Casting coated sand suitable for selective laser sintering forming and manufacturing method thereof

Abstract

The invention discloses casting coated sand suitable for selective laser sintering forming and a manufacturing method thereof. The coated sand is made from roughing sands, an organic binder, an inorganic binder, a coupling agent and a curing agent, further, additives, such as a lubricant, a light absorber and the like are not required; and the roughing sand is spherical pearl sand with the angular coefficient less than or equal to 1.1, wherein the sand grains consist of adjacent four-sieve sands or five-sieve sands. The manufacturing method of the casting coated sand comprises the following steps of: sieving the roughing sands to obtained the required four-sieve sands or five-sieve sands; carrying out thermal coating on the roughing sands by using phenolic resin powder, the coupling agentand the curing agent according to a certain proportion so as to obtain phenolic resin coated sand; and evenly mixing monoammonium phosphate fine powder and the phenolic resin coated sand which are ina certain proportion to obtain the casting coated sand suitable for the selective laser sintering forming. The coated sand laser sintering forming part has high preform strength, good forming accuracy and little gas forming amount and can be applied to a casting sand mold (core) with an intricate structure in laser fast forming, therefore, the fast trial-production and the manufacturing capacity of intricate castings are enhanced.

Description

technical field [0001] The invention belongs to the field of advanced manufacturing technology, and in particular relates to casting coated sand suitable for area-selective laser sintering and a preparation method thereof. Background technique: [0002] Casting is one of the basic processes of modern machinery manufacturing industry and an important component of advanced manufacturing technology. Among them, the casting method of coated sand is a kind of precision sand casting (Precision-type Sand Casting), its dimensional accuracy is greatly improved, and the dimensional accuracy of ordinary sand castings can be improved from CT9-10 to CT6-7. The roughness is reduced to Ra<3.2-6.3μm. As the main body of the coated sand casting process, the coated sand material has attracted the attention of a large number of researchers and suppliers. At present, the developed and applied coated sand materials are all formed by pressing the mold to prepare the coated sand mold (core). ...

AI Technical Summary

Problems solved by technology

[0004] However, there are the following main problems in the casting coated sand material and its preparation method used in SLS forming at present: most of the rapid laser forming is still directly used (or slightly added Modification) The phenolic resin coated sand materials used in traditional casting methods, even if a small part of them are foundry coated sand materials developed for SLS forming characteristics, also generally have low strength of the laser sintered preform, which leads to laser sintered forming Parts are easily broken, damaged or missing during the powder cleaning and transfer process. The main reason is that the laser sintering process is different from traditional heating. It is a "rapid melting and rapid cooling" method. Under the action of this instantaneous heat, the layer The curing reaction of the phenolic resin at the local and interlayer joints is incomplete or has no cross-linking and curing at all, the degree of resin curing is not high, and even locally between the particles, there is still a bond that only depends on the softening of the resin, resulting in the initial failure of the SLS molded part. Billet strength is low

In addition, the coated sand mold (core) formed by laser sintering has a large amount of gas generation, which is easy to cause casting defects such as pores and shrinkage porosity, which directly limits the popularization and application of coated sand rapid prototyping

The main reason is that the amount of phenolic resin added in the coated sand for laser sintering is too large (all greater than 3%). At the same time, some additives in the coated sand, such as the commonly used lubricant: calcium stearate, can also easily cause Air volume increased