WO2020127822A1

WO2020127822A1 - Identification of objects produced by a 3d printing method

Info

Publication number: WO2020127822A1
Application number: PCT/EP2019/086441
Authority: WO
Inventors: Patrick Leisching
Original assignee: Toptica Photonics Ag
Priority date: 2018-12-21
Filing date: 2019-12-19
Publication date: 2020-06-25
Also published as: EP3898179A1

Abstract

The invention relates to a 3D printing method, in which a material is applied one layer at a time and a three-dimensional workpiece (1) is thus produced. The invention also relates to a method for identifying a workpiece (1) produced by a 3D printing method. The invention addresses the problem of providing a method for secure coding and subsequent identification of a workpiece produced by 3D printing. To this end, the invention proposes that a material parameter is varied during or after the application of the material, such that the variation of the material parameter forms a pattern (2) in the produced workpiece (1), and furthermore that a pattern (2) which is produced in the workpiece (1) by a spatial variation of a material parameter and which forms a coding is detected by means of a spatially resolving process using electromagnetic radiation, and the identity of the workpiece (1) is deduced therefrom.

Description

The invention relates to a 3D printing method, in which a material is applied layer by layer and a three-dimensional workpiece is thus produced. The invention also relates to a method for identifying a workpiece produced in the 3D printing method.

3D printing, also known as additive manufacturing, additive manufacturing (AM), generative manufacturing or rapid prototyping, is a comprehensive term for all manufacturing processes in which material is applied layer by layer to create three-dimensional workpieces. The layers are built up computer-controlled from one or more liquid or solid materials according to specified dimensions and shapes, which are usually provided by a CAD system. During the set-up, physical or chemical flushing or melting processes take place. Typical materials for 3D printing are plastics, synthetic resins, ceramics and metals.

To date, the problem of secure coding and later identification of a workpiece produced in 3D printing has not been solved. State of the art are proposals to incorporate nanomaterials or RFID chips into the material, but the technical implementation is difficult. In addition, the code should be recognized through a paint job. WO 2018/140021 A1 describes the introduction of an invisible coding into the workpiece, which can be read out to identify the workpiece.

It is the object of the invention to provide a method for the safe coding and later identification of a workpiece produced in 3D printing. Furthermore, the coding should be able to be recognized through a coating as far as possible.

The invention achieves this object by a 3D printing method according to claim 1 and by a method for identifying a workpiece produced in the 3D printing method according to claim 8.

Advantageous refinements of the method are specified in the subclaims.

The method according to claim 9 is particularly suitable for identifying a workpiece produced in the 3D printing method according to claim 1. The invention proposes a 3D printing method, in which a material is applied layer by layer and a three-dimensional workpiece is thus produced, a material parameter being varied during or after the application of the material, so that the variation of the material parameter forms a pattern in the workpiece produced . By adapting the algorithm during printing or by post-processing with laser light, it is possible, for example, to specifically influence the density or other physical material parameters, so that suitable material constants are specifically influenced for detection using a corresponding imaging method. Conventional 3D printing technology can be used for the 3D printing method according to the invention, a process parameter of a physical or chemical hardening or melting process used to produce the composite material being used to vary the material parameter during the application of the material is varied. For this purpose, for example, the computer control of the 3D printer used can suitably control the print head. A particular advantage is that a uniform material can be used for printing the workpiece. With other values, the finished workpiece consists of a single material. No second material has to be used to generate the coding, which would make the printing process considerably more complicated.

The pattern preferably forms a coding for marking the workpiece.

The material parameter should be varied between two predetermined values or value ranges, so that the coding is a binary code, in particular a two-dimensional binary code, preferably a QR code. The reading of such a code is e.g. with radiation in the range of 50 GHz-2 THz, with thermometric analysis, magnetometry and / or other imaging methods possible.

It is thus possible, for example, to insert a 2D QR code pixel in the range of approx. 0.1-1 mm, so that in principle more than 256 bit resolution could be achieved per square centimeter. The depth of information of the coding can be variably adjusted by structuring the pattern. This enables a clear assignment of the workpiece to the production and to the manufacturer. The code read out can therefore be compared, for example for the purpose of authentication, with a data record stored on a trustworthy server.

However, an embossed 3-bit coding is already suitable, for example, for applications in plastic printing. Eight identical workpieces are manufactured simultaneously in one process. After production, these are transported unsorted to a collection container or the like. If there are now fluctuations in the quality of the workpieces, this is usually due to the 3D printer. The 3-bit coding allows each workpiece to be assigned a position in the manufacturing process so that the source of the quality fluctuations can be determined very quickly and the error can be remedied. For 3-bit coding, pixel sizes of approx. 1-2 mm are sufficient. As a further embodiment, encoded information can be contained in this coding. In this way, protection against plagiarism or the preservation of license rights can be ensured.

It is also advantageous if the areas in which the material parameter is varied have a polyhedral, conical or cylindrical structure. Depending on the application, the suitable shape of the varied areas makes it particularly easy to create and / or record a pattern that meets the respective requirements.

The pattern is preferably generated below an outer surface of the workpiece, so that it is not visible from the outside. The pattern can be generated in particular below a protective coating, for example under a coating of the workpiece. This means that the pattern cannot be viewed directly. This further complicates possible counterfeiting or imitation. The varied material parameters can be the density, the refractive index, the susceptibility and / or the thermal conductivity of the material. In contrast to other approaches to creating samples, one of these measures makes it possible to insert the samples into the workpiece in a cost- and time-efficient manner and less prone to errors. According to the invention, in order to identify a workpiece produced in the 3D printing method by means of a spatially resolving method using electromagnetic radiation, the pattern generated by the spatial variation of the material parameter in the workpiece, which forms a coding, is recorded and the identity of the workpiece is derived therefrom. A hidden pattern can also be detected by using the electromagnetic radiation. The absorption and / or reflection or scatter of the electromagnetic radiation is influenced by the variation of the material parameter. This creates a contrast that can be used to read the pattern. It is particularly advantageous if the detection of the pattern is carried out by means of electromagnetic radiation at a frequency higher than 250 GFIz. In this way, a sufficiently high resolution can be achieved for most applications. It also shows that with most plastic materials that are common in 3D printing, the variation of the material parameter can produce a contrast that is well suited for reading out the pattern at frequencies above 250 GFIz. In general, all types of spectroscopy can be used according to the invention, provided that they are suitable for the respective application. The method can advantageously be terahertz spectroscopy, thermometry or magnetometry, depending on which material parameter is varied and which spectroscopy method responds to the parameter variation.

The pattern can advantageously be acquired by means of a conventional, commercially available terahertz camera or by means of a thermal camera. A further development of the method according to the invention provides that the terahertz camera is integrated in a Fland scanner when the pattern is acquired and is operated by Fland by a user. This enables a particularly flexible inspection of the workpiece.

An additional development provides that the pattern and / or the coding formed from the pattern are compared with a data record stored on a trustworthy server for authenticating the workpiece. For example, a coding can be assigned to each workpiece when it is positioned. This further development according to the invention can thus be used to determine whether it is an original or a plagiarism. The invention is explained in more detail below on the basis of exemplary embodiments. Show it:

Fig. 1 shows schematically a 3D-printed workpiece with stripes introduced in terms of density from the rest

Distinguish the material of the workpiece;

Fig. 2 shots of the workpiece by means of a

Terahertz camera;

Fig. 3 is a schematic representation of the

Identification of a workpiece using a portable device.

In Figure 1, a workpiece is designated by the reference numeral 1. A pattern 2 in the form of a plurality of strip-shaped sections 2a is introduced into the workpiece 1 during the positioning process. The strip-shaped sections 2a are made of the same material as the rest of the workpiece 1, but have a different density. The density varies in the percentage range. The width of the strip-like sections 2a is in the millimeter range in this exemplary embodiment. FIG. 2 shows images of a terahertz scanner in transmission (left) and in reflection (right), in which the strip-shaped sections 2 introduced into the workpiece 1 can be clearly seen. A binary coding in the form of a bar code can be generated by such strip-shaped sections 2a. FIG. 3 schematically shows a cuboid workpiece 1 with a pattern 2 in the form of a QR code 2b introduced under the surface according to the invention. The QR code can be read using a portable Fland scanner 3 (e.g. a thermal camera with integrated image processing). A flexible assignment and authentication of the workpiece 1 is thus possible. Depending on the application, it is also possible to provide several 2D codes in different levels in workpiece 1. This allows the quality of the coding to be further enhanced.

In the method according to the invention, the density in the strip-shaped sections 2 in FIG. 1 can be adjusted by adapting the algorithm in 3D printing or manipulated by post-processing with laser light. It is also possible to specifically influence another material parameter on or just below the surface of the workpiece, so that the material parameters density, refractive index and / or thermal conductivity can be used in a targeted manner for detection with appropriate spectroscopy.

It makes sense to insert a QR code with pixels with diameters in the range of approx. 0.1 to 1 mm, so that in principle more than 256 bits can be encoded on one square centimeter. A release of approx. 0.5 mm can be achieved with high-frequency radiation of 400 GHz or purely optically 0.5-1 THz. Different approaches are available for this: For example, a phased array operating at the appropriate frequency, consisting of antennas with a low frequency and movement of a beam lobe for scanning the pattern, or a pulsed terahertz system with a high frequency.

The information depth of the coding can be set variably via the structuring. This enables the workpiece 1 to be clearly identified, e.g. possible to assign the manufacturing data and the manufacturer. The coding can contain encrypted information. In this way, protection against plagiarism or the preservation of license rights can be realized. One particular application here is the supply of spare parts. However, 3-bit coding can already be useful for other applications.

The spectroscopic or imaging reading of a code is e.g. with terahertz radiation in the range from 50 GHz to 2THz (1 THz = 300 pm wavelength), with thermometric analysis, with magnetometry or other spectroscopic methods possible.

In the common 3D printing processes there is an interruption in the printing process, e.g. for the insertion of RFID chips or the like, not possible, since you have to work in a protective gas atmosphere. The combination of different materials in the 3D printing process is also very difficult.

According to the invention, the algorithm of the printing method is instead adapted during printing, ie, for example, the density of the printed material specifically influenced on a scale in the sub-millimeter range. Typically, material densities of up to 99% are achieved in the target state, this parameter can be reduced by a few percent or more through the targeted intervention; in extreme cases, a pixel is not printed, but remains enclosed in the workpiece 1 as raw material.

As a result, material properties such as the refractive index, reflectivity, magneto-optical properties and / or thermal conductivity are changed in the percentage range. This is sufficient to e.g. read out the inserted code by reflection using a conventional terahertz scanner (typically a 1% change in refractive index is detectable when using terahertz radiation).

Alternatively, a coding can be introduced by post-treatment of the surface or the layer under the cover layer, e.g. through two-photon absorption in the focus of a laser beam in the material. The electromagnetic radiation in the terahertz range used for detection cannot penetrate metallic materials (skin effect, penetration depth only in the pm range), but the density variation or the targeted introduction of imperfections can also be applied to the top cover layer. Usually, a coating is applied to the components, which is penetrated by terahertz radiation (e.g. non-metallic paints).

Terahertz radiation penetrates into plastic materials, so the code can also be inserted here in depth.

It is also possible to carry out an analysis without a real picture. This means that the irradiation takes place with a broadband terahertz signal and the evaluation is based on the direct scattering pattern of the different frequencies. The scatter pattern depends strongly on the frequency and can be mathematically correlated with known information about the stored code. For this purpose, the pixels of the terahertz scanner must be frequency-sensitive or polled at a predetermined number of different frequencies can be. Optical systems that are in the terahertz range (> 0.5 THz) are superior to traditional high-frequency systems (<0.5 THz) because broadband is used in addition to high frequency (resolution) and information theory results are better because broadband is not used at all in known systems. A pure 2 THz signal would also work for a camera.

It is also possible to use a coherent terahertz detector. Such a detector is a good alternative to the pulsed systems for a camera.

Reference symbol list:

1 workpiece

2 patterns

2a strip-shaped section 2b QR code

3 hand scanners

Claims

1. 3D printing process, wherein a material is applied layer by layer and thus a three-dimensional workpiece (1) is produced,

characterized,

that a material parameter is varied during or after the application of the material, so that the variation of the material parameter forms a pattern (2) in the workpiece (1) produced.

2. 3D printing method according to claim 1, characterized in that the pattern (2) forms a coding for marking the workpiece.

3. 3D printing method according to claim 1 or 2, characterized in that the material parameter is varied between two predetermined values or value ranges, so that the coding is a binary code, in particular a two-dimensional binary code, preferably a QR code.

4. 3D printing method according to one of claims 1 to 3, characterized in that the areas in which the material parameter is varied have a polyhedral, conical or cylindrical structure.

5. 3D printing method according to one of claims 1 to 4, characterized in that the pattern (2) below an outer surface of the workpiece (1) is generated.

6. 3D printing method according to one of claims 1 to 5, characterized in that the pattern (2) is generated below a protective coating, in particular under a coating of the workpiece.

7. 3D printing method according to one of claims 1 to 6, characterized in that the varied material parameter is the density

Refractive index, the susceptibility and / or the thermal conductivity of the material.

8. 3D printing method according to one of claims 1 to 7, characterized in that to vary the material parameter during the application of the material, a process parameter of a physical or chemical hardening or melting process used to produce a composite material is varied.

9. Method for identifying a workpiece produced in the 3D printing method,

characterized,

that by means of a spatially resolving method using electromagnetic radiation, a pattern (2) generated by a spatial variation of a material parameter in the workpiece (1), which forms a coding, is detected and the identity of the workpiece (1) is derived therefrom.

10. The method according to claim 9, characterized in that the

Detection of the pattern (2) by means of electromagnetic radiation with a frequency higher than 250 GHz is carried out.

11. The method according to claim 9 or 10, characterized in that the method uses terahertz spectroscopy, thermometry or magnetometry.

12. The method according to any one of claims 9 to 11, characterized in that the detection of the pattern (2) is carried out by means of a terahertz camera or by means of a thermal camera.

13. The method according to claim 12, characterized in that the terahertz camera is integrated in the detection of the pattern (2) in a hand-held scanner and is operated by hand by a user.

14. The method according to any one of claims 9 to 13, characterized in that the pattern (2) and / or formed from the pattern (2)

Coding can be compared with a data record stored on a trustworthy server for the authentication of the workpiece (1).

15. The method according to any one of claims 1 to 12, characterized in that the workpiece (1) is produced by a 3D printing method according to one of claims 1-7.

16. workpiece (1), produced by means of a 3D printing process and comprising at least one material,

characterized,

that a pattern (2) formed by varying at least one material parameter is introduced into the workpiece (1).