Tool for piercing nut

A tool for piercing nuts that includes a die part, a punch part and a piercing nut feeder incorporated into the punch part. The piercing nut feeder is adapted to feed piercing nuts into a piercing nut holder in the punch part so that these nuts, when the punch part is pressed against the die part by a press, are to punch holes in and be attached to a metal sheet inserted between the punch part and the die part. A gas spring is arranged between the press and the punch part, which gas spring has at least one cylinder and a piston which is movably arranged in said cylinder and which is aligned with the press. The pressure in the cylinder to adjust the pressure exerted upon the piercing nut by the punch part.

FIELD OF THE INVENTION

The present invention relates to a tool for piercing nuts.

BACKGROUND ART

FIG. 1illustrates a prior art tool for piercing nuts which is adapted to fasten piercing nuts to metal sheet. This requires great accuracy for the nut or metal sheet so as to not damage the metal sheet and for the nut to be safely permanently connected to the metal sheet. A condition for such accuracy is that the punch of the tool for piercing nuts bottoms with the correct pressure against the piercing nut, i.e., that the stroke of the punch is correctly set for the used piercing nut and the metal sheet in question. To achieve this accuracy within some tenths of a millimeter, spacers, or shims, are currently used for adjustment in the shown prior art tool for piercing nuts. The shims are arranged between an adjusting plate and the tool for piercing nuts which thus is moved in its entirety by means of the shims. This mode of operation is time consuming and still does not provide exact information about the pressure to which the piercing nut and the metal sheet are subjected. A negative effect on, for instance, the strength of the piercing nut owing to a punch pressure which after all is incorrect, thus cannot be excluded. Moreover, it is necessary to completely stop the use of the tool for piercing nuts during the actual adjustment, which causes expensive production standstill when the tool is included as one of a plurality of tools in a long press line.

OBJECT OF THE INVENTION

Therefore, an object of the present invention is to eliminate the drawbacks of the prior art tool for piercing nuts.

SUMMARY OF INVENTION

According to the invention, this object is achieved by a tool for piercing nuts that comprises a die part and a punch part and a piercing nut feeder incorporated into the punch part, and adapted to feed piercing nuts into a piercing nut holder in the punch part so that the nuts, when the punch part is pressed against the die part by a press, are to punch holes in and be attached to a metal sheet inserted between the punch part and the die part. A gas spring is arranged between the press and the punch part. The gas spring has at least one cylinder and a piston which is movably arranged in the cylinder and which is aligned with the press. The pressure in the cylinder is settable for adjusting the pressure exerted upon the piercing nut by the punch part.

DESCRIPTION OF A PREFERRED EMBODIMENT

In the tool for piercing nuts according to the invention, the shims1, mentioned by way of introduction, of the prior art tool for piercing nuts2inFIG. 1are replaced by a gas spring3. The gas spring is shown in more detail inFIGS. 2-4and in its position of operation in a tool for piercing nuts4according to the invention inFIGS. 5-6.

The gas spring3comprises, as will be seen, three pistons5-7which are movably arranged in a cylinder8-10each. The cylinders8-10are in a manner not illustrated in detail connected with each other (connected in series) to be able to be pressurised by a common source of compressed air (not shown). This source of compressed air makes it possible to set in the cylinders8-10a pressure acting on the pistons5-7with a force that is suitable for the case of operation in question.

The advantage of the gas spring3is that it makes it possible to exactly adjust the pressure exerted upon a piercing nut by the tool for piercing nuts4. It will be appreciated that the pressure exerted by the gas spring3is dependent not only by the actual gas pressure but also by the surface area of the pistons5-7. It will also be appreciated that the gas spring3, when the tool for piercing nuts4bottoms when fastening a piercing nut, can perform a certain damping motion, the size of which greatly exceeds the damping motion which is allowed by the prior art shims (about 1.5 mm against about 0.1 mm).

Owing to the invention, just a single initial adjustment is therefore necessary, and subsequently appearing minor deviations will not be important since they can be compensated for by the gas spring3.

The maximum stroke of the pistons5-7of the shown gas spring3is about 12 mm. This means in practice that not even a case where two piercing nuts inadvertently land on top of each other in the tool for piercing nuts4will cause damage that will require stoppage for repair or even, as in the prior art tool for piercing nuts2with the shims1, exchange of the entire tool.

The above-mentioned connection in series of a plurality of cylinders8-10renders it possible to make the gas spring3elongate so that it well fits the tool for piercing nuts4as such and also a press line, in which the tool for piercing nuts4can be included as one among a large number of other tools and in which therefore the available space is extremely restricted.

A person skilled in the art understands that the above-described tool for piercing nuts4according to the invention can be modified in various ways within the scope of the claims and, for instance, that the number of cylinders5-7in the gas spring3can be different from the one shown.