Hardening of helical coil springs

FIELD: process engineering.

SUBSTANCE: invention relates to machine building and can be used in production of helical coil compression springs of steel. Proposed process comprises hardening of spring turn inner surface by surface cold-hardening. Along with the latter, crosswise flexure of spring turn is made in the pane perpendicular to spring axis. Surface cold-hardening is executed by hardening rolling by shaped rollers with working surface profiles made to allow the spring solid surface.

EFFECT: higher fatigue strength, longer life, lower noise, vibration and drawing force.

3 dwg

 

The invention relates to mechanical engineering and can be used in the production of cylindrical helical compression springs made of steel.

This method of peening a cylindrical helical spring lies in the combined action with one side surface hardening through hardening rolling from the other side of the transverse bending (extension) of the coil springs in a plane perpendicular to the axis of the spring, causing local plastic deformation on the inner surface of the coil.

Currently known method of hardening of elastic elements of machines, in particular of cylindrical helical springs by the method of blasting. Springs, intended for blasting, are placed on rotating rollers (conveyor) under flow fraction. The scatter fraction is carried out by rapidly rotating blades of the rotor (rotors). Treated spring pushers of the conveyor fed out of work hardening [1].

When shot blasting treatment in the surface layers of spring material is formed a hardened layer with high hardness containing residual compressive stresses, which ensures a longer life of the spring to fracture.

The main disadvantage of this type of treatment is very low efficacy in the area of the inner surface of the coil. When Oprah�specific geometric ratios of the sizes of springs (for example, for large railway springs, Elevator springs) the inner surface of the coil remains almost raw.

From the analysis of the stress state of the material of the coil spring and the operating experience of the helical cylindrical compression springs, it follows that the inner surface of the coil is experiencing overload (up to 40-60%) and fatigue crack originates on the inner surface of the coil [2].

There is also known a method described in patent RU 2462519 C1. The method consists in the hardening of cylindrical helical springs due to the work hardening of the inner surface using a mandrel or shock in addition to shot blasting treatment.

In the first case, inside mounted on a lathe spring introduces the mandrel, and the second reinforcing head with rollers. In the processing of the spring mandrel, the direction of rotation with a small number of revolutions (20-30 rpm), and in the second case hardening head receives the rotation from the additional electric motor and speed are chosen depending on the mass of the impactors (about 800-1000 rpm). After 2-3 seconds turns on longitudinal feed of the mandrel (head) to handle all inner surfaces of the turns of the spring. After processing all of the turns of the spring rotation turns off and the instrument is removed from the spring.

Specified in the patent RU 2462519 C1 method adopted for the prototype. When implementing this method is focused on the impact on the inner surface of the turns of the spring to the plastic deformation due to the local surface plastic deformation.

The disadvantages of the prototype running in the first scheme should include the following:

1) While pushing (pulling) the mandrel is processed a small portion of the inner surface of the coil;

2) a Significant driving force to the treatment of large springs;

3) Change the geometry of the coil (the appearance of the flats on the inner surface of the coil).

The disadvantages of the second schema should include increased noise and vibration during the treatment.

An object of the invention is to increase the fatigue strength and durability of cylindrical helical springs made of steel, increasing the internal surface area of revolution subjected to hardening treatment, and reduction of noise, vibrations and effort pulling during processing.

A distinctive feature of the proposed method of hardening of springs is that the hardening effect is achieved not only by the surface hardening of the inner surface of the coil as in all previous cases, but also due to the work hardening of the inner surface of the coil spring arising from transverse bending (extension) of the coil in the plane p�erpendicular spring axis.

The technical result consists in the implementation of purposeful influence on the inner surface of the coil spring plastic deformation due to the joint action of surface work hardening and transverse bending (extension) of a coil in a plane perpendicular to the axis of the spring.

Surface hardening of the inner surface of the coil 3 is due to the hardening of the rolling profile of the rollers 1, wherein the outer surface of the spring rests on the supporting roller 2 (figure 1). In parallel with the rolling of the inner surface is transverse bending (extension) of the coil springs in a plane perpendicular to the axis of the spring from position 1 to position 2 (figure 2). The ratio of the geometric parameters of the springs, rollers (grooving and support), their mutual arrangement and the load applied should ensure the occurrence of plastic deformation on the inner surface of the coil spring from the contact stresses and transverse stresses of bending. Move foci of plastic deformation along the envelope surface of the spring is achieved by rotation of the spring, as well as grooving and support rollers (one of these movements is the leading) to provide the internal surface of all turns. The proposed method of hardening is different from the one existing�related topics because of the static nature of ongoing efforts in the treatment process no vibration and noise; due to the profile of the working part of the grooving roller is much more cultivated area than when pulling a mandrel (figure 3) and the profile of the working surface grooving rollers are complementary, together forming a continuous hardened surface; the lack of tractive effort; with little contact loads there is a possibility of deeper deformations due to the additional bending stresses.

Thus, after the process of hardening on the inner surface of the coil spring is formed of work-hardened layer with enhanced mechanical properties (increased hardness, yield strength) and favorable residual compressive stresses (due to the change of the specific volume of metal at the growth in the number of dislocations). The level of residual compressive stresses on the inner surface of the coil is higher than in the known methods, due to the additional axial residual compressive stress from transverse bending of the coil.

The increase in the level of mechanical properties of material on the inner surface of the coil provides the necessary increase stress for the nucleation of a fatigue crack, while compressive residual n�voltage algebraically adding to the existing tensile stresses, reduce the level of operating voltages. In the end, significantly increases the service life of the springs.

When you implement this method it is possible to calibrate the diametral dimensions of the springs is obtained by cold coiling through a given magnitude of plastic deformations in extension coil springs.

Sources of information

1. Luzgin N. P. The manufacture of springs: a Textbook for training of workers at work. - 2-e Izd., revised and enlarged extra - M.: Higher. School, 1980; Ostroumov, V. P., Production of cylindrical helical springs. - M.: Mashinostroenie, 1970.

2. Ponomarev S. D., Andreeva L. E. Calculation of elastic elements of machines and devices. - M.: Mashinostroenie, 1980; GOST R 54326-2011. Springs for suspension of railway rolling stock. Test methods on fatigue life.

The method of hardening a cylindrical helical compression spring, comprising hardening the inner surface of the coil spring surface hardening, characterized in that together with the surface hardening is carried out transverse bending of the coil springs in a plane perpendicular to spring axis, with surface hardening hardening is carried out by rolling of the profile rollers made with profiles of working surfaces from the condition of joint processing areas, providing more inform� continuous hardened surface of the spring.



 

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