Method for eddy current testing of cast components in a production line

Abstract

Method for eddy current testing of cast components (100) in a production line, wherein the cast components (100) are tested individually, comprising the steps: - Arranging the cast component (100) to be tested in a holder (300) which has at least two eddy current sensors (310); - Measuring local electrical conductivities of the cast component (100), for which each eddy current sensor (310) performs at least one measurement; - Evaluating the measurements, for which the measured values ​​of each eddy current sensor (310) are compared with a specific target value range (S), whereby the correct position of the cast component (100) arranged in the holder (300) is first detected using the eddy current sensors (310) and the measurements are then started automatically; - Evaluate the cast component (100) as defective if at least one measured value is outside the specific target value range (S), otherwise evaluate the cast component (100) as free of defects.

Description

[0001] The invention relates to a method for eddy current testing of cast components in a production line.

[0002] Cast components, which in the context of this invention refer to metal castings and in particular light metal castings, can exhibit manufacturing defects or flaws. These include component cracks, but also deviations from the target hardness or strength (of the casting material), especially after heat treatment (e.g., after T5, T6, or T7 heat treatment), as well as defects in the alloy composition. For example, in an AlSiMg casting alloy, the Mg content is of particular importance.

[0003] The testing of strength and hardness (it is assumed that strength and hardness are correlated) as well as the alloy composition can be carried out on a sample basis during the production of the castings or before further processing, often using destructive testing methods (e.g., tensile testing or Charpy impact testing). Furthermore, such sample-based tests do not allow for comprehensive statements about an entire batch and only permit significant time lags in influencing the manufacturing process. Therefore, an inline testing system is desirable, enabling cycle-time-based testing of each casting within a production line, preferably for strength and hardness as well as alloy composition (especially with regard to the content of at least one alloy component).

[0004] US Patent 2013 / 0035873A1 describes a method for determining one or more mechanical properties during the manufacture of a metal alloy article, such as a sheet during rolling. The described method includes the non-destructive determination of the electrical resistivity or conductivity of the metal alloy article using pulsed eddy current testing, calculation of the dissolved alloying element content in the metal alloy based on the measured resistivity, and subsequent calculation of at least one internal mechanical property of the metal alloy, such as tensile strength or yield strength.

[0005] The nearest US 2006 / 0254679A1 describes, among other things, a procedure for eddy current testing of cast strands, with the following steps: - Moving the casting strand to be tested through a device (rotary eddy-current flaw detection apparatus) which has at least two eddy current sensors; - Measuring the casting strand using eddy current sensors; - Evaluating the measurements; - Evaluating the casting strand as defective or defect-free.

[0006] The invention aims to create a method for eddy current testing of cast components in a production line, enabling reliable individual testing of each cast component, particularly with regard to strength or hardness as well as alloy composition.

[0007] This is achieved with the inventive method of claim 1. Preferred further developments and embodiments of the invention are set out in the dependent claims, the following description of the invention and the drawing.

[0008] The inventive method for eddy current testing of cast components in a production line comprises at least the following steps, which are carried out in particular automatically: - Arranging the cast component to be tested in a holder or the like, which has at least two eddy current sensors; - Measuring local electrical conductivities, in particular local specific electrical conductivities, of the cast component, for which each eddy current sensor (of the holder) performs at least one measurement; - Evaluating the measurements, for which at least one measured value or the measured values ​​of each eddy current sensor are compared with a specific (i.e., predefined for the cast components to be tested or the type of cast component to be tested and the respective measuring point, in particular determined by reference measurements) target value range, whereby the correct position of the cast component arranged in the holder is first detected using the eddy current sensors and then the measurements are started automatically; - Evaluate the cast component as defective (bad part) if at least one measured value, i.e., at least one electrical conductivity measured by means of an eddy current sensor, lies outside the associated specific target value range; otherwise, i.e., if all measured values ​​lie within the specific target value ranges, evaluate the cast component as free of defects (good part); - if necessary, removing the cast component from the holder and inserting another cast component to be tested into the holder, especially in sync with the production line.

[0009] The method according to the invention enables process-integrated, cycle-based, non-destructive, sufficiently accurate, and largely automatable testing of each cast component (100% inspection) in a production line, e.g., during its manufacture or immediately after its manufacture and, if necessary, heat treatment (e.g., before palletizing), or before its installation or assembly. Defective cast components can then be sorted out. Furthermore, changes or fluctuations in the manufacturing process can be identified promptly, and, if necessary, corrective action can be taken, essentially in a quality control loop.

[0010] The method according to the invention enables, in particular, the verification of strength or hardness and / or alloy composition. The invention makes use of the knowledge or discovery that a correlation exists between electrical conductivity (or equivalently, electrical resistance) measured by eddy current and, on the one hand, strength or hardness, and on the other hand, alloy composition, especially the magnesium content of an aluminum (casting) alloy. For each cast component, the measured values ​​and / or the results of the evaluation can be documented or recorded (component-specifically).

[0011] To measure local electrical conductivities, the cast components to be tested are individually arranged in or held by a holder or similar device, which has at least two eddy current sensors arranged at different locations, since the cast components to be tested may exhibit locally different properties, particularly due to manufacturing processes. Preferably, these eddy current sensors are each designed with a transmitter or excitation coil and a receiver or measuring coil, which can also be arranged one above the other or even nested within each other. Preferably, the eddy current sensors are arranged on the holder in such a way that the generated magnetic fields do not interfere with each other, thus allowing the eddy current sensors to measure simultaneously. For this purpose, the eddy current sensors are preferably arranged with a minimum distance from each other that is at least three times the diameter (i.e.,≥ 3d, where d is the diameter of the active sensor area).

[0012] The cast components to be tested are preferably light metal cast components. In particular, they are heat-treated aluminum cast components (including die-cast components) made of an AlSiMg alloy, where the magnesium content and the strength or hardness (achieved through heat treatment) are to be tested. Such cast components are preferably automotive components, such as cylinder heads, engine blocks, chassis components, body components, etc.

[0013] Preferably, the cast component to be tested is positioned in the holder or inserted into the holder and, if necessary, removed again using a robot (industrial robot), e.g., using an articulated arm robot.

[0014] The eddy current sensors first detect the correct position of a cast component held in the holder. If the cast component is correctly positioned in the holder, measurements start automatically, particularly via a trigger signal. If the cast component is not correctly positioned in the holder, an error message can be generated, and the cast component can be aligned or repositioned, particularly with the help of a robot (see below).

[0015] Preferably, each eddy current sensor (on the mount) performs three measurements at varying frequencies. These frequencies are typically around 20 kHz.

[0016] Since temperature can affect electrical conductivity, it is preferred that temperature compensation be applied when evaluating the measurements. Particularly relevant are the ambient temperature, especially fluctuating ambient temperatures, and / or the temperature of the cast component, which may differ. The ambient temperature (room temperature) can be measured using a thermocouple. The temperature of the cast component can be measured using a pyrometer, which is preferably mounted on the fixture. Based on the measured ambient temperature and / or the measured temperature of the cast component, temperature compensation of the measured values ​​and / or the evaluation results can then be performed. The cast components to be tested may have residual heat from the preceding casting and / or heat treatment process (and thus a higher temperature than the ambient temperature).Using a mathematical component temperature or component cooling model, the casting component temperature can be simulated or calculated when measuring the local electrical conductivities (current process conditions and transport or transfer conditions can also be taken into account), so that a measurement of the casting component temperature for temperature compensation can then be omitted.

[0017] The cast components to be tested can be manufactured from different casting alloys, particularly in batches. It is preferred that, when evaluating the measurements, the corresponding specific target value ranges for the respective casting alloy (of the cast component to be tested) are selected (and used). The corresponding specific target value ranges can be determined, for example, by plausibility comparisons or plausibility checks from a group of possible target value ranges (which are stored, in particular, in a computer system, su). This preferably occurs automatically. Thus, the method according to the invention is able to recognize, virtually automatically, which casting alloy is currently being tested, so that no manual intervention is required. This automatic recognition of the casting alloy can also be used to sort the tested cast components according to their casting alloy.

[0018] After removing the (tested) cast component from the holder and before placing another (to be tested) cast component in the holder, i.e., between two consecutive measurement runs, the eddy current sensors can be calibrated. This involves adjusting or calibrating the eddy current sensors against the ambient air. This prevents or at least reduces signal drift.

[0019] The holder can be designed as a tray or the like. Alternatively, the holder can be designed as a gripping device mounted on a robot arm (of a transfer robot or the like). This allows the inventive method to be carried out within a production line during the (individual) transport or transfer of the cast components in a time- and space-neutral manner.

[0020] The measurements can be evaluated using a computer system equipped with at least one suitable software program. This computer system can also store the specific target value ranges, as well as the measured values ​​and / or evaluation results for each cast component. The computer system also enables batch-by-batch evaluation of the measured values ​​and / or evaluation results (batch analysis), particularly for determining defect rates, or for mathematical analysis of quality trends (e.g., through batch comparisons). The computer system can also be used to control the robot (handling robot) for inserting the cast components into the holder (and, if necessary, removing them from the holder).Preferably, this computer system is intended to automatically control the entire process (including evaluations) and, if necessary, also influence the production line or manufacturing process. For this purpose, the computer system can communicate with a central control unit for the production line (manufacturing plant).

[0021] A testing system for eddy current testing of cast components in a production line using the method according to the invention can comprise at least the following components: - a holder with at least two eddy current sensors in which the cast components to be tested can be arranged individually or in isolation; - a computer system (so) designed to evaluate the measurements taken with the eddy current sensors and, in particular, for the entire process control; as well as - possibly also a robot (handling robot) for placing the cast components to be tested into the holder and possibly also for removing the tested cast components from the holder, whereby this robot is preferably controlled by the computer system.

[0022] Alternatively, as explained above, the holder may be a gripping device attached to a robot arm (of a transfer robot or the like), and this robot, including the holder or gripping device, may be controlled by the computer system (so).

[0023] The invention is explained in more detail below by way of example and in a non-limiting manner with reference to the drawing. Fig. Figure 1 shows in a schematic diagram the qualitative relationship between the electrical conductivity of a cast component, measured by eddy current, and its strength or hardness. Fig. Figure 2 schematically shows a holder with a cast component to be tested arranged in it. Fig. Figure 3 illustrates the process of an inventive method for eddy current testing of cast components in a production line.

[0024] The in Fig. As shown in diagram 1, the electrical conductivity measured in a cast component by eddy current testing, and in particular the specific electrical conductivity, corresponds to a certain strength or hardness of the cast component. The hardness profile exhibits a maximum (peak). Within the region of this hardness maximum, the cast component is optimally manufactured, particularly including heat treatment, and the casting alloy has an optimal alloy composition. For an AlSiMg casting alloy, a magnesium content that is as precise as possible, i.e., conforming to the specifications, is of particular importance, especially with regard to hardenability and the resulting improvement in mechanical properties, but also potentially with regard to recycling or reusability.

[0025] Measuring electrical conductivity using eddy currents allows conclusions to be drawn about the strength or hardness of a casting, as well as its alloy composition, particularly the magnesium content of an AlSiMg casting alloy. This enables verification that the tested casting meets specifications. An electrical conductivity measured using eddy currents should therefore fall within a specific target range S, relevant to the casting under test and the respective (local) measurement point. This target range is determined primarily through prior reference measurements (on identical castings), possibly using destructive testing methods. The specific target range S can also be referred to as the characteristic conductivity range.

[0026] Fig. Figure 2 shows a holder 300 for a solid cast component 100. The holder 300 has several eddy current sensors 310, which can be either rigidly mounted or movably mounted (to minimize friction and wear). The eddy current sensors 310 can also be located on opposite surfaces of the cast component. Preferably, the eddy current sensors 310 are arranged and oriented such that their imaginary measuring axes do not intersect in the cast component 100 under test, in order to avoid mutual interference. Preferably, at least one of the eddy current sensors 310 is located at the thickest or thickest-walled point of the cast component, and another eddy current sensor 310 is located at the thinnest or thinnest-walled point of the cast component.

[0027] The eddy current sensors 310 are connected to a computer unit 400 for control, evaluation, and storage of the measurement and evaluation results. The holder 300 can be a storage tray already present in a production line for intermediate positioning or storage, which is configured accordingly. Alternatively, the holder 300 can be a separate measuring or testing station in a production line. Furthermore, the holder 300 can also be configured as a gripping device on a robot arm. The holder 300 and the computer unit 400 form a testing system 200.

[0028] Fig.Figure 3 illustrates a process flow according to the invention. To inspect cast components 100 in a production line, the cast components 100 to be inspected, particularly those with identical geometry, are individually arranged in the tray 300 (or picked up by a tray designed as a gripping device). Eddy current sensors 310 detect whether the cast component 100 to be inspected is located in or on the holder 300 and has the correct orientation or position (component and position detection). The measurement of the local electrical conductivity of the cast component 100 then begins automatically (the conductivity is measured or detected locally where an eddy current sensor 310 is located), for which each eddy current sensor 310 preferably performs three measurements, particularly with varying measurement frequencies. Depending on the arrangement, the eddy current sensors 310 can measure by contact or without contact.

[0029] For evaluation purposes, the measured values ​​recorded by each eddy current sensor 310 are compared in the computer unit 400 with a stored specific setpoint range S for that eddy current sensor 310. Temperature compensation can also be applied, as described above. Consequently, it can be determined whether the tested cast component 100 is free of defects and therefore a good part, or defective and therefore a bad part. The bad parts can then be sorted out, i.e., removed from the production line. The good parts remain in the production line.

[0030] The holder 300 is preferably designed for only one specific casting geometry, i.e., for geometrically identical castings. However, the holder 300 can also be designed for several different casting geometries, so that castings with corresponding geometries can be arranged or held in the holder. Preferably, the holder then has at least two eddy current sensors for each casting geometry, whereby individual eddy current sensors can also be provided for several casting geometries. After arranging a casting to be tested in such a holder, it can first be checked which eddy current sensors deliver plausible measured values ​​(or which eddy current sensors are not covered by the casting, i.e., remain virtually empty, and measure against the ambient air) and thus determine which casting geometry or which casting is involved. Subsequently, the (for this casting geometry orSpecific target value ranges associated with this type of cast component can be selected (and used). Optionally, the respective casting alloy can be taken into account, as described above. Reference symbol list 100 cast components 200 testing systems 300 bracket 310 eddy current sensor(s) 400 computer equipment S specific setpoint range

Claims

[1] Method for eddy current testing of cast components (100) in a production line, wherein the cast components (100) are tested individually, comprising the steps: - Arranging the cast component (100) to be tested in a holder (300) which has at least two eddy current sensors (310); - Measuring local electrical conductivities of the cast component (100), for which each eddy current sensor (310) performs at least one measurement; - Evaluating the measurements, for which the measured values ​​of each eddy current sensor (310) are compared with a specific target value range (S), whereby the correct position of the cast component (100) arranged in the holder (300) is first detected using the eddy current sensors (310) and the measurements are then started automatically; - Evaluate the cast component (100) as defective if at least one measured value is outside the specific target value range (S), otherwise evaluate the cast component (100) as free of defects. [2] Method according to claim 1, characterized by , that the cast component (100) is inserted into the holder (300) using a robot. [3] Method according to any of the preceding claims, characterized by , that during measurement each eddy current sensor (310) performs three measurements with varying measurement frequency. [4] Method according to any of the preceding claims, characterized by , that temperature compensation is applied when evaluating the measurements. [5] Method according to any of the preceding claims, characterized by , that the cast components (100) to be tested are made of different cast alloys, whereby when evaluating the measurements the corresponding specific target value ranges (S) are selected for the respective cast alloy. [6] Method according to any of the preceding claims, characterized by , that after removing the cast component (100) from the holder (300) and before placing another cast component (100) in the holder (300) a calibration of the eddy current sensors (310) is carried out, in particular comparing the eddy current sensors (310) with the ambient air. [7] Method according to any of the preceding claims, characterized by , that the holder (300) is a gripping device that is arranged on a robot arm. [8] Method according to any of the preceding claims, characterized by , that the measured values ​​and / or the evaluation results for each cast component (100) are documented.

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