KR20120002376A - Control arm for automobile using quenching hardening steel and method of manufacturing the same - Google Patents

Abstract

PURPOSE: A control arm for an automobile using quenching hardening steel and a method of manufacturing the same are provided to reduce the number of parts and processes for manufacturing a control arm because the portion of the control arm requiring buckling strength has a high hardness and the portion of the control arm to be coupled with other parts has a low hardness. CONSTITUTION: A control arm for an automobile using quenching hardening steel comprises steps of: preparing blank for manufacturing a control arm from quenching hardening steel(S110), heating the blank to an austenite temperature region(S120), hot-press forming the heated blank in a molding device(S130), cooling the molded product in the molding device closed, where the portion of the molded product requiring buckling strength is cooled rapidly in order to secure relatively high hardness and the portion of the molded product to be coupled with other parts is cooled at low speed(S140).

Description

Control arm for automobiles using heat-treated hardened steel and manufacturing method thereof {CONTROL ARM FOR AUTOMOBILE USING QUENCHING HARDENING STEEL AND METHOD OF MANUFACTURING THE SAME}

The present invention relates to a control arm manufacturing technology applied to a suspension device of an automobile, and more particularly, to use a separate reinforcement by having a locally dissimilar strength by using a hardening steel (quenching hardening steel) The present invention relates to a control arm made of a single part without welding a plurality of parts, and a control arm for an automobile manufactured by the method of manufacturing the same.

Suspension device in a vehicle is a device that prevents the shock is directly transmitted to the vehicle body or the engine to cushion the impact of the road so that the vehicle can run stably.

Suspension devices are mainly composed of major parts such as suspension springs, shock absorbers and control arms.

Among the parts constituting the suspension device, the control arm is a part that supports the wheel and controls the movement thereof.

An object of the present invention is to produce a control arm using heat-treated hardened steel, to ensure the strength and durability of the control arm by having a heterogeneous strength locally.

Another object of the present invention is to provide a control arm and a method of manufacturing the ball joint component assembly and the rubber bush assembly by hole expansion molding at a high burring ratio, so that no separate pipe welding is required on these parts.

Still another object of the present invention is to provide a control arm and a method of manufacturing the same, by reducing the manufacturing cost by configuring the control arm as a single component.

The present invention comprises the steps of (a) providing a blank for manufacturing a control arm using a heat-treated hardened steel material; (b) heating the blank to an austenite temperature range; (c) hot press forming the heated blank in a mold apparatus; And (d) cooling the molded material while the mold apparatus is closed, and a portion of the material that requires buckling strength is rapidly cooled to secure a relatively high strength and is assembled with other parts. The low-temperature cooling heat treatment step; provides a control arm manufacturing method for a vehicle comprising a.

At this time, in the step (a), it is preferable to punch the rubber bush assembly part and the ball joint part assembly part hole, and in the step (c), the part has a high burring ratio by expanding the hole. Do.

In addition, it is preferable to allow the central portion between the rubber bush assembly and the ball joint component assembly to be rapidly cooled.

The present invention includes a rubber bush assembly, a ball joint component assembly, and a central portion between the rubber bush assembly and a ball joint component assembly, wherein the tensile strength of the central portion is the rubber bush assembly and the ball joint. An automotive control arm is characterized in that it is greater than the tensile strength of the component assembly.

At this time, the tensile strength of the central portion is 1500 ~ 1700MPa, the tensile strength of the rubber bush assembly and the ball joint assembly is preferably 800 ~ 1000MPa.

The present invention reduces the number and process of parts required for manufacturing control arms by forming a control arm in which a part requiring buckling strength has a high strength and a part combined with other parts has a relatively low strength. In this case, the control arm manufacturing cost can be reduced.

In addition, the present invention by forming the ball joint assembly and the rubber bush assembly at a high burring ratio brings the effect that the separate pipe welding can be omitted in these parts.

1 is a view showing a state in which the front wheel lower control arm of the vehicle is assembled;
2 is a view showing the direction of the external force applied to the control arm and the site where the buckling occurs;
3 is a view showing a distribution of loads concentrated in the area A;
4 is a plan view showing the structure of a control arm according to the present invention;
5 is a cross-sectional view taken along line BB of FIG. 4;
Figure 6 is a process flow diagram showing a control arm manufacturing method for a vehicle according to an embodiment of the present invention.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention, and the manner of achieving them, will be apparent from and elucidated with reference to the embodiments described hereinafter in conjunction with the accompanying drawings. However, the present invention is not limited to the embodiments disclosed below, but may be implemented in various different forms, only the present embodiments to make the disclosure of the present invention complete, and common knowledge in the art to which the present invention pertains. It is provided to fully inform the person having the scope of the invention, which is defined only by the scope of the claims. Like reference numerals refer to like elements throughout.

1 is a view showing a state in which the front wheel lower control arm of the vehicle is assembled, Figure 2 is a view showing the direction of the external force applied to the control arm and the site where the buckling occurs.

Referring to FIG. 1, the control arm is a component that forms a suspension device coupled to a lower subframe or knuckle of a vehicle to mitigate an impact transmitted from a road surface when the vehicle is driven.

Referring to FIG. 2, the control arm 100 has an approximately L-shape, an upper portion 110 and a lower portion 120 of the right side are connected to a vehicle body frame, and an end 130 of the left side is connected to a steering knuckle. It is assembled to move up and down according to the vibration of the front wheel.

The external force input through the front wheels while driving the vehicle is transmitted to the control arm 100 through a portion connected to the steering knuckle, as indicated by the arrows in the figure. Therefore, the input external force is concentrated in the area A.

Figure 3 shows the distribution of the load concentrated in the A region.

Arrows shown in the figure indicate the magnitude and direction of the local load, and it can be seen that the load is concentrated in the center. This load distribution causes buckling, and therefore, high strength is required for this portion.

Due to the structural characteristics of the control arm, a plurality of press-formed parts are generally welded to secure a required buckling strength by having a box-shaped closed cross-sectional structure.

Another method for securing the required strength may be a method of improving the strength of the entire control arm. However, if only the control arm has an excessively high strength due to the characteristics of a part that is connected to other parts and transmits a load, This can adversely affect the overall durability.

The present invention is characterized in that the control arm is formed of a single part, but has a heterogeneous strength locally. More specifically, the part requiring buckling strength should have ultra high strength of 1500MPa class, and the part connected with other parts should have relatively low strength of 1000MPa or less, thereby securing buckling strength and durability. It is to provide a control arm and a method of manufacturing the same.

First, the structure of the control arm of the present invention will be described.

4 is a plan view showing the structure of a control arm according to the present invention, Figure 5 is a cross-sectional view taken along the line B-B of FIG.

In the example shown in FIG. 3, one side of the control arm becomes the rubber bush assembly part 310, the other side becomes the ball joint part assembly part 320, and the rubber bush assembly part 310 and the ball joint part assembly part 320. ) Is divided into a central portion 330. In addition, the control arm is provided with a tooling hole 341, jig holes 342 and 343, and the like.

In order to secure the assembly strength of the ball joint component assembly 320 and the rubber bush assembly 310, in the past, separate pipes were welded, but in the present invention, the parts are expanded in a high burring ratio. By providing a structure that can secure the assembly strength without welding a separate pipe.

When the hole expansion molding is performed at a high forming ratio in cold press molding, a molding defect (material bursting) occurs, and the present invention produces a heat-treated hardened steel material by hot forming, but by performing a hole expanding molding during hot forming, Buringbi can be secured.

Referring to FIG. 5, the control arm 300 for a vehicle according to the present invention has a U-shaped cross section opened downward. This cross-sectional shape improves the strength of the component compared to the flat plate shape. In particular, this shape helps to improve the buckling strength of the load applied to the control arm 300 in the horizontal direction.

In the present invention, the excellent workability before heat treatment, using heat-treated hardened steel to ensure high strength after heat treatment, the tensile strength of the central portion 330 through the manufacturing method described later, the rubber bush assembly portion 310 and the ball joint By providing a greater than the tensile strength of the component assembly 320, while ensuring the buckling strength of the central portion 330, it provides a structure that can maintain the appropriate strength of the parts assembled with other components.

Since the rubber bush assembly 310 and the ball joint component assembly 320 are portions that are combined with other components, if they have excessively high strength, they may cause problems with the durability of other components. To have.

Looking at the specific range of strength, the central portion 330 is about 1500 ~ 1700 MPa may have a tensile strength corresponding to the ultra-high strength of more than 1500 MPa, rubber bush assembly 310 and ball joint assembly 320 is 800 It can have a relatively low tensile strength of less than 1000 MPa as ~ ~ 1000 MPa.

Heat-treated hardened steel serving as a material for producing such a control arm is, in weight percent, C: 0.19 to 0.4%, Mn: 0.5 to 2.5%, Cr: 0.1 to 0.5%, B: 0.0015 to 0.004%, Mo: 0.05 0.2% or less, Si: 0.5% or less, P: 0.05% or less, S: 0.05% or less, Al: 0.03% or less and remaining Fe and other unavoidable impurities may be used, and Ni: 2% or less as necessary. And at least one of Nb: 0.1% or less and Cu: 1% or less.

The heat-treated hardened steel having the above composition may be hot rolled steel or cold rolled steel or steel produced in various ways such as aluminum plated steel, galvanized steel, electroplated steel, hot dip galvanized steel, alloyed hot dip galvanized steel, and the like.

Next, look at with respect to the control arm manufacturing method for automobiles using the heat-treated hardened steel according to the present invention.

6 is a process flowchart showing a control arm manufacturing method for a vehicle according to an embodiment of the present invention.

Referring to FIG. 6, the illustrated control method for manufacturing a vehicle includes a blank preparing step (S110), a heating step (S120), a hot forming step (S130), and a heat treatment step (S140).

In the blank preparation step (S110), the blank for manufacturing the control arm is cut by using the hardened hardened steel. Hole cutting can be performed on the necessary part when the blank is cut, and hole processing can be performed through a separate punching process.

Among the processed holes, the holes of the rubber bush assembly portion and the holes of the ball joint component assembly portion are expanded and molded at a high burring ratio in the hot forming step (S130). The expanded hole formed by the high burry can secure the assembly strength without welding a separate pipe as described above.

Examples of heat-treated hardened steel applied to the present invention include carbon (C): 0.19 to 0.4% (hereinafter, by weight), manganese (Mn): 0.5 to 2.5%, chromium (Cr): 0.1 to 0.5%, boron (B): 0.0015 to 0.004%, molybdenum (Mo): 0.05 to 0.2%, silicon (Si): 0.5% or less, phosphorus (P): 0.05% or less, sulfur (S): 0.05% or less, aluminum (Al): 0.03% or less And steel made of the remaining Fe and other unavoidable impurities.

Hereinafter, the role and content of each alloy component included in the heat treated hardened steel exemplified above are as follows.

Carbon (C)

Carbon is added to give strength. Carbon also contributes to lowering the quenching temperature by stabilizing austenite and lowering the Ac3 transformation point.

The carbon is preferably added at 0.19 to 0.4% by weight of the total weight of the heat-treated hardened steel. When the content of carbon is less than 0.19% by weight, securing strength is insufficient. On the contrary, when the carbon content exceeds 0.4% by weight, the toughness of the quenched portion may be sharply lowered.

Manganese (Mn)

Manganese is very effective as a solid solution strengthening element, and is an effective element to secure strength by improving hardenability of steel.

The manganese (Mn) is preferably added in 0.5 to 2.5% by weight of the total weight of the heat-treated hardened steel. When manganese is added in less than 0.5% by weight, the effect of strengthening the solid solution and improving the hardenability according to the addition of manganese is insufficient. On the contrary, when the manganese exceeds 2.5% by weight, there is a problem of greatly reducing the weldability.

Chrome (Cr)

Chromium is an effective element for stably securing strength after heat treatment hardening.

The chromium is preferably added in 0.1 to 0.5% by weight of the total weight of the heat-treated hardened steel. Chromium may be added at least 0.1% by weight to ensure strength, and when it exceeds 0.5% by weight, it may hinder the balance between strength and ductility without further strength improvement.

Boron (B)

Boron increases the hardenability of the steel sheet by delaying the phase transformation during continuous cooling transformation, and secures the strength after quenching as a strong hardenable element.

The boron is preferably added in 0.0015 ~ 0.004% by weight of the total weight of the heat-treated hardened steel. When boron is added less than 0.0015% by weight has no effect, when added in excess of 0.004% by weight the effect is saturated and may exhibit a problem that impairs the impact characteristics.

Molybdenum (Mo)

Molybdenum (Mo) increases the strength by securing the martensite phase fraction with chromium (Cr), and serves to improve the plating adhesion by preventing the surface concentration of silicon (Si), manganese (Mn).

The molybdenum is preferably added in 0.05 to 0.2% by weight of the total weight of the heat-treated hardened steel. When the content of molybdenum is less than 0.05% by weight, the addition effect is insignificant, and when the content of molybdenum exceeds 0.2% by weight of heat-treated hardened steel, ductility and weldability may be sharply lowered.

Silicon (Si)

Silicon exhibits a deoxidation effect and also has an effect of increasing stabilization of strength after heat treatment.

However, when the content of the silicon exceeds 0.5% by weight of the total weight of the heat-treated hardened steel, there is a problem of generating surface defects due to red scale, so that the silicon is added to 0.5% by weight or less of the total weight of the heat-treated hardened steel desirable.

Phosphorus (P), Sulfur (S)

Phosphorus is a useful element for securing strength. However, when a large amount is added, not only the workability is lowered but also the weldability is reduced. Therefore, the phosphorus is preferably added at 0.05% by weight or less of the total weight of the heat-treated hardened steel.

Sulfur may inevitably be added during the steelmaking process or may be added in small amounts to enhance processability. However, since excessive coagulation of sulfur may increase coarse inclusions and deteriorate fatigue properties and weldability, the sulfur content is preferably 0.05% by weight or less of the total weight of the heat-treated hardened steel.

Aluminum (Al)

Aluminum is used as the deoxidizer. In particular, in the case of soluble aluminum (Sol.Al) has a great effect to improve the strength through the refinement of grains. However, when the content of aluminum exceeds 0.03% by weight of the total weight of the heat-treated hardened steel, the strength may be lowered. Therefore, aluminum is preferably added at 0.03% by weight or less.

In addition, the heat-treated hardened steel applied to the present invention, in addition to the above alloy components, one or more components of nickel (Ni) 2% by weight or less, niobium (Nb) 0.10% by weight or less, copper (Cu) 1% by weight or more It may include.

These elements have the effect of increasing the stabilization of strength after heat treatment. However, when these contents exceed each upper limit, the effect will be saturated.

The heat-treated hardened steel having the above composition may be hot rolled steel or cold rolled steel, and may be plated steel such as aluminum plated steel, galvanized steel, electroplated steel, hot dip steel, alloyed hot dip galvanized steel, or the like.

Next, in the heating step S120, the blank is heated for hot press molding.

At this time, the heating is preferably heated to a temperature corresponding to the austenite temperature region of the heat-treated hardened steel so as to easily secure the strength in the heat treatment step (S140).

In the case of the heat-treated hardened steel having the above composition, it is preferable to heat to 850 ~ 950 ℃ corresponding to the austenite temperature range. In this case, if the heating temperature is lower than 850 ° C, other phases in addition to austenite may be generated, and it may be difficult to secure the target strength even after the heat treatment step (S140). May cause problems.

Next, in the hot forming step (S130), the heated blank is hot press formed using a mold apparatus including a lower mold and an upper mold.

In this case, the hot press molding may include hole expansion molding. A high burring ratio can be ensured by expanding and molding the hole previously drilled in the blank preparing step in the heated state.

Hole expansion molding may be performed at the rubber bush assembly part and the ball joint part assembly part of the control arm. When these parts are molded at high burring ratios, separate pipe welding for securing assembly strength can be omitted, thereby reducing the number of parts and simplifying the manufacturing process.

Next, in the heat treatment step (S140), the molded material is cooled and heat treated and cured while the mold apparatus is closed. At this time, the buckling strength (buckling strength) is required in the material to ensure high strength by rapid cooling, the other portion is low-speed cooling, so that the control arm is manufactured to have a heterogeneous strength locally.

Here, the portion where the rapid cooling is made is a portion that is compression-deformed by buckling at the time of external impact, in the material may be a central portion between the rubber bush assembly and the ball joint assembly.

Cooling channels may be formed in the mold apparatus for local rapid cooling. Cooling channels may be formed in the upper and lower regions of the control arm where buckling strength is required, ie in the upper and lower regions of the central portion between the rubber bush assembly and the ball joint component assembly of the control arm. Rapid cooling can be achieved by supplying a cooling fluid, such as a cooling liquid or a cooling gas, to the cooling channels in the mold apparatus.

The cooling rate, etc. may vary depending on the intensity targeted in each part. For example, the cooling may be performed up to about 150 ° C., which is below the martensite transformation point, and the average cooling rate of the rapid cooling part may be 50 to 150 ° C./s. In this case, it was found that martensite structure having excellent toughness with little variation in strength was obtained over the entire portion to be rapidly cooled. Such control of the cooling rate can be made by adjusting the temperature of the cooling fluid or the flow rate of the cooling fluid.

Through the control of the cooling rate, etc., the rapid cooling is able to secure the tensile strength corresponding to the ultra high strength of 1500 MPa or more, specifically 1500-1700 MPa, and the low-speed cooling is 1000 MPa or less. Can achieve a relatively low tensile strength of about 800 ~ 1000 MPa.

 Ultra high strength of about 1500 ~ 1700 MPa is formed in the part that needs to secure the buckling strength, and relatively low tensile strength of about 800 ~ 1000 MPa is formed in the part assembled with other parts.

Thus, it is possible to manufacture control arms with locally different strength in a single part.

In the above description, the embodiment of the present invention has been described, but various changes and modifications can be made at the level of those skilled in the art. Such changes and modifications may belong to the present invention without departing from the scope of the present invention. Therefore, the scope of the present invention will be determined by the claims described below.

S110: blank preparation step S120: heating step
S130: hot press molding step S140: heat treatment step
100, 300: control arm
310: rubber bush assembly 320: ball joint parts assembly
330: center portion 341: tooling hole
342, 343: jig hole

Claims (17)

(a) providing a blank for manufacturing a control arm using a heat treated hardened steel material;
(b) heating the blank to an austenite temperature range;
(c) hot press forming the heated blank in a mold apparatus; And
(d) Cooling the molded material in the closed state of the mold apparatus, where the buckling strength required in the material is rapidly cooled to secure a relatively high strength, and the parts assembled with other parts Method of manufacturing a control arm for a vehicle comprising a; heat treatment to cool at a low speed.
The method of claim 1,
In the step (a),
Punch the rubber bush assembly part and the ball joint part assembly part hole,
In the step (c),
The control arm manufacturing method for an automobile, characterized in that the expansion of the hole.
The method of claim 2,
The rapid cooling portion is
The control arm manufacturing method for a vehicle, characterized in that the central portion between the rubber bush assembly and the ball joint component assembly.
The method of claim 1,
In step (b),
The austenitic zone temperature is 850 ~ 950 ℃ automotive control arm manufacturing method characterized in that.
The method of claim 1,
Rapid cooling in the step (d)
Method for manufacturing a control arm for cars, characterized in that made by the cooling fluid supply.
The method of claim 1,
In the step (a), the heat-treated hardened steel,
By weight%, C: 0.19 to 0.4%, Mn: 0.5 to 2.5%, Cr: 0.1 to 0.5%, B: 0.0015 to 0.004%, Mo: 0.05 to 0.2%, Si: 0.5% or less, P: 0.05% or less , S: 0.05% or less, Al: 0.03% or less and the remaining Fe and other unavoidable impurities.
The method of claim 6,
The heat treated hardened steel
A method of manufacturing a control arm for automobiles, further comprising at least one of Ni: 2% or less, Nb: 0.1% or less and Cu: 1% or less.
The method according to claim 6 or 7,
The heat treated hardened steel
Hot rolled steel or cold rolled steel,
A method for manufacturing a control arm for an automobile, characterized in that the plating steel is selected from aluminum plated steel, galvanized steel, electroplated steel, hot dip galvanized steel, and hot dip galvanized steel.
The method of claim 1,
The step (d)
Cooling is controlled so that the tensile strength of the portion where the rapid cooling is made is 1500 MPa or more and the tensile strength of the portion where the slow cooling is made is 1000 MPa or less.
And a rubber bush assembly, a ball joint component assembly, and a central portion between the rubber bush assembly and the ball joint component assembly, wherein the tensile strength of the central portion is the tensile strength of the rubber bush assembly and the ball joint component assembly. Automotive control arm, characterized in that larger than.
The method of claim 10,
Tensile strength of the central portion is 1500MPa or more,
The tensile strength of the rubber bush assembly and the ball joint component assembly is less than 1000MPa, the control arm for a vehicle, characterized in that the whole is formed of a single part.
The method of claim 11,
Tensile strength of the central portion is 1500 ~ 1700MPa,
The tensile strength of the rubber bush assembly and the ball joint component assembly is 800 ~ 1000MPa automotive control arm.
The method of claim 10,
The control arm is
A control arm for an automobile, which has a U-shaped cross section opened downward.
The method of claim 10,
The rubber bush assembly unit or the ball joint component assembly is a control arm for an automobile, characterized in that formed by high burring ratio.
The method of claim 11,
The heat treatment hardened steel,
By weight%, C: 0.19 to 0.4%, Mn: 0.5 to 2.5%, Cr: 0.1 to 0.5%, B: 0.0015 to 0.004%, Mo: 0.05 to 0.2%, Si: 0.5% or less, P: 0.05% or less , S: 0.05% or less, Al: 0.03% or less, and the control arm for automobiles, characterized in that consisting of the remaining Fe and other unavoidable impurities.
16. The method of claim 15,
The heat treated hardened steel
By weight percent, automotive control arm, characterized in that it further comprises at least one of Ni: 2% or less, Nb: 0.1% or less and Cu: 1% or less.
16. The method of claim 15,
The heat treated hardened steel
Hot rolled steel or cold rolled steel,
Automotive control arm, characterized in that the plated steel selected from aluminum plated steel, galvanized steel, electroplated steel, hot-dip galvanized steel and alloyed hot-dip galvanized steel.

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