USE OF A THERMOSET BINDER FOR 3D PRINTING OF CEMENTED CARBIDE OR CERMET BODIES

Abstract

The use of a water-soluble thermoset binder for binder jetting of a cemented carbide or cermet green body is provided. The water-soluble thermoset binder includes a compound A, being at least one organic, non-aromatic substance, including at least two hydroxyl groups and a compound B, being at least one organic, non-aromatic substance, including at least two carboxyl groups, wherein the compound A and compound B are monomers or oligomers. The binder will lead to an increased strength of the printed green body.

Claims

1. A use of a water-soluble thermoset binder for binder jetting of a cemented carbide or cermet green body wherein the water-soluble thermoset binder comprises a compound A being at least one organic, non-aromatic substance, comprising at least two hydroxyl groups and a compound B being at least one organic, non-aromatic substance, comprising at least two carboxyl groups, wherein the compound A and compound B are monomers or oligomers with a molecular weight less than 2000 g/mol.

2. The use of the water-soluble thermoset binder according to claim h wherein compound A and B do not contain any epoxy group.

3. The use of the water-soluble thermoset binder according to claim 1, wherein compound A and B do not contain nitrogen, phosphorous, silicon, potassium, sodium or fluorine.

4. The use of the water-soluble thermoset binder according to claim 1, wherein the amounts of compound A and B are such that the molar ratio of the hydroxyl groups in compound A to the carboxyl groups in compound B is between 0.1 and 10.

5. The use of the water-soluble thermoset binder according to claim 1, wherein compound A is selected from propylene glycol, glycerol, maltodextrin, erythritol, xylitol, sorbitol and mannitol.

6. The use of the water-soluble thermoset binder according to claim 1, wherein compound B is selected from citric acid, tartaric acid, succinic acid, fumaric acid, maleic acid, polyacrylic acid oligomer and carballylic acid.

7. The use of the water-soluble thermoset binder according to claim 1, wherein the total amount of compound A and B is between 30 and 80 wt %:

8. The use of the water-soluble thermoset binder according to any of the preceding claims claim 1, wherein compound A is selected form glycerol or maltodextrin and compound B is citric acid.

9. The use of the water-soluble thermoset binder according to claim 1, wherein the binder includes glycerol in an amount of between 35 and 50 wt %, and citric acid in an amount of between 15 and 25 wt %.

10. A method of making a cemented carbide or cermet body comprising the steps of: providing a ready-to-print powder being a cemented carbide powder or cermet powder; providing a water soluble thermoset binder; printing said powder by binder jetting technique into a green body; curing said body by heating at a temperature between 100° C. and 250° C.; and sintering said green body, wherein the water soluble thermoset binder comprises a compound A being at least one organic, non-aromatic substance, comprising at least two hydroxyl groups and a compound B being at least one organic, non-aromatic, substance, comprising at least two carboxyl groups, wherein the compound A and compound B are monomers or oligomers.

11. The method according to claim 10, wherein the ready-to-print powder is a cemented carbide powder with a metallic binder in an amount of between 10 and 13 wt % and wherein the carbide particles have a D50 of between 17 and 21 μm and a porosity between 0 and 5 vol %.

12. The method according to claim 10, wherein compound A is selected from propylene glycol, glycerol, maltodextrin, erythritol, xylitol, sorbitol and mannitol.

13. The method according to claim 10, wherein compound B is citric acid, tartaric acid, succinic acid, fumaric acid, maleic acid, polyacrylic acid oligomer and carballylic acid.

14. The method according to claim 10, wherein the amounts of compound A and B are such that the molar ratio of the hydroxyl groups in compound A to the carboxyl groups in compound B is between 0.1 and 10.

15. The method according to claim 10, wherein compound A is selected form glycerol or maltodextrin and compound B is citric acid.

Description

EXAMPLE 1

[0070] Green bodies in shape of rectangular blocks of 60×15×5 mm were printed from a pre-sintered cemented carbide powder with mostly spherical-shaped granules that have a D10 of 11.1 μm, D50 of 20.3 μm and D90 of 33.6 μm. The composition of the powder was 12 wt % Co and balance WC. The average porosity of the granules is 0 vol %, or very close to zero.

[0071] The binder was prepared by mixing water, ethanol, glycerol and citric acid. The components were thoroughly stirred until all components had been dissolved. The composition is shown in Table 1. The molar ratio in Table 1 is thee molar ratio of the hydroxyl groups in compound A to the carboxyl groups in compound B.

TABLE-US-00001 TABLE 1 Glycerol Citric Acid Molar Water Ethanol (Compound A) (Compound B) ratio Invention 1 21.6 wt % 17.3 wt % 42.7 wt % 18.4 wt % 4.8/1

[0072] Printing was performed in a binder jetting printing machine with a layer thickness during printing of 50 μm. The printing of powder was done in a “ExOne Innovent+”. Saturation during printing was 110% and the scale factor of the parts were set to 1.

[0073] The saturation of printing binder is defined as the percent of the void volume that is filled with printing binder at a specified powder packing density (here the powder packing density is set to 60%). A higher saturation is needed when printing with a powder comprising a larger fraction of porous particles as compared to a lower fraction of porous particles.

[0074] During the printing the sequence for each layer was as follows: a 50 μm layer of the powder was spread over the bed, printing binder was spread in a pattern as defined in a CAD model, followed by drying of the printing binder to remove all or some of the solvent of the printing binder. This was repeated until the full height of the green body was printed. Thereafter curing was done overnight at 200° C. in vacuum. Depowdering was done manually by brush and pressurized air.

EXAMPLE 2

[0075] Green bodies were printed using the same process and cemented carbide powder as described in example 1 with difference that the binder was prepared by mixing Maltodextrin (dextrose equivalent around 18) and Citric acid with a commercial Aqueous Binder and that the saturation during printing was 100%. The components were thoroughly stirred until all Maltodextrin and Citric Acid had been dissolved. The composition is shown in Table 2. The molar ratio in Table 2 is thee molar ratio of the hydroxyl groups in compound A to the carboxyl groups in compound B.

TABLE-US-00002 TABLE 2 Competitor Aqueous Maltodextrin Citric Acid Molar Binder (Compound A) (Compound B) ratio Invention 3 96 wt % 2 wt % 2 wt % 1.23/1

[0076] For comparison, a green body using only the commercial Aqueous binder was printed with the same powder and the same process as in Example 2.

EXAMPLE 3

[0077] After depowdering the strength of the green bodies were tested by transversal flexural test with a speed of 10 mm/min and a preload of 0.05N. The results are shown in table 3.

TABLE-US-00003 TABLE 3 Flexural Strength [MPa] Invention 1 4.61 Invention 2 2.55 Comparative 1 1.65

[0078] In Table 3 it can clearly be seen that the green bodies with the binder according to the invention, Invention 1 and 2, shows a significant improvement in green strength compared to the commercial Aqueous binder.