1X18H9T at n = 2800 rpm, S = 30 mm, vibration amplitude A = 12 ... 15 μm, minimum frequencies of the order of f = 500 Hz, the duration of one revolution of the machine spindle is not more than 0.021 s, i.e. for one revolution of the drill. In this case, the chips are crushed to a minimum of four fractional parts. Such shavings can be easily removed, it does not clog the screw channels of the drill and almost does not impede the flow of cutting fluid to the cutting edges. Thanks to this method, it becomes possible to carry out a mechanical feed and automate the operation of drilling small holes. The advantage of the proposed method is that high-frequency vibrational vibrations, applied from the outside, stabilize the growth of the rake angle when cutting, and when leaving the cutting zone they reduce the rake angle of the drill, which increases the tool life, creates the effect of smoothing over the surface of the hole and improves the quality of processing.

Vibrations in the axial direction provide effective and reliable chip crushing, satisfactory roughness (up to Ra = 2.5 μm), increased tool life is within the statistical error (A. Sergiev. Vibration cutting of steel 110G13L / A.P. Sergeev, S. V. Voloshin, EG Shvachkin // Herald of mechanical engineering. 2000. No. 12. P.50-52) [4].

The implementation of the method. From the previously indicated conditions for the formation of holes and the imposition of forced axial vibrations on the tool, it is considered [2] that the electrodynamic vibration-excitation drive is most preferred. Such a drive is most productive in comparison with hydromechanical and electro-hydraulic drives. The goal when using an electrodynamic vibration exciter is to introduce additional energy into the cutting zone and temporarily stop the cutting process for thousandths of a second.

Thus, for the implementation of the method requires an autonomous vibration exciter. This will allow you to transfer to the drill the movement: rotation with a given frequency, as well as high-frequency reciprocating movement of the drill along its own axis, created by unlike constant and alternating magnetic fields and an oscillation generator.

The most preferred scheme for the general layout of the electrodynamic vibratory drive for the proposed processing method will be a circuit based on two inductors. In shape, they can be two cylinders, at the ends of which restrictive devices can be installed (see figure 2). This allows you to intensify the process of crushing chips during chip formation.

In this case, the upper electromagnet 1 is fixed motionless relative to the lower 2, which moves by a predetermined amplitude and acts on the shaft 4. The shaft 4 moves under the influence of a disturbing force, while the elastic elements 7 are compressed under the influence of a disk 6 fixed rigidly to the shaft 4. In the absence of additional energy from the electrodynamic vibration exciter elastic elements 7 return the shaft 4 to its original state. Gear 5, mounted on the shaft 4, is used to transmit rotation from the spindle of the machine to the drill 9, mounted in the chuck 8.

According to the calculations for this design of an autonomous exciter, the frequency of vibration of the drill is 500 ... 2000 Hz.

An example of using the proposed processing method when installing the device on a machine for vibratory drilling of holes in corrosion-resistant steel showed that this provides an increase in drilling performance by more than 2.0 times and to increase tool life by 40%. This proves the high efficiency of the proposed method of vibration drilling.

Claims (1)

A method of vibration drilling with fine crushing of chips, including the action of constant and variable magnetic fields on a spindle assembly with a shaft, elastic elements and a tool, providing tool vibrations in the form of reciprocating movements along its axis and performing rotation and feed movement of the tool, characterized in that - translational movement of the tool along its axis is carried out with a vibration frequency of from 500 to 2000 Hz by means of an electrodynamic vibratory drive and set the amplitude of oscillations equal to A ₁ ≤0.5S _p , where S _p is the tool feed, mm.

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