Method of manufacturing a crank shaft for a hermetic reciprocal compressor

Abstract

A method of manufacturing a crank shaft for a hermetic reciprocal compressor including the steps of providing a main shaft and a crank portion eccentric for a predetermined degree from the main shaft that are separately formed. The main shaft and the crank portion are joined through laser welding. The main shaft is a hollow pipe and the crank portion is made by sintering. The main shaft and the crank portion are connected, and an end portion of the main shaft is inserted into an annular groove formed at a main shaft connection side of the crank portion. Accordingly, the main shaft is a drawn steel pipe, and the crank portion is formed by sintering, thus the crank shaft becomes lighter and no post-process is needed. Therefore, the manufacturing process is remarkably reduced, and the crank shaft manufactured at a lower production cost.

Description

BACKGROUND OF THE INVENTION

[0001] 1. Field of the Invention

[0002] The present invention relates generally to a method of manufacturing a crank shaft for a hermetic reciprocal compressor, and more particularly to such a method in which the crankshaft production costs are improved and productivity is reduced.

[0003] 2. Description of the Related Art

[0004] It is well known that a hermetic reciprocal compressor has an electric driving portion and a compressing portion in a case. Rotational movement of the electric driving portion is converted into the reciprocal movement of the compressing portion by a crank shaft, and thus, as a piston of the compressing portion is reciprocally moved in a cylinder, refrigerant is compressed.

[0005] FIG. 1 shows a conventional hermetic reciprocal compressor. As shown in FIG. 1, the conventional hermetic reciprocal compressor has an electric driving portion 20, and a compressing portion 30 disposed in the case 10 having an upper shell 1 and a lower shell 2. The electric driving portion 20 and the compressing portion 30 are connected to each other by the crank shaft 40. The rotational movement of the electric driving portion 20 is converted into the reciprocal movement of the compressing portion 30 by the crank shaft 40.

[0006] The crank shaft 40 comprises a main shaft 41 inserted into a rotor 21 of the electric driving portion 20, and a crank portion 42 connected by the piston 31 and a connecting rod 32 of the compressing portion 30. In FIG. 1, reference numeral 22 represents a stator, 33 is a cylinder block, and 34 is a cylinder head.

[0007] The conventional method for manufacturing the above-described hermetic reciprocal compressor is to mold the crank shaft by casting. After molding, the molded crank shaft is processed to a desired size. In other words, parts of the forged surface of the molded crank shaft are removed by cutting such as by rough cutting and turning. Next, to increase the toughness of the crank shaft, it is put through a heat-treatment process. The heat-treated crank shaft is again clean cut and processed to provide the final crank shaft.

[0008] However, the conventional method of manufacturing the crank shaft described above does not offer a simple process for producing the finished molded product. In this process, the molded product needs to be post-processed by processing such as by rough cutting, turning, and grinding. This lowers productivity and increases manufacturing costs.

[0009] Additionally, since the amount of material that is cut increases as casting dispersion increases, the cycle time also increases, thereby causing low productivity. Moreover, since the dispersion is great, load conditions are different when processing and abrasion of the cutting tools are increased.

[0010] Furthermore, it is difficult to use the conventional method of manufacturing a crank shaft to manufacture a crank shaft which is hollow, which allows for increased toughness, greater than the toughness of the conventional crank shaft. Moreover, the conventional solid crank shaft, being solid, is heavy. Consequently, the efficiency of the compressor is lowered with a solid crank shaft because of the reciprocal motion of a heavier mass.

[0011] Lastly, in the conventional method for manufacturing the crank shaft, a deep oil passage is formed in the molded product through a post-process. Thus, this step also lowers the productivity in manufacturing the crank shaft due to the complexity of processing of the oil passage.

SUMMARY OF THE INVENTION

[0012] An object of the present invention is to provide a method of manufacturing a crank shaft for a hermetic reciprocal compressor capable of improving productivity and reducing production costs, thereby eliminating the need for initial cutting and post-processes, and simplifying the manufacturing process to form an oil passage.

[0013] Another object of the present invention is to provide a method for manufacturing a crank shaft, which having reduced weight.

[0014] In the method of manufacturing a crank shaft according to the present invention, a main shaft and a crank portion eccentric for a predetermined degree from the main shaft are separately made. The main shaft and the crank portion are then joined through laser welding. The main shaft is a hollow pipe and the crank portion is made through sinter molding. The material of the hollow pipe and the sinter molded product is a metallic alloy including less than 0.5% carbon by weight percent. It is preferable that the hollow pipe be a carbon steel pipe.

[0015] An annular groove for embracing an end portion of the main shaft is formed at the connection side of the crank portion, and the crank portion and the main shaft are connected with each other so that the end portion of the main shaft is inserted into the annular groove of the crank portion. Here, the annular groove is formed so that the main shaft can transition-fit relative to the annular groove.

[0016] According to the preferred embodiment of the present invention, a method of manufacturing a crank shaft for a hermetic reciprocal compressor having a main shaft and a crank portion which is eccentric for a predetermined degree from the main shaft, comprises the steps of: preparing the hollow pipe main shaft by drawing and cutting a carbon steel pipe of a predetermined length, and forming at least one oil passage in the carbon steel pipe; preparing the crank portion forming a molded product having an eccentric shaft and a weight balancer by sintering a metallic alloy powder, and then forming at least one oil passage in the molded product, and forming an annular groove at one side of the molded product for a predetermined depth; joining the main shaft and the crank portion by using a laser welder after inserting an end portion of the main shaft into the annular groove of the crank portion; forming an oxide coating on the joined crank shaft for increased corrosion and abrasion resistance of the joined crank shaft; and final clean cutting.

BRIEF DESCRIPTION OF THE DRAWINGS

[0017] The object and features of the present invention will become more apparent by describing the preferred embodiment of the present invention by referring to the appended drawings, in which:

[0018] FIG. 1 is an exploded perspective view showing a conventional hermetic reciprocal compressor;

[0019] FIG. 2 is a cross-sectional view showing the method of manufacturing a crank shaft of a hermetic reciprocal compressor according to the present invention; and

[0020] FIG. 3 is a perspective view showing a crank shaft of a hermetic reciprocal compressor manufactured according to the present invention.

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENT

[0021] Hereinbelow, the preferred embodiment of the present invention will be described in greater detail by referring to the appended drawings.

[0022] FIG. 2 is a cross-sectional view showing the method of manufacturing a crank shaft for a hermetic reciprocal compressor according to the present invention. FIG. 3 is a perspective view showing a crank shaft of an assembled hermetic reciprocal compressor manufactured according to the present invention.

[0023] As shown in FIGS. 2 and 3, the crank shaft, 40 manufactured according to the method of the present invention, comprises a main shaft 41 and a crank portion 42 extending in an eccentric direction for a predetermined amount from the main shaft 41. The main shaft 41 and the crank portion 42 are joined through laser welding.

[0024] The main shaft 41 is a hollow pipe. In the preferred embodiment of the present invention, a drawn carbon steel pipe is cut to a predetermined length, and at least one oil passage 41a is formed at a predetermined place through the cut carbon steel pipe. When the main shaft 41 comprises a hollow pipe, the weight is greatly reduced as compared to a solid shaft. Moreover, straightness of the hollow pipe is improved and dispersion, or flaring of the end of the cut pipe, is constant, thus there is no need to have an initial cutting process.

[0025] In the meantime, a carbon steel pipe for an automobile or a machine is used for the main shaft 41 in the preferred embodiment of the present invention. Yet, it is not limited to the above example. The main shaft 41 may be formed of a hollow pipe made of metallic alloy including less than 0.5% carbon.

[0026] The crank portion 42 has an eccentric shaft 42a and a weight balancer 42b. The crank portion 42 is formed by a powder metallurgy method for forming a product by sintering metallic alloy. Here, all kinds of alloy having less than 0.5% carbon may be used as the metallic alloy. Since the crank portion 42 is manufactured as a sintered product by the powder metallurgy method, the process is improved and cutting as a post-process can be omitted. Therefore, the process of manufacturing will be simplified. Moreover, the crank portion 42 has a hollow eccentric shaft 42a, and at least one oil passage 42c penetrating from the hollow to a back side thereof.

[0027] In addition, the crank shaft 41 has an annular groove 42d for embracing an end of the main shaft 41 at a connection side of the main shaft 41. The end of the main shaft 41 is inserted into the annular groove 42d of the crank portion 42 and stably connected during the laser welding of the main shaft 41 and the crank portion 42. The annular groove 42d is formed to so that a pipe of a nominal diameter may be inserted.

[0028] After separately forming the main shaft 41 and the crank portion 42 as a hollow pipe and a sintering product, and connecting the main shaft 41 to the crank portion 42 by inserting the main shaft 41 into the annular groove 42d of the crank portion 42, the main shaft 41 and the crank portion 42 are joined by laser welding. The welding process is described below in greater detail.

[0029] The main shaft 41 and the crank portion 42 are joined at the connection portions, where the main shaft 41 and the annular groove 42d intersect, by laser welding. The welding condition for an optimal tensile strength of the laser welded connection is 3 to 10 Kw of laser output, 0.51 to 1.78 m/min of transferring speed, and 20° to 70° of point of focus.

[0030] After laser welding the main shaft 41 and the crank portion 42 in accordance with the above welding process, an oxide coating is formed at the surface of the welded members for increasing corrosion proof and abrasion resistance, and a cutting operation is added.

[0031] According to the present invention, the step of rough cutting and turning for adjusting concentricity becomes mostly unnecessary and can be omitted or minimized. Most of all, productivity is elevated, and since a laser of high energy density is used, the welding is completed in a short time. Therefore, there is less deformation caused by the heat process, and more free design can be done with a non-contact style.

[0032] According to the present invention as described, since the main shaft of the crank shaft is a drawn steel pipe, the weight is reduced, and also dispersion during the cutting of the pipe end is constant. Thus, there is no need for an initial process. Moreover, as the crank portion is manufactured by sinter molding, the post-process is hardly needed and the manufacturing process is significantly reduced.

[0033] Additionally, according to the present invention, as the end portion of the main shaft is connected with the annular groove of the crank portion inserted thereinto by laser welding, a bead generated from the welding fills up the annular groove. Thus, there is no space around the welding area, and density will be increased. Moreover, the weld bead does not protrude to the outside, so a post-process for removing the weld bead can be omitted.

[0034] Furthermore, according to the present invention, the main shaft is a pipe shape, thus a simple oil passage is formed in a radial direction of the main shaft to form the oil passage. Therefore, the manufacturing process will be significantly reduced as compared to the conventional method for forming the oil passage.

[0035] Lastly, the crank portion is formed by sintering, so the degree of process accuracy is excellent and the post-process can be omitted.

[0036] Consequently, the present invention provides a crank shaft with a low production cost and a high density.

[0037] So far, the preferred embodiment of the present invention has been illustrated and described. However, the present invention is not limited to the preferred embodiment described herein. The scope of the invention is set forth in, and only limited by, the following claims.

Claims

1. A crank shaft for a hermetic reciprocal compressor,

wherein the crank shaft includes a main shaft connected with a rotor of the hermetic reciprocal compressor; and

a crank portion eccentric to a predetermined degree with respect to the main shaft connected with a connecting rod, and

the main shaft and the crank portion being joined to each other through laser welding, after the main shaft is formed as a hollow pipe, and the crank portion is formed by sinter molding.

2. The crank shaft of claim 1, wherein material of the hollow pipe and the sintering molded product is a metallic alloy including less than 0.5% carbon.

3. The crank shaft of claim 1, wherein the hollow pipe is a carbon steel pipe for use in a machine or an automobile.

4. The crank shaft of claim 1, wherein an annular groove for embracing an end portion of the main shaft is disposed at a connection side of the main shaft of the crank portion, and the crank portion and the main shaft are connected with each other by the end portion of the main shaft being inserted into the annular groove.

5. The crank shaft of claim 4, wherein the annular groove is formed so that the main shaft can transition-fit relative to the annular groove.

6. A method for manufacturing a crank shaft for a hermetic reciprocal compressor, comprising the steps of:

providing a crank shaft including a main shaft for connection with a rotor of the hermetic reciprocal compressor; and

connecting a connecting rod to a crank portion of the crank shaft so as to be eccentric to a predetermined degree with respect to the main shaft,

forming the main shaft as a hollow pipe;

and forming the crank portion by sinter molding; and

laser welding the main shaft and the crank portion.

7. The method of claim 6, wherein the hollow pipe and the sinter molded product further comprises a metallic alloy material including less than 0.5% carbon.

8. The method of claim 6, wherein the hollow pipe is comprises a carbon steel pipe for use in a machine or an automobile.

9. The method of claim 6, wherein an annular groove for embracing an end portion of the main shaft is formed at a connection side of the main shaft of the crank portion; and

the crank portion and the main shaft are connected with each other so that the end portion of the main shaft is inserted into the annular groove before the laser welding step.

10. The method of claim 6, wherein the annular groove is formed so that the main shaft can transition-fit relative to the annular groove.

11. A method of manufacturing a crank shaft for a hermetic reciprocal compressor having a main shaft and a crank portion eccentric to a predetermined degree from the main shaft, comprising the steps of:

preparing the main shaft by drawing and cutting a carbon steel hollow pipe of a predetermined length, and forming at least one oil passage in the hollow carbon steel pipe;

preparing the crank portion by forming a molded product having an eccentric shaft and a weight balancer by sintering a metallic alloy powder,

forming at least one oil passage in the molded product, and forming an annular groove in one side of the molded product at a predetermined depth;

connecting the main shaft and the crank portion by inserting an end portion of the main shaft into the annular groove of the crank portion;

joining the main shaft and the crank portion by laser welding the main shaft to the crank portion where the two intersect;

forming an oxide coating for increasing corrosion and abrasion resistance of the joined crank shaft; and

final clean cutting.