Print head for a 3D printer

Abstract

The invention relates to a print head (10) for a 3D printer (1), comprising a feed section (11) having a feeder (12) for a starting material (21) that is variable in the viscosity thereof; a plasticizing zone (14) having a heater (15) and an outlet opening (16) for the liquid phase (22) of the starting material (21); and a conveying device (30) for conveying the starting material (21) from the feed section (11) to the plasticizing zone (14), wherein the conveying device (30) comprises a piston (31) that can be inserted into the feed section (11). The invention is characterized in that the piston (31) has a first piston portion (5) facing the plasticizing zone (14) and having a guide surface (9), through which the piston (31) is guided in a bore (7) of the print head (10).

Claims

1. A print head (10) for a 3D printer (1), the print head (10) comprising an intake zone (11) with a feeder (12) for a raw material (21) of variable viscosity, a plasticization zone (14) with a heater (15) and a discharge opening (16) for a liquid phase (22) of the raw material (21), and a conveyor device (30) for conveying the raw material (21) from the intake zone (11) into the plasticization zone (14), wherein the conveyor device (30) comprises a piston (31) configured to be inserted into the intake zone (11), characterized in that the piston (31) has a first piston section (5) with a piston diameter (d2), the first piston section (5) faces the plasticization zone (14) and has a guide surface (9) defining the piston diameter (d2) and by which the piston (31) interacts with a bore (7) of the print head (10) such that the first piston section (5) is guided in the bore (7), wherein the piston (31) has a second piston section (6), with a piston diameter (d1) of which is smaller than the piston diameter (d2) of the first piston section (5), wherein the piston (31) has a groove (40) which is arranged between the first piston section (5) and a third piston section (41), the third piston section (41) being arranged between the first piston section (5) and the second piston section (6), wherein the groove is an empty space, and wherein the groove is configured to be checked for deposits during maintenance intervals to evaluate settings of the print head (10).

2. The print head (10) as claimed in claim 1, characterized in that an axial extent (L2) of the guide surface (9) is longer than a maximum axial extent (L1) of an opening area (8) of the feeder (12) leading to the bore (7).

3. The print head (10) as claimed in claim 2, characterized in that the axial extent (L2) of the guide surface (9) of the piston (31) is between 1.1 and 1.3 times the maximum axial extent (L1) of the opening area (8).

4. The print head (10) as claimed in claim 2, characterized in that the axial extent (L2) of the guide surface (9) of the piston (31) is 1.2 times the maximum axial extent (L1) of the opening area (8).

5. The print head (10) as claimed in claim 1, characterized in that an axial extent (L2) of the guide surface (9) of the piston (31) is between 1 and 2.5 times the piston diameter (d2) of the first piston section (5).

6. The print head (10) as claimed in claim 5, characterized in that the axial extent (L2) of the guide surface (9) of the piston (31) is 1.25 times the piston diameter (d2) of the first piston section (5).

7. The print head (10) as claimed in claim 1, characterized in that the first piston section (5) and the third piston section (41) have the same piston diameter (d2).

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) Further measures improving the invention are explained in detail below in conjunction with the description of the preferred exemplary embodiments of the invention, with the aid of the drawings.

EXEMPLARY EMBODIMENTS

(2) In the drawings:

(3) FIG. 1 shows a print head according to the invention;

(4) FIG. 2 shows a drawing in section of the print head in printing mode;

(5) FIG. 3 shows a drawing in section of the print head in non-printing mode;

(6) FIG. 4 shows a first exemplary embodiment for a print head; and

(7) FIG. 5 shows a second exemplary embodiment for a print head.

DETAILED DESCRIPTION

(8) FIG. 1 shows a print head 10 in a perspective external view. The print head 10 has a housing 19 which has a funnel-like feeder 12 for a raw material 21 in the form of pellets 21. The housing 19 merges at the top into an intermediate piece 38. This intermediate piece 38 comprises a cylinder 37 in which a piston 31 is guided. In the view chosen in FIG. 1, the piston 31 is covered by the cylinder 37 and is therefore only indicated. The movement of the piston 31 is driven by means of an electromotor 32a, the rotational movement of which is converted into a linear movement by a mechanical spindle 32b. The piston 31 and the drive source 32 together form a conveyor device 30 for conveying the pellets 21.

(9) The travel s of the piston 31 is measured by a travel measurement system 33. The force F with which the piston 31 presses against the pellets 21 is measured by a force sensor 34. The force F and the travel s are fed to an active control system 35 which moreover receives a target value F.sub.s for the force F as an input and actuates the electromotor 32a with the effect that the actual force F is maintained at a level matching the target value F.sub.s. By measuring the travel s, it is thus ensured that the constraint is met that the piston 31 is to come into contact only with the completely solid pellets 21 of the raw material 20 but not with an at least partially plasticized phase which clogs the piston 31.

(10) In the upper region which faces the feeder 12, the housing 19 is formed by cooling means 13 which comprise an active cooler 13a with a coolant and a passive cooler 13b with cooling ribs. In the lower region which faces the discharge opening 16, the housing 16 is in contrast surrounded at its outer periphery by a heating strip 15 which supplies the heating energy for plasticizing the raw material 21.

(11) FIG. 2 shows the inside of the print head 10 in the part of the working cycle in which the printing takes place. An intake zone 11 into which the pellets 21 or the raw material 21 can be fed via the funnel-like feeder 12 is situated in the housing 19 of the print head 10. The piston 31 conveys the pellets 21 from the intake zone 11 into the plasticization zone 14, also termed the metering zone because the measuring of the raw material 21 into portions takes place here. The intake zone 11 adjoins the plasticization zone 14 via a compression zone 11a. The boundary layer 11b between highly compressed but still solid and non-sticky pellets 21, on the one hand, and material 22 which has begun to liquefy, on the other hand, is situated inside the compression zone 11a. In the position shown in FIG. 2, the front end of the piston 31 is situated precisely in this boundary layer 11b.

(12) The interior of the housing 19 is formed in the upper region of the housing 19 up to and including the boundary layer 11b as an upright cylinder in which the piston 31 can be guided. The interior merges below into a fusion geometry 51. This fusion geometry 51 is distinguished, on the one hand, in that its internal cross-section tapers increasingly downward such that the pressure of the liquid material 22 or the liquid phase 22 increases more and more. On the other hand, the inner wall of the fusion geometry 51 has a structure which effects the mixing of the liquid phase 22 of the raw material 21. This structure can, for example, be rib-shaped, as drawn by way of example in FIG. 2. The heating strip 15, the heating output of which is distributed homogeneously over the liquid phase 22 by a heat transfer structure 52 (heat transfer torpedo) arranged in the interior of the housing 19, i.e. inside the liquid phase 22, is arranged in the plasticization zone 14 on the outer periphery of the housing 19. Any other type of heater is also possible instead of the heating strip 15 drawn by way of example in FIGS. 1 and 2. In the discharge opening 16 at the nearest front region 16a of the plasticization zone 14, the pressure p.sub.L of the liquid phase 22 is measured by a pressure sensor 17 and the temperature T.sub.L of the liquid phase 22 is measured by a temperature sensor 18. The region 16a is just a few cubic millimeters large such that no excess pellets 21 are fused. The heat transfer structure 52 ensures that the liquid phase 22 of the raw material 21 in the region 16a always has the highest possible viscosity without overheating.

(13) The measured values for p.sub.L and T.sub.L are forwarded to an evaluation unit 4 which additionally receives as an input the measured temperature value T* of a further temperature sensor 53 arranged at the very upper limit of the plasticization zone 14.

(14) A strand 23 is pushed through the discharge opening 16 of the print head 10, from the liquid phase 22 of the raw material, by the pressure p.sub.L generated by the piston 31 and is deposited on an object 60 to be manufactured. The evaluation unit 4 calculates, on the one hand, by what amount ΔV.sub.+ the volume of the strand 23 increases owing to the relaxation of the high pressure p.sub.L and, on the other hand, by what amount ΔV.sub.− this volume decreases owing to the cooling of the high temperature T.sub.L. At the same time, the energy input E into the object 60 by the deposited material 23 is also calculated.

(15) The piston 31 is guided in the housing 19 with a small ventilation gap 54. Ambient air which is contained in the bulk material of the pellets 21 and is freed when this bulk material is compressed can be discharged through this gap 54. Gases which occur during the plasticization or partial decomposition of the raw material 21 can also be discharged by the same route.

(16) As already indicated in FIG. 1, the housing 19 is cooled between the boundary layer 11b and the feeder 12 by cooling means 13 which are formed by the active cooler 13a with a flowing coolant and by the passive cooler 13b by means of cooling ribs. As a result, the temperature TS inside the intake zone 11, which rises gradually from top to bottom, is constantly maintained below the temperature TP above which the raw material 21 is plasticized. TP is reached at the very bottom end of the boundary layer 11b. Because the intake zone 11 is permanently temperature-controlled to a suitable temperature, premature fusion of the pellets 21, clogging of the intake zone 11, and the ingress of water due to condensation are prevented. This temperature control also controls the precise position of the boundary layer 11b and can maintain it in particular in a constant position.

(17) The temperature curve along the longitudinal axis 10a of the print head 10 from cold (−) to hot (+) is indicated qualitatively to the right of the print head 10.

(18) FIG. 3 shows the same print head 10 in the same view as in FIG. 2 except that here the piston 31 has been retracted upward, behind the intake zone 11. On the one hand, this has the effect that, in the state shown in FIG. 3, no strand 23 of raw material 21 is discharged from the discharge opening 16. On the other hand, the intake zone 11 is free for fresh pellets 21 to trickle in. When the piston 31 is lowered again, as shown in FIG. 2, the fresh pellets 21 are compressed and plasticized in the plasticization zone 14 before emerging from the discharge opening 16 as a strand 23.

(19) FIG. 4 shows a first exemplary embodiment of the print head 10 according to the invention in a drawing in section. The piston 31 has a first piston section 5, facing the plasticization zone 14, with a guide surface 9 by means of which the piston 31 is guided in a bore 7 of the print head 10 or the housing 19.

(20) The axial extent L2 of the guide surface 9 is longer than a maximum axial extent L1 of an opening area 8 of the feeder 12 leading to the bore 7. The opening area 8 of the feeder 12 leading to the bore 7 is designed such that the fed pellets 21 can be fed optimally into the bore or into the intake zone 11.

(21) In this embodiment, the axial extent L2 of the guide surface 9 of the piston 31 is 1.2 times the maximum axial extent L1 of the opening area 8.

(22) The first piston section 5 moreover has a piston diameter d2, wherein the axial extent L2 of the guide surface 9 of the piston 31 is preferably 1.25 times the piston diameter d2 of the first piston section 5.

(23) The piston 31 illustrated with the correspondingly dimensioned guide surface 9 prevents the piston 31 from jamming in the bore 7 and reduces the penetration of the deformed pellets into the gap between the guide surface 9 and the bore 7.

(24) The piston 31 moreover has a second piston section 6, the piston diameter d1 of which is smaller than the piston diameter d2 of the first piston section 5.

(25) FIG. 5 shows a second exemplary embodiment of the print head 10, wherein the piston 31 has a groove 40 which is arranged between the first piston section and a third piston section 41.

(26) The third piston section 41 is arranged between the first 5 and the second 6 piston section and has the same piston diameter d2 as the first piston section 5.

(27) The groove 40 is used to evaluate the quality of the print head settings by the groove 40 being checked for deposits during the maintenance intervals.

(28) In this embodiment, the axial extent L2 of the guide surface 9 of the piston 31 is 1.2 times the maximum axial extent L2 of the opening area 8 and extends as far as the groove 40.

(29) The print head 10 can be integrated into any 3D printer.