CS237834B1 - The method of removing residual strains in welds by ultrasound - Google Patents

Abstract

The invention relates to a method of removing residual stresses in welds by the action of ultrasound, where the entire system of the backing — both welded parts — filler metal — molten bath is subjected to ultrasound during the welding process. The subject of the invention is that the ultrasound is applied in a pulsed mode, selected with pulses at a repetition frequency of 10 to 1000 Hz, with a pulse duration of 1 to 100 µs.

Description

The present invention relates to a method of removing residual stresses in welds, wherein the whole assembly is subjected to pulse mode ultrasound during the welding process.

In the welded parts, due to the thermal intervention, the internal non-equilibrium state of the material structure occurs, which causes their internal tensile stress. This stress results in a reduction in the load-bearing capacity of the weld or its destruction without the external tensile load reaching the intended resp. allowable calculation value.

Currently, residual stresses are most often removed by heat treatment. However, this is uneconomical, both in terms of energy and in terms of volume loss of material by the formation of oxides. It is often not possible to calculate larger welds due to the unavailability of large-scale furnaces.

In the previously known continuous-mode ultrasonic welding process in the frequency range from 17 to 213 kHz, a reduction in the residual stresses in the weld is achieved, thereby eliminating the subsequent operation after welding-heat treatment, but the disadvantage is that it is necessary to experimentally determine the best frequency , from an efficiency point of view to reduce weld stresses. It is the frequency that causes resonance oscillation in the component. It is therefore preferable to replace the fixed frequency vibrations with more efficient frequencies that are capable of resonating in different bands of the crystalline lattice of the material being processed.

The drawbacks of the hitherto known method of removing residual stresses in the continuous-mode ultrasonic welding process in the frequency range from 17 to 213 kHz are eliminated by the method according to the invention, which is based on the entire system, namely the substrate, both welded diplets, whether the melting bath is subjected to a pulse mode ultrasound during the welding process, selected with pulses at a repetition rate of 10 to 1000 Hz with a pulse duration of 1 to 100 μδ.

The influence of the ultrasonic welding process according to the invention leads to a significant decrease in the residual stresses in the x-direction and

y. Tensile stresses are transferred to compressive stresses, which is a favorable phenomenon in terms of stress of the welded joint and its utility properties.

Example

According to the invention, a ferritic-pearlitic ductile iron of a chemical composition, as determined by chemical analysis in mass, was welded. % as follows: carbon C = 3.58%, silicon Si = 2.68%, manganese Mn = 0.50%, sulfur S = 0.029%, phosphorus P = 0.05%, magnesium Mg - 0.18%, chromium Cr = 0.09%, nickel Ni = 0.05%, molybdenum Mo = 0.13%.

The mechanical values of the material were: mechanical strength Rm = 531.9 MPa, ductility As = 9.75%, taper Z = 13.95 '%, Brinell HB strength = 186, notched toughness KCU2 = 6.33 Jcm ^-2 . The filler material was a nickel-based electrode Ni = 92%, coated for cast iron welding, designated ES 722.

The experimental material was welded without preheating. The weld was applied in three layers. The ultrasonic energy was supplied by pulsed ultrasonic wave generators at a frequency of 17 kHz at a repetition rate of 130 Hz, with a peak power of 150 W and a pulse width of 44 µs.

The destruction method was used to determine the surface residual stresses. Electrical resistance strain gauges were glued to the degreased weld and insulated against ambient humidity and mechanical damage. Initial strain gauges were measured, the spots were freed by the electro-spark method and the final strain gauges were measured. The stresses were calculated from the values determined. The influence of pulsed mode ultrasound on welding, as tested on a larger number of samples, has been shown to be beneficial in that tensile stresses have passed into compressive stresses, which is more advantageous in terms of stress on the weld joint and its performance.

The results of measurements of several tested samples are given in the following table:

Sample number Rx (MPa) R _y (MPa) electrode Frequency (kHz) Vibration Repetition Frequency (Hz) 10 409.5 231.1 E-S 722 0 0 11 419.0 243.6 722 0 0 12 419.4 245.1 E-S 722 0 0 20 -282.5 -352.3 E-S 722 17 130 21 -255.8 -334.3 E-S 722 17 130 22 -276.4 -348.2 E-S 722 17 130 Where R _x is the residual voltage in the x and a direction R _y is the residual stress in the y-direction.

Claims (1)

237834 SUBSTITUTE The ultrasonic remover method for remnants of residual welds, where a complete set of washers, both welded parts, filler metal, fusing bath is ultrasonic in the course of the welding process; 10 to 1000 Hz, with a pulse duration of 1 to 100 ps.