Plastic and nonmetallic article shaping or treating: processes – Direct application of electrical or wave energy to work – Using laser sintering of particulate material to build...
Reexamination Certificate
1998-10-27
2001-06-12
Ortiz, Angela (Department: 1732)
Plastic and nonmetallic article shaping or treating: processes
Direct application of electrical or wave energy to work
Using laser sintering of particulate material to build...
C264S460000, C264S125000
Reexamination Certificate
active
06245281
ABSTRACT:
BACKGROUND OF THE INVENTION
Field of the Invention
The present invention relates to a process for producing shaped articles by selective laser sintering of pulverulent materials, in which a nylon-12 (polylaurolactam; PA 12), having certain physical characteristics, is used as the pulverulent material.
DESCRIPTION OF THE BACKGROUND
In the development of machinery and apparatus, the production of samples, models and prototypes of the machinery and apparatus plays an important part in their development and has an influence on the development time. The production of such shaped articles is, however, time-consuming in its own right, which is another factor which influences the development time. In recent times, a process has become known which is termed selective laser sintering (or rapid prototyping) and which permits rapid and low-cost manufacture of such shaped articles from a pulverulent material, generally from a polymer powder. The process is the next step after a computer-aided design (CAD), which gives sectioned images of the desired shaped article in digitalized form.
In order to produce a shaped article, the polymer powder is applied in a thin layer onto a table, which is capable of being moved downward, in a sintering chamber which has been heated to a temperature slightly below the melting point of the polymer. The layer thickness is selected so that a melt layer is produced after the subsequent laser sintering. The laser sinters the powder particles together as controlled by the computer. After this step, the table is lowered by an amount corresponding to the layer thickness, usually from 0.2-2 mm. The procedure is repeated by applying a fresh layer of powder. After the preselected number of cycles has been completed, a block has been produced with the intended number of layers and consisting on the outside of powder, which hides an interior consisting of a highly viscous melt in the shape of the desired shaped article. Unmelted regions, in which the powder is still present in solid form, stabilize the shape of the melt.
The block, consisting of powder shell and melt, is then slowly cooled, and the melt solidifies as the temperature drops below the solidification point of the polymer. It is advantageous here if the block is held at the solidification point until the phase change is completed. This is achieved by selecting a low cooling rate in the temperature range of the phase change, so that the liberated heat of solidification holds the shaped article precisely at the solidification point in the interior of the block until the phase change is completed. After cooling, the block is removed from the sintering chamber, and the shaped article is separated from the unsintered polymer powder. The powder can be reused for the process.
The requirements for maximum suitability of a polymer for laser sintering are:
(i) A very high difference between melting point and solidification point. Since in pure polymer powders the solidification point is determined by basic physical data, an increase of the melting point by forming a new crystal modification implies a great advantage. The larger the difference, the smaller is the shrinkage on solidification and the more precise is the achievement of the desired dimensions of the shaped article. A lowering of the solidification point by means of additives or comonomers generally has an adverse effect on the mechanical properties.
(ii) A very high enthalpy of fusion. A very high enthalpy prevents powder particles located in the neighborhood of the particles affected by the laser beam from beginning to melt as a result of unavoidable conduction of heat, which results in sintering outside the desired area.
The pulverulent polymer most frequently employed is nylon-11 (PA 11). Other polymers which can be used include nylons, polyacetals, polypropylene, polyethylene and ionomers. Polycarbonates and polystyrene have also been used. The suitability of the polymer powders is a function of physical characteristics, as well as of their chemical nature. WO 95/11006 describes a polymer powder which is suitable for laser sintering and which, when its melting behavior is determined by differential scanning calorimetry (DSC) at a scanning rate of 10-20° C./min, shows no overlap of the melting peak and the solidification peak and which has a degree of crystallinity of from 10-90%, also determined by DSC, a number-average molecular weight Mn of from 30,000-500,000 and a polydispersity index of Mw/Mn in the range from 1-5. According to WO 96/04335, this powder is used together with a reinforcing powder whose melting point is considerably higher than that of the polymer, for example, glass powder.
Summary Of The Invention
Accordingly, one object of the present invention is to provide a pulverulent polymer material of improved laser sintering properties.
Briefly, this object and other objects of the present invention as hereinafter will become more readily apparent can be attained by a process for producing shaped articles, which comprises:
selectively laser sintering a nylon-12 pulverulent material having the following characteristics:
Melting point
185-189° C.
Enthalpy of fusion
112 ± 17 J/g
Solidification point
138-143° C.
REFERENCES:
patent: 4334056 (1982-06-01), Meyer et al.
patent: 5304329 (1994-04-01), Dickens, Jr. et al.
patent: 5342919 (1994-08-01), Dickens, Jr. et al.
patent: 5527877 (1996-06-01), Dickens, Jr. et al.
patent: 5648450 (1997-07-01), Dickens, Jr. et al.
patent: 29 06 647 (1980-04-01), None
patent: 44 21 454 (1995-12-01), None
patent: WO 96/06881 (1996-03-01), None
E. Schmachtenberg, et al., Kunststoffe, vol. 87, No. 6, pp. 773, 774 and 776, “Laser-Sintering Of Polyamide”, Jun. 1997.
Derwent Abstract, AN 92-121077, JP 04 067912, Mar. 3, 1992.
Gianna Cojazzi, et al., Macromolecular Chemistry and Physics, vol. 192, No. 1, 4 pages, “Phase Transitions in Nylons 8, 10 and 12 Crystallized From Solutions”, Jan. 1991.
Christoph Wolfgang
Scholten Heinz
Huels Aktiengesellschaft
Oblon & Spivak, McClelland, Maier & Neustadt P.C.
Ortiz Angela
LandOfFree
Use of a nylon-12 for selective laser sintering does not yet have a rating. At this time, there are no reviews or comments for this patent.
If you have personal experience with Use of a nylon-12 for selective laser sintering, we encourage you to share that experience with our LandOfFree.com community. Your opinion is very important and Use of a nylon-12 for selective laser sintering will most certainly appreciate the feedback.
Profile ID: LFUS-PAI-O-2515374