Research on localization of disc brake pads of the

2022-08-08
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Research on localization of disc brake pads of Audi car

Abstract: This paper studies and solves two key technologies in localization of disc brake pads of Audi car. Firstly, combined with the advantages of regional resources, the carbon fiber asbestos free composite friction material with better performance than foreign friction materials was successfully developed, and the fine blanking process of brake pad back plate was also developed. The research results lay a good foundation for the localization of the disc brake pads of Audi cars

key words: disc brake pad carbon fiber composite friction material back plate fine stamping

1 preface

disc brake is an important executive component in automotive braking system, which has been widely used in cars at present. The brake element in the friction pair of this kind of brake is a brake block composed of a friction block (brake pad) and a metal back plate, and the friction block is made of friction materials. For more than half a century, the friction materials of automobile brakes have been asbestos based friction materials. Due to the low service life of asbestos friction materials, it is prone to "heat recession" [1], especially asbestos dust pollutes the environment and endangers human health. Therefore, in the past 20 years, countries all over the world have restricted the production and use of asbestos friction materials, and began to develop and use a new generation of composite fiber reinforced friction materials to make friction blocks of automobile brakes. In view of this development trend, we have researched and developed the key technologies in the localization of the brake pads of Audi car disc brakes in combination with the abundant carbon fiber resources in Jilin Province

2 development of carbon fiber composite automobile brake friction block

the friction material of carbon fiber composite developed is a multi-element system composed of fiber, adhesive and friction performance regulator (filler) of the structure and operation method of reinforced concrete pressure testing machine. The orthogonal optimization design method is used to determine the best optimized formula of material components, so that the friction material has good comprehensive properties. Then, after mixing, hot pressing, heat treatment and other processes, the friction block of disc brake is pressed

2.1 determination of material formula

2.1.1 selection of materials

(1) selection of reinforcing fibers

because carbon fibers have excellent comprehensive properties: light weight, high specific strength and specific modulus (5 and 7 times that of metal respectively), good thermal conductivity, good wear resistance, good high temperature resistance (the performance is very stable at less than 400 ℃) [2]. Therefore, the carbon fiber with fast curing speed and rich resources in Jilin Province is selected as the reinforcing fiber of the friction material developed

(2) selection of binder

the function of binder is to combine multiple components into a whole to transfer the load and balance the load. Phenolic resin is usually used as adhesive because it has certain advantages in heat resistance, molding processability and economy. However, unmodified phenolic resin has high hardness and brittleness, and its ultimate heat-resistant temperature is about 250 ℃. When it exceeds 300 ℃, it decomposes seriously, reducing the tensile strength and impact resistance, so that the product is easy to form braking noise and slip. At the same time, due to its high elastic modulus, the product has poor compatibility with friction, which is easy to produce serious local overheating and cause hot cracking. Therefore, modified phenolic resin is used in practical applications. Based on our experience in studying asbestos and semi-metallic friction materials for many years, the phenolic resin modified by nitrile rubber (fh-908) is selected as the binder. The binder has the advantages of high temperature resistance and fatigue resistance, ranking first among the seven new material industries and national high-tech industrial bases in China. It has good labor performance, humidity and heat aging resistance, atmospheric aging resistance, good medium resistance and so on

(3) friction performance regulator

the function of adding various friction performance regulators (fillers) is to solve the problem that the friction coefficient of friction materials is stable and wear-resistant under various conditions, and can improve the heat decay property. The selection of fillers should follow the following principles: the hardness of fillers should not be greater than that of the opposite side of the couple; The melting point should be lower than the fusion temperature of the couple material. The actual filler composition is as follows:

1) metal powder: it is mainly used to improve thermal conductivity, reduce wear and maintain the stability of high-temperature friction coefficient. We choose copper powder (particle size 30 ~ 80 mesh) and HT200 cast iron powder (particle size 40 ~ 60 mesh)

2) solid lubricant: it can improve the stability of friction coefficient and reduce noise. Graphite and carbon black were used as solid lubricants in this study

3) friction agent: Although solid lubricant can reduce material wear and make friction materials work stably, it reduces the friction coefficient. Therefore, in order to improve the friction coefficient, it is necessary to add friction agent. In this study, Al2O3, SiO2 and chrome ore powder are used as friction agents [3]

2.1.2 the overall appearance of the friction material is more beautiful than that of other types of packing belts. The determination of the formula of the friction material is divided into two steps in the development process: the first step is to put forward the preliminary formula; The second step is to optimize the design. Finally, determine the reasonable formula

(1) preliminary formula

the original formula of carbon fiber composite friction material is put forward by consulting relevant data at home and abroad and combining our experience in developing Semi-metallic Brake linings [3]. L9 (34) orthogonal table, namely four factors and three levels orthogonal table, is used for screening and assessment. After two rounds of adjustment and testing, it was used as the preliminary formula of the study. The preliminary formula is as follows (wt%):

carbon fiber 16~25

adhesive 11~17

friction agent (SiO2 + Al2O3) 4~10

metal powder (cast iron powder) 19~28

solid lubricant (graphite + carbon black) 10~19

fixed component 10

(2) the final formula is determined

in order to obtain the optimized formula with less test times and understand the primary and secondary factors affecting the friction and wear performance, We use L16 (45), namely the orthogonal table of five factors and four levels, to screen and analyze. At the same time, the MM-200 friction and wear tester is used to conduct the wear test. The friction coefficient and volume wear are used to analyze the optimization level of components and the primary and secondary order of component influence. The thermal decay test was also carried out on the D-MS testing machine. According to the test results, the optimization level of components and the primary and secondary order of component influence were analyzed according to the friction coefficient. The optimization level of components and the primary and secondary order of various factors affecting the wear rate are also analyzed according to the volume wear amount

finally, by comprehensively analyzing the above test results, it is concluded that the better formula range of carbon fiber composite friction materials with good friction and wear performance is (wt%):

friction agent (z1) 6~8

carbon fiber (z2) 16~19

binder (Z3) 13~15

metal powder (Z4) 22~25

solid lubricant (Z5) 10~13

in order to reduce costs and expand the scope of application, on the basis of the above tests, The cheaper pre oxygenated carbon fiber (8mm in length) was selected for experimental research. On the basis of several rounds of tests, the economic formula in actual production is determined. Its composition range is: z1:8% - 10%; Z2:

19%~22%; Z3:15%~17%; Z4:22%~25%; Z5:13%~16%。

2.2 friction and wear properties of carbon fiber composite friction block

2.2.1 high friction coefficient

due to the high specific strength, specific modulus and self-lubricating performance of carbon fiber. When the designed carbon fiber content is 19% - 22%, the friction material has high friction coefficient and low volumetric wear rate

2.2.2 good heat decay resistance

carbon fiber composite friction material, under the action of high temperature friction, its plough cutting resistance increases, showing that the friction coefficient is large at high temperature, and the thermal decomposition layer is thin, which can keep the friction and wear performance stable at very high temperature, and has good heat decay resistance

the developed carbon fiber composite friction block has been inspected by the National Automobile Quality Supervision and inspection center, and its technical performance index conforms to the national standard gb5763-1986, and its service life is 2-3 times that of asbestos friction material [3]

3 fine blanking process of friction block back plate

the product diagram of Audi car disc brake friction block back plate is shown in Figure 1. According to the technical conditions of UK Lucas green company and the requirements of Volkswagen supply standard (tl-vw-110), the characteristics and technical requirements of the backplane are shown in Table 1

Figure 1 Audi car disc brake friction block backplane product figure

Table 1 Characteristics and technical requirements of backplane parts

in view of the high precision requirements of backplane parts and large consumption, using fine blanking process to produce has significant economic benefits

3.1 fine blanking process design and calculation

according to the product drawing and technical requirements of the back plate, domestic steel 35 (gbt699-1999) is used, and the thickness of the steel plate is t=5 ± 0.2mm. The main mechanical properties of the material are: tensile strength σ B= 530mpa, and the hardness in annealing state is 197hb when supplied

blanking force is calculated according to the following formula

w =1.2 L τ T (1)

where: W -- blanking force, kn

l-- perimeter of inner and outer contour of blanking part, mm

τ-- Shear strength of sheet, MPa

t-- sheet thickness, mm

substitute relevant values into formula (1) and calculate w=1250kn

blank holder force according to the following formula

p2=kl1*2h* σ B

where P2 -- blank holder force, kn

k-- coefficient, k=1.6

h -- height of V-shaped tooth, h=0.8mm

σ B -- tensile strength of sheet, σ b =530MPa。

after calculation, the blank holder force and back pressure of the strong gear ring are obtained: P2 =200kn

combined with the above two, the total tonnage of the blanking force is about 150t

determine the lap value of blanking according to literature [4], in which the lap value between workpieces is b=8mm, and the outer lap value is a=6mm

the blanking process is arranged as follows: hot rolled steel plates of gb3275-1991 are used, and acid pickling is carried out after cutting by the shearing machine, and the compound die is used for fine blanking on y domestic hydraulic fine stamping edge machine

3.2 key points of design and manufacturing of precision stamping die

in order to obtain the back plate stamping parts with flat surface and flush outer contour surface, the fixed convex mode compound die as shown in Figure 2 is adopted

jd003-82 series fine blanking die base is selected for this die to improve the quality of the die and shorten the processing cycle [5]

because the blanking plate is thick and medium hardness steel plate, the main working parts of the die are made of Cr12MoV steel, and the quenching hardness is 60~64hrc

take z=1.0t% as the blanking process gap, and you can receive better section quality. As shown in Figure 3, the single-sided V-shaped gear ring structure [4] is adopted, and the internal angle of the gear shape is α = 40o。

Figure 2 back plate fine blanking compound die

Figure 3 V-shaped blank holder ring gear

conclusion

Audi car disc brake brake pad is a key component with high scientific and technological content and long service life. According to the supply standard tl-vw-110 of Volkswagen AG, the friction block is asbestos free friction material; The back plate is a medium hard steel fine blanking part. At present, the brake pads of the disc brakes of domestic Audi cars have been matched with imported parts from lucasgreen company in the UK. In view of this background and under the condition of making full use of the rich carbon fiber resources in Jilin Province, this study independently studied the fine blanking process of asbestos free friction block and back plate made of carbon fiber composite, solved two key technical problems in the localization of this product, and laid a foundation for the localization of disc brake block of Audi car

references

1 Han Yingchun Development of asbestos free brake linings made of carbon fiber composites for automobiles Automotive engineering 2002,, 46 ~ 50

2 li Yinxi, Luo Xiuyun. Application Manual of automotive plastics. Beijing: Mechanical Industry Press, 1989

3 Jilin University of technology. Development work and technical report of asbestos free brake pads for carbon fiber composite vehicles. Changchun: 1998.10

4 Miyazaki Dakao. FB gold

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