EP1381479A2

EP1381479A2 - A method for making joint between sheet formed members

Info

Publication number: EP1381479A2
Application number: EP02727331A
Authority: EP
Inventors: Olivier Dubugnon
Original assignee: Bollhoff Attexor SA
Current assignee: Bollhoff Attexor SA
Priority date: 2001-02-26
Filing date: 2002-02-26
Publication date: 2004-01-21
Also published as: SE0100667D0; WO2002068139A8; WO2002068139A3; WO2002068139A1

Abstract

A method for making joints between overlaying sheet formed members (12, 13), at which an essentially coaxial arrangement of tools (10, 11) are caused to co-operate by means of their relative movement toward each other, and at which said overlaying sheet formed members (12, 13) before the operation are placed between the tools (10, 11). The complete operation on said sheet formed members to create the joint is achieved by means of one single stroke of one of the tools (10, 11) against the other and that the energy needed for making the joint is provided in the form of kinetic energy of an accelerated mass in contact with one of said tools. In one embodiment one of the tools (10, 11) is accelerated together with said mass against said other tool. In another embodiment said tools (10, 11) are first positioned on either side of said members in contact or close to contact with said members before the operation on the members is carried out and said accelerated mass is brought to impact on one of said tools or the associated tool-holder.

Description

A METHOD FOR MAKING JOINTS BETWEEN SHEET FORMED MEMBERS
AND AN APPARATUS FOR CARRYING OUT SAID METHOD.

Technical field
This invention relates to a method for joining together two or several overlaying sheet formed members and an apparatus for carrying out said method. The apparatuses or machines could be of stationary or hand-held type and the power source could e. g. be hydraulic or pneumatic.

Background art
Methods and apparatuses for joining sheet formed members together, thereby producing leakproof or non-leakproof joints, are previously known.

A joint of this type could be made by means of drawing said sheet formed members into a cup-shaped or protruding portion having a cylindrical or slightly conical side wall and a bottom wall and subsequently compressing said bottom wall creating a lateral extrusion of the same thereby forming a laterally enlarged shape which mechanically interlocks the sheet formed members.

Typically the machines used for making the joints provide very high forces especially at the end of the joining procedure during the lateral extrusion of the material when the workpiece is squeezed between a punch and a co-operating anvil. The counter forces are taken up by a C-frame which could have considerable dimensions due to the fact that the pressure between the two cooperating tools could be in the range of several tons.

The methods and tools according to the prior art make use of the well known one or two step principles. In the single step method the whole procedure for making the joint takes place during one single relative movement between a punch and a co-operating die and anvil. In a two step method the final compression of the material takes place during a second squeezing operation outside the die cavity.

One problem with prior art devices is that the deformation of the workpiece takes place under"static"conditions using very high forces. This leads to big and heavy C-frames. Consequently the use of these operating principles for e. g. hand held machines will have its limitations. Also in stationary machines it is of interest to reduce the size and weight of the C-frames.

A percussion method is also known from the prior art. According to this method an oscillating hammer is making a series of impacts on a mandrel connected to the tool. The joint is resulting from a large number of impacts. This method is very noisy due to the repeated elastic impacts of the metal hammer on the metal mandrel.

It is of course of interest to reduce the time for making a joint of the described type. In this respect the all known methods have their limitations.

Brief description of the invention
One object of the present invention is to provide a method for making joints between sheet formed members which is much faster than prior art methods. To make a joint with the inventive method typically takes only one tenth of the time needed with prior art methods.

A further object of the present invention is to provide a method which is generating much less noise than the known percussive method.

Another object of the invention is to provide a method and an apparatus which can make use of a less heavy C-frame than prior art methods.

A still further object is to provide a machine with very efficient damping of vibrations from the working process.

A still further object is to provide a machine which does not need a pressure booster for the operation. This means of course a considerable cost saving.

These objects are achieved by means of a method and an apparatus having the characteristics of the appended claims.

Brief description of the figures
Other objects, uses and advantages of this invention will be apparent from the reading of this description which proceeds with reference to the accompanying drawings forming part thereof and wherein:
Figure 1 shows partly in section a first embodiment of a machine according to the invention in an initial position.

Figure 2 shows the machine according to figure 1 with the tools positioned for the active stroke.

Figure 3 shows the machine according to figure 1 after the active stroke.

Figure 4 shows partly in section a second embodiment of a machine according to the invention in an initial position.

Figure 5 shows the machine according to figure 4 after the active stroke.

Figure 6 shows partly in section a third embodiment of a machine according to the invention in an initial position.

Figure 7 shows the machine according to figure 6 with the tools positioned for the active stroke.

Figure 8 shows the machine according to figure 6 during and after the active stroke.

Figure 9 shows schematically a simple hydraulic drive system for the machine according to the invention.

Figure 10 shows schematically a simple pneumatic drive system for the machine according to the invention.

Detailed description of the invention
Figure 1 shows one example of a machine according to the invention generally designated 100. The main parts are a C-frame 1 and an activation unit 2 mounted on said C-frame comprising a cylinder-piston assembly 3,4,5,6. The cylinder-piston assembly includes a pneumatic or hydraulic cylinder 3, a piston impactor 4 a second piston 5 and a piston rod 6 operated by said second piston 5. The lower end of the piston rod constitutes a first tool holder.
The C-frame has two opposing, generally parallel, legs 7,8 oriented horizontally in figure 1. Said cylinder-piston assembly 3,4,5,6 is in the example mounted on the upper leg 7 and a guiding part 9 for the piston rod 6 forming part of the cylinder-piston assembly reaches through a vertical hole in said leg. In this embodiment the leg 8 constitutes a second tool holder.

A co-operating set of tools 10,11 is arranged at the end of the piston rod 6 and the opposing leg 8 of the C-frame respectively. These tools could for instance comprise a punch 10 and a die 11 for carrying out an operation on a workpiece.

The punch and the die could of course also be arranged in the reverse positions.

A workpiece, in this example illustrated comprising two superimposed pieces of sheet material 12,13, have been placed on top of the die. It should be understood that more than two sheets could be joined by means of the same method and apparatus and that the material of the workpiece does not necessarily have to metallic.

The procedure is now as follows. A fluid, e. g. air or oil, is released through the outlet 14 from a chamber 15 in the cylinder 3 under the piston 5. Due to the action of a spring 16 arranged between the piston impactor 4 which is positioned at the upper part of the cylinder and the second piston 5 said piston 5 and the piston rod 6 will move downwards until contact between the punch 10, or a sidepressing element 17 arranged around the punch, and the upper sheet 12.

This position is shown in figure 2. It should be noted that no operation has yet been carried out on the workpiece. The machine has only been positioned for the active stroke. In figure 2 is also shown a second spring 18 between the piston 5 and the end portion of the cylinder. This spring could be of interest in certain embodiments.
The upper end of the cylinder piston assembly 2 is provided with an inlet 19 for a fluid e. g. air or oil. When a high pressure fluid is entering the inlet 19 the piston 4 will be accelerated against the force from the spring 16 and will hit the upper surface of the piston 5. The energy from the impact will be transferred through the piston rod 6 to the punch 10 which in co-operation with the die 11 will deform the workpiece, i. e. the two sheet formed members 12 and 13. In this way a joint could e. g. be created between the two members.

The end of the stroke could have been adjusted so that the punch is not touching the die in the absence of a workpiece between the tools. A fluid under pressure entering the chamber 15 through the inlet/outlet 14 will bring the two pistons 4,5 back to the initial positions ready for a new operating cycle.

Figure 4 shows a second embodiment of the machine according to the invention generally designated 200. The activation unit is in this case only comprising one piston 20. This piston could be brought to its starting position at the top of the cylinder 3 by means of e. g. pneumatic pressure as shown in figure 4 or by means of the force from a spring arranged in the cylinder. In the same way as described above high pressure fluid to the inlet 19 will accelerate the piston 20 downwards in the direction of the workpiece 12,13. In this case the operation on the workpiece will be carried out at the end of this single stroke, cf. figure 5. For security reasons a protection in the form of a coaxial tube could be arranged around the piston rod 6 as shown in figure 6.

This protection arrangement could be fixed as shown in figure 6 or have the form of a sliding tube e. g. activated from the activation unit 2. Such a tube could also be arranged to guide the piston rod and the associated tool against the impact point. An arrangement like the one shown in figure 6 will also considerably reduce the noise as the impact zone is completely surrounded by the tube.

The speed of the piston and thus the energy of the impact will be controlled by means of the pressure and volume of the fluid through the inlet 19. The end of the stroke could also be made adjustable e. g. by means of the position of the guiding part 9 relative to the cylinder 3.

Figure 6 shows a further embodiment of the invention. It differs from the embodiment according to figures 4 and 5 mainly in the arrangement of the Cframe. The C-frame 1 is here provided with an articulation so that the lower leg 8 can pivot around a pivot joint 21. The articulation is preferably arranged in the plane perpendicular to the axis of the motion of the piston rod 6 and in which the impact deformation of the workpiece will be created. In the initial or start position shown in figure 6 the C-frame is open in order to allow the workpiece to be positioned for the stroke. The piston 20 is kept in its starting position by means of the pressure in the chamber 15 or a spring (not shown). A protection in the form of a tube 22 is arranged around the moving tool 10. This tube 22 has in this case also the function as a positioning item for the workpiece 12,13.

A pneumatic or hydraulic cylinder-piston assembly 23 is schematically illustrated arranged between the fixed and the pivoting part of the C-frame. By feeding/releasing a working fluid to opposite sides of the piston in this assembly 23 through the in-and outlets 23'and 23"the length could be adjusted and thereby the position of the lower leg 8 of the C-frame.

Thus, by increasing the length of the cylinder-piston assembly 23 the leg 8 will be pivoted into the position shown in figure 7. This movement is for security reasons typically carried out with a relatively low force.

The pressure in the chamber 15 in front of the piston 20 is now released at the same time as the high pressure fluid is entered through the inlet 19. The piston 20 will therefore be accelerated downwards in the cylinder 3 as described above and the kinetic energy of the piston will be converted into mechanical work on the workpiece 12,13. The remaining kinetic energy will to a great extent be absorbed by the moving part 8 of the C-frame and the cylinder-piston assembly 23 and not transmitted to the rest of the machine.
A particularly advantageous damping can be achieved by designing the leg 8 so that the pivot axis will be positioned in a point of"free rotation". When an element, e. g. the part 8 of the C-frame, is exposed to the shock of an impact the result will be a combined translation-rotation movement of the element.

This means that there is a point where the resulting movement immediately after the impact is zero. The position of this point depends on the shape and mass distribution of the element. If the pivot point for the part 8 is arranged at this particular location the chock transmitted to the rest of the machine will be negligible. These design considerations will make it possible to reduce the total weight of the machine.

In this embodiment a cylinder-piston assembly 23 of pneumatic type would be advantageous.

The piston 20 will be brought back to its starting position by means of a pressurised fluid entering the inlet-outlet 14 or by means of a spring (not shown) arranged between the guiding element 9 and the piston 20.

Figure 9 shows schematically a simple hydraulic drive system for the machine according to the invention. Only the system for actuating the piston 4 is illustrated. A pump 24 is pumping oil from a reservoir 25 through a regulator 26 to an accumulator 27. A fast action valve 28 can be activated by means of a trigger 29 connecting the accumulator 27 to the inlet 19 of the cylinder 3. In the initial (rest position) the valve 28 connects the volume on top of the piston 4 through a return conduit 30 to the oil reservoir 25. The regulator is setting the pressure in the accumulator 27. This accumulator will assure that there is enough oil of the set pressure available for the stroke of the piston 4.

Figure 10 shows schematically a simple pneumatic drive system for the machine according to the invention. Inlet 31 is connected to a source of compressed air, e. g. the standard distribution network of 6 bars in the workshop. An accumulator/reservoir 32 is connected between the inlet 31 and a fast acting valve of the same type as described in figure 9.

Claims

Claims 1. A method for making joints between overlaying sheet formed members (12, 13), at which an essentially coaxial arrangement of tools (10,11) are caused to co-operate by means of their relative movement toward each other, and at which said overlaying sheet formed members (12,13) before the operation are placed between the tools (10,11), characterised in that the complete operation on said sheet formed members to create the joint is achieved by means of one single stroke of one of the tools (10,11) against the other and that the energy needed for making the joint is provided in the form of kinetic energy of an accelerated mass in contact with one of said tools.

2. A method according to claim 1, characterised in that one of the tools (10,11) is accelerated together with said mass against said other tool.

3. A method according to claim 1, characterised in that said tools (10,11) before the operation on the members is carried out are first positioned on either side of said members in contact or close to contact with said members and that said accelerated mass is brought to impact on one of said tools or the corresponding tool-holder.