Non-contact method for testing demoulding forces in tool-bound manufacturing processes using sound measurement

Abstract

The invention relates to a method for detecting sound waves during a tool-dependent manufacturing process in order to detect demolding problems during production. The tool consists of at least two mold halves (1 and 2), between which the manufactured component is formed. Using a sound measuring device (4), all relevant vibrations are recorded and evaluated via airborne sound. This recording is completely contactless, since the vibrations generated by the manufactured component (3) during demolding are only transmitted by the component into the air and cannot be measured through contact. The method can increase the quality of the manufactured components, reduce costs, and realize the feasibility of complex components.

Description

Technical Field of ApplicationThe present invention relates to a method for measuring occurring demolding forces, by means of detection of excited sound waves, during a tool-bound production process. This detection is completely contactless. For the detection of the sound waves in the form of frequencies, it is sufficient to place the acoustic measurement test means in the immediate vicinity of the component to be produced. There is therefore no direct contact between sensor system and production.The different frequencies of the manufacturing process are determined in a contactless manner during this sound measurement. As a result, the frequencies of the manufactured component are also recorded during demolding. In this process step, the component is set in vibration by the ejection. The stronger the component adheres in the tool due to adhesion, the greater is the required demolding force and thus the impulse which acts on the component during demolding. This pulse generates sound waves from the component, which sound waves can be unambiguously assigned to the demolding process and thus make changes visible during the demolding. The relevant frequencies occurring in this case begin in the single kilohertz range and can extend into the megahertz range. This detection is not possible with touching sensors, such as a piezo sensor system, for example, since the relevant sound waves are generated during demolding and there is no longer any contact with the tool. On the basis of the recorded frequencies during the demolding process, increased demolding forces can thus be detected and evaluated in a process-accompanying manner. The method to be patented can lead to a considerable cost reduction, since quality checks with regard to mould release problems are no longer necessary. In the case of components to be produced with extreme demolding problems, feasibility in series production can be implemented by the method, since waste can be sorted out directly in the process.Sound measurement is used in a wide variety of fields. Integration into different processes, even later, is very simple due to the contactless mode of operation. Loud noises or other sound sources, which are present continuously or repeatedly, generate frequencies which are also recorded. These fundamental frequencies are always present in corresponding production environments. Because of their different signature, they can be separated or neglected with respect to the oscillations occurring during the measurement, since they are either not picked up or masked out because of physical conditions. The main focus is therefore on the spontaneously occurring frequencies which characterize a deviation from the fundamental frequencies.Prior ArtFor the production of components, the method of tool-bound production is the most widely used method. The individual process steps must function reliably, since this is a highly automated process. One of the last process steps is the demolding of the component from the tool cavity. In order to ensure reliable demolding, in some production methods, already in the construction so-called draft angles are provided on the component, parting agent is sprayed into the tool cavity or additives are added to the material to facilitate demolding.Despite these methods, high demolding forces can occur due to disadvantageous molding geometries, low surface roughnesses or material requirements. In the case of unfavourable tool material pairings or process parameters, adhesive boundary surface forces can lead to a right-of-rule adhesion of the components to the tool surface. In the case of unfavourable moulding geometries, shrinkage of the component to be produced onto the tool can occur in the case of certain materials in the tool-bound production process. This results in additional frictional forces during demolding, which hold the component in the tool. To separate these boundary surface and frictional forces, a multiple of the expected demolding forces may be required. The consequences are components which are damaged by demolding or are completely unusable. The causes of defective components are manifold, so that a clear conclusion about the adhesion is not possible. The achievement of fault-free components therefore frequently depends on the experience of the setter of the machine or is associated with iteration loops in tool construction, which prove to be time-consuming and cost-intensive. By ascertaining the adhesion that may potentially occur, it is possible to speed up this process by making it possible to take optimization measures. Such optimization measures can be, for example, the change of the tool surface, by means of a mechanical machining or a coating, or the change of process parameters.In the tool-bound production process of injection molding, a determination of the demolding forces can be carried out outside industrial production. In this case, there are various measurement tools which have been developed explicitly for the demolding force measurement. The principle is that a test geometry is produced in each case in the injection molding process and is subsequently removed from the mold with the aid of ejector pins that are customary in the injection molding process. A force sensor is integrated into the tool, which measures the forces necessary for the ejection. To examine different material-tool surface pairings and to characterize the demolding forces, a specimen body that can be exchanged in the tool and has different coatings and surface topographies is used. The presence of adhesion is thereby manifested by high force peaks at the beginning of the demolding.The external measurement generally leads to a molding geometry in the test tool that differs from the production tool, which can have an influence on the demolding. The measuring tools must be manufactured explicitly and with great effort and can therefore only be found in research and test laboratories. Although it is possible to find general correlations with occurring forces and adhesion in defined material pairings, it is generally necessary to test the potentially problematic material pairing from production because of the multiplicity of existing and repeatedly newly developed materials and surfaces. A prerequisite for this is the production of a sample body with the corresponding surface. In this case, the exact replication of the surface from the production tool is required.The object of the present invention is therefore to carry out a measurement of the demolding force during the production process. With the aid of this measurement, a statement can be made in the production process about the quality of the produced component and a potentially required adaptation of the process can take place.SUMMARY OF THE INVENTIONThe object is achieved by the method according to claim 1. Advantageous embodiments of the method are the subject matter of the dependent patent claims or can be gathered from the following description and the exemplary embodiments. The proposed method is designed for the production process of components with a tool. Depending on the production method or the structure of the production process, the test means can be adapted and adapted. However, at least one acoustic measurement test means and a tool consisting of two halves are present in the proposed embodiment.The proposed structure is distinguished in that the test means is mounted outside the tool at a defined distance from the manufactured component. The test means must be located in the immediate vicinity of the tool and the component to be produced. If other elements are located between the test means and the tool, such as a protective disk, this can greatly impair a measurement of the relevant oscillations. The distance between the test means and the component to be produced is determined by the oscillations to be measured and the available installation space. The manufacturing process is not influenced by the method for checking the demolding forces. The oscillations to be detected are detected by the measuring device without a time delay. The evaluation can take place in process-related fashion and thus enable direct sorting out of bad parts or else take place downstream. For the evaluation, hardware is required which has the necessary resources in order to evaluate the oscillation in the frequency band to be examined and can in the process communicate with the various process participants. These resources also include the necessary software for evaluating the measurement data.The oscillations of the production process, which become visible in the evaluation, represent the totality of the oscillations that occur. By filtering out the ambient noise or by matching the oscillations which occur during the production of a product part with the oscillations which occur during the current production process, the oscillations which lead to a poor part can be identified. Analysis of functioning and defective components limits the frequency range which indicates difficulties in demolding the component to be produced. This enables optimization of the method, since a specific range of the frequencies to be measured is defined and all frequencies are no longer measured. If frequencies are present which indicate difficulties in mould removal, this indicates the production of a poor part. This can be sorted out directly or verified by a possible automated or manual check. Process parameters can likewise be adjusted during the production process by the result in order to further avoid mould release difficulties.The proposed method thus enables integration of the determination of the demolding forces with the series production of components in production. This makes it possible to make industrial production of components more efficient, since bad parts are recognized directly and sorted out. Likewise, the detection of the demolding forces can give rise to indications of a change in the process parameters, with the result that the production process can be further optimized.A production-accompanying test of the demolding forces does not take place in existing plants. This can lead to all manufactured components having to be subjected to quality control. Since demolding problems frequently occur at locations with high surface quality, automatic testing is usually not possible. For this reason, such quality controls are usually performed by human personnel with manual visual control. These quality controls are therefore at risk for human failure. There is an increased probability that defective parts are delivered. In the production of mould-release-critical components, the introduction of the proposed method as a production-accompanying test of the mould-release forces can therefore lead to considerable cost savings and thus to increased efficiency.List of FiguresThe proposed structure of the test method is explained in more detail below with reference to exemplary embodiments in conjunction with the drawings. The following are shown here: FIG. 1 is a schematic illustration of the structure of a measurement with a closed tool; FIG. 2 shows a schematic illustration of the structure of a measurement with the tool open; FIG. 3 shows a schematic illustration of the structure of a measurement with the tool opened and a component in ejection; FIG. 4 shows a schematic illustration of the structure of a measurement with the tool opened and a component ejected; FIG. 5 is a schematic illustration of the structure of a measurement with the tool opened and a finished component; FIG. 6 shows a schematic illustration of the structure of a measurement in the injection molding method with the tool opened and an ejected injection molding component; FIG. 7 shows a schematic representation of the measurement with an optical microphone as a testing means; FIG. 8 shows a schematic illustration of the measurement with an adjustable measurement range of the test means;WAYS OF CARRYING OUT THE INVENTIONAn exemplary embodiment of the method structure according to the invention can be seen in FIG. 1. The entire production sequence is illustrated in FIGS. 1 to 5. A tool is used to produce the component. This tool is divided into two halves. In this case, it is possible for the tool halves to assume other positions in space, for example one half at the top and the other half at the bottom. The manufactured component 3 is formed between the tool halves. The acoustic measurement test means 4 is located at a distance from the tool.In order to remove the manufactured component 3 from the tool, the tool is opened, as shown in FIG. 2. The left-hand tool half 1 and the right-hand tool half 2 move apart. In this manufacturing step, the acoustic measurement test means 4 starts to measure the oscillations that occur.As soon as the end positions of the left-hand tool half 1 and the right-hand tool half 2 are reached, the manufactured component 3 is ejected, as depicted in FIG. 3. The ejection of the component can be carried out in various ways. During this process, all oscillations to be measured are recorded by the acoustic measurement testing means 4. If the manufactured component 3 is now held in the tool by adhesion, then during demolding other oscillations occur than if the component is ejected without adhesion. The oscillations absorbed without adhesion serve as a basis for the production of parts of goods. If these oscillations change to a higher frequency at the beginning of demolding, this is an indication that adhesion and thus increased demolding forces are present.The manufactured component 3 is completely removed from the mold until it no longer makes contact with the mold halves 1 and 2, as shown in FIG. 4. The evaluation of the recorded oscillations by the acoustic measurement test means 4 can take place directly during this process step. Until the manufactured component 3 is removed from the tool, as shown in FIG. 5, it can be judged by the evaluation whether it is a good part or a bad part. The component produced can thus be sorted during removal according to quality, with regard to adhesion. Subsequent monitoring of the goods items with regard to the demolding force is no longer necessary. The bad parts can be subjected to a renewed visual inspection in order to minimize the waste, with smaller admissible quality deviations.FIG. 6 shows a further exemplary embodiment. The tool-bound production process is here injection molding with an injection unit 6. In this process, it is possible that increased demolding forces occur due to the hot material melt, which in turn can be detected using the acoustic measurement test means 4.A further exemplary embodiment is shown in FIG. 7. An optical microphone 7 is used here as a sound measurement test means 4. This optical microphone has a laser-based measurement method, so that process monitoring over a very large frequency range is possible.In order to keep the data to be evaluated as low as possible, it may be expedient to limit the measurement range of the acoustic measurement device 4 to be set. This is illustrated in a further exemplary embodiment in FIG. 8. The acoustic measurement test means 4 has an adjustable measurement range 8, whereby only frequencies within the set range can be detected and evaluated.List of reference characters1 Left-hand tool half 2 Right-hand tool half 3 Manufactured component 4 Sound measurement test means 5 Manufactured injection-molded component 6 Injection-molded unit 7 Optical microphone 8 Adjustable measurement range

Claims

Method for testing demolding forces during the production process of components (3) using a tool (1 and 2), in that the oscillations generated by the produced component (3) are detected and evaluated in a contactless manner in the high-frequency range, during the demolding process, by means of a sound-measuring-technical testing means (4) using airborne sound. The impulse generated by the demolding on the manufactured component ( 3) generates oscillations which can be clearly traced back to the demolding forces.Method according to Claim 1, wherein adhesion and frictional forces are determined via excited oscillations.Method according to claim 1, wherein the acoustic measurement test means (4) is an optical microphone (7).Method according to claim 1, wherein the oscillations to be measured are set to a region (8) to be measured via the acoustic measurement testing means (4).Method according to Claim 1, wherein, for example, injection-moulded components (5) are produced in the injection-moulding process.

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