METHOD OF PERFORATING TUBES

The invention relates to a method for forming slots in a section of a tube of rectangular section comprising inserting a die into the tube, the die having a width less than that of the tube and having a recess open on three faces extending across the die, a punch with a rectangular perforating portion perforating the tube and aligned with the recess to punch out a blank of material, which blank splits into two halves which curl away from the recess and remain secured to the tube.

Claims, 3 Drawing Figures <HR><HR>METHOD OF PERFORATING TUBES

The invention relates to a method for perforating slots in a tubular member of rectangular section, for example. In particular the method of the invention is used ? in forming horizontal slots in one surface of the member at spaced-apart locations. Such perforated tubular members may then be used to accommodate brackets or other fittings which support shelves or drawers.

Slots have been formed in tubular members by mill- 1 ing, but this is a time-consuming operation. The problem of forming slots in a surface of a tubular member by using a punch and die of the same shape and size as the slot to be formed has to be overcome. The problem of forming slots with a punch and die is that the residual blank of material punched out of the surface of the tubular member cannot be removed easily from the die as the die is enclosed within the tubular member during the perforating step. Furthermore, any irregularities in the inside dimensions of the tubular member, and in addition the clearance necessary between the die and the inner surfaces of the tubular member to enable the tubular member to be moved along the length of the die, prevents accurate location of the die laterally under the . punch during the perforating step.

According to the invention there is provided a method of forming slots in tubular members, comprising the steps of sliding a tubular member in which the slots are to be formed onto a die located in a deter- 3 mined position, which die has a lateral width less than that of the slot to be formed, an open-ended recess in the die extending across die, the open-ended recess being positioned adjacent the position at which the slot is to be formed in the tubular member, perforating the 3 surface of the member with a blow from a punch, so that the blank of material is split substantially into two halves and maintaining the halves of the blank secured to the inner surface of the tubular member at the sides of the lateral extremity of the slot and turned away 4 from the recess in the die so that a clean slot is obtained in the tubular member with no loose swarf in the die.

The method of the invention therefore prevents the blank of material punched out of the surface of the material when forming the slot in the surface of the tubu- 4 lar member from remaining in the recess in the die by splitting the blank substantially into two halves, and allows the ends of the two halves to remain attached to the tubular member in such a way that there is no residual or loose blank of punched-out material in the die, 5 and thus relative longitudinal movement between the tubular member and the die is not prevented. Moreover, as the die is of less lateral extent than the slot to be formed, and since the recess in the die is open on three faces, the necessity for accurate lateral location 5 of the die inside the tubular member is obviated.

Preferably, the die may be secured to the machine on which the punch is mounted by means of a connecting bar which passes through the tubular member and is connected at one end to the die.

One embodiment of the invention is diagrarnmat-ically illustrated, by way of example, in the accompanying drawings, in which:

FIG. 1 shows the relative positions of a punch and , die, in perspective, during perforation of a surface of a tubular member of rectangular section (not shown) to provide a slot; FIG. 2 shows an end elevation of the rectangular tubular member after perforation; and FIG. 3 shows a perspective view of a perforated tube having a series of horizontal slots formed therein. Referring to the drawings, the apparatus for perforating a tubular metal member is shown in FIGS. 1 and 2 and comprises a punch 1 having a shank portion 2 which is flat and has a cross-section corresponding to that of the slot to be formed and terminates at the per-0 forating end in a double taper so that it forms a triangular apex or point, and a die 4 having recess 5 which is open on the three faces as shown in FIG. 1. The lateral width of the die 4, and thus of the recess 5, is less than the width of the slot to be formed in a sur-: 5 face of a tubular member 6. The width of the slot to be formed is determined by the lateral width of the punch 1, which is thus wider than the width of the die. I have found that a die % inch wide is suitable to form a slot Vfc inch wide. It will be understood that the width of the !0 die should be sufficient to support the surface of the member in order to obviate denting of the surface during perforation, but must be narrow enough to allow withdrawal of the die longitudinally of the member 6. In use to form a slot in the tubular member 6, the die 4 is placed in the member 6 so that the surface 7 of the die abuts the underside 8 of the surface of the member 6, which is thus supported by the die. The die is held in position so that its upper surface engages the underside 8, and is secured to the machine on which the !0 punch is mounted by a bar passing longitudinally through the tubular member. The punch and die are thus mounted in the same vertical plane, the punch being aligned with the recess. The punch is then brought down sharply in a position aligned with the open recess 5 in the die. A slot 9 is thus formed in the surface of the tubular member. A blank of material punched from the surface of the tubular member is cut by the shearing action of the punch into substantially two halves, which are forced downwardly into the rew cess S. As the recess 5 has no side walls, the two halves of the blank are pushed apart by the punch and curl away from the slot 9 towards the underside 8 of the surface, and remain attached to the tubular member at roots and 10.

The member 6 is then drawn longitudinally of the die without hindrance while the die is held stationary by the bar passing through the tube and the punching operation is repeated at another predetermined position along the length of the tube. A tube having a plurality of perforations is shown in FIG. 3.

It will be appreciated that a plurality of slots may be formed simultaneously by providing a die with the required number of recesses or slots, and a corresponding number of punches mounted in a hammer (not shown). The punches would each be aligned with one recess in the die.

The invention thus provides a method of perforating tubular metal members in which the die is not clogged with loose swarf or blanks of metal