Rapid Development of 3D Printing Technology
Metal Printing Advances
Metal printing has become a hot topic in 3D printing research and applications. Current technologies include powder and filament materials. Powder-based methods can either spread powder in layers for surface melting or spray powder for laser melting during deposition. Filaments are melted using laser, electron beam, or ion beam. Each method has its advantages and limitations.
Selective laser melting of powder produces precise, complex parts but is limited to small items due to lower manufacturing efficiency. Laser cladding results in higher strength due to better powder melting, while filament melting is suitable for larger parts.
Material Versatility
Metal additive manufacturing can utilize various metals, including tool steel, high-speed steel, stainless steel, superalloys, titanium, aluminum, magnesium, copper, and tungsten alloys. This versatility allows a single machine to produce multiple materials.
In experiments, additive manufacturing produced materials with strengths, toughness, and ductility in some cases surpassing forged parts and greatly exceeding cast parts. However, the mechanical properties can vary based on the layering direction.
Challenges in Metal Additive Manufacturing
Efficiency, cost, and precision are ongoing challenges. Key factors include the energy source (laser, electron beam, ion beam) and core components like powder feeders. Energy sources with longer lifespans, higher power, and better focus can enhance precision. However, achieving high precision in large parts remains difficult and costly. Quality control is crucial, addressing issues like accuracy, surface roughness, and defects (e.g., trapped gases, impurities, oxidation).
Advances in Non-Metal Materials
Significant progress has also been made in non-metal materials. Traditional photopolymerization has seen efficiency improvements of up to 100 times. Continuous pull technology has increased efficiency by two orders of magnitude. The range of materials has expanded to include non-metals, metals, ceramics, and composites, enabling the creation of functionally graded structures and micro-nano 3D printed circuits and chips.
Composite Materials and Applications
Composite materials, such as those used in tank armor, can mimic natural structures like shells for high strength. Combining metals and ceramics yields both high wear resistance and good toughness.
In aerospace and rail transport, fiber-reinforced composites, like carbon fiber, are increasingly used for their lightweight and high strength properties. Unlike metals, which can quickly fail due to crack propagation, composites do not have this issue. For instance, a metal-composite hybrid printer was launched into space, operated for several days, and successfully returned, a world first.
Innovations in Fiber-Reinforced Composites
Fiber-reinforced composites can form parts through injection molding, especially in the automotive industry, offering high strength and lightweight properties. Micro-nano printing achieves precision up to 100 nanometers, allowing for the direct printing of chips.
Expansion to 4D and 5D Printing
4D printing involves smart materials that change shape under specific conditions. For example, a structure printed at one temperature may transform at another, useful in medical implants like stents.
5D printing, or bioprinting, aims to recreate human organs such as artificial lungs, hearts, skin, and nerves. These printed materials can grow into functional organs within the body, potentially revolutionizing tissue repair and organ transplantation. Challenges include developing capillary networks and ensuring integration with the body's circulatory and nervous systems.
