DE102014018081A1 - Process and plant for the additive production of metal parts by means of an extrusion process - Composite Extrusion Modeling (CEM) - Google Patents

Abstract

The invention relates to a method and a plant for the additive production of metallic components, the so-called composite extrusion modeling, preferably for closed hollow structures of metals consisting of the combination of the phases of the additive generation of a green part (b) and the heating of the green part (b). for binder removal and sintering of the metal parts, wherein a composite material by means of an extruder (7) plasticized briefly and two-dimensionally applied to the building platform (12) in the form of an extruded material thread, cooled and then the two-dimensional application and cooling of the extruded material thread until the completion of the Green part (b) is continued and after completion of the green part (b) of the building platform (b) removed and debind in a conventional manner and sintered. The plant for carrying out the method consists of a three-dimensional movable kinematics, from a construction platform (12) and arranged on the three-dimensional kinematics one or more extruder (7), wherein the extruder (7) from a mechanical drive (1), a heated housing (2) and one on the heated housing (2) arranged, replaceable nozzle (3).

Description

The invention relates to a method and a plant for the additive production of metallic components, the so-called composite extrusion modeling.

• • komplexe Formen mit Hinterschneidungen,
• • biologische Strukturen bis hin zu eins zu eins Kopien menschlicher Knochenstrukturen,
• • Leichtbauteile mit Gitter oder Wabenstrukturen,
• • thermisch beanspruchte, strömungsführende Teile (z. B. Raketentriebwerksteile)

The additive manufacturing of metal parts is still a costly and complex alternative to conventional manufacturing (prototyping, machining, etc.). Nevertheless, it is used in larger companies in the aerospace, automotive and medical industries. This is mainly due to the fact that additive manufacturing allows unprecedented design freedom:

• • complex shapes with undercuts,
• • biological structures down to one to one copies of human bone structures,
• • lightweight components with mesh or honeycomb structures,
• • thermally stressed, moving parts (eg rocket engine parts)

• • das Aushärten eines UV-empfindlichen Harzes
• • das Verfestigen eines Pulverbettes durch Bindemittel
• • das Aufschmelzen und Erstarren eines Pulverbettes durch Laser- oder Elektronenstrahlen
• • das Aufschmelzen und Erstarren eines Kunststoffdrahtes durch eine beheizte Düse

In the field of additive manufacturing processes, various processes have been established in the past 30 years, which are to be distinguished in particular by the manner of layer generation in connection with the starting material.

• • the curing of a UV-sensitive resin
• • the solidification of a powder bed by binders
• • the melting and solidification of a powder bed by laser or electron beams
• • the melting and solidification of a plastic wire through a heated nozzle

The most important additive manufacturing processes are Stereolithography (STL), 3D Printing (3DP), Selective Laser Sintering (SLS), Electron Beam Melting (EBM) and Fused Deposition Modeling (FDM). Stereolithography was first used in the US 45 75 330 A disclosed. In this process, a build platform is dipped by a certain layer thickness into a bath of liquid UV-curable resin. By means of a UV laser, the first layer of the component is solidified on the building platform. The steps of lowering and solidifying the component are repeated below, and so the component "grows" from bottom to top on the build platform. The method has very good detailing and surface qualities, but due to the resins used is mainly suitable for illustrative models and patterns.

The actual 3D printing describes a process in which a layer of a powdery starting material (polymers, ceramics, metal, sand) is applied with a doctor blade on a building platform. Next, a printhead, similar to that of an inkjet printer, travels over the powder and selectively sprays a binder into the powder to solidify the contour and filling of the component. These two processes are repeated until the component is completed.

Other powder processing methods are the sintering and melting processes, which solidify the contours of the components in the powder bed either with a laser (SLS, SLM), or with an electron beam (EBM). The layer application of the metallic powder is similar to the 3D printing in a closed space, which is vacuumed and is under protective gas. The high-energy rays are moved either by mirror mechanisms or by electromagnets on the powder bed. The powder bed is locally melted and then solidifies again.

In the SLM and EBM process, the energy input is so high that very dense components with up to 99% of the density of the solid material arise. In the SLS process, the individual powder particles are merely sintered, resulting in a more porous component.

The components of the melting process have very good mechanical properties, but the processes are due to the high cost (laser and mirror mechanics) and material prices and the maintenance-intensive technology among the most expensive processes. In addition, the systems are often up to 200 × larger than the actual installation space and when working with metal powders, there is always the risk of dust explosions and metal fires.

Another thermal process is the fused deposition modeling process. It will be in the US 51 21 329 A described. In this process, a thermoplastic plastic wire is forced through a heated die and, by moving the build platform and / or extruder, forms the individual layers of the component on the build platform. The second and all further layers are printed on the underlying structure. In contrast to the other methods, components are formed free form and are not surrounded by unconsolidated material.

The processes which are suitable for the production of metal and ceramic parts work with metal powders are expensive and require special protective measures. It is important to ensure that there is no time to blow powder and thus a dust explosion and a metal fire. The installation space must be freed of loose powder after a printing process and also on the component itself still adheres a powder crust, which must be removed with additional equipment. Due to the layer structure is the entire space around the actual component and also hollow structures in the component filled with loose powder.

There are already approaches to establish new additive manufacturing processes for the processing of metallic or ceramic components. In the WO 2000 051 809 A1 the so-called paste-polarization method is disclosed. This is similar in its mode of operation of stereolithography, with the difference that the starting material is not a liquid UV-sensitive resin but a paste is used. The paste consists of 35-60% metal or ceramic particles and a UV-sensitive resin. The resin serves as a binder and ensures the strength of the component after the printing process. However, the process has not been commercialized.

Another hybrid process which enables the production of metal parts by means of known additive manufacturing processes is described in US Pat DE 10 2005 056 260 B4 described. The 3D printing process is used to inject binders into metallic or ceramic powder. Layering is done in the same way as 3D printing. After the printing process, the cured binder provides the strength in the so-called green part, by subsequent burning out of the binder in an oven and sintering of the metal or ceramic particles creates a solid metal part, which has a low density due to the high binder content. The method can also be used to produce sand molds and cores. The method further has the disadvantage of high acquisition costs, which inhibit wider use.

The said methods also have the disadvantage that no closed hollow structures can be produced, and non-solidified material from the component interior and the environment of the component must be removed manually. Furthermore, when manufacturing metal and ceramic parts by means of 3DP, the demanding handling of the powdered starting material must also be taken into account.

Another method of producing molded parts from metal and / or ceramic particles bound in a binder is powder injection molding. In this case, molded parts are produced from powdered material by injection molding. A so-called feedstock is melted in a plasticizing unit with a screw by heat conduction from the outside via heating bands attached to the plasticizing cylinder and due to dissipation in the melt during mixing in the screw cylinder. The feedstock consists of a defined volume fraction of powder and a volume fraction of binder component. The ratio of powder to binder content influences the flow properties and determines the shrinkage of the component during sintering

The DE 10 2007 019 100 A1 relates to a method for injection molding an injection moldable mass in an injection molding machine comprising a screwed plasticizing unit, an injection unit, a machine control and a tool having a cavity, wherein injection moldable mass can be injected into the cavity, and wherein the injection moldable mass comprises at least one of Powder component and at least one binder component consists. The invention further relates to an injection molding machine. The binder component becomes molten in the plasticizing cylinder while the powder component remains in the solid state of aggregation. After the injection molding process, the sprayed parts are sintered. The feedstock is homogenized in compounding equipment on the injection molding machine prior to processing.

The disadvantage of this method is the use of molds, is injected into the feedstock material and cures there. With this method, no free-formable components are to be produced, since this is not an additive manufacturing process.

Furthermore, in the ceramic Magazine 04/2014 page 235 describes an FDM process for producing green compacts from ceramic materials, wherein a ceramic mass is filled into an injection tip and this is moved over x-, y- and z-axes, while the piston of the hypodermic syringe promotes the mass from the nozzle of the syringe , Here, no hot melt but a cold plastic mass is extruded through a nozzle and stored.

This method is used to produce green compacts from ceramic masses, but not the production of components. In addition, the surfaces are too uneven. With the method, only near-net shape semi-finished products for subsequent green or white processing can be produced.

With the solutions known from the prior art, it has hitherto not been possible to produce metallic, free-formable components with a high density or closed hollow structures made of metal, low shrinkage and thus with a high strength by means of additive thermoplastic processes, such as the FDM process. High acquisition and material costs, maintenance costs, the size of the systems and the complexity of the methods constitute a further disadvantage of the hitherto disclosed technical solutions of additive manufacturing. Furthermore, it was not possible with the known technical solutions to produce freeformable components using FDM methods Starting material Composite material of thermoplastic binder and a high metal particle content, for example, commercial feedstock materials.

The object of the invention is to provide a novel additive process for the production of metal parts made of composite material with thermoplastic binder and metal particles. The new process should also be attractive for small and medium-sized companies due to significantly lower costs and a better ratio of installation space to system size. This can improve the overall way product development and innovation promotion. Components should be generated freely on the construction platform, whereby no manual removal of unbound material or cleaning of the installation space will be required. Furthermore, the process should only process materials in bonded form to prevent the risk of dust explosion and to avoid the need for vacuum and inert gas during the printing process.

The object of the invention is achieved by a method and a plant for the additive production of metal parts by means of an extrusion process consisting of two phases, the additive production of the green part (phase 1-a) by means of an extruder, ( 7 ) arranged on a three-dimensional kinematics ( 8th ) and the subsequent binder removal and sintering of the component in an oven (b). In phase 1, a composite material consisting of a thermoplastic binder and metal particles, the so-called feedstock, which is present in solid form as granules or sticks with a metal content higher than 70%, by means of an extruder ( 7 ) plasticized for a short time and selectively onto the construction platform ( 12 ) in the form of an extruded material thread two-dimensionally applied. After the contour and filling of the first layer have been applied and cooled, the adjustment of the layer thickness follows either by raising the extruder or by lowering the building platform ( 12 ) around the layer thickness (dz). The steps of extruding a new layer and the process of building platform ( 12 ) or the extruder ( 7 ) in z-direction are repeated until the green part ( 10 ) was completed. In this case, only the thermoplastic binder is plasticized, for the strength of the green part ( 10 ).

In the second phase, the green part ( 10 ) are removed from the apparatus and placed in a conventional sintering furnace ( 9 ) for metallic components. Due to the thermal action, the binder is first released from the component (c). As a result of further heating, the metal particles form so-called sintering necks at their contact points. That is, the grains fuse together and form a strong bond. After completion of the sintering process, the finished component can be removed from the oven (d). Due to the dissolved binder, there is a defined volume loss of the component (e).

In a further embodiment of the invention, support structures (FIG. 2) are arranged by a second extruder arranged on the three-dimensional kinematics. 11 ) produced, for example, from the same thermoplastic material, which is already used as a binder in the composite material.

The debinding of the green part (b) can be carried out according to a further embodiment of the invention either only by thermal action or by chemical and thermal action.

The plant for carrying out the process of additive manufacturing of metal parts by means of an extrusion process - Composite Extrusion Modeling (CEM) - consists of one or more extruders which are rigidly movable on an x-, y-, or z-axis and the control of a 3D printer attached kinematics of the system for generating the three-dimensional component structure is mounted freely selectable. The movements of the extruder ( 7 ) take place via the x-, y- and z-axis of the kinematics, whereby the construction platform ( 12 ) immobile or via a combination of the movement of the extruder ( 7 ) with the movement of the building platform ( 12 ) is executed in the corresponding axes.

The extruder ( 7 ) consists of a mechanical drive ( 1 ), a heated housing ( 2 ) and from a heated housing ( 2 ) mounted replaceable nozzle ( 3 ), wherein the heated housing ( 2 ) with the mechanical drive ( 1 ) via suitable means for transporting the composite material from the mechanical drive ( 1 ) to the heated housing ( 2 ) is provided.

In further embodiments of the invention, the mechanical drive ( 1 ) as a stuffing screw or as a cell wheel ( 14 ) or as drive wheels ( 15 ) educated.

In one embodiment of the invention, the suitable means for transporting the composite material is designed as a hose.

The composite material in the form of granules, coarse powder or sticks is by means of the mechanical drive ( 1 ) in the heated housing ( 2 ), compacted and plasticized and by a replaceable nozzle ( 3 ) extruded. The assembly of the mechanical drive ( 1 ) can either be from full success ( 4 ), by an overpressure line ( 5 ) or a corresponding metering device ( 6 ).

The invention will now be explained in more detail with reference to an example wherein the 1 a schematic representation of the method, the 2 a sketch of the extruder, the 3 a sketch of the extruder with the possibilities of its filling, the 4 a sketch of a support structure that 5 a mechanical drive ( 1 ) as a cellular wheel ( 14 ) trained and the 6 a mechanical drive ( 1 ) as drive wheels ( 15 ), wherein:

LIST OF REFERENCE NUMBERS

1

mechanical drive

2

heated housing

3

jet

4

fill

5

Overpressure supply

6

dosing

7

extruder

8th

x-y-z kinematics

9

sintering furnace

10

green part

11

support structure

12

building platform

13

Stick

14

bucket wheel

15

drive wheels

For this purpose, the specially designed for this purpose extruder ( 7 ), consisting of a plug screw as a mechanical drive ( 1 ), a heated housing ( 2 ), to which a nozzle ( 3 ) is arranged, wherein the plug screw as a mechanical drive ( 1 ) with the heated housing ( 2 ) via a dosing unit ( 6 ) and equipped with a commercial metal-plastic composite material consisting of POM as a thermoplastic binder and stainless steel particles with a share of 93% of the composite material. The material is for example in the form of granules, which is usually used in powder injection molding as a so-called feedstock. It is set an optimum temperature of 240 ° C and an extrusion rate of 10 mm / s. The extruder was installed vertically on an XYZ portal kinematics and connected to the controller of a 3D printer. About the controller was then on the build platform ( 12 ) applied a two-dimensional thread-like structure of the material and cured. Thereafter, the extruder was moved in the layer thickness (dz) in the z-axis upwards and again the thread-like material structure through the nozzle ( 3 ) of the extruder ( 7 ) on the existing structure on the build platform ( 12 ) applied and cured. This is repeated until the component as a green part ( 10 ) is present. After the completion of the green part ( 10 ), it is executed by the build platform ( 12 ) and in a sintering furnace ( 9 ) are debind from the binder and by further heating form the metal particles at their contact points so-called sintering necks. That is, the grains fuse together and form a strong bond. After completion of the sintering process, the finished component can be removed from the oven. Due to the dissolved binder, a defined volume loss of the component can occur.

The green part strength corresponds to that of the thermoplastic binder and is thus sufficient to remove the component without being damaged by the build platform. Since the material is, for example, a standard granulate for powder injection molding, the feasibility of reworking the green part by means of a sintering furnace is ensured. From this point on, the process does not in fact differ from the sintering process in powder injection molding.

The invention makes it possible to produce complex components from high-strength ceramic or metallic materials z. As stainless steel, which correspond to a density of 98% of the solid material. The process is many times cheaper than comparable additive manufacturing processes and has a much better ratio of space to size. Due to the possibility of creating internal hollow structures, completely new construction elements in the field of lightweight construction can be developed. For example, parts with closed surfaces and internal honeycomb and lattice structures. Due to the low cost of the process these lightweight components are cheaper and thus made available to a wider group of users. Due to the fact that during the printing process (phase 1) only the thermoplastic portion of the composite material is plasticized, the metal or ceramic powder is never present in unbound form, whereby the risk of a dust explosion is banned. The printing process can therefore take place in ambient atmosphere and does not require any protective equipment. The systems for producing the components in phase 1 are relatively small and have a robust mechanism, thus the method is also suitable for mobile use. The layer structure of thermoplastic material is also suitable for weightlessness.

QUOTES INCLUDE IN THE DESCRIPTION

This list of the documents listed by the applicant has been generated automatically and is included solely for the better information of the reader. The list is not part of the German patent or utility model application. The DPMA assumes no liability for any errors or omissions.

Cited patent literature

• US 4575330 A [0004]
• US 5121329 A [0009]
• WO 2000051809 A1 [0011]
• DE 102005056260 B4 [0012]
• DE 102007019100 A1 [0015]

Cited non-patent literature

• Journal 04/2014 page 235 [0017]

Claims (10)

Process for the additive production of freeformable metal parts by means of an extrusion process consisting of the combination of the phases of the additive production of a green part (b) and the heating of the green part (b) for debindering and sintering of the metal parts, characterized in that a composite material by means of one or more extruders ( 7 ) plasticized for a short time and selectively onto the construction platform ( 12 two-dimensionally in the form of an extruded material thread, cooled, and then the two-dimensional application and cooling of the extruded material thread is continued until the completion of the green part (b), after which the green part (FIG. 10 ) from the build platform ( 12 ) is removed and debind in a conventional manner and sintered. Process for the additive production of metal parts according to claim 1, characterized in that the composite material consists of a thermoplastic binder and metal particles and is present in solid form. Process for the additive production of metal parts according to claim 1 and 2, characterized in that the composite material is present as granules, coarse-grained powder or as a stick with a metal content higher than 70%. Process for the additive production of metal parts according to claims 1 to 3, characterized in that support structures (of the thermoplastic binder of the composite material) 11 ) getting produced. Process for the additive production of metal and / or ceramic parts according to claim 1 to 4, characterized in that the debindering of the green part ( 10 ) by thermal action or by chemical and / or thermal action. Plant for carrying out the method according to claims 1 to 5, consisting of a three-dimensionally movable kinematics, from a building platform ( 12 ) and arranged on the three-dimensional moveable kinematics one or more extruder ( 7 ), characterized in that the extruders ( 7 ) from a mechanical drive ( 1 ) for the composite material to be extruded, a heated housing ( 2 ) and one on the housing ( 2 ), replaceable nozzle ( 3 ), wherein the heated housing ( 2 ) via suitable means for transporting the composite material with the mechanical drive ( 1 ) connected is. Installation according to claim 6, characterized in that the suitable means for transporting the composite material from the mechanical drive ( 1 ) to the heated housing ( 2 ) is formed as a hose. Plant according to claim 6 to 7, characterized in that the mechanical drive ( 1 ) as a stuffing screw or as a cell wheel ( 14 ) or as drive wheels ( 15 ) is trained. Plant according to claim 6 to 8, characterized in that on the mechanical drive ( 1 ) for the composite material to be extruded, an overpressure line ( 5 ) or a metering device ( 6 ) are arranged for placement in solid form composite material in the form of thermoplastic binder and metal particles. Plant according to claim 6 to 7, characterized in that on the three-dimensionally movable kinematics or on the building platform ( 12 ) One or more extruders are arranged.

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