What are the stages of the casting process?
Metal casting process (also known as liquid forming) refers to the forming method of metal products that are melted and cast into a pre made mold (making the liquid metal a solid casting container), and solidify to obtain a certain shape and performance.
Metal casting process (also known as liquid forming) refers to the forming method of metal products that are melted and cast into a pre made mold (making the liquid metal a solid casting container), and solidify to obtain a certain shape and performance. Liquid forming is one of the earliest manufacturing processes. Although hundreds of years of casting history have made this process no longer mysterious, it is still a basic molding technique. Castings have the characteristics of low production cost, high process flexibility, and strong adaptability, suitable for producing castings of different materials, shapes, and weights, and suitable for mass production. The disadvantage is that the tolerance (large limit size minus small limit size) is large, which can easily lead to internal defects and require more materials and equipment. Meanwhile, casting production produces dust, harmful gases, and noise, thereby polluting the environment.
The casting process usually includes the following three stages:
1. Mold preparation: According to the materials used, molds can be divided into sand molds, metal molds, ceramic molds, clay molds, graphite molds, etc. When the mold is removed from the casting, it is usually damaged. Its cavity is usually made of wax, wood, plastic, or metal. A mold is a high cost but reusable mold. Due to high costs and expensive on-site modifications, some of which cannot even be repaired, more design preparation time is required to prepare the mold. The quality of mold making is the main factor affecting the quality of castings;
2. Melting and pouring of cast metals: Cast metals (cast alloys) mainly include cast iron, cast steel, and cast non-ferrous alloys;
3. Casting treatment and inspection: Casting treatment includes removing foreign objects from the core and surface of the casting, removing gates and risers, removing burrs and protrusions such as welds, as well as heat treatment, forming, rust prevention treatment, and rough machining.
There are many types of castings, usually divided into: ordinary sand casting, including wet sand mold, dry sand mold, and chemically hardened sand mold.
1. Wet sand mold and dry sand mold
Wet sand mold is a method of compacting wet sand in a sand box using wooden or metal half molds. The assembled mold can be cast into the cavity with or without a core and molten metal. When removing the parts, the mold will be damaged. The wet moisture content of casting dry sand mold sand is slightly higher than that of wet sand mold sand. After the sand mold is ready, the surface of the mold cavity should be coated with a fireproof coating. Refractory materials can prevent sand from overheating and can then be dried in an oven. After cooling, it can be molded and poured. Drying clay sand molds takes a long time and consumes a large amount of fuel. The sand molds are prone to deformation during the drying process, which affects the casting accuracy of the molds.
2. Chemical hardening sand mold
The molding sand used for chemical hardening sand molds is called chemical hardening sand. Its adhesive is usually a substance that can undergo molecular polymerization and then transform into a three-dimensional structure under the action of a hardener. Commonly used are various synthetic resins and water glass. The characteristics of the chemical hardening sand casting process are:
(1) Casting molds can accurately reflect the size and contour shape of patterns, and the produced castings have high dimensional accuracy;
(2) The equipment has a light structure, low power, high productivity, and can simplify the sand treatment part;
(3) When using chemically hardened sand for molding, pattern materials such as wood, plastic, and metal can be selected according to production requirements.