JPH0679541A - Method for forming torque transmitting shaft for induction hardening - Google Patents

Abstract

PURPOSE: To provide a method for inexpensively forming a high frequency hardened torque transmission shaft having similar performance using iron instead of steel. CONSTITUTION: A preform of a torque transmission shaft is cast of iron. This preform is heat-treated to provide microscopic structure of pearlite, bainite or tempered martensite. This heat-treated torque transmission shaft is machined, and it is hardened for the surface and outer zones by an induction heating device, while, relatively, hardening is not performed to inner zones.

Description

Description: FIELD OF THE INVENTION The present invention generally relates to induction hardening processes.
process), in particular, a method of forming a torque transmission shaft that is induction hardened from iron. [0002] Metal torque transmission shafts and similar components are widely used in many types of applications. In particular, rotatable metal torque transmission shafts are often used in vehicle drive trains and include axles, yoke shafts and the like. During use, these shafts can be subjected to the relatively large torque loads exerted by the vehicle engine to move the vehicle. That is, such shafts must be hardened sufficiently to carry these loads. Vehicle drive train shafts are generally formed from hardened steel. Conventionally, these steel shafts have been through-quenched by a conventional quenching process (through ha.
rdened). That is, the entire shaft (from surface to core), typically hardened in the range of 45 RC to 50 RC, was able to withstand the required torque load, but had a relatively low fatigue life, and Hardened shafts have resulted in fracture resulting from repeated loading caused by vehicle engines and other sources. In recent years, the vehicle drive train shaft is formed of steel that is hardened only on the surface and in the vicinity thereof. That is, the cores of these shafts are either unhardened or relatively shallow hardened. The surface and outer regions of such shafts are hardened in the range of 50RC to 55RC, but their cores are left unquenched or 20R.
Quenched only in the C to 30 RC range. This surface hardening of the steel shaft is done by using the usual induction hardening method. It has been found that the shaft thus obtained is able to withstand the required torque loads and resist fracture due to impact and fatigue. [0005] Surface hardened steel shafts and other torque transmitting components have been found to work satisfactorily in vehicles, but other considerations are apparent. Has become. In particular, the cost of forming certain parts from steel is known as an area of potential cost savings. That is, it is desirable to form such parts from relatively inexpensive materials while constantly maintaining satisfactory performance. The present invention is directed to a method of forming a torque transmission shaft that is induction hardened from iron. First, a shaft preform is cast or otherwise formed. This preform is then heat treated to produce the desired microstructure of the ferrous material, such as pearlite,
Use bainite or tempered martensite. Following this heat treatment, the unquenched shaft is machined to obtain the desired tolerance or specific shape.
Finally, the surface of the shaft that has not been hardened and the outer region are hardened by an induction heating device. The surface and outer regions of the resulting iron shafts are therefore hardened, while the inner regions of such shafts remain relatively unquenched. An object of the present invention is to provide a forming method for forming an induction hardening torque transmission shaft from iron. Another object of the present invention is to provide a method of forming such a torque transmission shaft from a material which is less expensive than current materials and which provides satisfactory performance for many applications. is there. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Referring to the drawings for the embodiments,
The steps involved in the method of the present invention for forming an induction hardened rotary torque transmission shaft from iron will be described in detail. As used in this description, the term "shaft" refers to a component that rotates and transmits torque during use. The first step in this process is to form the preform for the shaft. This first step is performed by first forming a quantity of iron into the general shape of the shaft. For example, use any conventional casting process to do this. It is recommended to use ductile iron or ductile iron to form the preform. The next step is to treat the preform so that the ferrous material therein has a predetermined microstructure. This desired microstructure is generally formed by including a sufficient amount of carbon diffused into a matrix of ferrous material to enable subsequent preform quenching. To do so, the preform is heated above the austenite temperature (which is about 1450 ° F. for iron) and then cooled. As is well known, the rate of cooling the preform determines the microstructure of the ferrous material. The formation of pearlite, bainite or tempered martensite is desirable as it allows subsequent preform quenching, as described below. Formation of ferrite is generally undesirable. As a variation on this heat treatment step, in some cases the preform can be cast such that pearlite is formed when the casting is cooled. This can be done by adding some alloying material such as copper to the molten iron when the preform is first cast. Due to the presence of the alloy material in the molten iron, pearlite is formed when the preform is cooled. Thus, there is no need for a separate step of heat treating the preform to obtain the desired microstructure. However, the parts obtained in each case are non-quenched shafts having the general shape of the final shaft to be formed. Each unhardened portion of the shaft is then machined or otherwise removed as necessary to obtain the desired tolerances or particular shape. The usual machining process is
Used to carry out this step. Following this machining,
The unquenched shaft has the desired shape of the final shaft to be formed. The final step of the method is to quench the unquenched shaft surface and the outer region.
This quenching is preferably performed by a common induction heating device. The induction heating device raises the temperature of the unquenched shaft surface and the outer region to a high temperature, for example about 1650 ° F. The duration of such heating and the grade of iron material
The penetration depth of this heat treatment is determined. Heating of the unquenched shaft continues until such heat treatment reaches a predetermined depth, based on the intended use of the shaft and the load it is likely to experience. In any case, such heating is interrupted prior to the heating of the inner region of the shaft,
It is desirable to prevent subsequent quenching of such internal regions. After heating the unquenched shaft, the shaft is cooled at a relatively fast rate. Such speeds are determined by the desired hardness for the surface of the shaft and the external areas and by the grade of material used. The cooling process is performed by any ordinary means. It has been found that it is desirable to burn the outer region of the shaft in the range of 50 RC to 55 RC while keeping the inner region below the 30 RC hardness level. It has been found that the resulting hardened iron shaft produces a more satisfactory function in many applications than comparable steel shafts. The iron shaft thus formed is significantly cheaper to manufacture than an equivalent steel shaft. Since iron is generally a cheaper material than steel per unit, some cost savings are possible. The ferrous material used in this method generally requires less processing than steel, thus saving other costs. As mentioned above, the ferrous material may simply be cast to form the preform. However, when using steel, the preform is made from steel rather than casting. Machining steel into preform shapes is generally more difficult and time consuming than simply casting iron into such shapes. That is, the use of iron in the method of the present invention provides significant cost savings over known methods of forming parts from steel. Although the present invention has been described in detail with reference to its embodiments, it is needless to say that the present invention can be modified in various ways without departing from the spirit thereof.

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 shows a flow chart of the steps involved in a method of forming an induction hardening torque transmission shaft from iron according to the present invention.

Claims (1)

Claims: 1. A method of forming an induction hardening torque transmission shaft from iron, comprising: (a) forming a shaft preform from iron; and (b) heat treating the preform to a predetermined Forming a non-quenched shaft made of iron having a microstructure of (c), the surface and the external region of the shaft made of iron obtained by quenching the surface and the external region of the shaft not hardened A quenching step while the inner region of such a shaft remains relatively unquenched,
Forming method consisting of. 2. The method of claim 1 wherein step (a) is performed by casting iron to form the preform. 3. The forming method according to claim 1, wherein the step (b) makes it possible to obtain a pearlite microstructure in an iron material. 4. The method of claim 1, wherein the step (b) provides a bainite microstructure in an iron material. 5. The forming method according to claim 1, wherein the step (b) is performed to obtain a tempered martensite microstructure by tempering an iron material. 6. The method of claim 1, wherein step (b) further comprises machining the unquenched shaft after heat treating the preform. 7. The method according to claim 1, wherein the step (c) is performed by induction heating. 8. A method of forming an induction-hardened torque transmission shaft from iron, comprising: (a) forming an unhardened shaft having a predetermined microstructure from iron; and (b) this unhardened shaft. Hardening the surface and outer regions of the iron shaft obtained by quenching the surface and outer regions of the shaft, while the inner regions of such shafts remain relatively unquenched. Law. 9. In the step (a), the iron is heated until the iron is melted, an alloy material is added to the molten iron, and the alloyed iron is cast in a mold having a general shape of a shaft. 9. The forming method according to claim 8, wherein the cast iron alloy is cooled to form an unquenched shaft. 10. The forming method according to claim 8, wherein the step (a) makes it possible to obtain a particulate microscope structure in an iron material. 11. The method of claim 8 wherein step (a) further comprises machining a non-quenched shaft. 12. The method according to claim 8, wherein the step (b) is performed by induction heating.