How Rapid Prototyping Technology Promotes the Reform and Develop

Table of Contents

Since the advent of rapid prototyping technology in the 1980s, it has made great progress in prototyping systems and materials and has also promoted the development of rapid tooling technology (RT) and rapid manufacturing technology (RM). The development of rapid prototyping technology has greatly shortened the product design and manufacturing cycle, improved the first-time yield of product design and manufacturing, and reduced product development costs, thus bringing fundamental changes to the manufacturing industry. Rapid prototyping (RP) technology is an advanced manufacturing technology developed based on computer technology, CNC technology, laser technology, and new materials.

The development and current situation of rapid prototyping technology

Rapid Prototyping is a method that uses computer-aided design (CAD) and various manufacturing technologies to create physical models or prototypes quickly. Its core concept is to accelerate the product development process by breaking the design into multiple layers and building the object layer by layer.

The idea of layered manufacturing of three-dimensional objects can be traced back to the 1980s. Specifically, in 1981, Hideo Kodama first proposed the idea of creating three-dimensional objects by stacking materials layer by layer in Japan, which is the concept of three-dimensional printing based on photocuring technology. However, it was Charles W. Hull in the United States who really commercialized and widely used this technology. He invented stereolithography (SLA) technology in 1986 and founded the 3D Systems company in 1988. He launched the first commercial 3D printer. Hull’s work laid the foundation of modern 3D printing and rapid prototyping technology and promoted the rapid development of layered manufacturing technology.

In the early 1990s, with the maturity of rapid prototyping technology in the world, equipment similar to SLA (stereolithography), LOM (layered solid manufacturing), SLS (selective laser sintering), FDM (fused deposition modeling), and other process methods have been developed and gradually commercialized. China began to introduce relevant technologies and equipment, and many universities and research institutions began to pay attention to this emerging technology.

Tsinghua University first introduced the SLA-250 equipment and technology of the American 3D company and carried out research and development. It has now developed the “M-RPMS-II” multifunctional rapid prototyping manufacturing system. The system has two functions: layered solid manufacturing (LOM) and fused deposition modeling (FDM). In addition, Tsinghua University has also developed the fused deposition manufacturing system MEM-250 based on the FDM method and the layered solid manufacturing system SSM-500 based on the LOM method.

Huazhong University of Science and Technology has developed an HRP system based on layered solid manufacturing (LOM) with paper as the molding material; Xi’an Jiaotong University has developed an LPS based on stereolithography (SLA) and CPS systems; Nanjing University of Aeronautics and Astronautics developed a RAP system based on selective laser sintering (SLS). Since the development of SLA molding technology in the mid-1980s to the late 1990s, more than a dozen different rapid prototyping technologies have emerged, in addition to the above-mentioned ones, typical ones include 3DP, SDM, SGC, etc. However, SLA, LOM, SLM, and FDM are still the mainstream of rapid prototyping technology.

In 2014, Organovo in the United States successfully used 3D printing to manufacture biological tissues, reducing the need for animal experiments and promoting medical innovation; In 2016, GE Aviation significantly improved the performance of the LEAP engine nozzle produced by 3D printing, improving the efficiency and reliability of aircraft engines. In China, Peking Union Medical College Hospital began using 3D printing to make personalized surgical models in 2018 to improve surgical precision and safety. In 2019, Geely Auto used rapid prototyping technology to accelerate the development of new models; in 2021, BGI built affordable housing through 3D printing, demonstrating its application potential in the construction field.

Overall, rapid prototyping technology continues to develop globally, its application areas are becoming increasingly broad, and it is expected to continue to play an important role in the future.

The basic prototyping principle of rapid prototyping technology

Rapid prototyping technology (RP technology) is computer-aided design and manufacturing technology, reverse engineering technology, layered manufacturing technology (SFF) material removal forming (MPR) or material addition forming (MAP) technology, and their integration. Generally speaking, rapid prototyping technology is to use 3D CAD data to stack layers of materials into a physical prototype through a rapid prototyping machine.

Fig 1. Rapid prototyping system workflow

There are more than ten kinds of rapid prototyping technology methods, and the most widely used ones are stereolithography (SLA), selective laser sintering (SLS), layered object manufacturing (LOM), fused deposition modeling (FDM), etc. These process methods are based on the principle of material additive molding, combined with the physical and chemical properties of materials and advanced process methods, and are closely related to the development of other disciplines.

1. Stereolithography (SLA)

Stereolithography (SLA) technology magically transforms liquid resin into delicate three-dimensional objects. Through precise laser scanning, the resin solidifies in an instant, forming a layered structure with amazing details and smooth surfaces. Every time the laser scans, it is as if an artist is gently drawing on the canvas, eventually presenting complex designs and elegant shapes. This method is currently the most intensively studied, most mature, and most widely used rapid prototyping method in the world.

At present, the companies researching SLA methods include 3D System, EOS, F&S, CMET, D-MEC, Teijin Seiki, Mitsui Zosen, Xi’an Jiaotong University, etc. The SLA technology of 3D Systems in the United States accounts for the largest proportion of the international market. Since the launch of the SLA-250 model in 1988, its equipment has made great progress in technology by launching three models: SLA-250HR, SLA-3500, and SLA-5000 in 1997.

Among them, SLA-3500 and SLA-5000 use semiconductor-excited solid lasers, and the scanning speed reaches 2.54m/s and 5m/s respectively, and the minimum thickness of the molding layer can reach 0.05mm. In addition, a new technology called the Zephyer recoating system has also been adopted. This technology uses a vacuum adsorption scraper to apply a layer of 0.05-0.1mm to be cured resin on each molding layer, which shortens the molding time by an average of 20%. Compared with the SLA-5000 model, the SLA-7000 model launched by the company in 1999 has roughly the same molding volume, but its scanning speed reaches 9.52m/s, and the average molding speed is increased by 4 times, the minimum molding layer thickness can reach 0.025mm, and the accuracy is increased by 1 times. Domestic and foreign researchers have conducted a lot of research on the molding mechanism of SLA technology, controlling the deformation of parts, and improving the accuracy of parts.

2. Layered Object Manufacturing (LOM)

Layered manufacturing is an advanced additive manufacturing technology that builds complex three-dimensional objects by adding materials layer by layer. This method usually uses a computer-aided design (CAD) model, first breaking it down into multiple thin layers, and then stacking them layer by layer in a set order until the entire object is completed.

The core of this technology lies in its flexibility and efficiency, which can easily realize the design of complex shapes and internal structures, which is difficult to achieve with traditional manufacturing methods. In addition, layered solid manufacturing can effectively reduce material waste because it only adds material where it is needed.

At present, the companies researching LOM technology include Helisys, Huazhong University of Science and Technology, Tsinghua University, Kira, Sparx, and Kinergy. Helisys launched the LOM-1015 (table 380mm×250mm×350mm) model in 1992, and then launched the LOM-2030H model with a table of 815mm×550mm×508mm in 1996, which shortened the molding time by 30%. In addition to the original LPH, LPS, and LPF series of paper varieties, Helisys has also developed plastic and composite materials. The PLT-A4 model of Kira Company in Japan adopts a method of super-hard knife cutting and selective bonding. Tsinghua University launched the SSM series molding machine and molding materials. The HRP series molding machine and molding materials launched by Huazhong University of Science and Technology have a high performance-price ratio.

3. Selective Laser Sintering (SLS)

Selective laser sintering (SLS) is an additive manufacturing technology that uses a laser to sinter powdered materials layer by layer into a three-dimensional object. The process begins by spreading the powder evenly on the build platform, and the laser beam scans and sinters the powder according to the outline of the design drawing to form a solid structure. After each layer is completed, the platform is lowered, and a new layer of powder is then spread on top, and sintering continues until the entire model is completed.

The advantage of SLS technology is that it can use a variety of powder materials, such as nylon, metal, and ceramic, and has strong adaptability. The parts it generates with good mechanical properties and complex geometries, and are particularly suitable for functional prototypes, customized parts, and small-batch production. In addition, since no support structure is required, the design freedom is higher, Enabling designers to explore more innovative solutions.

DTM, EOS, and Beijing Longyuan are researching SLS. DTM launched Sinterstation2000, 2500, and 2500P1us in 1992, 1996, and 1999 respectively. The molding volume of 2500P1us is 10% higher than before. Meanwhile, the auxiliary time is reduced and the molding speed is improved by optimizing the heating system. Beijing Longyuan launched an AFS-300 molding machine and several materials. Huazhong University of Science and Technology developed the HRPS-I molding machine.

In terms of materials, DTM launches several new products every year, among which the parts produced by Dura Form GF material have higher precision and smoother surfaces. The recently developed elastic polymer So-mos 201 material has rubber properties and is heat-resistant and chemical-resistant. It is used to make leak-proof flexible parts such as snake-shaped pipes, gaskets, and door seals on automobiles. The mold made of Rapid Steel 2.0 stainless steel powder can produce 100,000 injection molded parts; Rapid Steel 2.0 has a shrinkage rate of only 0.20%, and its parts can achieve high precision and surface finish, and almost no subsequent polishing process is required.

4. Fused Deposition Modeling (FDM)

Fused Deposition Modeling (FDM) is a common 3D printing technology that is widely used in rapid prototyping and small batch production. Its working principle is to heat the thermoplastic material to a molten state, and then extrude it layer by layer through a nozzle to build a three-dimensional object layer by layer according to the computer-designed model.

In the deposition modeling process, the material is usually supplied in the form of wire, which is heated to a molten state by a nozzle at a high temperature and then deposited on the printing platform in a specific path. After each layer cools, the next layer will adhere closely to it to form a stable structure. This method can achieve complex geometries and fine details with high material utilization.

The main companies researching FDM are Stratasys and MedModeler. Stratasys developed the first FDM-1650 (table of 250mm×250mm×250mm) in 1993 and then launched FDM-2000, FDM-3000, and FDM-8000. Among them, the table of FDM-8000 is 457mm×457mm×610mm. Tsinghua University launched the MEM model. What is particularly eye-catching is the FDM-Quantun model launched by Stratasys in 1998, with a maximum modeling volume of 600mm×500mm×600mm.

Due to the use of the extruder magnetic levitation positioning (Magna Drive) system, two extruders can be independently controlled at the same time, so its modeling speed is five times faster than before. In 1998, Stratasys cooperated with Med Modeler to develop the MedModeler model specifically for some hospitals and medical research institutions, using ABS materials, and in 1999 launched the Genisys improved model – Genisys Xs, which can use polyester thermoplastics, with a modeling volume of 305mm×203mm×203mm. Several typical rapid prototyping processes are shown in Table 1.

Table 1 Comparison of several typical rapid prototyping processes

Characteristics of Rapid Prototyping Technology

1. Rapidity

It usually takes only a few hours to dozens of hours from CAD design to prototype parts manufacturing, which is much faster than traditional prototyping methods, making rapid prototyping technology particularly suitable for the development and management of new products.

2. Integration of design and manufacturing

The backward CAPP has always been a difficult obstacle to achieving the integration of design and manufacturing. However, for rapid prototyping, due to the use of discrete stacking processing technology, CAPP is no longer a difficult point. CAD and CAM can be well combined.

3. Free-form manufacturing

Freedom has two meanings: one is that it can be freely formed according to the shape of the part without the restriction of special tools, which can greatly shorten the trial production time of new products; the other is that it is not restricted by the complexity of the part shape.

4. Highly flexible

Part models with different shapes can be produced simply by changing the CAD model, re-adjusting, and setting parameters.

5. Extensiveness of materials

Rapid prototyping technology can produce resin and plastic prototypes, as well as paper, paraffin, composite materials, as well as prototypes of metal and ceramic materials.

6. High degree of technology integration

RP technology is a comprehensive integration of computers, computer technology, numerical control technology, data, lasers, materials, and machinery. Only today when laser devices and power control technology are highly developed, can rapid prototyping technology have distinct characteristics of the times.

7. Processing characteristics

Rapid prototyping technology breaks through the traditional parts processing mode of “blank → cutting → finished product”, creates a precedent for making parts without tools, and is an unprecedented thin layer superposition processing method. Compared with traditional cutting processing methods, rapid prototyping has the following advantages:

(1) It can quickly manufacture free-form surfaces and parts with more complex shapes, such as grooves, shoulders, and hollow parts in parts. The complexity of the parts and the production batch have little to do with the manufacturing cost. It greatly reduces the development cost and development cycle of new products.

(2) It is a non-contact processing, which does not require the tools and fixtures required for machine tool cutting processing, and is free of tool wear and cutting force;

(3) No vibration, noise, and cutting waste;

(4) Fully automated production can be achieved at night;

(5) High processing efficiency, capable of quickly producing product solid models and molds.

Application of Rapid Prototyping Manufacturing Technology

Over the past decade, RP technology has been applied in a wide range of fields and has shown its superiority. This technology has been applied not only in the manufacturing industries such as machinery, automobiles, aerospace, and electronics, but also in the medical, art, and architecture industries, playing a significant role.

1. Rapid mold manufacturing

At present, rapid tooling (Rapid Tooling RT) using rapid prototyping manufacturing technology is mainly used to manufacture casting molds and plastic molds. The molding method can be divided into two methods: indirect molding and direct molding.

(1) Indirect molding

Indirect molding is a molding method that combines RP technology with traditional molding technology to make part prototypes. Compared with CNC machining, RPM technology can design and manufacture various complex prototypes faster and better. Using rapid prototyping prototypes as samples for traditional mold manufacturing processes can usually reduce mold manufacturing costs and cycles by half. Indirect molding technology has matured and is widely used.

(2) Direct molding

Direct molding is to use RPM technology to directly manufacture molds. It does not require the production of prototypes and is a completely different method from traditional molding processes. Using this method to directly manufacture metal molds is a more promising rapid mold manufacturing method. For example, the American DTM company has successfully developed a technology for manufacturing metal injection molds.

This technology uses the selective laser sintering (SLS) process to sinter resin-coated steel particles to form a semi-finished mold and then undergoes copper infiltration and other post-processing processes to obtain a steel-copper alloy injection mold. Its dimensional accuracy is ±0.12mm/100mm, Ra＜lμm, and its service life can reach 50,000 pieces.

Table 2 Comparison between indirect molding and direct molding

2. Rapidly manufacture metal parts

The combination of RP technology and casting technology is the best way to transform rapid prototyping prototypes into metal parts. The methods include reproducing the mold by RP prototype, directly copying the mold or burning the lost mold casting investment pattern, and designing the model to directly obtain the shell and core (prototype).

Using the RP prototype to obtain the lost mold casting investment pattern is a faster precision casting method. 3D-Systems of the United States has developed Quickcast rapid precision casting technology using this method. It is to coat the surface of the prototype made by the SLA method with refractory materials, directly roast the prototype material to burn and gasify it, and then obtain the casting shell, which is used for casting and molding metal parts. The key to this technology is to use light-cured resin materials with low gas emissions and sufficient combustion. Ford Motor Company of the United States uses this technology to manufacture automobile molds.

3. Accelerate new product development

In the design stage of new product development, although design drawings and computer simulations can be used, prototypes cannot be displayed, and it is often difficult to make correct and quick judgments, which is especially important for products with complex shapes and beautiful appearances. The use of RP technology can make RP three-dimensional solid prototypes from design drawings or CAD models within a few hours or days without the support of other processing methods.

Based on this prototype, designers can evaluate, simulate and test design solutions in terms of appearance, assembly relationships, and production feasibility, and can quickly obtain user feedback on the design solution. In this way, possible problems can be solved in the design stage, significantly reducing the cost and time of new product development.

4. Used in medicine to make organ models

Many countries in the world attach great importance to the application of RP technology in the medical field and have achieved good results. This method combines diagnostic methods such as CT (tomographic imaging) and MRI (nuclear magnetic resonance imaging) based on digital imaging technology with the RP system, that is, to provide the obtained layered cross-sectional images of human body scans with the data after three-dimensional reconstruction by computer to the RP system to obtain the local human body or internal organs (prototype). In this way, the lesion and entity structure of the part can be displayed, which can be used for clinical auxiliary diagnosis and determination of complex surgical plans or teaching.

5. Combined with reverse engineering to form a rapid design and manufacturing closed-loop system

In RP technology, reverse engineering is to find a three-dimensional CAD model based on the existing physical object. For most products, their three-dimensional models can be designed on general CAD software. However, due to certain factors, such as function, process, appearance, etc., the shapes of some parts are very complex, and it is difficult to design solid models on CAD software. Therefore, a small-scale physical model is first manufactured, and then a three-dimensional solid model is obtained by measuring and processing the model data.

Currently, the commonly used measurement methods in reverse engineering include the three-coordinate measuring instrument method, laser triangulation method, nuclear magnetic resonance (MRI) method, tomography (CT) method, grating method, and automatic intermittent scanning method. Through reverse engineering, RP prototypes can also be measured quickly and accurately, and deficiencies in product design can be found. Redesign, after repeated iterations, can make the product more perfect. The introduction of reverse engineering in RP technology has formed a rapid design and manufacturing closed-loop feedback system including design, manufacturing, and testing.

Conclusion

Rapid prototyping technology is a high-tech technology in the process of development and improvement. The technology itself and its application fields still need a lot of development and research. The 21st century will be an era characterized by a knowledge economy and information society. The manufacturing industry faces severe challenges in the ever-changing market in the information society for small batches and multiple varieties of products. With the increasing internationalization of the manufacturing industry, shortening the product development cycle and reducing the investment risk of developing new products have become the key to the survival of enterprises. Therefore, rapid prototyping/molding/manufacturing technology will be further developed.