DE102020125278A1 - 3D printing methods, measurement methods to determine the magnetizability of a printed part containing nanoparticles and 3D printers - Google Patents

Abstract

The invention relates to a 3D printing method with the steps: (a) introducing a curable liquid (14) containing ferromagnetic and/or ferrimagnetic nanoparticles (24) into a working container (12), and (b) local curing of the liquid (14) by radiation. According to the invention, it is provided that (c) the nanoparticles (24) are selected in such a way that the pressure part (20) has an anisotropic magnetizability and has no permanent total magnetic moment to the outside.

Description

The invention relates to a 3D printing method with the steps (a) introducing a curable liquid containing ferromagnetic and/or ferrimagnetic nanoparticles into a working container and (b) local curing of the liquid by means of radiation.

According to a second aspect, the invention relates to a measurement method for determining the magnetizability of a printed part that contains nanoparticles. The invention also relates to a 3D printer with (a) a working container for introducing a curable liquid and (b) a curing device for local curing of the liquid, so that a printed part is created.

3D printing is becoming more and more popular. The 3D printing is preferably carried out in layers, for example by stereolithography. It is well known that the strength of 3D printed parts, also known as additively manufactured parts, is highly dependent on the build direction in which the part is printed.

In addition, it is often desirable to introduce a code into a printed part that does not affect the mechanical properties. It can be advantageous, for example, to incorporate a product number or an identifier for the respective printed part in the printed part. It is particularly advantageous if this identifier cannot be changed and/or can be easily read from the outside. In this way, for example, original parts can be distinguished from counterfeits.

The object of the invention is to reduce the disadvantages of the prior art.

The invention solves the problem through a generic 3D printing method, in which the nanoparticles are selected in such a way that the printed part has an isotropic magnetizability and has no permanent total magnetic moment to the outside.

According to a second aspect, the invention solves the problem by a measurement method for determining the magnetizability of a printed part that contains nanoparticles, in which a preferred orientation of the magnetizability of the printed part is determined.

The invention also solves the problem with a generic 3D printer that (c) has a container with nanoparticles that (i) have a uniaxial shape anisotropy and/or (ii) are designed in such a way that an ensemble of these nanoparticles has no magnetic remanence, (d) a mixing unit for mixing the nanoparticles into the curable liquid, a return line for returning curable liquid from the working tank or a storage tank into the mixing unit.

According to a further aspect, the invention solves the problem with a component made of a polymer which (a) contains nanoparticles, (b) has no magnetic remanence and (c) has a plurality of mutually disjoint magnetizability regions, (d) the magnetizability of the magnetizability regions being information coded via the component.

In its most general form, the invention solves the problem using a 3D printing method with the steps (a) building a printed part from a precursor, in particular a curable liquid containing ferromagnetic and/or ferrimagnetic nanoparticles, and (b) local curing of the precursor , where (c) the nanoparticles are selected in such a way that the pressure part has an anisotropic magnetizability and has no permanent total magnetic moment to the outside.

The advantage of the invention is that the orientation of the printed part can be read simply by measuring the magnetizability. In particular, it is possible that if a pattern of magnetizability has been introduced into the printed part, this pattern can often be measured comparatively easily. In this way, it is easily possible to clearly mark and recognize a component.

It is advantageous that a time-saving, precise and non-contact determination of the structure direction of additively manufactured molded parts is often possible with magnetic measuring methods.

The invention is based on the finding that the nanoparticles are aligned when the liquid or the precursor hardens or due to a predetermined preferred orientation of the magnetization in the precursor, provided they have a shape anisotropy. For example, if the nanoparticles are slightly ellipsoidal, they align themselves anisotropically in such a way that a preferred orientation of the main axes occurs. It is therefore possible to use the orientation of the nanoparticles to determine the direction along which the curable liquid has solidified. This alignment of the nanoparticles can in turn be determined by measuring the magnetizability.

The 3D printer is preferably a 3D Digital Light Processing (DLP) printer. as well it is possible that the 3D printing process is based on photopolymerization (e.g. stereolithography SLA) or on a powder bed process, e.g. selective laser sintering (SLS) or multijet fusion (MJF) or polyjet process, or on a filament printing process, e.g. fused deposition modeling (FDM). .

The precursor can, for example, be rod-shaped, for example a filament or a plastic wire.

In the context of the present description, the introduction of the curable liquid into a working container is understood in particular to mean that the curable liquid is introduced into a vessel in which curing takes place. The curable liquid is understood to mean, in particular, a substance which is flowable at the beginning and which can be cured by supplying energy in such a way that a dimensionally stable printed part is produced. A dimensionally stable pressure part is understood to mean, in particular, a component that is able to bear its own weight.

The feature that the component consists of a polymer is understood to mean in particular that the component consists of a polymer at least in the region in which the disjoint magnetizability regions are present.

It is favorable if the local curing takes place by means of optical light, X-rays, infrared light or particle radiation, for example an electron beam. The curing liquid can be a photopolymer, for example.

The precursor consists of a matrix material and the nanoparticles. In principle, the matrix material can be any type of object construction material, for example a photopolymer, plastic, wax and/or ceramic and is present in a suitable form, for example as a powder and/or liquid. A shaped body is produced from the precursor by preferably building up in layers, mediated by physical and/or chemical hardening and/or melting processes. Before and/or during 3D printing, an alignment of the magnetic moments of the nanoparticles in the precursor causes a coupling of the effective magnetic anisotropy in or relative to the build-up direction of the printed part. This embodiment gives the pressure part a preferred direction, axis or plane of magnetizability which is often advantageous in practice and which allows the direction in which the shaped body is built to be determined.

The curable liquid is a form of a precursor. According to one embodiment of the invention, the precursor preferably contains at least one monomer and/or at least one polymer. The use of several different monomers and/or polymers is also conceivable. Furthermore, the curable liquid has at least one photoinitiator and/or at least one crosslinker. The use of several photoinitiators and/or several crosslinkers is also possible. Photoinitiators are chemical compounds that trigger a polymerization reaction as soon as they break down into reactive molecules through absorption of light. Crosslinkers are monomers or polymers with at least three functionalities, for example more than two functional groups or more than one double bond per molecule, which can react through polymerization reactions. These bring about chain branching and thus crosslinking of the chain-like polymer molecules.

It is favorable if the direction-dependent magnetizability can be determined. This has the advantage that, in the case of shaped bodies built up in layers, an exact determination of the direction of build-up is possible with the aid of a non-contact magnetic measurement.

According to a preferred embodiment, the radiation is light, in particular visible light or UV light, which is concentrated in a curing area. It is favorable if the hardening area is punctiform, linear or planar. A curing area designed in this way leads to a curing front. The hardening front marks the area between the already hardened liquid and the not yet hardened liquid. This hardening front determines the anisotropic alignment of the magnetic particles and thus the anisotropic magnetizability. It is favorable if the curing takes place in such a way that the curing front is limited in one spatial direction, so that a planar orientation of the anisotropic nanoparticles is brought about in the curing area.

The feature that the hardening area is punctiform means in particular that an enveloping cuboid around the hardening front has a lower height, which is at least one-fifth of the other two side lengths of the same length.

The feature that the hardening area is linear means in particular that an enveloping cuboid around the hardening front has a lower height, which is at least one-fifth of a second side length and is at least as large as the third side length. The hardening area is considered to be planar in particular when two side lengths of the enveloping cuboid are at least five times the other side length. Under the enveloping cuboid, the cuboid becomes mini understood painting volume that completely encloses the curing front.

The 3D printing method preferably comprises the steps of (a) introducing the nanoparticles into the curable liquid in a mixing unit, (b) conducting the curable liquid into the working container and (c) returning curable liquid from the working container to the mixing unit. In other words, the nanoparticles are directed into a flow of curable liquid, which flow is at least partially returned from the working container.

In other words, the curable liquid is preferably at least temporarily partially returned from the working container into the mixing unit. As a result, sedimentation of the nanoparticles in the curable liquid in the working container is prevented. In addition, the dosing of the nanoparticles in the working container can be influenced, which means that each layer of the component can be equipped with a defined concentration of nanoparticles.

It is also advantageous if the concentration of nanoparticles is measured continuously. This can take place in front of and/or behind the mixing unit and/or inside the working container. The advantage of this is that the concentration of nanoparticles in the curable liquid can be set with greater accuracy.

The mixing unit can be an ultrasonic homogenizer, for example. In such an ultrasonic homogenizer, the curable liquid is subjected to an ultrasonic field, which disperses the nanoparticles introduced.

It is favorable when nanoparticles are used which have a uniaxial shape anisotropy.

wobei K die Energiedichte der magnetischen Anisotropie und V das Partikelvolumen sind (und damit KV die zu überwindende Energiebarriere) und v₀ die Frequenz der Magnetisierungsumkehr ist. Ein typischer Wert ist v₀ = 10⁹ s^-1). Dadurch, dass die Nanopartikel so gewählt sind, dass ein Ensemble dieser Nanopartikel keine magnetische Remanenz aufweist, wird erreicht, dass die Magnetisierbarkeit der Nanopartikel nicht nachträglich veränderbar ist. Wird ein Muster der Magnetisierbarkeit in das Druckteil eingebracht, so ist dieses Muster nachträglich nicht mehr veränderbar. Es ist daher zur dauerhaften Kodierung des entsprechenden Druckteils geeignet.It is also favorable if the nanoparticles are selected in such a way that an ensemble of these nanoparticles has no magnetic remanence. The feature that an ensemble of these nanoparticles has no magnetic remanence means, in particular, that for an ensemble of, for example, at least 50, in particular at least 100, of these nanoparticles without the presence of an external magnetic field, the average magnetization value over time during a measurement is zero . The reason for this is that a thermally induced reversal of the magnetic moment of the individual nanoparticles occurs. The mean frequency, with which the magnetic moment of the respective nanoparticle of the ensemble is reversed, results from the formula $$v=v_0\text{ex}\frac{-KV}{kT},$$

where K is the energy density of magnetic anisotropy and V is the particle volume (and hence KV is the energy barrier to be overcome) and v ₀ is the frequency of magnetization reversal. A typical value is v ₀ = 10 ⁹ s ^-1 ). The fact that the nanoparticles are selected in such a way that an ensemble of these nanoparticles has no magnetic remanence means that the magnetizability of the nanoparticles cannot be subsequently changed. If a pattern of magnetizability is incorporated into the printed part, this pattern can no longer be changed afterwards. It is therefore suitable for permanent coding of the corresponding printed part.

Since the nanoparticles are selected in such a way that an ensemble of these nanoparticles has no magnetic remanence, this has the further advantage that reversal of magnetization with alternating fields of sufficiently large amplitude is still possible in order to detect the preferred magnetic orientation of the nanoparticles. In other words, this feature leads to the magnetizability being detectable, but not subsequently changeable.

The nanoparticles can have any shape, preferably they have an elongated shape with dominating shape anisotropy. The nanoparticles can be magnetosomes, for example.

It is favorable if the nanoparticles have a particle size which is characterized in that at least 90 percent by weight of the nanoparticles have at least one dimension between 1 nm and 1000 nm. The feature that a nanoparticle has a dimension between 1 nm and 1000 nm in at least one dimension means in particular that for an envelope ellipsoid it applies that at least one of the main axes lies between 1 nm and 1000 nm.

Alternatively or additionally, preferably at least 90 percent by weight of the nanoparticles have an aerodynamic diameter of between 10 nm and 500 nm.

It is favorable if an imaginary compensating ellipsoid of revolution has an axis ratio of between 1.01 and 10, in particular between 1.02 and 2, for at least 90 percent by weight of the nanoparticles. It has been shown that such axis ratios lead both to reliable development of anisotropic magnetizability and are practically easy to produce.

It is favorable if at least 90 percent by weight of the nanoparticles have an energy barrier in the absence of a magnetic field that is less than 25 times the thermal energy. This feature means in particular that the energy barrier is at most 1/25th of the thermal energy at room temperature. As can be seen from the above formula 1, the energy barrier KV must correspond to approximately 25 times the thermal energy kT so that a reversal or reorientation of the magnetic moment takes place on average within 1 minute. The faster the reorientation takes place, the better it is, since the magnetizability does not change permanently as long as an external magnetic field is not permanently applied to the printed part.

The method preferably includes the step of changing an alignment of the curing area over time, so that a preferred direction of magnetizability of the printed part is created according to a predetermined pattern. In other words, the 3D printing method preferably includes the step of changing a curing direction over time, with which curing takes place, so that a predetermined magnetizability pattern is created in the printed part. This can be done, for example, by gradually tilting the construction platform on which the component is formed, which corresponds to a change in the direction of construction.

The cure direction is the direction in which the cure front progresses in the current component layer compared to the first layer of the component.

As described above, by introducing the predetermined pattern of magnetizability, a non-changeable pattern is introduced into the printed part. This magnetizability pattern can be read externally so that the printed part can be clearly identified.

The nanoparticles are preferably selected in such a way that the pressure part has no permanent total magnetic moment to the outside. Of course, this only applies if there is no external magnetic field. In other words, the printed part does not have a remanent magnetization that has a magnitude of 1000 times the saturation magnetization at room temperature for longer than 3 minutes after an external magnetic field has been switched off.

A measuring method according to the invention preferably comprises the steps (a) introducing at least one examination area of the printed part into a measuring area of a sensor, (b) applying an alternating magnetic field, (c) measuring the magnetic reaction of the magnetic nanoparticles to the alternating field and (d) integral and/or or spatially resolved determination of a preferred orientation of the magnetizability of the examination area by changing an orientation of the measurement field relative to the pressure field.

In this way, on the one hand, the preferred orientation of the printed part can be determined, which is an advantage in itself, particularly when the printing direction of the printed part is to be determined. The print direction is the direction in which the 3D printing process progresses. It is also possible to determine the magnetizability pattern by means of a spatially resolved determination on a correspondingly prepared printed part. This can be used, for example, to determine the identity of the printed part. In particular, according to a preferred embodiment, an identification code of the printed part is determined.

It is therefore preferably provided that the spatial distribution of the magnetic nanoparticles and/or the direction of construction of a shaped body is determined by means of a magnetic imaging and reconstruction method. Determining the direction of build-up is particularly advantageous in practice for shaped bodies that require precise alignment along the load paths. In this way, it is additionally ensured that a direct measurement of the build-up direction of, for example, covered, opaque and/or surface-treated molded bodies is possible for which optical and tactile methods, for example, reach their limits.

A 3D printer according to the invention preferably has a magnetization sensor for measuring the magnetizability of the curable liquid. It is possible, but not necessary, for this magnetization sensor to be arranged behind the mixing unit. In particular, it is also possible for the magnetization sensor to be arranged in such a way that the magnetizability of the curable liquid that is in the working container can be measured. It is also possible that there are two or more magnetization sensors.

The magnetization sensor is a device that measures the magnetic response of the magnetic nanoparticles to a changing magnetic field. In particular, the magnetization sensor is designed to measure the magnetizability of the curable liquid.

It is favorable if the component according to the invention is produced by 3D printing.

The nanoparticles advantageously have the properties described above. Advantageous on such a component is that the information about the component is stored in the component in a tamper-proof manner.

• 1a eine schematische Ansicht eines erfindungsgemäßen 3D-Druckers,
• 1b eine schematische Ansicht eines Teils eines mittels eines erfindungsgemäßen 3D-Druckverfahrens hergestellten erfindungsgemäßen Bauteils,
• 2a eine perspektivische Ansicht einer zweiten Ausführungsform eines Bauteils, das mit einem erfindungsgemäßen 3D-Druckverfahren hergestellt wurde,
• 2b schematische Darstellung der anisotropen Magnetisierbarkeit des Bauteils gemäß 2a,
• 2c die Abhängigkeit der Magnetisierbarkeit von der magnetischen Feldstärke,
• 2d die Abhängigkeit der dritten Harmonischen aus einer nicht linearen AC-Suszeptometrie-Messung an dem Druckteil gemäß 2a in Abhängigkeit von einem Drehwinkel θ (vgl. 2a),
• 3a eine weitere Ausführungsform eines erfindungsgemäßen Bauteils, das mittels eines erfindungsgemäßen 3D-Druckverfahrens hergestellt wurde, und
• 3b die Abhängigkeit von mechanischen Festigkeitskennwerten von einer Konzentration an Nanopartikeln.

The invention is explained in more detail below with reference to the accompanying drawings. while showing

• 1a a schematic view of a 3D printer according to the invention,
• 1b a schematic view of a part of a component according to the invention produced by means of a 3D printing method according to the invention,
• 2a a perspective view of a second embodiment of a component that was produced using a 3D printing method according to the invention,
• 2 B schematic representation of the anisotropic magnetizability of the component according to 2a ,
• 2c the dependence of the magnetizability on the magnetic field strength,
• 2d the dependence of the third harmonic from a non-linear AC susceptometry measurement on the pressure part according to FIG 2a as a function of a rotation angle θ (cf. 2a ),
• 3a a further embodiment of a component according to the invention, which was produced by means of a 3D printing method according to the invention, and
• 3b the dependence of mechanical strength parameters on a concentration of nanoparticles.

1a shows a schematic view of a 3D printer 10 according to the invention, which has a working container 12. A curable liquid 14 in the form of a photopolymer is introduced into the working container 12 . The liquid 14 can be hardened by means of a hardening device 16, which in the present case is a laser which emits a laser beam 18 of blue light. A pressure part 20 is then formed.

The 3D printer 10 also has a container 22 with nanoparticles 24.i (i=1, 2, 3 . . . ), which are shown schematically.

The nanoparticles can also be fully or partially covered with inorganic oxides ( WO 98/31461 , EP0343934 ), a polymer (eg US4421660 ; Horak et al. biotech. Prog. 17, 447, 2001; WO 97/04862 ; US4985166 ) and/or a natural component ( US4452773 , US5864025 ) be occupied. In addition, the coating can be modified with reactive groups, charge carriers and/or similar functionalities or can itself consist of these functional molecules (Liu et al. Colloids & Surfaces A 238, 127, 2004, Kobayashi et al. J. Colloid Interface Sci. 141, 505, 1991).

The nanoparticles 24.i are introduced into the curable liquid 14 by means of a mixing unit 26. In the present case, the mixing unit 26 is designed as an ultrasonic mixer.

The use of the mixer, which could also be referred to as an ultrasonic homogenizer, prevents the formation of particle aggregates, which tend to sediment during the additive manufacturing process and can cause a concentration gradient in the object. The homogeneity of the photopolymer particle mixture is preferably maintained during the printing process. Examples of photopolymers are commercially available polyethylene glycols, poly(ethylene glycol) diacrylates and gelatin methacrylates.

The concentration of the nanoparticles 24.i in the object is in the range from 0.00001% w/w to 50% w/w, preferably in the range from 0.0001% w/w to 10% w/w, particularly preferably in the range of 0.01%-w/w to 3%-w/w. Low concentrations are preferred in particular if the properties such as transparency or mechanical properties such as the tensile strength of the starting material are not to be significantly changed and/or the sensitivity of the measuring apparatus used is sufficient for determining the structural direction of the shaped body.

A return line 28 carries liquid 14 from the working container 12 to the mixing unit 26. From there it passes through a feed line 30 into the working container 12.

It is favorable if the 3D printer has a magnetization sensor 32 by means of which the magnetizability of the liquid 14 can be measured. In this way it is possible to adjust the magnetizability of the liquid 14 in the working container 12 . Alternatively or additionally, it is also possible for the magnetization sensor 32 or another magnetization sensor 32 ′ to be arranged in the return line 28 upstream of the mixing unit 26 in a flow direction S of the liquid 14 . It is also possible for the magnetization sensor 32 to be arranged in the working container 12 . However, it is not necessary for a magnetization sensor to be present; the 3D printer 10 can also be built without a magnetization sensor 32 .

A directional orientation of the otherwise randomly aligned magnetic moments or the preferred magnetic axis of the nanoparticles 24.i causes the additively manufactured printed part to have effective anisotropic magnetic properties and can therefore be magnetized to different degrees along different spatial directions. The preferred direction, preferred axis or preferred plane for the magnetization are mentioned here as possible characteristics. The arrangement of the nanoparticles 24.i required for this can arise as a result of the manufacturing process or be generated or reinforced by additional magnetic fields during additive manufacturing. A possible reason for the production-related development of an effective anisotropy of the object is assumed to be the assumption of a shape effect of anisotropic magnetic nanoparticles, which align during the polymerization of the precursor, here in the form of the liquid 14, and whose orientation is partially or completely retained after curing .

The formation of anisotropy before and/or during the manufacturing process using a magnetic field can lead to a preferred axis of magnetizability at room temperature. This has the advantage that the shaped body has no remanent magnetization. This requires the use of magnetic nanoparticles with a blocking temperature below room temperature. For magnetic nanoparticles whose blocking temperature is above room temperature, the formation of anisotropy before and/or during the manufacturing process with the help of a magnetic field leads to remanent magnetization and a preferred direction of magnetization.

According to one embodiment, printed parts in the form of a cylinder with a height of 5.3 mm and a diameter of 5.3 mm are produced from photopolymer with 1% w/w iron oxide nanoparticles using the 3D DLP method. The orientation of the magnetic moments or the preferred magnetic axis of the nanoparticles is influenced by the polymerization process in such a way that the surface normal of the preferred plane of magnetization is parallel to the direction of construction of the shaped body.

1b shows a section of a component 34 according to the invention in the form of a pressure part 20. It can be seen that the component 34 has a plurality of mutually disjunctive magnetization regions 36.j. The respective preferred directions of magnetizability are indicated by arrows P _j,k . It can be seen that the magnetizability M _j differ from one another in the respective magnetization regions 36.j. It is possible in this way to introduce a code, for example a binary code, into component 34 . For example, an orientation of the magnetizability M _j of the j-th magnetization region 36.j along a given axis A in the component 34 can be assigned the binary value zero, whereas a magnetizability perpendicular thereto can be assigned the logical value one. Of course, other types of coding are also possible.

2a shows another embodiment of a component 34 according to the invention in the form of a cylinder. The cylinder has a longitudinal axis A, which in the present case is interpreted as the X-axis of a coordinate system. A z-axis of the coordinate system runs perpendicularly to layers 38.n.

in der x-y-Ebene verlaufen. Durch Messung der Magnetisierbarkeit an jeder einzelnen der Schichten 38.k kann daher die Richtung ermittelt werden, in der die Schichten sich erstrecken. Entsprechend kann auch die Aufbaurichtung ermittelt werden, in die das Bauteil 34 aufgebaut wurde. 2 B shows the magnetizabilities 24.i. It can be seen that the respective magnetizability vectors ${\stackrel{\rightharpoonup }{M}}_{i,k}$

run in the xy plane. Therefore, by measuring the magnetizability of each of the layers 38.k, the direction in which the layers extend can be determined. The direction in which the component 34 was built can also be determined accordingly.

2c shows the dependence of the magnetization on the magnetic field strength H. It can be seen that the magnetizability changes for θ=zero (cf. 2a ) differs from θ=90°.

2d shows the dependency of the amplitude of the third harmonic of an excitation frequency f, with which a magnetic field applied to the component 34 changes, as a function of the angle of rotation θ. It can be seen that the angle of rotation θ can be deduced from the amplitude A ₃ of the third harmonic once it is known whether the angle of rotation θ lies in the range between 0 and 90°, 90° and 180°, 180° and 270° or 270° to 360°.

3a shows schematically another component 34, which was manufactured by means of 3D printing.

3b shows the dependency of the tensile stress, the tensile strain and the modulus of elasticity on a concentration of magnetic nanoparticles. It can be seen that the mechanical properties do not change or only change insignificantly.

To determine the structural direction of a shaped body, the magnetic properties of the object are determined depending on the direction using magnetic particle spectroscopy, as for example in Löwa et al. IEEE Trans. Magn. 1, 49, 2013. The magnetic anisotropy caused by the 3D printing leads to different measurement signals, in particular different amplitudes of the third harmonic A3, depending on the orientation of the printed part to the magnetic excitation direction and measurement direction.

in 2d In the case shown, the signal maximum indicates a preferential magnetic plane, from which conclusions can be drawn about the direction in which the shaped body is built up. In the embodiment mentioned, the surface normal of the preferred plane of the magnetization is parallel to the build-up direction or to the surface normal of the layers of the printed part.

Alternatively or additionally, the geometry and the build-up direction of a printed part are determined using multi-channel magnetic particle imaging (MPI), which is used in the US2003/0085703 A1 and the WO 2011/045721 A1 is described, shown. The orientation of the magnetic moments or the preferred magnetic axis of the nanoparticles is influenced by the polymerization process in such a way that the surface normal of the preferred magnetic plane of the magnetization is parallel to the direction of construction of the shaped body. In order to describe the relationship between the recorded measurement signal and the spatial distribution of the magnetic nanoparticles, knowledge of a spatially coded system response is required. For this purpose, a (ideally punctiform) calibration sample is measured at a large number of spatial positions in the image area of the MPI scanner and the measurement signals are stored in a so-called system matrix.

In order to be able to additionally determine the orientation of the preferential magnetic plane or the direction of construction of the shaped body, it is necessary to record several, at least two, system matrices. In the present embodiment, three system matrices are generated by measuring an additively manufactured calibration sample (e.g., a 3mm cube) in three orthogonal orientations. Using a reconstruction method that WO 2011/045721 A1 is described, both the spatial distribution of the magnetic nanoparticles (geometry of the object) and the orientation of the layers of a shaped body can be determined.

It is very generally preferred that a magnetic field of 25 mT is applied in the curing area during the polymerization, whereby an alignment of the magnetic moments of the magnetic nanoparticles in the magnetic field causes a preferred axis of the magnetizability of the shaped body. A better reconstruction of the orientation is possible due to the stronger polarization.

In addition, it is generally possible to determine the preferred magnetic direction, axis or plane based on the linear or non-linear alternating field (or AC) susceptibility, the magnetization in the constant field, the magnetic relaxation after a magnetic pulse, the temperature-dependent magnetization, to be determined based on the thermal fluctuation of the magnetization or other magnetic properties and/or effects.

A magnetic sensor is used for this purpose, for example an inductive sensor, an XMR sensor, a saturation core magnetometer, a SUID-based magnetometer, a Hall sensor, a proton magnetometer, a Kerr magnetometer, an optically pumped magnetometer or a Faraday magnetometer.

Reference List

10

3D printer

12

working container

14

liquid

16

curing device

18

laser beam

20

pressure part

22

container

24

nanoparticles

26

mixing unit

28

return line

30

induction line

32

magnetization sensor

34

component

36

magnetization range

38

layer

A

axis

A3

Third harmonic amplitude

f

excitation frequency

H

field strength

i

Running index of the nanoparticles

j

Running index of the magnetization areas

k

Running index of the arrows of a magnetization area

my

magnetizability

P

arrow

S

flow direction

θ

angle of rotation

QUOTES INCLUDED IN DESCRIPTION

This list of documents cited by the applicant was 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.

Patent Literature Cited

• WO 9831461 [0051]
• EP 0343934 [0051]
• US4421660 [0051]
• WO 9704862 [0051]
• US4985166 [0051]
• US4452773 [0051]
• US5864025 [0051]
• US 2003/0085703 A1 [0069]
• WO 2011/045721 A1 [0069, 0070]

Claims (12)

3D printing method with the steps: (a) introducing a curable liquid (14) containing ferromagnetic and/or ferrimagnetic nanoparticles (24) into a working container (12), and (b) local curing of the liquid (14) using Radiation, characterized in that (c) the nanoparticles (24) are selected in such a way that the pressure part (20) has an anisotropic magnetizability and has no permanent total magnetic moment to the outside. 3D printing process claim 1 , characterized in that (a) the radiation is light that is concentrated in a curing area, and that (b) the curing area is point, line or area. 3D printing method according to one of the preceding claims, characterized by the steps: (a) introducing the nanoparticles (24) into the curable liquid (14) in a mixing unit (26), (b) conducting the curable liquid (14) into the working container (12) and (c) returning curable liquid (14) from the process vessel (12) to the mixing unit (26). 3D printing method according to one of the preceding claims, characterized in that the nanoparticles (24) (a) have a uniaxial shape anisotropy and/or (b) an ensemble of these has no magnetic remanence. 3D printing method according to one of the preceding claims, characterized in that (a) the nanoparticles (24) have a particle size and at least 90 percent by weight of the nanoparticles (24) are large in at least one dimension between 1 nm and 1000 nm and/or (b ) for at least 90 percent by weight of the nanoparticles (24), an imaginary compensating ellipsoid of revolution has an axis ratio that is between 1.01 and 10, in particular between 1.02 and 2, and/or (c) at least 90 percent by weight of the nanoparticles (24) have an energy barrier less than 25 times the thermal energy in the absence of a magnetic field. 3D printing process according to one of the claims 2 until 5 , characterized by the step of changing an alignment of the curing area over time, so that a preferred direction of magnetizability of the printed part (20) varies according to a predetermined pattern. 3D printing process according to one of the claims 2 until 5 , characterized in that the nanoparticles (24) are formed so that the pressure part (20) has no permanent total magnetic moment to the outside. Measuring method for determining the magnetizability of a printed part (20) containing nanoparticles (24), characterized in that a preferred orientation of the magnetizable part of the printed part (20) is determined. Measuring method according to one of the preceding claims, characterized by the steps: (a) introducing at least one examination area of the pressure part (20) into a measurement area of a sensor, (b) applying an alternating magnetic field in the examination area, (c) measuring the magnetic reaction of the magnetic nanoparticles (24) to the alternating field and (d) determining a preferred orientation of the magnetizability of the examination area by changing an orientation of the measuring field relative to the pressure part (20). 3D printer with (a) a working container (12) for introducing a curable liquid (14) and (b) a curing device (16) for curing the liquid (14) locally, so that a printed part (20) is produced, characterized by (c ) a container with nanoparticles (24) which (i) have a uniaxial shape anisotropy and/or (ii) are designed such that an ensemble of these nanoparticles (24) has no magnetic remanence, (d) a mixing unit (26) for mixing the nanoparticles (24) into the curable liquid (14), and (e) a return line (28) for returning curable liquid (14) from the working vessel (12) or a storage vessel to the mixing unit (26). 3D printer after claim 10 , characterized by a magnetization sensor (32) for measuring the magnetizability of the curable liquid (14). Component (34) made of a polymer which (a) contains nanoparticles (24), (b) has no magnetic remanence and (c) has a plurality of mutually disjoint magnetizability regions, (d) the magnetizability (M _j ) of the magnet izbarkeitsbereiche encodes information about the component (34).

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