A tool that deforms a metal during drawing is called a die. The processing procedure itself has been used for quite some time. It is used in the case when it is necessary to reduce the transverse parameters of the workpiece, as well as its diameter.
Blanks for drawing
Most often, drawing is used in order to produce a variety of metal blanks. These can be profiles with a large or medium cross section, as well as various shapes. It is recommended to use such a processing procedure only if the width and thickness of the initial workpiece have a ratio of no more than 20.
In addition, metal drawing is also used in a situation where it is necessary that the surface of the metal is smooth and clean. Most often, metal products such as profiles with a large or medium cross section can be extended up to a maximum of 6 meters. Metal drawing is relevant for products with a small cross section and a long length of the workpiece, the ratio between which is not more than 12. Such products are usually understood as wires made of copper, steel, aluminum. The use of such an operation as drawing makes it possible to produce wire with a diameter of up to 8 millimeters. It is important to add here that if it comes to wire processing, then after the drawing operation, additional processing is necessarily carried out. This can be additional stretching on special devices or immersion in special compounds.
The third and final version of the blanks are pipes with any shape and cross-section. Metal drawing is especially effective if hollow structures need to be made. The fact is that this method allows the production of thin-walled in diameter (0.3-0.4 mm) pipe products.
The essence of the process
The essence of this method is as follows. Metal billets in the form of strips or strip-type steel with the same cross-section are fed to a drawing type machine. The equipment has a specific channel, after passing through which the product acquires the desired geometric shape and size.
The channels are either sufficiently close in diameter or exactly the same in diameter as the workpieces. It is important to note that during the processing of metals by drawing, the product does not immediately taper to the desired parameters. Throughout the entire channel from its inlet to the outlet, the diameter gradually decreases and only at the outlet itself is it equal to the indicator that you want to get as a result. It is important to note here that the cross section of the material, which is subjected to pulling, will always be larger than the cross section of the channel of the equipment itself. It is due to this difference that the effective change of parameters is carried out.
Procedure execution
Here you need to pay attention to several nuances. To begin with, it is important to know that the processing of metals by pressure (drawing) is carried out on a special installation called a drawing mill. Before proceeding with the pulling procedure, it is necessary to sharpen the end face of the workpiece. The procedure must be performed in such a way that the product can penetrate into the machine channel without any problems and at the same time go a short distance at the place where it ends. The end that “peeps out” is fixed by a device that is part of the drawing mill. After that, the process itself starts.
Types of drag operation
Metal pressing and drawing, like any other operation, have several types of execution:
- Finishing and roughing the workpiece. Naturally, if a finishing stretch is performed, then it will become the final one. This means that at the output the product will have the necessary parameters, cross section and so on. Rough stretching is also called procurement.
- Drawing can be multi-thread and single-thread. Here, everything is quite simple and understandable, with the first method, you can stretch several blanks at once, or rather, up to eight at a time. The only thing worth paying attention to is that the number of threads should always be even, that is, 8, 4, 2.
- There is a process of drawing metal, which is called wet. In this case, it is necessary to use a soap emulsion. Dry processing may also be possible. In this case, a container with an emulsion solution is used.
- The procedure itself can be multiple or single. In other words, it takes into account the number of pulls that the same workpiece has passed on the mill.
Additional ways
Separate options are hot and cold stretching. The difference is that these two procedures can be carried out on a mill that has dies rotating longitudinally with respect to its axis, as well as on a fixed version of the equipment.
Flawless processing method
There are many ways to draw metals and alloys, and therefore each one should be considered briefly.
A method such as safety pulling can be used. This method involves working with blanks of materials such as non-ferrous alloys and metals, as well as various tube blanks. Most often, this method is performed with two draggers. One is used to perform compression over the cross section, and the second for centering. The disadvantage is that the surface loses quality in such a procedure, and therefore the method is used only to reduce the diameter of the pipes.
Other ways to pull
When performing the operation, you need to know what values characterize the deformation of the metal during drawing. Such parameters are compression over the thickness of the workpiece, as well as its elongation, with respect to the initial size.
You can achieve better quality than with the previous processing method if you use other options:
- Bay. This procedure is considered quite optimal if it is necessary to process tube blanks from materials such as copper, brass, aluminum. It implies broaching a blank pre-wound into a bay. Using the method, thin-walled tubes with a thickness of 0.2 to 3 millimeters and a cross section of 1 to 70 millimeters can be obtained. Drying oil, water emulsion, vegetable or mineral oils are mandatory compounds, without which it is impossible to carry out such an operation.
- Carrying out an operation on a mandrel, which can be deformable, fixed.
- One of the common methods is called the rod method. The bottom line is that a rod made of a strong steel grade is inserted inside the workpiece. The pulling operation is performed with this rod, which is removed after the entire workpiece has passed through the die. Most often, capillary tubes are made, the cross section of which is no more than 1 mm.
There is also the option of broaching pipes on drums belonging to the pipe-drawing group, as well as on track mills that are equipped with chains. The choice of method is based not only on what equipment is available, but also on the properties and type of metal from which the workpiece is made.
Special mills for broaching
It can undergo metal processing by drawing in several passes. The picture will be presented for illustrative purposes.
As for the blanks, they are most often made of non-ferrous metal and steel. The initial section may be equal to 0.01 mm. The equipment is distinguished by the type of drag that is installed on it. For example, mills with diamond dies are used only for the thinnest products. Carbide dies are used for medium and thick workpieces. Steel equipment is used only for working with the largest products.
In itself, the device mills can also be quite different. Some of them can reach processing speeds of up to 50 meters per second. Others can be equipped with more than two dozen drags at once. Certain designs allow you to work with or without sliding. The reels for coiling processing can be horizontal or vertical, there may be an electric drive of an individual type or a group type.
Wire drawing options
In fact, there are several options for even such a simple operation as wire drawing.
- There is an option in which wire capture is not needed. The workpiece moves forward due to the force exerted on the reverse side. The method is called forget-free.
- There is a method called hydrodynamic. In this case, the use of combined equipment is intended. The composition of this technique includes a mounted ring, pressure ring, as well as a working draw. The mill is powered by high pressure pumps. The problem is that the installation, as well as the use of this mill, is too expensive in terms of cost. For these reasons, it is used only if the use of other options, more simple, is impossible.
What can be made on the camp
On drawing mills, it is possible to produce square, round or hexagonal rods without problems. In this case, they will be of a cold-deformed type. It is important to note here that even minor changes in the technological process of the procedure allow us to produce various blanks. Large products - with a cross section of more than 3 cm, small rods - with a cross section of less than 2.5 cm. The most standard processing scheme looks like this: the product in the bay is placed on the mill, and then the drawing procedure is performed. In standard processing, this is always a single drawing. After that, the design is sent to an automatic line, where it usually goes through the final stage of processing.
Special types of broaches
Since today the technology has developed quite strongly, sometimes drawing can be performed using one of two innovative technologies. The first is called electroplastic. The method is based on the principle that if an electric current is passed through the billet during drawing, the forces required for drawing are significantly reduced. This innovative method is used most often in the processing of alloys, which in themselves are quite poorly amenable to any deformation.
The ultrasonic method is used in particular for those structures that are initially prone to such disadvantages as deformation aging, as well as a decrease in plastic properties during heating.