Solid freeform fabrication of shelled objects
A method of layerwise solid freeform fabrication is disclosed. The method comprises, for each of at least a few of the layers, dispensing and hardening at least a first modeling material and a second modeling material to form a core region and one or more envelope regions at least partially surrounding the core region. In some embodiments, the ratio between the elastic moduli of adjacent regions, when hardened, is from about 1 to about 20.
1. A method of layerwise solid freeform fabrication, comprising, for each of at least a few of the layers:
dispensing and hardening at least a first modeling material and a second modeling material to form a core region and one or more envelope regions at least partially surrounding said core region;
thereby fabricating an object being constructed from a plurality of layers and a layered core constituting core regions and a layered shell constituting envelope regions, wherein a width of said envelope region is calculated separately for each layer, said width being defined within a plane engaged by said layer.
2. The method according to claim 1 , wherein said one or more envelope regions comprise a plurality of envelope regions.
3. The method according to claim 1 , wherein for at least one pair of regions in said layer, a heat deflection temperature (HDT) characterizing an inner region of said pair is above 50° C., and an HDT characterizing an outer region of said pair is below 50° C.
4. The method according to claim 1 , wherein for at least one pair of regions in said layer, an outer region of said pair has a lower elastic modulus than an inner region of said pair.
5. The method according to claim 1 , wherein for at least one pair of regions in said layer, an outer region of said pair has a higher elastic modulus than an inner region of said pair.
6. The method according to claim 1 , wherein for any pair of regions in said layer, an outer region of said pair has a lower elastic modulus than an inner region of said pair.
7. The method according to claim 1 , wherein for at least one pair of regions in said layer, a characteristic heat deflection temperature (HDT) is higher for an outer region of said pair than for an inner region of said pair.
8. The method of claim 1 , wherein each of said core and envelope regions is characterized by an elongation-at-break value (ε R ), when hardened, and wherein said characteristic ε R is higher for any of said envelope regions than for said core region.
9. The method according to claim 1 , wherein said first modeling material and said second modeling material are characterized by a glass transition temperature (T g ) which is below 10° C.
10. The method according to claim 9 , wherein a characteristic tensile tear resistance (TR) of said core region is lower than a characteristic TR of at least one of said envelope regions.
11. The method of claim 1 , wherein each of said regions is characterized by an Izod impact resistance (IR) value and a heat distortion temperature (HDT), when hardened, wherein for at least one pair of regions in said layer, an inner region of said pair is characterized a lower IR value and higher HDT value relative to an outer region of said pair.
12. The method according to claim 11 , wherein said outer region is an outermost region of said pair.
13. The method according to claim 1 , wherein a width of said envelope region is non-uniform across said layer.
14. The method according to claim 1 , further comprising dispensing at least one of said first modeling material and said second modeling material to form at least one shell part parallel to said layers, wherein a material property characterizing said at least one shell part is different from a material property characterizing said core.
15. The method according to claim 14 , wherein said at least one shell part has a thickness which is less than a lateral width of said envelope.
16. The method according to claim 1 , wherein, any two adjacent regions of said regions are bound to each other upon hardening.
17. The method according to claim 1 , wherein a ratio between the elastic moduli of adjacent regions, when hardened, is from about 1 to about 20.