Metal working – Means to assemble or disassemble – With control means energized in response to activator...
Reexamination Certificate
1999-01-13
2001-03-13
Hughes, S. Thomas (Department: 3726)
Metal working
Means to assemble or disassemble
With control means energized in response to activator...
C029S407010, C029S283500, C029S254000, C029S275000, C029S276000, C029S521000
Reexamination Certificate
active
06199271
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention concerns an apparatus and a method for mechanically joining metal sheets, profiles and/or multi-sheet joints lying on top of each other, wherein joining tools are moved by power means toward the parts to be joined and a joint is made between the parts to be joined by the force effect of the joining tools.
Mechanical joining techniques for connecting parts to be joined such as for example metal sheets are increasingly gaining in importance, as they have some advantages specific to the method. Patent DE 197 01 252.3 describes a method as well as connecting means for joining metal sheets by punch riveting. For this it is explained inter alia that punch riveting of 1 mm. sheets of ZSTE 420 material requires forces of 74 kN which are not attainable with ordinary riveting machines. The solution proposed there, of providing the rivet with a blunt circular or annular front surface with which the metal sheets are pierced, allows a reduction of the necessary work forces compared with the state of the art known at the time. Also the lateral or angular offset of the tools or tool portions, which would reduce the joint quality or make a connection completely impossible, is reduced by the shot-like operation. Whereas this process perfectly reduces the lateral or angular offset, the drawback of the shot-like operation lies in that considerable measures must be taken to make it safe to use. The propellant charges which are used for the shot-like operation are potentially, in case of improper handling, not completely risk-free.
In patent DE 197 18 576 are described an apparatus and a method for mechanical joining techniques. In particular in
FIGS. 4 and 5
is shown a typical force/displacement graph for the working movement of the stamp. Patent DE 197 18 576 however instructs only that individual or several working members for making a mechanical joint can be controlled or regulated in their movement and/or force, but without going into the basic problem of reducing the high forces for making a mechanical joint. According to the state of the art described there, the transforming energy required is applied by hydraulic cylinders which make the respective joint in a single quasi-continuous stroke movement. This publication contains no indication as to how the method and the apparatus for making joints can be improved by weaker joining forces.
Accordingly it is an object of the present invention to provide an apparatus and a method for mechanical joining which allow weaker reaction forces in the making of the mechanical joint.
It is a further object to provide an apparatus and a method for mechanical joining which allow a correspondingly lighter design and easier handling of the joining tools.
SUMMARY OF THE INVENTION
The objects are achieved, according to the method of the invention, by the transforming energy or joining force required being applied to the joint to be made by several impacts in rapid succession of a joining tool or in pulsed fashion at an exciting frequency, wherein the opposite joining tool, the excited joining tool and/or the parts to be joined are resiliently mounted and the characteristic frequency of the opposite joining tool, the excited joining tool and/or the parts to be joined is lower than the exciting frequency.
The apparatus according to the invention comprises at least one percussion mechanism which, to make a mechanical joint, within a short time applies several successive impacts or a pulsating force to one of the joining tools, wherein the opposite joining tool, the excited joining tool and/or the parts to be joined are resiliently mounted and the exciting frequency at which the joining tool can be excited is higher than the characteristic frequency of the opposite joining tool, the excited joining tool and/or the parts to be joined. Primarily single-part or multi-part stamps and dies are considered as the joining tools, and secondarily also strippers and hold-down devices.
The hold-down forces act statically on the parts to be joined. This static load remains unchanged even if the joining tools do not exert a working stroke, but several successive impacts, and this static load must be taken up by the frame and the one opposite the hold-down device. If an opposite joining tool is mounted flexibly in order to be isolated from vibrations, the static load of the hold-down device can cause a major deflection of the vibration-isolated opposite joining tool. In order to at least reduce this deflection and loading of the frame caused by the static load, it is proposed to synchronize the movement of the hold-down device by coupling means such as for example a mechanical drive link via a driver link plate or a hydraulic valve-controlled tracking control means with the movement of the joining tool. The same applies to strippers. If the hold-down force is applied non-dynamically as described above or controlled by magnets, the deflection caused by the static forces can be at least partially compensated by active position control at one or both joining tools, by the fact that the latter are movable by control means in a direction opposite the static deflection.
The several successive impacts of the percussion mechanism make it possible to work with smaller force peaks in the substructure in case of resilient mounting of the opposite joining tool and a large mass and/or weak springs of the opposite joining tool, as the joining force needed to make the mechanical joint is now no longer applied in a single stroke, but the exciting frequency of one joining tool which exceeds the characteristic frequency of the opposite joining tool allows vibration isolation of the resiliently mounted opposite joining tool. In this case it is important to form a vibrating system which is optimally matched to the joint to be made. Thus it is advantageous, with as large a mass as possible of the opposite joining tool and as weak as possible springing, to ensure that this unit exhibits as low as possible a characteristic frequency, because then at a frequency which is by contrast as high as possible, at which the other joining tool is excited, the reaction forces are reduced to a minimum. The substructure is therefore vibrationally uncoupled from the applied joining force, and only fractions of the applied joining force act on the substructure. High-frequency impacts in rapid succession allow most of the joining force to be used for plastic deformation of the sections of the parts to be joined which are involved in the joint as well as of any auxiliary parts to be joined such as rivets.
Here the rule that as the degree of isolation increases, the higher the exciting frequency in relationship to the characteristic frequency of the parts to be joined and of the opposite joining tool, holds good. For the present invention can be used not only when at least two joining tools are involved in making the joint, but also when the parts to be joined have sufficient inherent stability to remain in a still acceptable form when only one joining tool excited at one frequency is used. To this extent the term “opposite joining tool” as used within the scope of the description and claims can be understood to include “component” if an actual “opposite joining tool” is lacking. In such cases it is sufficient, instead of the opposite joining tool, to mount the parts to be joined in such a way that their characteristic frequency is as low as possible. An additional reduction of reaction forces results if not only the opposite joining tool but also the excited joining tool are vibration-isolated relative to the substructure. Such vibration isolation can be caused for example via the pressure medium of the delivery unit. Thus with a pneumatic mechanism the gas acts like a spring which causes vibration isolation. Naturally the vibration isolation can also take place via components with a preferably larger mass such as for example carrier plates and with a resilient mounting, which then for example isolate the percussion unit and/or the delivery unit from vibrations.
Nat
Hahn Ortwin
Schulte Volker
Hughes S. Thomas
Husch & Eppenberger LLC
Jimenez Marc
Kercher Kevin M.
Muir Robert E.
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