GB2104431A - Hardening shaped surfaces by plastic deformation - Google Patents

Abstract

A helical coil 14 of substantially round cross-section is surface- hardened by means of deforming elements E,F arranged at opposite sides of the coil 14 for forced rotation in engagement with the surface of the material, while the coil is rotated about its longitudinal centreline and subjected to ultrasonic oscillations. The deforming elements E,F are rotated in opposite directions so as to form on the surface a regular microrelief in the form of an intersecting mesh-like pattern. By changing the ratio between the angular rotational velocities of the deforming elements E,F a microrelief of desired geometry can be attained. <IMAGE>

Description

SPECIFICATION Hardening shaped surfaces by plastic deformation This invention relates to the surface hardening by plastic deformation of machine parts having com plex shaped surfaces, particularly surfaces of articles in the form of continuous helical coils. The invention can find particular application for surface hardening articles in the form of continuous helical coils whose turns are substantially round in cross-section.

The invention provides a method of hardening by plastic deformation surfaces of articles shaped as continuous helical coils and having essentially round cross-section by means of deforming elements adapted to engage with the surface of the articles, in which the deforming elements are arranged at the opposite sides of the article for forced rotation to contact the surface of the material of the article, rotation is provided to the article about its longitudinal centreline while ultrasonic oscillations are imparted thereto, and the deforming elements are rotated in the opposite directions so as to form on the surface of the article a regular pattern of microrelief in the form of intersecting mesh-like paths. A desired geometry of the microrelief can be attained by changing the ratio between the angular rotational velocities of the deforming elements.

Owing to its complex helical shape the article is subjected to three types of oscillations, viz. longitudinal, flexural, and torsional. The wavelength of each of these oscillations being different, all points of the article shaped as a helical coil are subject to complex oscillations, the total amplitude of each of the coil points being roughly identical. This allows one to carry out surface hardening at relatively low static strains exerted on the deforming elements, facilitating smooth rotation of the deforming elements, which ensures uniform depth of the hardened surface layer.

A desired depth of hardened surface layer can be attained through a certain ratio between a static force applied and ultrasonic oscillations imparted to the article being processed.

It is possible to obtain a desired regular pattern of microrelief on the surface of the article through selecting a corresponding ratio between the rotational velocities of the article and elements effecting plastic deformation to thereby substantially extend the fatigue life of the article.

The invention will be described further, by way of example, with reference to the accompanying drawings, in which: Figure 1 is a schematic illustrating how a method of hardening shaped surfaces by plastic deformation can be practised; Figure 2 is a section taken along the line ll-ll in Figure 1; Figure 3 is a section taken along the line Ill-Ill in figure 1; Figure 4 shows intersecting paths left by deforming elements on the hardened surface of an article when the angular rotational speeds of the deforming elements are equal; and Figure 5 shows intersecting paths left by the deforming elements on the hardened surface of the article when the angular rotational speeds of these elements are not equal.

With reference to Figures 1 and 2 there is shown diagrammatically an apparatus for hardening by plastic deformation shaped surfaces of articles in the form of continuous helical coils fabricated from materials of substantially round cross-section, while Figure 3 illustrates a method of surface hardening.

The apparatus comprises two variable-speed electric motors 1 and 2 (Figure 1) mounted on carriages 3. Pulleys 4 and 5 are secured on the shafts of the electric motors 1 and 2 to transmit rotation through belts 6 and 7 to deforming elements generally indicated by E and F and arranged in shackles 8 and 9. The deforming elements E and F are structurally identical and comprise antifriction spacers 10, balls 11 (Figure 2), separators 12, and pressure rings 13. A spring 14to be surface hardened is passed through the deforming elements E and F, the spring 14 being secured at the end of a waveguide 15 (Figure 3).

Another end of the waveguide 15 is fixedly attached to a source 16 of ultrasonic oscillations.

The spring 15 (Figure 3) fixed to the end of the waveguide 15 is first threaded through one deforming element, for example the element E. The spring 14 is arranged in the deforming element E with a preset tension representing a difference between the cross-sectional diameter of a turn of the spring 14 and the working diameter of the deforming element E. The deforming elements E and F are fitted on the spring 14 in sequence. First, one deforming element, such as the element E is assembled, for which purpose the balls 11 (Figure 2) are fitted into the separator 12 to be then inserted into the pressure ring 13. The antifriction spacers 10 (Figure 1) are then installed onto the side surfaces of the pressure ring 13. The spring 14 is thereafter passed through the thus-assembled deforming element E, while the drive belt 7 is passed around the pressure ring 13.

Ultrasonic oscillations are imparted to the spring 14 from the source 16 of ultrasonic oscillations by way ofthewaveguide 15, the spring 14 being rotated about its longitudinal centreline at a rate n. Simultaneously, the electric motor 2 acts to transmit rotation to the deforming element E through the pulley 4 and drive belt 6, the element E rotating about the cross-sectional periphery of a turn of the spring at a rate n1 (Figure 2). When half of the turn of the spring 14 has been processed, the spring 14 is stopped, while the electric motor 2 and the source 16 of ultrasonic oscillations (Figure 3) are de-energized.

This is followed by assembling the second deforming element F on the other side of the spring 14, which is done essentially similarly to what has been described with reference to the deforming element E.

The spring 14 is then again rotated and subjected to ultrasonic oscillations imparted thereto from the source 16 through the waveguide 15. The deforming elements E and F arranged in opposition to each other on the sides of the spring 14 and consequently the balls 11 are rotated by the motors 1 and 2 through the pulleys 4 and 5 and belts 6 and 7 in opposite directions at the rate of rotation n1 and n2, respectively.

For one revolution of the spring 14 each of the deforming elements E or F is displaced circumferentially of a turn of the spring 14 a distance L = zD, where D is the diameter of the spring. Assuming that So is the travei of the deforming element, such as the element E, along the spring turn for one revolution of this element about its own axis providing a required microrelief on the spring surface, then USO will represent the number of revolutions n1 of the deforming element for one revolution of the spring 14. In consequence, the rotation rate n1 of the element E exceeds the rate n of rotation of the spring by the same amount.

The deforming elements E and F by way of the balls 11 form on the surface of the spring 14 a regular microrelief in the form of intersecting meshlike paths or patterns; changing the ratio between the angular rotational velocity of the deforming elements E and F provides required geometrical parameters of the microrelief.

For one revolution of the spring 14 about its centreline the carriages 3 with the deforming elements E and F are moved a distance equal to a pitch t of the spring 14 (Figure 3). When the spring 14 is sufficiently rigid (spring wire diameter more than 5 mm), a special drive for moving the carriages 3 (Figure 1) can be dispensed with. Arrangement of the carriages 3 on guideways for movement conforming to the longitudinal centreline of the spring 14 makes it possible owing to rotation of the spring to provide a component force directed axially of the spring 14. This force will cause the carriages to move along the centreline of the spring 14 to thereby effect spring processing.

As a consequence of the complex shape of the spring 14 (Figure 3) three types of oscillations are induced in it when the source of ultrasonic osiliations is actuated, the oscillations being A - longitudinal, B - torsional, and C - flexural. Because the wavelength of each of these oscillations is different, all points of the spring 14 are subject to complex ultrasonic oscillations, this meaning that the overall amplitude of oscillations in each point of the spring has approximately the same value. The provision of ultrasonic oscillations in every point of the spring 14 augments the plasticity of the spring material being hardened and enhances the dislocating motions which in turn brings down the forces required for plastic deformation to take place and reduces the friction forces envolved.The ultrasonic oscillations imparted to the spring 14 (Figure 2) are transmitted to the balls 11 and due to the balls 11 being urged to the spring by the ring 13, the latter acts to provide additional low-frequency oscillations to the balls 11.

Therewith, the low-frequency oscillations ofthe balls 11 are modulated by the ultrasonic oscillations whereby a greater depth of hardening is obtained at lower deformation forces and reduced friction forces. This phenomenon helps to invigorate the hardening process and has hitherto never been applied in surface hardening technology.

The absence of ultrasonic oscillations causes an increase in the resistance of the material being hardened to plastic deformation and in the forces of friction which result in the slippage of the drive belts relative to the pressure rings 13 interrupting the spring treatment process. It is owing to subjecting the spring to ultrasonic oscillations that the entire cross-sectional periphery of a turn of the spring 14 can be processed by the deforming elements E and F to attain uniformly distributed compressive strains and surface roughness of 0.15 microns.

By adjusting the speed of rotation of the deforming elements E and F, as well as the pressure force exerted by these elements (or by the balls 11) through the replaceable rings 13 (Figure 2) and the intensity of ultrasonic oscillations of the spring 14, a regular microrelief is obtained having a required degree and depth of the hardened layer on the surfaces of the article. This also allows one to attain optimum compressive strains circumferentially of the cross-section of a turn of the spring being surface hardened, which enhances its cyclic strength.

In addition, the ultrasonic oscillations imparted to the spring 14 help detect visually undetectable microcracks on the surface thereof in the course of treatment.

A major aspect of the present invention resides in that the deforming elements E and F are rotated in the opposite directions, that is if one deforming element, for example, the E describes a right-hand helix on the surface of the turn of the spring being surface hardened, then the other element F rolls on the surface being hardened along a left-hand helical path. As a result, a mesh pattern is formed identical to that obtained during superfinishing or honing.

With reference to Figures 4 and 5, there are shown elements of intersecting paths from the two groups of balls. As in vibrorolling, a regular microrelief is formed on the processed surface, enhancing performance characteristics of the hardened surface, particularly its fatigue strength.

It will be noted that the above-described method has much wider capabilities in terms of the geometrical parameters of the microrelief. Shown in Figure 4 is a pattern of intersection of the ball paths on the hardened surface at equal angular velocities of the deforming elements E and F (n1 = n2 and a1 = whereas Figure 5 illustrates a different path pattern resulting from different rotational speeds (n > n2) with different helix angles (al > a2), which changes the mesh pattern formed on the surface. Alternatively, surface hardening at variable rotational speed of the deforming elements is possible, whereby by changing the angular rotational velocities n1 and n2 of the deforming elements E and F, as well as by changing the rate n of rotation of the spring 14, such conditions of processing are selected as to obtain desired hardened surface characteristics.

The arrangement of the deforming elements E and F on the opposite sides of the spring 14 is caused by the need to balance the radial forces induced by the drives, which is especially important when processing springs of low rigidity.

For hardening articles of high hardness, diamond pieces may be used in the deforming elements E and F instead of the balls 11, whereas for processing long articles use can be made of several deforming elements E and F to increase the process efficiency.

In view of the foregoing, the method of hardening by plastic deformation of surfaces of articles shaped as continuous helical coils and having a substantially round cross-sectional configuration makes it possible: (1) to obtain a regular surface microrelief which raises the fatique strength of the article hardened; (2) to have the article hardened at uniform depth circumferentially and lengthwise of the article; (3) to reduce surface roughness from 2.5 mic rows so 0.15 microns; and (4) to increase the fatigue strength of the article thus hardened, by a factor of 1.5 to 2.

Claims (3)

1. A method of hardening by plastic deformation the surface of an article in the form of a continuous helical coil of substantially round cross-section, in which deforming elements which bear on the surface of the article and are rotatable about the surface are arranged at the diametrically opposed sides of the coil, the coil is rotated about its longitudinal centreline and subjected to ultrasonic oscillations, and the deforming elements are rotated in opposite directions, so as to form on the surface of the article a regular mesh-like microrelief in the form of intersecting paths.

2. A method as claimed in claim 1, including changing the ratio between the angular rotational velocities of the deforming elements so that a desired geometry of the microrelief is attained.

3. A method of hardening by plastic deformation the surface of an article in the form of a continuous helical coil of substantially round cross-section, substantially as described with reference to the accompanying drawings.