The metal drawing process should be combined with the actual situation, comprehensively consider the quality, strength, environment and production, and choose a reasonable process plan, so as to reduce the process input as much as possible on the basis of ensuring that the production meets the requirements put forward on the drawing.
Types and process requirements of metal drawing process:
I. types of metal drawing processes.
(1) cylinder stretching: stretching of a flanged cylinder.
The flange and the bottom are straight, the cylinder is axisymmetric, the deformation is uniform on the same circumference, and the blank on the flange produces deep drawing deformation.
(2) Ellipse stretching: the blank on the flange is stretched and deformed, but the amount of deformation and the deformation ratio change accordingly.
The greater the curvature, the greater the deformation of the blank; the smaller the curvature, the smaller the deformation of the blank.
(3) rectangular stretching: a low rectangular part formed by one stretch.
When stretching, the tensile resistance at the fillet of the flange deformation zone is greater than that at the straight edge, and the deformation degree at the fillet is greater than that at the straight edge.
(4) Mountain stretch: the side wall is suspended in the process, and the die is not attached until the end of the forming.
The deformation characteristics of different parts of the sidewall are different during forming.
(5) mound stretching: the blank deformation of mound cover parts in the forming process is not a simple tensile deformation, but a compound forming with both stretching and bulging deformation.
(6) hemispherical drawing with flange: when the spherical part is stretched, the blank is in local contact with the spherical top of the punch, and most of the rest are in a suspended state.
(7) Flange stretching: shallow stretching of the stretched flange part.
The stress and strain is similar to that of compression flanging.
(8) Edge stretching: angular re-stretching of the flange requires good deformation of the material.
(9) Deep stretching: it takes more than two times of stretching to complete.
The wide flange drawing part is stretched to the required flange diameter at the first stretch, and the flange diameter remains the same when it is stretched again.
(10) tapered tension: due to the large degree of deep deformation, the deep conical parts are easy to cause local excessive thinning and even fracture of the blank, which needs to be formed gradually after many transitions.
(11) rectangular redrawing: the deformation of high rectangular parts formed many times is not only different from that of deep cylindrical parts, but also different from that of low box parts.
(12) curved surface forming: a stamping forming method in which the outer flange of the metal plate billet is reduced and the inner flange is elongated to become a curved surface with non-straight wall and non-flat bottom.
(13) step stretching: the initial stretch is re-stretched to form the bottom of the step.
The deeper part is deformed at the initial stage of drawing, and the shallow part is deformed at the later stage of drawing.
(14) reverse stretching: reverse stretching is a kind of re-stretching of the workpiece stretched in the previous process.
The reverse stretching method can increase the radial tensile stress and has a good effect on preventing wrinkling.
It is also possible to increase the tensile coefficient of re-stretching.
(15) thinning stretching: different from ordinary stretching, thinning stretching mainly changes the thickness of the tube wall of the stretched parts during the stretching process.
(16) Panel stretching: the surface shape of the panel is complex.
In the drawing process, the deformation of the blank is complex, and its forming property is not a simple drawing forming, but a compound forming in which deep drawing and bulging exist at the same time.
2. The scheme of metal drawing process.
The main contents are as follows: (1) according to the drawing of the workpiece, analyze the shape characteristics, size, precision requirements, raw material size and mechanical properties of the workpiece, combined with the available equipment and batch and other factors.
Good drawing technology should ensure less material consumption, less number of processes and less equipment.
(2) the main process parameters are calculated based on the analysis of stamping process, the characteristics and difficulties of stamping process are found out, and various possible drawing process schemes are put forward according to the actual situation, including the nature of process, the number of process, the sequence of process and the mode of combination.
Sometimes there may be several feasible process plans for the same kind of workpiece, and usually each scheme has its own advantages and disadvantages, which should be comprehensively analyzed and compared to determine the suitable one.
(3) process parameters refer to the data on which the process plan is based, such as various forming coefficients (drawing coefficient, bulging coefficient, etc.), unfolding dimensions of parts and various stresses, etc.
There are two cases of calculation, the first is that the process parameters can be calculated more accurately, such as the material utilization rate of the part layout, the area of the workpiece, and so on; the second is that the process parameters can only be calculated approximately, such as the general bending or drawing forming force, the blank expansion size of complex parts, etc., to determine this kind of process parameters are generally roughly calculated according to empirical formulas or charts, and some need to be adjusted through tests.
(4) according to the nature of the process to be completed and the power and energy characteristics of all kinds of equipment, the main factors such as the required deformation force and size are considered, and the type and tonnage of the equipment are reasonably selected according to the situation of the existing equipment.
Third, the method of selecting drawing oil products.
(1) because the silicon steel plate is a relatively easy material to stretch, the stamping oil with low viscosity will be selected on the premise of preventing scratches in order to make the finished product easy to wash.
(2) when selecting drawing oil for carbon steel plate, the better viscosity should be determined according to the difficulty of the process and the degreasing conditions.
(3) because of the chemical reaction with chlorine additives, galvanized steel sheet should pay attention to the possible white rust of chlorine drawing oil when selecting drawing oil, while the use of sulfur drawing oil can avoid rust.
(4) stainless steel is a hardening material, which requires the use of drawing oil with high oil film strength and good sintering resistance.
The drawing oil containing sulfur-chlorine compound additive is generally used to ensure the extreme pressure performance while avoiding burr, fracture and other problems of the workpiece.