1) According to the principles of fluid mechanics, a theoretical analysis and some calculations were conducted on the movement of liquid metal in the pressure chamber of a horizontal cold chamber die casting machine. Based on this analysis, it is believed that the slow injection process of the punch in the horizontal cold chamber die casting machine is a combination of accelerated and uniform motion, and the combined result directly affects the quality of the die casting. The amount of air entrained by liquid metal in the pressure chamber is related to the slow injection acceleration, slow injection velocity, initial filling degree, and pressure chamber diameter, and there exists a critical slow injection velocity and optimal acceleration. At this velocity and acceleration, the amount of air entrained can be minimized, and the porosity of the casting can be minimized.
2) The process of liquid metal filling during die casting production is a process where many conflicting factors are unified. Among the many factors that affect filling, the main ones are pressure, speed, temperature, and time. Time is the result of the coordination and synthesis of process parameters, and various process factors are interdependent and mutually restrictive. When adjusting a certain process factor, it will inevitably cause changes in the corresponding process factor, and may in turn affect the already adjusted process factor, causing it to change. Therefore, only by correctly selecting, controlling, and adjusting these process parameters to meet the needs of die-casting production can qualified die-casting parts be produced under other good conditions.
3) The basic characteristics of aluminum alloy die casting are filling under high pressure and high speed, crystallization under high pressure. During the entire rapid injection stage, the metal liquid enters the mold cavity in the form of a jet at a speed of 30-60m/s, and it is impossible for the metal liquid to not wrap up the gas. In this case, adjusting the process parameters and plan is the key to where and in what form the gas pores are reasonably distributed. Due to the high-pressure jet breaking gas into dispersed small pores and leaving them in the casting, it is not suitable to manufacture important safety components such as shells and outer covers through heat treatment. Improve strength and lower elongation of die castings. Therefore, die casting is generally suitable for producing thin-walled structures that do not require significant impact loads.
4) According to the process characteristics of aluminum alloy die casting, it is difficult to form large-area thin-walled parts. If the wall thickness is too large or severely uneven, defects and cracks are prone to occur. It is hoped that the wall thickness of the die casting will be as uniform as possible. For large aluminum alloy die castings, the wall thickness should generally not exceed 6mm. Under normal process conditions, the wall thickness of die castings should not exceed 4.5mm. To avoid defects such as shrinkage and porosity at the thick wall of the die casting, it is necessary to reduce the thickness of the thin wall and add strengthening ribs.
5) Due to the characteristics of aluminum alloy die-casting process, the alloy used requires a small range of crystallization temperature, low tendency for hot cracking, and low shrinkage coefficient.
6) The ability to cast deeper and smaller holes is a characteristic of die casting technology. For some holes with low precision requirements, they can be directly used without the need for mechanical processing, thereby saving machining time. The diameter and depth of the holes cast on the parts are related, and smaller holes can only be cast at shallower depths. The general aperture is not less than 2mm, and the hole depth is not greater than 4-8 times the aperture. The threaded holes on castings are often made by first die-casting a core hole that meets the requirements, and then machining (mostly by tapping) to create a threaded hole.
7) At the connection between the walls of die castings, whether it is a right angle, acute angle, or obtuse angle, it should be designed as a rounded corner. In order to facilitate the demolding of die castings from the mold cavity and core, prevent surface scratches, and extend the life of the mold, die castings should have a reasonable demolding angle. Its size depends on the wall thickness of the casting and the type of alloy. The thicker the wall thickness of the casting, the greater the clamping force of the alloy on the core, and the greater the demolding angle. The larger the shrinkage rate of the alloy, the higher the melting point, and the greater the demolding angle. In addition, the demolding angle on the inner surface or inner wall of the hole of the casting is larger than that on the outer surface. Within the allowable range, a larger demolding angle should be used to reduce the required ejection force or core pulling force. The general demolding angle is taken as 0.5 °~1.5 °.
8) In terms of die casting technology, threads can be directly cast under certain conditions.
9) Various convex patterns, mesh patterns, characters, logos, and patterns can be cast on the die casting.
10) Metal or non-metallic parts (inserts) can be first embedded in the die casting mold and then cast together with the die casting. This can fully utilize the properties of various materials (such as strength, hardness, corrosion resistance, wear resistance, magnetic conductivity, conductivity, etc.) to meet the requirements for use under different conditions, compensate for the shortcomings caused by poor casting structure and process, and solve the die-casting problem of parts with special technical requirements.
11) Die castings have precise dimensions and good casting surfaces, and generally do not require further mechanical processing. Meanwhile, due to the presence of internal pores in die casting, further mechanical processing should be avoided as much as possible. However, the parts produced by die casting cannot be directly assembled and used in any situation, so in some cases, mechanical processing is also required on some surfaces or parts. The surface of die-casting parts is dense and uniform, with good mechanical and physical properties. The thickness of this surface is approximately 0.5-0.8 mm, so the general machining allowance is recommended to be 0.3-0.5 mm.
0 comments:
Post a Comment