Method for producing a thermoformed plastic part

Abstract

The invention relates to a method for producing a thermoformed plastic part, specifically a dental splint, based on a plastic semi-finished product, preferably a plastic film, wherein: a model form (2) is supplied, together with the plastic semi-finished product, to a thermoforming device (1); the plastic semi-finished product is pre-heated to a processing temperature; and, in a shaping step, the plastic semi-finished product is pressed onto the model form (2) so that the contours of the model form (2) are transferred to the plastic semi-finished product; after which, in order to demould the shaped plastic part, said plastic part is separated from the model form (2). In order to design such a method so that, despite low production times or cycle times for producing dental splints, scrapping of faulty dental splints is reduced or at best completely prevented, according to the invention: a model form (2) is provided which has at least one fixing attachment (3) projecting from the model form (2); prior to the shaping step, the model form (2) is fixed in its position by clamping the at least one fixing projection (3); and, after demoulding the plastic part, the at least one fixing projection (3) is released again.

Description

[0001] Process for producing a thermoformed plastic part

[0002] Technical area

[0003] The invention relates to a method for producing a thermoformed plastic part, namely a dental splint, based on a semi-finished plastic product, preferably a plastic film. A model mold is fed together with the semi-finished plastic product to a thermoforming device, the semi-finished plastic product is preheated to a processing temperature, and in a forming step, the semi-finished plastic product is pressed onto the model mold such that the contours of the model mold are transferred to the semi-finished plastic product. Afterward, the molded plastic part is separated from the model mold to demold it. The invention also relates to a thermoforming device and a model mold, namely a denture model, for a method according to the invention.

[0004] State of the art

[0005] In the field of orthodontics, dental splints can be used to correct misaligned teeth. Their production requires several separate steps. After recording the actual position of a patient's teeth, a dental professional determines the desired position of the teeth. The actual and desired positions are then interpolated to determine a variety of individual model shapes, which can be used to gradually adjust the tooth position. These model shapes serve as molds for the thermoforming of thermoplastic films, which must be removed from the molded part, trimmed to size, and deburred so that the patient can use these processed films as dental splints. These work steps are usually carried out in specially designed workstations, with the production of the thermoformed plastic film taking place in a so-called thermoforming station.

[0006] The state of the art includes various thermoforming stations that shape plastic films based on 3D dental models. A precise fit is essential here, as even the slightest deviation from the ideal shape makes medical use of the subsequently obtained dental splints no longer practical. A disadvantage of the state of the art is that the 3D dental model tends to be moved or shifted on the model carrier away from a predetermined target position when pressure is applied. This can lead to errors in the production process and thus to the rejection of the manufactured dental splint, or if not recognized, even to the use of malformed dental splints on the patient. A further disadvantage is that the thermoformed plastic film can become stuck to the dental model due to the numerous undercuts, meaning that demolding is only possible with additional manual intervention.When demoulding the plastic film, it can be deformed in an undesirable way or even damaged.

[0007] Methods and model forms of the type described above are known, for example, from US2022280265A1, US2021 178639A1, US2020290262A1, WO20231 50124A1 and US10286594B2.

[0008] Description of the invention

[0009] The invention is therefore based on the object of designing a method of the type described above in such a way that, despite short production or cycle times for the manufacture of dental splints, the waste of malformed dental splints is reduced or, at best, completely avoided.

[0010] The invention achieves this objective by providing a mold having at least one fixing extension projecting from the mold and spanning a fixing region extending at least 180° around the mold. Prior to the molding step, the mold is secured in position by clamping the at least one fixing extension. After demolding the plastic part, the at least one fixing extension is released. These measures prevent unwanted slippage of the mold during the thermoforming process without subjecting sensitive parts of the mold itself to potentially damaging clamping forces.In addition, simple and reliable detachment of the plastic part from the model mold is made possible because the at least one protruding fixing extension remains clamped during the entire thermoforming process, so that even when transverse forces are applied, displacement of the model mold can be prevented by the force-fitting, preferably material-fitting, connection between the model mold and the at least one fixing extension. The uniform clamping of the at least one fixing extension and uniform force transfer are improved in that the at least one fixing extension spans a fixing area extending over at least 180° around the model mold. According to the invention, a protrusion of the at least one fixing extension from the model mold in the case of a denture model having a dental arch can basically be understood as a protrusion or projection from the dental arch. The at least one fixing extension preferably projects transversely orin particular radially with respect to a model mold vertical axis from the model mold. In a preferred embodiment, a plurality of fixing extensions can also be provided. A particularly favorable distribution of forces on the at least one fixing extension can be achieved if it is designed at least partially circumferentially as a fixing seam around the model mold. Preferred conditions arise if the model mold is designed as a single piece together with the at least one fixing extension and / or is produced by means of additive manufacturing, for example 3D printing, preferably FDM 3D printing. It is essential for the design of the model mold that the at least one fixing extension has a geometry that is as easy to 3D print as possible and that, on the other hand, the pulling forces can be dissipated favorably for a problem-free demolding process when the plastic part is pulled off the model mold.The invention also relates to a thermoforming device with a hood that is displaceable relative to a model mold carrier between a forming position and an open position, which, in the forming position, forms a pressure chamber together with the model mold carrier to which compressed air can be applied. To carry out the method according to the invention, a model fixing device is provided for clamping the at least one fixing extension of a model mold, which is arranged between the hood and the model mold carrier with respect to the installation height, and the model mold carrier is displaceable relative to the model fixing device between a base position and a fixing position. As a result of these measures, the model mold carrier can be displaced relative to the model fixing device, for example by means of a lifting device, until the fixing extension is clamped between the model mold carrier and the model fixing device.According to the invention, the hood is displaceable relative to the model mold carrier, and the latter relative to the model fixing device. All three components can be arranged so as to be movable, or one of the components, in particular the model fixing device, can be stationary, while the other two components, in particular the model mold carrier and hood, move relative to the stationary component during the process according to the invention. In a preferred embodiment, the pressure chamber, which can be pressurized with compressed air, has a corresponding seal that enables the required deformation pressure to be achieved. It goes without saying that the pressure chamber can have corresponding compressed air inlets and outlets.

[0011] In order to prevent damage to the fixing extension due to the clamping force of the model fixing device and to enable reliable clamping of the model mold, the model fixing device can have an insertion opening for the model mold carrier, which includes a shoulder that interacts with the model mold carrier in the fixing position to form a fixing gap. As a result, a defined clamping force with a constant clamping distance acts on the fixing extension. Preferably, the at least one fixing extension is designed such that it has an at least partially circumferential fixing seam for interacting with the shoulder of the fixing opening in the formed fixing gap. Preferably, the shoulder of the fixing opening and consequently the fixing gap in the fixing position can be designed to surround the fixing opening. In principle, the fixing opening can also be designed solely to accommodate the model mold.

[0012] To generally improve the handling of the plastic semi-finished product and enable a reliable thermoforming process with a compact design, it is recommended that a semi-finished product clamping device be arranged between the hood and the model fixing device with respect to the installation height. This clamping device has a semi-finished product carrier that can be moved between a base position and a clamping position relative to a clamping body, whereby both the semi-finished product carrier and the clamping body each have through-openings corresponding to the insertion opening of the model mold carrier. This allows the plastic semi-finished product to maintain its position even when subjected to tensile forces caused by the plastic deformation and compressive forces from the pressure chamber pressurized with compressed air during the thermoforming process. This prevents undesired slipping of the plastic semi-finished product during the thermoforming process.In a preferred embodiment, the through openings of the semi-finished product carrier and the clamping body are arranged coaxially to the insertion opening of the model fixing device.

[0013] In order to ensure the longevity of the thermoforming station with a compact design, even under high pressure from the components, it is proposed that the hood and the model mold carrier be displaceable along a common vertical axis extending parallel to the assembly height. As a result of these measures, no or only minimal transverse forces or moments occur during the implementation of the method according to the invention due to the various displacement movements along the vertical axis, so that the corresponding components are subject to reduced wear. In a preferred embodiment, the model fixing device and / or the semi-finished product clamping device can also be arranged so that they can be displaced along said vertical axis.The invention also relates to a model mold, namely a denture model, for a method according to the invention, which has at least one fixation projection protruding from the model mold and spanning a fixation area extending over at least 180° around the model mold. Structurally favorable conditions arise when the at least one fixation projection protrudes radially from the model mold with respect to the vertical axis of the model mold.

[0014] To prevent the model form from tilting or rotating due to the uniform clamping of the at least one fixing extension, it is advantageous if the at least one fixing extension forms a fixing seam that at least partially surrounds the model form. As a result of this measure, the clamping force can act equally over a large area around the model form, and a particularly advantageous force transfer can be achieved via the at least one fixing extension without deforming or even damaging sensitive areas on the model form, in particular any tooth fissures.

[0015] Improved demolding while simultaneously reducing manufacturing effort can be achieved by having the fixation seam comprise several fixation projections designed as fixation fingers and projecting radially from the model mold, arranged at a distance from one another. This radial design allows for a large clamping surface while simultaneously reducing material consumption during production. Particularly advantageous manufacturing conditions can be achieved if the fixation projections are manufactured in one piece with the model mold using an additive manufacturing process.

[0016] Brief description of the invention

[0017] The drawing shows an example of the subject matter of the invention.

[0018] Fig. 1 is a schematic oblique view of a thermoforming device according to the invention, Fig. 2 is a sectional view corresponding to Fig. 1 in the area of ​​the model fixing device and the model carrier in the basic position, on an enlarged scale,

[0019] Fig. 3 of Fig. 2 corresponding representation with model carrier and model fixing device in fixing position, and

[0020] Fig. 4 a schematic oblique view of a model form according to the invention with fixing projections

[0021] Ways to implement the invention

[0022] The process steps underlying a method according to the invention for producing a plastic part, namely a dental splint, are explained in more detail below. After determining the actual and desired state of a patient's tooth position, the interpolated steps of the tooth positions are designed as 3D models. To produce a dental splint in a thermoforming station 1, one of these 3D models can be printed as a model mold 2 using additive manufacturing in another workstation (not shown). The model mold 2 is therefore covered in the thermoforming station 1 with a previously heated plastic film in order to obtain a precisely fitting dental splint. To prevent possible errors due to slipping of the model mold 2 during the thermoforming process, the invention provides that the model mold 2 has at least one fixing projection 3, by means of which the model mold 2 can be temporarily fixed in its position.

[0023] A thermoforming device 1 for a method according to the invention for producing a thermoformed dental splint is shown schematically in Fig. 1. Using a preferably 3D-printed model mold 2, a preheated plastic film is pressed onto the model mold 2 so that the contours of the model mold 2 are transferred to the plastic film. The model mold 2 is clamped onto fixing projections 3 protruding from the model mold 2. For reasons of clarity, the plastic film is not shown in detail in the drawings. The model mold 2, which is a denture model, is arranged on a movable model mold carrier 4, which can be displaced relative to a movable hood 5 along a vertical axis H running parallel to the installation height.The model mold carrier 4 is also displaceable along the vertical axis H relative to a model fixing device 6, which has an insertion opening 7 for the model mold carrier 4.

[0024] For clamping the plastic film, the thermoforming device 1 has a semi-finished product clamping device, which comprises a semi-finished product carrier 8, preferably provided with holding domes, and a clamping body 9 movable relative thereto. The semi-finished product clamping device can be displaced along a sliding carriage 10 transversely to the vertical axis H in the direction of a film heating plate 11, which is arranged laterally spaced from the vertical axis H. The semi-finished product carrier 8 has a through-opening 12 for the model mold 2. The clamping body 9 also has a corresponding through-opening, which, according to the snapshot shown in Fig. 1, is partially penetrated in this case by the hood 5. Preferably, the through-openings 12 of the semi-finished product carrier 8 and the clamping body 9 run coaxially with the insertion opening 7 of the model fixing device 6.The through-opening 12 and the insertion opening 7 can be arranged substantially coaxially with each other with respect to their opening axes, so that in the molding position, the model mold 2, covered with the plastic film, can protrude into the pressure chamber formed by the hood 5 and the model mold carrier 4. The model mold carrier 4 and the hood 5 can be moved, for example, using a lifting device 13.

[0025] As shown with regard to the model fixing device 6 in Fig. 2 (basic position) and Fig. 3 (fixing position), this has a shoulder 14 surrounding the insertion opening 7 to form a fixing gap 15. The fixing extensions 3 of the model mold 2 can be clamped in this fixing gap 15 between the shoulder 14 of the model fixing device 6 and the model mold carrier 4 in a force-fitting manner, possibly with the formation of a certain pinching of the fixing extensions 3 in the fixing gap 15. In order to enable error-free thermoforming of a plastic film, the model mold 2 can be displaced by the lifting device 13 in the direction of a model fixing device 6, after which the fixing extensions 3 can be clamped in the fixing position between the shoulder 14 and the model mold carrier 4 in the fixing gap 15.The model form 2 passes through the insertion opening 7 of the model fixing device 6 so that the denture contours can protrude in the direction of the semi-finished product clamping device and the hood 5.

[0026] A model mold 2 according to the invention is shown schematically in Fig. 4. Evenly spaced fixing extensions 3 protrude radially from the model mold 2 with respect to the model mold vertical axis 16. The fixing extensions 3 are designed as fixing fingers and form a fixing seam that extends over a fixing area of ​​more than 180° around the model mold 2. When carrying out a method according to the invention, with the model mold 2 resting on the model mold carrier 4, the model mold vertical axis 16 and the vertical axis H preferably coincide or run parallel to one another.

Claims

Patent claims 1. A method for producing a thermoformed plastic part, namely a dental splint, based on a semi-finished plastic product, preferably a plastic film, wherein a model mold (2) is fed together with the semi-finished plastic product to a thermoforming device (1), the semi-finished plastic product is preheated to a processing temperature, and in a forming step, the semi-finished plastic product is pressed onto the model mold (2) so that the contours of the model mold (2) are transferred to the semi-finished plastic product, after which the molded plastic part is separated from the model mold (2) to demold it, characterized in that a model mold (2) is provided which has at least one fixing extension (3) projecting from the model mold (2) and spanning a fixing region extending over at least 180° around the model mold (2),that before the forming step, the model mold (2) is fixed in its position by clamping the at least one fixing extension (3), and that after demolding of the plastic part, the at least one fixing extension (3) is released again.

2. Thermoforming device (1) for carrying out a method according to claim 1, with a hood (5) which can be displaced relative to a model mold carrier (4) between a molding position and an open position and which, in the molding position, forms a pressure chamber which can be pressurized with compressed air together with the model mold carrier (4), characterized in that a model fixing device (6) is provided for clamping the at least one fixing extension (3) of a model mold (2) and is arranged between the hood (5) and the model mold carrier (4) with respect to the installation height, and the model mold carrier (4) can be displaced relative to the model fixing device (6) between a base position and a fixing position.

3. Thermoforming device (1) according to claim 2, characterized in that the model fixing device (6) has an insertion opening (7) for the model mold carrier (4), which in the fixing position with the model mold carrier (4) cooperating shoulder (14) to form a fixing gap (15).

4. Thermoforming device (1) according to claim 2 or 3, characterized in that with respect to the installation height between the hood (5) and the model fixing device (6) a semi-finished product clamping device is arranged, which has a semi-finished product carrier (8) which can be displaced relative to a clamping body (9) between a base position and a clamping position, wherein both the semi-finished product carrier (8) and the clamping body (9) each comprise through openings (12) corresponding to the insertion opening (7) of the model fixing device (6).

5. Thermoforming device (1) according to one of claims 2 to 4, characterized in that the hood (5) and the model mold carrier (4) are displaceable along a common vertical axis (H) extending parallel to the construction height.

6. Model form (2), namely a denture model, for a method according to claim 1, with at least one fixing extension (3) projecting from the model form (2), characterized in that the at least one fixing extension (3) spans a fixing area extending over at least 180° around the model form (2).

7. Model form (2) according to claim 6, characterized in that the at least one fixing extension (3) projects radially from the model form (2) with respect to the model form vertical axis (16).

8. Model form (2) according to claim 6 or 7, characterized in that the at least one fixing extension (3) forms a fixing seam which at least partially surrounds the model form (2).

9. Model form (2) according to claim 8, characterized in that the fixing seam comprises several fixing fingers designed as fixing fingers and extending radially from the Model form (2) comprises protruding fixing projections (3) which are arranged at a distance from one another.

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