Sinterable semi-crystalline powder and near-fully dense article formed therewith
First Claim
1. A laser-sinterable powder product, adapted to be sintered in a selective laser sintering machine to form a sintered part, said powder consisting essentially of an unblended .polymer which provides signs of crystalline order under X-ray examination, and shows a crystalline melting point Tm as well as a glass transition temperature Tg, said polymer having a two-tier particle size distribution said powder having the following properties:
- (a) freely-flowable semi-crystalline powder having a crystallinity in the range from 10-90% measured by [DSC] differential scanning calorimetry;
(b) a major portion by weight of the powder having a sphericity in the range from greater than 0.5 to 0.9, and a two-tier distribution in which substantially no primary particles has an average diameter greater than 180μ
m, provided further that the number average ratio of particles smaller than 53μ
m is greater than 80%, the remaining larger particles being in the size range from 53μ
m to 180μ
m;
a layer of said powder no more than 250μ
m deep absorbing essentially all infra-red energy beamed therethrough at a wavelength of 10.6μ
m, and a layer of said powder no more than 180μ
m thick absorbing more than 50% of said energy;
(c) a number average molecular weight in the range from about 30,000 to 500,000, and a molecular weight distribution Mw /Mn in the range from 1 to 5; and
, (d) a window of sinterability in the temperature range from near said powder'"'"'s softening temperature Ts to said powder'"'"'s caking temperature Tc ;
whereby when said powder is sintered layer-wise in said window of sinterability to form a slice, it will not curl.
6 Assignments
0 Petitions
Accused Products
Abstract
A laser-sinterable powder product has been prepared having unique properties which allow the powder to be sintered in a selective laser sintering (SLS) machine to form a sintered part which is near-fully dense. For most purposes, the sintered part is indistinguishable from another part having the same dimensions made by isotropically molding the powder. In addition to being freely flowable at a temperature near its softening temperature, the powder has a two-tier distribution in which substantially no primary particles has an average diameter greater than 180μm, provided further that the number average ratio of particles smaller than 53μm is greater than 80%, the remaining larger particles being in the size range from 53μm to 180μm. When the powder is a semicrystalline synthetic resin having a number average molecular weight in the range from about 30,000 to 500,000; a molecular weight distribution Mw /Mn in the range from 1 to 5; and, provides a window of sinterability in the temperature range from near the powder'"'"'s softening temperature Ts to its caking temperature Tc, it is sintered layer-upon layer to form a near-fully dense part of arbitrary shape.
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Citations
16 Claims
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1. A laser-sinterable powder product, adapted to be sintered in a selective laser sintering machine to form a sintered part, said powder consisting essentially of an unblended .polymer which provides signs of crystalline order under X-ray examination, and shows a crystalline melting point Tm as well as a glass transition temperature Tg, said polymer having a two-tier particle size distribution said powder having the following properties:
- (a) freely-flowable semi-crystalline powder having a crystallinity in the range from 10-90% measured by [DSC] differential scanning calorimetry;
(b) a major portion by weight of the powder having a sphericity in the range from greater than 0.5 to 0.9, and a two-tier distribution in which substantially no primary particles has an average diameter greater than 180μ
m, provided further that the number average ratio of particles smaller than 53μ
m is greater than 80%, the remaining larger particles being in the size range from 53μ
m to 180μ
m;
a layer of said powder no more than 250μ
m deep absorbing essentially all infra-red energy beamed therethrough at a wavelength of 10.6μ
m, and a layer of said powder no more than 180μ
m thick absorbing more than 50% of said energy;
(c) a number average molecular weight in the range from about 30,000 to 500,000, and a molecular weight distribution Mw /Mn in the range from 1 to 5; and
, (d) a window of sinterability in the temperature range from near said powder'"'"'s softening temperature Ts to said powder'"'"'s caking temperature Tc ;
whereby when said powder is sintered layer-wise in said window of sinterability to form a slice, it will not curl. - View Dependent Claims (2, 3, 4, 15)
- (a) freely-flowable semi-crystalline powder having a crystallinity in the range from 10-90% measured by [DSC] differential scanning calorimetry;
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5. A bed of a laser-sinterable powder in a selective laser sintering zone, said bed consisting essentially of particles of an unblended synthetic resinous material which provides signs Of crystalline order under X-ray examination, and shows a crystalline melting point Tm as well as a glass transition temperature Tg, said material in particulate form having a two-tier particle size distribution from which powder, a laser-sintered part is formed and removably embedded in said bed, said powder being a freely-flowable semi-crystalline powder having primary particles in the size range smaller than 180μ
- m and a sphericity in the range from greater than 0.5 to 0.9, provided further that the number average ratio of particles smaller than 53μ
m is greater than 80%, the remaining larger particles being in the size range from 53μ
m to 180μ
m;
having a crystallinity measured by differential scanning calorimetry in the range from 10% to 90%, and when sufficiently heated, having a softening temperature Ts, and a caking temperature Tc from about 2°
-25°
C. above Ts , and, when sintered, has a melt viscosity in the range from 100-104 poise (10-1000 Pa-sec) when said powder'"'"'s temperature as it is being sintered, exceeds Tc in less time than is required to melt contiguous large particles >
53μ
m;
said bed having a porosity in the range from 0.4 to 0.55, and providing, during operation, a temperature profile defined by sequential positive and negative temperature gradients in a vertical plane through upper and lower portions of said bed, respectively, when said bed'"'"'s uppermost layer, less than 25082 m thick, is in the range from near said Ts to said Tc ;
said bed maintaining said positive temperature gradient from said upper surface to a maximum temperature in a horizontal zone in which said sintered part lies, said upper temperature gradient being in the range 0.2°
C./cm (0.5°
C./in) to 2°
C./cm (5°
C./in); and
, said bed maintaining a negative temperature gradient from said maximum temperature to the bottom of said bed, said negative lower temperature gradient being in the range from 0.2°
C./cm (0.5°
C./in) to 2°
C./cm (5°
C./in).
- m and a sphericity in the range from greater than 0.5 to 0.9, provided further that the number average ratio of particles smaller than 53μ
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6. A bed of a laser-sinterable powder in a selective laser sintering zone, said bed consisting essentially of finely divided particles of an unblended synthetic resinous material which provides signs of crystalline order under X-ray examination, and Shows a crystalline melting point Tm as well as a glass transition temperature Tg, said material in finely divided particulate form having a two-tier particle size distribution from which particles a laser-sintered part is formed, said powder being a freely-flowable semi-crystalline powder having a crystallinity measured by differential scanning calorimetry in the range from 10% to 90%, said powder having primary particles in the size range smaller than 180μ
- m, having a sphericity in the range from greater than 0.5 to 0.9, provided further that the number average ratio of particles smaller than 53μ
m is greater than 80%, the remaining larger particles being in the size range from 53μ
m to 180μ
m;
said bed having a porosity in the range from 0.4 to 0.55 allowing a pressure drop of less than 6.89 kPa when cooling gas is flowed in a direction from top to bottom through said bed at a rate of 5 L/min and said bed is 30 cm deep. - View Dependent Claims (7, 8, 16)
- m, having a sphericity in the range from greater than 0.5 to 0.9, provided further that the number average ratio of particles smaller than 53μ
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9. A laser-sintered article or `part` of arbitrary shape sintered in a selective laser sintering machine containing a laser-sinterable powder of a semi-crystalline synthetic resin, said part consisting essentially of a sintered mass of said powder, said part having a density in the range from 80% to 90% of the density of an isotropically molded part of said powder and fracture surfaces, when broken by bending, which are visually identical to fracture surfaces of said molded part but including a profusion of cavities having an average diameter in the range from 1μ
- m-30μ
m randomly scattered throughout said part which has substantially the same flexural modulus and maximum stress at yield (psi) when fractured in bending, but substantially less ultimate elongation (%), and notched Izod impact (ftlb/in), than a compression molded article molded from a portion of said powder. - View Dependent Claims (10, 11, 12, 13, 14)
- m-30μ
Specification