Advances and application prospects of rapid prototyping

Table of Contents

Rapid prototyping (RPM) is a technology based on the principle of layer-by-layer stacking. By layering the 3D model, discrete points, lines, and surfaces are gradually stacked to form the required parts. Compared with traditional manufacturing methods, RPM does not require special tools, the manufacturing process is simpler, and the speed is much faster, which is also called “free-form manufacturing.”

Since this technology is several times or even dozens of times faster than traditional methods, it has become the core technology of rapid prototyping. RPM has changed the traditional way of making solid models and greatly accelerated the development and updating of products.

RPM technology involves many technical fields, such as CAD, data processing, numerical control, test sensing, laser and other mechanical and electronic technologies, material technology, and computer software technology. It is the organic integration and cross-application of various high-tech technologies.

RPM technology has a good application prospect and practical value. Government departments, enterprises, colleges and universities, and research institutions in the world’s major advanced industrial countries have invested heavily in the development and research of RPM technology. Some colleges and universities and scientific research institutions are also conducting research and development of RPM technology, and have achieved gratifying results, and have been successfully applied to mold manufacturing.

Main methods and principles of RPM technology

The specific implementation process of RPM technology is diverse, Generally, according to the different forming materials used and the treatment methods of the materials, they can be summarized into the following methods, which are introduced as follows:

1. Selective liquid curing method

The selective liquid curing method is to focus the laser on the surface of liquid photocurable material (such as photocurable resin) to cure it according to a pre-set rule, first from point to line and then to surface, to complete the construction of a layer. Then move the lifting platform a distance from the layer’s thickness, and re-cover a layer of liquid material to build another layer. In this way, layers are superimposed to finally become a three-dimensional entity. Typical processes of this method include stereolithography (SL–Stereolithography, as shown in Figure 1), solid grinding Laser lithography laser lithographycuring (SGC-Solid Ground Curing), and laser lithography (LS–Light Sculpting).

Fig 1. SL (stereolithography) process schematic diagram

2. Layer addition method

The layer addition method uses a laser or a tool to cut the foil material to obtain a layer of the model. Specifically, the process border and the edge contour of the prototype are cut out first, and then the material that does not belong to the prototype is cut into a grid. By continuously moving the lifting platform and giving the foil material, new layers can be cut and bonded to the previous layers. In this way, a three-dimensional solid model can be formed by stacking layers.

Finally, the small pieces of material grid that do not belong to the prototype are removed to obtain the required three-dimensional solid model. There are many kinds of foil materials used in the layer addition method, such as coated paper (paper coated with an adhesive coating) coated with ceramic, metal foil, or other material-based foils. The typical process for slice addition is layered solid manufacturing (LOM–Laminated Object Manufacturing), as shown in Figure 2.

Fig2. LOM (Layered Entity Manufacturing) process schematic diagram

3. Selective powder sintering/bonding method

The basic principle of the selective powder sintering/bonding method is to use special powder to lay it into a layer with a certain density and flatness, and then selectively melt or bond the powder directly or indirectly to form an integral layer. Spread powder on the formed layer and compact it, then sinter or bond it into another layer, and sinter or bond it with the original layer into one. In this way, layer by layer, a three-dimensional entity is finally formed. Powder materials include non-metallic powders such as wax, polycarbonate, and washed sand, as well as metal powders such as iron, cobalt, chromium, and their alloys. Typical processes of the selective powder sintering/bonding method include selective laser sintering (SLS—Selective Laser Sintering, as shown in Figure 3) and three-dimensional printing (3DP—3D Printing, as shown in Figure 4).

Fig3. SLS (Selective Laser Sintering) process schematic diagram

Fig 4. 3DP (three-dimensional printing) process principle diagram

4. Melt extrusion molding method

The melt extrusion molding method is to melt the hot melt material by heating, then extrude and spray it out to accumulate a forming layer, and then form the next layer in the same way and fuse it with the previous layer. In this way, a three-dimensional solid model is finally formed by stacking layers. Hot melt materials include ABS, nylon wax, etc. The typical process of melt extrusion molding is fused deposition modeling (FDM–Fused Deposition Modeling), as shown in Figure 5.

Fig 5. Schematic diagram of the melt extrusion molding (FDM) method

5. Inkjet printing method

Inkjet printing is to melt the solid material， and then use the principle of inkjet printing to spray it out in an orderly manner, stacking one layer after another to form a three-dimensional entity. The typical process for inkjet printing is Ink-Jet Printing, as shown in Figure 6.

Fig 6. Inkjet printing principle

6. Digital light processing

Digital light processing (DLP) is mainly used for 3D printing of photocurable resins. Its working principle is to project the 2D image generated by slicing the 3D model onto the photosensitive resin layer by layer through a digital projector. The resin is quickly cured under light to form a solid structure. During the printing process, the printing platform is immersed in the resin pool. After each layer of curing is completed, the platform is slightly lifted and covered with a new layer of resin again. The curing is repeated until the model is completed, as shown in Figure 7.

Fig 7. Digital light processing schematic

Table 1. Comparison table of five rapid prototyping methods

The development trend of RPM technology

RPM technology is of great significance in the manufacturing industry. This manufacturing model has developed rapidly since its inception. RPM has undergone fundamental changes and improvements in manufacturing goals, manufacturing capabilities, and manufacturing technologies compared to the past. The development prospects of this technology are very promising, and the technology itself will continue to improve.

1. Manufacturing goals develop relatively independently

From the manufacturing goal point of view, RPM technology can be used for rapid concept manufacturing prototypes, functional test prototypes, manufacturing molds, functional parts, etc. Concept design prototypes have fast molding speed, Small equipment, reliable operation, clean, no noise, easy operation, etc., such as 3DSYSTEM’s Actua2100 system, EOS’s DESKTOP200 system, etc. Functional test prototypes have certain requirements for strength, rigidity, temperature resistance, corrosion resistance, and precision, so it is necessary to research and develop special forming materials. Rapid model prototypes have corresponding requirements for materials and also have a significant impact on manufacturing modes, such as 3DSYSTEM’s QuickCast manufacturing mode. Rapid model prototyping technology is mainly used for rapid manufacturing of various molds, such as vacuum injection molds, lost wax casting molds, sand casting molds, lost foam casting molds, etc. Rapid functional parts have always been the hot spot and the most challenging topic in RPM research.

Fig 8. Lost Wax Casting Mold

Fig 9. Sand casting mold

Rapid concept manufacturing and rapid tooling manufacturing both have huge market and technical feasibility and will become the focus of research and commercialization. Due to the large differences in their characteristics, both will tend to develop relatively independently.

Rapid testing has a limited scope of use and unclear characteristics, so it will not form an independent direction and will be attached to rapid concept manufacturing. Rapid functional parts manufacturing will be an important direction for the development of RPM technology, but the technology is difficult and will remain limited to the research field for a long time in the future.

Fig 10. Relationship and difference

2. Large-scale Manufacturing and Micro-Manufacturing

By analyzing the product lines of major companies, it can be found that the size of prototype manufacturing is increasing. Due to the difficulty of manufacturing large molds and the advantages of RPM in mold manufacturing, it can be predicted that a certain proportion of the RPM market will be large prototype manufacturing in the future.

With the rapid development of the automotive industry, the application scope of large-scale rapid prototyping technology is becoming wider and wider, and most of them are generally used for the rapid manufacturing of automotive molds. As the speed of vehicle model replacement is getting faster and faster, higher requirements are also put forward for the manufacturing accuracy and speed of automotive cover molds. Large-scale rapid manufacturing technology is precisely adapted to the requirements of this situation.

In sharp contrast, RPM has also entered the field of micro-manufacturing. For example, an important development direction of SL technology is microlithography, which is used to manufacture micron parts. The diameter of the formed laser spot can reach 5um. During the forming process, the prototype remains stationary, and the laser beam is precisely focused on the formed prototype through a transparent plate. The XY scanning stop accuracy is 0.25μm, and the Z stop accuracy is 1um. Parts with a size of 5μmX5μmX3μm can be manufactured, such as venous valves, integrated circuit parts, etc.

The desktop manufacturing system is a hot spot in product development in the RPM field. The RPM equipment system is widely accepted as a peripheral for 3D graphics output of CAD systems. This requires that the RPM system be operated in an office environment to reduce the impact on the existing CAD room. The current commercialized RPM system is generally large, has high environmental requirements, and requires special personnel for operation and daily maintenance.

The Desktop system is small in size, simple to operate and maintain, has less noise and pollution, has no special requirements for the environment, and has a fast forming speed, but the accuracy requirements are appropriately reduced. Stratasys and SandersPrototype in the United States have launched low-cost desktop systems Genisys3DPriter and ModelMaker. It is reported that it has only been on the market for a few months, and it has shown the huge market potential of desktop manufacturing systems.

Fig 11. RPM technology distribution diagram

3. Strive for excellence in manufacturing technology

The strategy of rapid prototyping (RPM) companies is not only to launch new models but also to continuously improve existing processes, equipment, materials, software, and electromechanical systems. Their goal is to achieve faster production speed, higher precision, and better reliability, or to find a balance between these goals. This trend will continue.

Modern manufacturing technology is developing in a highly integrated direction. It combines CAD (computer-aided design), data processing, numerical control, test sensing, laser, and other mechanical and electronic technologies, as well as material and software technologies to form a new way of manufacturing.
At the same time, modern manufacturing is becoming more and more flexible. The biggest advantage of RPM technology is its high flexibility, and it no longer relies on special tools.

Under computer management and control, RPM can manufacture parts of any complex shape. It integrates programmable, reconfigurable, and continuously variable production equipment with information management into one system, so the production cost is independent of the production batch. When the shape, requirements, or production volume of a part changes, there is no need to redesign or manufacture tools. Just modify the CAD model and adjust the parameters to produce a new part.

Fig 12. The integration of various technologies

4. Installation of peripherals and intelligent operation

RPM technology is developing in the direction of “directly driving through CAD models and quickly manufacturing complex three-dimensional models”. Now, some RPM equipment in the United States has begun to become simpler and easier to use like computer peripherals. In the future, the installation and operation of such equipment will be very convenient, and ordinary users will also be able to easily get started, without the need for specialized technicians. At the same time, the operation will become more intelligent.

In the current RPM manufacturing process, there are many selection strategies, such as the design of support structures, the selection of scanning methods, the arrangement of multiple parts, the segmentation of large parts, and the setting of various process parameters. These operations usually require professionals to perform. However, with the rapid development of artificial intelligence technology and people’s in-depth understanding of RPM technology, the intelligence of RPM equipment will soon be realized, and ordinary people will be able to use this technology easily.

5. RPM industry standardization and integration with product manufacturing system

The various RPM process methods have been developed independently, so there is a lack of standards. On the one hand, this is an inevitable phenomenon of the development of new technologies. It is precisely because there is no standard that the development of RPM has been promoted.

However, as RPM rapidly develops into an industry, reasonable industry standards are necessary, otherwise it will be detrimental to the promotion and application of RPM. The de facto RPM industry standard is in the field of product data exchange, that is, STL files, but many people also use CLI, HPGL, DXF, and other files to replace STL files, so it is very realistic to take standardization work seriously; in addition, the standardization of materials and equipment models will also develop further.

According to the 11th issue of Rapid Prototyping Report magazine in 1996, Whirlpool introduced the use of FDM equipment to successfully conduct rapid feedback design of the lighting unit of the refrigerator refrigeration room. Due to the use of FDM technology, it took about one year from the redesign of the lighting unit to the start of mold making, and the design was revised five times more than manual mold making. As a result of the redesign, Whirlpool estimated that it saved at least $650,000.

A golf club design company in the United States used to work with designers and craftsmen to make models with brass, which was time-consuming and laborious and only produced three plans. When designing a new club, they used a LOM-1015 RPM machine and made 90 models in one year. In this way, a better plan can be determined in a short time at a low cost. As an industry, the relationship between RPM and the entire product manufacturing system, as well as related standards, are also worth further discussion.

For example: how to describe RPM data in the STEP model, how to develop and apply RPM in a rapid product development system, etc. Describing RPM data in the STEP model and developing and applying RPM technology in a rapid product development system involve the following two core aspects: data representation and integration, and the role of RPM technology in rapid development.

5.1 How to describe RPM data in the STEP model

(1) Geometric data description

3D model data: The core data used by RPM is usually a 3D model that describes the shape and structure of the product. The STEP format allows complete geometric information storage and supports 3D printing of RPM.
Feature data: The STEP model can save the features in the design (such as holes, slots, etc.), which helps the processing process of RPM technology.

(2) Material information

The properties of the manufacturing material can be described in the STEP file. The material information (such as density, melting point, hardness, etc.) directly affects the process method selected in the RPM process (such as laser sintering or melt extrusion).

(3) Process parameters

Manufacturing process data: STEP scalability allows the storage of process data related to the RPM process, such as layer thickness, printing speed, laser power, etc., which is very important in executing the manufacturing process.

(4) Assembly information

The multi-part assembly of RPM can be managed through STEP model data. STEP supports complete assembly hierarchical structure description, which facilitates simulation and adjustment in the production process of complex parts.

(5) Manufacturability Check

During the design phase, STEP can include analysis data related to manufacturability to ensure that the designed parts are suitable for manufacturing through the RPM process.

5.2 How to develop and apply RPM in a rapid product development system

(1) Shorten the design verification cycle

RPM technology allows companies to generate physical prototypes in a few days or even hours. Product design teams can quickly test, verify, and modify designs, greatly shortening the traditional verification cycle.

(2) Concurrent Engineering

By integrating with STEP-data models and CAD systems, RPM can perform multiple design iterations in parallel in the early stages of development, avoiding the traditional linear development process. This allows different stages of product development to proceed simultaneously, further accelerating product launch.

(3) Prototype testing and functional verification

In the rapid product development system, RPM can produce functional prototypes, not just appearance models. This means that the product can pass real functional tests before entering mass production, reducing the risk of design defects.

(4) Agile manufacturing and small-batch production

RPM technology also supports small batch production for market testing and personalized customization, which is particularly suitable for the initial promotion of innovative products. In an agile manufacturing environment, RPM enables companies to quickly adjust product designs based on market feedback.

(5) Collaborative design and cross-team cooperation

In the modern development system, the combination of the STEP model and RPM facilitates global collaborative design. Designers, engineers, and manufacturing teams can share data and update design progress in real time, thereby optimizing the production process and reducing the error rate.

(6) Cost-effectiveness

By reducing the intermediate links such as design modification, tooling manufacturing, and mold production, RPM makes the development process more economical, especially in the early development stage.

Conclusion

With the continuous advancement of rapid prototyping technology, it has become an indispensable part of modern manufacturing. From design to production, this technology has brought huge efficiency improvements to all walks of life.

Different RPM technical methods provide diverse options for different needs and application areas, promoting the development of mold manufacturing and other related industries. Looking to the future, rapid prototyping technology will continue to develop in the direction of higher precision, larger scale,e, and wider application, helping the manufacturing industry to usher in a more intelligent and flexible era.