DISPENSING HEAD AND METHOD FOR DISPENSING SOLIDIFYING MATERIAL

Abstract: A dispensing head (1) for an apparatus for making three-dimensional physical objects of predetermined shape by sequentially depositing multiple layers of solidifying material on a base member is disclosed. The dispensing head (1) comprises a tubular passage (2), extending from a receiving inlet (3) to a dispensing outlet (4). As a special feature, the tubular passage (2) comprises integrated drive means (9), such that the drive means (9) can arrange strands (8) of solid material to be processed in a driving zone (D) located between the receiving inlet (3) and a liquifying zone of the tubular passage.

Description: Dispensing head and method for dispensing solidifying material. The invention relates to a dispensing head for an apparatus for making three-dimensional physical objects of predetermined shape by sequentially depositing multiple layers of solidifying material on a base member, comprising an annular passage, extending from a receiving inlet for receiving strands of solid material to a dispensing outlet for dispensing the material in a liquified state, heating means, operatively associated with the annular passage to form a liquifying zone for liquifying material in the annular passage, located between the input opening and the dispensing outlet, and drive means for driving material through the annular passage by engagement of the stands of solid material. Such a dispensing head is known from EP 0 833 237 and is used for liquifying solid strands of solidifying material and for depositing the liquified material in repeated layers wherein the material solidifies until a three- dimensional object is formed in a process generally known as Fused Deposition Modelling (FDM). In use, a solid strand of material having a cross section substantially corresponding to the cross section of the annular passage is fed into the passage and is liquified, after which the material is dispensed to solidify after dispensing in a layer. A problem associated with the known dispensing head is that, in practice, difficulties arise when processing strands of material having a relatively high viscosity in liquified state and/or which have a relatively low stiffness. In particular, in the known dispensing head, processing the strands includes the risk of buckling of the strand and/or disturbance of the desired rate of flow of liquified material from the dispensing outlet. In practice, only strands of a limited number of materials can be processed using the known dispensing head. The object of the invention is to provide a dispensing head of the above-identified type in which the above-mentioned problems are alleviated and which is capable of processing strands of a wider range of materials. Thereto, the dispensing head according to the invention is characterized in that the drive means are integrated in the annular passage, such that they are arranged to engage the strands of solid material in a driving zone located between the receiving inlet and the liquifying zone of the annular passage. This way, the annular passage forms a continuous support surface extending from at least the area where the drive means engage the >. strand to the area where the strand is liquified, such that buckling of the strand is prevented. Furthermore, the annular passage with integrated drive means provides for an increased material transport reliability, thereby preventing disturbance of the predetermined rate of flow due to leakage of material. By providing the drive zone between the receiving inlet and the liquifying zone the drive elements can engage the strand when it is still solid. Preferably, the drive means comprise drive elements for engaging the strands of solid material, the drive elements being arranged to reach through corresponding apertures in the wall of the annular passage. This way, the force exerted by the drive elements on the strands in radial direction can be adjusted, such that the force in axial direction of the strand provided by friction can reach the required level for driving the material through the relatively narrow dispensing outlet. By providing the apertures in the wall of the annular passage such that they sealingly surround the drive elements, it can be prevented that, even when materials with a relatively high elasticity or a relatively high viscosity are processed, material exits the annular passage at the apertures. The drive means may also comprise e.g. a screw thread rotationally disposed on the inner wall of the annular passage at the drive zone. In a further advantageous embodiment, the annular passage is at least at the drive zone defined by a tubular member. This allows for a relatively simple construction of the dispensing head. Advantageously, the drive elements comprise drive wheels, which may be juxtaposed in radially opposite pairs for increased grip. Preferably, the drive means comprise two or more of such pairs which may be distributed radially and/or axially in the drive zone. To optimize the traction exerted by the tread surfaces of the drive wheels onto the strand, each drive wheel is driven. Preferably, the drive wheels have a common drive. It should be noted however, that the drive wheels can each be driven independently and that it is also possible to provide non-driven idler wheels. By providing the tread surface with a profile for enhancing friction, the traction of the drive wheels and thus the axial force on the strand can be increased. By providing the drive wheels with at least a tread surface of metal or ceramic material, it is possible to engage the strands at relatively high temperatures and/or relatively high contact forces. In another embodiment, the dispensing head comprises preheating means for preheating strands of solid material, the preheating means being arranged to provide a preheating zone located on an input side of the drive zone. This way, it can be ensured that the strands are processed while having the proper phase and/or temperature for processing. In particular, when processing metal strands it can be assured that due to preheating, in the liquifying zone the metal can be heated in a controlled way, so that a preselected solid fraction can be obtained. The solid fraction determines the viscosity of the partially liquified material so that it can be deposited more accurately. The invention further relates to a method of liquifying and dispensing solidifying material from a dispensing head, as well as to an apparatus for making three-dimensional objects comprising a dispensing head. Further advantageous embodiments are discussed in the appended claims. The invention will be further elucidated using an example shown in a drawing. In the drawing: fig. 1 shows a perspective view of a dispensing head; and fig. 2 shows a perspective view of an apparatus for making three- dimensional physical objects using the FDM technique. The drawings are schematical representations and only serve as no -limiting elucidations of a preferred embodiment of the invention. In the drawings, identical parts are denoted with the same reference numerals. Fig. 1 shows a dispensing head for an apparatus for making three- dimensional physical objects of predetermined shape by sequentially depositing multiple layers of solidifying material on a base member. The dispensing head 1 comprises an annular passage 2 in the form of a canal with a circular cross section. The annular passage 2 extends from a receiving inlet 3 to a dispensing outlet 4. The dispensing head 1 further comprises heating means 5, shown as a coil of wire forming an electrical resistance heater. The coil is wrapped around the thin-walled tubular member 6 to form a liquifying zone L, located between the receiving inlet 3 and the dispensing outlet 4 of the annular passage 2. The dispensing head 1 further comprises drive means 7 for driving material through the annular passage 2. The drive means 7 are integrated in the annular passage 2, such that they can engage the strands 8 of solid material in a driving zone D located between the receiving inlet 3 and the liquifying zone L of the annular passage 2. In particular, the drive means 7 comprise drive elements, in the form of drive wheels 9, that reach through corresponding apertures 10 in the wall 11 of the tubular member 6. At the apertures, the wall 11 of the annular passage 2 sealingly surrounds the drive wheels 9. The drive wheels 9 are disposed, to reach with a part of their circumference through the apertures 10 in the wall 11 of the annular passage, such that, in each rotational position of a drive wheel, a portion 12 of the tread surface 13 of the drive wheel extends in the passage 2. At any rotational position, a portion 12 of the tread surface 13 is integrated with the wall 11 of the annular passage 2 and is used to engage a strand 8 inserted through the receiving inlet 3 and extending into the annular passage 2 at its circumference. To enhance friction between the tread surface 13 of the drive wheels 9 and the strand 8, the tread surface is provided with a profile, e.g. an hatched or knurled profile. The drive wheels 9 are juxtaposed in radially opposite pairs relative to the central axis A of the annular passage 2. In the drawing, two pairs of . juxtaposed drive wheels are shown that are axially distributed in the drive zone. To prevent any slippage, the drive wheels may be rotationally coupled. The drive wheels are made of metal, preferably hardened steel. The tread surface 13 may be slightly convex to improve cooperation with the cilindrical outer surface of the strand 8. In operation, a strand 8 is inserted into the annular passage 2 through the receiving inlet 3. By rotation of the drive wheels 9 in the direction of arrows 14, the circumference of the strand 8 is engaged to be driven by the portions 12 of the tread surfaces 13 of the drive wheels 9 that reach through the apertures 10 in the wall 11 of the tubular member 6. This way, the strand 8 is transported in a processing direction indicated with an arrow 15 towards the liquifying zone L. In the liquifying zone the solid strand 8 is liquified. Under piston action of the solid portion of the strand 8, the liquified strand material is subsequently forced through ( the remaining portion of the annular passage 2 where it is dispensed through the dispensing outlet 4. Preheating means 16, shown as an electrical wire resistance heater, are provided in a preheating zone P located on an input side S of the drive zone D. This way, a strand 8 to be processed can be preheated to have the proper phase and/or temperature for processing. With the dispensing head according to the invention, strands of numerous materials can be processed, including: PA (polyamide), polyesther (PET,PBT), poly-buthene-terephtalate (PBTP), poly-ethene-terephtalate (PETP), polycarbonate (PC), acrylonitrile-butadiene-styrene copolymer (ABS), acrylonitrile styrene acrylic copolymer (ASA), Styrene acrylonitrile copolymer (SAN), polyacetal (POM), cellulose acetate (CA), polymethyl-methacrylate (PMMA), modified polyphenyloxide (PPO), polyphenylenesulfi.de (PPS), polysulphone (PSO), polytetrafluorethylene (PTFE), Polyethersulphone (PES), polyether-ether-ketone (PEEK), polymethylpentene (PMP), polyphenylether+polystyrene (PPE/PS), polyimide (PI), polyetherimide (PEI), polyvinylchloride (PNC), polystyrene (PS), polyolefins (PE, PP), polyvinylydenefluoride (PNDF), tetrafluorethene-ethene copolymer (ETFE), watersoluble polymers: poly aery la ide (PAA), polyethylene oxide (PEO), biopolymers, thermoplastic elastomers: polyesther, polyether or polyolefin based bloc copolymers (SBS, Hytrel, Arnitel), above polymers in unfilled, inert filled or grafted grades (fillers such as glass, minerals, fibres, grafted with maleic acid etcetera) and semi solid metals. The strands may be composed, e.g. be built up of different filaments or coaxial layers. It should be noted that the preheating means may also be used advantageously in an FDM apparatus incorporating a conventional dispensing head. It shall also be clear that the preheating means need not be part of the dispensing head, but may be arranged on a different portion of the machine such that it is associated with a portion of the strand to be processed that is streamupward from the liquifying zone in processing direction 15. Referring to fig. 2, an apparatus 20 is shown for making three- dimensional physical objects 21 of a predetermined shape by sequentially depositing multiple layers of solidifying material on a base member. The apparatus 20 comprises the dispensing head 1 of fig. 1 and means for supplying strands of solidifying material to the receiving inlet of the dispensing head 1, shown as a filament spool 27 on which a strand 8 is wound. The apparatus 20 further comprises a base member 22 disposed in working proximity to the dispensing outlet 3 of the dispensing head 1 and means for moving the dispensing head 1 and the base member 22 relative to each other in three dimensions. The means for moving the dispensing head are shown as linear drives 23A, 23B and 23C in which the dispensing head 1 can be moved in the X, Y and Z direction respectively. The apparatus 20 further comprises control means 24, e.g. a computer, for controlling the linear drives 23 and the drive means 7 of the dispensing head 1, such that the dispensing head 1 can move relative to the base member 22 in three dimensions in a predetermined sequence and pattern with respect to the dispensing outlet 3 of the dispensing head 1 and the strand 8 of solid material can be driven through the annular passage 2 of the dispensing head, such that a sohdifying material is dispensed in a liquified state from the dispensing outlet in a predetermined rate onto the base member, so as to thus form a three-dimensional object. The constructional details and workings of the dispensing head and the apparatus are known to the skilled man and are e.g. discussed in EP 0 833 237 to Stratasys Inc. The base member 22 is preferably disposed in a working chamber 25 having a controlled atmosphere. In particular, the working chamber 25 may contain a neutral gas environment which is particularly useful when strands of material are processed that are prone to contamination, degradation or crystallisation, e.g. strands containing metal. Furthermore, the temperature of the environment in the working chamber 25 may be controlled, e.g. using a heater 26. To enable processing of strands of material having a high liquifying temperature, it is observed that the temperature of the working area should be kept at or preferably closely under the glass transition temperature, e.g. 5- 30°C lower in order to enable stress relaxation to prevent (stress induced) warpage and shrinkage. It shall be clear that the ways of providing a controlled atmosphere may each be used advantageously in combination with conventional FDM methods and equipment. It shall further be clear that the invention is not limited to the specific embodiments described herein and that many variations are possible within the scope of the appended claims. In particular, an additional driving zone D' may be provided. Such an additional driving zone D' may be provided integrated in the annular passage, but may also be provided streamupward from the dispensing head in processing direction. Preferably, the additional driving zone D' is provided on an input side S' of the preheating means, such that the preheating means are located between driving zones. When the additional drive zone D' is integrated in the annular passage, the annular passage may provide support against buckling.

Claims: Claims 1. A dispensing head for an apparatus for making three-dimensional physical objects of predetermined shape by sequentially depositing multiple layers of solidifying material on a base member, comprising: an annular passage, extending from a receiving inlet for receiving strands of solid material to a dispensing outlet for dispensing the material in a liquified state, heating means, operatively associated with the annular passage to form a liquifying zone for liquifying material in the annular passage, located between the receiving inlet and the dispensing outlet, and drive means for driving material through the annular passage by engagement of the strands of solid material, wherein the drive means are integrated in the annular passage, such that they are arranged to engage the strands of solid material in a driving zone located between the receiving inlet and the liquifying zone of the annular passage. 2. A dispensing head according to claim 1, wherein the drive means comprise drive elements for engaging the strands of solid material, the drive elements being arranged to reach through corresponding apertures in the wall of the annular passage. 3. A dispensing head according to claim 2, wherein, at the apertures, the wall of the annular passage sealingly surrounds the drive elements. 4. A dispensing head according to any of the preceding claims, wherein at least at the drive zone the annular passage is defined by a tubular member. 5. A dispensing head according to any of claims 2-4, wherein the drive elements comprise drive wheels. 6. A dispensing head according to claim 5 wherein the drive wheels are disposed to reach with a portion of a tread surface thereof through the corresponding apertures in the wall of the annular passage. 7. A dispensing head according to claim 5 or 6 wherein the tread surface of the drive wheels is provided with a profile for enhancing friction. 8. A dispensing head according to any of claims 5-7 wherein at least the tread surface of the drive wheels is made of metal. 9. A dispensing head according to any of claims 5-7 wherein at least the tread surface of the drive wheels is made of ceramic material. 10. A dispensing head according to any of the preceding claims, further comprising preheating means for preheating strands of solid material, arranged to provide a preheating zone located on an input side of the drive zone. 11. An apparatus for making three-dimensional physical objects of a predetermined shape by sequentially depositing multiple layers of sohdifying material on a base member, comprising a dispensing head according to any of the preceding claims, further comprising means for supplying strands of sohdifying material to the receiving inlet of the dispensing head, a base member disposed in working proximity to the dispensing outlet of the dispensing head, moving means for moving the dispensing head and the base member relative to each other in three dimensions and control means for controlling the moving means and the driving means, such that the dispensing head can move relative to the base member in three dimensions in a predetermined sequence and pattern with respect to the dispensing outlet and the drive means drive the strands of solid material through the annular passage such that material is dispensed in a liquified state from the dispensing outlet in a predetermined rate onto the base member, so as to form a three-dimensional object. 12. A method for making three-dimensional physical objects of predetermined shape by sequentially depositing multiple layers of solidifying material on a base member, wherein a strand of solid material is driven through a liquifying zone located between a receiving inlet for receiving the strand of solid material and a dispensing outlet for dispensing the material in a liquified state of an annular passage and wherein the strand of sohd material is engaged to be driven in a driving zone located between the receiving inlet and the liquifying zone of the annular passage.

Inventors: FEENSTRA FRITS KORNELIS, FINKE STEFFI, FEENSTRA, FRITS, KORNELIS, FINKE, STEFFI
Applicants: FEENSTRA FRITS KORNELIS, FINKE STEFFI, TNO, FEENSTRA, FRITS, KORNELIS, FINKE, STEFFI, NEDERLANDSE ORGANISATIE VOOR TOEGEPAST-NATUURWETENSCHAPPELIJK ONDERZOEK TNO
Application year: 2000
Main classification: B05C17
IPC codes: B05B1, B05C5, B05C9, B05C17, B05D1, B05D5, B29C41, B29C67