Rapid prototyping ( RP ) is an innovative technology that can directly produce complex parts from 3D CAD design graphics within a few hours . It is divided into laser rapid prototyping ( SLA ), layer-by-layer rapid prototyping ( LOM ), powder sintering rapid prototyping ( SLS ), melt deposition method rapid prototyping ( FDM ) and 3D printing. Since the first rapid prototyping system appeared in 1988 , more than twenty systems have been developed, each with some minor differences. Initially, these systems were used in the automotive and aviation fields, and later in many other fields, such as toys, computers, jewelry and medicine.
Stereolithography ( SLA )
SLA is the earliest commercialized RP technology with the highest market share . It uses photosensitive resin as raw material. Computer-controlled ultraviolet laser scans the surface of photosensitive resin point by point according to the information of each layered section of the part, so that the thin layer of resin in the scanned area undergoes photopolymerization reaction and solidifies to form a thin layer of the part. After one layer is cured, the workbench moves down a layer thickness so that a new layer of liquid resin can be applied to the surface of the previously cured resin, and then the next layer of scanning can be carried out. The newly cured layer is firmly attached to the previous layer, and this is repeated until the entire prototype is manufactured.
Fused Deposition Modeling ( FDM )
FDM was invented in 1988. The molten material ejected from the nozzle is spread on the base plate according to the cross-sectional shape under the drive of the XY table, and processed layer by layer to finally produce the part. Commercial FDM equipment uses a wide range of materials, such as casting wax, nylon, thermoplastics, ABS , etc. In addition, multiple nozzles can be used to improve efficiency.
Selective Laser Sintering ( SLS )
The SLS method uses infrared lasers as energy sources, and the modeling materials used are mostly powder materials. During processing, the powder is first preheated to a temperature slightly lower than its melting point, and then the powder is flattened under the action of a flattening stick; the laser beam selectively sintered according to the layered cross-sectional information under computer control, and the next layer is sintered after one layer is completed. After all sintering is completed, the excess powder is removed, and a sintered part can be obtained. At present, the mature process materials are wax powder and plastic powder, and the process of sintering with metal powder or ceramic powder is still under research.
Lamination Method ( LOM )
The LOM method appeared in 1985. First, a layer of foil (such as paper) is laid on the substrate, and then a certain power infrared laser is used to cut out the contour according to the layering information under the control of a computer. At the same time, the non-part part is cut into pieces according to a certain grid shape for removal. After processing one layer, another layer of foil is laid, and it is rolled with a hot roller so that the newly laid layer adheres to the formed body under the action of the adhesive, and then the shape of the layer is cut, and this is repeated until the processing is completed. Finally, the excess shredded part is removed to obtain a complete part.
3D printing technology
3D printing technology is similar to laser forming technology ( SLA ) in function. It uses layered processing and additive forming, that is, it generates 3D entities by adding materials layer by layer. The printing process of each layer is divided into two steps. First, a layer of special glue is sprayed on the area that needs to be formed. The glue droplets themselves are very small and not easy to spread. Then a layer of uniform powder is sprayed. The powder will quickly solidify and bond when it encounters glue, while the area without glue remains loose. In this way, the entity model will be “printed” and formed by alternating a layer of glue and a layer of powder. After printing, just sweep away the loose powder to “plan” out the model, and the remaining powder can be recycled.
