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Rapid prototyping technology (RP technology) integrates materials technology, laser technology, mechanical engineering technology, numerical control technology, CAD technology, and other disciplines and technologies. It can accurately, automatically, quickly, and directly manufacture molds/parts from CAD models, eliminating the need for costly and time-consuming machining, tool design, and mold design. It can significantly shorten the product development cycle, thereby improving the flexibility and production efficiency of manufacturing.

At present, the machinery industry usually uses machining methods to manufacture presses, molds, core boxes, templates, etc., and sometimes even requires skilled fitters to help with trimming, especially automobile cylinder blocks, aircraft engine blades, automobile cylinder heads, marine propellers, and other complex thin-walled castings are more difficult to manufacture. The integrated forming manufacturing of rapid prototyping and casting technology provides broad development prospects for the rapid manufacturing of small batches and single-piece molds/parts. This article discusses the integrated forming manufacturing of rapid prototyping and casting technology.

Typical rapid prototyping technologies

 

At present, 3DP, SL, SLS, FDM, LOM, and other technologies are rapid prototyping processes with relatively mature applications in the world. These processes can be divided into two categories, namely, the digital jet-forming process based on microdroplets and the rapid prototyping process based on lasers. The digital jet-forming process based on microdroplets refers to the use of microdroplet technology to form adhesive droplets or to form material droplets, while the laser-based rapid prototyping process refers to the use of laser technology to bond, separate, solidify, and melt formable materials.

1. Typical laser rapid prototyping processes

 

(1) DLF process (direct light forming process) – The DLF process is a direct metal forming process that selectively sintered metal powder and then stacked it layer by layer. The energy used for sintering is a high-energy laser;
(2) SL process (stereolithography process) – SL process uses ultraviolet light or ultraviolet laser to cure resin and stack it into shape;
(3) SGC process (solid contour curing process) – The SGC process uses an ultraviolet laser to cure resin and stack it into shape. The technology used is mask technology;
(4) LE NS process (laser near net shape process) – LENS process selectively sintered metal powder, and then stacked it layer by layer to form a shape. The energy used for sintering is a high-energy laser;
(5) LOM process (layered solid manufacturing process) – The LOM process uses a laser cutting method to selectively sinter metal sheets, paper materials, and other foils, and stacks them layer by layer to form a shape;
(6) SLS process (selective laser sintering process) – The SLS process uses a CO2 laser to selectively sinter resin sand, metal powder, plastic powder, wax powder, and other powder materials, and stack them layer by layer to form a shape.

2. Typical micro-droplet digital jet-forming processes

 

(1) 3DP process (three-dimensional printing process) – The 3DP process sprays a binder from the nozzle to bond the powder material, and stacks it layer by layer to form a shape;
(2) EFF process (free extrusion manufacturing process) – EFF process adjusts the mixing ratio of multiple different materials in real-time, and uses continuous micro-droplet technology to gradually accumulate them into gradient material parts;
(3) SDM process (deposition forming manufacturing process) – The SDM process is a direct metal mold forming process that combines molten metal micro-droplet accumulation forming with cutting removal forming;
(4) PCM process (moldless casting manufacturing process) – The PCM process continuously sprays a binder on the sand layer to bond the mold sand to form a shape;
(5) 3DW process (three-dimensional welding process) – The 3DW process uses the principle of surfacing to stack metal wires;
(6) MJS Process(Multi-nozzle jet forming process) – The MJS process uses piston extrusion to extrude the molten material from the nozzle, and then uses continuous droplet technology to form a wire pile;
(7) BPM process (Ballistic particle manufacturing process) – The BPM process uses a nozzle to spray the molten material to form a pile. It is worth noting that the nozzle used has five-axis freedom;
(8) UDS process (Uniform droplet spraying process) – The UDS process uses electromagnetic field control to form a pile of molten materials;
(9) FDM process (Fused deposition modeling process) – The FDM process heats nylon, wax, plastic, and other materials in the nozzle, and uses a fine nozzle to spray continuous droplets to form a wire pile;
(10) CC process (Contour forming) – The CC process uses a combination of molten material casting and contour accumulation to form a pile.

RP and casting process integration

 

The rapid part/mold manufacturing technology produced by the integration of RP technology and the casting process is an integration of casting technology, CAD technology, RP technology, CAE technology, CAM technology, etc. It has a high degree of technical integration and can convert CAD models into physical models in a short time, which can effectively reduce production costs and manufacturing cycles.

It is worth noting that the dimensional accuracy of the molds/parts manufactured using this process will be affected by many factors, among which the most important influencing factor is the shrinkage rate of the metal during the casting process. To make the forming metal mold/part more accurate, it is necessary to accurately determine the shrinkage rate of the metal. This paper numerically analyzes the solidification process of the casting and then optimizes the casting process parameters to meet the technical requirements of the dimensional accuracy of the parts/molds.

At present, the numerical simulation work on the solidification process of castings in China mainly focuses on the analysis of the casting stress field, casting temperature field, and the prediction of a series of defects such as hot cracking, shrinkage, shrinkage cavity, and so on during the solidification process of castings, but there is still little research on the numerical simulation of the dimensional accuracy of castings during the solidification process.

The casting stress field and casting temperature field are usually in a state of mutual influence during the casting solidification process. The casting solidification process analysis belongs to the typical category of thermal coupling. In the past, many studies have simplified the problem of thermal coupling solution, have not considered the temperature change caused by stress deformation work, and shortened the calculation time of coupling analysis. This simplified method does not affect the analysis of the casting stress field, casting temperature field, and the calculation of hot cracking, shrinkage, and shrinkage cavity of castings during the solidification process, but it will affect the dimensional accuracy of castings.

The organic combination of finite element simulation technology and CAD data can qualitatively simulate the solidification of mold/part size changes, and can also effectively predict the size change law of mold/part during the solidification process, and gradually achieve the purpose of optimizing the CAD model. At the same time, the dimensional errors that occur during the conversion of precision casting, RP prototypes, and other processes can be compensated during 3D CAD modeling, thereby realizing the compensation and feedback of error data. In addition, it can also organically integrate material technology, laser technology, finite element simulation technology, RP technology, CAD technology, etc. to quickly manufacture metal molds and metal parts.

Since the prototype forming process is realized by computer control, the relevant production process and design process are completed by computer technology, and the rapid manufacturing of high-quality prototype parts can be realized. Unlike other manufacturing processes, the integrated forming manufacturing of rapid prototyping and casting technology can use computer technology to modify the CAD model in real-time to compensate for dimensional errors such as dimensional shrinkage, dimensional accuracy control, and geometric deformation, to ensure that the manufactured parts/molds are of high quality.

1. Manufacturing of metal parts/molds directly driven by CAD models

 

CAD can directly drive the manufacturing of molds without the need for core boxes or patterns. The shell molding materials used are all common materials used in the casting workshops of various manufacturing companies. The part model can be directly converted into a mold in the CAD environment. The non-part part needs to be bonded or sintered during the forming process, while the part is still powder during the forming process. After the forming process is completed, the powder is poured out and the sand mold and sand core can be directly manufactured.

In this way, it is no longer necessary to make a large number of foam plastic molds and wax molds as in the past traditional precision casting, which effectively saves time and cost, especially for the production of complex parts and small batches. The main processes currently include direct shell casting DSPC, SLS sand mold sintering, and PCM woodless mold forming process. These processes can realize the integrated manufacturing of sand cores and molds, and there is no assembly relationship between sand cores and molds, which is particularly suitable for the production of complex parts and small batches.

The manufacturing of metal molds/parts that are directly driven by CAD models includes three-dimensional digital models of risers and gates. First, it can simulate the shrinkage rate of metal solidification; second, it can optimize and modify the CAD model; third, it can layer the model and drive the rapid prototyping machine so that the mold can be directly manufactured; finally, after subsequent process technologies such as roasting the mold are used, the metal alloy can be cast to manufacture metal molds/parts.

2. Manufacturing of metal parts/molds indirectly driven by CAD models

 

First, design the 3D CAD model of the metal mold/part, and design the riser and gate together to better simulate the solidification process of metal shrinkage; secondly, use MARC software to simulate the solidification process of metal shrinkage, and optimize the process parameters and boundary conditions between the part and the mold to better determine the shrinkage of the metal, especially to achieve real-time tracking of key dimensions, thereby effectively ensuring the dimensional accuracy of the final designed metal mold/part; finally, optimize the CAD model and use it to drive the production of the required casting pattern and rapid prototype.

Organically combining casting technology and rapid prototyping technology can achieve low-cost and rapid manufacturing of small batches of metal parts. Using the BMP process, FDM process, SGC process, and SLS process, CAD can be directly driven to manufacture wax mold prototypes, and they can be applied to the investment casting process. For example: based on FDM prototypes, metal molds/parts are quickly manufactured, and the wax molds in investment casting are replaced with FDM prototypes, and the refractory slurry is directly coated on the FDM mold; after the refractory slurry is solidified, the FDM prototype is fired and removed, and only the casting shell is left, and then casting is performed. It is particularly suitable for the manufacture of small and medium-sized metal parts/molds with medium complexity.

Rapid prototyping technology (RP technology) can also be directly combined with ceramic mold casting, gypsum mold casting, sand mold casting, etc. to manufacture metal parts/molds with high mechanical strength and high hardness, and the manufactured prototypes have high durability, small deformation and shrinkage, no warping, and low internal stress.

Conclusion

 

In short, the integrated forming and manufacturing of rapid prototyping and casting technology can maximize the advantages of casting technology and rapid prototyping technology, can pre-eliminate defects, has low cost and fast manufacturing speed, and can quickly manufacture complex parts, which is worthy of promotion and application.