KR20180012465A - Method for forming a bolt with flange head using quenched and tempered high strength steel - Google Patents

Abstract

The present invention relates to a method of manufacturing a bolt for use in an automotive air conditioner compressor using an ancillary steel.
The method includes the steps of cutting a steel wire of an ancillary steel material to a predetermined length, forming a cylindrical bolt head preform having a diameter larger than a diameter of a steel wire at one end of the steel wire, Forming a hexagonal cross section of an upper section of the bolt head preform and molding the hexagonal head preform into a hexagonal head preform; molding a flange head on the disk under a head of the hexagonal cross section to form a flange head; And the upper body is extruded so that the lower part of the upper body around the neck part of the inclined face decreases in diameter and an increase in length occurs.
INDUSTRIAL APPLICABILITY The present invention has an effect of inducing dispersion and reduction of load applied during a forging process so as to prevent deterioration of bolt durability due to stress concentration at the bolt neck portion and to prolong the life of the mold.

Description

TECHNICAL FIELD [0001] The present invention relates to a method for manufacturing a flange head bolt for a vehicle air conditioner,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a method of manufacturing a bolt for use in an automotive air conditioner compressor, and more particularly, to a method of manufacturing a bolt using a forged steel bolt for cold forging a wire made of a high- A method of manufacturing a vehicle air conditioner compressor flange head bolt using a fore-and-aft cylinder to prevent the deterioration of bolt durability due to stress concentrated on the body neck portion of the bolt by inducing dispersion and reduction of load applied during the process, And a manufacturing method thereof.

칭 (quenching)과 템퍼링(tempering) 열처리를 행함으로써 볼트 제품이 얻어지게 된다.Generally, the bolts used for fastening parts of various machines and appliances are mainly made by cold forging. In the process of manufacturing the bolts through the conventional cold forging, first, the material steel wire is subjected to spheroidizing annealing for a long time so as to secure the ductility, and then cut to a predetermined length and formed into a predetermined bolt shape through cold forging . And then heated to a high temperature of about 850 DEG C or higher to increase strength and toughness

The bolt product is obtained by performing quenching and tempering heat treatment.

However, in the above-mentioned conventional bolt manufacturing method, loss of thermal energy is inevitable in the spheroidizing annealing for the improvement of cold forging, and there is a high possibility that deformation of the forged part in the heat treatment process performed before and after cold forging In particular, in the case of a long product, it is pointed out that it is disadvantageous in terms of workability and productivity because an additional correction work must be performed.

칭, 템퍼링 열처리된 강선으로서 인장강도가 70∼130Kgf/㎟ 의 고강도임에도 냉간 단조 전의 구상화 소둔이 없이도 통상적인 냉간단조 가공이 원활하게 이루어지게 되고, 또한 냉간 단조가공 후에도 각종 기계구조용 부품에서 요구되는 높은 강도를 나타내어 별도의 후열처리(Q/T)를 필요로 하지 않는다고 밝히고 있다. A quenched and tempered steel wire rod for cold rolling is known which can produce a bolt without requiring a separate heat treatment after cold working in view of the problems pointed out in such conventional bolt cold forging methods . A typical example of the pre-forming steel for cold rolling is Patent Document 1, and the steel wire material of Patent Document 1

A cold-forging process can be performed smoothly even without spheroidizing annealing before cold forging, even when the tensile strength is 70 to 130 kgf / mm < 2 >, which is a high strength required for various mechanical structural parts even after cold forging. Strength and does not require a separate post heat treatment (Q / T).

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Patent Document 1: Registration No. 10-0568058 Among the bolts, the bolts used to bind the housing of the automotive compressor in a closed state are fastened through the front and rear head mounted on the front and rear sides of the cylinder head, so that the length of the electric field is about 20 times It is very long. Particularly, since the vehicle air conditioner must continuously discharge high-pressure refrigerant while directly receiving the vibration and heat generated from the engine, it is required to discharge the refrigerant at a very high quality Characteristics are required. The SCM435 material is mainly used as the fastening bolt for the automotive air conditioner compressor in the prior art. The material is subjected to spheroidizing annealing in advance of the cold forging mentioned above, and after the cold forging, post heat treatment (QT ), The process is troublesome and the production cost is high. In view of the above problems, the inventors of the present invention have attempted to manufacture a bolt for a compressor for a vehicle air conditioner by using a steel wire rod made of the above-mentioned pre-formed steel wire for cold forging. Figs. 1 (a) to 1 (e) show steps of manufacturing a flange head bolt in the same manner as the conventional bolt manufacturing method using SCM435 using an ancillary steel. Fig. 1 (A) shows a steel wire of a pre-formed steel wire cut into a predetermined diameter (D) and a length (L). The material steel wire thus prepared is extruded by using a first mold and a first punch (not shown) as shown in Fig. 1 (B) to form a neck The first cold forging is performed so that the length of the remaining portion of the body portion L1b except for the portion L1a is increased along with the decrease in diameter. Accordingly, D> D1, L <L1, and the diameter of the L1a portion maintains the original D value. Subsequently, preforming is performed on the bolt head using the second mold and the second punch as shown in FIG. 1 (D), and D <D2. Next, in step (d) of FIG. 1, the preformed material for the bolt head is moved to the third mold, and the head part is formed into a hexagon, for example, through the third punch. In the final step, the material of the hexagonal head moved to the fourth mold in FIG. 1 (e) is formed by the action of the fourth punch, so that the formation of the flange head bolt through a series of cold forging Is completed. As described above, in the cold forging process of the flange head bolt using the conventional pre-forming steel, the body portion of the bolt is extruded to stretch the lower body side so as to vary the diameter of the upper and lower portions starting from the neck portion N, And a step of applying a punching load for forming a head part over the third through the fourth mold. 2 (A) is a longitudinal sectional view of a mold S at a position where the "A" portion is seated and a punch P which acts on the plastic deformation load in the step (E) ) Is an actual photograph showing the state of the mold S shown in (A). In Fig. 2 (A), the arrow indicates the load acting direction of the punch P. As shown in the figure, when the bolt head is repeatedly subjected to the load, the neck portion N constituting the inclined lower step of the flange restrains the A portion, so that the forging load is concentrated on the A portion, The load is also concentrated in the neck portion of the mold which is in contact with the mold. This concentration of the punching load is caused by the shape characteristics of the warp-like neck portion N. [ As a result, in the neck portion of the corresponding metal mold, the mechanical strength of the flange head bolt that has been molded is inevitably weakened by the stress concentration at the portion A, and in the neck portion of the corresponding metal mold, It becomes a starting point of fracture in accordance with concentration. The load concentration due to the neck portion N of the bolt body and the load concentration of the mold contacting portion where the A portion and the flange are seated are repeatedly performed three times during the steps (c) through (e) of Fig. do. On the other hand, it is known that ancillary steel has a high strength and is excellent in cold-forging so that cold forging of various mechanical parts and bolts is possible without post-heat treatment. However, the length of the body relative to the diameter When cold forging a long flange head bolt having a neck portion N serving as a starting point for changing the diameter in the middle of the body, the residual stress is concentrated at the portion A below the flange head of the formed bolt, And the fracture occurs from the A-site and the flange-site contact surface where the punching load is concentrated in the metal mold during cold forging, and the life of the metal mold is inevitably shortened

The present invention has been made in view of the above-mentioned conventional problem of cold forging a flange head bolt of a car air conditioner compressor using a pre-formed steel as a raw material. In cold forging, load is not concentrated at a body- The present invention provides a method of manufacturing a flange head bolt for a vehicle air conditioner compressor using an ancillary steel to improve the durability of the formed bolt and to prolong the life of the forging die.

The above object of the present invention can be achieved by a method of manufacturing a steel sheet for a cold forging according to the present invention, which comprises the steps of forming a neck portion acting as a starting point of a diameter change in a multistage cold forging, This is accomplished by ensuring that the neck portion N, which is the cause of the load concentration during the multistage forging process for bolt head molding, is not present in the body region by performing after the molding of the flange head is otherwise completed.

A method of manufacturing a vehicle air conditioner compressor flange head bolt using an ancillary steel of the present invention includes the steps of cutting a steel wire of a pre-formed steel material to a predetermined length, A method of manufacturing a bolt head, comprising the steps of: forming a cylindrical bolt head preform; shaping an upper section of the bolt head preform into a hexagonal section and molding the same into a hexagonal head preform; And a step of extruding the straight body below the flange head so that the lower part of the linear body under the flange head is centered on the inclined neck portion and the length is increased with the decrease in diameter.

The pre-welded material steel wire used in the method of the present invention is a Q / T heat treated steel wire, and preferably a high strength wire having a tensile strength in the range of 70 to 130 kgf / mm &lt; 2 &gt;. The chemical composition of the ancillary steel has a composition of C of 0.10 to 0.40 wt%, Si of 1.0 wt% or less, Mn of 0.30 to 2.0 wt%, P of 0.03 wt% or less, and S of 0.03 wt% or less and the balance of Fe and unavoidable impurities desirable.

Hereinafter, the process of each step will be described in detail with reference to FIG. 3 (a) through FIG. 3 (e) showing one embodiment of the method of the present invention.

3 (a) is a workpiece steel wire W cut by a cutting blade so as to have a predetermined length (I), wherein the diameter d and the length l of the workpiece steel wire W are The length and the diameter are changed while the forging process is performed, and the dimension is determined in accordance with the specification of the bolt product to be finally formed.

Next, the workpiece steel wire W cut to a predetermined length shown in Fig. 3 (A) is punched (cold forging) in the primary metal mold as shown in Fig. 3 (B) Primary preforming is performed. The bolt head preform H obtained through the primary die has a flat cylindrical shape in which the diameter d1 thereof is increased compared to the diameter d of the workpiece wire W, It forms a straight line with no change in diameter over the entire section.

3 (C) shows a bolt head preform (H) molded with a hexagonal head by using a hexagonal punch in a secondary die. The hexagonal head preform (H1) at this time is a bolt head preform H, except for a part of the lower part of the entire length, and the lower part thereof is left in a circular shape. At this time, the body (B) is in the form of a straight line with no change in diameter over the entire section.

Next, in FIG. 3 (D), the hexagonal head preform (H2) is formed into a final shape through extrusion (forging) by a hexagonal punch in the third mold, and the flange (H2) formed in the final form so that the thickness decreases with the increase of the diameter. For this purpose, the hexagonal punch used in this step is formed with a punch formed such that the inner diameter of the hexagon is increased and the depth of the hexagonal punch is reduced as compared with the hexagonal punch used in FIG. 3 (C). In addition to the final shape of the bolt head, a chamfer C (chamfer) is formed at the lower end of the body B. At this time, the body B is formed in a straight line shape with no change in diameter over the entire section excluding the chamfer at the lower end.

As a final step, in (E) of FIG. 3, the intermediate molding material having the linear body B on the formed flange head H2 is extruded by using the fourth metal mold, The extrusion is performed such that the diameter of the lower portion of the portion N is reduced and the length thereof is increased. In the forging (extrusion) step of this step, the shape of the flange head H2 and the shape of the body on the upper side B1 of the neck portion N are not substantially changed (plastic deformation) Only the plastic deformation with respect to the body of the first and second molds B2 and B2 is performed.

As the above steps are all completed, the molding with a predetermined flange head bolt is completed. After the cold forging, rolling is performed to form threads on the outer circumferential surface of the lower body of the body until it becomes a final product, electro-galvanizing treatment for corrosion prevention, baking for brittle removal, and torque stabilization for uniform axial force This is performed in the same manner as in the conventional bolt manufacturing process.

In the method of the present invention, since the steel wire made of the pre-formed steel is used as the material, the post-heat treatment process for improving the mechanical properties such as tensile strength following the completion of the molding through the forging at the time of manufacturing the conventional SCM435 bolts is excluded, And the quality characteristics (tensile strength, etc.) required by the product can be stably secured.

Further, in the manufacturing method of the present invention, in forming the flange head bolts of the automotive air conditioner compressor by cold forging the pre-formed steel wire material, the neck portion of the body in which the load applied during the forging process is concentrated is formed after the forming of the bolt head is completed The load applied during the forging process is guided to be evenly dispersed without being concentrated at a specific portion of the body, so that the durability of the bolt due to the concentration of stress due to the bolt neck portion N is prevented, So that the life of the mold is prolonged.

1 (a) to 1 (e) are front views showing a cold forging step by step of a conventional flange head bolt.
Fig. 2 (A) is a longitudinal sectional view of the mold and the punch during the step (E) of Fig. 1, and Fig. 2 (B) is an actual photograph showing the broken state of the mold shown in Fig.
3 (a) through 3 (e) are front views showing a cold forging step by step of a flange head bolt according to an embodiment of the present invention.
Fig. 4 is a stress concentration distribution diagram and a shear line for a section between the head and the neck portion N of the formed flange head bolt. Fig. 4 (a) is a flange head bolt formed by the conventional method of Fig. Is a flanged head bolt formed according to the method of the present invention in Fig.

The mechanical properties of the formed bolts through a more detailed stepwise process of the invention and the process of the present invention will be more clearly understood from the following examples.

First, we selected the materials produced from the ancillary steel wire.

The material steel wire had a wire diameter d of 7.04 mm and a tensile strength of 110 kgf // mm 2, which was cut as shown in FIG. 3 (a). The length l of the cut material wire was 121 mm.

The cut material wire thus cut was punched with a first punch using a first die to form a bolt head preform (H) at one end of the steel wire as shown in Fig. 3 (B). The formed bolt head preform H had a diameter d1 of 9.2 mm and a height h1 of 8.7 mm.

Subsequently, the intermediate molding material molded with the bolt head preform (H) is transferred to a secondary mold and punched with a second punch as a hexagonal punch to obtain a hexagonal bolt head as shown in FIG. 3 (c) H), and molded with the hexagonal head preform H1.

Next, the hexagonal punch used in FIG. 3 (C) is increased in the inner diameter of the hexagonal punch, and the depth of the hexagonal punch is increased by the third punch, which is a hexagonal punch having a reduced inner volume, The hexagonal head as a final bolt head formed body as in the first embodiment of the present invention is formed into a final shape and the flange F on the disk below the flange head F is formed into a final shape in which the thickness is reduced H2 were formed. In addition to forming the final shape of the bolt head, a chamfer (chamfer) is simultaneously formed at the lower end of the body.

At this time, the diameter of the flange was 13.3 mm, the height of the bolt head including the flange was 6.8 mm, and the height of the chamfer C (the tip of the inclined edge) was 4.0 mm.

 Subsequently, as a final step, an intermediate molding material having a straight body on a formed flange head (H2) is extruded by using a fourth metal mold, and the neck portion (N) The diameter was reduced and the length was increased so that a final formed flange head bolt was produced in the same manner as in FIG. 3 (e). The diameter of the upper body part B1 from the neck part N to the upper side of the flange head H3 was 7.10 mm and the diameter of the lower body part B2 was 6.25 mm, (C1) height was 2.0 mm, which was reduced to half compared to before extrusion. The length of the entire body B including the chamfer C1 was 134.5 mm, the height of the flange head H3 was 6.8 mm, and the length of the steel wire before cold forging in the initial cut state was 121.1 mm , There is a considerable increase in length for the body (B).

At this time, the length of the upper body B1 of the neck portion N from the bottom of the flange head H2 is preferably in the range of 4.5 to 5.5 mm, more preferably 5 mm.

4 is a view showing a stress distribution and a short-circuit line with respect to a section between the head and the neck portion N of the formed flange head bolt. Fig. 4A is a flange head bolt formed by the conventional method of Fig. 1, (B) is for a flanged head bolt formed according to the method of the invention of FIG. As shown in Fig. 4, the stress (995 MPa) concentrated in the section between the head and the neck portion of the flange head bolt formed by the method of the present invention is significantly higher than the stress (1105 MPa) of the flange head bolt formed by the conventional method , And the shear line is also relatively gentle, indicating that it has a stable structure.

Claims (5)

Forming a cylindrical bolt head preform having a diameter larger than a diameter of a work steel wire at one end of the work steel wire; Forming an upper section into a hexagonal section and molding the hexagonal section into a hexagonal head preform; molding a flange head by forming a disk flange under the hexagonal section head; and forming a straight body under the flange head Wherein the step of extruding the flange head bolt comprises the step of extruding the neck portion of the flange head bolt so that the diameter of the neck portion is reduced and the length thereof is increased. The method according to claim 1, wherein the tensile strength of the material steel wire is 70 to 130 Kgf / mm &lt; 2 &gt;. The steel wire according to claim 2, wherein the chemical composition of the material steel wire comprises 0.10 to 0.40 wt% of C, 1.0 wt% or less of Si, 0.30 to 2.0 wt% of Mn, 0.03% or less of P and 0.03 wt% or less of S, Wherein the impeller is formed of unavoidable impurities. The method for manufacturing a flange head bolt for a vehicle air conditioner compressor according to claim 1, The method according to claim 1, wherein a chamfer is simultaneously formed at a lower end of the body in the step of forming the flange head. The method according to claim 1, wherein the length from the bottom surface of the flange head to the neck portion (N) is 4.5 to 5.5 mm in the step of extruding the body.

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