AT527166A1 - Extrusion head for the additive manufacturing of a molded body - Google Patents

Abstract

An extrusion head for the additive manufacturing of a molded body is described with a tubular body (1) that opens into an extrusion nozzle (3) and forms a ferromagnetic jacket (2), and with at least one induction coil (10, 11) that encloses the ferromagnetic jacket (2) of the tubular body (1) in a melting zone (4). In order to create advantageous heating conditions, it is proposed that the ferromagnetic jacket (2) has a jacket thickness that changes repeatedly and alternately over the jacket circumference, at least in one axial section (5, 7) of the melting zone (4).

Description

The invention relates to an extrusion head for the additive manufacturing of a molded body with a tubular body opening into an extrusion nozzle and forming a ferromagnetic shell and with at least one ferromagnetic shell enclosing the ferromagnetic shell of the tubular body in a melting zone.

induction coil.

In order to be able to advantageously provide the heat energy required for melting a thermoplastic polymer strand fed to an extrusion head, it is known to provide an electrical induction heater instead of the usual electrical resistance heater. This electrical induction heater comprises a tubular body provided in the extrusion head, which receives the polymer strand to be melted, and at least one induction coil enclosing the ferromagnetic jacket of the tubular body, which induces eddy currents in the ferromagnetic jacket of the tubular body. The ferromagnetic jacket heated by the eddy currents gives off its heat to the thermoplastic polymer strand guided through the tubular body, which is thus heated and melted during its conveyance through the tubular body in order to be discharged as a melt strand from the extrusion nozzle closing the tubular body. The thermoplastic polymer strands used for the additive manufacturing of molded bodies are, however, sensitive to overheating, so that a

A temperature profile dependent on the type of polymer strand is desired.

For this purpose it is known (WO 2016/102 669 A1) to coat the

Pipe body made of several ferromagnetic sleeves with intermediate layer

he buys.

In order to avoid the control effort for several induction coils, it is also known (EP 3 148 293 A1) for extrusion heads for the additive manufacturing of molded bodies to divide the ferromagnetic shell of the tube body that holds the polymer strand into several axial shell sections that have a different Curie temperature, so that these shell sections can only be heated inductively up to the Curie temperature. Apart from the fact that axial shell sections made of different ferromagnetic materials are required for the construction of the tube body, there is the disadvantage that the inductive heating requires a power that exceeds the power requirement.

service offering must be provided.

For improved heat input into the polymer strand to be melted, it is also known in extrusion heads with an electrical resistance heater (WO 2017/183992 A1) to provide a heat conduction device in the form of a heat conducting body extending from the jacket of the pipe body towards the middle of the pipe in the pipe body receiving the polymer strand, in order to be able to heat the polymer strand not only from the outside via the heat-conducting jacket of the pipe body, but also in a core area via the heat conducting body. The disadvantage of the heat transfer caused by the electrical resistance heating from a heating block to the jacket of the pipe body and to the heat conducting body is that the heat input into the polymer strand depends on the one hand on the cross-section of the heat-conducting material available for the heat flow and on the other hand on the length of the heat flow.

between the heating block and the polymer strand, so that a

become.

The invention is therefore based on the object of designing an extrusion head for the additive manufacturing of a molded body in such a way that the temperature profile along the melting zone of the tubular body can be adjusted with a comparatively simple design effort according to the polymer strand to be melted.

can be largely predetermined.

The invention solves the problem by providing that the ferromagnetic shell has, at least in an axial section of the melting zone, a

The jacket circumference has a repeatedly alternating changing jacket thickness.

Through the interaction of the jacket thickness, which changes repeatedly and alternately over the jacket circumference, and a magnetic field excited at a corresponding frequency by the induction coil in the ferromagnetic jacket, a skin effect can be used in an advantageous manner, as a result of which the induced eddy currents concentrate in a surface layer area of the jacket, so that the jacket is heated more strongly in the area of the axial section of the jacket with the alternating jacket thickness in the surface area than in the other axial sections with a uniform thickness over the circumference. With the help of a ferromagnetic jacket designed according to the invention with an alternating jacket thickness at least in one axial section, the heat input along the melting zone can thus be controlled in accordance with a

control the specified temperature profile.

can.

Since the skin effect requires a repeated alternating change in thickness over the circumference of the ferromagnetic jacket, the jacket can form a circular cylindrical flow channel for the polymer strand to be melted over the melting zone, so that the flow conditions of the pipe body for the polymer strand cannot be adversely affected by the jacket thickness changing alternately over the circumference in an axial section of the melting zone. However, if the ferromagnetic jacket forms a circular cylinder on its outside in the area of the melting zone, the axial ribs resulting from the alternating changes in thickness protrude radially inwards, which results in an increase in surface area and thus a larger heat transfer area for

the polymer strand.

In order to achieve a predetermined course of heat input along the melting zone in

To be able to follow a sufficient level for the melting process, the

adjust.

The drawing shows the subject matter of the invention as an example.

show

Fig. 1 shows the tubular body of an extrusion head according to the invention for the additive manufacturing of a molded body, provided with an inductive heater, in an axial section,

Fig. 2 is a section through the casing of the pipe body along the line II-II of Fig. 1 on a larger scale,

Fig. 3 is a section along the line III-IIl of Fig. 1 on a larger scale,

Fig. 5 is a section along the line V-V of Fig. 4 on a larger scale.

In the drawing, only the area of an extrusion head used for the additive manufacturing of a molded body is shown schematically which is used for melting the supplied thermoplastic polymer strand. This thermoplastic polymer strand is fed by a conveyor device to a tubular body 1 held in a carrier, the ferromagnetic jacket 2 of which opens into an extrusion nozzle 3. The ferromagnetic jacket 2, which is inductively heated along a melting zone 4, has a jacket thickness that changes repeatedly and alternately over the jacket circumference in at least one axial section 5. Due to this repeatedly changing jacket thickness, axial ribs 6 are formed in section 5 of the melting zone 4 distributed over the circumference of the jacket 2, which run on the inside of the jacket 2 of the tubular body 1 according to Figs. 1 to 3, but also on the outside according to Figs. 4 and 5.

can be arranged on the outside of the jacket.

At least one section 5 with a repeatedly alternatingly changing jacket thickness over the jacket circumference is to be provided along the melting zone 4. The jacket 2 can also form two or more such sections. In Fig. 1, in addition to section 5, a further section 7 is shown, in the area of which the repeatedly alternatingly changing jacket thickness has a different period length 8 and a different thickness difference 9 compared to section 5.

, which results in a different cross-section of the ribs 6.

In order to use the skin effect in a section 5 with an alternating sheath thickness to advantage, provided that the period length 8 of the thickness change and the thickness difference are comparatively small, as can be seen from Figs. 2 and 5, a correspondingly higher excitation frequency for the magnetic excitation field must be provided in order to limit the penetration depth. For a design according to Fig. 3, i.e. in the case of comparatively

large cross-sections for the ribs resulting from the differences in thickness

to ensure a greater penetration depth.

As can be seen from Fig. 1, when two sections 5 and 7 are provided with a jacket thickness that changes repeatedly and alternately over the jacket circumference, two induction coils 10, 11 can be provided, which are particularly matched with regard to their excitation to the two sections 5, 7, which are designed differently in terms of the differences in thickness, but extend concentrically over the entire melting zone 4. With an alternating excitation of the two induction coils 9, 10, magnetic excitation fields with different frequencies act alternately in the jacket 2 along the entire melting zone 4. This means that, depending on the excitation frequency, different effects occur in sections 5 and 7 due to different penetration depths with the result that different amounts of heat can be made available along sections 5 and 7 in order to adapt to a predetermined temperature profile along the

melting zone 4.

If the jacket 2 has only one section 5 along the melting zone 4 with a jacket thickness that changes repeatedly and alternately over the jacket circumference, an induction coil extending over the length of the melting zone 4 is sufficient, regardless of the area of the melting zone 4 over which the section of the jacket 2 with a thickness that changes repeatedly and alternately over the jacket circumference is located.

mantle thickness.

Claims (5)

(345094.3) II Patent claims 1. Extrusion head for the additive manufacture of a molded body with a tubular body (1) opening into an extrusion nozzle (3) and forming a ferromagnetic jacket (2) and with at least one induction coil (10, 11) enclosing the ferromagnetic jacket (2) of the tubular body (1) in a melting zone (4), characterized in that the ferromagnetic jacket (2) has a magnetic field extending over the The jacket circumference has a repeatedly alternating changing jacket thickness. 2. Extrusion head according to claim 1, characterized in that the induction coil (10, 11) is operated at a frequency dependent on the period length (8) of the alternatingly changing jacket thickness and the thickness difference (9). is excitable. 3. Extrusion head according to claim 1 or 2, characterized in that the ferromagnetic jacket (2) in the region of the melting zone (4) has a circular cylindrical outer surface. 4. Extrusion head according to one of claims 1 to 3, characterized in that the ferromagnetic jacket (2) in the region of the melting zone (4) has at least two sections (5, 7) spaced apart from one another in the axial direction with a jacket thickness that changes alternately over the jacket circumference and that the changes in the jacket thickness in the two axial sections (5, 7) of the melting zone (4) are different. 5. Extrusion head according to claim 4, characterized in that the two axial sections (5, 7) with an alternating are excitable.