Metal working – Method of mechanical manufacture – With testing or indicating
Reexamination Certificate
2000-08-15
2003-04-08
Cuda-Rosenbaum, I (Department: 3726)
Metal working
Method of mechanical manufacture
With testing or indicating
C029S407010, C029S407080, C029S559000, C029S709000, C029S798000, C029S716000, C072S453070
Reexamination Certificate
active
06543115
ABSTRACT:
The invention relates to a method as well as to an apparatus for manufacturing a punch riveted joint.
In the automotive industry, in particular, riveted joints are increasingly gaining in importance because they may form an alternative to a weld joint. For material pairings which are difficult to weld, riveted joints are a suitable alternative. By means of punch riveting, the parts to be joined are connected without pre-punching. The pre-punching of the joint parts which is necessary with conventional riveting is replaced by a corresponding cutting operation of the punch rivet.
When punch riveting using a semitubular rivet, the components to be joined are placed onto a die. Said components are fixed on the die by means of a holding-down device. The semitubular rivet cuts through the layer directed towards the semitubular rivet. Then the semitubular rivet is plastically deformed in the bottom layer or layers so as to form a closing head. The configuration of the closing head is determined substantially by the shape of a die. The material punched out of the top layer and, occasionally, out of further layers fills the hollow rivet shank of the semitubular rivet and is held captive therein. The semitubular rivet is then upset so that, on the one hand, a further formation of the closing head is effected and, on the other hand, the head of the semitubular rivet terminates substantially flush with the top layer.
From the article by L. Budde and W. Lappe “Riveting without pre-punching—punch riveting has a promising future in sheet metal working”, which appeared in the periodical “Strips Sheets Pipes” 5-1991, pages 95-100, it is known that crucially important factors for a high-quality punch riveted joint by means of a semitubular rivet are, on the one hand, trouble-free fixing of the positioned components so that the relative position of the components is not varied as a result of an after flow movement during punching and, on the other hand, joint-specific selection of a suitable punch rivet in terms of material-specific composition and its rivet geometry.
To ensure that an after flow movement during punching does not occur, it is known from WO 94/14554 for the clamping force of the holding-down device used to fix the components on the die to increase considerably towards the end of the punch riveting operation. A further object to be achieved by said refinement of the method of manufacturing a punch riveted joint is that no annular indentations or distortions arise in the region of the head of the punch rivet.
For effecting the method, WO 94/14554 proposes an apparatus which comprises a die, a holding-down device and a punch. At least two layers of components are clampable between the holding-down device and the die. The holding-down device is movable by means of a first piston/cylinder unit. A second piston/cylinder unit is provided as a drive unit for the punch. The first and the second piston/cylinder unit are operable independently of one another.
A similar refinement of an apparatus for manufacturing a punch riveted joint is known from WO 93/24258. Said apparatus also comprises a piston/cylinder unit, by means of which the required clamping force of the holding-down device may be generated. Differing clamping forces may be generated by suitable pressure control. The apparatus according to WO 93/24258 comprises a second piston/cylinder unit as a drive unit of the punch.
The mechanical properties of a punch riveted joint, in particular the strength characteristics of the punch riveted joint, are dependent upon the formation of the closing head. The strength characteristics are also influenced by the configuration of the region of the components between the head and the closing head of the punch rivet.
Against said background, the object of the present invention is to develop the known method of manufacturing a punch riveted joint in such a way as to achieve, on the one hand, material-sparing manufacture of a punch riveted joint and, on the other hand, a punch riveted joint of greater strength. A further object of the invention is to indicate an apparatus for manufacturing a punch riveted joint, which is suitable for effecting material-sparing manufacture of a punch riveted joint. High strength values of the punch riveted joint manufactured by means of the apparatus are also to be achieved by virtue of the apparatus.
The effect achieved by the method according to the invention for manufacturing a punch riveted joint is that during a punch riveting operation a clamping force exerted by the holding-down device upon the at least two layers may be varied in accordance with a preset characteristic. A variation of the clamping force exerted by the holding-down device upon the at least two layers is achieved in that the holding-down device is connectable by a coupling unit to the punch in such a way that during a punch riveting operation a coupling of the holding-down device to the punch may be varied between a substantially rigid coupling state and an uncoupled state. The effect achieved by said process management is that in the rigid coupling state the holding-down device is movable synchronously with the punch, in particular in the direction of the die. In the uncoupled state a movement of the punch may be effected while maintaining or varying the clamping force exerted by the holding-down device upon the components.
By virtue of the fact that the clamping force exerted by the holding-down device upon the components is variable on account of said clamping force being dependent upon the movement of the punch, the effect is also achieved whereby the requisite clamping force for individual portions of the punch riveting operation is always produced. The amount by which the clamping force is varied is dependent upon the coupling state. In particular, it is proposed that the coupling state is varied as a function of the punch travel or a parameter derived from the punch travel.
Depending upon material pairings as well as upon mechanical properties of the materials of the layers, it may be advantageous for the layers to be pressed initially with a reduced clamping force against the die. Later, the layers may be pressed with a—compared to the reduced clamping force—varying clamping force against the die. In particular, the clamping force should be increased during the upsetting operation. This has the advantage that, in the event of formation of a bead at least partially surrounding the head of the tubular rivet, said bead is upset by the holding-down device in such a way that the head of the tubular rivet terminates flush with the layer. The clamping force may in said case also be much higher than the customary clamping force.
The variation of the coupling state as a function of the punch travel may be effected continuously or discontinuously. Continuous variation of the coupling state is preferred because it does not lead to any abrupt alteration of the clamping force. Alternatively, given discontinuous variation of the coupling state, the jumps in the clamping force may be selected in such a way that no pronounced abrupt alteration of the process parameters occurs.
By virtue of a rigid coupling of the holding-down device to the punch, the holding-down device executes the same movement as the punch. The holding-down device exerts substantially the same force as the punch. In accordance with a preset clamping force characteristic, the holding-down device may be uncoupled from the punch through control of the coupling unit. The further exertion of clamping force by the holding-down device is controlled by means of the coupling unit. When after a preset punch travel the holding-down device is to exert a higher force upon the layers, the holding-down device may be re-coupled to the punch by the coupling unit.
In particular, it is proposed that the holding-down device is moved with the punch relative to the layers to be joined in such a way that the holding-down device presses the layers with a preset clamping force against the die. The holding-device is uncoupled from the punch and the punch
Hermann Dirk
Mauer Dieter
Möser Joachim
Opper Reinhold
Cuda-Rosenbaum I
Hong John C.
Murphy Edward D.
Newfrey LLC
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