Casting is a kind of hot metal processing technology which has been mastered by human beings for about 6000 years. China entered the heyday of bronze casting around 1700 ~ 1000 BC, and reached a high level in technology. Casting is a method in which liquid metal is poured into a casting cavity corresponding to the shape of the part, and after it is cooled and solidified, the part or blank is obtained. Most of the cast materials are metals (e.g., copper, iron, aluminum, tin, lead, etc.) that were once solid but heated to liquid state, while the casting materials can be sand, metal or even ceramics. Depending on the requirements, different methods will be used.

Casting is a kind of hot metal processing technology which has been mastered by human beings for about 6000 years. China entered the heyday of bronze casting around 1700 ~ 1000 BC, and reached a high level in technology. Foundry is the process of melting a solid metal into a liquid form and pouring it into a mold of a certain shape for solidification. The cast metals are: copper, iron, aluminum, tin, lead, etc. The ordinary cast materials are raw sand, clay, water glass, resin and other auxiliary materials. The special casting includes investment casting, lost foam casting, metal casting and ceramic casting. (raw sand includes: quartz sand, magnesia sand, zirconium sand, ferrochrome sand, magnesium olivine sand, orchid sand, graphite sand, iron sand, etc.)

In the early

(2) stress relief annealing.Machining die steel with residual stress will lead to deformation after machining. Assuming that there is still stress after machining, there will be a great deformation or quenching crack during quenching.In order to avoid these problems, it is necessary to conduct stress relief annealing.

Three times of stress relief annealing are generally carried out in the mold manufacturing process:

(1) when cutting away more than 1/3 of the volume of raw materials or deep processing 1/2 of the thickness of raw materials, the processing allowance is left at 5 ~ 10mm and the first stress relief annealing is carried out.

(2) the second stress relief annealing is carried out when there is a margin (2 ~ 5mm) left in the finishing.

(3) after the mold test, the quenching line for the third stress relief annealing.

3, the mold cooling quenching tempering to about 100 ℃, the tempering shall promptly, in order to avoid deformation of sustained attack, and even cracking.Tempering temperature determined by the hardness of the operation, generally three times tempering.

4, nitriding treatment general casting mold after quenching, tempering (45 ~ 47HRC) can be used, but in order to travel the mold wear resistance, corrosion resistance and oxidation resistance, to avoid sticky mold, extending the life of the mold, it is necessary to carry out nitriding treatment.The depth of nitride layer is generally 0.15 ~ 0.2mm.After nitriding, polish is required to remove the bright white layer (about 0.01mm thick).

5. Several clarifications

(1) the heat treatment deformation of precision casting molds is caused by the combined action of phase change stress and thermal stress and is affected by a variety of factors.Therefore, under the premise of the correct selection of materials, but also pay attention to the blank casting, to choose the six-sided casting method, repeated upsetting.Together, in the design stage of the mold is necessary to pay attention to, make the wall thickness as uniform as possible (when the wall thickness is not uniform to open the process hole);For the disordered shape of the mold, to choose the Mosaic structure, rather than all the structure;For the die with thin wall and sharp Angle, we should choose the fillet transition and increase the fillet radius.In the heat treatment to make data records, the length, width, thickness of the upward deformation, heat treatment conditions (furnace loading method, heating temperature, cooling speed, hardness, etc.), for the future heat treatment of mold piling record.

(2) generally there are two kinds of process flow in the processing of casting mold, which are determined according to the actual situation.First kind: general casting die.Forging, spheroidizing annealing, rough machining, first stress relief annealing (with a margin of 5 ~ 10mm), rough machining, second stress relief annealing (with a margin of 2 ~ 5mm), finishing, third stress relief annealing (after mold test and before quenching), quenching, tempering, clamping and nitriding.The second kind: especially messy and quenching very easy to deformation of the mold.Forging, spheroidizing annealing, rough machining, first stress relief annealing (with a residual amount of 5 ~ 10mm), quenching, tempering, mechanical and electrical processing, second stress relief annealing (with a residual amount of 2 ~ 5mm), mechanical and electrical processing, third stress relief annealing (after mold test), clamping and nitriding.