What are the concepts of precision casting?

The basic concept of Dongguan precision casting: it includes: investment casting, ceramic mold casting, metal mold casting, pressure casting, and lost foam casting. One of the more commonly used is investment casting: select suitable investment materials to make the investment mold of the gear honing machine; repeat the process of coating and sanding the investment mold, harden the shell and dry; then melt the internal investment mold to obtain Cavity; baking the shell to obtain sufficient strength, burning off the residual investment material, pouring the required metal materials, and cleaning the sand after shelling, so as to obtain a high-precision finished product. According to product needs or heat treatment and cold processing.
Ceramic mold casting:
The casting method of using ceramic slurry to make molds to produce castings. The ceramic slurry is mixed with ethyl silicate hydrolyzate and fine refractory sand with pure texture and high thermal stability, such as fused quartz, zircon, corundum, etc. In order to make the ceramic slurry gel in a short time, calcium hydroxide or magnesium oxide is often added as a catalyst. Because the composition and appearance of the refractory materials used are similar to those of ceramics, it is called ceramic type. Ceramic mold casting is a new technology developed on the basis of ordinary sand casting.

There are two types of ceramic type:

①The ceramic type is made by pouring ceramic slurry. The manufacturing process is to first fix the pattern on the mold plate, coat the sand box, and then pour the adjusted ceramic slurry into the sand box. After the glue is hardened, the mold is removed, and the mold is baked at high temperature.

②Using a bushing, pouring ceramic slurry in the gap between the bushing and the pattern to make a mold. The bushing can be sand type or metal type. Pouring ceramic shells with bushings can save a lot of ceramic slurry, which is more widely used in production. The surface roughness of ceramic castings can reach Ra10～1.25 microns, and the dimensional accuracy can reach grades 3～5, which can achieve the purpose of less cutting and processing. Ceramic mold casting has a short production cycle and high metal utilization. The largest castings can reach more than ten tons, which are mainly used for casting large thick-wall precision castings and casting single small batches of die, forging dies, plastic molds, metal molds, die-casting molds, glass molds and other molds. The service life of ceramic casting molds is comparable to that of molds made by machining methods, and the manufacturing cost is lower than that of molds made by machining methods.
Brief introduction of sand casting:
Give priority to sand casting. According to statistics, 60-70% of all castings are produced with sand moulds, and about 70% of them are produced with clay sand moulds. The main reason is that sand casting has lower cost than other casting methods, simple production process, and short production cycle. Therefore, castings such as automobile engine cylinder blocks, cylinder heads, and crankshafts are all produced by the clay green sand process. When the wet type cannot meet the requirements, consider using the clay sand surface dry sand type, dry sand type or other sand types. The weight of castings from clay green sand can range from a few kilograms to dozens of kilograms, while the weight of castings produced by dry clay can reach dozens of tons.
Generally speaking, for medium and large castings, iron castings can be produced with resin self-hardening sand moulds, and steel castings can be produced with water glass sand moulds. Castings with precise dimensions and smooth surfaces can be obtained, but the cost is higher.
Of course, the casting precision, surface finish, material density, metallographic structure, and mechanical properties of sand castings are often poor. Therefore, when the performance requirements of the castings are higher, other casting methods, such as investment (lost molds), should be used. Wax) casting, die casting, low pressure casting, etc.
The Dongguan precision casting method should be compatible with the production batch:
For example, in sand casting, mass-production factories should create conditions to adopt advanced modeling and core-making methods with honing tool technology. The old-fashioned shock-type or shock-type molding machine production line is not high in productivity, the labor intensity of the workers is large, the noise is large, and it is not suitable for the requirements of mass production, so it should be gradually reformed. For small castings, a boxless high-pressure molding machine production line with horizontal or vertical parting can be used. The production efficiency of solid molding is high and the floor space is small; for middle parts, various box-type high-pressure molding machine production lines and gas can be used. Molding line to meet the requirements of fast, high-precision molding production line, core-making methods can be selected: cold core box, hot core box, shell core and other high-efficiency core-making methods.
Medium-volume large castings can consider the application of resin self-setting sand molding and core making.
For heavy castings produced in small batches of a single piece, manual molding is still an important method. Manual molding can adapt to various complex requirements and is more flexible, and does not require a lot of process equipment. Water glass sand molds, VRH water glass sand molds, organic ester water glass self-hardening sand molds, clay dry molds, resin self-hardening sand molds and cement sand molds can be used; for heavy castings produced by a single-piece gear measuring instrument, the pit modeling method is used. Low and quick to start production. It is more suitable for mass-produced or long-term shaped products to adopt multi-box modeling and split-box modeling. Although the initial investment in molds and sand boxes is high, it can be compensated by saving modeling man-hours and improving product quality.
Low pressure casting, die casting, centrifugal casting and other casting methods are only suitable for mass production due to the expensive equipment and molds.
The precision casting molding method should be suitable for the factory conditions:
For example, the same production of large-scale machine bed and other castings generally adopts the core assembly method, instead of making the pattern and sand box, the core is assembled in the pit; while in other factories, the sand box modeling method is used to make the pattern. Different companies have different production conditions (including equipment, site, staff quality, etc.), production habits, and accumulated experience. According to these conditions, we should consider what products are suitable and what products are not suitable (or not).
It is necessary to take into account the accuracy requirements and cost of castings:
The accuracy of castings obtained by various casting methods is different, the initial investment and productivity are also inconsistent, and the final economic benefits are also different. Therefore, in order to be more, faster, better, and less expensive, we should take all aspects into consideration. A preliminary cost estimate should be made for the selected casting method to determine a casting method that has high economic benefits and can guarantee the requirements of the casting.