Not all can be compression molded
Each, who is engaged in designing aluminum profiles - Profile customers or manufacturers, sooner or later confronted with limitations, superimposed most aluminum pressing technique. Of course, These restrictions also depend on the particular press equipment and experience it, and the correct choice of aluminum alloy.
Sketch of the customer and technology opportunities
If the process of production of aluminum profiles - and not only the pressing - inadequately controlled, and the profile design and aluminum alloy does not take into account the manufacturing process, the result is bound to be low-quality products and a large number of marriage.
Therefore, manufacturers of aluminum profiles to establish common rules of their design. These rules must be followed by development of drafts profiles, how the customer, and the manufacturer. These rules are intended to ensure the harmony of shapes and cross-sectional dimensions of aluminum profiles with the possibilities of aluminum pressing process and its alloys. Some of these rules are general in nature, while others relate to specific sizes and shapes, depending on the applied pressure equipment, as well as aluminum alloy.
Profile of drawings or sketches of the customer
Designer products or machine parts made of extruded aluminum profile tends to make it as functional and flight of his imagination nothing limits. Thus was born the, what is often called "profiles according to plan" or “profile custom-design”. Sometimes it can be very difficult to press.
In general, there are very few profiles, which would be impossible in principle, pressed on the extrusion press. However, it may be so, because of the high failure rate of the quality or the price of hard for the profile molding would be unacceptable for the customer.
In order to develop a quality product - aluminum profile - Designer, factory or customer, I should try to reach in his drawing of the cross-sectional profile, which would be "friendly" to the technology. And it should concern not only the pressing process, but all subsequent process steps from the exit profile of the matrix and to its packaging.
The keyword of the metal extrusion process (metal molding), including, aluminum and its alloys, is the word "symmetry". For asymmetric profiles typical nonuniform and uneven flow of metal, that require complex designs extrusion dies. the metal flow rate through the cross section should be as aligned, a, To achieve this often has to be compressed at very low speeds. Moreover, the asymmetric section profile of the matrix undergoes inhomogeneous strain, which is fraught with an increased risk of its destruction, particularly during pressing high-strength aluminum alloys.
The asymmetric profiles may also be the cause of temperature gradients, in the matrix, and the profile during cooling. Moreover, different parts of the profile will have different thermomechanical processing and, Consequently, vary in microstructure and mechanical properties.
Examples deviations from symmetry aluminum profiles are shown in Figure. Weight distribution over the cross-section of the profile should not be too uneven. Profiles with a large ratio of the maximum and minimum thicknesses are very difficult to transmit through the extrusion press, and large eccentric cavity can produce poorly managed metal flows.
Too large profiles
There are natural limits on the maximum size of the profiles. If the profile has a very large diameter of the described circle – minimum circle, in which it can be inscribed – there may arise problems with the hit in the profile of the workpiece material from its surface, contaminated, layers.
The solid matrix for large profiles are usually difficult to reliably maintain and bolster pads. The hollow matrices for large sections of the mandrel are experiencing high loads. As a result, large profiles characterized by large dimensional deviation and the lower surface quality. This reduced quality of the profile surface is most often expressed in a large number of scratches (matrix traces), as well as the appearance of inhomogeneity due to the profile strips, which in different ways reflect the light incident on them.
Too small profiles
On the other hand, too small profiles give too high a stretch ratio (pressing ratio). In this case, the press may be unable to provide the necessary force, to extrude profile. In this case, compressed to improve performance multiple threads simultaneously Profile.
Ease of aluminum profile
Simplicity - this is another keyword for almost all industries. This applies particularly to the process of pressing aluminum profiles, although his main merit lies in the ability to produce complex profiles.
Hollow profiles and profiles with long "language" significantly complicate the production of profiles and should be avoided as far as possible. Extrusion dies for these profiles are more complicated and therefore more expensive. However, the biggest problem is that these matrices, that they occur much more effort because of the obstacles, that they impose on the flow of metal. On the other hand, their more complex construction makes them weaker, limiting efforts, which they may be subjected to. Related to this is their tendency to deviation size and low surface quality.
So often we try to do "tongues" with a small ratio of length to width, and hollow profiles often do in the form of two continuous profiles, which are then joined together to form a cavity.
Functional elements Profile
Special aluminum profiles usually include a lot of different special items. properly, these elements and make a special profile, and they are often very important for the customer. However, the addition of even a small part in the profile drawing can lead to big changes in productivity, well as products. Therefore you should always weigh, Is it really necessary or that functional part profile and whether it is possible to make it more convenient form for the pressing process.
Sharp corners Profile
Excessive aluminum profile sharp corners may lead to insufficient filling of the matrix metal, and in other cases - to the occurrence of discontinuities in the form of discontinuities at these acute angles (see. drawing). Moreover, the emergence of cracks and their growth is more likely to occur in those parts of the matrix, which form acute angles. Therefore, all corners - internal and external - should be properly rounded. The minimum corner radius at the corners of the profile the drawing should be from 0,4 to 1.0 mm. Only in some cases - if it is really necessary to the customer - the figures put the fillet radius 0,2 mm.
Abrupt changes in the thickness profile
Abrupt changes in wall thickness of the aluminum profile, a, Consequently, a sharp change in the length of the working belts of the matrix should be avoided (see. drawing). Such abrupt changes result in two types of problems in the course of metal. One side, It is necessary to ensure complete filling of the metal around sharp corners by varying the length ingenious working belts. On the other hand, at such sharp transitions vary plastic deformation conditions, It is leading to differences in microstructure adjacent portions of the profile. The result is a visual defect aluminum profiles in the form of strips with different light reflection. "The people," this defect for obvious reasons, is called "skiing".
The solution to this problem is possible a smooth transition from thick to thin profile elements. If for some reason it is impossible to, it is often on the border of thick and thin walls as agreed with the customer to perform a special decorative risk.
In a sense,, pressing the thin-walled profile element always presents a challenge. In such areas a matrix is characterized by high friction forces, and metal flow rate is difficult to control. As a result in these portions of the matrix may be incomplete filling of some metal elements of the cross-sectional. Moreover, matrix such areas require higher compaction effort.
If the thin wall is inside the profile (see. drawing), the problem with filling it with metal even more serious. The pressure in the welding chamber can be insufficient for forming a good weld. Weak weld or its complete absence is a disaster for the quality profile, and to detect this defect is very difficult. Therefore, internal thin walls need to be avoided, and to convince the customer.
Sometimes it is better to apply a thicker inner wall, to ensure its reliable quality filler metals and weld, despite, that the value of the profile is on the increase.
Another limitation to Profile
Further constraints for the profile construction, which are associated with features of the pressing process, There are other limitations. Such constraints can be linked, for example, with the use of the product in use. One such limitation, is an, for example, corrosion prevention products due to the fact, Profile construction that does not contain elements, which would be collected by the water from rain or snow. These operating features an aluminum structure should be discussed with the customer at the stage of development of the profile drawing.
Источник: Handbook of Metallurgical Process Design / ed. George E. Totten, Kiyoshi Funatani, Lin Xie / Marcel Dekker Inc, 2004