JP3067480B2 - Laser absorber for laser hardening - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a laser absorbent particularly suitable for laser hardening a work made of cast iron.

[0002]

2. Description of the Related Art For example, in a diesel engine using a cast iron cylinder block, a wear-resistant liner is inserted into the inner surface of a cylinder hole (cylinder bore) of the cylinder block, but the number of parts is reduced. There is a demand for a cylinder block that does not use a liner in order to reduce the cost and cost. In such a linerless cylinder block, the piston and piston ring are in direct contact with the inner surface of the cylinder hole. Is an important issue.

Therefore, as means for improving the wear resistance of the cylindrical hole, it has been considered that the inner surface of the cylindrical hole is tempered by heat treatment such as quenching. For this reason, the present inventors have developed a technique for performing spot-shaped quenching by the laser beam on the inner surface of the cylinder hole of the cylinder block, and have performed various tests and trial production. The quenching by the laser beam is performed by concentrating high-density energy on the inner surface of the cylindrical hole, performing local rapid heating for a short time, and then quenching by self-cooling action by heat diffusion into the cylinder block to obtain a martensitic structure. I have to. Therefore, in the laser quenching, a laser absorbent is applied to the surface of the work in order to efficiently absorb the laser beam.

[0004]

It is important that the above-mentioned laser absorbent has a high laser beam absorption efficiency.
If the laser beam absorption efficiency is simply high, chilling (melting) occurs in the quenched part depending on the material of the work,
The quenching quality may worsen. For example, at the time of laser hardening of the aforementioned cast iron cylinder block,
When a laser absorber containing graphite as a main component is used, the temperature of the quenched portion becomes higher than the melting temperature of the cast iron, and chill occurs. Further, as described in JP-A-2-19420, a laser absorber made of boron nitride is also known, but cannot be said to be suitable for laser hardening of a cast iron work.

Accordingly, an object of the present invention is to provide a laser absorber capable of rapidly heating a work surface to just before a melting temperature in performing a laser quenching of a work made of cast iron, thereby preventing damage due to melting. Is to do.

[0006]

Means for Solving the Problems The laser absorber of the present invention developed to achieve the above object has a MoS ₂ content of 15 to
It is characterized by containing 19% by weight and 2 to 5% by weight of graphite, with the balance being mainly binder and solvent. Hydrochlorofluorocarbon (HCFC) is suitable for the solvent,
Acrylic resin is suitable for the binder when this solvent is used.

[0007]

After applying the laser absorbent of the present invention to the surface of a work, spot quenching is performed by a laser beam output from, for example, a CO ₂ laser oscillator. Since the quenching by the laser has a small heating area, the high-density energy by beam irradiation is concentrated on the work surface while the beam is traveling in a certain direction. The irradiated laser beam is instantly absorbed by the laser absorbent, and effective local rapid heating is performed in a short time. After the laser irradiation, the heat of the heated portion is rapidly cooled by diffusing the inside of the work, so that a quenched martensite structure is obtained by this self-cooling action.

The laser absorber of the present invention decomposes near the melting temperature of cast iron and reduces the laser absorption effect, so that melting of the work surface is avoided. 1.7 to 4.5 mass% of carbon in cast iron
This is an iron-carbon alloy contained, and may contain Si, Mn, P, and S for improving castability or as an impurity. The melting point of cast iron is lower than that of general steel.
It is around 160 ° C.

[0009]

An embodiment of the present invention will be described below with reference to the drawings. FIG. 3 shows a cylinder block 10 as an example of a work. This cylinder block 10
Is cast by cast iron such as FC250, and the piston 11
Is formed. On the inner surface 12a of the cylindrical hole 12, a tempering portion 16 including a number of spot-shaped laser hardened portions 15 as shown in FIG.

The quenched portions 15 have substantially the same shape as each other, and each have a horizontally long shape along the circumferential direction of the cylindrical hole 12. An example of the length L of the quenched part 15 is 15 mm and the width W
Is about 3.5 mm. An example of the quenching depth is 0.
2 mm or more is desirable, but 10 to 1 depending on the purpose of refining.
The effect may be recognized even at a quenching depth of about 5 μm. These quenched portions 15 are provided at a plurality of locations at a predetermined pitch P1 in the circumferential direction of the cylindrical hole 12 and are formed at the same time.
A plurality of rows are provided at a predetermined pitch P2 in the direction of the axis 2. One example of the pitch P2 is 5 mm.

The tempering portion 16 including the quenching portion 15 is subjected to a process such as laser quenching through a series of steps illustrated in FIG. In the machining step S1, the inner surface 12
a is cut to a predetermined inner diameter by a machine tool such as a boring machine. Since the grinding oil adheres to the inner surface 12a of the cylindrical hole 12 on which the step S1 has been performed, the cleaning step S2 is performed after the machining, and the inner surface of the cylindrical hole 12 is cleaned and dried.

After the cleaning step S2 is completed, in the laser absorbent coating step S3, the coating apparatus 40 illustrated in FIG.
The laser absorbent is applied to the inner surface 12a of the cylindrical hole 12 by using. The coating device 40 includes a coating nozzle 41 inserted into the cylindrical hole 12 and a mechanism 42 for rotating the coating nozzle 41.
And an elevating mechanism 43 for raising and lowering the application nozzle 41. The laser absorber is sprayed onto the inner surface 12a of the cylindrical hole so as to have a predetermined thickness.

The laser absorber of the present embodiment used for the cast iron cylinder block 10 is 15 to 19 wt% as a main component.
MoS ₂ and ₂ to 5 wt% of graphite, and 6 to 10 wt% of an acrylic resin as a binder,
Hydrochlorofluorocarbon (CF ₃ C
_{F 2 CHCl 2 + CClF 2 CF} 2 CHClF) 66~
It melted at 77 wt%. Particularly preferred MoS ₂ content was 16 wt%, and graphite was 3 wt%. The coating thickness of the laser absorbent is preferably about 25 μm to 45 μm.

When the content of graphite is less than 2 wt% and when the content of MoS ₂ exceeds 19 wt%, C
Since the absorption efficiency of the O ₂ laser is too low, an excessive laser beam power is required, and it is difficult to reach a predetermined temperature with a small power. On the other hand, when the amount of graphite exceeds 5 wt%,
If the MoS ₂ is less than 15 wt%, the laser absorption efficiency is too high and melting occurs in the case of cast iron. Therefore, the contents of MoS ₂ and graphite are limited to the above ranges.

Hydrochlorofluorocarbon (H
CFC) is used because it has a low ozone destruction coefficient and is nonflammable as compared with a chlorofluorocarbon-based solvent. However, HCFC is disadvantageous in that the type of binder that can be dissolved is small. This problem has been solved by using an acrylic resin having good solubility in HCFC as the binder.

In the quenching step S4, quenching by a laser beam is performed by the laser quenching device 50 illustrated in FIG. An example of the quenching device 50 includes a processing head 51 inserted into the cylindrical hole 12, a CO ₂ laser oscillator 52 as an example of a laser generating unit, and a laser beam having a wavelength of 10.6 μm generated by the laser oscillator 52. And an optical system 53 for guiding the light to the processing head 51.

The laser quenching device 50 allows the cylindrical hole 1
The high-density energy is concentrated while running the laser beam at predetermined intervals in the circumferential direction on the inner surface 12a of the second 2, and rapid heating is performed in a short time to a temperature at which chill (melting) is not generated. An example of the heating temperature is 980 ° C. to 1120 ° C., that is, the heating temperature is set to a temperature equal to or higher than the A ₁ transformation point of the cast iron. An example of the heating time is about 0.2 seconds.

The laser oscillator 52 is individually set to a power in consideration of the heat storage condition in each quenching section 15,
Power control is performed. When the laser beam is stopped, the heat rapidly diffuses through the cylinder block 10 when the laser beam is stopped, and the portion is rapidly cooled, so that the mixed structure of pearlite and ferrite before quenching is quenched. Changes to martensite. Thus, quenching is performed sequentially in the circumferential direction of the cylindrical hole 12.

FIG. 6 shows the workpiece surface temperature when the laser absorber (molybdenum / graphite) of this embodiment is used and when the comparative example (boron nitride-based and molybdenum-based laser absorber) is used. I have. In the case of using the laser absorbent of this embodiment, the material is rapidly heated until immediately before the melting temperature is reached, but MoS ₂ is decomposed immediately before the melting temperature and the laser absorption effect is reduced, which may cause chill on the work surface. Effective and rapid heating can be performed.

After performing the above-described quenching step S4,
Tempering step S5 is performed. In the tempering step S5, the inner surface 12a of the cylindrical hole is heated to a predetermined temper temperature (for example, 30 ° C.) by a high-frequency induction coil as an example of a heating unit.
(0 ° C. to 350 ° C.) and then left in the air.

Thereafter, in the honing step S6,
Honing is performed on the inner surface 12a of the cylindrical hole 12 by a honing machine. The honing machine is provided with a grindstone on a rotary head that is rotated by a rotary drive mechanism. By rubbing the grindstone spirally on the inner surface 12a of the cylindrical hole, a large number of fine slopes called a so-called cross hatch are formed. Is formed. The rub grooves serve to retain oil during engine operation.

[0022]

According to the present invention, rapid heating to a temperature suitable for quenching can be performed without melting the work surface with good laser beam absorption efficiency.

[Brief description of the drawings]

FIG. 1 is a side view schematically showing a laser absorbent coating device.

FIG. 2 is a schematic diagram of a laser hardening device.

FIG. 3 is a perspective view of a cylinder block having a spot-shaped quenched portion by a laser.

FIG. 4 is a developed view of a part of the inner surface of the cylinder hole of the cylinder block shown in FIG.

FIG. 5 is a process explanatory view showing a working process of the inner surface of the cylinder hole of the cylinder block shown in FIG. 3;

FIG. 6 is a time chart showing the workpiece surface temperature when the laser absorbent of the present invention is used and when the laser absorbent of the comparative example is used.

[Explanation of symbols]

10: Cylinder block (work), 15: Hardened part, 4
0: Laser absorber application device, 50: Laser hardening device.

──────────────────────────────────────────────────続 き Continued on front page (58) Field surveyed (Int.Cl. ⁷ , DB name) C21D 1 / 09,1 / 34,1 / 70

Claims (2)

(57) [Claims] 1. A laser absorbing agent applied to the surface of the workpiece when performing laser hardening, the MoS ₂ 15 to 19 wt%, graphite containing 2-5 wt%, the balance being primarily binder and a solvent A laser absorbent for laser quenching characterized by the fact that 2. The method according to claim 1, wherein the binder is an acrylic resin, and the solvent is hydrochlorofluorocarbon.
The laser absorber according to the above.