Research status of Moldless sand casting and composite mold

The traditional mode of manufacturing and service capacity expansion has been difficult to meet the growing demand for products. Applying the best technology in the world to manufacturing may reduce energy use and carbon dioxide emissions by another quarter to a third. Therefore, in recent years, a variety of new technologies have emerged and applied in the mechanical manufacturing industry, such as additive manufacturing and reduced material manufacturing technology, which appear in the casting market with the characteristics of high precision and high completion. According to the forming characteristics, it is mainly divided into laser selective sintering technology (SLS), inkjet bonding 3D sand mold printing technology and extrusion cutting integrated dieless casting composite forming technology. Additive manufacturing technology has been widely used in casting production in recent years to make prototypes, patterns, sand molds, sand cores and even castings themselves. It not only solves the process difficulties of traditional sand casting to a certain extent, but also has some advantages in economy. Christian weller discussed the impact of AM technology on enterprises and industries, and determined the economic and technical characteristics of am.

Sand mold 3D printing technology has attracted extensive attention from scholars in mold performance, mold process design and material system. In the study of mold properties, curing temperature and curing time will affect the mechanical properties such as mold strength and permeability. Considering the action mechanism of the individual and comprehensive effects of process parameters on the permeability and strength of the mold in the printing process, reasonable process parameters are conducive to obtain ideal mold properties. X-ray CT was used to predict and characterize the mass transport characteristics of 3D printed mold samples, so as to optimize and improve the casting structure. Because the forming rules are different from the traditional sand casting, there are some innovations in the mold design. The unconventional design rules of gating system are developed based on sand mold 3D printing technology, which greatly improves the performance of castings. In addition, the mold design of shell truss structure can save at least 60% of sand and effectively reduce the sand falling time by more than 20%. The obtained castings also have good dimensional accuracy and surface quality. Compared with the traditional sand casting rules, the constrained topology optimization method for part redesign developed for sand mold 3D printing not only improves the safety factor by 30%, but also effectively reduces the weight of mechanical parts by 50%.

In terms of 3D printing material system, for the steps required by 3D printing new material system, studying the formula of powder, adhesive and printing liquid will help to speed up the development of new materials and adhesive system. Comparing the binder characteristics and tensile strength of sand mold 3D printing and traditional chemical bonding molding materials, it shows that increasing the binder content can enhance the mold strength, but it has an adverse impact on the quality of parts. The effects of 3D printing media on the formability of castings, including microstructure and porosity, were studied. On the other hand, milling is a very representative processing method in material reduction manufacturing technology. It is often used to process the contour or groove of complex rotating body in machining, but it belongs to a new field in sand casting. The bonded molding sand is removed by the cutting force of the milling tool on the mold sand blank to realize the forming from the sand blank to the mold with cavity contour characteristics. At present, there is still a lack of research on sand mold milling technology, mostly focusing on the surface roughness of milling surface, tool wear and milling strategy.

For example, the wear degree of different tools in sand mold milling is studied to act on sand blocks with appropriate strength. The influence of NC milling parameters on milling mold accuracy, as well as the prediction and calculation of cutting force and tool wear mechanism in milling process. Both of them are rapid prototyping technology based on Dieless casting. While obtaining better mold accuracy, they can realize complex gating system design and optimize liquid metal flow to reduce the influence of oxide effect, so as to obtain good casting surface accuracy (less than 25%) μ m)。

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