Laser sintering

Prime and J.C. Seferis, Journal of Polymer Science, Part C Polymer Letters, 1986,24,12, 641. 

Pritchard, Anti-Corrosion Polymers PEEK, PEKK and orther Polyaryls, Rapra Review Report No. 80, Rapra Technology, Shawbury, Shrewsbury, UK, 1995. 

Mensitieri, A. Apicella, M. Del Nobile and L. Nicolais, Journal of Reinforced Plastics and Composites, 1993, 12, 11, 1138. 

Kemmish and R. Leibfried, inventors Victrex, assignee WOOl/62841 A2, 2001. 

---

Methods are used to produce the more costly rapid prototypes include those that produce models within a few hours. They include photopolymerization, laser tooling, and their modifications. The laser sintering process uses powdered TP rather than chemically reactive liquid photopolymer used in stereolithography. Models are usually made from certain types of plastics. Also used in the different processes are metals (steel, hard alloys, copper-based alloys, and powdered metals). With powder metal molds, they can be used as inserts in a mold ready to produce prototype products. These systems enable having precise control over the process and constructing products with complex geometries. 

Finally, surface analysis has been used in the investigation of metal silicides used to form rectifying Schottky barrier contacts to semiconductors. These silicides are formed by thermal or laser sintering of the metal after deposition onto the substrate. Excess unreacted metal is removed by chemical etching. XPS has been used to show that the metal has been oxidized if the excess metal cannot be removed (52). 

Selective laser sintering Fused deposition modeling... 

Fischer, P., Blatter, A., Romano, V. and Weber, H.P. (2004) Highly precise pulsed selective laser sintering of metal powders. Laser Physics Letters, 620-628. 

Figure 7.32 Selective laser sintering process. A laser is bounced off a mirror, which is controlled by a scanner to selectively trace the outline of a cross section of a part on a powder bed. When one layer has been traced, the part is lowered and fresh powder is rolled into place. After finishing, the part is removed from the loose, unfused powder.

Indirect tooling methods are many. Examples include cast aluminum, investment metal cast, cast plastics, cast kirksite, sprayed steel, spin-castings, plaster casting, electroforming, room temperature vulcanizing (RTV) silicone elastomer (Chapter 2 Silicone Elastomer), elastomer/ rubber, reaction injection, stereolithography,338 344 (Table 17.4), direct metal laser sintering, and laminate construction. 

SFF encompasses many different approaches to additive fabrication, including Stereolithography (SLA), Selective Laser Sintering (SLS), Electron Beam Melting (EBM), Laminated Object Manufacturing (LOM), Fused Deposition Modeling (FDM), and 3D Printing. 

Despite the fact that Selective Laser Sintering (SLS) is not an Inkjet 3D printing process, due to its industrial importance, a brief description of this method is included here. 

STRUCTURE EVOLUTION DURING LASER SINTERING OF FINE... 

The structure evolution in the course of laser sintering of fine SiOr powder is studied experimentally. A specific correlation between different types of pores and the rate of the pore reduction during sintering is revealed. 

The aim of this paper is to study the evolution of stmcture in the course of laser sintering of fine Si02 powder. It should be noted that there are some technical difficulties in the study of sintering kinetics in case of traditional powder technology when the long time furnace sintering is used. It is especially difficult to carry out the study using such technique in the case of nanopowders. 

In the paper, a specific approach to investigation of sintering kinetics was proposed. The experiments on laser sintering were carried out with the use of a number of testing samples. The duration of laser processing, t, was varied for different samples. This allowed to elucidate important features of structural evolution at different stages of the sintering process. 

Laser sintering of ceramic fine powders deposited onto ceramic substrates is show to be an appropriate technique to fabricate micro- and nanoporous ceramic filters. The requirements to the filter materials are discussed. 

The membrane nanoporous layers are proposed to be formed by laser sintering of nanopowders deposited onto the surface of microporous structure by sol-gel sedimentation/centrifugation technique. In principle, the method of laser sintering is well known [1], However, there is no wide application in practice of nanopowder processing up to date. A number of constraints defines what quality of sintered stmcture may or may not be achieved by this technique. On the whole, the comprehension of nanopowder sintering mechanisms by laser radiation is rather low. 

It is supposed that due to the short time of laser sintering undesirable recrystallisation processes are prevented or limited. Besides, optimum conditions for formation of nanoporous layer during laser sintering are provided due to specific ability of nanoparticles to consolidation. As a result, the filter materials possess increased filtration fineness and throughput in comparison with the analogical... 

Experiments were started with the metal powder in order to reveal principal possibilities of laser sintering of powder layers deposited onto a substrate [2], In these experiments, the layer of Ni powder (with particle size about 0.5 pm) was deposited onto the surface of Ni substrate manufactured by traditional powder metallurgy (with particle size about 5 pm) and subjected to sintering by CW-Nd YAG laser (X = 1.06 pm). Layer thickness was about 2 pm. The joining of powder layer with the substrate was provided during sintering. The graded porous structure was formed on the surface as it is shown in Fig. 1 (the size of pores is about 2 pm for the sintered layer and 6 pm for the substrate). 

---