Method for the manufacture of a shaped body as well as a green compact
A method for manufacturing a shaped body, comprising creating a mixture of a metal powder and binding agent, compacting the mixture to form a green compact, heating the green compact to a debinding start temperature T 1 , debinding the green compact by controlled heating of the green compact from start temperature T 1 to end temperature T 2 at a heat-up rate R 1 , presintering the debindered green compact to the presinter end temperature T VS at a heat-up rate R HVS , cooling the green compact from the presinter end temperature T VS at a cool-down rate R KVS , whereby at least the heat-up rate R HVS , the presinter end temperature T VS , and the cool-down rate R KVS are tuned relative to each other in such a way that the presintered green compact forming a blank has a surface porosity of 16% to 22% after presintering, and machining and sintering of the blank to form the shaped body.
1. A method for the manufacture of a shaped body, a dental prosthesis, or part thereof, the method comprising:
preparing a mixture of a metal powder and a binding agent;
compacting the mixture to form a green compact;
heating the green compact from room temperature to a debinding start temperature T 1 ;
debinding the green compact, wherein the green compact at first is heated to the debinding start temperature T 1 , with 350° C.≦T 1 ≦550° C., and subsequently is heated in a temperature range between T 1 and the debinding temperature T 2 , with 550° C.≦T 2 ≦650° C., and wherein T 2 >T 1 , at a heat-up rate R 1 , with 1 K/min≦R 1 ≦5 K/min, to T 2 , so that the green compact suffers no damage;
presintering of the debindered green compact to a presinter end temperature T VS at a heat-up rate R HVS ;
cooling the green compact from the presinter end temperature T VS at a cooling rate R KVS , whereby at least the heat-up rate R HVS , the presinter end temperature T VS , and the cooling rate R KVS are tuned relative to each other in such a way that the presintered green compact, forming a blank, possesses a surface porosity between 16% and 22% after presintering,
material-removing machining of the blank; and
sintering to final density of the machined blank to form the shaped body.
2. The method of claim 1 , characterized in that after being heated to the presinter end temperature T VS , the green compact is held at the presinter end temperature T VS for the duration of a holding time t VS before it is cooled at the cooling rate R KVS .
3. The method of claim 2 , wherein the green compact is cooled at the cooling rate R KVS to a temperature T 3 where 450° C.≦T 3 ≦650° C.
4. The method of claim 1 , wherein the green compact is held at the debinding end temperature T 2 for a time period t 2 with 1 min≦t 2 ≦20 min.
5. The method of claim 1 , characterized in that the compacted green compact used is a green compact with a surface porosity between 16% and 27%.
6. The method of claim 5 , wherein the surface porosity of the compacted green compact is between 18% and 22%.
7. The method of claim 1 , characterized in that a nickel-chromium alloy, or a cobalt-chromium alloy is used as the metal powder, wherein, for a cobalt-chromium alloy, the following composition is used:
Cobalt: 50% to 70% by weight
Chromium: 20% to 35% by weight
Molybdenum: 0% to 10% by weight
Tungsten: 0% to 20% by weight
Other elements: less than 10% by weight,
wherein the sum total adds up to 100% by weight,
wherein, for a nickel-chromium alloy, the following composition is used:
Nickel: 50% to 70% by weight
Chromium: 20% to 35% by weight
Molybdenum: 0% to 10% by weight
Tungsten: 0% to 20% by weight
Other elements: less than 10% by weight
with a sum total of 100% by weight.
8. The method of claim 1 , characterized in that the green compact is held for the duration of a holding time t VS at the presinter end temperature T VS , such that when a higher T VS is selected, a shorter holding time t VS is set.
9. The method of claim 8 , wherein 650° C.≦T VS ≦1100° C.
10. The method of claim 1 , characterized in that for a presinter end temperature T VS of 650° C.≦T VS <750° C., the holding time t VS is 10 min≦t VS ≦200 min.
11. The method of claim 10 , wherein 30 min≦t vs ≦100 min.
12. The method of claim 10 , wherein 50 min≦t vs ≦80 min.
13. The method of claim 10 , wherein 1 K/min≦R HVS ≦200 K/min and 1 K/min≦R KVS ≦200 K/min.
14. The method of claim 13 , wherein 1 K/min≦R HVS ≦50 K/min.
15. The method of claim 13 , wherein 1 K/min≦R HVS ≦20 K/min.
16. The method of claim 13 , wherein 1 K/min≦R KVS ≦50 K/min.
17. The method of claim 13 , wherein 1 K/min≦R KVS ≦20 K/min.
18. The method of claim 10 , wherein 1 K/min≦R KVS ≦200 K/min.
19. The method of claim 1 , characterized in that for a presinter end temperature T VS of 750° C.≦T VS <850° C., the holding time t VS is 5 min≦t VS ≦60 min, and the heat-up rate R HVS and the cool-down rate R KVS is 5 K/min≦R HVS ≦200 K/min and 5 K/min≦R KVS ≦200 K/min.
20. The method of claim 19 , wherein 10 min≦t vs ≦30 min.
21. The method of claim 19 wherein 5 K/min≦R HVS ≦20 K/min.
22. The method of claim 19 , wherein 5 K/min≦R KVS ≦20 K/min.
23. The method of claim 1 , characterized in that, for a presinter end temperature T VS with 850° C.≦T VS <950° C., the holding time t VS is set to 5 min≦t VS ≦30 min and 15 K/min≦R KVS ≦200 K/min.
24. The method of claim 23 , wherein 10 min≦t vs ≦20 min.
25. The method of claim 23 , wherein 15 K/min≦R HVS ≦200 K/min and 15 K/min≦R KVS ≦200 K/min.
26. The method of claim 25 , wherein 15 K/min≦R HVS ≦50 K/min.
27. The method of claim 25 , wherein 15 K/min≦R KVS ≦50 K/min.
28. The method of claim 1 , characterized in that for a presinter end temperature T VS with 950° C.≦T VS ≦1100° C. the holding time t VS is set to 5 min≦t VS ≦20 min.
29. The method of claim 28 , wherein 30 K/min≦R HVS ≦200 K/min and 30 K/min≦R KVS ≦200 K/min.
30. The method of claim 29 , wherein 30 K/min≦R HVS ≦100 K/min.
31. The method of claim 29 , wherein 30 K/min≦R KVS ≦100 K/min.
32. The method of claim 1 , characterized in that the green compact is kept at a presinter end temperature T VS (in K) for a time period t VS whereby
t/ 2< t VS <2 t
with:
t
=
t
0
·
ln
(
c
0
c
)
·
exp
(
T
0
T
VS
)
with
c=Desired surface porosity fraction of the green compact after presintering with 16%<c<22%,
c 0 =surface porosity fraction of the green compact after debinding with c 0 −c<5%,
t 0 =matter constant with t 0 =0.0125 min
T 0 =matter constant with T 0 =11000 K
T VS =presinter end temperature for a holding time t vs with 650° C.≦T VS ≦1100° C.
33. The method of claim 32 , characterized in that the heating time with an approximately constant heat-up rate R HVS and the cooling time with an approximately constant cool-down rate R KVS are set within the range between 650° C. and the presinter end temperature T VS , specified in degree Celsius, in a way so that they satisfy the condition:
T
VS
-
650
°
C
.
R
HVS
+
T
VS
-
650
°
C
.
R
KVS
<
2
t
whereby
t
=
t
0
·
ln
(
c
0
c
)
·
exp
(
T
0
T
VS
)
and T VS and c 0 −c are tuned relative to each other so that negative heat-up and cool-down times are ruled out.
34. The method of claim 32 , wherein c 0 −c<2%.
35. The method of claim 32 , wherein c 0 >c.
36. The method of claim 32 , wherein 18%<c<20%.
37. The method of claim 1 , characterized in that the metal alloy is atomized into a powder and is mixed with a wax- and/or cellulose-based binding agent to produce a mixture.
38. The method of claim 37 , wherein the green compact is produced by way of isostatic or axial pressing of the mixture consisting of the metal powder and the binding agent, at a pressure p with 100 MPa≦p≦1,000 MPa, or using a metal powder injection moulding process.
39. The method of claim 38 , wherein 200 MPa≦p≦600 MPa.
40. The method of claim 37 , wherein at least the debinding and presintering are carried out in the absence of oxygen.
41. The method of claim 40 , wherein at least the debinding and presintering are carried out in a member selected from the group consisting of an inert gas atmosphere, a reducing atmosphere, a forming gas atmosphere, and a vacuum.