SU1754330A1 - Method of vibrodeformation machining - Google Patents

Abstract

The invention relates to the processing of materials by cutting and can be used in the processing of cylindrical parts of medium and low rigidity, mainly torsions. In the process of cutting in the surface layer, deformation stresses are created by periodically loading with mechanical high-frequency or ultrasonic overload cycles with the magnitude of the maximum force corresponding to the material deformation. pre-hardening value. The oscillation details are torsional in the direction of the cutting speed. This allows changing the mechanical properties of the material and narrowing the zone of intense plastic deformations in the cutting zone, bringing together in time the time of pulling and the onset of plastic instability, and contribute to the fragile development of destruction. At the same time, mechanical oscillations are imposed on the tool in the direction of the main movement with a period caused by overload cycles, while taking into account the safety factor of the part with unrestricted operation of 2 sludge.

Description

The invention relates to the processing of materials by cutting and can be used in the processing of cylindrical parts of medium and low rigidity, mainly torsions.

A known method of machining a rotating part consists in fastening it over end sections and deformation prior to treatment by loading one of the ends with a torque with efforts that create a state of plasticity in the surface layer of the part.

The disadvantage of this method is the formation of the primary and secondary zones of plastic deformation areas, which reduces the energy intensity of the process.

cutting: the power of the main cutting process, which characterizes the reduction in the specific removal of the allowance due to the cutting of a smaller depth and width of the chip, decreases, and the dissipative energy consumption of the cutting process to overcome the associated phenomena (deformation of the part and tool, tool wear, heat and vibrations in the internal stresses in parts).

The purpose of the invention is to improve the accuracy of processing and the specific energy intensity of the cutting process due to the approaching time of moving and the onset of plastic instability in the cutting area in time.

VI

cl

C CJ 00 About

creating a state of preliminary strengthening in the surface layer of the part.

The goal is achieved by the fact that according to the method of machining a rotating part, according to which the part fixed on the end sections is deformed before the treatment with efforts that create deforming stresses in the surface layer of the metal, the deforming stresses create periodic or high load ultrasonic frequency with a maximum force value corresponding to the deformation of the material for a given amount of preliminary hardening and coefficient of cone concentration of fatigue stresses equal to 1.4-2.0, while simultaneously imposing forced mechanical oscillations on the tool in the direction of the main cutting motion g with a period equal to the period of loading with cycles of overload.

The deformation of the part with the efforts to create a state of preliminary hardening in the surface layer of the part allows, as a result of loading the workpiece above the yield strength, somewhat change the mechanical properties of the material, increase the proportionality limit, reduce the relative permanent deformations, narrow the zone of intense local plastic deformations, when only elastic deformations develop in the material, while due to the narrowing of the zone of intense local plastic deformations, the moment of Ivanov and the occurrence of plastic instability approach each other in time, which contributes to the fragile development of destruction.

The deformation of a part with a predetermined strain hardening value allows slightly changing the mechanical properties of the material, narrowing the zone of intense local plastic deformations, facilitating the transition from viscous to brittle fracture due to depletion of plasticity, while increasing the accuracy of processing and reducing the forces corresponding to the deformation conditions.

The imposition of mechanical high-frequency or ultrasonic vibrations on the instrument in the direction of the main motion increases its rigidity by 2-3 times, since the rigidity increases in direct proportion to the square of the frequency increase.

The imposition of mechanical high-frequency or ultrasonic vibrations on an instrument allows one to achieve a degree of geometric and other parameters approaching the set, when the difference between the actual and set design parameters decreases to the theoretically possible, reduces the amount of work and the cutting force by increasing the rigidity, some changes in the mechanical properties material, using the advantages of ultrafast cutting, narrowing the zone of intense plastic

0 deformations.

In general, they increase the machining accuracy by increasing the rigidity of the workpiece and the tool, increase the energy intensity of the cutting process by increasing

5 of the power of the main cutting process, which characterizes the increase in the specific removal of the allowance due to the cutting of a greater depth and width of the chip; adding to the main cutting process

0 energy factors: strain hardening for processing plastic parts, the imposition of high-frequency or ultrasonic vibrations, characterizing the increase in machinability of materials,

5 and also by reducing the dissipative energy consumption of the main cutting process to overcome the attendant phenomena of deformation of the part and tool, tool wear, heat and vibration in the area of cutting, internal stresses in the part.

The safety factor for unrestricted operation is determined by a value of 1.4-2.0 as a concentration factor of fatigue stresses according to the method of calculation

5 uniaxial stress state, The need to take into account the safety margin is due to ensuring the strength of the part under multi-cycle loading,

Fig. 1 is a sketch for reference.

0 the process of the method; in fig. 2 is a block diagram of a system for implementing the proposed method.

The system contains a machined non-rigid part 1, fixed in patro5 not 2 front headstock, and a torsional vibration vibrator-clamping mechanism 3, as well as a vibrator 5 connected in series, mounted on a machine caliper, cutting tool 6

0 and control unit 4 (microcomputer) connected to the CNC system 7.

Vibrators 3 and 5 and the input of the CNC 7 are connected to the control unit 4.

The method is carried out as follows.

Item 1 is installed in the cartridge 2 and clamp it. The second end of the part 1, facing the tailstock, is clamped into the mechanism 3 of the clamping vibrator torsional vibrations.

In accordance with the block diagram (Fig. 2), control unit 4 starts the control program and turns on torsional vibration vibrator 3, which informs the part 1 of mechanical high-frequency or ultrasonic vibrations in the direction of rotation of the workpiece with a predetermined torque to create pre-strengthening in the surface layer the details

At constant torque values along the length of the workpiece and the cross-sectional dimensions, the total twisting angle p is determined by the formula

W MKI / Gb,

 s

torque is determined by

Mk t ° 10 / g,

where G is the shear modulus;

I lt4 / 2 is the polar moment of inertia;

g is the radius of the preliminary hardening zone;

t ° 0.5 ° o - tangential stress in the surface layer of the part;

0 ° is the pre-hardening voltage in the surface layer of the part, taking into account the safety margin with unlimited operation.

The expression for the voltage about ° is written as

o0-from + 0v

where From - yield strength;

OB - ultimate strength;

k is the coefficient of concentration of fatigue stresses under shock loading.

At the same time, the control unit 4 switches on the vibrator 5, which excites mechanical high-frequency or ultrasonic oscillations of the tool 6 in the direction of the main movement with a period caused by the cycles of overload on the parts 1 and in antiphase.

The oscillations of the tool 6 are reported from the condition of stability and discontinuity of cutting as an expression

, 5 / о1фрасчТ-103мк,

where a is the amplitude of the forced oscillations of the instrument;

VoKp.pacn. - circumferential speed of the treated surface;

five

ten

five

0

five

T is the period of oscillation of the instrument.

The period of mechanical or ultrasonic oscillations is chosen in the range of 18-30 kHz, which is due to the fact that vibrations below 10 kHz can be transmitted not only through the means of fastening the part and the tool, but also through the machine nodes. Oscillations above 30 kHz attenuate strongly when passing through the joints, therefore, they require a higher power of vibrators, which causes an increase in their dimensions.

The amplitude limitation is due to the fact that it is limited by the editing of the impact of the material on shock impacts within the limits of the strain rate e 10 ° - the cutting speed V 50–500 m / s, when plastic deformation prevails.

After the part 1 and the tool 6 are in the state of oscillations, the CNC 7 starts the machining program on the machine.

When tool b moves in the direction (+ OZ) from position O with speed Vn а ш cos (1) 1 in section OiAi (Fig. 1), the component 1 is twisted in the direction of rotation. At point AI, tool 6 comes into contact with the surface to be machined and deformed to a state of hardening, and during the cutting time r tool 6 and part 1 form the elements of the pair (contact) in section AIВ1. Upon further movement of the tool 6 in the direction (-OZ), the element of the pair is broken and the part 1 is unloaded from the torque. Load cycle 5 is repeated. On the next blank, the processing cycle is repeated.

Example. Grind the part length (L) 450 mm, diameter (D) 20 mm.

Cutting Modes:

the design value of the linear velocity of the surface to be treated (X / surrounding area) 150 m / min;

depth of cut (t) 0.25-0.75 mm;

feed (s) 0.054-0.11 mm / rev;

the period of forced oscillations of the part and tool (T) 50 s;

the calculated amplitude of the forced oscillations of the instrument (a) 100 microns.

The cutter is a straight-through, hard-alloy plate T15K6.

Processed material;

steel is normalized circle

20 -4 GOST 7417 -75 45 - T - 2 - B GOST 1050 - 74

5 yield strength (From) 36 kg / mm2; tensile strength (crc) 61 kg / mm; shear modulus (0) 8.110 kg / mm. The coefficient of concentration of fatigue stresses under shock loading (k) is 1.4-2.0.

Estimated values:

preliminary hardening stress in the surface layer of the workpiece, taking into account the safety margin in inorganic operation

36 +61

one

1.7

28.53 kg / mm2;

, 5 ° 14.26 kg / mm2;

 Mkl t ° 1A

r-y

14.26 450

8.1 103 -9.5

/ 4 ° 46.

When pulsed cutting, the rigidity of the tool and the workpiece increases by 3-4 times due to an increase in their natural frequencies, and the machining accuracy rises almost to the theoretically possible and is determined only by the cut due to the machining length in each tool oscillation cycle.

Impulse application of the load leads to a decrease in loads and cutting forces by at least 10 times, which allows reducing the power of the loading mechanisms, thus creating conditions such as

which zone of intensity of local plastic deformations is narrowed.

The absolute cutting speed in each cycle of oscillation reaches a value of 1000-1200 m / min, which makes it possible to take advantage of high-speed cutting.

Claims (1)

Invention Formula The method of vibroreformation processing, according to which a part fixed along end sections, before machining, is deformed with the forces by which in the surface layer Metals create deforming stresses, which are caused by the fact that, in order to increase the machining accuracy and specific energy intensity of the cutting process, the deforming stresses are created by periodic loading with high frequency overload cycles with a maximum force value corresponding to the material deformation at the specified preliminary hardening and a fatigue stress concentration of 1.4-2.0, while simultaneously imposing forced mechanical vibrations on the tool in the direction of the main cutting movement with a period of equal to the period of loading cycles overload. about, Fia, 1 fig 2