Creating a miniature plastic aeroplane using a household computer and a 3-D printer is no longer just a dream for aircraft enthusiasts. But what about printing out a real plane?
Chinese scientists and aviation engineers says it's possible.
And they're now starting to print out aircraft components from a 3-D printer without the help of traditional manufacturing processes such as casting, forging and assembling.
These can even include key structures such as landing gear, which has to be able to withstand extreme forces.
3-D printing, also known as laser rapid forming, is an emerging manufacturing technology in which blueprints made on computers can be turned into actual products by printers that add layer after layer of material until the finished shape is achieved.
It's not clear how many materials Chinese scientists can use when printing out aircraft parts, but Stratasys, the world's leading manufacturer of 3-D printers, says its machines can combine more than 100 different materials to form 3-D products, including wood, plastics and metals. Reports on the mainland have said 3-D printing technology has been used by China's aviation industry.
It features in the country's first home-grown commercial airliner, the C919, its first aircraft-based jet fighter, the J-15, its multi-role fighter and bomber, the J-16, its first home-made stealth jet fighter, the J-20, and its mid-sized, fifth-generation jet fighter, the J-31.
Former US defence secretary Dr Robert Gates once said that China would not have a "fifth-generation aircraft by 2020".
Beijing responded by showing him the J-20's successful maiden test flight when he visited the country in January 2011.
In the 1980s and 1990s, China took at least 10 years to develop the J-10, its third-generation all-weather jet fighter, currently a mainstay of the People's Liberation Army Air Force. But the development of the J-15 took just three years and it made its maiden test flight on August 31, 2009.
The PLA Navy announced the formal establishment of an aviation force for future carrier-based operations earlier this month, and the next day China Central Television reported that the first of its J-15s had been put on the production line early this year.
Sun Cong , deputy chief engineer at the Aviation Industry Corporation of China (AVIC), the nation's leading military aircraft manufacturer, said the unprecedented adoption of 3-D printing technology for his J-15 project had made a significant contribution to its success.
"I would like to say that … the world was not astonished by our technology, but by China's efficiency in aviation industry development," Sun, the J-15's chief engineer, told Science and Technology Daily in March.
"The J-15 project started without a solid technical basis … but now it has caught up to the technical level of the US' most advanced third-generation, carried-based aircraft, the F/A-18 Hornet." Sun told the Beijing Times the primary force-bearing structure of the J-15, including its landing gear, was formed by high-tensile titanium alloy powder sprayed from a 3-D printer.
Aviation engineer Huang Weidong , a professor at the College of Material Science and Engineering at Northwestern Polytechnic University in Xian , Shaanxi , produced a three-metre-long titanium structure that is a key component of the C919's wing, on New Year's Eve last year.
He told the Chinese industry website lasterfair.com  he had been using 3-D printing technology since 1995, with the output of his research commonly used in the aviation, aerospace, machinery, medical and other sectors.
"After near 20 years of research and development, [3-D printing technology in China] can produce … products that can replace metal structures made by complicated traditional manufacturing processes," he said.
"We have applied the technology to [the aviation] industry, including sizeable titanium alloy structures and aircraft engine renovation, as well as some other high-end components."
Another aviation materials specialist, Professor Wang Huaming , from the Beijing University of Aeronautics and Astronautics, told a workshop at the Chinese Academy of Sciences late last year that China now needed just 55 days to "print out" four hyperboloid cockpit window frames for the C919.
He said a European aircraft maker had said it would need at least two years to do the same job, with the cost of making a mould put at US$2 million.
"The traditional aircraft manufacturing industry doesn't only need much more time, but also wastes too many expensive materials," Wang said in a video clip of the workshop posted on the internet. "Normally, just 10 per cent of raw materials would be utilised, with the rest all cut and dropped during the processes of casting moulds, forging, cutting and polishing."
For example, US-based Lockheed Martin Aeronautics needed 2,796kg of titanium alloy to produce an F-22 fighter jet, but only 144kg of the material actually made it into the plane, he added.
Wang, who formed a team of researchers to study 3-D printing materials in 2000, said they were now able to mix many different kinds of materials together to imitate some sophisticated, high-end aircraft components.
He said his research team had made many breakthroughs in 3-D printing technology, such as printing out key titanium alloy structures as big as 5 square metres which had been used in many new-generation military aircraft projects.
"For me and many Chinese aircraft engineers, we all dream of 'printing out' all kinds of plane components we need one day," he said.
He believed 3-D printing technology could soon help the country overcome a long-standing technical bottleneck that was hampering its production of sophisticated aviation engines.
Sidney Wong, an engineer and associate director of the Hong Kong Polytechnic University's Institute for Enterprise, said 3-D printing technology could help China speed up the research and development of new generation aircraft.
"As 3-D printing technology can save both time and materials, researchers can easily print out all kinds of high-end and sophisticated components they need to assemble prototypes within a short period," he said. "Without the hindrance of making moulds and other complicated traditional manufacturing procedures, the cost of making prototypes is much lower, and scientists and engineers can repeatedly produce more and more duplicates for tests and modification."
Wang said China's large-scale 3-D printing technology had surpassed that of the United States because many US counterparts were just using the new technology to produce "knick-knacks".
But Luo Jun , chief executive of the Beijing-based Asian Manufacturing Association, said there was "still a certain gap" that Chinese scientists needed to bridge to catch up with their US and European counterparts in the development of 3-D printing.
"It's a fact that all sizeable and intricate metal structures and components made by 3-D printers in China can replace those parts made by traditional manufacturing processes … but such an achievement still fails to solve the core problem of China's aircraft manufacturing," Luo said, referring to the engine problem.
"3-D printing is an emerging technology, but it still needs to be underpinned by traditional industry … there is still a certain gap between China and the US' technology, including its stability, accuracy, materials and related skills."
In August, US President Barack Obama announced the formation of the National Additive Manufacturing Innovation Institute, with an initial investment of US$30 million, the National Journal reported.
It said the US Army had deployed a helicopter-borne 3-D printing laboratory to Afghanistan, and the military already used 3-D printers to manufacture some non-critical aircraft components.
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