Metal 3D Printing Technology: Key to Intelligent Mold Manufacturing

Editor’s Note

Metal 3D printing is the most representative additive manufacturing technology, and its engineering applications help improve the digital and intelligent design and manufacturing levels of complex precision molds. Due to its common industrial characteristics with the mold manufacturing industry, metal 3D printing technology is becoming a new key technology for efficient and high-precision manufacturing of molds. China’s mold industry is seizing the opportunity to promote the innovative development of 3D printing technology in mold making, enhancing the high-level foundation of the mold industry and modernizing the industrial chain, thus transforming the mold industry from large to strong.

1 Introduction

Additive manufacturing (Additive Manufacturing) is a technology that creates solid parts or products by gradually adding materials. Since additive manufacturing technology can quickly produce workpieces and products of any shape without the need for complex molds and multiple processing techniques, it has achieved rapid development in technology research and industrial applications over the past 30 years. Therefore, it has become one of the three basic technologies for material processing, alongside subtractive manufacturing (mainly machining) and formative manufacturing (mainly mold forming). Additive manufacturing, especially the fully digital 3D printing technology, achieves the goal of “three reductions and one increase” (reducing the number of parts, reducing weight, reducing assembly, and producing highly complex parts) through the design of 3D printed components or complete machines and 3D printed manufacturing.

2 3D printing technology has become the main body of additive manufacturing technology

The widespread application of 3D printing technology not only promotes the application of high-energy density processing technologies such as lasers and electron beams in the manufacturing industry but also has the potential to revolutionize the entire design and manufacturing process of the manufacturing industry. As a rising intelligent manufacturing method, it has received high attention and importance from governments and the engineering technology community worldwide. The digital additive manufacturing technologies that have been developed so far are listed in Table 1.

Table 1 Digital Additive Manufacturing Technologies

Metal 3D Printing Technology: Key to Intelligent Mold Manufacturing

The National Standardization Technical Committee for Additive Manufacturing has combined the existing foundation and characteristics of China’s additive manufacturing technology and standardization work to launch the framework for the additive manufacturing standard system (see Figure 1).[1].

Figure 1 Additive Manufacturing Standard System (Key Technologies and Industry Applications)

As shown in Figure 1, most of the key processes and equipment technologies in additive manufacturing belong to “3D printing technology.” Since they best reflect the technical characteristics of additive manufacturing and the direction of digitalization and intelligence, they have become the main body of additive manufacturing technology. Among them, metal powder bed fusion technology (see Figure 2) and sintering technology represent the forefront of additive manufacturing technology and industrial application level, making them the crown jewels of 3D printing technology.

Figure 2 Metal Laser 3D Printing Manufacturing (Powder Bed Laser Fusion) Schematic

3 Metal 3D printing has established a relatively complete industrial chain

In the 1980s, 3D printing technology was already developed for commercial use, but the initial printing materials were mainly non-metallic materials. Therefore, 3D printing was mainly used for the manufacturing of non-metallic products such as models, crafts, packaging, and medical devices. Entering the 21st century, metal 3D printing technology has rapidly developed, and the preparation technology of metal powders has also matured, allowing the engineering application scope of 3D printing technology to quickly expand from the initial product development prototype manufacturing, jewelry, dental, and packaging manufacturing fields to all areas of precision forming in product manufacturing, becoming the most competitive manufacturing means for special complex parts and highly personalized products. Companies such as Germany’s EOS and America’s 3D Systems once led the development of 3D printing technology with their 3D printing equipment and corresponding slicing software. At the same time, various consumables used in 3D printing, such as non-metallic materials (nylon, ceramics, etc.) and metal materials (stainless steel, tool steel, heat-resistant alloys, aluminum alloys, copper, etc.), have gradually achieved industrialization and commercialization in terms of research, production, and supply. However, the current variety of metal 3D printing consumables is relatively small, prices are high, and the investment in printing equipment is large, coupled with relatively low printing efficiency. As a result, the current engineering application scope is mainly concentrated in the aerospace, artificial joints (including teeth), and other non-marketized products and special mold manufacturing industries.

In metal 3D printing technology, powder bed fusion technology is currently the most commonly used technology in engineering. One of its key technologies, the printing heat source, generally uses laser beams or high-energy electron beams. Laser heat sources can perform laser cladding and selective laser sintering processing, while high-energy electron beams are mainly used for electron beam melting processing. Due to the different propagation methods of lasers and electron beams in the processing space, their working environments differ—laser 3D printing is performed in air or inert gases (such as nitrogen) (see Figure 3), while electron beam 3D printing requires a relatively high vacuum to reduce energy loss caused by collisions between the electron beam and gas molecules before reaching the working surface (see Figure 4). Currently, both types of metal 3D printing equipment have established research and development design and production supply systems.

Figure 3 Laser Metal 3D Printing Schematic

Figure 4 Electron Beam Metal 3D Printing Schematic

Another key technology in metal 3D printing is the preparation of printing materials. Powder bed fusion technology requires the continuous and uniform spreading of metal powders, therefore, the powder shape should be as spherical as possible to facilitate smooth powder flow, and the uniformity of the powder’s particle size and composition must meet the design requirements of the materials. Currently, the preparation technology for low-carbon content stainless steel, high-temperature alloys, titanium alloys, aluminum, and copper metal powders is relatively mature, and the variety is quite rich. However, for high-carbon content tool steel powders, controlling carbon loss during preparation and use (melting) affects the performance of printed products, resulting in fewer varieties and higher prices for tool steel powders.

Since the 12th Five-Year Plan, China’s scientific and technological community has focused on becoming a strong manufacturing nation through intelligent manufacturing, closely tracking the development trends of international 3D printing technology, especially metal 3D printing technology. Based on the introduction and digestion of technology, continuous innovation of the 3D printing technology system has been carried out, expanding the application fields of 3D printing technology, and gradually establishing a 3D printing industrial chain that includes printing raw materials, printing equipment, and printing service platforms. This has gradually achieved the localization of key technology equipment for metal 3D printing and established a relatively stable supply chain (see Table 2).^[²^].

Table 2 Overview of China’s 3D Printing Technology Supply Chain

4 Metal 3D printing technology has been successfully applied in the mold manufacturing field

Molds are essential basic process equipment in the product manufacturing industry, characterized by complex structures, high manufacturing precision, harsh working conditions, and high reliability and lifespan requirements. Currently, most mold materials are made of metal (over 90%), with 90% being steel materials. To efficiently and accurately complete the manufacturing of complex molds, the mold industry has always been exploring various new processing methods and manufacturing technologies. However, even so, the processing technology level of the 20th century still cannot meet the rapid improvement in mold design precision required by advancements in digital design technology. This has led to many advanced design schemes being unachievable or forced to reduce manufacturing precision, such as the cooling systems of precision complex plastic injection molds, where traditional machining techniques struggle to create the conformal cooling channels designed by CAE, resulting in significant local deformation of the molded parts.

Since the beginning of the 21st century, with breakthroughs in key technologies such as laser power, spot focusing, and mold steel powders, metal 3D printing technology has been successfully applied in the production of conformal cooling channels for injection molds, as shown in Figure 5. For large and complex injection parts, the cross-sectional shape and path of the cooling channels are designed based on analysis using simulation software. Conformal cooling channel inserts are made using 3D printing technology and embedded into the mold base processed by cutting. The cooling channels of the two parts are connected externally with hoses, allowing this additive-subtractive hybrid manufacturing technology to avoid the weaknesses of high prices and low printing efficiency of mold steel powders while addressing the unreasonable local cooling issues of traditional cooling channels. For small precision structural injection molds, conformal cooling channels are optimized and designed using CAD and CAE software, and the entire mold is directly printed using metal 3D printing technology. The resulting injection mold with conformal cooling channels is shown in Figure 6. Additionally, some complex molds or mold components, such as rubber tire mold patterns and shoe sole pattern molds (see Figure 7), have also established metal 3D printing production lines. Currently, metal 3D printing technology can control the comprehensive costs of such molds or mold parts within an acceptable market range.

a）Traditional Cooling Channels (Before Improvement)

b）Conformal Cooling Channels (After Improvement)Figure 5 Optimization Design of Cooling Channels in Injection Molds

Figure 6 3D Printed Injection Mold with Conformal Cooling Channels

a）Tire Mold Pattern Block

b）Shoe Sole Pattern Mold Figure 7 Metal 3D Printed Molds

5 Metal 3D Printing Technology: An Important Link in Intelligent Mold Design and Manufacturing

5.1 The design and manufacturing of molds share common industrial characteristics with metal 3D printing technology

Mold forming is a precise and efficient processing method for parts (products), and the design and manufacturing of molds typically feature “multi-variety, small batch” (in most cases, single-piece production). Metal 3D printing technology has an undisputed advantage in meeting the highly personalized needs of high-end customers, aligning perfectly with the industrial characteristics of the mold manufacturing industry, and providing new technology for efficient and high-precision mold processing.

5.2 Metal 3D printing technology accelerates innovation and development driven by market demand, promoting breakthroughs in mold cooling system design and manufacturing

Encouraged and motivated by feedback from engineering applications, metal 3D printing technology is actively advancing to meet the high-quality development requirements of user industries for metal 3D printing technology.

(1) Developing more metal 3D printing processes aimed at improving efficiency: Powder bed fusion metal 3D printing technology has advantages in controlling the precision of printed products. The geometric structure of the processed parts can be extremely complex. Selective Laser Melting (SLM) and Direct Metal Laser Sintering (DMLS) are typical representatives of powder bed fusion metal 3D printing processes, but this process strongly depends on the size of the heat source spot and the quality of the powder particle preparation, leading to lower printing efficiency and higher costs. The continuously developed Direct Energy Deposition technology (see Figure 8) balances dimensional precision and printing efficiency (forming efficiency can reach 2 to 10 times that of powder bed technology), and the preparation cost of printing materials (wires, powders) is relatively low, suitable for mold manufacturing with larger cross-sections and slightly lower structural complexity, as well as for repairing some locally failed molds.

a）Wire Material b）Single Nozzle Powder Feeding

c）Dual Nozzle Powder Feeding d）Conical Nozzle Powder FeedingFigure 8 Direct Energy Deposition Metal 3D Printing Process

The binder jetting metal 3D printing technology provides new opportunities for the production of molds that require uniform venting or vacuum forming.

(2) Optimizing the preparation process of mold steel powders to reduce 3D printing production costs: The performance and quality of powders are key factors in controlling the shape and properties of metal 3D printing. With a deeper understanding of the physical mechanisms affecting the quality of printed products in the metal 3D printing process, new results have been achieved in the study of different printing processes concerning powder composition, particle shape, particle size, particle distribution (see Figure 9), and ratios (see Table 3), leading to the development of different powder preparation technologies.^[³^], and based on the research results, various powder manufacturing technologies have been developed.

Figure 9 Distribution of Powder Particles in Metal Powder Bed 3D Printing

Table 3 Technical Parameters of Powders Used in Mold 3D Printing Manufacturing

To prepare metal powders that meet the above reference standards, companies in Europe and America have developed gas atomization, ion atomization, and electrolysis powder-making methods. For powder bed fusion processes, high-quality and expensive metal powders are typically used. These powders are usually prepared using gas atomization or plasma atomization processes, which melt the metal through induction heating or plasma torches, as shown in Figure 10. The molten metal is injected into the atomization chamber, where it is broken into small droplets by high-speed air flow and gradually solidifies during the descent process. Gas atomization has high powder-making efficiency, with over 80% of metal 3D printing powders (including mold steel powders) produced by this method. The powders produced by plasma atomization have a higher sphericity than those produced by gas atomization; both types of powders exhibit a Gaussian distribution in particle size.

a）Gas Atomization Powder Production

b）Plasma Atomization Powder ProductionFigure 10 Atomization Powder Production Technology Schematic

European and American countries began producing 3D printing mold steel powders (S316 stainless steel, P20 plastic mold steel, etc.) around 2010, with particle sizes of 20-40μm and prices ranging from 200 to 250 USD/kg. They have also manufactured conformal cooling channels and other injection mold inserts using steel powders. ^[⁴^]In China, around 2015, mold steel powders suitable for laser cladding were successfully developed, with prices gradually stabilizing below 300 RMB/kg (some stainless steel powders used for 3D printing shoe molds even below 150 RMB/kg), which has also driven down the prices of imported mold steel powders, which have now decreased to below 100 USD/kg.

(3) Increased design freedom for mold cooling systems, improving mold forming production efficiency: The engineering application of metal 3D printing technology has greatly enhanced the design freedom of mold cooling systems, eliminating concerns about how the manufacturability of the cooling system affects result precision.

Taking the design of conformal cooling channels for TPE cable sleeve mold inserts (see Table 4) as an example for analysis. In Figure 11, design 6 is based on the traditional “drilling” process, while the other 5 designs are based on metal 3D printing technology. Using 316L stainless steel, these 6 mold inserts were printed and heat-treated to a hardness of 54HRC. Actual tests showed that designs 5 (fountain type), 1 (thin U type), and 4 (coarse spiral type) had the best cooling performance. The physical objects of these three mold inserts are shown in Figure 11. Using the conformal cooling inserts in injection molds can reduce the cooling time from about 30s in design 6 to approximately 6s, shortening the injection cycle from 60.5s to 14.7s, thus reducing the production cycle by 75%.

Table 4 Design of Conformal Cooling Channels for TPE Cable Sleeve Mold Inserts

a）Coarse Spiral Type b）Fountain Type c）Thin U TypeFigure 11 Mold Inserts with the Best Cooling Performance Featuring Conformal Cooling Channels

In addition to directly printing molds with conformal cooling channels using metal 3D printing technology, a hybrid manufacturing approach combining mechanical processing has also been developed for the production of molds with conformal cooling channels (see Figure 12). This additive-subtractive hybrid manufacturing technology is also referred to as “3D printing grafting.” This method can meet the design cooling conditions while improving the efficiency of mold manufacturing.

Figure 12 Schematic of Hybrid Manufacturing of Mold Conformal Cooling Channels

5.3 Metal 3D printing technology supports the intelligent design and manufacturing of molds

1) The innovative development of metal 3D printing technology promotes the enhancement of digital collaborative design freedom for parts (products) from product development, forming process design, and mold design, allowing for the comparison of various forming schemes in a virtual space to complete the design of high-precision and high-efficiency mold forming schemes, revolutionizing the entire mold design and manufacturing process.

2) The engineering application of metal 3D printing technology helps improve the digital, networked, and intelligent design and manufacturing levels of complex precision molds or mold parts, becoming a new key technology for efficient and high-precision mold manufacturing.^[⁵^].

3) Since the 13th Five-Year Plan, China has maintained its position as the world’s largest consumer, manufacturer, and exporter of molds for several consecutive years. However, in terms of original innovation capability and industrial chain competitiveness, China’s mold industry is still “large but not strong.” From the perspective of enhancing the high-level foundation of the mold industry and modernizing the industrial chain, China’s mold sector must seize the revolutionary opportunity presented by metal 3D printing technology for the intelligent design and manufacturing of molds, striving to transform the mold industry from large to strong.

6 Conclusion

Based on the above analysis, the following suggestions are proposed: ① Actively carry out basic theoretical research on metal 3D printing mold-making technology, especially the research on the organizational evolution mechanism of commonly used mold steel powder 3D printing processes, striving to synchronize or lead with international standards. ② Innovate in metal 3D printing processes and equipment technology research and development, establishing a standard system for metal 3D printing mold-making technology, including processes, equipment, printing materials, post-processing, and evaluation methods. ③ Optimize the mold design and manufacturing process based on the characteristics of the molds or mold parts being processed and the 3D printing technology used, accelerating the construction of application platforms and supply chains for 3D printing mold-making technology. It is expected that by 2035, metal 3D printing for mold-making will account for 15% to 20% of the national mold output (450 to 600 billion RMB).

Honorary President of the China Mold Industry Association: Wu Bingshu

References:

[1] Lu Bingheng, Hou Ying, Zhang Jianxun. Construction and Development Plan of the National Standard System for Additive Manufacturing [J]. Metal Processing (Cold Processing), 2022 (4): 1-4.

[2] Wu Bingshu. Research and Development of China’s Strategic Emerging Industries: Molds [M]. Beijing: Mechanical Industry Press, 2018.

[3] KHAIRALLAH S A, MARTIN A A, LEE J, et al. Controlling interdependent meso-nanosecond dynamics and defect generation in metal 3D printing [J]. Science, 2020, 368 (6491): 660-665.

[4] Wu Bingshu. Direct Metal Laser Sintering Technology Will Fully Optimize Mold Manufacturing Processes [J]. China Mold Information, 2012 (11): 13-14.

[5] China Mechanical Engineering Society. China Mechanical Engineering Technology Roadmap [M]. Beijing: Mechanical Industry Press, 2021.

This article was published in Metal Processing (Cold Processing), 2022, Issue 6, pages 1-8, by Wu Bingshu of the China Mold Industry Association, originally titled: “Metal 3D Printing Technology is Becoming a Key Technology for Intelligent Mold Manufacturing.”

☞ Source: Metal Processing

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