JPH0379271A - Surface treatment of coil spring - Google Patents

Abstract

PURPOSE:To reinforce the inner peripheral surface of a coil spring and to increase the fatigue strength by shot-peening the inner peripheral surface at least of the coil spring. CONSTITUTION:The inner peripheral surface at least of a coil spring (valve spring) 1 subjected to forming is subjected to shot-peening. The inner peripheral surface at least of the coil spring 1 subjected to shot-peening is subjected to a magnetic polishing by a magnetic abrasive 6. The fatigue strength of the peripheral wall face 13 of the spring 1 can be improved.

Description

[Detailed description of the invention] [Industrial application field] The present invention relates to a surface treatment method for a coil spring.

[Prior Art] Conventional coil springs, for example, valve springs used in valve mechanisms such as intake valves and exhaust valves as part of an engine, have a coil inner diameter side on which the maximum shear stress is most applied when a load is applied. Fatigue failure is likely to occur at the starting point. For this reason,
Processing means are used to improve the fatigue strength of the inner diameter side of the valve spring.

The processing means include: (1) Shot peening processing for the purpose of applying compressive residual stress to the inner diameter side of the valve spring.

(2> Power brush treatment to improve the surface roughness of the inner diameter side of the coil after shot peening (References,
Spring Technology Research Group, 1985 Autumn Lecture Preprint Collection [January 1980] pp. 45-4B).

(3) Electrolytic polishing process to improve the surface roughness of the inner diameter side of the valve spring after shot peening (References, Spring Technology Research Group, 1985 Spring Lecture Preprint Collection [June 1988]
] pages 9-12).

etc. are known.

[Problems to be Solved by the Invention] According to the processing means (1) above, when shot peening causes surface roughness on the inner diameter surface of the valve spring, there is a possibility that breakage occurs from this portion. Furthermore, in the case of overpeening, the compressive residual stress on the surface is partially reduced, and therefore the shot peening effect is reduced.

According to the processing means (2) and (3) above, it is difficult to uniformly remove surface roughness, surface scratches, etc. caused by shot peening over the entire surface, so the circumference on the inner diameter side of the valve spring is Variations in surface roughness occur in the direction. The reason for this is that the material of the valve spring material is extremely hard (HV600
~650) It is presumed that this is because there was no suitable abrasive material for this, and it was not possible to polish the coil portion uniformly in the circumferential direction. That is, in the power brush processing described in (2) above, the rotating brush does not uniformly and accurately contact the arcuate surface inside the coil spring, and therefore the entire surface cannot be polished uniformly. In addition, in the electrolytic polishing process (3) above, the unevenness of the surface previously formed by shot peening is completely polished, and the surface roughness is improved considerably compared to the power brushing process (2) above, but even with this It's not enough. In addition, in the case of processing (3), the grain boundaries of the spring material may be selectively corroded and the fatigue strength may be reduced.

The present invention provides a method for manufacturing a coil spring that solves the above problems.

[Means for Solving the Problems] The method for manufacturing a coil spring of the present invention includes the steps of shot peening at least the inner circumferential surface of a formed coil spring, and at least the inner surface of the shot peened coil spring. This method is characterized by comprising a step of magnetically polishing the peripheral surface.

The shot peening process is performed for the purpose of increasing the hardness of the surface of the coil spring and improving the fatigue limit. That is, the shot peening process is performed on a coil spring that is formed by drawing a spring wire in advance and then completing the steps of oil tempering, coiling, and low-temperature annealing. This shot peening can use conventional processing means. The shot delivery device can be either a centrifugal shot device that is accelerated by the blades of a rotating impeller, or a pneumatic blow shot device that uses the air velocity when compressed air is ejected from a nozzle. . As the shot, sand, cast iron shot, cast steel shot, steel wire shot, etc. can be used. Shot peening conditions such as shot diameter, projection speed, and projection time are appropriately selected depending on the material of the part, the size of the part, and the like.

The magnetic polishing process, which is a feature of the present invention, is to polish at least the inner circumferential surface of the coil spring that has been subjected to shot peening in the shot peening process. In this magnetic polishing process, after the surface has been strengthened by shot peening, the surface is roughened by magnetic polishing to be polished almost uniformly, thereby eliminating surface roughness and scratches on the surface caused by shot peening. This is to remove compressive residual stress and to apply compressive residual stress.

In magnetic polishing, either a coil spring placed in a magnetic field or a magnetic abrasive material adsorbed to the surface of the coil spring are slightly vibrated, and the two move relative to each other while in contact, causing the surface of the coil spring to become magnetic. It is polished using an abrasive material. As the magnetic abrasive material used for magnetic polishing, use ferromagnetic powder made of a sintered body of iron powder and ceramics (alumina A9203, etc.), or ferromagnetic powder made of other substances. I can do it. Further, while these magnetic abrasive materials or coil springs are in contact with each other, one of them is imaged by a device that applies micro vibrations at an imaging cycle of 20 KHz to 200 KHz to perform magnetic polishing.

The coil spring can be magnetically polished in a stretched state, that is, in a state in which a tensile strain is applied to the coil spring. In this case, the same effect as stress peening can be obtained, the residual stress distribution can be roughly improved, and the fatigue strength can be improved.

A magnetic polishing device used in the magnetic polishing process includes, for example, a chuck that holds both ends of a coil spring in the axial direction and has a vibration drive source that gives constant motion to the coil spring and a rotation drive source that gives rotation to the coil spring, and a chuck. The magnetic field generator consists of a ferromagnetic material held at the inner periphery of the coil spring, and a magnetic field generating device arranged on the outer periphery of the coil spring. The ferromagnetic body consists of a plurality of permanent magnets arranged to face the inner peripheral surface of the coil spring. The magnetic strength of this permanent magnet is 4GsO
It is preferable to use one in the range of e (Gauss-Oersted) to 40GSO8. This permanent magnet is disposed so that it moves as the position of the inner circumferential surface changes when the coil spring rotates, so that its north and south poles can face the inner circumferential surface. For example, there is a cylindrical holding member arranged at the center of the axis of a coil spring, and the central part is pivoted to this cylindrical holding member with a distance corresponding to the pitch of the coil spring in the axial direction, and the pivot point Both ends can be moved around the center. The magnetic field generating device may be an electromagnetic device made of electromagnetic soft iron or the like, which has N and S poles arranged at a constant interval on the outer periphery of the coil spring and opposed to each other at 180 degrees. can.

[Operations and Effects] According to the surface treatment method for a coil spring of the present invention, a step of subjecting at least the inner circumferential surface of a pre-formed coil spring to shot peening is performed. As a result, at least the inner circumferential surface of the coil spring is strengthened by shot peening. Thereafter, at least the inner peripheral surface of the coil spring is magnetically polished almost uniformly by a magnetic polishing process. In addition, if overpeening occurs, that portion is also polished.

Surface scratches caused by shot peening are removed, surface roughness is improved and reduced, and residual stress is imparted to the surface.

Therefore, according to the method for manufacturing a coil spring of the present invention, the inner circumferential surface of the coil spring after the shot peening process can be more roughly strengthened than in the conventional case, thereby increasing the fatigue strength. Therefore, it becomes possible to use a high-hardness material, which was conventionally considered to be too sensitive to surface scratches and could not be used as a coil spring material.

In addition, when a coil spring that has been strengthened and has increased fatigue strength using this manufacturing method is used as a valve spring in an engine valve mechanism, it can be used as a valve spring that has been subjected to conventional shot peening processing or a brushed spring that has been subjected to shot peening processing. Alternatively, the durability can be significantly improved compared to a valve spring that has been subjected to electrolytic polishing. Since the valve spring is strengthened, it can be made smaller, and it is also possible to reduce the weight of the head portion of an engine using this valve spring and to increase the number of valves (5 to 6 valves).

[Example] The surface treatment method for a coil spring of this example consists of a shot peening process and a magnetic polishing process. In this embodiment, a case will be described below in which a valve spring used as a coil spring is incorporated into a valve operating mechanism of an engine intake system or an exhaust system.

Using the spring material (SWO3C-V) shown in Table 1, wire drawing, oil tempering treatment, coiling, and
The valve spring 1 having the specifications shown in Table 2 is formed by low-temperature annealing. This valve spring 1 is subjected to shot peening to strengthen its entire surface. Thereafter, the shot peened valve spring 1 is placed in a magnetic polishing device, and the chemical composition and second spring specifications of the first spring material (SWO3C-V) are magnetically polished.

During the process of magnetic polishing the valve spring 1 of this embodiment,
A magnetic polishing apparatus as shown in FIG. 2 is used. This first magnetic polishing device includes a pair of ring-shaped chucks 2.3 that hold the valve spring 1, a ferromagnetic member 4 disposed on the inner circumference of the valve spring 1, and a ferromagnetic member 4 disposed on the outer circumference of the valve spring 1. It consists of an electromagnet section 5 capable of forming an N pole 50 and an S pole 51, which are arranged and placed at positions facing each other.

-iJ's chuck 2.3 is attached to both axial ends 1 of the valve spring 1.
0.11, the axis I of the valve spring 1 is rotated by the rotational drive source of the enclosure. It is designed to be able to rotate 3600 times around P. Also, this pair of chucks 2.
3, the valve spring 1 can be vibrated by a drive source in the enclosure.

The ferromagnetic member 4 includes a plurality of permanent magnets 42 arranged on the inner circumference of the valve spring 1 . This permanent magnet 42 has an N pole 420 and an S pole 421 at both ends, and is arranged along the axis P of the valve spring 1. The intermediate portions are pivotally connected to each other by a support shaft 41 and are attached at regular intervals,
It is held so that its mounting angle can be changed.

The magnetic abrasive material 6 is made of powder obtained by sintering iron powder and ceramics (alumina).

In the magnetic polishing process, the valve spring 1 is held fixed at one end 10 and the other end 11 by a chuck 2.3 of a magnetic polishing device, as shown in FIG. 2, and is held in a state where tensile strain is applied. . An N pole 420 is provided on the inner circumference of this valve spring 1.
．． Permanent magnet 42 with magnetic abrasive material 6 adsorbed to S pole 421
will be placed.

Further, this valve spring 1 is disposed at a position where its outer peripheral portion faces the electromagnet portion 5. When the power to the enclosure of the electromagnet section 5 is turned on in this state, the N pole 50 and the S pole 51 facing each other
is formed, and magnetic lines of force are generated between the north pole 50 and the south pole 51, forming a magnetic field. and magnetized valve spring 1
A magnetic abrasive material 6 is pressed onto the inner circumferential surface 12 of. In this state, the valve spring 1 is rotated around the axis P while applying slight vibrations to the valve spring 1 through the chuck 2.3 from an external drive source (not shown) and a rotation source. The poles 420 and S poles 421 face the inner circumferential surface 12 of the valve spring 1, which is magnetized at this portion by the S pole 51 and the N pole 50 of the electromagnet section 5, and support against changes in the position of the inner circumferential surface 12. The angle changes in the vertical direction about the shaft 41. As a result, the inner peripheral surface 12 of the rotating valve spring 1 has the N poles 420 and S of the permanent magnet 42 at the positions of the S pole 51 and N pole 50 of the electromagnet section 5. A magnetic field is formed between the poles 421 and the inner circumferential surface 12 of the valve spring 1, and the amount of magnetic abrasive material 6 necessary for magnetic polishing is always held by this magnetic field. The inner peripheral surface 12 of the valve spring 1 and the highly hard magnetic abrasive material 6 move relative to each other while coming into contact with each other as the valve spring 1 moves and rotates.
2 is closely polished by a magnetic abrasive material 6.

Therefore, the inner circumferential surface 12 of the valve spring 1 can be magnetically polished to remove surface scratches caused by shot peening, and the surface depth where overpeening occurs is 50 μm.
The range of m can also be polished.

The valve spring 1 obtained by the surface treatment method of this example and the conventional processing methods (1), (2), and (3) described in the prior art section)
The surface roughness, compressive residual stress, and fatigue strength of this valve spring and a conventional valve spring are shown in comparison with each other in FIGS. 3 to 5.

As shown in FIG. 3, the surface roughness of the peripheral wall surface 13 of the valve spring 1 of this embodiment is determined by conventional processing methods (1), (2>, (3)).
This is improved to approximately 115 compared to . Further, compressive residual stress (kgf/Irun2) is applied to the valve spring 1 of this embodiment by contact with the magnetic abrasive material 6, and the peak value thereof is as shown by the symbol in FIG. The conventional processing methods (1), (2) indicated by the mouth mark and the Δ mark
This is higher than (3). Furthermore, the fatigue strength (kQf/m2) of the peripheral wall surface 13 of the valve spring 1 of this embodiment is also
As shown in the figure, conventional processing methods (1), <2), (3)
improved compared to

[Brief explanation of drawings]

FIG. 1 is a diagram showing the process sequence of the method for manufacturing a valve spring of this embodiment. FIG. 2 is a schematic diagram showing a polishing apparatus used in the magnetic polishing step in FIG. 1. Figures 3 to 51 show valve springs produced by the method of manufacturing valve springs of this embodiment and those produced by conventional methods (1), (2>, and (3)) described in the prior art section. These are comparison diagrams with the obtained valve spring. Figure 3 shows the surface roughness, Figure 4 shows the residual stress distribution range, and Figure 5 shows the fatigue strength. 1...Valve spring (coil spring) ) 2.3...Pair of chucks

Claims (1)

[Claims] (1) It is characterized by comprising the steps of shot peening at least the inner peripheral surface of the formed coil spring, and magnetic polishing the at least inner peripheral surface of the shot peened coil spring. Surface treatment method for coil springs.