KR20190054631A - Brake disc for reducing brake judder and method for manufacturing the same - Google Patents

Abstract

Provided are a brake disc to minimize a judder phenomenon caused by a thickness irregularity of the brake disc and a method for manufacturing the same. The method of manufacturing the brake disc, to uniformly control a solidification rate of molten metal injected into a mold, forms a gate in any one of a pair of molds corresponding to an inboard portion and an outboard portion of the brake disc to inject the molten metal into a mold, and controls a coarse graphite distribution ratio of an arbitrary region of the brake disc for the coarse graphite distribution ratio to have difference of 5% or less with respect to an average coarse graphite distribution ratio.

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a brake disk for reducing judder and a manufacturing method thereof,

BACKGROUND OF THE INVENTION 1. Field of the Invention [0001] The present invention relates to a brake disk for judder reduction and a manufacturing method thereof, and more particularly, to a brake disk capable of minimizing judder phenomenon due to uneven thickness of a brake disk and a method of manufacturing the same.

Due to the recent development of the automobile industry and the high penetration rate of automobiles, consumers are demanding high levels of NVH (Noise, Vibration & Harshness) performance. Therefore, there is a growing interest in braking device technology for vibration reduction during vehicle braking. Generally, a vehicle braking device is composed of a brake disc and a caliper. When a vehicle is braked, vibration occurs between the disc and the pad, which is caused by vibration of the steering wheel and pedal. This is called a brake judder phenomenon.

The cause of brake judder can be divided into braking torque variation (BTV) and disc thickness variation (DTV). Among them, brake judder caused by disc thickness non-uniformity (DTV) There is a problem that not only vibration but also noise is caused. Particularly, when there is a difference in the microstructure or homogeneity of the inside of the disk, as the use period of the vehicle becomes longer, irregularities are generated on the surface of the disk, and the judder phenomenon due to the disk thickness unevenness (DTV) tends to be intensified.

On the other hand, the brake disk is usually manufactured by a casting process, and a vertical molding machine or a horizontal molding machine is used in accordance with a mold division method. In the case of a horizontal molding machine, since the mold is divided into upper and lower parts, the brake disk is formed in the horizontal direction, so that the brake disk is hardly affected by temperature difference or gravity in the vertical direction during solidification, have. Therefore, when a brake disk is manufactured using a horizontal molding machine, almost no judder phenomenon due to the disc thickness non-uniformity (DTV) is found.

From the viewpoint of commercialization, the process using the vertical molding machine is superior to the horizontal molding machine in cost and productivity. However, in the case of a vertical molding machine, since the mold is divided into left and right, the brake disk is formed in the vertical direction, so that it is influenced by the temperature difference and gravity in the vertical direction. In particular, the gate is injected into the mold, It is difficult to obtain a uniform microstructure due to the difference in heat capacity and thermal gradient with other regions. This leads to judder phenomenon according to the disc thickness non-uniformity (DTV).

Therefore, when casting a brake disk with a vertical molding machine having excellent productivity, research and development for improving the judder phenomenon due to the disc thickness non-uniformity (DTV) is urgently required.

SUMMARY OF THE INVENTION It is an object of the present invention to provide a method of manufacturing a brake disk for judder reduction capable of uniformly controlling the solidification rate of a molten metal injected into a mold when a brake disk is manufactured using a vertical molding machine.

Another problem to be solved by the present invention is to provide a judder reducing brake disk manufactured by such a method.

The problems to be solved by the present invention are not limited to the above-mentioned problems, and other matters not mentioned can be clearly understood by those skilled in the art from the following description.

According to another aspect of the present invention, there is provided a method of manufacturing a brake disc for judder reduction, comprising the steps of: preparing a brake disc for a judder reduction using a vertical molding machine using a mold having a gate to which a molten metal is injected, (P), 0.3 wt% or less of phosphorus (S), 0.3 wt% or less of sulfur (S), 3.2 to 3.8 wt% of carbon (C), 1.7 to 2.7 wt% 0.3% by weight or less of chromium (Cr), the balance of iron (Fe) and other unavoidable impurities. In order to uniformly control the solidification rate of the molten metal injected into the casting mold, it corresponds to the inboard and outboard of the brake disc Wherein a distribution of the coarse graphite in an arbitrary region of the brake disk is equal to or less than 5% of an average coarse graphite distribution ratio To control the distribution ratio of coarse graphite.

While the temperature of the molten metal is maintained at 1350-1500 degrees, the injection rate can be injected at 3-5 kg / s and the carbon equivalent can be maintained at 4.1-4.4.

The microstructure of the brake disk may be 80% or more of A type flake graphite based on ISO 945-1.

When the abrasion test is performed on the brake disc using a dynamometer, the disc thickness non-uniformity (DTV) of the brake disc may be less than 10um over the entire area.

When performing the abrasion test on the brake disk by using a dynamometer, the following braking pattern (1) to braking pattern (7) are defined as one cycle, and when performing a plurality of cycle abrasion tests on the brake disk, The disc thickness non-uniformity (DTV) of the brake disc may be less than 10 [mu] m over the entire area.

Braking pattern 1: initial velocity = 100 kph, slave velocity = 70 kph, deceleration = 2 m / s ² and frequency = 5%;

Braking pattern 2: initial speed = 50 kph, slave speed = 0 kph, deceleration = 2.5 m / s ² and frequency = 22%;

Braking pattern (3): initial velocity = 45 kph, slave velocity = 0 kph, deceleration = 2 m / s ² and frequency = 60%;

Braking pattern 4: initial velocity = 40 kph, slave velocity = 0 kph, deceleration = 2.5 m / s ² and frequency = 3%;

Braking pattern 5: initial speed = 40 kph, slave speed = 0 kph, deceleration = 2 m / s ² and frequency = 8%;

Braking pattern 6: initial velocity = 45 kph, slave velocity = 45 kph, deceleration = 0 m / s ² and frequency = 1% (hold for 360 seconds); And

Braking patterns (7): = initial velocity is also 0kph, dependent = 0kph also, deceleration = 0m / s ² and a frequency = 1% (keeping 360 seconds).

According to another aspect of the present invention, there is provided a judder reducing brake disk, which is manufactured by the manufacturing method.

The details of other embodiments are included in the detailed description and drawings.

As described above, according to the brake disk for judder reduction and the method of manufacturing the brake disk according to the present invention, even if a vertical molding machine is used, a gate is formed in only one of the pair of molds corresponding to the inboard and outboard of the brake disk, By injecting the molten metal into the mold, the increase in the heat capacity near the gate is minimized, and consequently, the solidification speed of the molten metal in the mold is uniformly controlled as a whole to obtain a uniform microstructure. Furthermore, uniform microstructure can be obtained by controlling the distribution ratio of the coarse graphite in the brake disk within a certain range. As a result of obtaining such a uniform microstructure, judder phenomenon due to disc thickness non-uniformity (DTV) can be minimized even if the brake disc is used for a long period of time.

1 shows an image of a brake disk according to the present invention.
2 shows an image of a mold used in a method of manufacturing a brake disk according to the present invention.
Fig. 3 shows the dynamometer used in the wear endurance test simulating the brake operation.
4 shows a static DTV device for measuring DTV before and after the wear test.
Fig. 5 shows the position of the tissue inspection of the brake disk for microstructure analysis.
6 shows microstructure photographs of Example (a) and Comparative Example (b).
Fig. 7 shows the distribution of coarse graphite in Example (a) and Comparative Example (b).
8 shows a DTV profile of a brake disc in which a wear test is performed using a dynamometer.

BRIEF DESCRIPTION OF THE DRAWINGS The advantages and features of the present invention and the manner of achieving them will become apparent with reference to the embodiments described in detail below with reference to the accompanying drawings. The present invention may, however, be embodied in many different forms and should not be construed as being limited to the embodiments set forth herein. Rather, these embodiments are provided so that this disclosure will be thorough and complete, and will fully convey the scope of the invention to those skilled in the art. Is provided to fully convey the scope of the invention to those skilled in the art, and the invention is only defined by the scope of the claims. Like reference numerals refer to like elements throughout the specification.

The brake disk of the present invention can be made of gray cast iron. Gray cast iron has high abrasion resistance and thermal conductivity compared to other materials, but it is excellent in price competitiveness. Particularly, the composition of the brake disk of the present invention for minimizing the judder phenomenon due to the disc thickness unevenness (hereinafter referred to as "DTV") is 3.2-3.8 wt% of carbon (C), 1.7-2.7 wt% of silicon (Si) , Iron (Fe) and other inevitable impurities in an amount of 0.4-1.1 wt% of manganese (Mn), 0.3 wt% or less of phosphorus (P), 0.3 wt% or less of sulfur (S) . It is also preferable that the carbon equivalent of the brake disk is maintained at 4.1-4.4. Further, it is preferable that the microstructure of the brake disk is 80% or more of the type A flake graphite based on ISO 945-1.

Here, the carbon (C) content is preferably 3.2-3.8 wt%. If the carbon content is lower than 3.2% by weight, the A-type flaky graphite is hardly produced. If the carbon content is higher than 3.8% by weight, the coarsening of the graphite structure is excessively high and the mechanical performance of the disk is deteriorated.

Silicon (Si) promotes crystallization of graphite solidified in iron, with a silicon content of preferably 1.7-2.7 wt%. When the silicon content is lower than 1.7 wt%, nucleation of graphite is difficult and the carbon equivalent is low, so that uniformly distributed A type flake graphite is difficult to be produced. If the silicon content is higher than 2.7% by weight, a deterioration reaction may occur in the crystallized graphite structure and the mechanical strength of the entire disc may be lowered.

Manganese (Mn) reacts with sulfur (S) to form a manganese sulfide (MnS) compound, which neutralizes the harmful effects of sulfur, which inhibits the crystallization of graphite. The manganese content is preferably 0.4-1.1 wt%. If the manganese content is lower than 0.4 wt%, FeS is formed to increase the brittleness. If the manganese content is higher than 1.1 wt%, excessive MnS is formed and the hardness is inhibited.

Phosphorus (P) inhibits workability and precipitates on the grain boundaries to lower the impact strength. Therefore, the phosphorus (P) is preferably limited to 0.3 wt% or less. Sulfur (S) causes brittleness when present in the steel, so it is preferable to limit it to 0.3 wt% or less. Cr (Cr) is preferably limited to 0.3 wt% or less as an element which inhibits the growth of graphite.

The content of carbon (C), silicon (Si) and phosphorus (P) in the brake disk composition of the present invention should be maintained at a level of 4.1-4.4, which satisfies the following formula (1) A brake disk having graphite of 80% or more can be obtained.

[Equation 1]

CE = C + (Si + P) / 3

Hereinafter, the method for manufacturing the brake disk of the present invention having the above composition will be described in detail.

First, cast iron pig iron and scrap iron are blended into the melting furnace, and melted at 1500 ° C. to prepare a molten metal. As a sufficient temperature for graphite growth, the melt temperature is maintained at 1350-1500 degrees.

Subsequently, molds are produced by molding sand using a vertical molding machine (DISA230-C ™) equipped with a pair of molds corresponding to the inboard and outboard of the brake disc, and a core made of resin coated sand is molded into a mold .

The melt is then injected into the mold at an injection rate of 3-5 kg / s using an automatic injector (OCG-50 ™). When the molten metal is injected, the injection temperature is maintained at 1350-1450 degrees. After cooling, the mold is separated, and the brake disk is completed through a shot blasting process and a finishing process.

Hereinafter, the mold used in the present invention will be described in detail with reference to FIG. 1 and FIG. Fig. 1 shows an image of a brake disk according to the present invention, and Fig. 2 shows an image of a mold used in a method of manufacturing a brake disk according to the present invention. The brake disk is comprised of an outboard facing outward when the vehicle is mounted and an inverse (not shown). The mold for the brake disc is formed by a pair of the first mold corresponding to the outboard and the second mold corresponding to the inboard, thereby forming the mold. In the mold, a gate for injecting the molten metal and a riser for discharging the gas in the mold are formed. In the present invention, in order to uniformly control the solidification rate of the molten metal in the mold, Only one of them forms a gate. For example, a gate may be formed only in the first mold. The reason for this is as follows. During the solidification of the molten metal in the mold, solidification takes place at the gate as well as at the disk forming portion. In the disk adjacent to the gate, the heat capacity is increased by the molten metal filled in the gate, and the coagulation rate is relatively slow. . This leads to microstructure irregularity and judder caused by DTV. In order to minimize such a problem, if the gate is formed only in one of the first and second dies, the thickness of the gate is substantially reduced to half, and the thermal capacity affecting the solidification rate can be minimized. Likewise, the same principle can be applied to the riser in the mold. That is, when the riser is formed only in one of the first and second dies, the increase in the heat capacity of the disk adjacent to the riser is minimized, and a uniform solidification rate can be obtained throughout the disk. In the preferred embodiment of the present invention, by forming the gate and the riser only in the first metal mold corresponding to the outboard of the disk, a uniform solidification speed and microstructure can be obtained throughout the disk.

Hereinafter, the present invention will be described in more detail with reference to examples and comparative examples.

<Examples>

3.56 wt% of carbon (C), 1.99 wt% of silicon (Si), 0.68 wt% of manganese (Mn), 0.029 wt% of phosphorus (P), 0.076 wt% of sulfur (S), 0.192 wt% of chromium Brake discs were fabricated using a Braille disc composition consisting of iron (Fe) and other inevitable impurities at a carbon equivalent of 4.1-4.4, a molten bath temperature of 1350-1500, and an injection rate of 3-5 kg / s. At this time, a vertical molding machine having a gate and a riser formed in only the first metal mold corresponding to the outboard was used.

<Comparative Example>

Compared with the above embodiment, a conventional vertical molding machine having a gate and a riser formed on both molds was used to manufacture a brake disk.

&Lt; Experimental Example 1: Dynamometer test and DTV profile >

The wear characteristics were analyzed to investigate the DTV judder improvement effect on the brake disk manufactured according to the embodiment of the present invention and the comparative example. Fig. 3 shows the dynamometer used in the wear endurance test simulating the brake operation. The dynamometer has an inertia moment of up to 160 kg · m ² and a rotational speed of 2800 rpm. A ventilated type disc with a diameter of 320 mm and a 45 mm twin piston caliper were used. The abrasion test of each brake disk was performed using the dynamometer. Specifically, DTV growth was induced by defining the braking pattern (1) to the braking pattern (7) shown in Table 1 below as one cycle and performing wear test for 10 cycles or more.

Braking pattern No. Initial speed (kph) Dependency (kph) Deceleration (m / s ² ) Frequency One 100 70 2 5% 2 50 0 2.5 22% 3 45 0 2 60% 4 40 0 2.5 3% 5 40 0 2 8% 6 45 45 0 1% (360 seconds remaining) 7 0 0 0 1% (360 seconds remaining)

Then, the DTV before and after the abrasion test was measured using the Static DTV apparatus shown in FIG.

<Experimental Example 2: Microstructure analysis>

The microstructure of each brake disk subjected to the wear test using the dynamometer was inspected. Fig. 5 shows the position of the tissue inspection of the brake disk for microstructure analysis. The tissue examination samples were extracted from the A portion corresponding to the riser, the C portion corresponding to the gate, the other B portion and the D portion, and the samples collected from each region were extracted for six regions (# 1 to # 6) . For microscopic examination, a 100x optical microscope was used. The distribution state and length of graphite in the gray iron were determined for the microstructure of the observed brake disk. The distribution of graphite was determined according to the ISO 945-1 standard of Table 2 below and according to the length of eight sections ranging from less than 0.015 mm to more than 1.0 mm in length.

Mark Distribution Orientation Type A (Type A) Uniform distribution Random Type B (Type B) Rossette groupings Random Type C (Type C) Superimposed flake size Random Type D (Type D) Inter-dendritic segregation Random Type E (Type E) Inter-dendritic segregation Preferred

<Experimental result 1: Change of microstructure according to solidification rate control>

6 shows microstructure photographs of Example (a) and Comparative Example (b). Fig. 7 shows the distribution of coarse graphite in Example (a) and Comparative Example (b). The microstructure was determined to be gray cast iron, lamellar graphite, type A uniform distribution over 80% and length of 0.12-0.5 mm. In addition, the microstructure was analyzed by using an image analysis function of an optical microscope.

In the examples, the average coarse graphite distribution ratio was 1.387%. By controlling the sizes of the risers and gauges of the mold, the distribution of the coarse graphite in all regions (portions A to D) of the brake disk had a uniform value , And preferably the coarse graphite distribution ratio is controlled so as to have a difference of 5% or less with respect to the average coarse graphite distribution ratio. Specifically, the A portion was 3.0% larger, the B portion 1.7% smaller, the C portion 1.8% larger, and the D portion 1.3% smaller than the average coarse graphite distribution ratio. In order to control the solidification speed of the molten metal in the vertical molding machine, uniform rough graphite distribution was obtained by reducing the size of the riser, reducing the width of the gate, and changing the position and width to disperse the thermal gradient in the mold.

On the other hand, in the case of the comparative example, the average coarse graphite distribution ratio was 1.735%, which was higher than the example. Specifically, the ratio of A and B was measured to be as small as 33.2% and 37.9%, respectively, as compared with the average coarse graphite distribution ratio, and the distribution of coarse graphite was not uniform.

<Test result 2: Evaluation of DTV profile>

FIG. 8 shows a DTV profile of a brake disk subjected to a wear test using a dynamometer, in which (a) is a DTV profile before a wear test, (b) is a DTV profile of the embodiment after a wear test, This is the DTV profile of the comparative example after the test.

DTV growth was induced by using a dynamometer on the brake disc of the embodiment, but the DTV of the brake disc was measured to be less than 10um over the entire area. It was confirmed that no specific peak was found in the DTV profile, and the disk wear characteristics were uniformly uniform throughout.

In the case of the brake disk of the comparative example, the DTV was increased after the abrasion test, and a specific interval peak was found. These peaks were found at positions corresponding to the risers and gates of the mold, with peaks in the DTV profile due to the uniformity of the distribution of microstructure or coarse graphite in the area.

As a result of checking the DTV profile, it was found that when the brake disk is manufactured by the vertical molding machine of the present invention, the influence of the gate and the riser of the mold on the microstructure is minimized, and uniform uniform coarse graphite distribution can be obtained as a whole, Characteristics were obtained.

While the present invention has been described in connection with what is presently considered to be practical exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but, on the contrary, You will understand. It is therefore to be understood that the above-described embodiments are illustrative in all aspects and not restrictive.

Claims (6)

In manufacturing a brake disk for judder reduction using a vertical molding machine using a mold having a gate into which molten metal is injected,
Wherein the composition of the brake disk is 3.2-3.8% by weight of carbon (C), 1.7-2.7% by weight of silicon (Si), 0.4-1.1% by weight of manganese (Mn) By weight or less of chromium (Cr), 0.3% by weight or less of chromium (Cr), the balance of iron (Fe) and other unavoidable impurities,
In order to uniformly control the solidification speed of the molten metal injected into the mold, a gate is formed in only one of the pair of molds corresponding to the inboard and outboard of the brake disk, the molten metal is injected into the mold through the gate, Wherein the coarse graphite distribution ratio is controlled such that the coarse graphite distribution ratio of an arbitrary region of the disk has a difference of 5% or less with respect to the average coarse graphite distribution ratio. The method according to claim 1,
Wherein the molten metal is injected at a rate of 3 to 5 kg / s while the temperature of the molten metal is maintained at 1350 to 1500 degrees, and the carbon equivalent is maintained at 4.1 to 4.4. The method according to claim 1,
Wherein the microstructure of the brake disk is 80% or more of A-type flake graphite based on ISO 945-1. The method according to claim 1,
Wherein the disc thickness non-uniformity (DTV) of the brake disc is less than or equal to 10 mu m over the entire area when the abrasion test is performed on the brake disc using a dynamometer. The method according to claim 1,
When performing the abrasion test on the brake disk by using a dynamometer, the following braking pattern (1) to braking pattern (7) are defined as one cycle, and when performing a plurality of cycle abrasion tests on the brake disk, (DTV) of the brake disk is not more than 10 mu m over the entire area, the method of manufacturing a brake disk for judder reduction,
Braking pattern 1: initial velocity = 100 kph, slave velocity = 70 kph, deceleration = 2 m / s ² and frequency = 5%;
Braking pattern 2: initial speed = 50 kph, slave speed = 0 kph, deceleration = 2.5 m / s ² and frequency = 22%;
Braking pattern (3): initial velocity = 45 kph, slave velocity = 0 kph, deceleration = 2 m / s ² and frequency = 60%;
Braking pattern 4: initial velocity = 40 kph, slave velocity = 0 kph, deceleration = 2.5 m / s ² and frequency = 3%;
Braking pattern 5: initial speed = 40 kph, slave speed = 0 kph, deceleration = 2 m / s ² and frequency = 8%;
Braking pattern 6: initial velocity = 45 kph, slave velocity = 45 kph, deceleration = 0 m / s ² and frequency = 1% (hold for 360 seconds); And
Braking patterns (7): = initial velocity is also 0kph, dependent = 0kph also, deceleration = 0m / s ² and a frequency = 1% (keeping 360 seconds). A judder reducing brake disk produced by the manufacturing method according to any one of claims 1 to 5.

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