Integrated die casting is metal die casting process of heating the whole workpieces and cooling them at appropriate speed so as to change their mechanical properties. Integrated steel casting can be divided into four processes below: annealing, normalizing, quenching and tempering.
(1) Annealing means that workpieces are heated to appropriate temperature, and cooled slowly based on heat preservation time length determined by corresponding workpiece materials and standards so that internal structure of metals gets or almost gets homogeneous, internal stress retained from former process can be relieved, certain excellent properties can be achieved and good preparations are made for further quenching.
(2) Normalizing means that workpieces are heated to proper temperature and then cooled in the air, with the final effect similar to that of annealing except slight difference, namely, normalizing gets more compact. Normalizing is often used to improve cutting function of materials, and sometimes used as the final process of die casting when high properties of machining parts are not required.
(3) Quenching means that workpieces are heated and kept warm and then quickly cooled in quenching medium such as water, oil, inorganic salt solution, organic aqueous solution and so on. After quenching, steel parts get hardened and brittle.
(4) To reduce brittle performance, steel parts after quenching should go through heat preservation for relatively long time at certain appropriate temperature higher than room temperature but lower than 650 °C, and then are cooled—such process can be called tempering.
Annealing, normalizing, quenching and tempering are four processes in integrated die casting, among which quenching and tempering are closely connected and often used to work together.
Based on different heating temperatures and cooling methods, the above-mentioned four processes can develop into other new casting processes. In order to get certain strength and durability, quenching and high-temperature tempering are combined, which can be called quenching and high temperature tempering process. Some alloys after quenching turn into supersaturated solid solution and such solid solution should be stored at room temperature or slightly higher but appropriate temperature for relatively long time so as to improve hardness, strength and electric and magnetic properties—such process can be called solid solution and aging treatment process.
Pressure processing deformation is effectively incorporated into die casting process to make workpieces achieve good strength and durability, which is called deformation die casting. The die casting under negative pressure or in a vacuum is called vacuum die casting, which can not only make workspieces free from oxidation and decarburization, feature bright surface and improve the properties of workpieces, but also develop into chemical die casting by adding permeating agents. The surface die casting is a metal die casting process of heating surface of workpieces to change surface mechanical properties. In order to just heat their surface instead of transferring too much heat to their internal part, heat sources should have high energy density, namely relatively large amount of thermal energy is applied in workpieces per unit area, to make surface get high temperature instantaneously or in a short time. The primary processes of surface die casting include flame hardening and induction heating die casting. The commonly used heat sources are flame like oxyacetylene, induction current, laser, electron beam, etc.
Chemical die casting is a metal die casting process of changing chemical components, structure and properties for surface of workpieces. It differs from surface die casting in that the former changes chemical components. It is process of putting workpieces into medium (gaseous, liquid or solid state) like carbon, nitrogen and other alloy elements and going through heat preservation for relatively long time so as to make surface of workpieces contain such elements. Beyond that, other die casting processes like quenching and tempering are sometimes required afterwards. The primary methods of chemical die casting are carburizing, nitriding and metallic cementation.
Die casting process is an important process of manufacturing mechanical parts, tools and moulds. In the whole, it can guarantee and improve various properties of workpieces, such as wear resistance and corrosion resistance, and can also improve structure and stress conditions of semi-finished products, so as to adapt to cold or hot processing conditions.