What are the typical process methods of RPM technology?

There are more than 30 specific processes for PRM technology, and the following describes several methods that are the most technically mature and have been well commercialized.

(1) Layered solid manufacturing.

Layered entity modeling (Laminated Object Manufacturing, LOM) process principle is the use of CAD layered model of the data obtained in accordance with the parts of the continuous layering of geometric information cutting sheet, will be obtained from the layers of the sheet bonded into a three-dimensional entity. The back of the sheet is previously coated with a layer of hot melt adhesive. During processing, a hot press roller hot presses the sheet to bond it to the formed workpiece below; a CO2 laser is used to cut the part cross-section contour and the outer frame of the workpiece on the new layer just bonded, and a mesh is cut in the excess area between the cross-section contour and the outer frame that is easy to peel off during post-processing; after the laser cuts the cross-section of a completed layer, a worktable drives the formed workpiece down and separates it from the strip sheet; the feeding mechanism rotates the Receiving rollers and feeding rollers, drive the material belt to move, so that the new layer moved to the processing area: the table rises to the processing plane; hot pressure roller hot pressure, the number of layers of the workpiece increased by one layer, the height of the increase in the thickness of a material; and then cut the cross-section contour on the new layer. So repeated until all sections of the part bonding, cutting, to get the layered manufacturing of solid parts. The principle of the layered solid modeling process is shown in Figure 5-56.The materials used in the LOM method can be coated paper (paper coated with an adhesive overlay), coated ceramic foils, metal foils, or other material-based sheets. A formed car brake caliper body manufactured by the layered solid modeling process is shown in Figure 5-57, and a finished casting made by forming and turning is shown in Figure 5-58.

Figure 5-56 layered solid manufacturing process schematic (2) selective laser sintering.

Selective Laser Sintering (SLS) is the use of precision-guided laser beams to make the solid powder sintered or melted solidified to form a three-dimensional solid.

The principle of the SLS process and molding process shown in Figure 5-59. Forming machine in accordance with the computer output of the formation of layered contours, using a laser beam in the specified path to selectively scan and sintering table very thin (0.1 ~ 0.2mm) and uniformly layered solid powder. The powder in the scanned area selected by the layering pattern is fused together by the laser beam. The powder in the unscanned area remains loose. When a layer of sections is sintered, the table is moved to form a new layer, the powder is compacted, and a new layer of sections is selectively sintered and bonded to the previous layer, and so on to obtain the desired part prototype. The powder itself can be used as a support for the molding entity during the molding process, and there is no need to design another support structure. The powder materials for this method are mainly wax, polycarbonate, washed sand and other non-metallic powders and metal powders such as iron, cobalt, chromium and their alloys. Thus, it is particularly suitable for the manufacture of complex structures of molding or parts, and can sinter almost any shape of molding. Figure 5-60 shows the work of the German EOSINT P700 laser forming machine.

Figure 5-57 Layered solid manufacturing of car brake calipers

Figure 5-58 Formed turned car brake calipers

Figure 5-59 Schematic diagram of the selective laser sintering process

Figure 5-60 Works made by the laser forming machine (3) Fused deposition modeling.

Fused Deposition Modeling (FDM) is based on the geometric information determined by the CAD model, the filament material is fed into the nozzle by the filament feeding mechanism, and a heater is used inside the nozzle to heat the filament material into a semi-fluid state. The nozzle under the control of the computer according to the lamella parameters along the part cross-section contour and filling trajectory movement, while squeezing and control the flow rate, so that the viscous fluid evenly spread on the cross-section layer, layer by layer buildup, so as to create a prototype of the part. The principle of operation is shown in Figure 5-61. Materials used in FDM include ABS engineering plastics, wax, polyethylene, polypropylene, ceramics, and nylon.

(4) Stereolithography.

Stereo Lithography (Stereo Lithography Apparatus, SAL) forming principle shown in Figure 5-62. Its working principle is similar to SLS, the difference with SLS is that its molding material is liquid photosensitive resin, rather than powder material. First of all, the use of CAD systems to design a three-dimensional model of the part, and its model layered "slicing", and then the use of laser forming machine in the laser beam scanned according to CNC commands, so that the liquid photosensitive resin held in the container layer by layer curing and bonded together. The curing process starts with the first layer of liquid on the working platform. When the first layer is cured, the working platform is lowered by one height along the z-axis. A new layer of liquid resin is made to cover the top of the cured layer for the second layer to be cured. This process is repeated until the last layer is cured, and a 3D solid of the part is generated. When a layer is scanned, the resin that has not been irradiated by the laser is still liquid. The platform is then lowered by the elevator one more layer, the newly formed layer is covered with another layer of resin, and a second layer is scanned, creating a new machined layer that is securely attached to the cured part.

Figure 5-61 Fused deposition modeling schematic

Figure 5-62 Stereolithography process schematic