Aluminium alloy bracket die-casting mould design and process simulation
Overview of aluminium alloy die-casting technology
1.1 Principle of the die-casting process
The mold casting method can be divided into two categories: hot chamber mold casting and cold chamber mold casting. In the hot chamber mold-casting, the pressure chamber of the injection system is placed inside the crucible. When filling, the injection punch can directly push the metal liquid in the crucible into the pressure chamber and then enter the cavity through the gooseneck tube of the injection system. The crucible for melting metal is separated from the cold chamber mold casting machine in cold chamber mold casting. The production efficiency of cold chamber mold casting is lower than that of hot chamber. Still, its application is wider, and non-ferrous alloys such as aluminium, zinc, magnesium and copper can be processed by the cold chamber mold casting method.
1.2 mold-casting process characteristics
mold-casting filling pressure is generally a few MPa to tens of MPa, and the maximum filling speed can reach hundreds of meters per second, so the entire mold-casting process is extremely short pressure injection time, reflecting the advantages of high speed and high-pressure pressure casting technology. Due to the pressurization process during filling, the resulting mold casting is dense and can guarantee the required strength and hardness. Interchangeability, in the same mold-casting plant, the same type of parts are moulded by the same mold-casting mould, so the interchangeability of parts is good. mold-casting process of the above characteristics improves non-ferrous metal alloy casting precision level, surface quality and production efficiency, etc., showing a large advantage.
1.3 Aluminum bracket
The sub-unit bracket is the direct support to fix the accessories, such as the power steering pump and water pump on the sub-unit engine of the car, and it is responsible for the transportation of the oil channel and water channel to guarantee the normal operation of the engine. During the car’s driving process, this part must keep the sub-unit engine, power steering pump and other accessories fixed and smooth on the one hand on the other hand; it also needs to bear the torsional force effect when the car vibrates. Therefore, it is a safety part of the car engine power system, and the product has strict requirements on its surface quality and internal denseness.
The structure of the part is shown in Figure 1, which is a complex thin-walled casting with a volume of 8.51*1.05mm3, an average wall thickness of 4.3mm, a projected area of 1.39*104mm2, a mass of 2.2kg, a total of 32 machined surfaces, and a basic outline size of about 380mm*158mm*135mm.
The structure of this sub-unit bracket is complex, asymmetrical from all directions, with a curved shape in both front and rear view surfaces and tubular openings in many places. There are two fixed stands with certain angles at the lower end of the bracket and one countersink hole on each stand, which are on the same plane and are the main parts to bear torsional force.
Overall design of the mould
mold casting mould is an important guarantee for the normal operation of pressure casting. It directly determines the high rate of finished mold castings, its manufacturing costs are expensive, and manufacturing completed can not be substantially modified, so the mold casting mould design is particularly important; we generally need to consider the following points.
（1) The mould design should be combined with the actual situation, grasp the existing equipment and equipment, and design the mould structure should meet the site requirements so that the production capacity of the mold-casting machine to maximize the play.
(2) Adopt the casting system that matches the specific structure of the casting, pay attention to the layout and direction of the internal gate to ensure the smooth filling of the alloy liquid, and try to make all the air in the mould to avoid the generation of porosity defects.
(3) mold-casting mould to have enough strength, enough to withstand the clamping force and alloy liquid pressure, and in the mold-casting manufacturing does not produce deformation, to ensure safe and reliable production.
(4) try to make the mold-casting mould structure design simple to ensure that the moving mould stroke is smooth and reliable.
(5) to ensure that the mould, pouring, and overflow system in the mould after the trial can be modified.
(6) The structure of mold-casting mould is reasonably designed and convenient for maintenance and disassembly.
(7) Select proper mould material and a good heat treatment process to prolong the service life of the mould.
8) try to select standard mould common parts, shorten the manufacturing cycle, and have good interchangeability, saving maintenance costs.
Draw up the overall design of the mould
The overall design principle of the mold casting mould is to make the mould meet the requirements of the casting moulding process and, at the same time, have high efficiency and low consumption economic efficiency. The main elements of mold-casting mould design have been mentioned above. After the preliminary scheme is drawn up, the site research is conducted. The design scheme is supplemented and amended to make the mold casting mould structure more reasonable, practical and economical.
Drawing of parts
Firstly, draw the main parts, and correct and supplement some poorly considered places in the assembly sketch.
When drawing the parts, the following points should be noted.
(1) The drawing is drawn on a scale of 1:1 as far as possible to facilitate the detection of problems.
(2) reasonable selection of the perspective of each view, pay attention to the correct expression of the projection, section, etc., to avoid tedious, repetitive: (3) labelling dimensions and manufacturing tolerances.
(3) Marking dimensions, manufacturing tolerances, form accuracy, surface roughness and technical requirements such as heat treatment.
(4) The mold-casting machine selected the chamber’s inner diameter and the nozzle’s diameter.
(5) the mold casting alloy, pressure injection ratio pressure, pushing out the stroke of the mechanism, the import and export of the cooling system, etc
(6) the technical requirements of mould manufacturing.
Develop the simulation process
According to the actual production conditions and the designed casting system, the model meshes and parameters are set; the shrinkage and loosening rate is the investigation standard, the casting temperature, the press injection speed, and the mould temperature are the investigation factors, and the mold-casting process is simulated numerically. The simulation results are analyzed to examine the mold-casting process, obtain reasonable process parameters through reasonable analysis means, and analyze the causes of problem formation.
Theoretical basis of mold-casting numerical simulation technology
The main content of casting process simulation
Numerical simulation of casting filling process: filling sequence and the flow of metal liquid is an important evaluation factor of the casting filling process, which is related to many casting defects such as rolled gas, inclusions, shrinkage, etc. The traditional means is difficult to observe and control the filling state and flow, the emergence of computer numerical simulation technology, the visualization of the filling process simulation has become a reality.
Casting solidification process of numerical simulation
mold-casting solidification process is a very complex physicochemical process. Most of the casting defects are generated in the solidification process. Therefore, the solidification process of numerical simulation to predict a variety of casting defects, improve the quality of castings, optimize the casting process, and improve production efficiency are very important. In the pressure casting process, the high-temperature metal liquid transfers heat to the mould and its surroundings during cooling and solidification.
Casting stress field numerical simulation
Stress field simulation of casting solidification and cooling process, due to the different shrinkage rates of various parts, different temperature zones appear box change, casting or core by continuous heating and cooling resulting in expansion and contraction will make the casting in the forming process subject to different stresses, through numerical simulation software to analyze the stress field of the casting solidification process, can help casting process personnel to predict in advance the possible deformation of castings, The size of the residual stress and the possible location of the casting cracks, reduce the defects caused by strain, optimize the casting process at a lower cost, and improve the accuracy and performance of the casting.
Casting microstructure numerical simulation
Computer numerical simulation technology can predict the formation of the microstructure of the casting and to further predict the mechanical properties and process properties to control the quality of the casting. Usually, the finite element method or finite difference method is used to solve macroscopic quantities such as temperature and velocity. At the same time, the analytical method analyses the microscopic field of dendritic ends, thin eutectic layers or the dynamics of the spherical growth state.