Preparations before forging include raw material selection, material calculation, blanking, heating, deformation force calculation, equipment selection and mold design. The lubrication method and lubricant shall also be selected before forging.
The profile formed by the rim and tread on the radial section of the forging. The choice of the flange and tread shape of the wheel forging not only affects the wear and service life of the wheel forging on the track, but also directly affects the curving performance and walking quality of the equipment. The wheel flange enables the wheel forging to pass through the curve and turnout reliably without derailment.
The tread is conical, and the conicity is 1:10 near the rolling circle. When passing through the curve, the outer wheel rolls on the outer rail with a larger diameter close to the rim, and the inner wheel rolls on the inner rail with a smaller diameter. In this way, on the one hand, wheel forgings can play a guiding role with the change of line direction. At the same time, different rolling distance of inner and outer wheels can also compensate for the influence of the length difference between inner and outer rails.
When running in a straight line, if the wheel set deviates from the center of the line, the difference between the rolling radii of the two wheels will make the wheel set return to the center position. The outer taper of the wheel is 1:5, which can increase the difference between the rolling radii of the two wheels, so that they can easily pass the curve with small radius. Reducing the tread taper is helpful to restrain the snake's movement, but the flange wear is significantly increased, greatly reducing the rotation cycle and the service life of the wheel. This method is only applicable to some high-speed passenger trains.
The shape of the forged flange tread is worn rapidly at the initial stage of operation, and then gradually tends to be stable and wear slows down. The shape after rotary repair cannot be maintained for a long time, and the metal cutting amount is large. Therefore, some railways adopt a wheel set tread shape, which is close to wear and reaches a relatively stable state, called concave tread, also known as worn tread. The use of this shape can not only reduce wheel wear, prolong the rotation repair cycle, but also reduce the contact stress, because it improves the wheel rail contact state.
Forging materials cover a wide range of surfaces, including various brands of steel and superalloys, as well as aluminum, magnesium, titanium, copper and other non-ferrous metals; It can be processed into bars and profiles of different sizes and ingots of various specifications at one time; In addition to a large number of domestic materials suitable for China's resources, there are also foreign materials. Most forging materials have been included in the standard, and many are new materials developed, tried and promoted. As we all know, the quality of forging products is often closely related to the quality of raw materials. Therefore, workers in forging factories must have necessary material knowledge and be good at selecting appropriate materials according to process requirements.
Forging forming is caused by external force. Therefore, correct calculation of deformation force is the basis for selecting equipment and verifying dies. It is also necessary to optimize the technological process and control the microstructure and properties of forgings.
There are four main deformation force analysis methods. Although the principal stress method is not very strict, it is relatively simple and intuitive, and can calculate the total pressure and stress distribution on the contact surface between the forging and the tool. The sliding line method is strict to the plane strain problem and relatively intuitive to the stress distribution of high local deformation, but its application scope is narrow. The upper bound method can give the overestimated load, and the upper bound element can also predict the shape of the forging during deformation. The finite element method can not only give the change of external load and forging shape, but also give the distribution of internal stress and strain. The disadvantage is that it takes more time to use the computer, especially according to the elastic plastic finite element method, the computer capacity is large and the machine time is long. Recently, joint methods have been used to analyze the trend of problems, such as. The upper bound method is used for rough calculation, and the finite element method is used for detailed calculation in key parts.
Reducing friction can not only save energy, but also improve the service life of the die. Because the deformation is relatively uniform, it is helpful to improve the microstructure and properties of the forgings. One of the important measures to reduce friction is the use of lubricants. Due to the different forging processing methods and working temperatures of forgings, the lubricants used are also different. Glass lubricant is mainly used for forging of superalloys and titanium alloys. For hot forging of steel, water-based graphite is a widely used lubricant. For cold forging, phosphate or oxalate treatment is usually required due to high pressure.