Mobile processing chamber for laser polishing of glass workpieces, as well as the use of several mobile processing chambers

Abstract

A mobile processing chamber for laser polishing of glass workpieces comprises a workpiece carrier, a shielding element for the laser radiation used in the polishing process, and a protective enclosure. The shielding element is designed and positioned to surround a receiving area for the workpiece to be polished on the workpiece carrier, thus shielding the workpiece carrier from direct exposure to the laser radiation during the polishing process. The protective enclosure, either alone or in conjunction with the workpiece carrier, forms a closed chamber around the surface of the inserted workpiece to be polished and has a removable lid. The workpiece carrier, shielding element, and protective enclosure are made of materials that can withstand temperatures up to at least 500 °C. The material of the workpiece carrier is additionally selected to have a low thermal conductivity, preferably less than 10 W / (m K).The mobile processing chamber enables laser polishing of glass workpieces on an industrial scale with high yield.

Description

Technical application area

[0001] The present invention relates to a mobile processing chamber for the laser polishing of workpieces made of glass, in particular optics, and to the use of several of these mobile processing chambers in laser polishing.

[0002] The surface of glass workpieces, especially optical components and optics, often needs to be polished during or after manufacturing to meet the required surface quality standards for a given application. Laser polishing offers significant advantages, achieving a very high surface quality and reducing polishing costs by up to 90% compared to mechanical polishing methods, particularly for small to medium production runs and non-spherical optics. Laser polishing uses CO2 laser radiation to heat and soften the surface layer of the optics. In this softened state, the roughness peaks flow into the roughness valleys, and the surface is smoothed by surface tension. Laser polishing achieves processing rates of more than 1 cm³. 2The process also works on more complex surfaces such as aspheres or freeform surfaces, achieving a microroughness comparable to conventional A / 20 polishing. The high processing rates induce large temperature gradients, which can cause thermally induced stresses and lead to both lens deformation and, if the strength limit is exceeded, cracking. The latter is successfully prevented by preheating the optics before laser polishing. State of the art

[0003] For the production of small to medium quantities of glass optics, mechanical grinding and polishing techniques are typically used. Polishing aspheres is a time-consuming and expensive process performed on CNC machining centers. Laser polishing offers significant advantages here, as the polishing time for an asphere is only a matter of seconds. In comparison, mechanical polishing can take anywhere from minutes to hours, depending on the size of the optics. Examples of laser polishing of optics can be found, for instance, in EP 1516068 B1 or EP 2683521 B1.

[0004] However, one problem with laser polishing of optics is the limited applicability of this technique in industrial settings. On a laboratory scale, due to the numerous manual steps and time-consuming processes on hot plates, only a very small number of optics can currently be polished to optical quality using a laser each day.

[0005] Another problem with laser polishing is that temperature inhomogeneities occurring during preheating, sometimes amounting to a few Kelvin, lead to shape defects and waviness in the laser-polished optics, thus limiting their usability.

[0006] DE 10 2022 109 123 A1, KR 10 1 425 410 B1, EP 4 338 959 A2 and DE 295 18 138 U1 each disclose mobile processing chambers for the processing of workpieces using laser radiation.

[0007] US patent 2019 / 0291214A1 discloses a plasma processing chamber that has a removable lid and multiple shields.

[0008] The object of the present invention is to provide means by which workpieces made of glass, in particular optical elements or optics, can be polished with high yield by means of laser polishing, even on an industrial scale. Description of the invention

[0009] The problem is solved by providing a mobile processing chamber according to claim 1. Claim 16 relates to the use of several such processing chambers for laser polishing of glass workpieces. Advantageous embodiments of the mobile processing chamber are the subject of the dependent claims or can be found in the following description and the exemplary embodiments.

[0010] The proposed mobile processing chamber comprises at least one workpiece carrier, a shielding element, and a protective enclosure. The workpiece carrier is designed to hold a workpiece to be polished within the processing chamber. The shielding element, which protects against laser radiation used for laser polishing, is arranged around the workpiece carrier's receiving area. This shielding element is designed to surround the receiving area on the workpiece carrier in such a way that it largely protects the workpiece carrier from direct exposure to the laser radiation during laser polishing. This is important because, during laser polishing, the laser beam must extend slightly beyond the workpiece surface to be polished. Without the shielding element, it would strike the workpiece carrier and further heat it up.The shielding element is designed so that it does not break when irradiated with the laser radiation used for laser polishing and should ideally not release any particles (> 5 µm) under thermal stress. The protective enclosure is designed to form a closed chamber around the surface to be polished of a workpiece held by the workpiece carrier, either alone or in conjunction with the workpiece carrier. The protective enclosure has at least one side wall and a removable lid. The workpiece carrier, the shielding element, and the protective enclosure are made of materials that can withstand temperatures up to at least 500 °C, preferably up to at least 800 °C, and particularly preferably up to at least 1100 °C. The material of the workpiece carrier is also selected to have a relatively low thermal conductivity, which (at 500 °C) is less than 20 W / (m K).Preferably, the workpiece carrier material has a thermal conductivity of less than 10 W / (m K), particularly preferably less than 1 W / (m K). Alternatively or in addition to the low thermal conductivity of less than 10 W / (m K) or less than 1 W / (m K), the contact surface of the workpiece carrier for a workpiece to be polished can be very narrow and / or structured in order to minimize heat transfer from the workpiece to the workpiece carrier.

[0011] A mobile processing chamber is understood to be one that can be moved by means of appropriate handling devices or manipulators, for example, from an oven to the laser polishing system, and is therefore not stationary or fixed in place. The workpiece carrier preferably has an opening or recess, in particular a central opening or recess, for receiving the workpiece to be polished and is designed such that a received workpiece rests on the workpiece carrier only at the edge of the opening or recess. For this purpose, a corresponding groove or fit can also be provided at the transition from the opening or recess to the surrounding area of ​​the workpiece carrier.

[0012] The proposed processing chamber enables laser polishing of glass workpieces, particularly optics such as lenses or mirror substrates, on an industrial scale. The workpieces to be polished—one per processing chamber—are placed in the respective workpiece carrier, and the processing chamber is closed with the lid. The entire process, from preheating and laser polishing to tempering and the transfer between these individual stations, then takes place with the entire processing chamber, without having to remove the workpiece. For laser polishing, only the lid of the protective enclosure needs to be lifted and then replaced. The inventors recognized that, in addition to achieving low micro-roughness, minimizing distortion during laser polishing is crucial for high yield in an industrial process.Distortion has not been addressed in this context so far. The design and construction of the proposed mobile processing chamber ensures high dimensional accuracy of the polished optics. Key factors in achieving this accuracy include the low thermal conductivity of the workpiece carrier, the shielding element that protects the workpiece carrier from direct laser radiation (which would cause undesirable heating), the protective enclosure with its side wall (which prevents unwanted air movement around the workpiece and thus avoids unwanted temperature fluctuations and the ingress of particles), the use of high-temperature-resistant materials, and the removable lid, which allows for laser polishing of the workpiece within the processing chamber. These features largely prevent undesirable temperature inhomogeneities within the workpiece during laser polishing, which would otherwise lead to distortion.The proposed mobile processing chamber enables fully automated laser polishing of glass workpieces, including aspheres, on an industrial scale.

[0013] For example, aspheres with diameters of 10-50 mm can be polished to optical quality in a cycle time of ≤ 1 minute. The special design and use of the processing chambers ensures a very homogeneous temperature control within the workpiece, resulting in high dimensional accuracy.

[0014] In a preferred embodiment, the protective enclosure is designed such that the removable lid projects laterally beyond the side wall of the enclosure. This allows it to be easily lifted off and replaced on the machining chamber using a suitable manipulator or other mechanical system. The protective enclosure can also enclose the workpiece carrier, thus potentially including an additional base. Preferably, however, the workpiece carrier forms the base of the machining chamber, so that the protective enclosure only comprises the side wall(s) and the lid.

[0015] In a particular embodiment, the shielding element and the protective housing are designed to be removable from the workpiece carrier. In this embodiment, the workpiece can be turned over within the laser polishing arrangement while heated, and thus polished from both sides, as will be explained in more detail in an exemplary embodiment. Preferably, the lid of the protective housing is formed by an identical workpiece carrier.

[0016] Suitable materials for the workpiece carrier include ceramic materials such as aluminum oxide, zirconium oxide, and silicon carbide. The protective enclosure, i.e., the side walls and lid, can be made of quartz glass, for example, to allow a view into the processing chamber from the outside. However, this is not strictly necessary.

[0017] The shielding element is preferably plate- or disc-shaped and has a central opening corresponding to the workpiece receiving area. It should be positioned as close as possible to the workpiece placed in the workpiece carrier without touching it, even after thermal expansion. Furthermore, the shielding element should have a high thermal conductivity to dissipate the heat generated by the incident laser radiation as quickly as possible across its entire surface. Additionally or alternatively, the shielding element can be coated to reflect a large portion of the incident laser radiation. This coating could, for example, be gold or platinum. With a reflective coating, the shielding element can then also have a low thermal conductivity.The shielding element should continue to have the smallest possible contact area with the workpiece carrier, preferably only at the outer edge of the shielding element, in order to introduce as little heat as possible into the workpiece carrier.

[0018] When using the proposed mobile processing chambers, several of these chambers are each loaded with a workpiece to be polished, then closed with the lid and preheated in one or more ovens with the workpieces inside. Preheating can be omitted when processing quartz glass. Preheating temperatures can reach up to 1100 °C, but for many types of glass, they are in the range of 400 to 700 °C. The processing chambers, preheated in this way, are then transferred to the laser polishing setup with the workpieces inside. In this laser polishing setup, the lid of each processing chamber is automatically lifted, preferably immediately before the laser polishing of the workpiece inside, in order to polish the workpiece with the laser. The lid is then automatically replaced. The processing chambers with the polished workpieces can then, for example,They can be cooled down or transferred to an oven and tempered together there.

[0019] The proposed mobile processing chambers can be used in all areas where glass workpieces need to be polished on at least one side using laser polishing. The processing chambers and the workpiece carriers (and shielding elements) they contain must be adapted to the size and shape of the workpiece being polished. The process is particularly advantageous for the laser polishing of optical components or optics on an industrial scale. Brief description of the drawings

[0020] The proposed mobile machining chamber and its use are explained in more detail below using exemplary embodiments in conjunction with the drawings. These show: Fig. 1 a schematic representation of an example of a process flow for laser polishing of optics with the proposed mobile processing chamber; Fig. 2 a schematic cross-sectional representation of an example of a mobile machining chamber according to the invention; Fig. 3 a schematic cross-sectional view of a further example of a mobile processing chamber according to the invention with a reversible optic; and Fig. 4 A schematic representation of a process for turning the optics when using the mobile processing chamber of the Fig. 3. Ways to implement the invention

[0021] The proposed processing chamber and its use are explained in more detail below using the example of polishing optics, especially aspheres. A possible process sequence for laser polishing is described in Fig. Figure 1 is shown schematically. Several of the mobile processing chambers 10 according to the invention are used, with one of the optics to be polished being inserted into each of the mobile processing chambers 10. For this purpose, the lids of the mobile processing chambers 10 are opened and closed again after the optics have been inserted. Fig. Figure 1 shows, in step A, a loading station 11 with the loaded mobile processing chambers 10, each containing an optic to be polished. Subsequently, the individual mobile processing chambers 10 are transferred B to suitable preheating equipment, such as individual furnaces, a carousel furnace, or a continuous furnace. In this process step C, the mobile processing chambers 10, with the optics they contain, are preheated to temperatures within ±50 K of the glass transition temperature of the optic to be polished. When processing optics made of quartz glass, the preheating step may be omitted depending on the process configuration, as quartz glass does not necessarily require preheating. Following preheating, the mobile processing chambers 10 are transferred D to a laser polishing system.In this system, the mobile processing chambers are opened inside a further oven by automatically removing the top cover and their surfaces are polished with a laser 12. This laser polishing step E takes only a few seconds for a single optic, during which surface temperatures of up to 2200 °C can occur, depending on the optic material. After laser polishing E of each optic, the cover of the mobile processing chamber is automatically replaced. The mobile processing chambers 10 are then collected in a further transfer F, in this example in an oven 13, and annealed together. After this annealing process G, the polished optics can be removed from the mobile processing chambers 10.

[0022] Fig. Figure 2 shows a cross-sectional view of part of a mobile machining chamber 10, as it is used in Fig. 1 was used. In the present example of aspheres as optics to be polished, this processing chamber is rotationally symmetrical. However, the outer shape of the mobile processing chamber can also have a different cross-sectional shape, for example, a rectangular cross-sectional shape, as long as the workpiece holder and the associated shielding are correspondingly rotationally symmetrical. Of course, non-rotationally symmetrical glass workpieces can also be polished with the proposed mobile processing chamber, in which case the workpiece holder and the shielding element must be adapted accordingly.

[0023] Fig. Figure 2 shows a schematic representation of an example of the proposed mobile processing chamber with a workpiece carrier 4, which holds the optic 5 to be polished, a shielding element 3, and the protective housing, which in this example consists of a cylindrical side wall 2 and a removable lid 1. A key element of this mobile processing chamber is the workpiece carrier 4, for example, made of a ceramic material. The workpiece carrier 4 has a recess into which the optic 5 to be polished is inserted. For this purpose, a suitable fit can be provided on the workpiece carrier 4, adapted to the size of the optic 5 to be polished, as shown in Figure 2. Fig. 2. The thermal expansion of the workpiece carrier 4 and the optics 5 to be polished must be taken into account so that no mechanical stresses arise in the optics 5 during heating. The receiving opening or recess for the optics to be polished in the workpiece carrier 4 is designed such that the optics 5 rests evenly around its entire circumference in a peripheral area. The contact surface can also be suitably structured or microstructured to reduce the overall contact area. The workpiece carrier 4 must be made of a material that is as thermally inert as possible with respect to the optics 5 to be polished. This means that during laser polishing, the heat dissipation from the optics 5 to the workpiece carrier 4 should be comparable to the heat dissipation from the optics 5 to air.This is achieved by selecting a material for the workpiece carrier 4 that is stable at the temperatures occurring during the process, i.e., can withstand temperatures of preferably up to 1100 °C, and has the lowest possible thermal conductivity of less than 20 W / (m K), preferably less than 10 W / (m K), and particularly preferably less than 1 W / (m K).

[0024] As from the Fig. As can be seen in Figure 2, the workpiece carrier 4 supports the side wall 2 of the protective enclosure and the shielding element 3, which in this example is plate-shaped. This shielding element 3 represents another essential feature of the proposed mobile processing chamber. It rests on the workpiece carrier 4 only at its outer edge and extends close to the optics 5 to be polished, without actually touching them. It is designed and positioned to shield the workpiece carrier 4 from the laser radiation that extends beyond the optics 5 during laser polishing, i.e., to absorb, reflect, or scatter it. During laser polishing, the reversal points of the laser beam's scanning motion lie outside the optics being polished.If this laser radiation were to strike the workpiece carrier 4, it would be absorbed by the carrier, causing it to heat up and then conduct the heat into the optics being polished. This would lead to undesirable temperature inhomogeneities within the optics, negatively impacting dimensional accuracy. Destruction of the workpiece carrier due to this heating would also be possible. The material of the shielding element 3 should preferably have sufficient thermal conductivity to distribute the heat generated locally by the laser beam across its entire surface, thus conducting it away from the optics being polished. The shielding element 3 can, for example, be made of a metallic material and should be selected so that it does not emit particles (> 5 µm) under thermal stress and remains stable at the high temperatures encountered (preheating temperature and absorbed laser power).As a shielding element, quartz glass can be used in addition to metal if the optics to be polished are not made of quartz glass and / or if the quartz glass is coated so that the laser radiation used for laser polishing is reflected by >50%.

[0025] The protective enclosure, in this example the side wall 2 and the lid 1, protects the optics 5 to be polished from contamination during preheating, transfer to the laser polishing setup, transfer to the tempering oven, and tempering. This is essential because any dust particle on the optics to be polished would lead to surface defects during preheating, laser polishing, and tempering. In this example, the lid 1 of the protective enclosure is designed to extend laterally beyond the side wall 2 of the enclosure. This allows it to be easily and automatically lifted off in the laser polishing station. This is necessary because, to the best of our knowledge, no material is currently available that is transparent to the CO2 laser radiation typically used for laser polishing glass and simultaneously stable at temperatures up to 1100 °C.The protective enclosure must be able to withstand temperatures up to 500 °C, and in some cases even up to 800 or 1100 °C, during preheating and tempering, depending on the type of glass used in the workpiece. This also applies to laser radiation scattered during laser polishing of the optics being polished. One possible material for the protective enclosure is quartz glass, as it allows for process observation from the side and transmits a broad spectrum of thermal radiation during preheating.

[0026] Fig. Figure 3 shows another example of a possible design of the proposed processing chamber. In this example, the processing chamber is designed such that the optic 5 to be polished can be easily turned over in a heated state during the process, particularly in the laser polishing arrangement, to allow laser polishing from both sides. The side wall 2 of the protective enclosure and the shielding element 3 are designed to be removable from the workpiece carrier 4, as shown in the example in the Fig. Figure 3 illustrates this. In this example, the shielding element 3 is not connected to the workpiece carrier 4, but rather to an intermediate piece 6 made of the same material as the workpiece carrier, in this example in the form of a support ring. This intermediate piece 6 not only supports the shielding element 3, but also the side wall 2 of the protective enclosure and is placed on the workpiece carrier 4, as can be seen in the figure. In this example, another workpiece carrier 4, identical in construction to the lower workpiece carrier 4, is used as the lid of the protective enclosure.

[0027] With such a mobile processing chamber, the optic 5 can be rotated or turned within the process, i.e., while hot, as shown schematically in Fig. Figure 4 illustrates this process. In the first step (A), the first surface of the inserted optic is heated and processed. In the next step (B), the upper workpiece carrier or cover is lifted from the processing chamber and set aside. Then, the intermediate piece, including the side wall of the protective housing and the shielding element, is lifted and set aside (step C). In step D, the upper workpiece carrier is picked up again and placed onto the lower workpiece carrier, which holds the optic. In the next step (E), the two workpiece carriers are clamped against each other and rotated 180° so that the upper workpiece carrier becomes the lower one. The processing chamber is then reassembled in reverse order, as indicated by the arrow in Figure 4. Fig.As indicated in Figure 4. After assembly, the optics can then be laser-polished on the second surface, which is now facing upwards. In this example, the second workpiece carrier was used as the lid of the protective housing. This is not strictly necessary. Suitable second workpiece carriers can also be kept ready (and heated) and then, after removing the lid of the protective housing, used to turn the optics over as shown. Reference symbol list 1 Cover of the protective enclosure 2 Side wall of the protective enclosure 3 Shielding element 4 workpiece carriers 5 Optics to be polished 6 Intermediate piece 10 Mobile processing chambers 11 Loading station 12 polishing lasers 13 Tempering oven

Claims

[1] Mobile processing chamber (10) for laser polishing of workpieces (5) made of glass, which at least - a workpiece carrier (4) that can hold a workpiece (5) to be polished in the machining chamber (10), - a shielding element (3) against laser radiation used for laser polishing, which surrounds a receiving area for the workpiece (5) to be polished on the workpiece carrier (4) in such a way that it largely shields the workpiece carrier (4) against direct incidence of the laser radiation during laser polishing of the workpiece (5) in the workpiece carrier (4), and - a protective enclosure (1, 2) which, alone or in conjunction with the workpiece carrier (4), forms a closed chamber around a surface to be polished of a workpiece (5) held by the workpiece carrier (4) and has a removable lid (1), - wherein the workpiece carrier (4), the shielding element (3) and the protective enclosure (1, 2) are made of materials that can withstand temperatures up to at least 500°C, and the material of the workpiece carrier (4) is selected to have a thermal conductivity of less than 20 W / (m K) at a temperature of 500°C. [2] Mobile processing chamber (10) according to claim 1, characterized by , that the material of the workpiece carrier (4) is selected such that it has a thermal conductivity which is less than 10 W / (m K) at a temperature of 500 °C. [3] Mobile processing chamber (10) according to claim 1, characterized by , that the material of the workpiece carrier (4) is selected such that it has a thermal conductivity which is less than 1 W / (m K) at a temperature of 500 °C. [4] Mobile processing chamber (10) according to one of claims 1 to 3, characterized by, that a support surface of the workpiece carrier (4) for a workpiece (5) to be polished is structured, so that a received workpiece (5) has a smaller contact area to the workpiece carrier (4) than without structuring of the support surface. [5] Mobile processing chamber (10) according to one of claims 1 to 4, characterized by , that the workpiece carrier (4) has an opening or recess for receiving the workpiece (5) to be polished and is designed such that a received workpiece (5) only rests on the workpiece carrier (4) at the edge of the opening or recess. [6] Mobile processing chamber (10) according to one of claims 1 to 5, characterized by , that the workpiece carrier (4), the shielding element (3) and the protective enclosure (1, 2) are made of materials that can withstand temperatures up to at least 800 °C. [7] Mobile processing chamber (10) according to one of claims 1 to 5, characterized by, that the workpiece carrier (4), the shielding element (3) and the protective enclosure (1, 2) are made of materials that can withstand temperatures up to at least 1100 °C. [8] Mobile processing chamber (10) according to one of claims 1 to 7, characterized by , that the removable lid (1) extends laterally beyond a side wall (2) of the protective enclosure (1, 2). [9] Mobile processing chamber (10) according to one of claims 1 to 8, characterized by , that the workpiece carrier (4) forms a base of the mobile machining chamber (10). [10] Mobile processing chamber (10) according to claim 9, characterized by , that the shielding element (3) and the protective enclosure (1, 2) are designed to be removable from the workpiece carrier (4). [11] Mobile processing chamber (10) according to claim 10, characterized by , that the removable cover (1) of the protective enclosure (1, 2) is identical to the workpiece carrier (4). [12] Mobile processing chamber (10) according to one of claims 1 to 11, characterized by , that the workpiece carrier (4) is made of a ceramic. [13] Mobile processing chamber (10) according to one of claims 1 to 12, characterized by , that the shielding element (3) is only in contact with the workpiece carrier (4) at an outer edge. [14] Mobile processing chamber (10) according to any one of claims 1 to 13, characterized by , that the shielding element (3) is plate-shaped. [15] Machining chamber (10) Mobile according to one of claims 1 to 14, characterized by , that the shielding element (3) has a reflective coating. [16] Use of several of the mobile processing chambers (10) according to one of claims 1 to 15 in the laser polishing of glass workpieces, in the - each of the workpieces (5) to be polished is placed in the workpiece carrier (4) of one of the mobile processing chambers (10) and the processing chambers (10) are closed with the lid (1); - the processing chambers (10) are subsequently preheated with the workpieces (5) contained therein in one or more ovens and fed to a laser polishing arrangement or directly fed to a laser polishing arrangement; and - the lid (1) of each processing chamber (10) is automatically lifted, the workpieces (5) are polished in the processing chambers (10) with a laser (12) and the lid (1) is then automatically replaced. [17] Use according to claim 16, wherein the processing chambers (10) are conveyed into an oven (13) after laser polishing with the workpieces (5) contained therein and cooled there in a controlled manner. [18] Use according to claim 17, wherein the processing chambers (10) are tempered together before cooling in the furnace (13). [19] Use according to any one of claims 16 to 18, wherein the shielding element (3) and the protective housing (1, 2) of the mobile processing chambers (10) are designed to be removable from the workpiece carrier (4) and the respective workpiece (5) is turned over in the laser polishing arrangement after laser polishing of a first side and then a second side of the workpiece (5) is polished with the laser (12), wherein for turning the workpiece (5) - the shielding element (3) and the protective housing (1, 2) are removed from the workpiece carrier (4), hereinafter referred to as the first workpiece carrier (4), - a second workpiece carrier (4) with its receiving area directed towards the workpiece (5) is placed on top of the workpiece (5), - the two workpiece carriers (4) with the intermediate workpiece (5) are turned by 180°, - the first workpiece carrier (4) is removed from the workpiece (5), and - the shielding element (3) and the protective housing (1, 2) are placed on the second workpiece carrier (4). [20] Use according to claim 19, wherein the second workpiece carrier (4) is either held separately or forms the removable cover (1) of the protective enclosure (1, 2).

Images