Application of Rapid Forming of Industrial Titanium Plate Products in Investment Casting
Select industrial titanium plate products (nbs) technology to sinter alkali corrosion-resistant valve PS-based powder prototype parts, and contact investment casting technology to produce castings. Discussed the integrated skills of nbs rapid forming and investment casting, and then completed the rapid casting skills from the three-dimensional model of the computer to the metal parts.
Industrial titanium plate products (nbs) rapid molding technology uses the principle of discrete/stack molding, which is to convert the CAD three-dimensional appearance parts modeled on the computer into the STL file format, and then use discrete software to disperse from the STL file A series of ordered layers of a given thickness are produced, and then the above-mentioned discrete data is transferred to the molding machine. The scanner in the forming machine scans and sinters layer by layer under the control of the computer information. Through the accumulation of layers to generate samples. Because it transforms the messy three-dimensional production into a series of simple two-dimensional production superpositions. Therefore, it can generate simply messy parts without the need of molds and tools, which greatly improves the production power and the flexibility of production. It is connected with multi-category production skills to complete rapid mold, rapid casting, and rapid product production.
The product related to the rapid forming skills and casting skills is the quick casting skills (QuickCasting, referred to as QC). Compared with the traditional investment casting, the casting investment mold is directly produced by the rapid forming system, eliminating the need for wax mold molding. The process of pressing and making has greatly improved the company's competitiveness. The following introduces the PS prototype provided by nbs rapid forming technology as a "wax model" for investment casting technology discussion
1.1 The production of "wax model"
Using nbs special polystyrene (PS) powder materials, PS prototype parts of the valve body and valve core are sintered on the AFS rapid molding machine. After waxing and finishing treatment, it is called "wax mold".
1.2 Determination of the pouring system
The pouring system is the channel that guides the liquid metal into the cavity in the mold, and it is a reasonable description of the pouring system. Probably according to the layout characteristics of castings, technical conditions, alloy varieties. Select the layout type of the pouring system, and determine the position of the gate. Is the description of the pouring system reasonable? It directly affects the quality of the casting. Anycasting, a casting simulation analysis software produced in Korea, is used to simulate the casting filling and coagulation process numerically, and to make predictions about the defects that can occur in the castings, and to judge whether the casting system is reasonable and whether it needs to be adjusted through the simulation results.
1.3 Welding of the pouring system
According to the scale of the imitation casting system, the wax casting system standard parts are selected for welding. Because the surface of the wax model has been treated with wax penetration, it has good weldability and a strong connection.
1.4 Shell making
The mold shell is made up of a binder, refractory materials, and sanding materials, etc., and is made through the processes of coating, dipping, sanding, drying, and hardening, dewaxing, and roasting.
(1) Water glass shell making skills In this experiment, the water glass shell making skills are selected, and 7-layer half-shaped shells are coated according to the size of the parts. Each layer has to go through five processes: coating, sanding, emptying, hardening and drying.
(2) The process of dewaxing and losing the mold is generally called dewaxing. And here refers to the removal of the casting system wax. The PS prototype "wax mold" melts during the firing period. When using the hot water method for dewaxing, the boiling time should be reduced as much as possible, and the core can be removed.
(3) Roasting, Generally speaking, the purpose of roasting is to remove volatiles in the shell, such as moisture, remaining wax, etc., so that the shell has low gas evolution and outstanding air permeability during casting, and avoids pores, etc. shortcomings. Roasting can make thermophysical and chemical reactions between binders, refractory materials, and other substances, change the phase composition and microscopic arrangement of the shell, and improve the high-temperature mechanical properties of the shell. Firing can also make the shell cast at the required temperature. In order to reduce the temperature difference between the molten metal and the shell, improve the filling ability of the molten metal. In this skill, during dewaxing, only the waxy pouring El system is melted away. The PS powder prototype made by rapid molding is differentiated and gasified at high temperatures during the roasting process. This is also the difficult point of this skill. When roasting, the cup is facing down, that is, the mold shell is placed upright and overhead; after entering the furnace, it is roasted from room temperature to above 950℃; small pieces are roasted in 2 furnaces (about 1.5h), and large pieces are roasted in 3 furnaces or more (about 3.0h) Or above), so that the residue in the cavity (including the casting system and the part cavity) is fully melted and discharged. The margin is divided and missing. Improve cavity cleanliness.
1.5 Pouring
After passing the above steps, it can be cast. Because the trial production was carried out according to the actual conditions of the factory, the ZG25MnCrNiMo alloy melt was poured in practice in this experiment. After pouring, it must be cooled at a certain time, and the cooling time is related to the alloy of the casting. After cooling, the sand is shaken out and the castings are sorted, and the valve body and valve core are castings.
(1) This article uses nbs rapid forming prototypes as "wax molds" to directly use investment casting to obtain metal castings, which perfectly completes the technical path from nbs prototypes to metal castings. Because this rapid molding technology does not require the production of wax molds, the preparation time for casting investment molds is greatly shortened.
(2) Practice has proved that nbs skills thoroughly support investment casting skills and become a useful technique for rapid mold making. It inherits the advantages of high precision investment casting, less waste, and freedom from data constraints. And it can quickly produce “wax molds” with messy shapes, which makes up for the lack of traditional molds with long production cycles and high costs. At the same time, this skill also links the leading casting numerical simulation skill, which is conducive to the promotion of casting skill level. Therefore, the connection between nbs skills and investment casting skills is a promising leading production skill.
