A JIG FOR WELDING MITRED JOINTS BETWEEN THE MEMBERS OF MOULDED PLASTIC WINDOW AND DOOR FRAMES

Abstract: A jig for welding mitred joints between members of moulded plastic window and door frames, comprising four mutually positionable clamp assemblies (TA, TB, TC, TD), one to each corner of the frame, each of which comprises a pair of horizontal rests (3A-4A, 3B-4B, 3C-4C, 3D-4D) serving to support the members of the frame, and respective upwardly-projecting fences (2SA-1SA, 2SB-1SB, 2SC-1SC, 2SD-1SD) disposed transversely and parallel to the horizontal exit path followed by the frames, which register against the external faces of the rails (1, 4) and the uprights (2, 3) of the frame; each clamp assembly (TA, TB, TC, TD) further comprises a pair of plates (1A-2A, 1B-2B, 1C-2C, 1D-2D), located above the corresponding pairs of rests, that serve to hold the frame members fast against the rests as and when necessary. The fences (2SA, 2SB, 2SC, 3SD) disposed transversely to the exit path of the welded frame are embodied independently of the relative rests (3A, 3B, 3C, 3D), and capable of movement between a first limit position, in which the rails (1, 4) are checked, and a second limit position in which the rails are freed and the fences themselves completely clear of the transverse dimension of the frame.

Description: The present invention relates to a jig designed for welding the mitred corners of window and door frames fashioned from moulded plastic section. Conventionally, the sash and surround frames of plastic window and door fixtures are best embodied by effecting a flush mitre between the ends of each two joined members, which are previously cut to size and shaped to the necessary 45° angle at either end, and welding the joined surfaces together. The prior art (see Document DE 3.203.431) embraces welding jigs with special clamp assemblies, mounted on sliding carriages, that can be traversed during operation into positions corresponding to the four corners of the frame. Each such clamp assembly affords a substantially square surface by which the mitred ends of the two relative members of the frame are supported; the surface is embodied in two distinct parts that appear as a pair of horizontal triangular rests, associating by way of their hypotenuses in such a way that the join between them coincides substantially with the 45° angle if the weld line between the mitred ends of the two frame members. Each of the single triangular rests (of which there are eight, clearly enough) is integral with a respective fence designed to check the relative member laterally and ensure its correct position in the horizontal plane. More exactly, of the eight fences, four are positioned transversely, engaging the rails of the frame; the remaining four engage the uprights, and lie parallel to the path along which the frame exits from the jig. Finally, each assembly comprises pairs of plates, positioned above the rests, that serve to clamp the members (uprights and rails) when being positioned, and during the subsequent welding step. Work is fed manually to welding jigs of this prior art type by an operator, standing alongside, who first positions one rail, then the two uprights, and finally, the remaining rail. The most convenient procedure is to position the two clamp assemblies farthest from the operator initially within reach, so that the first rail can be introduced without difficulty, before traversing them away through a distance that will accommodate the length of the uprights; the uprights are then positioned, and the frame completed by adding the second rail. Having proved successful as far as regards the faultless fabrication of frames for moulded plastic fixtures, these conventional jigs nonetheless are beset by certain serious drawbacks. A first drawback is that the operator experiences no small difficulty in positioning the longitudinally disposed, upright members of the frame, inasmuch as the clamp fences are fixed, and the four transverse fences therefore constitute a permanent obstacle placed across the jig. Accordingly, to negotiate these four transverse fences and insert the upright members of the frame between them, parallel with the longitudinal axis of the jig along which the welded frame is removed, the operator has to grasp the mouldings by one end, cantilever them forward, and man-handle them into place. This method of proceeding gives rise to an inherent handling difficulty, affecting the operator; being obliged to effect the positioning operation repeatly during continuous production, an individual will be subjected to increasing physical strain of an order commensurate with the length of the frame uprights being handled. A second drawback, likewise stemming from the fact that the transverse fences are fixed, is that the conventional jig can not be set up for automatic feed through a horizontal path tangential to the plane occupied by the frames, precisely because of the obstruction caused by the fences. Accordingly, the object of the invention is one of eliminating the aforementioned drawbacks. The stated object is realized by adoption of a jig as characterized in the appended claims, in which the positioning of the upright members of the frame in readiness for welding is rendered substantially problem-free. In effect, one simple manual operation only is required in offering the uprights to the first rail; the following step, namely, longitudinal traverse and positioning of the upright members, is entirely automatic. A jig embodied according to the invention provides this notable advantage, thanks to its constructional features, namely: it can be installed in line with automatic feed equipment set up to supply rails and uprights to the clamps through a longitudinal path, by virtue of the simple fact that no obstacles are encountered along the approach toward the position occupied by the first rail. The invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which: figs 1...6 illustrate the jig, viewed in plan, in the various steps of its operation; fig 7 illustrates one of the clamp assemblies of the fig, seen in perspective, with certain parts omitted better to reveal others; fig 8 shows the console of a microprocessor device by which the jig is controlled. With reference to the above drawings, a jig embodied according to the invention substantially comprises a bed 10, and two essentially longitudinal carriages TVF and TVM disposed parallel one with the other, which are mounted on the bed 10 and in their turn support four clamp assemblies, arranged in sets of two: TA-TB and TC-TD, respectively. Two of the four clamp assemblies TA and TD occupy a fixed position on their carriage, TVF and TVM respectively, whereas the remaining two TB and TC are capable of movement along horizontal longitudinal tracks 11 afforded by the top of the same respective carriages. The first carriage TVF is fixed, anchored rigidly to the fixed bed 10 beneath, whilst the second carriage TVM can be traversed along a pair of transversely disposed ways 12 afforded by the bed 10 beneath, displaced parallel with its own axis, to the end of distancing it from or drawing it toward the first carriage TVF. The four clamp assemblies TA, TB, TC and TD, which are located to coincide with the four corners of the frame, each comprise a pair of horizontal triangular rests 3A-4A, 3B-4B, 3C-4C and 3D-4D that serve to support the members of the frame; the two rests of each pair are matched together along their longest angled side, in such a way that this same side lies parallel with the mitre line along which the frame members 1, 2, 3 and 4 will ultimately be welded. Each triangular rest 3A, 4A, 3B, 4B, 3C, 4C, 3D and 4D is provided with a relative upwardly-projecting fence 2SA, 1SA, 2SB, 1SB, 2SC, 1SC, 2SD and 1SD, that serves to check the side of the relative frame member 1, 4 (rails) 2 and 3 (uprights) and to ensure its alignment in the transverse dimension (axis 'y') and in the longitudinal (axis 'x'), respectively. Each clamp assembly TA, TB, TC and TD also comprises a pair of plates 1A-2A, 1B-2B, 1C-2C and 1D-2D that is located above the relative pair of rests 3A-4A, 3B-4B, 3C-4C and 3D-4D and serves to clamp the ends of the two relative frame members against them until the positioning and welding steps are completed. These plates are supported by vertical posts 20, which also support the means 21 by which the clamp plates are actuated. It will be observed that the fences denoted 1SA, 1SB 1SC and 1SD (see fig 7), all lie parallel with the horizontal path followed by the frames when exiting from the jig, and are rigidly associated with the respective rests 4A, 4B, 4C and 4D, as well as with the posts 20 supporting the clamp plates 2A, 2B, 2C and 2D; these four fence-and-rest components can be shifted in relation to the remainder of the clamp assembly by suitable first actuator means 40, which distance them from the frame, moving at right angles to the longitudinal axis 'x', in such a way as to free it once the welding step has been accomplished. By contrast, the fences denoted 2SA, 2SB, 2SC and 3SD, which are disposed parallel with axis 'y′ hence transversely to the horizontal exit path followed by the frames, are capable of movement in relation to the relative rests 3A, 3B, 3C and 3D which, in this instance, are rigidly associated with the respective clamp assembly TA, TB, TC and TD. These fences are therefore capable of movement relative to the clamp assembly, and are operated by actuator means 30 that shift them between a first limit position, in which the rails 1 and 4 are checked, and a second limit position in which the rails 1 and 4 are left free to move and the fences themselves remain clear of the transverse dimension of the frame; accordingly, further frame members (rails and uprights) can be fed into the jig, tangentially to the plane occupied by the frame, without encountering any obstruction along their path. R1A and R1D denote a pair of transport elements, located beneath the uprights 2 and 3 of the frame and between the two clamp assemblies at either side TA-TB and TC-TD, which are capable of vertical movement between a lowered, at-rest limit position, and a raised, operative position in which contact occurs with the upright members of the frame by simple rolling friction; more exactly, such contact occurs with the uprights 2 and 3 both during the step in which these are offered to the first rail 1 and positioned, and during the successive step in which, clamped between the plates 2B and 2C and the rests 4B and 4C beneath, they are carried forward by traversing the relative assemblies TB and TC along the tracks 11 through a prescribed distance that reflects the longitudinal dimension of the frame. The step in which the frame members are welded together is a hot process involving the application of pressure to the clamp assemblies; experience has shown that a bead is left on the frame, coincident with the mitre line of the weldment, produced as a result of the plastic material melting and filling the gaps between the paired rests and clamp plates. On the underside in particular, material penetrates between the triangular rests and solidifies, causing an obstruction when the moment comes to raise the welded frame and remove it; accordingly, the jig disclosed is provided with centralizers 60 (fig 6) that operate within a horizontal plane on the rear corners of the frame, considered in relation to the direction of its removal from the jig. More exactly, the centralizers 60 move through paths that converge, and are angled substantially at 45° in relation to axis 'y'; the paths described by the centralizers 60 do not coincide with the mitre line however, but will be marginally advanced in relation thereto in order to ensure that the bead formed on each weldment separates from the corresponding pair of rests 3A-4A, 3B-4B, 3C-4C, and 3D-4D. The jig thus described operates a regular cycle of steps, as illustrated in figs 1...6, which may be summarized as follows: ('far' and 'near' are referred to operator) A - at the beginning of the cycle, the jig appears as in fig 1, thus: clamp plates in the raised position; longitudinal rests 4A, 4B, 4C and 4D and relative fences 1SA, 1SB, 1SC and 1SD spread apart at maximum distance transversely to axis 'x'; near transverse fences 2SA and 2SD spread at maximum distance apart (second limit position); far transverse fences 2SB and 2SC drawn together at minimum distance apart (first limit position), the relative clamp assemblies TB and TC lying within arm's reach of the operator to enable positioning of the first rail 1. B - With the first rail 1 in position (fig 2), the operator depresses button P1 at the console 70 to raise a first pair of locators PB and PC; the first actuator means 40 are operated to draw together the far longitudinal rests 4B and 4C and their fences 1SB and 1SC; the transport elements R1A and RID are raised; the operator introduces the two upright frame members 2 and 3, running them forward against the relative locators PB and PC. C - The operator depresses button P2 at the console, causing the far clamp plates 1B, 2B, 1C and 2C to descend toward the relative rests 3B, 4B, 3C and 4C, gripping the rail 1 and the two uprights 2 and 3, now mitred together, between them (fig 3); the far clamp assemblies TB and TC are traversed longitudinally along axis 'x' away from the near assemblies TA and TD through a prescribed distance (entered previously) marginally greater than the length of the uprights 2 and 3, whereupon the clamp plates are raised to release all three members 1, 2 and 3; the transport elements R1A and R1D retract, and two further locators PA and PD are raised; the near longitudinal rests 4A and 4D and their fences 1SA and 1SD are drawn together; the operator positions the second rail 4, offering it to the locators PA and PD. D - The operator depresses buttons P3 and P3′, with the result that the two near transverse fences 2SA and 2SD are moved in by the relative actuators 30 (fig 4); the far clamp assemblies TB and TC are positioned at a distance equal to the longitudinal dimension of the frame, whilst the moving carriage TVM shifts toward the fixed carriage TVF (axis 'y'), shortening the transverse distance between the respective pairs of assemblies TC-TD and TA-TB to match the length of the rails 2 and 3; all the clamp plates descend, locking the entire frame in position. E - The four corners of the frame are hot welded, in accordance with prior art methods (fig 5). F - With the weld effected, the clamp plates are raised, and the longitudinal rests 4A, 4B, 4C and 4D drawn apart together with their fences 1SA, 1SB, 1SC and 1SD; the far transverse fences 2SB and 2SC retract, and a number of movements occur simultaneously: the far clamp assemblies TB and TC are moved further along axis 'x', parallel with one another, and positioned at a distance from the near clamps TA and TD that is greater than the length of the frame uprights; the moving carriage TVM is traversed away from the fixed carriage TVF, and positioned at a distance greater than the length of the rails; the centralizers 60 are operated. This final set of coordinated movements ensures, on the one hand, that the welded frame separates from the longitudinal fences 1SA, 1SB, 1SC and 1SD, and on the other, that the beads of plastic material separate from the four pairs of triangular rests by which the frame is supported. Only in these conditions, and with the two near fences 2SA and 2SD spread apart at their maximum distance either side of axis 'x', does it become possible to remove the welded frame from the jig, given that there is no further obstacle to prevent its being lifted and traversed away from the clamps; accordingly, cylinders CN will be activated at this juncture to raise a pair of belt loops NT1 and NT2 for the very purpose. With the belts raised, their drive motors MNT1 and MNT2 will be set in motion, and the frame conveyed away from the jig and onto a roller table. This same movement of the frame away from the jig will excite transducers that trigger a general reset of the various components in readiness for the next cycle. In a preferred embodiment of the jig, use will be made of a micropressor 99 by which all the movements of the different drive systems and actuators can be controlled according to program cycles entered using a set of keys 81. Such microprocessor control is of particular importance both in controlling operation of the first actuator means 40 following the welding step, to separate the relative triangular rests 4A, 4B, 4C and 4D from the beads of plastic left by the weld, and in coordinating the operation of second actuator means 98 (by which the moving carriage TVM is traversed, in particular during step F), of third actuator means 91 (by which the centralizers 60 are operated), and of the actuator means 90 by which the far clamp assemblies TB and TC are distanced from the near clamps TA and TD; only with these movements faultlessly coordinated can it be ensured that the longitudinal fences 1SA, 1SB, 1SC and 1SD separate completely from the frame, and by the same token, that with movement of the post-welding beads neither impeded nor creating any impediment, the subsequent lifting movement that precedes ultimate removal of the frame will not be obstructed. It will be evident from the foregoing that the jig disclosed is eminently suited to further automation, for example, the application of an automatic feeder; adopting the conventional positioning sequence when assembling frames, in fact, rails and uprights fed automatically to the clamp assemblies will encounter no obstacles in their path.

Claims: A jig for welding mitred joints between the members of moulded plastic window and door frames, of the type comprising four clamp assemblies (TA, TB, TC, TD) that occupy positions corresponding to the four corners of the frame and operate in pairs, of which a first pair (TB-TC), located farther forward along the horizontal exit path followed by the welded frame than a second pair (TA-TD), can be traversed forward and away from the second pair by actuator means (90) so as to facilitate the initial step, effected by an operator stationed near the clamps, of positioning the first rail (1) of the frame; each clamp assembly (TA, TB, TC, TD) comprising a pair of horizontal triangular rests (3A-4A, 3B-4B, 3C-4C, 3D-4D) that serve to support the members of the frame, the matched sides of which are paired together along a line parallel with the mitre line along which the frame members are ultimately welded; each of the single triangular rests (3A, 4A, 3B, 4B, 3C, 4C, 3D, 4D) associating with a relative upwardly-projecting fence (2SA, 1SA, 2SB, 1SB, 2SC, 1SC, 2SD, 1SD) that serves to check the side of a relative frame member and to ensure its alignment, transversely in the case of a rail (1, 4), parallel in the case of an upright (2, 3), in relation to the horizontal exit path followed by the welded frame; each clamp assembly (TA, TB, TC, TD) further comprising a pair of plates (1A-2A, 1B-2B, 1C-2C, 1D-2D), located above the corresponding pair of triangular rests (3A-4A, 3B-4B, 3C-4C, 3D-4D) and serving to hold the frame members fast during the positioning and welding steps, characterized in that the fences (2SA, 2SB, 2SC, 2SD) disposed transversely to the horizontal exit path followed by the welded frames are embodied independently of the corresponding triangular rests (3A, 3B, 3C, 3D) and capable of movement in relation thereto through the agency of corresponding actuator means (30) by which they are shifted between a first limit position, in which the rails (1, 4) are checked, and a second limit position in which the rails are free to move and the fences themselves remain completely clear of the transverse dimension of the frame. A jig as in claim 1, comprising at least one pair of transport elements (R1A, R1D), located beneath the uprights (2, 3) of the frame and between the two clamp assemblies on each side (TA-TB, TC-TD), which are capable of vertical movement between a lowered, at-rest limit position, and a raised operative limit position in which contact occurs with the upright members (2, 3) by simple rolling friction, both during the step in which the uprights are offered to the first rail (1), and during the successive step in which the uprights are clamped between the plates (2B, 2C) and the rests (4B, 4C) and carried forward by traversing the first pair of clamp assemblies (TB-TC) through a prescribed distance corresponding to the longitudinal dimension of the frame. A jig as in claim 1, comprising: first actuator means (40), serving to spread apart and draw together the integrally-embodied fences (1SA, 1SB, 1SC, 1SD) and rests (4A, 4B, 4C, 4D) by which the uprights (2, 3) are checked and supported; second actuator means (98), by which a moving carriage (TVM), disposed parallel with the exit path followed by the frames and supporting two clamp assemblies (TC, TD), one of which forming part of the first pair (TB-TC) and the other forming part of the second pair (TA-TD), is traversed in a direction at right angles to the exit path; third actuator means (91), serving to operate at least two centralizers (60) that are carried by the second pair of clamp assemblies (TA-TD), shaped to match the corners of the welded frame, and impinge thereon through respective paths that converge and are angled substantially at 45° in relation to the exit path followed by the frames; a microprocessor (99) serving to control the cycle of movements implemented by the different actuator means, programmed by way of a set of keys (81) in such a way as to occasion operation of the first actuator means (40) and ensure initial separation of the relative triangular rests (4A, 4B, 4C, 4D) from the bead of plastic material that forms beneath them during the welding step, and thereafter, to occasion simultaneous operation of the second actuator means (98) and the third actuator means (91), together with the actuator means (90) by which the first pair of clamp asssemblies (TB-TC) is distanced from the second pair (TA-TD), in such a way that the fences (2SA, 2SB, 2SC, 2SD) engaging the upright members (2, 3) are drawn completely clear of the transverse dimension of the frame, and the bead formed on the underside of the frame at each mitred join lies in space no longer occupied by the corresponding rests (3A-4A, 3B-4B, 3C-4C, 3D-4D), thereby enabling a pair of belt loops (NT1, NT2) positioned below the level of the clamp assemblies to rise, lift the welded frame, and remove it from the jig unimpeded. A jig as in claim 3, wherein the converging paths described by the centralizers (60) do not coincide with the weld mitre lines of the relative corners of the frame, but are marginally advanced in relation thereto in order to ensure that the bead formed on each weldment separates from the corresponding pair of triangular rests.

Inventors: PASQUINI, LUCIANO
Applicants: UNIVAL S.R.L.
Application year: 1988
Main classification: B29C65
IPC codes: B25B5, B29C65