Understanding Rapid Prototyping Technology

With the increasing complexity of industrial design objects and the implementation of concurrent engineering aimed at improving design efficiency, shortening design cycles, and increasing the one-time success rate, the demand for rapid prototyping in the first version of product development has become more urgent.

Currently, computer-aided design (CAD) technology helps designers balance innovation and risk. However, the emergence of CAD models cannot completely replace other forms of models. For example, in product styling design, it is necessary to examine not only the product’s appearance and color effects, but also its hand feel. In the design of aircraft and spacecraft, aerodynamic wind tunnel testing has not been abandoned because of the use of CAD. In the transportation industry, crash tests for structural safety must be carried out during the development of any new vehicle model. All of this stems from the limitations of CAD models. The main disadvantages of CAD are as follows:

1. CAD models cannot provide all the information about the product, such as touch sensation.
2. CAD models can only simulate known environmental conditions.
3. Physical solid models in three-dimensional space have a stronger sense of realism and touchability than CAD models on a two-dimensional screen.
4. CAD models also need to be verified.

Therefore, while studying and applying virtual design and virtual manufacturing based on three-dimensional CAD, we must also research and adopt rapid prototyping technology, which is also developed based on CAD. The combination of CAD and rapid prototyping technology brings an ideal solution to designers.

Overview of Rapid Prototyping Technology

There are four main ways of manufacturing prototypes or components: subtractive manufacturing, compressive manufacturing, additive manufacturing, and growth-based manufacturing.

Subtractive Manufacturing

Subtractive manufacturing uses separation techniques to orderly remove excess material from the base. Traditional CNC milling and turning, grinding, drilling, planing, electrical discharge machining, and laser cutting all belong to subtractive manufacturing.

Compressive Manufacturing

Compressive manufacturing uses the plasticity of materials to form them under specific external forces. Traditional forging, vacuum casting, powder metallurgy, and other technologies belong to compressive manufacturing. Compressive manufacturing is mostly used for model making in the blank stage, but there are also examples of direct forming of workpieces, such as precision casting and forging, which are net-shape forming methods and belong to compressive manufacturing.

Additive Manufacturing

Additive manufacturing uses mechanical, physical, chemical, and other methods to build parts by orderly adding materials.

Growth-based Manufacturing

Growth forming refers to the method of manufacturing using the activity of materials. The growth and development of biological individuals in nature belong to growth-based manufacturing. With the development of active materials, bionics, biochemistry, and life sciences, growth-based technology will achieve significant progress.

Rapid prototyping technology is an integrated technology developed based on modern CAD/CAM, laser, computer numerical control technology, servo drive, and new materials. In a narrow sense, it mainly refers to additive manufacturing technology. Different types of rapid prototyping systems use different materials, so their forming principles and system characteristics are also different. However, their basic principle is the same: layer-by-layer manufacturing, layer-by-layer stacking, which is similar to the mathematical integration process.

From the perspective of manufacturing technology, rapid prototyping technology breaks through traditional methods. Through the combination of rapid automatic systems and computer data models, it can manufacture prototypes of various complex shapes without any molds or mechanical processing. This shortens the product design and production cycle and reduces production costs. This is the revolutionary significance of rapid prototyping technology to manufacturing.

Common Rapid Prototyping Technologies

At present, more than a dozen rapid prototyping processes have been developed. The more mature and commercialized methods mainly include: Laminated Object Manufacturing (LOM), Stereolithography Apparatus (SLA), Fused Deposition Modeling (FDM), Selective Laser Sintering (SLS), and others.

Laminated Object Manufacturing

Laminated Object Manufacturing is one of the most mature rapid prototyping technologies. LOM technology uses materials such as paper and PVC film, which are inexpensive and offer high accuracy. Therefore, it is widely used in product design visualization, styling design evaluation, assembly inspection, and investment casting.

LOM technology uses low-cost raw materials, so the production cost is extremely low. It is suitable for forming large-sized workpieces. The forming process does not require support structures, excess material is easy to remove, and the accuracy is quite good. Nevertheless, because LOM technology has low material utilization and serious material waste, with the development of new technologies, the LOM process may gradually be phased out.

Stereolithography (SLA)

Stereolithography (SLA) uses photosensitive resin as the material. Under computer control, an ultraviolet laser scans the liquid photosensitive resin layer by layer to solidify it. The SLA process can manufacture geometric solid models with extremely high accuracy in a simple and fully automatic way.

This additive manufacturing process has high forming efficiency, relatively stable system operation, and guaranteed smooth surface and accuracy of the formed parts. It is suitable for making models with extremely complex structures and can directly produce intermediate molds for investment casting. Although SLA has high forming accuracy, it also has large limitations on forming size and is not suitable for making very large workpieces. The physical and chemical changes during the forming process may cause workpiece deformation, so the formed parts need support structures.

Currently, the materials supported by the SLA process are still relatively limited. Liquid photosensitive resin has certain toxicity and odor, and the material needs to be stored away from light to prevent premature polymerization. SLA-printed products have relatively low hardness and are quite brittle.

Fused Deposition Modeling (FDM)

Fused Deposition Modeling (FDM) does not require the support of a laser system, and the materials used are relatively cheap. This is also the main technical solution adopted by desktop 3D printers.

Fused deposition heats and melts filamentary thermoplastic material, then extrudes it through an extruder with a fine nozzle. When using the FDM process to make prototypes with overhanging structures, support structures are needed. To save material costs and improve efficiency, FDM equipment often uses a dual-nozzle design: one nozzle extrudes the modeling material, and the other nozzle extrudes the support material.

Selective Laser Sintering (SLS)

Selective Laser Sintering (SLS) uses powder materials. The laser, controlled by a computer, scans and irradiates the powder to sinter and bond the material. The material is stacked layer by layer to achieve forming.

SLS technology uses a relatively wide range of materials, mainly including wax, polycarbonate, nylon, ceramics, and even metals. After the workpiece is fully formed and completely cooled, the worktable rises to its original height. The part is then removed, and the unsintered powder on the model surface is removed using a brush or compressed air.

The SLS process does not require support structures and has high material utilization. However, SLS equipment is expensive. The material needs to be preheated before sintering, and the material releases odor during the sintering process.

Polymer Jetting

PolyJet technology is one of the most advanced 3D printing technologies currently available. The working principle of PolyJet is similar to that of an inkjet printer, except that the print head jets photosensitive polymer. When the photosensitive polymer material is jetted onto the worktable, UV lamps following the print head emit ultraviolet light to cure the photosensitive polymer material. During the forming process, two different types of photosensitive resin materials are used: one for generating the actual model, and the other is a gel-like resin material used as support.

PolyJet polymer jetting has very high accuracy, with the thinnest layer thickness reaching 16μm. The equipment provides a closed forming environment, making it suitable for ordinary offices.

Applications of Rapid Prototyping Technology

At present, Rapid prototyping technology has been applied in various fields, including industrial design, mechanical manufacturing (automobiles, motorcycles), aerospace, military, architecture, film and television, household appliances, light industry, medicine, archaeology, culture and art, sculpture, and jewelry. The main application directions include the following:

Design and Concept Visualization

RP technology is not limited by shape and can quickly turn design ideas into three-dimensional physical objects. In the home appliance and automotive industries, where aesthetics and novelty are pursued, prototypes provide intuitive bases for product evaluation.

Assembly Verification

RP prototype parts can be used for assembly simulation, allowing us to observe how various parts fit together and influence each other. Therefore, before putting a new product into production, making part prototypes with RP technology and then performing trial assembly helps verify the rationality of the design, discover problems in installation processes and assembly in time, and quickly and conveniently correct issues in the design.

Product Function Testing

Samples or models made with RP technology can not only be used for design evaluation of product appearance and structural verification, but can also directly undergo testing of product-related performance and functional parameters, such as flow and stress analysis, fluid and aerodynamic analysis, etc. Therefore, RP technology can quickly produce models for product function testing to determine whether they meet the needs of designers and users, thereby further optimizing product design and developing new products.

Rapid Tooling

Mold design and manufacturing is a complex multi-step process. For a long time, it relied on experience. Designing and manufacturing a suitable mold often requires repeated cycles of design, manufacturing, trial molding, and mold modification, sometimes inevitably leading to mold scrapping. Rapid tooling is a new mold manufacturing technology developed on the basis of RP technology. With the help of this technology, mold production costs and manufacturing cycles can be reduced. Models made with RP technology can be used to create mold cores or mold sleeves. Combined with casting, sintering, and other technologies, molds for the required products can be quickly manufactured. The manufacturing cycle is 1/10 to 1/5 of traditional manufacturing methods, and the cost is only 1/5 to 1/3 of traditional methods.