Welcome to Auto Parts Forum
Thanks for visiting our brand new online forum for automotive parts. We are just starting to build content and invite you to join us here in our new online discussion forum for automotive parts topics. Whether you are a veteran automotive parts guru or just someone looking for some quick auto parts advice, register today and start a new topic in our forum. Registration is free and you can even do it with social network platforms such as Facebook, Twitter, Google, and LinkedIn.
By 袁春凤 (Tiffany)
The phenomenon that two objects move relative to each other to produce motion resistance between their contact surfaces is called friction, which is called friction. The existence of friction not only increases the power consumption, but also causes the wear of parts' contact surfaces. Therefore, lubricating oil is usually used between the relative moving surfaces of automobile parts to reduce friction. Failure of automotive parts 75% is caused by friction.
Friction can be divided into dry friction, liquid friction, boundary friction and mixed friction according to the lubrication state of the parts.
(1) dry friction
The friction between the frictional surfaces without any lubricating medium is called dry friction.
When the parts are in the state of dry friction, the surface of the parts is abraded sharply, so the surface of the moving parts of the automobile should avoid the occurrence of dry friction as far as possible.
Dry friction and boundary friction are the main friction between the upper part of cylinder wall and piston ring. Dry friction will occur when the journal and bearing are subjected to impact load in the working process.
(2) liquid friction
Two the friction of the friction surface when the lubricant is completely separated is called liquid friction.
In liquid friction, the two friction surfaces are completely separated by a layer of lubricating oil film with a thickness of 1.5-2.0um, which avoids direct contact between the working surfaces of the two parts. Friction only occurs between the lubricating fluid molecules, so the friction resistance is very small, and the wear of the parts is very slight.
Most of the relative motion parts of a car are carried out under the condition of liquid friction (for example, crankshaft and bearing).
(3) boundary friction
Two friction surface separated by a very thin boundary film is called boundary friction.
The oil film thickness is usually below 0.1um. Friction only occurs between the outer molecules of the boundary film, reducing the friction and wear of the parts. But its thickness is very small, and it is easy to be destroyed by impact and high temperature, so it is not as reliable as liquid friction.
For example: between cylinder wall and piston ring; if the work crankshaft and journal between the insufficient supply of lubricant, easy to produce boundary friction.
(4) Mixed friction
The friction between two friction surfaces in the presence of dry friction, liquid friction and boundary friction is called mixed friction.
In the actual working state, the parts usually work under the mixed friction state, and the friction state varies with the working conditions.
By 袁春凤 (Tiffany)
Melt mold casting
One is to make the wax into a mold, coat it with several layers of refractory paint to make a mold shell, and then heat the mold, so that the mold melt, flow out, and baked into a certain strength mold, and then poured, shell and get a casting method. Process features: take the melting pattern as the starting mode. The precision of casting is high, and it is a method of little cutting. Its equipment is simple and production quantity is not restricted. It is mainly used for mass production and mass production. The drawback is that the process is complex and the production cycle is long.
Pressure casting - a casting process in which molten metal is rapidly pressed into the cavity of a metal mold under high pressure and solidified under pressure to obtain a casting. Process characteristics: High speed and high pressure were added to the metal mold casting to enhance the metal fluidity, which was mainly used in the batch production of non-ferrous alloy (such as aluminum, copper, magnesium, etc.) precision castings.
Centrifugal casting - a casting process in which molten metal is poured into a high-speed rotating mold to solidify liquid metal under centrifugal force to obtain a casting. Process features: compact structure, good casting quality. It is used to produce hollow castings.
By Erica Zhu Feilong Jiangli
Automobile surface drawing parts have the following characteristics:
The deformation characteristics of large curved surface parts are as follows: the periphery is deep drawing, and the interior has bulging components. The surface shape is supplemented by the exterior material of the pressing surface and the interior by the material extension to meet the bulging requirements. At the same time, due to the deep drawing depth and complex shape, the distribution of deformation parts is uneven. Therefore, controlling the direction and velocity of material is extremely important. The part of large curved surface is easy to wrinkle and crack easily.
2.There must be enough stable blank holder force.
Large curved surface parts require not only certain drawing force, but also enough stable blank holder force in the process of drawing. This kind of workpiece is often a large contour size, deep space surface, so the need for deformation and blank holder force are larger. In the ordinary single-action press with air cushion, the blank holder is only about 1/6 of the nominal tonnage, and the blank holder force is not stable, it is difficult to meet the technological requirements of such parts, so in a large number of production, the drawing of such parts are carried out on double-action press. The double-action press has two sliders for drawing and blank-holder, i.e. inner slider and outer slider. The blank-holder force can reach more than 40% - 50% of the total drawing force. It can satisfy the requirement of uneven distribution of deformation around the workpiece, and the blank-holder force is stable, and it is easy to get the deep-drawing parts with better stiffness.
3.The drawing parts must have enough stiffness.
Most of these parts are used as the exterior of the machine, requiring sufficient stiffness (no trembling and noise in use) and dimensional stability (to ensure the quality of welding and assembly). This requires that all parts of the material be subjected to uniform tensile stress (ideally a two-way tensile stress state) in the drawing process, and that the tensile stress exceeds the yield limit, but is lower than the strength limit, so that the elastic recovery of the workpiece is reduced to a minimum, so that the shape is not distorted, but also not rupted.
By 袁春凤 (Tiffany)
Fatigue life prediction of rubber bushing in vehicle system
1.Response analysis of rubber bushing under random excitation The Monte Carlo method is used to simulate the random excitation spectrum.
2. The fatigue life calculation of rubber bushing under random load can calculate the maximum strain energy density of rubber bushing under different excitation by using the response characteristics of rubber bushing under engine and road excitation obtained previously. The fatigue life of rubber bushing can be calculated under different load conditions. The maximum strain energy density U = 0.5134Nmm2 and the fatigue life N = 771371 were predicted under the excitation of engine speed n = 3000r/min and class B pavement, while U = 0.6893Nmm2, N, = 146774 under the excitation of engine speed n = 3000/min and class D pavement.(Thanks for the help and support of Chongqing Feilong Jiangli Auto Parts technical department.)
3. The test verification of the front sub-frame module is expensive because of the fatigue test of the whole vehicle system. Now the former sub-frame module is the research object, and the calculation results are compared with the test results. The front sub-frame is installed in accordance with its layout in the vehicle, and the six points connected with the body on the sub-frame are restrained. Sinusoidal excitation is carried out at the midpoint of the rear beam, and the maximum frequency which can be reached under the condition of satisfying the amplitude of the force is taken as the test frequency. The amplitude of force is 2.45.2kN. Fatigue failure criteria of rubber bushing: 2mm crack (equivalent to 20% of tensile coefficient).