(6)Others such as quick casting (3D System, US), baking ceramic-coated SL prototype to get ceramic casting shell; and unbaked ceramic mould tooling (Tsinghua Univ, China), reversing a ceramic mould from the middle silicone mould reversed from RPM prototype。

4。4Machines for finish usable part

The concept prototypes and moulds can not exert full power of RPM, actually, it can be used in producing single or small batch of finish usable parts。 These parts are of high precision, can be fitted with certain re- quirements of strength, stiffness, and other functions。 And the forming efficiency should be acceptably high。

YAN Yongnian (颜永年) et al：Rapid Prototyping and Manufacturing Technology … 9

3D System Corporation in US, cooperated with DSM Somos Corporation in US, developed a new type of photopolymer resin with which the formed  fan could be used in the wind tunnel test。 Stratasys Corpo- ration developed an FDM Titan equipment, which could use polycarbonate (PC) and polyphenylsulfone (PPSF) to make parts with high impact strength, good thermal and chemical stability, its made belt pulley could replace the damaged aluminum belt pulley in production line with normal operation。

As for the most important finish metal part, there are kinds of novel techniques as follows:

(1)Methods based on laser beam cladding/sintering such as laser engineered netshaping (LENS) (Optomec Design, US), direct metal deposition (POM Inc, US), laser additive manufacturing (Aero Met, US), direct metal selective laser sintering (3D System, US, F&S/MCP, Germany; and EOS, Germany), and selec- tive laser melting (Fraunhofer Institute, Germany; MCP, Germany; TRUMPF, Germany; Leuven Uni- versity, Belgium; and Liverpool University, UK)。 Tak- ing LENS as example, it uses Nd-YAG laser to sinter metal powder with the protection of inert gas, thus it can make aluminum-alloy, titanium-alloy, tungsten- alloy semi-refined rough parts while the precision sur- passes traditional closed-die forging, and the internal quality is over the integral forging。

(2)Methods based on electron beam melting such as electron beam melting (Arcam, Sweden) and EBSM (Tsinghua University, China)。 EBSM uses high-energy electron beam to melt metal powders, and by control- ling of electromagnetic field, the beam can be regu- lated to determined site。 With this equipment, parts with good mechanical strength have been made of stainless steel powder, and titanium powder。

(3)Methods based on laser-induced chemical depo- sition such as rapid prototyping of laser-induced chemical vapor deposition (Connecticut University, US) and rapid prototyping of laser-induced chemical liquid deposition。 The former deposits  metal  material from the photochemical, thermochemical, photodecomposi- tion, and thermaldecomposition reactions of gas in- duced by laser while the latter is from liquid。

4。5Nano-/mirco- RPM

Traditional nano-/micro- processing techniques are restrained in forming abnormal microstructures such as

with high depth-width ratio。 While RPM may surpass this shackle。 For example, based on the two-photon absorption and light-cured manufacturing, researchers in Osaka University attained a 120-nm microstructure。 And a nano bull of 10 μm long and 7 μm high was made。

Some researchers in University of Illinois jetted the polymer mixtures into solution through a micro pen to create 3-D network structures with 0。5-5。0 μm diame- ter of filaments。 And the Mirkin team at Northwestern University first proposed the dip-pen nanolithography (DPN) to achieve direct high-precision patterns。 It uses the atomic force microscope (AFM) probe to coat self assembly monolayer (SAM) material onto the sample surface。 The line width is as small as 10-15 nm,  and the space distance can be 5 nm。

The RP center in Nanjing University of Aeronautics and Astronautics, China also developed an electro- deposition technique simliar to electroforming。 And some parts were made of nano materials such as Ni, Cu, Co, Ni-Fe, Ni-P,  and  Ni-SiC。  The  grain  size  is  30- 50 nm。