EP3650238A1 - Method for marking workpieces and workpiece - Google Patents

Abstract

In one embodiment, the method is used for marking metallic workpieces (1) which are subsequently hot-formed, and comprises the following steps: A) providing the at least one workpiece (1), B) locally applying an ink (20) for a marking ( 2) on the workpiece (1), C) fixing the ink (20) to the marking (2), the workpiece (1) being heated locally in an area (3) with the marking (2) and when fixing on the Ink (20) a temperature of at least 400 ° C is applied.

Description

A method for marking workpieces is specified.

From the publication EP 3 109 058 A2 A method is known in which a marking is made on a workpiece by means of a laser and by means of a phosphor.

In the publication DE 10 2015 107 744 B3 there is a marking process for workpieces that are hot formed.

One task to be solved is to specify a method with which a workpiece can be efficiently and permanently connected with a temperature-stable marking.

This object is achieved, inter alia, by a method and by a workpiece with the features of the independent claims. Preferred developments are the subject of the dependent claims.

According to at least one embodiment, the method is used to apply a marking to a workpiece. With the marking it is preferably possible to uniquely identify the workpiece. The marking is, for example, a lettering, a number, an identification, a bar code or a matrix code, for example a data matrix code, for short DMC, or a QR code. The marking is preferably machine-readable.

In accordance with at least one embodiment, the method comprises the step of providing the at least one workpiece. The workpiece can be a blank. The blank is, for example, a metal sheet and / or a piece of metal to be processed, such as a cast part.

In accordance with at least one embodiment, the method comprises the step of applying at least one ink for a marking to the workpiece. It is possible that multi-colored markings should be created and that accordingly several different inks can be used. Only exactly one ink is preferably used.

In accordance with at least one embodiment, the ink is applied only locally. In particular, the ink is only applied to the workpiece where the ink is actually required for the marking. Subsequent removal of material colored in relation to the workpiece from the ink can thus be avoided.

In accordance with at least one embodiment, the method comprises the step of fixing the ink to the marking. When fixing, the ink is preferably brought briefly to a temperature of at least 400 ° C or at least 500 ° C or at least 600 ° C. Alternatively or additionally, this temperature is at most 1200 ° C or at most 1000 ° C or at most 950 ° C. The components of the ink forming the marking are firmly connected to the workpiece by the action of temperature.

It is possible that not all components of the originally applied ink are present when fixing. For example, the ink can be pre-dried when it is fixed, for example by evaporating a solvent. With such an optional predrying, it is particularly preferred if there is no or no pronounced temperature treatment. This means that predrying can take place at temperatures below 150 ° C. or below 100 ° C., preferably at room temperature, that is to say approximately 25 ° C.

According to at least one embodiment, the workpiece is heated locally or only locally in an area with the marking during the fixing. Other areas of the workpiece are then not or not significantly affected by the temperature effect when fixing. In particular, non-significant means that the workpiece's mechanical, optical or functional properties do not change in a process-relevant manner. If heating is generally only local, for example for hot forming, then the area of the marking is also preferably heated. This means that there can then be several local temperature entries laterally and / or temporally.

1. A) Bereitstellen des mindestens einen Werkstücks,
2. B) lokales Aufbringen einer Tinte für eine Markierung (2) auf das Werkstück,
3. C) Fixieren der Tinte zu der Markierung, wobei das Werkstück lokal, insbesondere nur lokal, in einem Bereich mit der Markierung erhitzt wird und beim Fixieren an der Tinte eine Temperatur von mindestens 400 °C appliziert wird.

In at least one embodiment, the method serves to mark preferably metallic workpieces, which can subsequently be hot-formed, and comprises the following steps, in particular in the order given:

1. A) providing the at least one workpiece,
2. B) locally applying an ink for a marking (2) to the workpiece,
3. C) Fixing the ink to the mark, taking the workpiece locally, in particular only locally, is heated in an area with the marking and a temperature of at least 400 ° C. is applied when fixed to the ink.

With the method described here, it is possible to preferably permanently label and / or print on products and objects, including for their identification.

When applying pigmented inks, a fixing process can be carried out in two steps: First, there is drying, that is, the removal of water and / or organic solvents. This step is typically done at room temperature. This is followed by firing and / or sintering for compaction, for solidification and / or for contrast enhancement and / or long-term fixation of the marking at high temperatures of, for example, at least 250 ° C. or 400 ° C. A substrate material of the workpiece and ink pigments are integrally bonded by this temperature effect. In addition, the sintering of the ceramic pigments, in particular, and / or the adhesion promoter, which is preferably likewise based on a glass, a ceramic or a glass ceramic, is preferably carried out.

In metal processing in particular, the entire component has been heated up to now, which leads to relatively high energy costs and stresses the component. For this purpose, fixing is usually carried out in an oven environment that is either only used for this purpose or that primarily serves another purpose and can also fix the marking in parallel. If an oven is used for a main purpose other than to fix the marking, you have to rely on a position of the printer on or near the oven when printing the marking, or the marking must be so firmly connected to the component that it is already unburned the marking is not lost or damaged by handling the workpiece and other work steps. This reduces the flexibility of the possible uses and / or prevents relevant areas of the process chain from being identified using the marking.

In the method described here, on the other hand, only the, for example, printed area for the marking for sintering pigments and / or the adhesion promoter is locally heated. This local heating takes place, for example, by means of a laser, by means of induction, by means of an electrical resistance, electrodes being attached to the workpiece, or by means of high-energy light pulses. Alternatively, a process can also be used which leads to local heating and primarily serves another purpose, for example local heating for forming the workpiece.

The information of the marking, which is carried by the inorganic adhesion promoter and the pigments in the form of a pre-structured marking and which is preferably applied by means of inkjet printing, is thus firmly connected to the workpiece or component in the method described here by local heating.

With the method described here, there is in particular a direct fixation of the marking and thus its application possible along the entire process chain that the workpiece has to go through. Energy savings and cost savings are possible compared to operating a separate furnace. The workpiece is also protected. A simpler ink, which is therefore easier to process and less expensive, can be used, since organic binders, in particular in the finished marking, can be dispensed with. Furthermore, an improved integration of the marking in metal processing processes can be achieved.

The described method and the marking generated with it can be used, for example, in the fields of application of direct part marking of metallic components, sheet metal forming, hot soldering and / or in metal casting.

In accordance with at least one embodiment, the ink additionally comprises an inorganic binder, which is preferably also contained in the finished marking. The inorganic binder is preferably present in the form of particles in the ink. An average particle diameter of the particles of the binder in the ink is preferably at least 10 nm or at least 0.1 µm or at least 0.2 µm and / or at most 0.1 mm or at most 50 µm or at most 10 µm.

In at least one embodiment, the ink contains ceramic pigments. The ceramic pigments preferably give the coloring and / or a contrast of the marking to the workpiece. The term "ceramic pigments" includes glass ceramics that have amorphous and crystalline sub-areas. It is possible that such a glass ceramic only forms when it is fixed in place, such a glass ceramic then being preferred consists of the binder and the ceramic pigments.

For example, the ceramic pigments and / or the finished marking are made from one or more of the following materials: oxides such as BeO, MgO, Al ₂ O ₃ , SiO ₂ , CaO, TiO ₂ , Cr ₂ O ₃ , MnO, Fe ₂ O ₃ , ZnO, SrO, Y ₂ O ₃ , BaO, CeO ₂ , UO ₂ ; Carbides such as Be ₂ C, Be ₄ C, Al ₄ C ₃ , SiC, TiC, Cr ₃ C ₂ , Mn ₃ C, Fe ₃ C, SrC ₂ , YC ₂ , ZrC, NbC, Mo ₂ C, BaC ₂ , CeC ₂ , HfC, TaC, WC, UC; Nitrides such as Be ₃ N ₂ , BN, Mg ₃ N ₂ , AlN, Si ₃ N ₄ , Ca ₃ N ₂ , TiN, VN, CrN, Mn ₃ N ₂ , Sr ₃ N ₂ , ZrN, NbN, Mo ₃ N ₂ , HfN, TaN, WN ₂ , UN; Borides such as AlB ₄ , CaB ₆ , TiB ₂ , VB2, CrB ₂ , MnB, FeB, CoB, NiB, SrB ₆ , YB ₆ , ZrB ₂ , NbB ₂ , MoB ₂ , BaB ₆ , LaB ₆ , CoB ₆ , HfB ₂ , TaB ₂ , WB; Silicides such as CaSi, Ti5Si3, V ₅ Si ₃ , CrSi ₂ , FeSi, CoSi, ZrSi ₂ , NbSi ₂ , MoSi ₂ , TaSi ₂ , WSi ₂ . Also oxidic glasses, such as silicate or borate glasses, as well as multi-phase materials, such as Al ₆ Si ₂ O ₁₃ , or mixed crystals such as those from the Al ₂ O ₃ -Cr ₂ O ₃ , MgSiO ₄ , CaSiO ₄ , ZrSiO ₄ , MgAl ₂ O _{4 system} , CaZrO ₃ , SiAlON, AlON and / or B ₄ C-TiB ₂ can be used. It is also possible to use ceramic pigments with a non-stoichiometric composition.

• lila Pigmente wie BaCuSi₂O₆, Kobalt-Orthophosphate wie NH₄MnP₂O₇,
• blaue Pigmente wie schwefelhaltiges Sodiosilikat Na_8-10Al₆Si₆O₂₄S_2-4, (Na,Ca)₈(AlSiO₄)₆(S,SO₄,Cl)_1-2, Kobalt(II)stannat, CaCuSi₄O₁₀, BaCuSi₄O₁₀, Cu₃(CO₃)₂(OH)₂, Fe₇(CN)₁₈, YIn_1-xMn_xO₃,
• grüne Pigmente wie CdS in Kombination mit Cr₂O₃, (Cr₂O₃·H₂O), CoZnO₂, Cu₂CO₃(OH)₂, CuHAsO₃ oder K[(Al,FeIII),(FeII,Mg)](AlSi₃,Si₄)O₁₀(OH)₂,
• Gelbpigmente wie As₂S₃, BiVO₄, PbCrO₄, K₃Co(NO₂)₆, Fe₂O₃·H₂O, PbSnO₄, Pb(Sn,Si)O₃, SnS₂, Cadmiumsulfoselenid, PbCrO₄ + PbO,
• rote Pigmente wie As₄S₄, Cd₂SSe, Pb₃O₄, HgS,
• schwarze Pigmente wie Fe₃O₄, MnO₂, Ti₂O₃.

For example, one or more of the following materials are used for the ceramic pigments, alone or in combination:

• purple pigments such as BaCuSi ₂ O ₆ , cobalt orthophosphates such as NH ₄ MnP ₂ O ₇ ,
• blue pigments such as sulfur-containing sodiosilicate Na _8-10 Al ₆ Si ₆ O ₂₄ S _2-4 , (Na, Ca) ₈ (AlSiO ₄ ) ₆ (S, SO ₄ , Cl) _1-2 , Cobalt (II) stannate, CaCuSi ₄ O ₁₀ , BaCuSi ₄ O ₁₀ , Cu ₃ (CO ₃ ) ₂ (OH) ₂ , Fe ₇ (CN) ₁₈ , YIn _1-x Mn _x O ₃ ,
• green pigments such as CdS in combination with Cr ₂ O ₃ , (Cr ₂ O ₃ .H ₂ O), CoZnO ₂ , Cu ₂ CO ₃ (OH) ₂ , CuHAsO ₃ or K [(Al, FeIII), (FeII, Mg )] (AlSi ₃ , Si ₄ ) O ₁₀ (OH) ₂ ,
• Yellow pigments such as As ₂ S ₃ , BiVO ₄ , PbCrO ₄ , K ₃ Co (NO ₂ ) ₆ , Fe ₂ O ₃ .H ₂ O, PbSnO ₄ , Pb (Sn, Si) O ₃ , SnS ₂ , cadmium sulfoselenide, PbCrO ₄ + PbO,
• red pigments such as As ₄ S ₄ , Cd ₂ SSe, Pb ₃ O ₄ , HgS,
• black pigments such as Fe ₃ O ₄ , MnO ₂ , Ti ₂ O ₃ .

According to at least one embodiment, an average particle diameter of the ceramic pigments in the ink and / or in the finished marking is at least 10 nm or at least 50 nm or at least 0.1 μm and / or at most 30 μm or at most 5 μm or at most 500 nm or at most 200 nm. The term “average diameter” preferably refers to a D50 value, that is to say to a median value. It is possible that the average diameter of the ceramic pigments in the ink is larger or smaller than the average diameter of the particles of the binder, for example by at least a factor of 2.

According to at least one embodiment, the marking has at least in a part of the near ultraviolet, the visible and / or the near-infrared spectral range, both with respect to the workpiece, a difference in reflectance and / or a difference in reflectance and / or an albedo difference of at least 15 percentage points or 25 percentage points or 40 percentage points . This difference is due to, for example, a color of the ceramic pigments and / or a difference in refractive index and / or a material-specific absorption difference and / or difference in emissivity of the ceramic pigments, in particular, to an environment of the pigments.

In other words, the marking can be clearly distinguished from a surface of the workpiece due to its optical properties, for example by a camera or by the human eye. In other words, the marking has a high contrast to a surface of the workpiece, at least under suitable lighting conditions that can be used to read out the marking. The near ultraviolet spectral range is understood to mean in particular the range from 300 nm to 420 nm, the visible spectral range denotes wavelengths from 420 nm to 760 nm and the near infrared spectral range is wavelengths from 760 nm to 1500 nm.

Optical filters can be used to read out the marking, for example blocking an excitation wavelength of a phosphor, so that then only the radiation generated by the phosphor due to the excitation is detected. In particular, the marking with regard to contrast and / or a difference in brightness meets the current standard ISO / IEC 15415, which is required for directly marked components.

In accordance with at least one embodiment, the ceramic pigments are made of Al ₂ O ₃ , TiO ₂ and / or ZrO ₂ . The binder preferably comprises SiO ₂ as the main component.

According to at least one embodiment, in step C) the temperature is at least 400 ° C. for at most 1 min or for applied for a maximum of 0.5 min or for a maximum of 10 s or for a maximum of 1 s. This means in particular that an energy source for reaching the relevant temperature in step C) is active on the ink and / or on the marking for a maximum of the stated time period.

In accordance with at least one embodiment, the workpiece is a metal sheet, such as an iron sheet or a steel sheet. A thickness of the metal sheet is, for example, at least 0.1 mm or 0.3 mm or 0.5 mm and / or at most 8 mm or 5 mm or 3 mm. The metal sheet can have a constant thickness or can also vary in thickness.

According to at least one embodiment, after step C), the workpiece is subjected to hot forming in a step D), for example pressing or deep drawing, for example of stamped, planar sheets at a forming temperature. In the case of steel sheets or iron sheets in particular, the deformation temperature is preferably at least 700 ° C. or at least 800 ° C. or at least 880 ° C. Alternatively or additionally, the deformation temperature is at most 1100 ° C or at most 1000 ° C or at most 950 ° C. In particular, the deformation temperature is approximately 920 ° C. The marking is preferably fixed at a temperature below the deformation temperature, for example at least 200 ° C. below the deformation temperature.

According to at least one embodiment, the workpiece has a protective layer against scaling. The anti-scaling layer is designed to prevent oxidation of the metal sheet, in particular in the area of Prevent or slow down deformation temperature in an oxygen-containing atmosphere.

In accordance with at least one embodiment, the scale protection layer comprises or consists of aluminum, silicon, zinc and / or at least one metal oxide. For example, the anti-scaling layer is a layer made by hot-dip galvanizing or a layer made of an aluminum-silicon alloy. Protective layers made of or with metal oxides such as aluminum oxide can also be used. The scaling protection layer can also be a protective layer with particles on the nanometer scale, for example an x-tec coating from the manufacturer NANO-X GmbH. A thickness of the anti-scaling layer is, for example, at least 100 nm or 250 nm or 1 µm and / or at most 30 µm or 10 µm or 2 µm. A preferred composition of the anti-scaling layer is: 87% Al, 10% Si and 3% Fe. The preferred thickness of the anti-scaling layer is between 1 µm and 40 µm.

According to at least one embodiment, the marking is generated directly on the anti-scaling layer. This means that the ink can be printed on the anti-scaling layer. Alternatively, the ink is applied directly to the metal sheet.

In accordance with at least one embodiment, the marking can still be read, in particular machine-readable, even after step D). That means that the hot forming does not destroy the marking. However, it is possible, albeit not preferred that the area with the marking changes its shape during hot forming.

According to at least one embodiment, fixing in step C) is carried out by means of a radiation flash. Radiation of the radiation flash is absorbed in the ink and / or on a workpiece surface. This applies the temperature for fixing. The flash of radiation can be short and last, for example, for a maximum of 1 s or 0.1 s or 0.01 s. The radiation flash is preferably incoherent radiation, but alternatively coherent radiation, that is to say laser radiation, can also be used.

In accordance with at least one embodiment, the radiation from the radiation flash is predominantly ultraviolet radiation. In this case, a wavelength of maximum intensity of the radiation flash is preferably between 250 nm and 370 nm inclusive. Alternatively, infrared radiation can be used, in particular with a wavelength of maximum intensity between 1 µm and 2 µm. It is possible that a component is added to the ink that specifically absorbs the radiation. This component can also be realized by the ceramic pigments and / or by the inorganic binder.

According to at least one embodiment, fixing in step C) takes place by means of electrical and / or magnetic fields. For example, the heating takes place inductively, in particular via alternating magnetic fields, which can generate eddy currents locally in the area of the marking. The heating can be carried out without contact. Alternatively, a current can be impressed directly via an electrical contact for heating.

According to at least one embodiment, the ink in step B) comprises at least one organic binder. With this binder it can be achieved that the ink is already wipe-proof on the workpiece before step C). The organic binder is, for example, an acrylic-based material. The binder therefore acts as a kind of adhesive for the ceramic pigments and the particles of the inorganic binder until the fixing takes place at high temperatures. After fixing, the organic binder is preferably no longer present or at least has no function.

In accordance with at least one embodiment, the ink in step B) comprises at least one solvent, in particular water or an organic solvent such as an alcohol. The ink can be dried by evaporating the solvent. For example, drying such that the ink becomes smudge-proof.

In addition, the ink can have a dispersant and / or a plasticizer. The ink can also be designed as a paste, for example as in the publication DE 602 18 966 T2 described. The disclosure content of this document with regard to the ink is included by reference.

The dried ink preferably consists of the organic binder, the ceramic pigments and the inorganic binder. The finished marking preferably consists of the ceramic pigments and the inorganic binder, whereby these can be fused or sintered to form a ceramic or a glass ceramic.

According to at least one embodiment, the ink consists of the solvent, the ceramic pigments and the inorganic binder and the dried ink and the fixed marking consist of the ceramic pigments and the inorganic binder. If the ink is free of an organic binder, the marking is less influenced when it is fixed, for example by decomposing the organic binder and / or by outgassing components of the possibly decomposed organic binder, whereby bubbles can form. Inks without organic binders can also be produced more cheaply.

According to at least one embodiment, a form of the marking is already defined in step B). This means that in step C) no material is removed from the preferably dried ink or from the marking with which an information content of the marking is changed. The marking with regard to its information content is thus complete immediately after step B).

In accordance with at least one embodiment, the area with the marking which is heated in step C) during fixing has at most three times the size of the marking itself. This means that the marking and the heated area are approximately the same size.

According to at least one embodiment, the area with the marking makes up at most 2% or at most 10% of the workpiece. The marking is therefore relatively small compared to the entire workpiece.

According to at least one embodiment, the marking is at least in the area with the marking above Raised metal sheet of the workpiece. This means that the marking can be a relief that rises from the workpiece.

According to at least one embodiment, the marking is planarized in a step E) after step C), preferably also after step D). This planarization takes place, for example, by painting with a paint. Such a lacquer can be applied continuously over the marking. The lacquer can be transparent to radiation used to read the marking. Alternatively or additionally, the lacquer is at least impervious to visible light. If, for example, the marking is intended to be read out in the infrared spectral range, the lacquer in the relevant spectral range can be permeable.

According to at least one embodiment, fixing to the marking C) is carried out with a separate heating means. This means that the heat source for applying the elevated temperature is only used for fixing and not for other process steps when machining the workpiece. Alternatively, a tool, such as a forming tool, can be used as the heat source for fixing, with which other process steps can also be carried out. In the latter case, the fixing to the marking is preferably carried out simultaneously, that is to say simultaneously, with a further process step.

In accordance with at least one embodiment, the ink and the marking comprise at least one phosphor. A contrast between the marking and the workpiece can be increased by the at least one phosphor. In particular, the ceramic pigments consist of at least one ceramic or glass-ceramic phosphor.

The phosphor preferably contains or consists of one or more of the following substances: Eu ²⁺ -doped nitrides such as (Ca, Sr) AlSiN ₃ : Eu ²⁺ , Sr (Ca, Sr) Si ₂ Al ₂ N ₆ : Eu ²⁺ , (Sr, Ca) AlSiN ₃ * Si ₂ N ₂ O: Eu2 ⁺ , (Ca, Ba, Sr) ₂ Si ₅ N ₈ : Eu ²⁺ , (Sr, Ca) [LiA1 ₃ N ₄ ]: Eu ²⁺ ; Grenade from the general system (Gd, Lu, Tb, Y) ₃ (Al, Ga, D) ₅ (O, X) ₁₂ : RE with X = halide, N or divalent element, D = trivalent or tetravalent element and RE = rare earth elements such as Lu ₃ (Al _lx Ga _{x) 5} O _12: Ce ^3+, Y ₃ (Al _1-x Ga _{x) 5} O _12: Ce ^3+; Eu ²⁺ -doped sulfides such as (Ca, Sr, Ba) S: Eu ²⁺ ; Eu ²⁺ -doped SiONs such as (Ba, Sr, Ca) Si ₂ O ₂ N ₂ : Eu ²⁺ ; SiAlONe from the system Li _x M _y Ln _z Si _{12- (m + n)} Al _{(m + n)} O _n N _16-n ; beta-SiAlONe from the system Si _6-x Al _z O _y N _8-y : RE _z ; Nitrido orthosilicates such as AE _2-xa RE _x Eu _a SiO _4-x N _x , AE _2-xa RE _x Eu _a Si _1-y O _4-x-2y N _x with RE = rare earth metal and AE = alkaline earth metal; Orthosilicates such as (Ba, Sr, Ca, Mg) ₂ SiO ₄ : Eu ²⁺ ; Chlorosilicates such as Ca _a Mg (SiO ₄ ) ₄ Cl ₂ : Eu ²⁺ ; Chlorophosphates such as (Sr, Ba, Ca, Mg) ₁₀ (PO ₄ ) ₆ Cl ₂ : Eu ²⁺ ; BAM phosphors from the BaO-MgO-Al ₂ O ₃ system such as BaMgAl ₁₀ O ₁₇ : Eu ²⁺ ; Halophosphates such as M ₅ (PO ₄ ) ₃ (Cl, F): ( Eu ²⁺ , Sb ³⁺ , Mn ²⁺ ); SCAP phosphors such as (Sr, Ba, Ca) ₅ (PO ₄ ) ₃ Cl: Eu ²⁺ .

The phosphor can be set up to shorten the wavelength of an excitation radiation, also referred to as an upconversion, and convert infrared light into visible light, for example. Alternatively, the phosphor can convert short-wave light into long-wave light. It is possible that the phosphor in particular due to the temperatures during hot forming Luminescence properties is changed. This also enables quality control to be carried out to determine whether hot forming has been carried out with the correct process parameters.

In accordance with at least one embodiment, the phosphor is a thermoluminescent material, that is to say a material that is luminescent when a threshold temperature is reached. The threshold temperature is preferably at least 125 ° C. or 175 ° C. The phosphor then comprises as doping and / or as part of a crystal lattice or a host lattice preferably one or more of the following elements: Pr, Nd, Pm, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb. The thermoluminescent phosphor is particularly preferably NaYF ₄ : Er, Yb. The use of such phosphors is for example in the publication DE 10 2017 125 006 A1 described. The disclosure content of this document with regard to the use of such phosphors is included by reference.

A workpiece is also specified. The workpiece is marked with a method as specified in connection with one or more of the above-mentioned embodiments. Features of the method are therefore also disclosed for the workpiece and vice versa.

In at least one embodiment, the workpiece has the marking, the workpiece only showing discoloration and / or a changed material structure in the region of the marking, which is caused by heating to a temperature of at least 400 ° C. in step C). The workpiece is preferably a hot-formed one Metal part or a metal blank, which is intended for hot forming.

The minimum temperature for fixing the marking can be determined via the materials from which the marking is composed. The local discoloration and / or changed material structure of the workpiece at the marking can be used to determine the spatial area in which the temperature was applied for fixing to the workpiece, that is to say whether only local heating took place. For example, the local heating manifests itself when the marking is fixed in a tarnish around the marking.

A method described here and a workpiece described here are explained in more detail below with reference to the drawing using exemplary embodiments. The same reference numerals indicate the same elements in the individual figures. However, no true-to-scale references are shown; rather, individual elements can be exaggerated in size for better understanding.

• Figuren 1 bis 6 schematische perspektivische Darstellungen von Schritten eines hier beschriebenen Verfahrens zur Markierung von hier beschriebenen Werkstücken,
• Figuren 7 bis 9 schematische Schnittdarstellungen von Schritten eines hier beschriebenen Verfahrens zur Markierung von hier beschriebenen Werkstücken,
• Figuren 10 und 11 schematische perspektivische Darstellungen von Fixierschritten hier beschriebener Verfahren zur Markierung hier beschriebener Werkstücke, und
• Figuren 12 bis 14 schematische perspektivische Darstellungen von Schritten eines hier beschriebenen Verfahrens zur Markierung von hier beschriebenen Werkstücken.

Show it:

• Figures 1 to 6 schematic perspective representations of steps of a method described here for marking workpieces described here,
• Figures 7 to 9 schematic sectional representations of steps of a method described here for marking workpieces described here,
• Figures 10 and 11 schematic perspective representations of fixing steps described methods for marking workpieces described here, and
• Figures 12 to 14 schematic perspective representations of steps of a method described here for marking workpieces described here.

In the Figures 1 to 6 An embodiment of a method for marking workpieces 1 is illustrated. According to Figure 1 a metal sheet 11 with a workpiece surface 10 is provided. The metal sheet 11 is preferably a steel sheet, for example a stamped but still flat sheet.

In Figure 2 it is shown that an ink 20 for a marking 2 is printed on the workpiece surface 10. The printing takes place with a printing nozzle 5. The marking 2 can thus be produced in a structured manner by means of ink jet printing. The marking 2 is already essentially generated with its final shape. The marking 2 is, for example, a lettering.

After printing, the still moist ink 20 can preferably dry to a dried ink 20 'at room temperature. The dried ink 20 'preferably adheres to the workpiece surface 10 in a smudge-proof manner, but would disappear again if there was greater friction or if solvents were to influence it.

According to Figure 3 the dried tine 20 'is irradiated with ultraviolet radiation with the aid of an irradiation head 31. The radiation concentrates on a small area 3 around the later, finished marking 2. Because of the Irradiation, the dried tine 20 'is strongly heated, for example to about 600 ° C. This fixes the ink 20 'to the mark 2. The irradiation can be unstructured and coherent across the entire marking 2. This means that the marking 2 is then not scanned with a laser beam.

The irradiation takes place, for example, with UV radiation around 360 nm with an energy density of approximately 8 J / cm ² . For example, the irradiation lasts only around 100 microseconds. Thermal loads on the metal sheet 11 outside the area 3 with the marking 2 can thus be greatly reduced. The radiation used is, in particular, incoherent radiation, for example from a flash lamp.

In Figure 4 the finished, fixed marking 2 is shown. Due to the irradiation and the associated temperature increase in the area 3, it is possible that a color change 6 occurs around the actual marking 2. However, the color change 6 is limited to a small area around the marking 2.

In the optional step of Figure 5 the workpiece 1 is hot stamped. The fixed marking 2 can be applied in areas of the workpiece 1 which are affected by the hot stamping. Alternatively, the marking 2 is located outside of areas in which hot forming takes place. The hot stamping of the marking 2 is not or only slightly impaired in its legibility.

With the method described here, the marking 2 is therefore already in an early production stage of the workpiece 1 and attachable and captive to the component regardless of other process steps. This enables efficient and reliable tracking of the workpiece even over long process chains.

According to the optional step of Figure 6 a coating 4 is applied to the workpiece surface 10 in areas or over the entire surface. The coating 4 is, for example, a lacquer. It is possible that the marking 2 is hidden by the coating 4 from the human eye, but the coating can optionally still be machine-readable.

In the Figures 7 to 9 the formation of the mark 2 from the ink 20 is explained in more detail. According to Figure 7 the ink 20 is applied to the workpiece 1. The ink 20 is composed of ceramic pigments 21, particles of an inorganic binder 22, an organic binder 23, a solvent 24 and a dispersing aid 25.

In Figure 8 the dried ink 20 'is illustrated, which no longer has a solvent 24. The pigments 21 and the binder 22 as well as the optional dispersing aid 25 are held together via the organic binder 23, so that the dried ink 20 ′ is attached to the workpiece 1 in a smudge-proof manner.

According to Figure 9 sintering and fixing to mark 2 has taken place. The organic binder 23 and the dispersing aid are no longer present or are only present in traces which no longer fulfill a specific function. By sintering and / or fixing preferably coherent areas of marker 2 are formed for individual characters. Within a coherent area, the marking 2 preferably shows a homogeneous color impression for a viewer and / or for a camera.

The contiguous areas can be formed as smooth elevations over the workpiece. The contiguous areas are preferably formed by a glass ceramic which is produced from the pigments 21 and the binder 22.

The ink 20 as in the Figures 7 to 9 described, can also be used in all other exemplary embodiments.

In the Figures 10 and 11 are alternatives to the step of heating the Figure 2 shown. According to Figure 10 contact needles 32 are placed on the electrically conductive workpiece 1, wherein more than two contact needles 32 can be used. Via the contact needles 32, electrical currents are generated in the area 3 in the workpiece 1, which lead to a strong local heating of the workpiece 1 and thus the dried ink 20 '. In this way, the fixation to mark 2 can be carried out. Alternatively, eddy currents in particular can be used in the workpiece for fixing without contact via magnetic fields.

In contrast, according to Figure 11 a heating tip 33 near the ink 20 or the optionally dried ink 20 '. The heating tip 33 is heated, as a result of which the ink 20 is dried and heated or the already dried ink 20 ′ is heated and fixed to the marking 2. The heating tip 33 is preferably operated only over the dried ink 20 '. The whole is preferred Mark 2 completed in a single heating step with the heating tip 33.

In addition, in Figure 10 illustrates that the mark 2 is formed by a bar code. In Figure 11 the marker 2 is a matrix code. Such types of markings 2 can accordingly also be used in all other exemplary embodiments.

According to the Figures 2 , 10 and 11 a separate heating means 31, 32, 33 is used in each case, which is used only for fixing the dried ink 20 ′ or for drying and fixing the ink 20. In contrast, the fixation to mark 2 according to the Figures 12 to 14 combined with another process step.

So according to Figure 12 the workpiece 1 is provided with the only schematically indicated dried ink 20 '. In the step of Figure 13 the workpiece 1 is deformed with a shaping tool 34a, 34b. At least the forming tool 34b, which covers the dried ink 20 ', is heated. The resulting, hot-formed workpiece 1 with the finished marking 2 is in Figure 14 shown.

It is therefore not absolutely necessary to provide a separate heating means 31, 32, 33 for fixing the marking 2. The same can apply in all other exemplary embodiments.

Unless otherwise indicated, the components shown in the figures preferably follow one another directly in the order given. Yourself in the Layers not in contact with figures are preferably spaced apart from one another. If lines are drawn parallel to one another, the corresponding areas are preferably also aligned parallel to one another. Unless otherwise indicated, the relative positions of the drawn components to one another are also correctly represented in the figures.

The invention described here is not limited by the description based on the exemplary embodiments. Rather, the invention encompasses every new feature and every combination of features, which includes in particular every combination of features in the patent claims, even if this feature or this combination itself is not explicitly specified in the patent claims or exemplary embodiments.

Reference symbol list

1

workpiece

10th

Workpiece surface

11

Sheet metal (sheet steel)

2nd

mark

20th

ink

20 '

dried ink

21

ceramic pigments

22

inorganic binder

23

organic binder

24th

solvent

25th

Dispersing agents

3rd

Marked area that is being heated

31

Radiation head

32

Contact pin

33

Heating tip

34

Forming tool

4th

Coating

5

Pressure nozzle

6

Discoloration

Claims (15)

Method for marking workpieces (1) with the following steps: A) providing the at least one workpiece (1), B) locally applying an ink (20) for a marking (2) to the workpiece (1), C) fixing the ink (20) to the marking (2), the workpiece (1) being heated locally in a region (3) with the marking (2) and a temperature of at least 400 when fixed to the ink (20) ° C is applied. Method according to the preceding claim,
in which the ink (20) contains ceramic pigments (21) which bring about a coloring and / or a contrast of the marking (2) with respect to the workpiece (1),
wherein the ink (20) additionally contains an inorganic binder (22) which is also contained in the finished marking (2), and
wherein the ink (20) is applied by means of a printing process. Method according to claim 2,
in which the ink (20) in step B) consists of a solvent (24), the ceramic pigments (21) and the inorganic binder (22) and optionally a dispersing aid (25) and the marking (2) after step C) consists of the ceramic pigments (21) and the inorganic binder (22). Method according to claim 1 or 2,
in which the ink (20) in step B) comprises an organic binder (23), so that the dried ink (20 ') due to the organic binder (23) is smudge-proof even before step C). Method according to one of the preceding claims,
in which in step C) the temperature of at least 400 ° C is applied for a maximum of 1 min. Method according to one of the preceding claims,
in which the workpiece (1) is an iron sheet or a steel sheet (11),
the temperature when fixing in step C) is between 500 ° C and 1200 ° C,
wherein the workpiece (1) undergoes hot forming in a step D) after step C), and
the marking (2) being legible even after step D). Method according to one of the preceding claims,
in which the fixing in step C) takes place by means of a flash of radiation,
radiation of the radiation flash is incoherent and is absorbed in the ink (20) and / or on a workpiece surface (10) and the temperature is thereby applied for fixing,
the radiation of the radiation flash is predominantly ultraviolet radiation. Method according to one of claims 1 to 6,
in which the fixing in step C) takes place without contact and by means of induction. Method according to one of the preceding claims,
in which a form of the marking (2) is already defined in step B), so that no material is removed in step C) from the ink (20) or from the marking (2), which changes an information content of the marking (2). Method according to one of the preceding claims,
in which the area (3) with the marking (2), which is heated in step C) during fixing, has at most three times the size of the marking (2) itself, the area (3) with the marking (2) at most Accounts for 10% of the workpiece (1). Method according to one of the preceding claims,
in which at least in the area (3) with the marking (2) the marking (2) is raised above a metal sheet (11) of the workpiece (1). Method according to one of the preceding claims,
in which the marking (2) is planarized in a step E) after step C),
wherein in step E) a lacquer (4) is applied continuously over the marking (2). Method according to one of the preceding claims,
in which a separate heating means (31, 32, 33) is used in step C), which is not used for any further process steps for machining the workpiece (1). Method according to one of the preceding claims,
in which the ink (20) and the marking (2) comprise at least one phosphor. Workpiece (1) which is marked by a method according to one of the preceding claims and which comprises the marking (2), the workpiece (1) only having a discoloration (6) and / or in the area (3) with the marking (2) or one has changed material structure, which is caused by heating to a temperature of at least 400 ° C.

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