Q: What is precision casting?

Answer: Basic concept of precision casting: It includes investment casting, ceramic mold casting, metal mold casting, pressure casting, and lost foam casting. One of the most commonly used is investment casting: selecting suitable investment materials to manufacture honing machine investment molds; Repeat the coating and sanding process on the mold, harden the mold shell and dry it; Dissolve the internal mold to obtain the mold cavity; Roast the shell to obtain sufficient strength, burn off residual investment materials, pour the required metal materials, and remove the sand after shell removal to obtain high-precision finished products. According to product needs or undergo heat treatment and cold processing.

Ceramic mold casting:

A casting method for producing castings using ceramic slurry as a casting mold. The ceramic slurry is composed of a mixture of ethyl silicate hydrolysate and fine refractory sand with relatively pure texture and high thermal stability, such as fused quartz, zircon, corundum, etc. In order to make ceramic slurry bond in a short period of time, calcium hydroxide or magnesium oxide are often added as catalysts. Due to the similarity of the composition and appearance of the refractory material used to ceramics, it is called a ceramic type. Ceramic mold casting is a new process developed on the basis of ordinary sand mold casting. There are two types of ceramic molds: ① Ceramic molds are all made by pouring ceramic slurry. The production process is to first fix the pattern on the molding board, coat it with a sand box, and then pour the prepared ceramic slurry into the sand box. After the cement hardens, the mold is lifted, and after high-temperature roasting, it becomes the casting mold Using a liner, a ceramic slurry is poured into the gap between the liner and the pattern to manufacture the mold. The liner can be made of sand or metal.

Casting ceramic shells with bushings can save a large amount of ceramic slurry and is widely used in production. The surface roughness of ceramic mold castings can reach Ra10-1.25 microns, and the dimensional accuracy can reach 3-5 levels, achieving the goal of less and no cutting processing. Ceramic mold casting has a short production cycle and high metal utilization rate. Castings can reach over ten tons, mainly used for casting large thick walled precision castings and various molds such as single and small batch stamping, forging, plastic, metal, die-casting, glass, etc. The service life of ceramic mold casting can be comparable to that of molds made by mechanical processing methods, while the manufacturing cost is lower than that of molds made by mechanical processing methods.

Introduction to Sand Casting:

According to statistics, 60-70% of the total casting output is produced using sand molds, and about 70% of them are produced using clay sand molds. The main reason is that sand casting has lower costs, simpler production processes, and shorter production cycles compared to other casting methods. So castings such as the engine cylinder block, cylinder head, and crankshaft of automobiles are all produced using the clay green sand process. When the wet mold cannot meet the requirements, consider using clay sand surface dry sand mold, dry sand mold, or other sand molds. The weight of castings cast with clay green sand can range from a few kilograms to tens of kilograms, while castings produced with clay dry mold can weigh tens of tons.

Generally speaking, for medium to large castings, cast iron can be produced using resin self hardening sand molds, and steel castings can be produced using water glass sand molds. Castings with precise dimensions and smooth surfaces can be obtained, but the cost is relatively high.

Of course, the precision, surface finish, material density, metallographic structure, mechanical properties, and other aspects of castings produced by sand casting are often poor. Therefore, when these performance requirements of castings are higher, other casting methods should be used, such as investment casting (loss of wax), die casting, low-pressure casting, and so on.

The casting method should be suitable for the production batch:

For example, in sand casting, factories that produce in large quantities should create conditions to adopt advanced modeling and core making methods using honing tool technology. The production line of old-fashioned shock or shock compression molding machines is not high enough in productivity, and workers have high labor intensity and high noise, which is not suitable for the requirements of mass production. Therefore, it should be gradually transformed. For small castings, a box less high-pressure molding machine production line with horizontal or vertical parting can be used, which has high production efficiency and less floor space for solid molding; For mid size components, various box high-pressure molding machine production lines and air impact molding lines can be selected to meet the requirements of fast and high-precision molding production lines. The core making methods can include efficient core making methods such as cold core box, hot core box, shell core, etc.

Medium batch large castings can be considered for resin self hardening sand molding and core making.

For heavy castings produced in small batches, manual molding is still an important method. Manual molding can adapt to various complex requirements and is relatively flexible, without requiring many process equipment. It can be applied to 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; For heavy castings produced by a single gear measuring instrument, using the pit molding method has low cost and fast production. Mass production or long-term production of standardized products using multi box modeling or split box modeling is more suitable. Although the initial investment in molds, sandboxes, etc. is high, compensation can be obtained from saving molding time and improving product quality.

Low pressure casting, die casting, centrifugal casting, and other casting methods are only suitable for mass production due to the high cost of equipment and molds.

The modeling method should be suitable for the factory conditions:

For example, when producing castings such as large machine tool beds, the core forming method is generally used, without making patterns or sand boxes, and the core is assembled in the pit; And other factories use the sand box molding method to create patterns. Different enterprises have different production conditions (including equipment, venue, employee quality, etc.), production habits, and accumulated experience. Based on these conditions, it is necessary to consider what products are suitable for production and what products are not suitable (or cannot) for production.

To balance the accuracy requirements and cost of castings:

The casting accuracy obtained by various casting methods is different, and the initial investment and productivity are also different. The final economic benefits also vary. Therefore, in order to achieve abundance, speed, quality, and economy, it is necessary to take into account all aspects. A preliminary cost estimation should be conducted on the selected casting method to determine the casting method that has high economic benefits and can meet the casting requirements.