Method for determining a soaking time

Abstract

Method for the automated determination of a heating time when heating preferably fiber-reinforced thermoplastic semi-finished products (2) by means of an infrared oven (1) and arrangement suitable for carrying out such a method.

Description

[0001] The disclosure relates to a method for determining a soaking time of preferably fiber-reinforced thermoplastic semi-finished products.

[0002] The disclosure further relates to a method for controlling or regulating an infrared furnace in a production process processing the semi-finished product.

[0003] The disclosure also relates to an arrangement which is suitable for carrying out one of the two aforementioned methods.

[0004] The control of the heating process in an infrared furnace is based on the surface temperature of the semi-finished product to be heated. The semi-finished product is heated to a target surface temperature. This temperature is then maintained for a certain period of time (the soak time) to ensure that the same temperature prevails in the center of the semi-finished product as on the surface.

[0005] The soaking time depends on the thermal conductivity and material thickness of a semi-finished product and can be determined for a given half-life through preliminary tests. For this purpose, a thermocouple is placed in the center of the semi-finished product and the prevailing temperature there is recorded. This allows the time required to reach the surface temperature in the core, i.e., the soaking time, to be determined.

[0006] It is an object to provide a method and an arrangement with which a simpler determination of the soaking time of a semi-finished product is possible.

[0007] It is a further object to provide a method and an arrangement which enable the processing of semi-finished products in a production process using the determined soaking time.

[0008] These objects are achieved by a method having the features of claim 1, a method having the features of claim 8 and an arrangement having the features of claim 11.

[0009] In a method for determining a soaking time of preferably fiber-reinforced thermoplastic semi-finished products, wherein the thermoplastic semi-finished products have two surfaces spaced apart from each other by a material thickness, at least the following steps are provided: a. Providing a thermal conductivity of the thermoplastic semi-finished product b. Providing a material thickness of the thermoplastic semi-finished product c. Applying energy to at least one section of each of the surfaces of the thermoplastic semi-finished product until a specified target temperature is reached on both surfaces and recording the temperature profiles on both surfaces d. Carrying out a numerical simulation to calculate the temperature rise at at least one position within the material thickness of the thermoplastic semi-finished product and determining the soaking time, the simulation being used as input data - the thermal conductivity of the thermoplastic semi-finished product provided in step a - the material thickness of the thermoplastic semi-finished product provided in step b - the temperature curves recorded in step c - used and the heating time is determined from the input data as the time required until a given target temperature was reached at at least one position in the numerical simulation e. Providing the specified warm-up time in an electronically transferable form.

[0010] The order in which steps a and b are carried out is of course irrelevant and they can also be carried out simultaneously.

[0011] Steps a to e do not have to be carried out immediately one after the other.

[0012] In a method for controlling or regulating an infrared oven in a production process that processes the thermoplastic semi-finished product, the heating time of the thermoplastic semi-finished product determined and provided by means of such a method is used as a control variable for the infrared oven.

[0013] Protection is also sought for a computing unit configured to perform at least one of steps a, b, c, d and e of claim 1.

[0014] Protection is also sought for an arrangement comprising an injection molding machine, an infrared oven and at least one such computing unit, wherein it is preferably provided that at least one of the at least one computing unit is designed in the form of a machine control or machine regulation of the injection molding machine or the infrared oven.

[0015] Protection is also sought for a computer program which, when executed by a computing unit, configures the computing unit to carry out at least one of steps a, b, c, d and e of claim 1, and for a data signal which transmits such a computer program.

[0016] If a thermoplastic semi-finished product has a varying material thickness, the maximum material thickness is preferably used as “the material thickness” and is used as the basis for the methods of the present disclosure.

[0017] Suitable techniques for performing the numerical simulation in step d are known from the prior art and therefore need not be explained in detail here. As soon as the calculated (simulated) temperature at the at least one position corresponds to a predefined target temperature determined by the operator, the numerical simulation can be stopped and the current time value (that is, the time it took to reach the target temperature at the at least one predefined position) can be set as the soaking time.

[0018] A suitable technique, for example, is as follows: Based on the input data, a one-dimensional numerical calculation is carried out based on a Laplace equation, in which the temperature is calculated for at least one position within the semi-finished product thickness (preferably only for the central point, corresponding to the core temperature).

[0019] Advantageous embodiments are defined in the dependent claims.

[0020] In one embodiment, it can be provided that in step a, the following is carried out to provide the thermal conductivity of the thermoplastic semi-finished product: - Applying energy to at least one section of at least one of the two surfaces (optionally both surfaces) of the thermoplastic semi-finished product and recording the resulting temperature on at least the other of the two surfaces - Calculate the thermal conductivity of the thermoplastic semi-finished product based on the - the material thickness of the thermoplastic semi-finished product provided in step b, the temperature on at least the other of the two surfaces (preferably on both surfaces) and the time until this temperature is reached using calculation methods known from the prior art.

[0021] Alternatively, the thermal conductivity can be taken from a data sheet.

[0022] In one embodiment, it can be provided that the application of energy provided in the above-mentioned embodiment and / or in step c is carried out by means of: - thermal radiation, preferably in the form of a heat pulse, for example generated by an infrared oven or a halogen radiator; or - coherent radiation, for example generated by a laser; - or thermal radiation and coherent radiation

[0023] The measuring process carried out in one embodiment for providing the thermal conductivity of the thermoplastic semi-finished product can be carried out in such a way that - the energy is applied to only one of the two surfaces; and / or - the energy is applied with a pulse duration of less than 30 seconds, preferably less than 5 seconds, particularly preferably less than 2 seconds; and / or - the resulting temperature(s) are recorded using a pyrometer, infrared camera or temperature sensor; and / or - the resulting temperature(s) are recorded in the form of five to fifteen, preferably ten data points per second

[0024] In one embodiment, step c can be performed using an infrared oven into which the thermoplastic semi-finished product is placed. The measurement process is then preferably performed when the infrared oven is cold to avoid background noise.

[0025] In one embodiment, it can be provided that it is ensured that the predetermined target temperature is maintained on both surfaces for a predetermined time, preferably for approximately 20 seconds per millimeter of semi-finished product thickness.

[0026] In one embodiment, at least one of steps d and e can be performed by a processing unit of a machine control or machine regulation system of an assembly processing thermoplastic semi-finished products in a production process (preferably comprising an injection molding machine and an infrared oven). Alternatively, some or all of these steps can be performed by a processing unit of a general-purpose computer.

[0027] In one embodiment, it can be provided that in step b, the material thickness of the thermoplastic semi-finished product is determined automatically, preferably by laser measurement. Alternatively, the material thickness can be entered by an operator, for example, after measuring with a caliper.

[0028] In one embodiment, it can be provided that the heating time provided in electronically transferable form is automatically transmitted to a control or regulation system of the infrared oven by means of a data connection or that the control or regulation system of the infrared oven automatically queries the determined heating time by means of a data connection.

[0029] In one embodiment, quality control can be performed based on the gradient of a heating curve. For this purpose, the measured temperature profiles are compared with a reference profile stored for the respective thermoplastic semi-finished product. Deviations from the target profile indicate a possible quality problem, such as air bubbles in the thermoplastic semi-finished product, a deviating fiber material distribution from the target, or a defect in the infrared oven.

[0030] Additionally or alternatively, the calculated individual heating time (time until the target temperature on the surface is reached) can be used as a quality criterion.

[0031] Optionally, in both of the above-mentioned embodiments, the method can be supplemented with known methods for thermographic quality control (e.g., image analysis of the surface temperature distribution, etc.) when using an IR camera to measure the surface temperature.

[0032] Fig. 1 shows an infrared oven for heating thermoplastic semi-finished products.

[0033] Fig. Figure 2 shows a representation of a temperature curve of an energized surface of a thermoplastic semi-finished product over time.

[0034] In Fig. 1 shows a known infrared oven 1 with infrared radiators 3, into which a thermoplastic semi-finished product 2 is inserted. Shown is an example of a temperature measuring system (preferably contactless, particularly preferably a pyrometer) 4 for determining the temperature of one of the surfaces of the thermoplastic semi-finished product 2. Contrary to what is shown, multiple temperature measuring systems 4 can be provided, for example, a further temperature measuring system 4 for determining the temperature of the other of the two surfaces of the thermoplastic semi-finished product 2.

[0035] In Fig. Figure 2 shows how a deviation in a temperature profile (here too slow heating) can be used to infer a quality defect of the measured thermoplastic semi-finished product 2. Reference symbol: 1 infrared oven 2 thermoplastic semi-finished product 3 infrared heaters 4 Temperature measurement system

Claims

[1] Method for determining a heating time of preferably fiber-reinforced thermoplastic semi-finished products (2), wherein the thermoplastic semi-finished products (2) have two surfaces spaced apart from each other by a material thickness, comprising at least the following steps: a. Providing a thermal conductivity of the thermoplastic semi-finished product (2) b. Providing a material thickness of the thermoplastic semi-finished product (2) c. Applying energy to at least one section of each of the surfaces of the thermoplastic semi-finished product (2) until a predetermined target temperature is reached on both surfaces and recording the temperature profiles on both surfaces d. Carrying out a numerical simulation to calculate the temperature rise at at least one position within the material thickness of the thermoplastic semi-finished product (2) and determining the heating time, wherein the simulation is used as input data - the thermal conductivity of the thermoplastic semi-finished product provided in step a - the material thickness of the thermoplastic semi-finished product (2) provided in step b - the temperature curves recorded in step c used and the soaking time was determined as the time required until a given target temperature was reached at at least one position in the numerical simulation e. Providing the specified warm-up time in an electronically transferable form. [2] Method according to the preceding claim, wherein in step a, the following is carried out to provide the thermal conductivity of the thermoplastic semi-finished product (2): - applying energy to at least one section of at least one of the two surfaces of the thermoplastic semi-finished product (2) and recording the resulting temperature on at least the other of the two surfaces - Calculating the thermal conductivity of the thermoplastic semi-finished product (2) on the basis of the material thickness of the thermoplastic semi-finished product (2) provided in step b, the temperature on at least the other of the two surfaces, preferably on both surfaces, and the time until this temperature is reached [3] Method according to one of the two preceding claims, wherein in step b for providing the material thickness of the thermoplastic semi-finished product (2) this is determined automatically, preferably by a laser measurement. [4] Method according to at least one of the preceding claims, wherein step c is carried out using an infrared oven (1) into which the thermoplastic semi-finished product (2) is placed. [5] Method according to at least one of the preceding claims, wherein at least one step of steps d and e is carried out by a computing unit of a machine control or machine regulation of an arrangement processing thermoplastic semi-finished products (2) in a production process. [6] Method according to at least one of the preceding claims, wherein it is ensured that the predetermined target temperature is maintained on both surfaces for a predetermined time [7] Method according to at least one of the preceding claims, wherein a quality control of a thermoplastic semi-finished product (2) is carried out based on a gradient of a heating curve and / or a calculated individual heating time. [8] Method for controlling or regulating an infrared oven in a production process processing the thermoplastic semi-finished product (2) using the heating time of the thermoplastic semi-finished product (2) determined and provided by means of a method according to at least one of the preceding claims as a control variable for the infrared oven (1). [9] Method according to the preceding claim, wherein the heating time provided in electronically transferable form is automatically transmitted by means of a data connection to a control or regulation of the infrared oven (1) or the control or regulation of the infrared oven (1) automatically queries the determined heating time by means of a data connection. [10] A computing unit configured to perform at least one of steps a, b, c, d and e of claim 1. [11] Arrangement with an injection molding machine, an infrared oven (1) and at least one computing unit according to the preceding claim. [12] Arrangement according to the preceding claim, wherein at least one of the at least one computing unit is designed in the form of a machine control or machine regulation of the injection molding machine or the infrared oven (1). [13] A computer program which, when executed by a computing unit, configures the computing unit to carry out at least one of steps a, b, c, d and e of claim 1. [14] Data signal transmitting a computer program according to the preceding claim.

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