Principles and Characteristics of Printing Rapid Prototyping Technology

Knowledge sharing by Guangdong Shunde Teamwork Model Technology Co., Ltd, whom with over 20 years rapid prototyping experience.

Email: ken@gdtwmx.com

Website: www.gdtwmx.com

RP (Rapid Prototyping) is a high-tech product developed rapidly in the 1990s. It is based on the principle of layer-by-layer material addition. It is directly driven by CAD data to generate solid models or parts. The essence of RP technology lies in the geometric topology of the objects to be processed. It is described and determined by the CAD model. The numerical control instructions for driving tools and materials are obtained by high-dispersion processing, and the molding and manufacturing are performed by using RP technology equipment. The distinctive features of this technology are: rapid production of models or parts, short cycle times and low cost; almost no restrictions on the complexity of parts; no molds, fixtures, knives, and no machining required in the manufacturing process. The following is an introduction to the principle of RP technology that is relatively mature and can be used in the industrial field.

1. Stere-lithography or stereolithography of photo-curing stereolithography The principle of software is to plane-separate three-dimensional data created by CAD to obtain the cross-sectional shape of each layer, using a certain wavelength of ultraviolet laser beam. The two-dimensional cross-sectional shape of each cut layer scans the liquid photo-curable resin to form a layer of a specific shape of solidified layer. Due to the existence of a certain depth of curing, each layer is cured and adhered to the previous solidified layer (the initial layer is stuck to the upper surface of the lifting platform), and then the lifting platform is submerged in a layer thickness (0.01-0.02mm), and then new One layer forming. In this way, the laser beam irradiates one layer, solidifies one layer, adheres one layer, and sinks one layer. The final solidified material is a three-dimensional model entity designed according to the CAD data. Its molding material is a photocurable resin. If a thermosetting resin is used instead, the liquid surface is scanned with a laser beam, and thermal polymerization is caused by the thermal action of the laser spot, and a three-dimensional model entity designed by CAD can also be obtained. Before the two resins are cured, they are liquid, all of which have the characteristics of flow, plasticity, and easy coating. However, the photocurable resin can be operated at room temperature, stable during storage, short curing time, and good lap bonding performance. Therefore, the light curing technology is bound to be rapid. development of. When the product is used as a practical sample, due to the limited mechanical properties of the existing resin, it cannot be used to manufacture products that have large loads, alternating stresses, and large frictional forces. In order to improve the mechanical properties of the material, a method using a silicone Rubber Material and a high-performance polyurethane material has been adopted at present.

Molding accuracy is one of the key issues of RP technology in industrial applications. In the SL process, factors such as resin cure shrinkage, depth of cure, coating quality, laser scan linewidth, scan error, and CAD model networking all affect the molding accuracy.

2. Layered object manufacturing LOM (Lominated Object Manufacturing) layered object manufacturing technology is the use of laser beams and thin materials (paper, plastic film or composite materials, etc.) to generate any shape of three-dimensional objects. That is, when the work starts, the feeding drum lays the raw material on the base surface of the workbench, and the hot-pressing roller flattens the material and sticks it to the bottom layer. The laser beam of the two-dimensional numerically controlled Laser Cutting head is given by the computer data system. The information instructions, cut out the cross-sectional shape of the workpiece, and chopped around the excess material. The workbench then descends to a height of one layer thickness and a new layer is placed on the loading drum. This is repeated layer by layer until the workpiece is manufactured.

3. Fused Deposition Modeling (FDM) Fused Deposition Modeling (FDM) is a method of rapid prototyping using electric heating and thermoplastic materials under the control of a computer. The system consists of a numerical control nozzle, a liftable table, and a feeding device. The semi-fluid or linear melted thermoplastic material is a molding material (eg, ABS plastic, cast wax, rubber, etc.). That is, the work begins, the workbench is in a high position, the raw material is heated and melted by the nozzle, and is continuously extruded and sprayed on the selected area (ie, the cross section of the workpiece) according to the computer's control instructions, followed by cooling and solidification. The workbench descends one layer thick, and then squeezes the second layer. This is repeated until the work piece is fully formed.

4. Selective laser sintering SLS (Selective Laser Sintering) Selective laser sintering technology is similar to SL technology. It also uses a laser beam to scan each layer of material, but uses powder (plastic powder, metal powder, ceramic powder) instead of liquid polymer. The powder is preheated to a temperature slightly below its melting point, and then the laser is used to scan and heat the powder to its sintering temperature so that it is bonded to the matrix material and the non-lasered powder remains in place. After a layer of sinter is fired, the workbench is lowered by a layer of height, and the long two layers are sintered until the entire part is manufactured. Since the unsintered powder surrounds the unsintered part, it has a supporting effect on it, so no complicated support system is required in the production.

In the selective laser sintering system, laser types, laser scanning patterns, computer slice thickness, computer control of the laser scanner, and powder material selection all affect the forming accuracy and performance of the workpiece. Most powders shrink when they are sintered. The result is internal residual stress and strain deformation that affects accuracy. The thickness of the powder particles also affects the surface quality of the part. After the ceramic powder is laser sintered, in order to improve its mechanical properties and heat resistance, it must be post-processed, ie the sintered ceramic body is put into a temperature-controlled furnace and fired at a higher temperature.