SU1474175A1 - Method and apparatus for relieving residual strain in metal structures - Google Patents

Abstract

This invention relates to the reduction of residual stresses in metal products by vibro-processing. The purpose of the invention is to improve the quality of the vibration treatment process. The essence of the invention is that the vibro-processing is performed by the driving force of the oscillating frequency in the frequency range including the resonant frequency. For this, under the control of the pulse generator formed from the adder 8 and register 11, the frequency changes according to the change in the code value on the bus G. The sweep frequency limits are set on buses A and B. The device for implementing this method is based on discrete elements. 2 sec. f-ly, 1 ill., 1 tab.

Description

The invention relates to mechanical engineering, namely to the means of reducing the residual stresses in metal products by means of vibration loading.

The aim of the invention is to improve the quality of the vibro-processing process.

The drawing shows a functional block diagram of a control device for relieving residual stresses.

The method of relieving internal stresses is carried out as follows.

Vibration processing technology by the proposed method involves scanning the entire frequency range and selecting the most pronounced 2-3 resonant frequencies. Then, depending on the frequency of the resonant peak and its width, the swing limits are set by the swing limit, and the swing speed device is set by the swing speed. During tests on prototypes of designs, the swing limits are set so that the resonant frequency in the process of vibro-processing, moving to a lower frequency, does not go beyond the limits of the specified frequencies of the swing limits.

The shift of the resonant frequency of high-Q structures is about 1-3% of the frequency of the resonant peak, t = e0 at 300 Hz. The shift of the resonant frequency is about 8 Hz, and the width of the peak is not more than 2 Hz, therefore the swing range is within 2 -4 Hz. In this mode, oscillations occur at the resonant frequency or on the slopes of the resonant peak. The minimum swing range is determined by sampling the tuning frequency.

The device for removing internal voltages in metal structures contains a swing limit unit 1, the individual outputs of which are connected to the first and second digital switches 2 and 3, and the output of the first digital comparator 2 is connected to the first input of the RS flip-flop 4, the output of the second digital comparator 3 through the element NOT 5 - to the second input of the trigger 4, connected through switch 6 and the reversible counter 7 with the first input of the adder 8, with the second inputs of the first 2 and second 3

digital comparators and through the converter 9 of codes with the display unit 10, the first output and the second input of the adder 8 are connected respectively to the first input of the parallel register 1 1 and its output, and the second output of the adder 8 is connected to the second input of the parallel register 11, the second input of the divider 12 frequency and vibrator 13 through the power supply unit 14; in addition, the crystal oscillator 15 is connected to the third input of the parallel register 11, the start unit 16 is connected to the first input of the element OR 17, and the master unit 18 of the speed of swing is connected to the first The input to the frequency divider 12 is connected to the second input of the element OR 17 whose output is connected to the second input of the switch 6. The adder 8 and the register 11 perform the functions of the accumulating adder and are controlled by a pulse generator. I

The manual control unit 19 is designed with an integrated interface to enable the connection of the system to the control computer, can be used for manual control or for matching the control system with the control computer and connected to the second input of the power supply unit 14, the first input of the programmable frequency divider 20 , the second input of the switch 21, with the first input of the comparator 22, the first input of the subtracting unit 23 and the first input of the summing unit 24. In addition, the output of the swing limit unit 1 is connected to the first input of the comparison circuit 25, with the second input of the digital comparator 22 and the second inputs of the subtraction unit 23 and the summation unit 24. The output of the digital comparator 22 through the first trigger 26 is connected to the first input of the switch 21, the first and second outputs of which are respectively connected to the third input of the switch 6 and the reversible counter 7. The output of the comparison circuit 25 through the serially connected programmable frequency divider 20 and the second trigger 27 is connected to the third input of the switch 21. The output of the starting block 16 is connected to the second inputs of the flip-flops 26 and 27. The sensor 28 of the acceleration mounted on the product 29 is connected via an amplifier 30 to the acceleration indicator 31-connected with a recorder 32. And,

the amplifier 30 through the pulse shaper 33, the phase detector 34, the zero-block 35 is connected to the second input of the comparison circuit 25 and the third input of the swing limit unit 1. The following data bus designations are introduced: the frequency reference frequency bus, 3 — the oscillation range reference tire, L — the const fpe assignment bus,.

The determination of the resonant frequency is as follows.

The signal from the acceleration sensor 28 mounted on the article 29 is amplified by the amplifier 30 and supplied to the pulse shaper 33. The bipolar pulses from the output of the pulse generator 33 are fed to the phase detector 34, to which control pulses also arrive, and when phase coincides, the zero is detected at the output of the phase detector 34. Next, the signal determining the phase is fed to the block 35 zero, at the output of which a pulse of a definite duration is produced when the signal determining the phase passes through zero. Consequently, when scanning the control frequency at the moment of transition of the resonant frequency of the product, at the output of block 35, pulses appear that record the moment of resonance of the product (resonance pulse). With the amplifier 30, the signal is also fed to the acceleration indicator 31 and then to the recorder 32, which allows recording the amplitude-frequency characteristic of the product 29, which determines the resonant frequencies at which it is necessary to perform vibro-processing, as well as the swing band.

Depending on the signal sent from the manual control unit 19 to the switch 21, the device can operate in two modes: single pass of the range to the frequency specified by the code on the bus I, automatic tracking of the resonance, approximately defined by the code on the bus I and the swing band given by the code on the bus 3.

The operation of the device in the mode of a single passage of resonance.

The switch 21 outputs a signal (logical zero) to the switch 6, which switches to direct counting mode, switching the output of the trigger 26 with the set zero input of the counter 7. The start pulse sets

0

five

0

five

0

five

0

five

0

five

the trigger 26 is in the zero position and this allows the operation of the counter 7.

The digital comparator 22 compares the code of the current frequency on bus G with a given frequency on bus K and, if the codes are equal, outputs a switch signal to trigger 26, which then resets counter 7 to zero via switch 21, which means the end of work.

In order to repeat the range, it is necessary to re-initiate the trigger pulse from block 16, and the process is repeated.

The operation of the device in the automatic tracking resonance. Switch 21 switches the trigger output 26 with the input of the Account + l switch 6 and the output of the trigger 27 with the input of Set 0 of the counter 7.

The start pulse sets trigger 26 and 27 to the zero position and this allows the counter to operate only in the direct counting mode,

In this mode, a code is set up on the G bus whose value is several hertz higher than the resonant frequency of the product at which vibration processing is performed. When the codes on the buses G and G are equal, the digital comparator 22 switches the trigger 26 and the signal of the logical unit through the switch 21 is fed to the switch 6, which, in turn, enables the forward or reverse counting mode depending on the code values on the buses A and B.

The process of tracking the resonant frequency is as follows.

The subtraction unit 23 and the summation unit 24 are fed the code of the current frequency from the bus G and the code of half a swing from the bus 3. Consequently, at the output of the subtraction unit, the code will be equal and at the output of the summation unit. At the moment of the transition of the swing frequency through the resonant frequency of the product, a resonance pulse selected in the indicator 35 zero is supplied to the swing limit unit 1, which is a parallel register, and the value of the I and K bus codes is written to the A and H buses, which automatically sets the swing limits relative to resonant frequency.

51

The process of terminating vibration treatment is based on the principle of stabilizing the resonant frequency.

The comparison circuit 25 is supplied with the code of the current frequency G and the pulses of the resonance and EoN In the comparison circuit 25, at the moment of resonance, the previous value of the resonant frequency on the bus G is overwritten and the current value of the resonant frequency is recorded on the bus G, a comparison is given and on a programmable frequency divider 20.

In the case of stabilization of the resonant frequency of the product, after a certain number of swing half-periods set by code L, the pulse produced by a programmable 20 frequency divider switches trigger 27 to a state of logical one. The signal of the logical unit through the switch 21 sets the counter 7 to zero, than ends the sweep frequency.

The device works as follows.

When the power is turned on, trigger 4, counter 7 and register 11 assume a zero state. A single start pulse from the start block 16 through the element OR 17 and the switch 6 is fed to the forward input of the counter 7 at the output of the latter, i.e. on the bus G, the initial code value appears and the pulse generator formed from adder 8 and register 11 starts working. With each clock pulse of the crystal oscillator 15, the value of the digital bus code E, is copied to the div bus of adder 8, summed with the bus code G. If a

756

on bus G, the code is not zero, then with each clock pulse the code value on bus E increases by an amount equal to the value of code G. When the adder 8 overflows, an output appears at its output, setting register 11 to the zero state, and the counting starts first . Overflow pulses are followed by a frequency equal to

 W

G f f

N j

where G is the code value on the bus G; N is the capacity of the adder (bits); fQ is the frequency of the quartz oscillator.

From the output of the adder 8, the control pulses through the frequency divider, the element OR 17 and the switch 6 are fed to the change counter 7, and the code value on the bus G per unit

/ V

at intervals equal to:

G- "1

c - n1

where n is the division factor of the divider 12.

The change in the frequency of the funp occurs in accordance with the change in the value of the code on the bus G.

Comparators 2 and 3 compare the code value on bus G with the code values on buses A and B. The signal from comparator 2 is fed to the input R of the setup of the RS flip-flop 4, and from the comparator 3 through the element 5 to the input S of the unit setup.

The state of the trigger 4, depending on the signals of the comparators 2 and 3, is presented in the table.

The output signal from the trigger 4 is fed to the switch 6, which provides the switching of the inputs of the reversible counter 7 in accordance with the table.

The code value on bus A sets the lower limit of the frequency of oscillations, and on bus B the upper limit. The value of the code on the bus determines the coefficient

dividing the frequency divider, which determines the frequency sweep rate and is carried out by the sweep speed driver 18. A bus G is connected to a code converter 9 that converts the binary code to a binary-tenth, which is fed to the frequency indication node.

Control pulses with a sweeping frequency are supplied to a power supply unit 14, the load of which is an electromagnetic vibration exciter 13.

The vibration exciter creates a force of the oscillating frequency that loads the structure to be processed.

When using the system operating according to the proposed method, the stability issues are completely absent, since there is no feedback to keep the system at resonance, and the resonant frequency is fixed and its value is transmitted to another system, discretely moving the swing band towards lower frequencies. When choosing a narrow swing range, which is 0.5 or less than the width of the resonant peak, high efficiency of vibro-processing is ensured.

In addition, the provided possibility of connecting the system to the control computer allows the system to be used in flexible automated productions, where the modes for each workpiece (swing limits, oscillation amplitude and processing time) are recorded in the control program,

In such systems, electromagnetic exciters with a reciprocating motion of an elastic-suspended mass are mainly used, since the use of unbalance, in the frequency sweep mode, causes great difficulties and is very difficult to implement due to the large inertia of the rotating unbalance, which leads to a decrease in swing speeds.

The proof of the validity of the statement that the moment of the end of vibration processing is determined by the stability of the resonant frequency is the experiment conducted on the welded structures of coordinate measuring machines. The first part of the machined parts is excited by a sequence.

ten

15

0 5 o

five

50

0

at the resonant frequencies of 504, 351, 284 Hz, the second part - at the resonant frequencies of 465, 352, 250 Hz. Comparison of the frequency response before and after vibro-processing shows the shift of the resonant frequencies in the direction of decreasing the frequency by an average of 8 Hz and their stabilization.

At the same time, the logarithmic decrement of free damped oscillations is measured and the moment of its stabilization is determined. For the first part, the value of the logarithmic decrement of free damped oscillations stabilized at a value of 0.150 (initial value 0.109), the second part - at a value of 11212 (initial value - 0.084).

The decrement of damped oscillations depends on the level of residual voltages and increases in the process of their redistribution, as a result of which the resonant frequency decreases. The use of this method allows to accurately determine the relative change in voltage and the moment of voltage stabilization.

In addition, the residual voltages are measured by the magnetically anisotropic method, which showed a decrease in the residual voltages and their stabilization simultaneously with the stabilization of the resonant frequency.

Thus, vibro-processing using a frequency-based method not only improves the quality of vibro-processing, but also makes it possible to simplify the design of the control device and increase its stability, which is especially important when operating under production conditions.

Claims (2)

1. Method of removing residual stresses in metal structures, including excitation of resonant oscillations in the workpiece and registering the end of the process at the moment of stabilization of the resonant frequency, characterized in that, in order to improve the quality of the vibro-processing process, the excitation is produced by the forcing force of the oscillating frequency in the frequency range specified in the technology, which includes the resonant frequency. 2. A device for removing residual stresses in metal structures containing a power supply unit, a vibration exciter, an acceleration sensor mounted on the workpiece, an amplifier, an indicator and a recorder connected in series, characterized in that, in order to improve the quality of the vibration treatment process, it additionally contains a master unit for swing limits, a trigger unit, a master unit for swing speed, three digital comparators, two frequency dividers 9 OR and NOT elements, three triggers, two switches, a reversible counter k, crystal oscillator, two adders, parallel register, manual control unit, pulse shaper, phase detector, zero indicator, comparison circuit, subtraction unit, code converter and second indicator, the outputs of the span limit unit connected to the first and second digital comparators, output the first digital comparator is connected to the first input of the first trigger, the output of the second digital comparator is NOT connected to the other, the input of the first trigger connected via a switch and reversing Meters withstand the first input of the first adder, with the second inputs of the first and second digital comparators, the comparison circuit, the third switch, the subtraction unit, the second adder via the inverter and codes - a second indicator, the first output and the input of the first adder .vtoroy respectively connected to the first input a parallel register and its output, and the second output of the first adder is connected to the second input of the first frequency divider, the second input of the parallel register, the input of the phase detector and through the power supply unit to the exciter, a crystal oscillator is connected to the third input of the parallel register, the trigger unit is connected to the first input the OR element and the inputs of the second and third triggers, the second input of the OR element through the first frequency divider is connected to the output of the master unit of the swing speed, and the output of the OR element is connected to the second the switch input, the outputs of the manual control unit are connected to the second input of the power supply unit, the first input of the second frequency divider, through the third comparator and the second trigger - to the first input of the second switch, the second input of which is connected to another output of the manual control unit, 5 next output of the manual control unit connected to the inputs of the subtraction unit and the second adder, the outputs of which are connected to the inputs of the master unit of the swing limits, the third input of which is connected to the input of the comparison circuit and through the driver signal , A phase detector and indicator zero - with output amplifier, the output of comparison circuit via a second frequency divider, and a third flip-flop is coupled to a third input of the second switch, the outputs of which -soedineny with first switch-input up-down counter. 0 0 five