Reasons for deformation of aluminum alloy components
(1) Deformation of raw materials during processing The deformation caused by the residual stress generated by the raw materials during extrusion production. Such as: the cooling rate is inconsistent during the extrusion process, the extrusion equipment debugging is abnormal.
(2) The deformation caused during the manufacturing process of the product is mainly caused by external forces. Such as the shear extrusion stress generated during the shearing process, the shrinkage stress generated by the thermal expansion and contraction during the thermal cutting process, and the like.
(3) Deformation generated during welding The main cause is the lateral and longitudinal contraction stress generated around the weld, which is usually called deformation caused by welding stress.
(4) The essence of component deformation No matter what kind of deformation of the component, the main reason is that there are different degrees and different forms of residual stress inside the structure, so that some of the fibers in the structure are lengthened by the surrounding compressive stress, and another part of the fiber Shortening is affected by the surrounding tensile stress, which causes deformation of the metal material.
Correction principle and common methods
The principle of correction is to shorten the length of the fiber, shorten the elongation of the fiber by external force or local heating, and finally make the fiber length of each layer tend to be consistent, or reach the fiber length we require, thereby eliminating deformation or reducing deformation. Within the prescribed range.
In the process of using the various methods, various correction methods should be selected according to the different structural characteristics, deformation forms, workpiece size and other conditions. If necessary, a comprehensive correction method combining multiple correction forms is needed. Among them, flame correction is the most widely used method, which has the best deformation correction effect for large components and members with high strength. However, flame correction is also an difficult method to correct, such as heating position, temperature control, and cooling. Improper ways can also cause new deformations of the components, and even lead to scrapping of the product. Therefore, in addition to a wealth of practical experience, flame correction workers must also master the heat treatment properties of aluminum alloys.
Aluminum alloy component deformation correction method
(1) Mechanical correction The common correction equipment for aluminum alloy profiles and thick plates of 8 mm or more is a press. In general, the thicker the plate, the easier it is to level, and the thinner the plate, the more difficult it is to correct. When using mechanical correction, it is necessary to add a pad to the force part to avoid crushing on the surface of the material. Correction with a press is usually a bending deformation in one direction of the profile steel. Usually also equipped with special blocks and pressure blocks to ensure the direction of the force is stable, while avoiding the surface damage of the material to ensure the quality of correction, as shown in Figure 1, Figure 2.
(2) Manual correction For local deformation with small deformation, manual correction can be used. The effect of manual correction depends on the correct choice of the hammering position, the hitting tool and the way the hit is made.
Aluminum alloy products should be cautious when choosing manual correction. When performing manual correction, consider using appropriate impact tools such as wooden hammers, rubber hammers, nylon hammers, etc., as shown in Figure 3.
When hitting with force, it is also necessary to consider adding rubber pads, wood chips or wooden blocks to the stressed parts and pads and pressing parts to ensure that the surface of the material is not damaged during the correction process.
(3) Flame Correction Flame correction often uses the following three heating methods: linear heating method, point heating method, and triangular heating method, as shown in Fig. 4.
(1) Principle and implementation difficulty of flame correction Flame correction is to use the plastic deformation generated by local heating of metal to offset the original deformation and achieve the purpose of correction. The flame correction uses the flame to heat the convex portion of the deforming member, so that the heating and expansion of the convex metal is blocked to generate compressive stress. When the compressive stress exceeds the yielding point of the heated metal, the metal fiber of the convex portion is plastically deformed, thereby achieving the purpose of correction.
Flame correction is a difficult process to operate. Improper method control and improper temperature control will cause new deformation of the aluminum alloy component and even lead to material burning. Therefore, the flame correction operator must have a wealth of practical experience. In actual production, the operators often heat all the parts that need to be corrected, and then water and quench them to obtain deformation. The direction and size of the deformation are uncontrollable, and often need to be corrected repeatedly. Manpower and material waste are serious, and the process is implemented in scale production. It is very difficult.
(2) Factors that must be considered when the aluminum alloy component is in flame correction. 1 The heat treatment characteristics and heating temperature of the heated aluminum alloy should be mastered first. After correction, the material properties are significantly reduced, and flame correction cannot be used. 2 The choice of heating flame in flame correction is very important. Aluminum alloys generally use a neutral flame or a slightly carbonized flame. 3 Before the correction, the deformation should be carefully observed, considering the heating position, heating sequence and correction steps.
(3) Factors affecting the effect of flame correction 1 Workpiece rigidity. 2 heating position. 3 flame heat. 4 heating area. 5 heating method (point heating, linear heating, triangular heating). 6 cooling method (water cooling, air cooling, air cooling).
(4) Temperature control during heating of aluminum alloy Since the color of the aluminum alloy does not change significantly during the heating process, it is extremely cautious and careful in the flame correction process. The heating temperature is tested with a temperature pen, as shown in Figure 5.
(5) Typical process for flame correction of 5 series aluminum alloy components 1Measure the structural dimensions and geometric tolerances of the components, determine the location and direction of the heating of the flame, and then determine the size of the heating zone by the amount of deformation, mark the heating position and heat with a marker form. 2 Place the workpiece on the adjustment platform or bracket, and fix the workpiece with auxiliary tools such as long bolts, F-clamps, presses and pressure plates, and apply external force to plastically deform (pre-deform) the pre-heating zone. 3 Adjust the heating flame and prepare the cooling medium (water). 4 Apply a 250 °C temperature pen to the heated area. 5 Heat the marked area, stop heating immediately when the heating temperature causes the temperature pen to change color, and water it to cool. 6 After a heating correction cycle, loosen all the pressure plates, clamps, etc. to release the external force. Check the dimensions and geometric tolerances of the workpieces in a free state. A further flame correction is performed at the local failure. The second heating part must avoid the first heating part, try to avoid repeated heating of the same part, and check the size after cooling.
Note: When heating, the torch will stop shaking and prevent local high temperature. The temperature of the heating zone should be measured in time with the temperature pen for about 5s. It is strictly prohibited to exceed 350°C. In particular, the temperature of the center of the heating zone should be strictly controlled. The effect of water direction on deformation.
An example of an aluminum alloy flame correction is shown in Figure 6.
Application of mechanical correction in actual production
In the production of the flight attendant door of the CRH6 motor train driver's cab, the crew door is out of line with the straightness of the post. The main advantage is that the adjustment is easy to operate and control, without the influence of additional deformation, and Material strength has less influence and high production efficiency.
The correction process is as follows:
(1) Place the waiter door to be corrected on the work platform and pad with the support positioning block. The support positioning block is made of aluminum alloy and nylon block, which requires a smooth surface and no angular burrs.
The shape of the support positioning block is adapted to the contour of the workpiece to be adjusted. The support positioning block is set so that the workpiece to be repaired is perpendicular to the direction of the adjustment force, so that the force direction of the workpiece is consistent with the direction of deformation thereof to ensure the adjustment effect.
(2) When the door post is being repaired, the distance between the two ends of the door post supporting the positioning block to the indenter should be equal or approximately equal (d≈d') to ensure that the workpiece at both ends of the indenter is uniformly deformed during the pressure adjustment process, and Maintain a stable state. When the distance d between the support positioning block and the indenter is large, the adjustment force required for the adjustment is small, but the workpiece rebounds greatly, and is suitable for uniform deformation with less deformation; when d is small, the required adjustment is needed. The force is large, the adjustment effect is obvious, but the surface of the workpiece is prone to indentation. Therefore, the placement position of the support positioning block should be determined according to the deformation of the workpiece.
(3) During the repair process, the press head cannot directly contact the workpiece to apply pressure, and the block must be added at the pressure applied portion. The size and shape of the spacer should be adapted to the workpiece, and the spacer is required to have sufficient rigidity and appropriate hardness. The pad should be made of a smooth aluminum alloy plate, nylon block or wooden block.
There are two main functions of the pad: one is to increase the force area of the workpiece, to prevent the indenter from indenting the surface of the workpiece, and to ensure the direction of the force is stable; the second is that the pad and the surface of the workpiece can produce a slight relative relationship during the repair process. Sliding to reduce the impact on the deformation process of the workpiece.
(4) The selection of the pressing position of the door column by the press should select the position where the rigidity of the door column is large, that is, the most severe part of the door column deformation. Pay attention to the feed stroke of the indenter during the adjustment. Firstly set a smaller feed stroke. After loosening, check the effect of deformation correction. If the correction effect is not good, increase the indenter stroke appropriately when correcting again. Repeatedly explore the force required for deformation and repair, and gradually correct the deformation to meet the technical requirements, as shown in Figure 7.
There are many common aspects between the correction method and the correction principle of aluminum alloy components and the correction of steel structure. The key is to master the metal characteristics and heat treatment properties of the aluminum alloy, especially the difference between the hot processing temperature and the control method. The principle is to use a reasonable correction means to correct, that is, to obtain a good correction effect.