WO2020201759A1

WO2020201759A1 - Temperature mapping apparatus and method

Info

Publication number: WO2020201759A1
Application number: PCT/GB2020/050882
Authority: WO
Inventors: Federico MELOTTI; Alistair David Foster
Original assignee: Impression Technologies Limited
Priority date: 2019-04-02
Filing date: 2020-04-02
Publication date: 2020-10-08
Also published as: GB201904654D0; GB2582787A

Abstract

An apparatus 10 for determining a temperature map across at least part of a blank 10 having first and second surfaces 102a,102b. The apparatus comprises a temperature measuring device 20A, 20B, for measuring the temperature of a first spot S1 on the blank 100 and for producing an output temperature signal. The apparatus also comprises a thermal camera 30 for taking a thermal image of the blank 100 and for producing a thermal image output. A transmitter 40A, 40B is provided for transmitting the output temperature signal from the temperature measuring device 20A, 20B. An adjuster 50 is connected to receive the thermal image output from the thermal camera 30 and to receive the output temperature signal from the transmitter 40A, 40B and for adjusting the thermal image output of the thermal camera 30 in accordance with the output temperature signal from the temperature measuring device 20A, 20B to create the temperature map.

Description

TEMPERATURE MAPPING APPARATUS AND METHOD

The present invention relates to an apparatus for and method of mapping the temperature of a surface and relates particularly but not exclusively to such an apparatus and method for mapping the temperature of sheet metal blanks prior to being formed by pressing or other forms of forming process. In particular the present invention is of application to forming processes for metal blanks which have variable surface emissivity, such as those made from an aluminium alloy or a magnesium alloy. The present invention is also suitable for use with non-metal blanks such as blanks made from glass.

It is well known that the successful forming of metal components from sheet material such as aluminium or magnesium alloys can be very dependent upon the temperature at which the sheet material is at prior to and during the forming process itself. Advances in sheet metal forming processes such as, for example, that known as Hot Quench Forming (HFQ) have enabled operators to form more complex and more deeply drawn components than has been known before. The HFQ process allows these complex and deeply drawn components to be formed in a single pressing action and to good dimensional tolerances. However, such a process is even more dependent upon accurate establishment of the desired temperature in the sheet metal immediately prior to the forming step. Any deviation from the desired or design temperature may cause difficulties in meeting the intended performance requirements of the finished formed part. Also, any such temperature deviation may result in difficulties in the forming process itself. The HFQ process uses a heating stage, such as might be carried out using a furnace, to heat the sheet metal blank (the blank) to a desired temperature before it is transferred to the press for subsequent forming. The handling of the blank during transition from the heating stage to the pressing stage and the amount and duration of contact with the press die surface prior to forming must be carefully controlled to ensure that the entire portion of the blank which is to be formed is at the desired or design temperature immediately before forming. In addition, material variations in the blank itself or regions of non-uniformity, such as may be created by contamination being present on the surface of the blank may act to cause the blank temperature to be locally varied either upwards or downwards from the desired temperature.

It is also known to produce thermal images of a surface of a blank, or of both of the surfaces of the blank (for example an upper surface and a lower surface), prior to pressing and to use such thermal images to monitor the thermal map of the surface, or surfaces, of the blank prior to pressing. Typically, the temperature measured at one surface of a blank will be very similar l to the temperature measured on the other surface because of the thin gauge of the blank and the high conductivity of the material of the blank. Thermal imaging camera systems are well known for being used to generate surface thermal maps of components and do not require contact of the surface being measured. The temperature measurement accuracy of thermal cameras is known to vary and is dependent on many factors, which usually require specific material calibration and or calibration to a contact measured temperature such as a thermocouple, which adds in additional measurement error and measurement drift over time. Furthermore, measuring temperature of varying emissivity materials is normally achieved by knowing or fixing the emissivity value of the material to be measured, which either reduces the ability of the process system to manage materials of varying emissivity or becomes reliant upon correct pre-measurement and entry of the material emissivity prior to heating and measurement. In view of the above, there exists a requirement for an apparatus for enabling accurate surface temperature measurement of materials with varying emissivity and for a method of using such an apparatus.

A thermal map is a collection of raw data that relates to a spatial distribution of the temperature of an object being analysed, i.e. the temperature at a plurality of discrete measurement points. The raw data within the thermal map is typically obtained from a thermal camera and is not subjected to any calibration.

A thermal image is a visual representation of the temperature of the surface of an object that is created by processing of the raw data of the thermal map.

A temperature map is a collection of calibrated data that relates to a spatial distribution of the temperature of an object being analysed.

Pyrometers are another form of non-contact temperature measurement device which are able to determine the temperature of a spot on a surface of the blank. In use, a pyrometer must be focussed on a specific location of the surface, typically a spot of a few millimetres in diameter, for a period of time before it can capture accurate thermal data. Thus using a pyrometer to process the entire surface of the blank (or using two pyrometers, one to process an upper surface and one to process a lower surface of the blank) will consume too much time to be practicable in many situations, or will require a system of pyrometers to be used that adds greatly to measurement system complexity, control and cost. In addition, presently known systems are unable to operate speedily enough to manage the throughput of continuous pressing lines and any delay in processing the blank temperature measurement data received will further exacerbate the temperature control problem. Furthermore, presently available pyrometers cannot provide a temperature reading with a sufficiently high degree of accuracy because the measured temperature depends upon the emissivity of the surface of the blank. In the case of an aluminium alloy blank, for example, the emissivity is not a fixed value and when the emissivity changes the measured temperature will change. The Applicant has found, through testing, that the accuracy of existing pyrometers is not good enough when measuring the temperature of heated aluminium blanks. Very large errors have been seen, for example an error of 70 degrees for an aluminium blank at a temperature of 470 degrees Celsius. This level of inaccuracy is incompatible with hot aluminium forming processes, such as HFQ, where the forming temperature is critical to delivering forming and subsequent part performance, such as draw depth and final part strength. The Applicant requires a temperature measurement that is +/- 1 % of the actual temperature, e.g. within 5 degrees and more preferably within 3 degrees, for a blank that is between 150 degrees Celsius to 600 degrees Celsius. It is known that thermal imaging devices can provide thermal maps with temperature measurements having accuracies of +/- 1 % of the actual temperature. However, the problem with such thermal imaging devices is that the accuracy can become +/-10% of the actual temperature if the emissivity of the aluminium blank is not known. The varying emissivity of an aluminium blank means that, in practice, it is not possible to achieve the desired accuracy of temperature measurement using a thermal imaging device alone.

There also exists a need for a system which is more able to capture and store thermal image information of a blank (i.e. thermal image information for one side, or for both sides of a blank) prior to pressing such as to allow for the successful and speedy rejection of formed components which may have not been formed at the desired or design temperature, or to aid control of the heating and pressing system processes to cater for variances in heated blank temperature.

It is an object of the present invention to provide an apparatus and method of mapping the temperature of a surface of a sheet metal blank prior to being formed by hot form pressing, or other forms of forming process, which reduces and possibly eliminates one or more of the above-mentioned problems.

Accordingly, in a first arrangement of the present invention there is provided an apparatus for determining a temperature map across at least part of a blank having a first and second surface wherein the apparatus comprises a temperature measuring device for measuring the temperature of a first spot on the first or second surface of the blank and producing an output temperature signal (OTS) and a thermal camera for taking a thermal image of the first or second surface of the blank and for producing a thermal image output (TIO) which can be used in conjunction with an adjuster to adjust the thermal image from the thermal camera. In that way the thermal image is calibrated using the temperature measuring device so as to produce a more accurate temperature map of the surface of the blank from a thermal camera. A secondary benefit is that the temperature map can be produced more speedily. The apparatus further comprises a transmitter for transmitting the output temperature signal (OTS) from said temperature measuring device and an adjuster connected to receive the thermal image output (TIO) from the thermal camera and to receive the output temperature signal (OTS) from the transmitter and for adjusting the thermal image output (TIO) in accordance with the output temperature signal (OTS) from the temperature measuring device (20A, 20B) to create the temperature map.

By adjusting the thermal image output (TIO) as described it will be appreciated that the entire thermal map will be adjusted accordingly such as to produce a temperature map which more accurately and speedily corresponds with the actual temperature measured from the combination of a spot temperature sensor and a thermal camera which is able to rapidly capture thermal image data for the entire surface of the blank.

A compiler may be used for compiling a corrected temperature map of the first or second surface of the blank from the thermal image output (TIO) of the thermal camera and such may, for example, be stored electronically for the purposes of product quality control. The control of quality can be achieved by enabling the forming process step to occur in an improved way based on the corrected temperature of the heated blank, or by rejecting the heated part from the forming process system, or by adjusting the forming process settings used to form that measured heated blank, or by alerting the forming system of a change in the system operation that requires subsequent system setting parameter changes either automatically or by the operator. The compiler takes the data from the thermal camera and presents it in a visual form, e.g. a form suitable for presentation to a human user of the system.

Preferably the adjuster comprises a calibrator for calibrating the thermal camera prior to it being used to create a thermal image output (TIO) to be transmitted to said compiler.

Preferably the adjuster comprises a signal processor for processing the thermal image output (TIO) of the thermal camera (30) after it has been produced.

Preferably the temperature measuring device (20A) is a two-frequency pyrometer and the output temperature signal (OTS) is a product of a ratio model thereof. The apparatus may use more than one pyrometer. Two or more pyrometers might be used if it is found that the measurements obtained from the pyrometer across a surface of the blank vary too much (such as might be the case if there is interference from other sources of heat reflecting off the surface). It might also be necessary to use two or more pyrometers if it desired to quantify an error, by measuring the temperature at two points on the surface of the blank, whilst only using one pyrometer to conduct the calibration.

Preferably the temperature measuring device is a two-frequency pyrometer and the output temperature signal (OTS) is a product of a signal model thereof. Preferably the apparatus includes a visible light camera for detecting any contamination or non-uniformity or an identification tag on the surface of the blank and for generating a non uniformity signal (NUS) for transmittal to said compiler. It is advantageous to include a visible light camera because it can act as an initial quality acceptance measure for the subsequent infrared thermal image. If the visible camera detects a non-uniform surface, such as a paint or grease mark, then the compiler can react and reject the part before heating or post heating prior to forming or post forming. The apparatus may include two or more visible light cameras. This enables viewing of both sides of the blank for the purposes of inspecting for any debris on those surfaces. The term ‘visible light’ is used here to mean the spectral regions of electromagnetic radiation that include the spectrum of visible light and the near parts of the adjacent regions, i.e. near-infrared radiation.

Preferably the apparatus includes an emissivity detector for determining the emissivity of the surface of the metal blank.

Preferably the emissivity detector comprises said pyrometer.

Preferably the emissivity detector includes an output generator for generating an emissivity signal (ES) and a transmitter for transmitting said emissivity signal (ES) to said adjuster.

Preferably the temperature measuring device comprises a pyrometer.

Preferably the temperature measuring device comprises a thermocouple.

Preferably the emissivity of the blank varies across its surface.

Preferably the material of the metal blank is an aluminium alloy or a magnesium alloy. Preferably the temperature of the surface of the metal blank is between 250°C and 500°C.

According to a further arrangement of the present invention there is provided a method of determining a temperature map across at least part of a blank having a first surface and a second surface having the following steps: measuring the temperature of a first spot (S1) on the first or second surface of the blank using a temperature measuring device; producing an output temperature signal (OTS) indicative of the temperature of said first spot (S1) measured by said temperature measuring device); taking a thermal image of the first or second surface of the blank including said first spot (S1) using a thermal camera and producing a thermal image output (TIO); and adjusting the thermal image output (TIO) of the thermal camera in accordance with the output temperature signal (OTS) from the temperature measuring device to create the temperature map. Such a process allows for the accurate determination of a spot temperature to be used to adjust the entire thermal map captured by the thermal camera which is, itself, relatively rapidly able to capture the thermal image.

Preferably the method includes the step of calibrating the thermal camera such that the thermal image output (TIO) from the thermal camera for the spot (S1) on the first or second surface of the blank correlates with that of the output temperature signal (OTS) from the temperature measuring device, wherein the output temperature signal (OTS) is the temperature calibration signal. Preferably the method includes the step of processing the thermal image output (TIO) of the thermal camera after it has been produced such that the thermal image output (TIO) from the thermal camera for the spot (S1) on the first or second surface of the blank correlates with that of the output temperature signal (OTS) from the temperature measuring device.

Preferably the method includes the step of using a pyrometer as the temperature measuring device to produce said output temperature signal (OTS.)

Preferably the method includes the steps of detecting any contamination or non-uniformity on the first or second surface of the blank and producing a non-uniformity signal (NUS) from a visible light camera, transmitting said non-uniformity signal (NUS) to said adjuster and adjusting the thermal image of the thermal camera dependent upon the non-uniformity signal (NUS).

Preferably the method includes the step of fitting the output temperature signal (OTS) by a polynomial to secure a more accurate determination of temperature.

Preferably the method includes the steps of using a thermocouple to secure the temperature of the first spot (S1) on the first or second surface of the object and producing a spot thermocouple temperature signal (STTS) and using said spot thermocouple temperature signal (STTS) in an initial calibration of the thermal camera. Preferably the method includes the steps of: determining the emissivity of the first or second surface of the blank, creating an emissivity signal (ES), transmitting said emissivity signal to said adjuster and adjusting said the thermal image output (TIO) from the thermal camera dependent upon said emissivity signal (ES). Aspects of the present invention will now be more particularly described by way of example only with reference to the following drawings, in which:

Figure 1 is a diagrammatic representation of the components of the calibration arrangement of the temperature measurement apparatus arranged to illustrate the exchange of information between the components;

Figure 2 is a graph of signal intensity for two different frequencies over time;

Figure 3 is a graph showing the pyrometer signal calibration;

Figure 4 is a graph illustrating the quality of the temperature reading taken from the pyrometer;

Figure 5 is a graph of a thermal profile obtained from temperature measurements taken after calibration of the system comparing the temperature reading from a thermocouple attached to a blank and the output from a thermal camera;

Figure 6 illustrates a first arrangement of a temperature mapping apparatus and its method of operation in which the temperature measurement from the pyrometer is passed directly to the thermal camera;

Figure 7 illustrates a second arrangement of a temperature mapping apparatus and its method of operation in which the temperature measurement from the pyrometer is passed to a calibrator;

Figure 8 illustrates a third arrangement of a temperature mapping apparatus and its method of operation in which the temperature measurement from the pyrometer is passed to a calibrator and in which the calibrator calibrates the thermal camera; and

Figure 9 is a table comparing the temperature measurements for a first temperature T 1 taken from a number of measurement devices.

Between them, Figures 1 , 6, 7 and 8 illustrate the various arrangements of the apparatus 10 and the inter-connection between the various components thereof. Referring initially to Figure 1 , there is illustrated a calibration arrangement of an apparatus 10 for determining the temperature map of a component such as, for example, a metal blank 100 having a surface 102 (the blank also has a second surface, on the other side of the sheet, which is not referenced). The calibration arrangement includes an infrared pyrometer 20A and a thermocouple 20B, the different functions of which will be explained in detail later herein. A thermal camera 30 is provided for taking a thermal image of the surface 102 and for providing a thermal image output (TIO) (there may be more than one thermal camera 30 and if there are two or more thermal cameras then a thermal camera 30 may be arranged to take a thermal image of the surface 102 and a different thermal camera may be arranged to take a thermal image of the second surface). A transmitter 40A is provided on the pyrometer 20A and a transmitter 40B is provided on the thermocouple 20B for transmitting the output temperature signal (OTS) from each of the pyrometer 20A and thermocouple 20B to an adjuster 50 by communication lines 42A, 42B respectively, as shown in Figure 1 , or by other means such as wireless or Bluetooth transmission (not shown). The adjuster 50 is connected to receive the thermal image output (TIO) from the thermal camera 30 via communication line 32, or by alternative means such as wireless or Bluetooth transmission (not shown) and to receive the output temperature signal (OTS) from of the transmitters 40A, and 40B. The adjuster 50 may comprise any one of a number of processors but, conveniently, may comprise a computer. Whatever arrangement is adopted, the adjuster 50 is configured to adjust the thermal image output (TIO) of the thermal camera 30 in accordance with the output temperature signal (OTS) from the pyrometer 20A such that the thermal image output (TIO) from the thermal camera 30 for the spot S on the surface 102 of the metal blank 100 correlates with that of the output temperature signal (OTS) from the pyrometer 20A. The temperature measurement from the pyrometer 20A having been calibrated by reference to the temperature measurement from the thermocouple 20B. To adjust the thermal image output (TIO) of the thermal camera 30 the adjuster 50 effectively increases or reduces the entire thermal output of the thermal camera 30 By doing this one can use a relatively high accuracy spot temperature measuring device such as pyrometer 20A to, effectively, calibrate the output of a thermal camera 30 which is able to more rapidly capture the entire temperature map of the entire surface 102 of the blank 100. The adjuster 50 may take the form of a signal processor 54 well known in the art and, therefore, not described further herein, which processes the digital input data from the thermal camera 30 so as to adjust and produce a digital or visual output. The thermal camera 30 and the pyrometer 20A may be arranged to take a thermal image or a measurement, respectively, of the same surface of the blank 100, or the thermal camera 30 may be arranged to take a thermal image of one surface of the blank and the pyrometer 20A may be arranged to take a measurement of the other surface of the blank.

The advantage of the above process step is one of generating an accurate surface temperature map of the surface 102 in a short period of time as, whilst it is possible to use a pyrometer 20A or a thermocouple 20B to scan the entire surface of the sheet 102 so as to capture multiple spot temperatures (ST’s) with extreme accuracy such a process is slow and the temperature T of the surface 102 will be reducing rapidly whilst the data is being compiled (because to obtain the temperature map the blank must be removed from the heating device, typically a furnace). A further advantage associated with the proposed approach resides in the fact that the thermal image output (TIO) can be digital and, as such, can be stored and tagged or associated with a given blank 100 to help manage quality control. Still further, it will be possible to rapidly assess the digital thermal image output (TIO) so as to detect areas of over or under temperature of the blank 100 and, thus, accept or reject the blank 100 prior to pressing or to ensure that the temperature map of the blank 100 is known and recorded so as to allow for post formation defect analysis techniques to be used with a greater degree of accuracy. Furthermore, an accurate temperature map of the surface 102 will allow for the forming process parameter settings to be altered to account for the change in temperature of the measured blank 100 that is to be formed.

A compiler 60 may also be provided specifically for compiling a corrected temperature map of the surface 102 of the blank 100 from the thermal image (Tl) of the thermal camera 30. This compiler 60 will take the adjusted individual components of the thermal image output (TIO) and compile a digital data map or a visual representation thereof such as may be presented in the form of a temperature map having different colours representing different temperatures. The digital map may simply comprise thermal data for each of a multiplicity of individual coordinates C1 , C2 etc on the surface 102 as such data points can then be processed by a processor 62 such as to compare actual (adjusted) temperature data with desired temperature data for each of the multiplicity of individual coordinates C1 , C2 etc and allow for the blank temperature profile before pressing to be assessed and either accepted or rejected based on a comparison of the nearness of the determined temperature from the desired pre-recorded temperature for each individual coordinate C1 , C2 etc. The same can be done by processing the visual image, although this is more likely to be done by the human eye whilst monitoring.

It will be appreciated that the thermal image and / or the thermal map and / or the temperature map may be stored either digitally or physically and may be used for fault analysis or quality control purposes. Such a record may be stored centrally for future use or may be passed with the pressed component produced from the blank 100 recorded in this manner. Fault, defect or failure analysis may be used to improve the pressing process or amend the temperatures or process parameters or material selections for given shapes of component formed. The component produced from the blank 100 may be tagged with a barcode or other such tracking system which may be associated with the thermal data and / or heat map so as to allow for easy subsequent retrieval in the event of an undesired failure or defect.

Additions, modifications or amendments of the apparatus and the process will now be described by way of example with reference to the figures as and where identified.

One such addition comprises a calibrator 52 for allowing the calibration of the thermal camera 30 prior to use, which may be used as an alternative to the previously described method of adjustment of the thermal image output (TIO) from the thermal camera 30, or which may be used in combination with that method of adjustment. Calibration is important as it ensures the accuracy of the collected data but it is a step which need only be done as and when required. In a typical situation, the calibrator 52 may comprise the pyrometer 20A itself as such are, generally, accurate instruments and the calibration method may simply comprise the steps of comparing a spot temperature at an individual coordinate CX determined by the pyrometer 20A and comparing it with the received thermal image for the same spot CX such as to allow for any adjustment necessary. This adjustment may take the form of adjusting the calibration of the thermal camera itself 30 so that the received thermal signal for the individual coordinate CX matches that of the pyrometer 20A for the same coordinate 30. Alternatively, one could use the thermocouple 20B in place of the pyrometer 20A. Once calibrated the output from the thermal camera 30 would be guaranteed accurate and no further adjustments would be needed before displaying or recording the output therefrom.

It will be appreciated that calibration could be done as an initial step for each blank 100 being pressed or could be done on a batch basis or a daily basis or a periodic basis depending on the need for accuracy. It will also be appreciated that it may be desirable to choose a spot CX on the blank 100 which is equivalent to a critical forming area, which many include the area of maximum deformation in any subsequent pressing operation as the material surrounding such a spot is likely to experience the most deformation and accurate temperature would ensure optimum processing and final formed part performance results.

Whilst one of a variety of different types of pyrometer could be used, it has been found that a two-frequency pyrometer is of particular use, because it is known that a two-frequency pyrometer has a lower temperature measurement error compared to a single frequency pyrometer. The output from a two-frequency pyrometer is an output temperature signal (OTS) which is a product of the ratio of the two signals produced thereby or a product of a signal model thereof. The apparatus 10 may further include a visible light camera 70 for capturing an image of the surface 102 and for detecting any contamination or non-uniformity or the presence of a foreign object, for example a blank identification tag on the surface 102. If any such contamination, non-uniformity or foreign body is detected then the visible light camera 70 generates an image or signal which may be called a“non-uniformity signal” (NUS) and which is then sent to said compiler 60 or processor 74 by means of communication channel 72. Such a channel 72 may go directly to the compiler 60 or processor 74, or it might go indirectly to the compiler 60 or processor 74 via the thermal camera 30 so as to allow for the superimposition of a defect image over the thermal image. Alternatively, the NUS may be sent directly to the compiler 60 or processor 74 where it can be superimposed on the thermal image or thermal image data or stored separately. Alternatively, the data relating to defects could simply be used to identify a non-conformity which causes, or would cause, the heated blank 100 to fall outside of a desired requirement specification or range and cause the rejection of that blank 100 before or after the heating or pressing, and/or the triggering of an alarm. The defect image may also be stored and tagged to the product produced from the pressed blank 100 in question so as to allow for post-production analysis should that be required.

It is also envisaged that the visible light camera 70 could be utilised to identify the material of the blank 100 and thereby check that the blank 100 is the correct one to be submitted to the subsequent forming step. In this way, the system could be alerted if the blank 100 is made of the wrong material allowing an appropriate action to be taken, for example, calling a temporary halt to the process whilst the blank 100 is removed.

The emissivity of a material affects the perception of temperature that one may associate with the surface being monitored and, hence, it may be beneficial to also determine the emissivity E of the surface 102 of the blank 100 and feed that information into the thermal camera 30, the adjuster 50 and/or the compiler 60. An emissivity detector 80 may be used to determine the emissivity E which can then be used to adjust the output values of the thermal camera 30 or to adjust the thermal image (Tl) or thermal graph (TG) presented to a user or stored by the apparatus 10 for potential further use. Typically, one is likely to be processing multiples of the same types of blank 100 and, hence, the emissivity measurement E may need only be taken once at the commencement of production from a fixed selection of blanks 100, or periodically throughout production. Factors such as external light conditions may also influence the emissivity E and, hence, as many process parameters as possible should be kept uniform or monitored for non-compliance with uniformity. Deviations therefrom may be used to initiate a re-taking of the emissivity reading E and a further modification of the thermal signals as discussed above. It will be appreciated that any one of a number of different types of emissivity detectors 80 may be used but it has been found that one might reasonably use the pyrometer 20A, if one is provided, and the emissivity measure E may be communicated to the thermal camera 30 by communication channel 42C or to the adjuster 50 or compiler 60 by communication channel 42A. Whatever system is used for determining the emissivity E, it may also include an output generator 82 for generating an emissivity signal (ES) for subsequent transmission to said adjuster 50 or compiler 60.

As discussed above, the initial spot temperature ST of the blank 100 used in the adjustment of the thermal camera 30 or the output therefrom may be done by using a thermocouple 20B. Whilst such thermocouples are able to accurately determine a spot temperature ST they, by necessity, have to contact the surface 102 of the blank 100 and may have a slight impact on the temperature reading that is taken, as the contact will cause heat to be taken away from the spot S. This may be compensated for by simply adjusting the output temperature signal OTS of the thermocouple 20A or compensating for the contact in subsequent processing.

A first operational arrangement of the apparatus 10 is shown in Figure 6 from which it will be appreciated that the output temperature signal (OTS) from the pyrometer 20A is transmitted to the thermal camera 30 where it is used to calibrate the camera 30 such that any output from the thermal camera 30 can be sent directly for use in the compiler 60 without any further adjustment being necessary.

Figure 7 illustrates a second operational arrangement where the output temperature signal (OTS) from the pyrometer 20A is sent first to a computer or PC board device 76 which produces an output by way of an algorithm which is sent to the thermal camera 30 and applied to the thermal image (Tl) taken thereby such as to create an accurate temperature profile. That accurate temperature profile is than available for transmission onwards to any device in which that profile can be utilised without the need for any further correction or adjustment.

Figure 8 illustrates a third operational arrangement where the output temperature signal (OTS) from the pyrometer 20A is sent to a calibrator, the calibrator using the data from the pyrometer 20A to calibrate the thermal camera 30.

The arrangements of each of Figures 1 , 6, 7 and 8 each show an optional visual display 110 which may be used to present a visual thermal image (Tl) or a temperature profile graph TG.

Figure 2 is a representation of a typical temperature profile graph (TG) and illustrates the cooling curve of a blank 100 creating using data obtained from a two-frequency pyrometer where the intensity of the signal is proportional to the temperature of a blank 100. Each of the two curves represents a different frequency and the provision of two curves allows for the calibration to be undertaken using either a ratio model (RM) or a signal model (SM). A ratio model is one where the ratio between the signals is used for the calibration whilst a signal model is one where each channel is fitted individually. These calibration methods are well known in the art and, therefore, not described further herein. Figure 3 illustrates the use of the second channel where the output temperature signal (OTS) is fitted to a polynomial and is then used to predict the temperature of the heated blank 100. Figure 4 is a graph of temperature over time from which it can be seen there is a significant degree of cooling. The two channels produce the predicted temperature 1 and predicted temperature 2 and from which the real temperature (RT) can be projected. The Real Temperature RT being shown in the graph as lying between the two predicted temperatures. Predicted Temperature 2 has a bias factor of 12°C whilst the Predicted Temperature 2 channel is good at temperatures above 450°C (closest to the real temperature). When both of the channels are used the bias will be compensated for which illustrates the advantage of the two-channel approach and allows the pyrometer 20A to predict the temperature with significant accuracy whereas with a single channel the accuracy would depend on the calibration values. It will be appreciated that the thermal camera 30 works more effectively if the emissivity of the blank 100 is also known and used in the adjustment or correction of the thermal image output TIO. By changing the emissivity value of the blank 100, the sensed temperature profile of the blank 100 will change. In the present arrangement, the emissivity value of the blank 100 which is used to correct for variations in emissivity was changed or adjusted until the temperature in the region of interest ROI matched the reading from the pyrometer 20A which, in effect, corrects the thermal data before use. By adopting this approach it will be appreciated that the arrangement is able to use a“corrected temperature” from the pyrometer 20A and one does not need to know the real or actual emissivity of the blank 100 itself.

Figure 5 is a graph of temperature over time and illustrates for the region of interest (ROI) the cooling curve comparison between the thermocouple attached to the blank 100 and the thermal camera 30 and illustrates that there is a very good correlation which, in turn, indicates that the temperature system works and can be relied upon.

Figure 9 is a comparative table between two examples (A and B) which are illustrative of lower and higher emissivity samples of aluminium alloy blanks and from which it will be appreciated what degree of measured temperature variation there may be between readings depending on the emissivity. The comparison between the pyrometer temperature reading and the thermocouple TC reading illustrates the problem of thermocouples under reading due to their physical contact. It also illustrates the upper and lower temperatures detected on the aluminium alloy blanks. As part of a typical Hot Quench Forming (HFQ) process an aluminium alloy blank has to be fully solutionised before correct and effective pressing can take place. For 7075 series aluminium alloy the solution heat treatment (SHT) temperature is between 480°C and 500°C and more typically 490°C (between the solvus and the solidus temperatures). In the example A of figure 8 the pyrometer detected 497°C which indicates a fully solutionised aluminium alloy blank but the thermal camera 30, which is capturing the thermal image of the entire surface 102, measured the temperature of one portion as 468°C, indicating that it was not yet at temperature and, therefore, not fully solutionised. If this aluminium alloy blank were to be pressed the optimum mechanical properties would not be realised in the underheated region and the resulting component may either be rejected or fail in use, both of which are clearly undesirable. In the example B of Figure 8 which relates to 6082 aluminium alloy the SHT temperature is above 535°C. Without correction, the thermal camera 30 detected a temperature of 550°C and 538°C at different positions which suggests the aluminium alloy blank is fully solutionised and acceptable for HFQ. However, after the temperature is corrected it is noted that the real temperature is 460°C which is too far below the SHT temperature and the aluminium alloy blank is not fully solutionised and would fail or be defective and not achieve the right performance requirements if subjected to a subsequent HFQ forming step.

The method of operation of the above will now be more particularly described by way of example so as to illustrate the benefits of the present invention. To obtain a temperature map of a surface 102 of a metal blank 100, which surface 102 might exhibit varying emissivity, we may use the above-described apparatus 10 of Figure 1 so as to do the following steps: detecting the temperature of a first spot S1 on the surface 102 of the blank 100 using a temperature measuring device such as a pyrometer 20A or a thermocouple 20B before creating an output temperature signal (OTS) indicative of the temperature of said first spot S1 detected by the pyrometer 20A or thermocouple 20B. The output temperature signal (OTS) is then transmitted to the adjuster 50 and the thermal camera 30 is used to take a thermal image of the surface 102 of the blank 100 including said first spot S1 such as to produce a thermal image output (TIO). The thermal image output (TIO) is then adjusted in accordance with the output temperature signal (OTS) from the pyrometer 20A or the thermocouple 20B such that the thermal image output (TIO) from the thermal camera 30 for the spot S1 on the surface 102 of the blank 100 correlates with that of the output temperature signal (OTS) from the pyrometer 20A or the thermocouple 20B. The apparatus 10 may then produce a corrected thermal image, i.e. a temperature map, of the entire surface of the blank 100 from said thermal camera 30. It is envisaged that two or more pyrometers 20A may be used to detect the temperature of a spot S1 , or spots, on one or both surfaces of the blank 100.

To maximise the benefit of the apparatus 10 and process it is desirable to calibrate the thermal camera 30 such that the thermal image output (TIO) from the thermal camera 30 for the spot S1 on the surface 102 of the blank 100 correlates with that of the output temperature signal (OTS) from the pyrometer 20A or the thermocouple 20B. The thermocouple 20B may be used to secure the temperature of the first spot S1 on the surface of the object and producing a spot thermocouple temperature signal (STTS) and said spot thermocouple temperature signal (STTS) may be used in an initial calibration of the thermal camera 30. Once produced, the thermal image output (TIO) of the thermal camera 30 is then processed such that the thermal image output (TIO) from the thermal camera 30 for the spot S1 on the surface 102 of the blank 100 correlates with that of the output temperature signal (OTS) from the pyrometer 20A or the thermocouple 20B. This adjustment or correction step may be done by using the pyrometer 20A to produce said output temperature signal (OTS) or by using the thermocouple 20B itself, although the latter is not as effective as the former.

In order to more accurately determine the suitability of the blank 100 for pressing, the method may include the step of checking for any contamination or non-uniformity in temperature on the surface of the blank 100 and producing a non-uniformity signal (NUS) before transmitting said non-uniformity signal (NUS) to said adjuster 50 or any other suitable device and adjusting the thermal image of the thermal camera 30 dependent upon the non-uniformity signal (NUS). The detection of a non-uniformity may also be used to reject the blank 100 as not being suitable for pressing but often when a non-uniformity is detected it can be ignored if it is in an area of the sheet which is not likely to be subjected to bending or forming which might cause the creation of a defect due to the imperfection or non-uniformity being present. The method may also include the step of fitting the output temperature signal (OTS) by a polynomial to secure a more accurate determination of temperature. Alternatively, one may use a thermocouple 20B to secure the temperature of the first spot S1 on the surface of the object. Each arrangement will produce a spot thermocouple/pyrometer temperature signal (STTS or SPTS) which may be used in the initial calibration of the thermal camera 30. Significant advantage is also gained by determining the emissivity of the surface 102 of the blank 100 and creating an emissivity signal (ES) before transmitting said emissivity signal to said adjuster 50 or other such suitable device and adjusting said the thermal image output (TIO) from the thermal camera 30 dependent upon said emissivity signal (ES). This simple step will greatly enhance the accuracy of the temperature determination.

In the apparatus 10 of Figure 6 the pyrometer 20A takes a temperature reading for a point S1 on the surface 102 of the blank 100 and generates an output temperature signal (OTS). The transmitter 40A sends that output temperature signal (OTS) to the thermal camera 30 and the thermal image output (TIO) from the thermal camera 30 is adjusted so that the temperature of the spot S1 measured by the thermal camera 30 is the same as the temperature of the spot

51 measured by the pyrometer 20A. The method may involve temperature readings being taken by the pyrometer 20A at multiple spots, for example S1 , S2 and S3, and the thermal camera 30 being adjusted so that the temperatures measured at spots S1 , S2 and S3 by the thermal camera 30 are the same as those measured by the pyrometer 20A. The thermal image output (TIO) from the thermal camera 30 is passed to a signal processor 54 located within an adjuster 50. A non-uniformity signal (NUS) from the visible light camera 70 is also passed to the signal processor 54. The signal processor 54 then processes the thermal image output (TIO) taking into account the non-uniformity signal (NUS). The last step of the process is for the compiler 60, which is located within the adjuster 50, to compile a temperature map of the surface 102 of the blank 100. The compiler 60 can also be used to generate a rate of change of temperature of the blank 100 over time by creating multiple temperature maps from temperature measurements taken at intervals.

In the apparatus 10 of Figure 7 the pyrometer 20A takes a temperature reading for a point S1 on the surface 102 of the blank 100 and generates an output temperature signal (OTS). The transmitter 40A sends that output temperature signal (OTS) to a calibrator 52. The calibrator

52 calibrates the thermal camera 30 before any thermal images are taken by it. The method may involve temperature readings being taken by the pyrometer 20A at multiple spots, for example S1 , S2 and S3, and the thermal camera 30 being calibrated by the calibrator 52 so that the temperatures measured at spots S1 , S2 and S3 by the thermal camera 30 are the same as those measured by the pyrometer 20A. Once the thermal camera 30 has been calibrated it takes a thermal image of the surface 102 of the blank 100 and the thermal image output (TIO) from the thermal camera 30 is sent to the adjuster 50. The compiler 60, which is located within the adjuster 50, takes the thermal image output (TIO) and any non-uniformity signal (NUS) from the visible light camera 70 and compiles a temperature map of the surface 102 of the blank 100. The compiler 60 can also be used to generate a rate of change of temperature of the blank 100 over time by creating multiple temperature maps from temperature measurements taken at intervals. In the apparatus 10 of Figure 8 the pyrometer 20A takes a temperature reading for a point S1 on the surface 102 of the blank 100 and generates an output temperature signal (OTS). The transmitter 40A sends that output temperature signal (OTS) to a calibrator 52. The thermal camera 30 takes a thermal image and generates a thermal image output (TIO) which is sent to a calibrator 52. Calibrator software calibrates the thermal camera 30 so that the temperature of the spot S1 measured by the thermal camera 30 is the same as the temperature of the spot S1 measured by the pyrometer 20A.The method may involve temperature readings being taken by the pyrometer 20A at multiple spots, for example S1 , S2 and S3, and the thermal camera 30 being calibrated by the calibrator 52 so that the temperatures measured at spots S1 , S2 and S3 by the thermal camera 30 are the same as those measured by the pyrometer 20A. Once the thermal camera 30 has been calibrated it takes a thermal image of the surface 102 of the blank 100 and the thermal image output (TIO) from the thermal camera 30 is sent to the adjuster 50. The compiler 60, which is located within the adjuster 50, takes the thermal image output (TIO) and any non-uniformity signal (NUS) from the visible light camera 70 and compiles a temperature map of the surface 102 of the blank 100. The compiler 60 can also be used to generate a rate of change of temperature of the blank 100 over time by creating multiple temperature maps from temperature measurements taken at intervals. Measurement of the temperature at two or more spots S1 , S2 to provide a corrected thermal image can be carried out if the blank 100 to be pressed is made up of more than one material, or has a surface treatment that varies across the surface 102 of the blank 100. Multiple spot measurements might also be needed if regions of a blank 100 have been heated at different rates or to different temperatures in the heating device. Also, if the blank 100 is particularly large, it may be advantageous to take temperature measurements at multiple locations.

Whilst we have described the apparatus 10 and method to the fullest extent possible at this juncture, those skilled in the art will appreciate that modifications and alteration to various elements may be possible without adversely affecting the validity of this approach.

Claims

1. An apparatus (10) for determining a temperature map across at least part of a blank (100) having a first surface (102a) and a second surface (102b) comprising:

a) a temperature measuring device (20A, 20B), for measuring the temperature of a first spot (S1) on the first or second surface (102a, 102b) of the blank (100) and producing an output temperature signal (OTS);

b) a thermal camera (30), for taking a thermal image of the first or second surface (102a, 102b) of the blank (100) and for producing a thermal image output (TIO); c) a transmitter (40A, 40B) for transmitting the output temperature signal (OTS) from said temperature measuring device (20A, 20B); and

d) an adjuster (50) connected to receive the thermal image output (TIO) from the thermal camera (30) and to receive the output temperature signal (OTS) from the transmitter (40A, 40B) and for adjusting the thermal image output (TIO) of the thermal camera (30) in accordance with the output temperature signal (OTS) from the temperature measuring device (20A, 20B) to create the temperature map.

2. An apparatus (10) as claimed in claim 1 and wherein said adjuster (50) comprises a calibrator (52) for calibrating the thermal camera (30) prior to it being used to create a thermal image output (TIO) to be transmitted to a compiler (60).

3. An apparatus (10) as claimed in claim 1 or claim 2 and wherein said adjuster (50) comprises a signal processor (54) for processing the thermal image output (TIO) of the thermal camera (30) after it has been produced.

4. An apparatus as claimed in any one of claims 1 , 2 or 3 and wherein said temperature measuring device (20A) is a two-frequency pyrometer and the output temperature signal (OTS) is a product of a ratio model thereof.

5. An apparatus as claimed in any one of claims 1 , 2 or 3 and wherein said temperature measuring device (20A) is a two-frequency pyrometer and the output temperature signal (OTS) is a product of a signal model thereof.

6. An apparatus as claimed in any one of claims 1 to 5 and including a visible light camera (70) for detecting any contamination or non-uniformity or an identification tag on the surface of the blank and for generating a non-uniformity signal (NUS) for transmittal to said compiler (60).

7. An apparatus (10) as claimed in any one of claims 1 to 6 and including an emissivity detector (80) for determining the emissivity of the surface (102a, 102b) of the metal blank (100).

8. An apparatus (10) as claimed in claim 7 and wherein said emissivity detector (80) comprises said pyrometer (20A).

9. An apparatus (10) as claimed in claim 7 and wherein said emissivity detector (80) includes an output generator (82) for generating an emissivity signal (ES) and a transmitter (84) for transmitting said emissivity signal (ES) to said adjuster (50).

10. An apparatus as claimed in any one of claims 1 to 9 and wherein said temperature measuring device (20A, 20B) comprises a pyrometer (20A).

1 1. An apparatus (10) as claimed in any one of claims 1 to 9 and wherein said temperature measuring device (20A, 20B) comprises a thermocouple (20B).

12. An apparatus (10) as claimed in any preceding claim in which the emissivity of the blank (100) varies across its surface (102a, 102b).

13. An apparatus (10) as claimed in any preceding claim in which the material of the metal blank (100) is an aluminium alloy or a magnesium alloy.

14. An apparatus (10) as claimed in any preceding claim in which the temperature of the surface (102a, 102b) of the metal blank (100) is between 250°C and 500°C.

15. A method of determining a temperature map across at least part of a blank (100) having a first surface (102a) and a second surface (102b) having the following steps: a) measuring the temperature of a first spot (S1) on the first or second surface (102a, 102b) of the blank (100) using a temperature measuring device (20A, 20B);

b) producing an output temperature signal (OTS) indicative of the temperature of said first spot (S1) measured by said temperature measuring device (20A, 20B); c) taking a thermal image of the first or second surface (102a,b) of the blank (100) including said first spot (S1) using a thermal camera (30) and producing a thermal image output (TIO);

d) adjusting the thermal image output (TIO) of the thermal camera (30) in accordance with the output temperature signal (OTS) from the temperature measuring device (20A, 20B) to create the temperature map.

16. A method as claimed in claim 15 and including the step of calibrating the thermal camera (30) such that the thermal image output (TIO) from the thermal camera (30) for the spot (S1) on the first or second surface (102a, 102b) of the blank (100) correlates with that of the output temperature signal (OTS) from the temperature measuring device (20A, 20B), wherein the output temperature signal (OTS) is the temperature calibration signal.

17. A method as claimed in claim 15 or claim 16 and including the step of processing the thermal image output (TIO) of the thermal camera (30) after it has been produced such that the thermal image output (TIO) from the thermal camera (30) for the spot (S1) on the first or second surface (102a, 102b) of the blank (100) correlates with that of the output temperature signal (OTS) from the temperature measuring device (20A, 20B).

18. A method as claimed in any one of claims 15 to 17 and including the step of using a pyrometer (20A) as the temperature measuring device to produce said output temperature signal (OTS.)

19. A method as claimed in any one of claims 15 to 18 and including the steps of detecting any contamination or non-uniformity on the first or second surface (102a, 102b) of the blank (100) and producing a non-uniformity signal (NUS) from a visible light camera (70), transmitting said non-uniformity signal (NUS) to said adjuster (50) and adjusting the thermal image of the thermal camera (30) dependent upon the non-uniformity signal (NUS).

20. A method as claimed in any one of claims 15 to 19 and including the step of fitting the output temperature signal (OTS) by a polynomial to secure a more accurate determination of temperature.

21. A method as claimed in any one of claims 15 to 20 and including the steps of using a thermocouple (20B) to secure the temperature of the first spot (S1) on the first or second surface of the object and producing a spot thermocouple temperature signal (STTS) and using said spot thermocouple temperature signal (STTS) in an initial calibration of the thermal camera (30).

22. A method as claimed in any one of claims 15 to 21 and including the steps of: determining the emissivity of the first or second surface (102a, 102b) of the blank (100), creating an emissivity signal (ES), transmitting said emissivity signal to said adjuster (50) and adjusting said the thermal image output (TIO) from the thermal camera (30) dependent upon said emissivity signal (ES).