EP1758728A1

EP1758728A1 - An ultrasonic welding device

Info

Publication number: EP1758728A1
Application number: EP05740423A
Authority: EP
Inventors: Fulvio Boldrini; Roberto Ghiotti; Stefano Cavallari
Original assignee: Azionaria Costruzioni Macchine Automatiche ACMA SpA
Current assignee: Azionaria Costruzioni Macchine Automatiche ACMA SpA
Priority date: 2004-05-18
Filing date: 2005-05-17
Publication date: 2007-03-07
Also published as: WO2005113218A1; ITBO20040311A1

Abstract

An ultrasonic welding device (1) comprises a housing (2) fastened rigidly to an automatic machine, an ultrasonic welder (4) mounted to the housing (2), and a set of coil springs (5) installed between the housing (2) and the ultrasonic welder (4), by which the position of a welding tip (11) is adjusted automatically in relation to the surface being welded, so that the tip (11) can be maintained firmly in contact with the surface throughout the welding operation.

Description

An ultrasonic welding device

Technical Field The present invention relates to an ultrasonic welding device . Preferably, though not exclusively, the present invention is applicable to automatic machines used in the manufacture of containers made from specially treated paper material suitable for preserving edible products .

Background Art A container of the type in question is fashioned from a flat diecut blank bent initially along crease lines to form a tubular body. The tubular body is sealed along one longitudinal edge, whereupon the two opposite open ends are folded in and sealed to form the top and bottom end faces of the container. The top of the container will usually incorporate a plastic neck, secured by means of a sealing or welding operation, and moulded with a threaded spout to which a screw cap can be attached. The sealing or welding operations are performed typically by means of a conventional heat-seal tool with electric elements, or using ultrasonic energy. Ultrasonic welding is widely considered preferable to traditional heat sealing since it offers greater precision, safety and hygiene, and has none of the drawbacks deriving from thermal inertia and from the heat generated around the areas being sealed. An ultrasonic welder normally comprises a pulse generator and, wired to the generator, a transducer by which a pulsed electrical signal can be utilized to activate a vibrating element known commonly as a sonotrode . The vibration of the sonotrode, when offered to two overlapping edges of the material being welded, generates an ultrasound output that will cause these same edges to fuse and bond together. Conventionally, ultrasonic welding devices are mounted to motion-inducing arms and manoeuvrable thus toward and away from the overlapping edges being welded, which will be suitably supported. In effect, the overlapping edges to be joined are pinched between the sonotrode and a respective anvil . To obtain a good quality weld, the sonotrode must remain faultlessly in contact with the joined edges throughout the entire process. During the course of the welding step, however, as the two overlapping edges fuse gradually together and their combined thickness tends consequently to vary, it can happen that the sonotrode loses contact partially or totally with the material and the weld will appear irregular or remain complete along the full length of the joined edges. The drawback in question is accentuated in cases where ultrasonic welders of the type in question are utilized in automatic machines characterized by high operating speeds. The object of the present invention is to provide an ultrasonic welding device free of the drawbacks mentioned above.

Disclosure of the Invention The stated object is realized, according to the present invention, in an ultrasonic welding device of which the features are as recited in claim 1. The invention will now be described in detail, by way of example, with the aid of the accompanying drawings, in which:

-figure 1 illustrates an ultrasonic welding device according to the present invention, viewed in section;

-figure 2 is an exploded view of the welding device illustrated in figure 1;

-figure 3 shows the welding device of figure 1 in smaller scale, viewed partly in section with certain parts omitted and illustrated in use on a machine for manufacturing food containers . Referring to the drawings, 1 denotes an ultrasonic welding device, in its entirety, embodied according to the present invention. The device 1 will be incorporated preferably into a machine for manufacturing containers A (figure 3) in which edible products are packaged, and in particular liquid products such as fruit juice, milk, mineral water and the like. A container of the type in question comprises a tubular body appearing square in section, relative to a predominating longitudinal axis, with four walls arranged in two mutually opposed and parallel pairs. The tubular body is enclosed at one end, providing the bottom or base, whilst the opposite end presents a frustopyramidal portion terminating in a neck, with a mouth that can be closed by means of a screw cap. As a result of the folding operation by which the frustopyramidal portion is formed, the four pyramidal corner edges present four respective triangular fins occupying relative mutually orthogonal planes aligned on the longitudinal axis. These same fins are then flattened and welded against two opposite side walls of the frustopyramidal portion. The machine is equipped with at least one heat-seal or welding assembly as described and illustrated in Italian patent application n° BO2004A 000312 entitled "A machine for forming containers" , filed on the same date as the present application and in the name of the same applicant, to which reference may be made for a full description; the assembly in question is equipped with at least one welding device 1 according to the present invention, and with motion-inducing means by which to move the device 1 toward or away from a mandrel type support S insertable into a blank of tubular shape presenting two longitudinal edges L destined to be bonded together. It will be appreciated furthermore, still referring to the Italian patent application aforementioned, that the welding device 1 according to the present invention can also be utilized in the successive steps of forming the container, namely closing the top end and applying the neck, securing the fins to the side walls of the frustopyramidal portion, and finally closing the bottom end. The ultrasonic welding device 1 comprises a support or housing 2 fastenable to the automatic machine, and is equipped with an anchoring component 3 by means of which to mount an ultrasonic welder 4 internally of the housing 2. Interposed between the welder 4 and the housing 2 are spring means 5 such as will adapt the position of the welder 4 automatically to the surface being welded, which in the example of figure 3 is presented by the two longitudinal edges L aforementioned, and thus ensure that the welder 4 remains in contact with the surface throughout the entire welding step. More exactly, and in conventional manner, the ultrasonic welder 4 comprises at least one vibrating element 6 referred to commonly as a sonotrode, of which the tip is positionable in contact with the edges L to be joined. The sonotrode 6 is associated rigidly with a first end 7a of a transducer 7 wired to an ultrasonic signal generator, indicated in figure 1 by a block 8. The transducer 7, preferably a piezoelectric type, receives electrical pulses from the generator 8 and converts them into vibrations which are transmitted, possibly through an amplifier, to the sonotrode 6. In the example illustrated, the external outline of the transducer 7 is cylindrical in shape and extends predominantly along a longitudinal axis X coinciding substantially with the axis of the sonotrode 6. A second end 7b of the transducer 7 presents an electrical connection 9 providing the interface with the generator 8, also an inlet port 10a and an outlet port 10b for a cooling duct, preferably conveying air and routed internally through the transducer 7. The sonotrode 6 is usually wedge-like in appearance and presents a first portion 6a of appreciable mass, connected to the corresponding end 7a of the transducer 7, also a second portion 6b, slender and lighter by comparison, integral with the first portion and tapering away from the transducer 7. The free end of the second portion 6b presents a welding surface 11 by which the joined edges L of the container A are engaged in contact and subjected to the vibratory action that causes them to fuse and bond together. The shape of the welding surface 11 is not uniquely definable, but selected on a case-by-case basis, for example depending on the geometry of the weld line and the positioning of the line on the container A. The housing 2 appears as a hollow body 12 furnished with an opening 13 (figure 2) by which the ultrasonic welder 4 is accommodated, slidably, positioned with the sonotrode 6 projecting from the body 12. The welder 4 is caused to shift internally of the opening 13 through the agency of the spring means 7 interposed between the transducer 7 and the hollow body 12. In a preferred embodiment, the opening 13 is a clearance hole, so that the rear end of the welder 4, which coincides with the second end 7b of the transducer 7, is also able to project from the hollow body 12, thereby affording ease of access to the electrical connection 9 and the ports 10a and 10b of the air cooling circuit. More exactly, and as illustrated in figure 2, the hollow body 12 appears prismatic in shape, presenting a substantially square section, viewed transversely to the longitudinal axis X. The opening 13 likewise is of substantially square section and able to accommodate a similarly square auxiliary body or slide 14 presenting dimensions matched substantially to those of the opening 13 and consequently slidable therein along a direction coinciding with the longitudinal axis X. The slide 14 presents a clearance opening 15 of circular section, in which the transducer 7 is inserted and fixed. The transducer 7 in its turn presents an annular boss 16 affording two shoulders 17 and 18 disposed transversely to the longitudinal axis X. A first shoulder 17 is directed toward the second end 7b of the transducer 7, and a second shoulder 18 toward the sonotrode 6. The first shoulder 17 locates against a respective circular stop 19 created internally of the clearance opening 15 in the slide 14. A cover plate 20 fixed to the slide 14 by means of screws 20a is positioned tight against the second shoulder 18, clamping the transducer 7 internally of the selfsame slide 14. The plate 20 affords a circular hole 21 serving to admit the first end 7a of the transducer 7 carrying the sonotrode 6. As discernible from figure 1, the slide 14 covers the longitudinal dimension of the transducer 7 and the longitudinal dimension of the hollow body 12 only in part, so that the spring means 5 can also be housed internally of the selfsame hollow body 12. The spring means 5 comprise one or more tension elements 22, each interposed between the housing 2 and the slide 14, with which the welder 4 is rigidly associated. To advantage, the tension elements 22 are embodied as coil springs centred on respective axes parallel to the longitudinal axis X, albeit other elements with comparable elastic properties might be employed, such as blocks of elastomer material, or pneumatic cylinders designed to exploit the compressibility of air or some other gas . Should it be necessary to offset the energy stored by the tension elements 22, at least in part, these can be complemented by suitable cushioning means (not illustrated) interposed between the housing 2 and the slide 14, such as will provide a suitably dimensioned mass-spring-reaction system. In the preferred solution illustrated, the tension elements 22 are interposed between the hollow body 12 and respective abutment surfaces 23 afforded by the four corners of the slide 14. More particularly, the slide 14 presents an area 24 at the rear, directed toward the second end 7b of the transducer 7, of which the four corners 25 are shaped with four corresponding recesses 26 each delimiting an abutment surface 23 disposed transversely to the longitudinal axis X. Each of the four coil springs 22 is installed with a first end 22a seated against one of the abutment surfaces 23 of the slide 14 and a second end 22b seated against the housing 2. In addition, each of the four springs 22 is paired coaxially with a respective guide pin 27 mounted to the slide 14. The single pin 27 is inserted into a hole 28 afforded by the relative abutment surface 23, anchored rigidly thus and extending perpendicular to the selfsame surface 23, parallel to the longitudinal axis X of the ultrasonic welder 4 (figure 2) . The second ends 22b of the springs 22 are seated against a bearing plate 29, which in turn is offered to a bearing surface 30 presented by the rear wall of the housing 2. The bearing plate 29 presents a central opening 31 affording a passage to the rear end of the welder 4, and four holes 32 at the four respective corners affording respective passages to the aforementioned guide pins 27. Whenever the welder 4 and the slide 14 are caused to shift relative to the hollow body 12, the bearing plate 29 stays rigidly associated with the housing 2 whilst the welder 4 slides through the opening 31 and the pins 27 slide in the holes 32 of the plate 29. It will be seen also that the unattached ends of the pins 27 are freely insertable in further holes 33 afforded by the rear end of the hollow body 12 and aligned coaxially with the holes 32 of the plate 29 (figure 1) . Also presented by the hollow body 12, at the end affording the opening 13, are two mutually opposed lateral appendages 34 each provided with a pair of holes 35 such as will accept respective screws 36 serving to clamp the housing 2 to a plate 37 forming part of the aforementioned anchoring component 3 , by means of which the welding device 1 is mounted to a motion-inducing arm of the automatic machine. The mounting plate 37, illustrated to advantage in figure 2, is equipped with fastener elements 38 such as screws or bolts by means of which it can be anchored to the aforementioned motion-inducing arm, and presents a slot 39 freely accommodating the first end 7a of the transducer 7. The plate 37 in question is positioned between the cover plate 20 and the first portion 6a of the sonotrode 6. The slot 39 extends full width to one edge 40 of the plate 37 in such a way as will allow the device 1 to be separated from the selfsame plate 37 without removing the sonotrode 6, given that the dimensions presented by the first portion 6a of the sonotrode 6 would otherwise prevent the device 1 from sliding out along the direction of the axis X. In operation, the device 1 is positioned in close proximity to the mandrel supporting the item to be welded, and the welding surface 11 then pressed against the material, causing the springs 22 to deform and the sonotrode 6 to retract toward the housing 2. The device 1 therefore operates with the springs 22 partly compressed, in such a way that any relative movement between the sonotrode and the surface being welded will be taken up by the elastic deformation of the selfsame springs 22. The problems encountered with the prior art are overcome, according to the present invention, and the stated objects duly realized. In effect, a device embodied in accordance with the present invention will produce ultrasonic welds of high quality and with high levels of repeatability. By positioning spring means between the welder and the housing, in particular, it becomes possible to reduce the suspended mass and guarantee uniform and constant contact between the sonotrode and the entire surface to be welded. With the device disclosed, moreover, suspension elements can be eliminated from the supports on which items for welding are positioned, and from the arms by which motion is induced in the welders, thereby reducing the cost of the welding assemblies and of a machine in which the assemblies are installed. Finally, thanks to the novel manner of positioning the spring means to which the invention relates, the structure of the relative welding assemblies and of the machine to which they are mounted is rendered simpler, as also is their maintenance, given that each device can be fitted to and removed from the machine without difficulty.

Claims

1) in ultrasonic welding device, comprising: a supporting element or housing (2) fastenable to an automatic machine, and an ultrasonic welder (4) mounted to the housing (2) , characterized in that it further comprises spring means (5) interposed between the housing (2) and the ultrasonic welder (4) , such as will adapt the position of the welder (4) automatically to the surface being welded and ensure that the welder (4) remains in contact with the selfsame surface.

2) A device as in claim 1, of which the ultrasonic welder (4) comprises at least one sonotrode (6) , and at least one transducer (7) wired to an ultrasonic signal generator (8) and associated rigidly with the sonotrode (6) , wherein the spring means (5) are interposed between the transducer (7) and the housing (2) .

3) A device as in claim 1 or claim 2, wherein the housing (2) appears as a hollow body (12) furnished with an opening (13) through which the ultrasonic welder (4) is slidably inserted and allowed freedom of movement when displaced by an elastic deformation of the spring means (5) .

4) A device as in claims 1 to 3 , wherein the spring means (5) comprise at least one tension element (22) . 5) A device as in claims 1 to 3, wherein the spring means (5) comprise a plurality of tension elements (22) .

6) A device as in claim 4 or 5, wherein each tension element (22) consists in a spring.

7) A device as in claim 6, wherein the spring (22) is a coil spring.

8) A device as in claim 4 or 5, wherein each tension element (22) consists in a block of elastomer material .

9) A device as in claim 4 or 5, wherein each tension element (22) is pneumatic in operation.

10) A device as in preceding claims, further comprising cushioning means interposed between the housing (2) and the ultrasonic welder (4) and serving to dissipate part of the energy stored in the spring means (5) .

11) A device as in claim 3, wherein the opening (13) of the hollow body (12) is a clearance opening, and the ultrasonic welder (4) slidably inserted with a rear end (7b) projecting from the selfsame hollow body (12) . 12) A device as in claims 3 to 11, further comprising an auxiliary body or slide (14) rigidly associated with the transducer (7) and presenting abutment surfaces (23) against which to seat the spring means (5) interposed between the housing (2) and the ultrasonic welder (4) .

13) A device as in claim 12, where dependent on claim 5, wherein each of the tension elements (22) presents a first end (22a) seated against one of the abutment surfaces (23) of the slide (14) and a second end (22b) seated against the housing (2) .

14) A device as in claim 13, wherein each tension element (22) consists in a coil spring extending parallel to a longitudinal axis (X) of the ultrasonic welder (4) .

15) A device as in claim 14, wherein the slide (14) further comprises a plurality of guide pins (27) fixed to the selfsame slide (14) , each extending axially through the hollow centre of a respective coil spring (22) .

16) A device as in claim 15, wherein a second end (22b) of each coil spring (22) is seated against a bearing plate (29) mounted in turn against a bearing surface (30) of the housing (2) . 17) A device as in claim 16, wherein the bearing plate (29) presents a single opening (31) affording a passage to a rear portion of the welder (4) , and a plurality of holes (32) each affording a passage to a respective guide pin (27) .

18) A welding unit for manufacturing containers, comprising at least one welding device (1) as in claims 1 to 17, and means by which to induce motion in the device (1) toward or away from a support carrying a blank to be welded.

19) An automatic machine for manufacturing containers, comprising at least one welding unit as in claim 18.