Layered soft magnetic composite material, system and device for providing the same

Abstract

A layered soft magnetic composite material comprising iron-containing layers and layers comprising a compound of a non-ferrous metal element, wherein the thickness of the iron layer is 20-200 µm, the thickness of the layers comprising a compound of a non-ferrous metal element is 20-100 µm, and wherein the compound of a non-ferrous metal element is titanium nitride or titanium oxide.

Description

[0001] The invention relates to a soft magnetic composite material with a layered structure, comprising iron-containing layers and inorganic layers with poor electrical conductivity. The invention further relates to a system for producing a layered soft magnetic composite material, comprising the following steps: a) iron in powder form and a non-ferrous metal element are loaded, without mixing, into separate powder containers of a recoater of a 3D printer, wherein the two powders are remotely dispensed from the two containers of the recoater at a predetermined location; b) after software setting of the predetermined layer sequence, the feeder dispenses a predetermined amount of powder of one of the iron or the non-ferrous metal element onto the printing area, which is distributed in a uniform layer by the blade of the recoater of the 3D printer;c) the laser then melts the powder based on the corresponding portion of the 3D model; d) steps b) and c) are repeated according to the layering scheme to obtain a layered composite; and e) if necessary, the resulting layered composite is subjected to a heat treatment to achieve improved electrical insulation. The invention also relates to a recoater for 3D printers, wherein the recoater is configured to dispense at least two different powdered materials. STATE OF THE ART

[0002] The development of highly efficient and energy-saving electronics, such as motors or transformers, as well as the conversion and transmission of electromagnetic energy, is only possible through the use of suitable soft magnetic materials that exhibit advantages such as high saturation magnetization, high magnetic permeability, near-zero magnetostriction, or even low magnetic losses. One possible solution to achieve higher performance is, for example, the manufacture and use of iron cores that operate at higher frequencies. However, when large eddy currents are induced in the iron core, large losses are induced in the higher frequency range (several tens or hundreds of MHz), which are dissipated as heat. This heat causes the organic insulators to decompose, thereby burning the iron core.With appropriate cooling, the operating frequency range of these organic iron cores can be somewhat extended, but a cooling module must be incorporated into the system, which further degrades its power performance. Therefore, the development of inorganic metal-insulator composites should be a key focus. Ferromagnetic layers as thin as possible should be separated by inorganic electrically insulating layers. This should be done in such a way that as much of the total volume as possible is ferromagnetic, thus resulting in a high fill factor, which has a significant impact on the saturation induction. A low ferromagnetic volume fraction results in a low saturation induction, meaning that only a low-performance device can be manufactured with the given iron core.

[0003] In a scientific publication ("Soft magnetic composites prepared by 3D laser printing", Acta Physica Polonic, 137 (2020) 5:886-888), Kocsis et al. describe a soft magnetic iron-iron phosphate composite with a core-shell structure, produced by both conventional powder metallurgy and 3D printing. Comparison of the two composites, prepared by different methods, revealed that it is not possible to simultaneously ensure adequate mechanical strength and electrical insulation properties for this material pair (iron and iron phosphate). The conventionally produced sample is more compact and more resistant to mechanical impacts, but its electrical insulation properties are imperfect, and it cannot be used effectively in the higher frequency range.The eddy current losses of the 3D-printed sample only start to increase in the 10 MHz range, but its mechanical properties, density, and homogeneity are worse than those of the conventionally manufactured sample.

[0004] In another paper ("Metallographic and magnetic analysis of direct laser sintered soft magnetic composites," Journal of Magnetism and Magnetic Materials, 501 (2020) 166425), Kocsis et al. describe a 3D-printed iron-silicon composite. The goal of the publication was to develop a composite in which Si easily diffuses into the Fe layer—further improving magnetic properties (e.g., lower magnetostriction)—and the Si layer, if thick enough, exhibits a quasi-pure Si layer, which, as a semiconductor, would slightly increase the electrical resistance of this layer, thereby reducing the induced eddy currents. However, the results show an almost completely homogeneous iron core made of an Fe-Si alloy with a gradient transition of the Si or Fe content (depending on which content is being investigated) depending on the layer arrangement.Thus, the Si layer also became Fe-Si, drastically reducing the cutoff frequency of the iron core, which was approximately 10 kHz. Microscopic examinations showed that the diffusion movements destroyed the sample and that the originally pure Si layer had no insulating function, meaning the technical goal had not been achieved.

[0005] International patent application WO 2009060895 A1 discloses a high-strength soft magnetic composite material. According to the cited document, the composite material—unlike the composite material according to the present invention—has a core-shell structure and is manufactured by pressing / firing, with the ferromagnetic iron grains surrounded by a magnesium oxide shell.

[0006] International patent application WO 2012115137 A1 also discloses a core-shell composite material. The composite material has low magnetostriction and high magnetic flux density. The composite material contains pure iron-based powder particles and Fe-Si alloy powder particles, with the iron-based powder particles covered with a magnesium- or phosphate-containing film as an insulating layer. According to the cited document, the composite material is produced by pressing and heat treatment in a non-oxidizing atmosphere, with methyl-, methylphenyl-, or phenyl-based silicone resins being added as auxiliaries. During heat treatment, the products of these resins separate the powder particles that form the composite.From the preparation it can be seen that, in contrast to the present invention, organic material is used for separation to separate the ferromagnetic grains from each other and to produce the composite material.

[0007] US Patent No. 6,338,900 B1 discloses a soft magnetic composite material and its production. In the production process, a sintered powder of soft magnetic ferrite (Mg-Zn ferrite) is dispersed in a polymer. The polymer is polyolefin, polyamide, or poly(arylene sulfide). A key feature is that the sintered powder particles have a random shape and a particle size of at least twice the average crystal particle size found in them. The sintered powder is granulated into granules by spray-drying with ferrite powder. The resulting granules are sintered and then ground.

[0008] US Patent No. 9767956 B2 discloses a composite particle having a core made of a soft magnetic metallic material, the core being covered with coating particles made of a different soft magnetic material than the core material to form a so-called fusion-bonded coating. According to the document, the essence of a fusion-bonded coating is that the core and the coating are chemically bonded together by temporarily melting the core and its material under pressure. The core is an Fe-Si-based material, and the coating is pure iron, Fe-B-, Fe-Cr-, or Fe-Ti-based. BRIEF DESCRIPTION OF THE DRAWINGS Fig. 1: A 3D model of the 3D-printed toroidal iron core according to Example 1 (a), the printed toroidal sample (b) and a microscopic image of the Fe-TiN layer change (c). Fig. 2: The graphical result of a scanning electron microscope (SEM) composition analysis along the Fe-Ti layer variation of the 3D-printed toroid according to Example 1. Fig. 3: Magnetic permeability spectrum of the 3D-printed toroid according to Example 1. Fig. 4: CT scan of the 3D-printed toroid according to Example 1 for porosity measurement. Fig. 5: An embodiment of a recoater according to the invention. THE TECHNICAL PROBLEM TO BE SOLVEN BY THE INVENTION

[0009] The technical problem to be solved by the invention is to provide a soft magnetic composite material with the following advantageous properties: (a) it contains ferrous layers and layers of poor electrical conductivity in thicknesses of a few tens of micrometres, between which a chemical bond is formed to provide sufficient mechanical strength; (b) it is more resistant to thermal stresses than state-of-the-art soft magnetic composite materials containing layers of organic insulators; c) it has a high saturation induction and a high cut-off frequency, which ensures a high energy density during operation.

[0010] A high saturation induction is necessary to deliver the correct power. Furthermore, the high operating frequency is required to reduce the size of the iron core and thus ensure better energy balance. DISCOVERY ON WHICH THE INVENTION IS BASED

[0011] To achieve these goals, we conducted systematic experimental work that led to our invention. During our experiments, we were surprised that we were able to achieve the technical goal we had set for ourselves. a) when soft magnetic composite materials with a layered structure are provided by 3D printing to ensure the thinnest possible ferromagnetic layers (Fe layer thickness: 20-200 µm, thickness of the poorly conductive layer: 20-100 µm); b) if the ferromagnetic layers in this laminated composite are separated by inorganic layers with poor electrical conductivity; and c) when said layered composite is provided from iron and another metallic element, the other metallic element being selected according to the following properties (i) have a sufficiently low diffusion rate so that the iron and the other metallic element are not completely mixed during the printing process; and (ii) be capable of forming a strong cohesive bond with the iron layer, thus ensuring adequate mechanical properties of the final product; and (iii) the electrical resistance of the other metallic element may be increased by a chemical or thermal treatment (e.g. nitriding or oxidation), i.e. to form a poorly conductive layer, simultaneously with or after the provision of the composite. BRIEF DESCRIPTION OF THE INVENTION 1. A layered soft magnetic composite material comprising iron-containing layers and layers comprising a compound of a non-ferrous metal element, wherein the thickness of the iron layer is 20-200 µm, the thickness of the layer comprising a compound of a non-ferrous metal element is 20-100 µm, and wherein the compound of a non-ferrous metal element is titanium nitride or titanium oxide. 2. The soft magnetic composite material according to item 1, wherein the ferrous layers and the layers comprising a compound of a non-ferrous metal element are arranged alternately, the number of the ferrous layers being 1-10 and the number of layers comprising a compound of a non-ferrous metal element being 1-10, and the thickness of the layers being about 20-40 µm. 3. The soft magnetic composite material according to any one of items 1 to 2, wherein the iron and the non-ferrous metal element have a volume ratio of 1:2 to 10:1. 4. A soft magnetic composite material according to any one of items 1 to 2, wherein the volume ratio of iron to non-ferrous metal element is 1:1 to 1:2. 5. A system for providing a layered soft magnetic composite material, the system comprising: a) Iron in powder form and a metallic element other than iron are filled, without mixing them, into 1-1 separate containers of a recoater of a 3D printer, whereby the two powders can be dispensed from the two containers of the recoater; b) the stratification scheme is determined, c) according to the layering scheme, a predetermined amount of powder of one of the ferrous or non-ferrous metal elements is introduced into the printing area by the feeding device and distributed in a uniform layer by the blade of the recoater of the 3D printer; d) the laser melts the powder; and e) steps c) and d) are repeated one or more times, preferably up to 20 times, to obtain a layered composite material; and f) optionally, the resulting layered composite material is heat treated to achieve better electrical insulation. 6. System according to point 5, wherein the 3D printing is carried out under a protective gas atmosphere, preferably nitrogen or argon. 7. System according to item 5, where titanium is used as a metallic element other than iron. 8. The system according to any one of items 5 to 7, wherein the layering scheme is such that the iron powder and the non-iron metallic element in powder form are alternately fed into the printing area by the recoater. 9. System according to any of items 5 to 8, wherein the parameters used in 3D printing are the following: layer thickness: 20 µm, laser beam wavelength: 1016 nm, scanning speed: 500-1000 mm / s, laser power: 110-185 W, table temperature: 40-100 °C, scanning strategy: 60° rotation per layer. 10. The system according to any one of items 5 to 9, wherein the heat treatment is carried out in an oxygen-rich environment with a heat treatment time of 0.5 to 20 hours at a temperature of 500 to 850 °C. 11. Apparatus comprising a powder dispensing adapter, the powder dispensing adapter being adapted to dispense at least two different raw materials in powder form, the powder dispensing adapter comprising two separate powder containers 4 and a housing 5 for receiving them; the two powder containers 4 containing the raw materials 6 in powder form being contained in the housing 5, as well as the fastening, bearings and seals 7 of the splined shafts 8 and the electric motors responsible for driving them; an adapter according to the invention is mounted on the original recoater mechanism of the laser sintering machine, as well as sensors 10 for distance measurement connected to a computer 1 by means of a vacuum-tight (gas-tight) cable outlet, the power supply 9 for the electric motors and the ultrasonic sensors 10 also being introduced by means of a vacuum-tight cable outlet; and the component 11 is printed on the work surface 12. DETAILED DESCRIPTION OF THE INVENTION

[0012] In the context of the invention, “a printing cycle” means the entire printing process from the laser sintering of the first layer of the 3D model of the part to be manufactured to the last layer.

[0013] In implementing our invention, we discarded the possibility of using ceramic or other inorganic materials in the design of the layered composite. The disadvantage of organic insulating layers (decomposition of organic insulating materials under thermal stress) was already mentioned above. Printing ceramics requires a laser source with a wavelength of approximately 10 µm, while melting metal requires a wavelength of 1 µm. This is only possible if two different laser sources (e.g., a solid-state laser and a CO2 laser) are used. However, there is no commercially available equipment for this. Furthermore, building such a system would be quite expensive and time-consuming. Another question is how the ceramic layer will behave under the enormous internal stresses that would arise during printing.Therefore, in the implementation of our invention, we came to the discovery that we print iron and another metallic element, where the diffusion rate of the other metallic element is low, so that the iron and the other metallic element are not completely mixed during the printing process, but at the same time a strong cohesive bond is formed between them, which gives the final product good mechanical properties.

[0014] We also recognized that the second metallic element, which is not iron, must be chosen so that its electrical resistance can be increased by a chemical or thermal treatment (such as nitriding or oxidation) simultaneously with or after printing.

[0015] In view of the foregoing, examples of metallic elements other than iron that can be used in providing the composite material of the invention include, without limitation, titanium, aluminum, nickel, cobalt, chromium.

[0016] For example, titanium is highly susceptible to oxidation, more so than iron. When melted in a nitrogen atmosphere, it undergoes nitriding. Since the EOSINT M270 fixture we used used nitrogen as a standard shielding gas, the Ti layer that was melted was always nitrided during the printing process. The preparation and properties of the resulting Fe-TiN composite are described in Example 1.

[0017] In another embodiment, the 3D printer is modified so that an argon cylinder is connected to the machine instead of a nitrogen generator, and printing takes place under argon inert gas. Thus, at the end of the printing process, pure Ti and Fe, or a mixed phase of the two elements, are present at the interface. Ti is then oxidized by annealing in an oxygen-rich environment to obtain TiO, which has a higher electrical resistance than titanium nitride (see Example 2).

[0018] Based on the above statements, the invention is a soft magnetic composite material with a layered structure comprising iron-containing layers and inorganic layers with poor electrical conductivity.

[0019] In one embodiment of the composite material according to the invention, the thickness of the iron layer is 20-200 µm, while the thickness of the layer having poor electrical conductivity is 20-100 µm.

[0020] In a preferred embodiment of the composite material according to the invention, the iron-containing layers and the inorganic layers with poor electrical conductivity are arranged alternately, the number of iron-containing layers being 1-10 and the number of electrically poorly conducting layers being 1-10 and the thickness of the layers being about 20 µm.

[0021] In a preferred embodiment of the composite material according to the invention, the inorganic layers with poor electrical conductivity comprise a compound of the metallic element other than iron, wherein the metallic element is preferably titanium and the compound of the metallic element is titanium nitride or titanium oxide.

[0022] In one embodiment of the composite material according to the invention, the volume ratio between the iron and the non-ferrous metal element is 1:2-10:1.

[0023] In a preferred embodiment of the system according to the invention, the volume ratio between the iron and the non-ferrous metal element is 1:1-1:2.

[0024] The invention also relates to a system for providing a layered soft magnetic composite material, comprising the following steps: a) Iron in powder form and a metallic element other than iron are loaded - without mixing them - into 1-1 separate containers of a recoater of a 3D printer, whereby the two powders can be dispensed from the two containers remotely at a specific location; b) after the software setting of the specified layering scheme, a predetermined amount of powder of one of the ferrous or non-ferrous metal elements is dispensed onto the printing area by the feeding device and distributed in a uniform layer by the blade of the recoater of the 3D printer; c) the laser then melts the powder based on the corresponding section of the 3D model; and d) steps b) and c) are repeated according to the layering scheme s to obtain a layered composite material; and e) optionally, the resulting composite material is heat treated to achieve better electrical insulation.

[0025] In one embodiment of the system according to the invention, a protective gas is used during 3D printing. Examples of the protective gases mentioned above are nitrogen and argon.

[0026] In a preferred embodiment of the system according to the invention, the non-iron metallic element is titanium. In a preferred embodiment, the layering scheme is such that the iron powder and the non-iron metallic element are alternately introduced into the printing area in powder form by the recoater.

[0027] In one embodiment of the system according to the invention, the following parameters are used for 3D printing: layer thickness: 20 µm, wavelength of the laser beam: 1016 nm, scanning speed: 500-1000 mm / s, laser power: 110-185 W, table temperature: 40-100 °C, scanning strategy: 60° rotation per layer.

[0028] In one embodiment of the system according to the invention, the heat treatment is carried out in an oxygen-rich environment within 1 hour, keeping the temperature at 500-850 °C.

[0029] The invention also relates to a layered soft magnetic composite material comprising iron-containing layers and the inorganic layers with poor electrical conductivity, wherein the composite material can be obtained according to the system according to the invention.

[0030] The invention also relates to a device comprising a recoater, wherein the recoater is arranged so that at least two different raw materials can be dispensed in powder form.

[0031] In one embodiment (see Fig. 5) The recoater consists of two separate powder containers 4 and housings 5 for their mounting. Various raw materials 6 in powder form were filled into the two 4 powder containers. The housings 5 are used to mount the splined shafts 8, their bearings, seals 7, and the electric motors that drive them. The inventive adapter was mounted on the original mechanism of the laser sintering recoater units 2, as well as ultrasonic sensors 10 for distance measurement. These allow us to control the location where our customized recoater system should start dispensing the powder. The ultrasonic sensors 10 were connected to a computer 1 via a vacuum-tight cable outlet. A gas-tight connection solution is essential to prevent an increase in the oxygen concentration in the printing work spaces 3.This connector is also used to connect the power supply 9 for the electric motors and the ultrasonic sensors 10. In each case, the parts 11 are printed on a pre-printed worksheet 12.

[0032] In the following, the invention is explained using exemplary embodiments which are not to be understood as limitations of the invention. EXAMPLESExample 1: Preparation of a Fe-TiN composite

[0033] In this embodiment, the provision of the Fe-TiN composite and its properties are described.

[0034] The sample composite was produced using an EOSINT M270 3D printer equipped with a custom-built recoater that, when mounted on the 3D printer's recoater unit, could process two different materials (in this case, high-purity elemental iron powder and titanium powder) within a single print cycle. Production parameters are: The volume ratio of iron to titanium: 1:2 The average particle size of the raw material powder is 50 µm. Number of layers formed: Fe: 5 layers, TiN: 10 layers.

[0035] The essential parameters of printing are: - Shielding gas: nitrogen, - Layer thickness: 20 µm, - Wavelength of the laser beam: 1016 nm, - Scanning speed: 800 mm / s, - Temperature of the build platform: 100 °C.

[0036] Scanning electron microscopy (SEM) line analyses were performed to visualize the individual Fe-TiN layers. It was demonstrated that there is an intersection point in the Ti layer where almost 0 wt% iron is present. This means that, with proper nitriding (or oxidation), the insulating function is expected to function.

[0037] Fig. Figure 1 shows the 3D model of the 3D-printed toroidal iron core (a), the printed toroidal sample (b) and a microscopic image of the Fe-TiN layer change (c).

[0038] Fig. Figure 2 shows the results of the composition analysis of the 3D-printed toroid using a scanning electron microscope (SEM) along a Fe-Ti layer change.

[0039] The permeability spectrum of the 3D-printed sample was investigated. The measurement results are shown in Fig. 3. In addition, Fig. 4 the CT scan for porosity measurement can be seen.

[0040] After the measurement, the printed sample was placed in an oven at 500 °C in an air atmosphere for 1 hour to test the oxidation behavior of nitrided titanium. This experiment did not result in a significant change in the magnetic properties (see Fig. 3). Fig.Figure 3 shows the real (µ') and imaginary (µ'') parts of the magnetic permeability spectrum. The frequency limit of the iron core lies where the maximum of the imaginary part (µ'') is found. In the present case, it can be seen that TiN insulates the Fe layers much better than Si in the case of the prior art Fe-Si composite. The frequency limit in the composite of the present example is in the range of 40 MHz, compared to the range of 10 MHz in the prior art. Eddy current losses in the inventive composite increase significantly at much higher frequencies. Example 2: Preparation of a Fe-TiO composite

[0041] Everything was performed as described in Example 1, except that printing was performed under argon inert gas, ensuring that the final product was pure Ti and Fe and that the interface between the two elements was a mixed phase of the two elements. After printing, Ti is subsequently oxidized by annealing in an oxygen-rich environment to obtain TiO, which has a higher electrical resistance than titanium nitride. The heat treatment was carried out at 500°C in an air atmosphere for various times (1, 4, 8, and 12 hours). The sample was placed in a 500°C furnace and cooled in air after the heat treatment. INDUSTRIAL APPLICABILITY

[0042] The invention provides soft magnetic composite materials with a layered structure that can be used in the construction of highly efficient and energy-saving electronic devices, such as motors or transformers. These composite materials are more resistant to thermal stress than the soft magnetic composite materials (e.g., composites of ferromagnetic layers impregnated with polymer resins) known from the prior art. QUOTES CONTAINED IN THE DESCRIPTION

[0000] This list of documents submitted by the applicant was generated automatically and is included solely for the convenience of the reader. This 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

[0000] WO 2009060895 A1

[0005] WO 2012115137 A1

[0006] US 6338900 B1

[0007] US 9767956 B2

[0008] Zitierte Nicht-Patentliteratur

[0000] Soft magnetic composites prepared by 3D laser printing“, Acta Physica Polonic, 137 (2020) 5:886-888

[0003] Metallographic and magnetic analysis of direct laser sintered soft magnetic composites“, Journal of Magnetism and Magnetic Materials, 501 (2020) 166425)

[0004]

Claims

[1] A layered soft magnetic composite material comprising iron-containing layers and layers comprising a compound of a non-ferrous metal element, wherein the thickness of the iron layer is 20-200 µm, the thickness of the layers comprising a compound of a non-ferrous metal element is 20-100 µm, and wherein the compound of a non-ferrous metal element is titanium nitride or titanium oxide. [2] A soft magnetic composite material according to claim 1, wherein the iron-containing layers and the layers comprising a compound of a non-ferrous metal element are arranged alternately, the number of the iron-containing layers being 1-10 and the number of the layers comprising a compound of a non-ferrous metal element being 1-10, and the thickness of the layers being about 20-40 µm. [3] A soft magnetic composite according to any one of claims 1 to 2, wherein the iron and the non-ferrous metal element have a volume ratio of 1:2 to 10:

1. [4] A soft magnetic composite material according to any one of claims 1 to 2, wherein the volume ratio of iron to non-ferrous metal element is 1:1 to 1:

2. [5] System for providing a layered soft magnetic composite material, characterized by that it includes the following steps: a) Iron in powder form and a metallic element other than iron are filled, without mixing them, into 1-1 separate containers of a recoater of a 3D printer, whereby the two powders can be dispensed from the two containers of the recoater; b) the stratification scheme is determined, c) according to the layering scheme, a predetermined amount of powder of one of the ferrous or non-ferrous metal elements is introduced into the printing area by the feeding device and distributed in a uniform layer by the blade of the recoater of the 3D printer; d) the laser melts the powder; and e) steps c) and d) are repeated one or more times, preferably up to 20 times, to obtain a layered composite material; and f) optionally, the resulting layered composite is heat treated to achieve better electrical insulation. [6] System according to claim 5, characterized by that the 3D printing is carried out using a protective gas atmosphere, preferably nitrogen or argon. [7] System according to claim 5, characterized by that titanium is used as a metallic element other than iron. [8] System according to one of claims 5 to 7, characterized by that the layering scheme is as follows: The iron powder and the non-iron metallic element in powder form are alternately fed to the printing area by the recoater. [9] System according to one of claims 5 to 8, characterized by that the parameters used in 3D printing are the following: layer thickness: 20 µm, laser beam wavelength: 1016 nm, scanning speed: 500-1000 mm / s, laser power: 110-185 W, table temperature: 40-100 °C, scanning strategy: 60° rotation per layer. [10] System according to one of claims 5 to 9, characterized by that the heat treatment is carried out in an oxygen-rich environment with a heat treatment time of 0.5 to 20 hours at a temperature of 500 to 850 °C. [11] Device comprising a recoater, the recoater being adapted to dispense at least two different raw materials in powder form, the recoater comprising two separate powder containers (4) and a housing (5) for receiving them; the two powder containers (4) containing the powdered raw materials (6) contained in the housing (5), as well as the fastening, bearings and sealing (7) of the splined shafts (8) and the electric motors responsible for driving them;an adapter according to the invention is mounted on the original recoating mechanism (2) of the laser sintering machine, as well as sensors (10) for distance detection, which are connected to a computer (1) via a vacuum-tight (gas-tight) cable outlet, wherein the power supply (9) for the electric motors and the ultrasonic sensors (10) is also introduced by means of a vacuum-tight (gas-tight) cable outlet, and the component (11) is printed onto the work surface (12);

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