Method for forming an engagement portion in a workpiece

Abstract

A method for forming an engagement portion in a workpiece is provided, said workpiece preferably consisting at least partially of wood, materials containing wood fibers, wood composite materials, veneer, plastics materials and combinations thereof. The method has the following steps of: providing the workpiece having a cutout, introducing a predetermined volume of a curable filling compound into the cutout and introducing an engagement element into the curable filling compound, wherein the engagement element has an engagement structure which at least partially represents a geometric counterpart to the engagement portion, the engagement portion takes up a predetermined position in the workpiece, and the engagement structure is arranged at least partially in the filling compound.

Claims

1. A method for forming an engagement portion in a workpiece, the workpiece comprising any of wood, materials containing wood fibers, wood composite materials, veneer, plastic materials, and combinations thereof, the method comprising the steps of: providing the workpiece with a cutout; introducing a predetermined volume of a curable filling compound into the cutout; and pushing an engagement element having an engagement structure into the curable filling compound such that the engagement structure is at least partially disposed in the filling compound, wherein a connection between the curable filling compound and the engagement element is a form-fit connection, and wherein the engagement element is unscrewed from the hardened filling compound and afterwards the engagement element is screwed back into the engagement portion formed in the workpiece.

2. The method of claim 1, comprising holding the engagement element in a predetermined position for a predetermined period of time after the filling compound is introduced.

3. The method of claim 1, wherein the predetermined volume corresponds to a volume of the cutout minus a volumetric displacement of the engagement element in the filling compound.

4. The method of claim 1, wherein the predetermined volume of the curable filling compound is determined by a porosity of the workpiece.

5. The method of claim 1, wherein the curable filling compound comprises a paste-like compound.

6. The method of claim 1, wherein introducing the filling compound comprises: feeding a granulate comprising a wood material to an extruder; and melting the granulate in the extruder to form the curable filling compound.

7. The method of claim 1, wherein the curable filling compound comprises a thermoplastic compound which transforms into a thermoplastic state when heated and hardens when cooled, and comprising heating the curable filling compound before or during introduction into the cutout.

8. The method of claim 1, wherein the curable filling compound can be hardened by a supply of energy, and comprising hardening the curable filling compound by a supply of energy.

9. The method of claim 1, wherein the curable filling compound can be formed from a raw mass by a supply of energy, and comprising: introducing the raw mass into the cutout; and transforming the raw mass located in the cutout into the curable filling compound by the supply of energy.

10. The method of claim 1, wherein the curable filling compound comprises biological polymers, comprising any of lignin and natural fibers, wherein the natural fibers are formed from any of wood, flax, hemp, sisal, jute, and/or other plant fibers.

11. The method of claim 1, wherein an indentation in the workpiece is formed around the cutout, the indentation being dimensioned such that, in the indentation, at least a part of the engagement element protruding from the cutout can be accommodated.

12. The method of claim 1, wherein the cutout comprises an undercut relative to a pushing-in direction of the engagement element.

13. The method of claim 1, wherein the engagement structure of the engagement element comprises a thread.

14. The method of claim 1, wherein the engagement element comprises a screw, the screw comprising any of a countersunk head and a round head.

15. The method of claim 14, wherein the screw comprises a self-tapping thread.

Description

BRIEF DESCRIPTION OF THE DRAWINGS

(1) FIGS. 1A to 1C schematically present the different steps of one embodiment of the method according to the invention, with cross-sections in different stages of the method being shown in each.

(2) FIGS. 2A to 2E depict further embodiments of the method according to the invention with the help of cross-sections.

(3) FIG. 3 depicts in a simplified form of one preferred embodiment of a device, with which the method according to the invention can be performed.

(4) FIGS. 4A to 4D depict further embodiments in the form of cross-sections.

DETAILED DESCRIPTION

(5) Preferred embodiments of the present invention will be described in detail below with reference to the accompanying drawings. Further modifications cited in this connection can each be combined with one another to form new embodiments.

(6) In the partial FIGS. 1A to 1C, FIG. 1 represents the essential steps of a method according to the invention for forming an engagement portion in a workpiece 10. An inner thread to be formed on or in the workpiece 10 is considered here to be an example of the engagement portion.

(7) Firstly, as shown in FIG. 1A, a workpiece 10 is provided which has a cutout 11. In the next step, a curable but not-yet-hardened filling compound 20 is introduced into this cutout 11.

(8) In this case, curable means that the filling compound can change its viscoelastic properties by a hardening process to the extent that in the hardened state, under normal conditions, it no longer displays viscoelastic flow properties, and its form also does not change by itself at least in a stress-free condition (i.e. without additional external forces). In the hardened state, it is furthermore preferred that the hardened filling compound either withstands the occurring stresses or breaks, i.e. in particular it does not display plastic flow such as an expansion increase without a simultaneous tension increase (whereas a limited elastic deformation under stress can certainly be desirable for several uses).

(9) Not-yet-hardened designates a state in which the filling compound has viscous properties and can be plastically deformed into the material without too great a permanent tension increase (essentially without a permanent tension increase). However, it is simultaneously preferred that the filling compound is not completely fluid since this would make introducing the filling compound into the cutout more difficult. In this not-yet-hardened (curable) state, the filling compound can consequently be designated, for example, as paste-like or gel-like. It is thereby especially preferred if the viscoelastic properties of the curable filling compound state are adjusted such that the filling compound does not essentially flow, for example, under the influence of gravity at least until introduction of the engagement element (until the start of the hardening process). This enables the filling compound to be processed overhead or on an inclined workpiece.

(10) It is simultaneously preferred that the viscosity is at least initially so low that the filling compound can at least partially penetrate into the rough surface of the cutout 11 in the workpiece and can mesh with the workpiece during hardening. The rough surface is considered to be the cut edges of particle boards that are often rough.

(11) For example, a suitable viscosity range for the not-yet-hardened filling compound is from 20,000 mPas to 100,000 mPas. However, other viscosities can also be used depending on the specific application.

(12) During introduction into the cutout 11, the filling compound 20 has a predetermined volume V. After introducing the filling compound 20, an engagement element 30 is pushed into the not-yet-hardened filling compound 20. As depicted in the example of the screw shown in FIG. 1C, the engagement element 30 has an engagement structure (presently the outer thread of the screw) in the hardened filling compound, that represents the geometric counterpart or negative to the engagement portion (presently an inner thread) that is to be formed in/on the workpiece.

(13) The cutout 11 is preferably limited by the workpiece 10 at least on the bottom side. The cutout 11 depicted in the drawings is milled into the workpiece 10, for example, in the shape of a straight circular cylinder. However, any arbitrary different shape of the cutout can be used according to the requirement and the application (for example, a cuboid cutout or a cutout having a generally polyhedral cross-section, as well as a conically tapered cutout).

(14) The cutout 11 thereby has a larger cross-section than the part of the engagement element 30 which is to be introduced into the cutout (see FIG. 1C). It is thereby preferred that the volume of the cutout 11 is marginally larger than the part of the engagement element 30 which is to be arranged in the cutout. This ensures an appropriate displacement of the filling compound 20 when the engagement element 30 is pushed into the filling compound 20 that is in the cutout 11.

(15) By introducing the engagement element 30 into the filling compound 20, the engagement element 30 occupies a predetermined position relative to the workpiece. A case is presently depicted here in which the engagement element is arranged perpendicular to the surface of the workpiece. However, arbitrary inclined orientations are conceivable as well.

(16) After the hardening of the filling compound 20, the engagement element 30 is then essentially solidly arranged in the predetermined position relative to the workpiece.

(17) In the case of the screw depicted in the drawings as engagement element 30, the workpiece 10 together with the screw can now be packed into a construction kit. At the location of assembly, the user must only unscrew the screw 30 from the hardened filling compound 20 in which an inner thread (engagement portion) is formed by the pushing in and hardening. Afterwards, the workpiece 10 can be connected to a suitable counterpart (for example, a further workpiece having a corresponding through hole) in that the screw (engagement element) is screwed (introduced) back into the inner thread (engagement portion) formed in the workpiece.

(18) This process is characterized both by a very high connection precision as well as by an especially simple operation since the user can revert to a thread (engagement portion) which has already been formed, and does not have to firstly cut (form) a thread (engagement portion) into the workpiece with greater physical effort. Additionally, other screws, and not only particle board screws, can also optionally be used which where necessary ensure higher resistances to being ripped out or pulled out or broken out.

(19) To support a precise assembly, the predetermined volume V of the filling compound 20 that is filled into the cutout 11 is preferably measured so that it essentially corresponds to the volume of the cutout 11 minus the volumetric displacement of the engagement element 30. This is depicted, for example, in the transition from FIG. 1B to FIG. 1C. If the engagement element is then pushed into the filling compound, the filling compound is essentially closed flush with the edge of the workpiece (see FIG. 1C). A possible reworking is not necessary. Additionally, as regards the predetermined volume, the amount which penetrates into the workpiece when the engagement element is pushed into the workpiece can be taken into account. This amount can be correspondingly added to the predetermined volume.

(20) However, different volumes can also be advantageous for several embodiments. For example, overfilling the filling compound can lead to the filling compound protruding from the edge of the workpiece 10, by which it could fulfil the function of a washer or a spacer element.

(21) Conversely, a volume V that is smaller than the volume of the cutout 11 minus the volumetric displacement of the engagement element 30 can safely ensure that the engagement element can be sunk into the cutout and that a portion of the hardened filling compound 20 does not protrude beyond the edge of the workpiece 10.

(22) To support the correct arrangement of the engagement element 30 in the predetermined position in the hardened filling compound 20, it is furthermore preferred in step 1C to hold the engagement element 30 in the predetermined position until the filling compound 20 is at least partially hardened.

(23) In this connection, it is furthermore preferred that the viscosity of the curable, not-yet-hardened filling compound 20 be formed such that it is possible to easily push in the engagement element 30, however, a lateral shifting or a tipping of the engagement element 30 is made more difficult.

(24) Regarding the material of the filling compound 20, it is preferred that the material is a thermoplastic compound which transforms into a thermoplastic state when heated and hardens when cooled.

(25) Here, it is preferably heated to a temperature of 180 C. to 220 C.

(26) Accordingly, a filling compound 20 having suitable properties can be provided in that the thermoplastic filling compound 20 is heated before introduction into cutout 11. Hardening the filling compound by cooling after the engagement element 30 has been introduced is commonly performed without an additional processing step, alone by the cooling of the softened material by the cooler ambient air. The cooling of the filling compound can, however, also be supported by a determined cooling step. This can, for example, comprise blowing cooled air.

(27) Especially preferred is a filling compound 20 which has a biopolymer that is characterized by biodegradability and is essentially biologically based in that it is produced, for example, from sugar by fermentative and polymer-chemical processes. In particular, the biopolymer has lignin. Moreover, natural resins, natural waxes, natural oils, cellulose, and natural reinforcing fibers such as, for example, wood fibers, flax fibers, hemp, sisal, jute or other plant fibers can be contained in the material. Moreover, the material of the filling compound can have polyhydroxyalkanoates, polyhydroxybutyrates, polycaprolactone, polyester and/or starch. In particular, biodegradable thermoplastics or thermoplastic polyesters are used as the thermoplastic part such as, for example, polyhydroxyalkanoates, polyhydroxybutyrates, and polycaprolactone.

(28) Furthermore, further advantages to these materials are good biodegradability and the opportunity for a resource-saving production. Thus, it is even conceivable that wood dust or wood flour from a previous processing step is used for the filling compound. Furthermore, with regard to a recycling process when disposing of the furniture, the filling compound does not need to be taken into account.

(29) Furthermore, the filling compound 20 can also be formed such that it is hardened by a supply of energy. Thus, for example, a filling compound 20 which is cross-linked by heat (chemically) is conceivable. The filling compound then preferably has two components, a basic compound and a cross-linker, with the cross-linking reaction being activated by heat. The required heating is then, for example, in a region of approximately 195 C. After introducing the engagement element 30, the filling compound 20 can then, for example, be hardened by radiation with infrared energy or (laser) light or exposure to ultrasound energy.

(30) A workpiece produced by the method depicted in FIGS. 1A to 1C is characterized by a cutout which is filled in with a hardened filling compound 20 in which in turn an engagement portion is formed that is engaged with an engagement structure of an engagement element. The engagement portion is the geometric counterpart (negative) to the engagement structure and the engagement essentially occurs in a complete form fit.

(31) If the screw 30 depicted in the drawings is used as the engagement element, an arrangement is formed in which the engagement element 30 can only be removed from the workpiece 10 with great difficulty by pulling on the engagement element.

(32) Experiments with an M8 screw and a particle board showed that the arrangement according to the invention withstands tensile forces which would greatly exceed the strength of common dowel connections. Usually such tensile tests ended with the destruction of the particle boardand not for instance with a failure of the hardened filling compound or the hardened filling compound being torn out of the workpiece. This underpins the advantage in strength that can be achieved with the method according to the invention.

(33) Feeding a granulate of wood-like material, in particular a mixture of biodegradable polymers and natural fibers, into an extruder has proven an effective method for introducing the filling compound into the cutout 11. The granulate is then melted down in the extruder to form the curable (not-yet-hardened) filling compound which then hardens again when cooled.

(34) In this application, the method according to the invention was described with a screw as an example of an engagement element. However, other engagement elements are also still conceivable here. For example, a hook which has an outer thread on one end is imagined. Engagement elements are also conceivable which have (circumferential) grooves, or projections (in particular circumferential ring-shaped projections). If these are suitably dimensioned and if the elasticity of the hardened filling compound 20 is correspondingly adjusted, the engagement element can be detached from the workpiece by pulling on the engagement element after the hardening of the filling compound. The reconnection then occurs by clicking the engagement element into the filling compound and latching the engagement structure into the engagement portion of the hardened filling compound.

(35) In any case, after the final processing of the workpiece with the method according to the invention, the engagement element can firstly remain in the engagement portion in the filling compound 20 and thereby in the workpiece 10. For the furniture construction kit, plural of such workpieces 10 can optionally be assembled into packages and correspondingly sent.

(36) However, in this case as well as with the storage of such a workpiece 10, a protruding engagement element 30 (see FIG. 1C) can be disadvantageous.

(37) In such cases, it is preferable that an indentation 12 depicted in FIG. 2A is formed around the cutout 11 in the workpiece. In doing so, a blind hole is formed in which the part of the engagement element 30 that is protruding from the actual cutout 11 can be accommodated such that the engagement element 30 does not protrude beyond the workpiece 10. The indentation 12 and the cutout 11 are then dimensioned such that the engagement element 30 in the predetermined position does not protrude beyond the contour A of the workpiece 10. A screw head of a screw 30 can thus be sunk, for example, into the workpiece 10 for transportation.

(38) In FIG. 2A, the indentation 12 is depicted in cross-section as a depression that is cuboid. However, the depression can also be conical in the cross-section and having diagonal side walls (see FIG. 2C).

(39) Thus, a workpiece such as depicted in FIG. 2B is characterized in that the workpiece has a cutout 11 which is filled with a hardened filling compound 20 which in turn has an engagement portion with which an engagement element is engaged via an engagement structure formed thereon. The engagement portion is thereby the counterpart (negative) to the engagement structure and the engagement essentially occurs in a complete form fit. Furthermore, an indentation 12 is formed around the cutout 11 that is dimensioned such that the indentation 12 can accommodate at least the part of the engagement element 30 that is protruding from the cutout 11 in such a way that it does not protrude beyond the contour A of the workpiece 10.

(40) To further support the meshing between the filling compound and the workpiece, the cutout, as shown in FIGS. 2D and 2E, can have an undercut 14 relative to the pushing-in direction of the engagement element. In other words, on a portion which faces away in the pushing-in direction of the engagement element from that side which the engagement element is pushed in, the cutout has an area which has a larger inner diameter than the portion of the cutout from which the engagement element is pushed in. Such an undercut 14 can be formed in the cutout in the shape of a reversed countersunk drill hole (FIG. 2D) or a step portion at the transition to a portion having enlarged diameter (FIG. 2E).

(41) In the above-mentioned method, the filling compound can alternatively be introduced into the cutout 11 in a raw state, for example, in the form of a granulate or a pre-shaped body. The filling compound is formed thereby such that it can be transformed from this raw state into the not-yet-hardened state to form the curable filling compound, in particular by an energy supply. In doing so, after introducing the filling compound in the raw state, the filling compound can subsequently be transformed in the cutout 11 into the not-yet-hardened state. This can occur, for example, by heating the filling compound or by exposing the workpiece to ultrasound, with ultrasound electrodes which are not shown then being applied to the workpiece. As alternatives, a heating can be provided in particular by hot air, laser radiation and microwaves, which (optionally with ultrasound exposure) can also be used in combination. In the case of laser radiation or microwaves, this can furthermore be supported by the addition of polymers which deliberately absorb the form of energy.

(42) An example of a device for performing the method according to the invention is described below with reference to FIG. 3.

(43) The device has a jig 120 for the workpiece 10. Furthermore, the device has a tool holder 130 in which different tool heads 101, 110 and 140 can be accommodated.

(44) These tool heads comprise, for example, a drilling/milling device 110 to form a corresponding cutout 11 (optionally including an indentation 12) in the workpiece 11. Furthermore, the device has a holding device 140 as a tool head for picking up, holding and subsequently putting down the engagement element 30.

(45) A further tool head is provided by the application unit 101, with which the filling compound 20 can be introduced into the cutout 11. In the shown example, the application unit 101 has an extruder 103 which preferably feeds granular raw material into an outlet opening 102 by heating. The raw material for the filling compound can thereby be stored in a storage container 105 which is connected to the extruder 103 by a hose 104.

(46) For a simplified representation, these tool heads 101, 110 and 140 are depicted on top of one another in the device shown in FIG. 3. However, it is noted that these can be accommodated in the tool holder 130 with the help of a magazine which permits a cycling of the tool heads. Furthermore, the tool holder 130 can also be formed such that for each method step it also takes an individual tool head from a separate magazine and returns this tool after finishing the corresponding step.

(47) The tool holder 130 preferably has a spindle unit to drive the drilling/milling tool and the extruder 103.

(48) Furthermore, it is preferred that the tool holder 130 is realized as a so-called five-axes tool holder which can be driven and oriented in five directions relative to the workpiece being held by the jigs 120. These directions can relate to longitudinal shifts along the three spatial directions as well as rotational movements around two independent axes. For example, known structures such as systems having a five-axis spindle head and the like can be used for this. Overall, such an embodiment has the advantage that the cutouts 11 can formed in diverse geometries and locations on the workpiece 10, and the filling compound 20 as well as the engagement elements 30 can also be flexibly introduced or inserted. Alternatively/additionally, with a suitable device it can also be provided to move the workpiece 10 relative to a tool holder.

(49) Furthermore, the device can have energy sources 150 which are formed such that they apply energy to the filling compound. This can, for example, be used to harden the filling compound after introduction of the engagement element or for transforming the filling compound from a raw state into a not-yet-hardened but curable state (which can then be hardened).

(50) Such energy sources can, for example, consist of infrared radiation application devices, microwave application devices or ultrasound application devices.

(51) Furthermore, the device can also have a control unit that is not shown, which is formed such that it firstly controls the forming of a cutout 11 having a certain volume in the workpiece 10 and then, on the basis of this volume of the cutout, calculates the predetermined volume of the filling compound 20 that is to be introduced into the cutout 11, with the predetermined volume V preferably being adjusted such that this corresponds to the volume of the cutout 11 minus the known volumetric displacement of the engagement element 30 that is to be introduced into the filling compound 20.

(52) The porosity of the workpiece can also additionally be taken into account here. Since the filling compound penetrates into the pores of the workpiece, an additional amount is to be added to the volume calculated above, depending on the porosity of the workpiece.

(53) As an alternative to the above-described five-axes tool holder 130, the device can also be constructed such that the tool holder 130 can only be shifted in an X-, Y-, and Z-direction relative to the workpiece 10 that is being held by the jigs 120. Additionally, the workpiece 10 can also be transported relative to the tool carrier 130 by a not shown conveyor to perform the method according to the invention in throughfeed.

(54) It is possible with the above-described device and said variations to simply perform the method according to the invention for forming an engagement portion in a workpiece.

(55) In FIG. 4, several possible embodiments are schematically shown once more in this regard in cross-section. FIG. 4A shows a cutout 11 having the indentation 12, after the curable filling compound has been introduced. The amount or the volume of the filling compound 20 can be measured such that the indentation 12 is essentially completely filled out with engagement element 30 and the displaced filling compound 20 after the engagement element 30 is introduced (FIG. 4B). Alternatively, the volume of the filling compound 20 can also be adjusted so that only a small amount of the displaced filling compound oozes into the area of the indentation 12 (FIG. 4C).

(56) Lastly, one embodiment is shown in FIG. 4D which once more emphasizes the versatility of the method. Here, a screw as the engagement element 30 holds a cladding layer 15 to the workpiece 10. In doing so, the engagement element 30 is realized as a head screw which is guided through a corresponding through hole of the cladding layer 15. During the production, it is conceivable to prepare the cladding layer 15 together with the engagement elements 30 that are disposed thereon and to then press it onto the workpiece 10 as a whole such that the engagement elements 30 penetrate into the cutouts 11 in the workpiece 10, which are filled with the not-yet-hardened filling compound 20. After curing the filling compound, the cladding layer 15 is securely attached to the workpiece 10. A screwing of the workpiece 10 with the cover layer 15 that had conventionally been required is no longer necessary.

(57) As a result of the fact that an engagement element, the engagement structure thereof is to some extent a negative or geometric counterpart of the engagement portion to be formed in the filling compound (or the workpiece), is pushed into a curable filling compound that is poured into a cutout 11 of the workpiece 10, a processable workpiece can be provided after the hardening of the filling compound, which is particularly suited for further use in furniture construction kits and is characterized by a secure and simple connection to an engagement element.