Contact welding tool and method for operating a contact welding tool

Abstract

A contact welding tool (1) has at least one heating element (2) arranged to be in contact with a workpiece and at least one heating source for heating the heating element (2), wherein at least one heating source is an IR radiation source (6) which emits IR radiation (IR) in the short-wave infrared range. In a method for operating a contact welding tool (1), the heating element (2) of the contact welding tool (1) is heated by means of short-wave infrared radiation (IR) and then brought into contact with the workpiece to be formed. The invention can be used particularly advantageously for hot riveting, for example, plastic rivets.

Description

Technical Field

[0001] The invention relates to a contact welding tool having at least one heating element arranged to be in contact with a workpiece and at least one heating source for heating the heating element. The invention also relates to a method for operating a contact welding tool, wherein the heating element of the contact welding tool is heated and then brought into contact with the workpiece to be formed. The invention can be used particularly advantageously for hot riveting, for example, plastic rivets. Background Art

[0002] To date, heating elements have been used for joining thermoplastics, which have been manufactured as milled parts, for example from aluminum, aluminum-bronze alloys, brass, steel or stainless steel. Electric heating elements with resistance heating elements are installed in these milled parts, the heat of which is transferred to the corresponding milled parts by contact. Depending on the material, the manufacturing accuracy and the tool specifications, the heating of the heating elements can take disadvantageously long times. Heating times of up to one hour are not uncommon for temperatures exceeding 300° C. to be reached.

[0003] Another possibility for heating, for example, the rivet ball is to use the resistance of the heating element. However, this has the disadvantage that a transformer is required, which generates a high voltage and is operated nearly short-circuit. However, these assemblies are relatively large and require corresponding installation space in the switch cabinet. Summary of the invention

[0004] The object of the present invention is to provide a contact welding tool which is distinguished on the one hand by a short heating time and on the other hand by rapid coolability, using components which are as simple in structure as possible. The contact welding tool can be suitable in particular for plasticizing and shaping thermoplastics.

[0005] This object is achieved by the subject matter of the independent claims. Advantageous developments of the invention are described in the dependent claims, the description and the drawings.

[0006] The contact welding tool according to the invention has at least one heating element arranged to be in contact with a workpiece and at least one heating source for heating the heating element, wherein at least one heating source is an infrared (IR) radiation source which emits infrared radiation in the short-wave infrared range.

[0007] The use of short-wave IR radiation as a heat source for heating the heating element results in the advantages of high efficiency, high energy density and fast controllability. In particular, a reduction in cycle time or tact time can be achieved advantageously by faster heating and faster cooling of the heating element, for example in hot contact riveting. Another advantage is that a reduction in energy consumption can be achieved by reducing the mass of the heating element and improving the efficiency. It is also advantageous that the suitability of hot contact riveting for partially crystalline materials (such as partially crystalline high-performance polymers, such as polyamide, etc.) can be expanded due to faster temperature regulation. In addition, the advantage of reducing the required installation space of the tool is achieved.

[0008] The IR radiation source or IR radiator is particularly designed (ie constructed and arranged) to heat the heating element to an operating temperature sufficient for joining the workpieces. The heating element has at least one contact point, which is provided for contacting the area of ​​the workpiece to be formed by the action of heat.

[0009] The heating element can be configured as a shaped body. It can also be referred to as a forming tool.

[0010] The contact welding tool can therefore have one or more heating elements. At least one IR radiation source can be assigned to each heating element.

[0011] In a development, the heating element can be heated to an operating temperature of 150° C. or more, in particular 200° C. or more, in particular 250° C. or more, in particular 300° C. or more, by means of the at least one assigned heating source.

[0012] In order to bring the heating element into contact with the workpiece, the heating element can be moved onto the workpiece and pressed onto the workpiece or vice versa. This can be done manually or automatically. If necessary, the workpiece can be shaped at the same time, for example to produce a friction-locking connection between two workpieces, as is known, for example, from riveting thermoplastics. For example, two or more workpieces welded by means of a contact welding tool can be joined to one another by a press stroke following heating, as is known, for example, from thermal element welding.

[0013] In a further development, the heating source is an IR radiation source which emits short-wave infrared radiation in a wavelength range between 0.78 μm and 3.0 μm. This wavelength range is also referred to as the NIR range, so that the IR heat source can also be referred to as an NIR radiation source or NIR radiator.

[0014] In a development, the IR radiation source emits IR useful radiation predominantly in the NIR wavelength range (eg with a power component of 50% or more, in particular 70% or more, in particular 80% or more), in particular exclusively in the NIR wavelength range.

[0015] In one embodiment, the heating source is an IR-A heating source, that is to say an IR radiation source which emits infrared radiation in the IR-A wavelength range between 0.78 μm and 1.4 μm. The use of the IR-A range is characterized by a particularly high efficiency, a particularly high energy density and a particularly fast controllability.

[0016] A development is that the IR radiation source emits IR useful radiation predominantly in the IR-A wavelength range (eg with a power component of 50% or more, in particular 70% or more, in particular 80% or more), in particular only in the IR-A wavelength range.

[0017] The IR radiation source can be a heating source which radiates IR radiation in a point-like or area-like manner.

[0018] The heating element which can be heated by means of an IR radiation source can already be produced as a turned part, a milled part, a sintered part, a punched part or by means of other shaping methods.

[0019] The heating element can be made of metal or of another material with good thermal conductivity and heat resistance, such as ceramic, etc. As metal, aluminum, brass or steel can be used, for example. The use of V2A steel is particularly advantageous.

[0020] In one embodiment, the heating element has a thin-walled area (hereinafter referred to as a "molded area" or bottom without limiting the generality), which has at least one contact surface for contacting a workpiece on the front side and can be irradiated with IR radiation on the back side by means of an IR radiation source.

[0021] In a further development, the profiled region has a metal sheet, in particular serving as a base for at least one contact projection. The wall thickness of the metal sheet is advantageously in the range [0.5 mm; 3 mm], in particular in the range [0.75 mm; 2 mm]. This allows a sufficiently high stability to be achieved, while the thermal capacity and thus the inertia during heating and cooling are kept low.

[0022] In one embodiment, the contact welding tool has at least one cooling device for cooling the heating element. This achieves the advantage that the heating element can be actively cooled and thus can be cooled particularly quickly. This enables particularly fast cycle times or cycle times when using the contact welding tool.

[0023] In a further development, the cooling device is configured to apply a cooling medium to the heating element. The cooling medium can be a gaseous and / or liquid cooling medium, such as compressed air, dry ice, cooled nitrogen or the like.

[0024] As an alternative or in addition, the cooling device can have at least one Peltier element or the like, which is in particular thermally connected to the heating element.

[0025] One embodiment provides that a gap, which can be acted upon by a cooling medium, is present between the IR radiant heater or the IR emitting surface of the IR radiant heater and the heating element. As a result, the heating element can be cooled particularly quickly using cost-effective components. Particularly fast cooling can be achieved in particular in that the heating element represents a wall of the gap. In particular, the back side of the heating element facing away from the contact region represents a wall of the gap.

[0026] One development is that the IR radiant heater is thermally insulated with respect to the intermediate space, for example by means of an IR-transmissive window. Advantageously, the thermal load of the IR radiant heater is thereby reduced, in particular with respect to periodic thermal fluctuations.

[0027] In a further development, the cooling chamber is designed as a through-chamber having at least one inlet and at least one outlet for the cooling medium. The through-chamber can otherwise be sealed.

[0028] The object is also achieved by a method for operating a contact welding tool, wherein

[0029] - heating the heating element of the contact welding tool by means of short-wave infrared radiation and then

[0030] - Bringing the heating element into contact with the workpiece to be formed.

[0031] The method can be designed similarly to a contact welding tool and produce the same advantages.

[0032] Thus, for example, the heating element can be heated by means of NIR radiation, in particular IR-A radiation.

[0033] A further development is to press the heating element onto the workpiece if the heating element is to be brought into contact with the workpiece to be formed. Thus, the heating element can also be used as a forming tool.

[0034] In one development, the workpiece is made of plastic, in particular a thermoplastic, optionally partially crystalline, plastic, at least in its intended contact region with the contact welding tool.

[0035] One embodiment provides that, while the heating element is still in contact with the workpiece to be subsequently formed, the heating element is cooled by means of a cooling medium at least to the demolding temperature. The heating element can then be released from the workpiece. While the heating element is cooling, it is no longer irradiated with IR radiation.

[0036] One embodiment provides that, in order to cool the heating element, the cooling medium is guided through a gap between the heating element and the IR radiation source or IR radiator. In particular, a wall of the gap corresponds to a wall of the heating element.

[0037] The cooling medium (for example compressed air) can be introduced into the intermediate space, for example, under pressure (for example at a pressure of approximately 6 bar) via lines (“cooling pipes”). BRIEF DESCRIPTION OF THE DRAWINGS

[0038] An advantageous embodiment of the present invention is explained below with reference to the accompanying drawings.

[0039] Figure 1 A schematic diagram of a contact welding tool 1 in the form of a hot riveting tool is shown as a sectional view in the region of its heating element 2. The heating element 2 has a contact region (hereinafter referred to as "base" 3) for contacting a workpiece (not shown). DETAILED DESCRIPTION

[0040] The base 3 here has a thin wall with a thickness or wall thickness d as a base 3a, on which a suitably shaped contact projection 4 protrudes on the front side. This arrangement can also be called a rivet ball base. The workpiece can only come into contact with the contact projection 4 additionally on another area of ​​the front side of the base 3, in particular on the entire front side of the base 3.

[0041] At least the bottom 3 is made of metal (as an alternative, for example, ceramic), for example brass, aluminum or steel, in particular high-grade steel. The use of V2A steel is particularly advantageous, since V2A steel has not only a fast heating curve and short cooling time but also a high resistance to mechanical damage, for example due to glass fiber filling in the plastic of the workpiece, and also good chemical resistance.

[0042] The wall thickness d of the base 3a can be, for example, in the range d=[0.5 mm; 3 mm], in particular in the range d=[0.75 mm; 2 mm]. The base 3a can be designed in particular as a sheet metal or formed from a sheet metal part.

[0043] In order to shape the workpiece (for example for hot welding or hot pressing), the heating element 2 can be moved toward the workpiece (or vice versa) and pressed onto the workpiece, as indicated by the arrow F. The workpiece can thus be shaped. The workpiece can be made of a thermoplastic, possibly partially crystalline plastic and can be, for example, a rivet or a rivet head.

[0044] The rear side of the bottom 3 or base 3a facing away from the contact projections 4 serves as a wall or boundary of a gap 5 between the bottom 3 and an IR-A radiator 6 arranged at a distance therefrom. The IR-A radiator 6 is designed to irradiate the rear side of the bottom 3 with short-wave IR radiation IR in order to heat the bottom 3 including its front side and the contact projections 4, for example to an operating temperature of more than 250° C., for example 280° C. Since the base 3a is designed as a thin-walled structure, its heat capacity is small, so that the bottom 3 can be quickly heated or heated to the desired operating temperature by absorbing the IR radiation IR.

[0045] The bottom 3 can also be cooled particularly quickly to or below the desired demoulding temperature (e.g. 100° C.), and more precisely by purging the interspace 5 with compressed air DL after the IR-A radiator 6 has been switched off or deactivated. The interspace 5 thus serves as a through-space. The compressed air DL can be introduced into the interspace 5, for example, via a cooling tube 7, which has a pressure of, for example, between 4 and 8 bar, for example, approximately 6 bar. The diameter of the cooling tube 7 can be, for example, between 2 mm and 4 mm, for example, 3 mm.

[0046] For venting the intermediate space 5 , an outlet opening in the form of a vent hole 8 is provided.

[0047] The contact welding tool 1 enables particularly short cycle times or tact times for heating the bottom 3 from the demoulding temperature to the operating temperature and back. Thus, for example, when using a base 3a made of a V2A steel sheet with a thickness of d=2 mm, a heating time in the range of 20 seconds from a demoulding temperature of 100° C. to an operating temperature of 280° C. and a cooling time in the range of 10 seconds back to the demoulding temperature can be achieved.

[0048] The drawings are merely schematic and serve only to explain the invention. Identical or identically acting elements are continuously provided with the same reference numerals.

[0049] List of reference numerals:

[0050] 1 Contact welding tool

[0051] 2 Heating elements

[0052] 3 Bottom

[0053] 3a Bottom base

[0054] 4 Contact bumps

[0055] 5. Gap

[0056] 6 IR-A-Radiator

[0057] 7 Cooling pipe

[0058] 8 Exhaust holes

[0059] d Wall thickness

[0060] DL Compressed Air

[0061] F Arrow

[0062] IR Infrared-Radiation

Claims

1. Contact welding tool, with: at least one heating element arranged to contact the workpiece, at least one heating source for heating the heating element, wherein at least one heating source is an IR radiation source emitting IR radiation in the short-wave infrared range, and at least one cooling device for cooling the heating element, which is designed to apply a gaseous and / or liquid cooling medium to the heating element, wherein Between the IR radiation source and the heating element there is a gap which can be acted upon by a cooling medium, wherein the rear side of the heating element facing away from the contact region represents a wall of the gap and the IR radiation source is thermally insulated relative to the gap, The heating element has a thin-walled region which has at least one contact surface for contact with a workpiece on the front side and which can be irradiated with IR radiation on the rear side by means of at least one IR radiation source, The thin-walled region is produced from a sheet metal part having a wall thickness in the range [0.5 mm; 3 mm].

2. The contact welding tool according to claim 1, wherein the IR radiation source is an IR-A-heating source.

3. The contact welding tool of claim 1, wherein the thin-walled region is comprised of V2A steel.

4. The contact welding tool according to any one of claims 1 to 3, wherein the heating element is configured for performing thermal contact riveting.

5. A method for operating a contact welding tool, wherein - Providing a contact welding tool according to any one of claims 1 to 4 - heating the heating element of the contact welding tool by means of short-wave infrared radiation and then - Bringing the heating element into contact with the workpiece to be formed. 6 . The method according to claim 5 , wherein the heating element is cooled at least to the demolding temperature by means of a cooling medium while the heating element is still in contact with the workpiece to be subsequently formed. 7 . The method as claimed in claim 5 , wherein the cooling medium is conducted through a gap between the heating element and an IR radiator which generates short-wave infrared radiation in order to cool the heating element.

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