METHOD FOR PUNCHING A SHEET OR A MULTI-LAYER SHEET STRUCTURE

Description

technical field

[0001] The present invention relates to the field of materials processing, such as sheet metal.

[0002] More specifically, the invention relates to the field of punching sheets, particularly metallic ones, and more specifically to the field of punching tools.

[0003] The invention is particularly useful in the automotive sector, but also in any industrial field requiring perforations in sheet metal. For example, it can be useful in automotive body repair. Previous art

[0004] Punching tools are used in industry to create perforations in sheet metal, for example in high-strength sheet metal parts.

[0005] Punching is a shearing process on a closed contour, performed by a punch acting on a die. It is used to create holes and cut out complex, sometimes non-rectangular, shapes, making them difficult or even impossible to achieve by shearing.

[0006] Cutting vehicle body parts by punching is a technique that has been used for many years. Indeed, compared to drilling, punching is faster, which represents a valuable time saving when cutting such sheet metal.

[0007] In the automotive sector in particular, most of the sheet metal used for punching is high-strength (HR) steel, also known as hardened steel, which reduces vehicle weight while improving occupant safety in the event of a collision. These typically have a mechanical resistance between 200 and 1600 MPa.

[0008] As a result, the wear on the punches used to punch these sheets is significant and it is necessary to replace them regularly, which is time-consuming.

[0009] A sheet metal punching device has been proposed, comprising a die and a punch with a movable punching shank mounted on a punching ring that allows for better control of the hole shape. Once the hole is punched, the washer falls from the die side along with the waste material formed during the cutting, and the punching shank passes back through the punched hole in the opposite direction so that it is extracted.

[0010] This prior art device is unsatisfactory because the crown, which has a small diameter, is difficult to handle and position on the punching rod. Furthermore, it is difficult to retrieve once it has fallen to the other side of the pierced sheet.

[0011] Furthermore, the crown is for single use only because it wears out very quickly.

[0012] Document WO2018 / 157983 discloses a punch screwed onto a punch holder.

[0013] The document JP H10 6296, on which the preamble of claim 1 is based, relates to a drilling solution for a thin metal plate or, in particular, a circuit board for electronic components.

[0014] There is therefore a need to improve the existing technique in order to provide a punching device and process which allows high-strength sheet metal to be perforated without damaging the drilled holes and to quickly replace worn punches after the punching operation. Description of the invention

[0015] The invention addresses this need by proposing a punching process according to claim 1.

[0016] The invention thus proposes to implement a one-piece punch mounted removably on a punch holder.

[0017] Only the one-piece punch is designed to pierce the sheet metal; the punch holder that carries the punch is not intended to pass at least partially through the hole made by the punch and then back through the hole in the opposite direction. The punch holder is therefore not configured to pierce the sheet metal but only to carry and move the punch, without engaging in the hole made by the punch.

[0018] The punch, which is made of a single piece, is mounted on the punch holder in a removable way, without screws, so that it cuts the sheet metal initially, then detaches from the punch holder when the latter is removed after cutting, the punch then remaining lodged in the drilled hole.

[0019] Therefore, and also because of its size and the material from which it is made, such a punch is very easy to position on the punch holder and easy to remove from the sheet metal forming the part to be drilled. Furthermore, it is easy to find if it falls to the other side of the sheet metal.

[0020] The punch is more robust, because it is more massive, than the crowns of earlier art, and can be reused many times.

[0021] Said cutting punch may have an undercut and an end, opposite said undercut, said end being configured to fit into said impression, said end having a shape complementary to that of said impression.

[0022] The said end of the said cutting punch may have a substantially cylindrical shape.

[0023] According to a particular aspect of the invention, the method includes a preliminary step of positioning said cutting punch in said impression of said punch holder.

[0024] According to a particular aspect of the invention, the step of removing said cutting punch from said part is carried out by pushing said cutting punch through the part in the direction of drilling said hole.

[0025] According to a particular aspect of the invention, the method includes a preliminary step of placing said part to be punched against said die. Presentation of the figures

[0026] Other objects, features and advantages of the invention will become more apparent upon reading the following description, given by way of simple illustration and not limitation, in relation to the figures, among which: [ Fig 1] is a perspective view of a punching tool used in the process; [ Fig 2 ] is a cross-sectional view of a punching tool mounted on a gooseneck, the step of positioning the sheet metal part(s) to be drilled; [ Fig 3 ] is a cross-sectional view of the punching tool of the figure 2 illustrating the punching stage of the sheet metal part(s); [ Fig 4 ] is a cross-sectional view of the previous punching tool, illustrating the punch holder removal step; [ Fig 5 ] is a cross-sectional view of the previous punching tool, illustrating the step of clearing the sheet metal part(s); [ Fig 6 ] is a cross-sectional view of the previous punching tool, illustrating the punch removal step from the sheet metal part(s), and [ Fig 7 ] is a diagram illustrating the different stages of the process of punching a sheet metal part according to an embodiment of the invention. Detailed description of an embodiment of the invention

[0027] The general principle of the invention is based on the use of a punching tool for creating holes in the surface of a part made of a single sheet of metal or a multi-layered assembly of sheets (i.e., an assembly of two or more thicknesses of metal, the sheets being all made of the same material (steel, for example) or the sheets being made of different materials (at least one steel sheet and at least one aluminum sheet, for example)). Such a part is, for example, a body panel of a vehicle. The punching tool comprises a punch holder which carries a one-piece punch removably housed in a recess formed in this punch holder.In this way, when the punch holder moves from its working position—that is, the drilling position—to its resting position, the cutting punch detaches from the punch holder without any action from the operator and remains attached to the punched workpiece so that it can then be pushed through the drilled hole. Since the punch is larger than the crown of the prior art, this facilitates the placement of the cutting punch on the punch holder for the next punching operation.

[0028] In the example described below, the punching tool is of the C-shaped gooseneck type. However, it could be in another form.

[0029] As illustrated on the figures 1 to 6 , this punching tool therefore includes a punch holder 2 supporting a one-piece cutting punch 3, and a punching die 4 arranged opposite the punch holder 2.

[0030] Here, the punching die 4 is in the form of a cylindrical hollow body with a bore (also called an orifice or evacuation channel) allowing the passage of punched material after drilling part T, which is made of a sheet or a multi-layered assembly of sheets. These sheets can be made of very hard steel, such as UHLE (for "ultra-high yield strength"), for example, like boron steel.

[0031] The two parts, namely on one side the punch holder 2 and on the other the punching die 4, are connected by means of a gooseneck 9. This gooseneck 9 here forms a C-shaped frame allowing the two parts to be held in place relative to each other.

[0032] In order to be held on the gooseneck 9, the punch holder 2, which is generally cylindrical, includes a first retaining element 20 suitable for cooperating with a first housing implemented at one end of the gooseneck.

[0033] Similarly, and so as to be held on the gooseneck 9, the punching die 4 includes a second retaining element 40 suitable for cooperating with a second housing implemented at the opposite end of the gooseneck.

[0034] There figure 1 shows the punch holder 2, the punching die 4 and the punch 3 when disassembled from the gooseneck 9. All these elements are cylindrical.

[0035] The punch holder 2 is mounted movable and is designed to move from a rest position to a working position to drive the punch 3 towards the die 4, along a displacement axis A, until the punch 3 enters the sheet metal piece T arranged between the punch holder 2 and the die 4 to cut a hole in it.

[0036] By cutting the sheet metal part(s) T, the punch 3 pushes a scrap piece of the sheet metal, corresponding to the material removed by drilling, into the bore of the punching die 4.

[0037] The movement of the punch holder 2 and the punch 3 can, depending on the embodiment, be carried out by means of an actuator (not shown in the figures).

[0038] This punch 3, which is one piece, is implemented here in the form of a rod with a diameter of 6 to 10 mm for example which can be made of resistant steel.

[0039] Punch 3 has an undercut 30 allowing drilling of the sheet metal part T, in working position.

[0040] The punch 3 is removably housed in a recess 21 formed in the punch holder 2 so that, when the punch holder 2 moves from its working position to its resting position, the punch 3 detaches from the punch holder 2 and remains attached to the sheet metal part(s) T (the punch 3 remains housed in the drilled hole).

[0041] Due to its dimensions and the material from which it is made, punch 3 is reusable and easier to recover after the punching operation.

[0042] In other words, the punch 3 is placed in the recess 21 of the punch holder 2, without clamping or screwing, so that the punch 3 is free in translation along an axis of displacement of the punch holder 2 which corresponds to the axis A of displacement.

[0043] This imprint 21 is, as illustrated on the figure 1 , located opposite the retaining element 20 of the punch holder 2.

[0044] The clearance between the die 21 and the punch 3 must be sufficient to allow the punch to detach from the punch holder when the latter is removed after punching. This clearance must also not be too large to prevent the punch from falling from the punch holder before punching and to ensure effective punching of the sheet metal to be pierced. The external diameter of the punch can therefore be slightly smaller than the internal diameter of the die 21.

[0045] In one variant, the punch 3 can be held in the recess 21 of the punch holder 2 by friction. In other words, the punch 3 is held in the recess 21 by friction. This friction force is chosen so that, when the cutting punch 3 has pierced the hole and is located within it, it can disengage from the punch holder 2 when the latter retracts by moving in the opposite direction to the drilling direction.

[0046] More particularly, and in this embodiment, the punch 3 has an end 31, opposite the undercut 30, which is configured to fit into the cavity 21.

[0047] In order to facilitate this sliding, and in the illustrated embodiment, the end 31 and the imprint 21 have a substantially complementary respective shape.

[0048] Here the end 31 of the punch 3, and therefore the impression 21 of the punch holder 2, each have a substantially circular section, the two sections being complementary.

[0049] However, in other embodiments, a punch impression and punch end could be provided with a different cross-section, for example a triangular, square, or more generally polygonal shape, the respective cross-sections of the impression and the punch end being complementary.

[0050] We now present, in relation to the figures 2 to 7, an embodiment of process 100 of punching a part T formed of a single sheet or of several layers of sheets using a punching tool.

[0051] According to the invention presented, and as illustrated in figure 7 This process includes the following successive steps: Positioning 101 of the part T to be drilled between the punch holder 2 and the die 4 of the punching tool which are located opposite each other; punching 102 of the part T by the punch only so as to drill a hole by moving the punch holder 2 from its rest position to its working position (from left to right here) in a first direction of movement; withdrawal 103 of the punch holder 2 by moving the latter from its working position to its rest position (from right to left) in a second direction of movement opposite to the first direction of movement, the punch 3 detaching from the punch holder and remaining in the hole of the punched part T; release 104 of the punched part T in which the punch 3 is retained; withdrawal 105 of the punch 3 from the part by pushing the punch 3 through the hole cut in the part T.

[0052] There figure 2illustrates in cross-section the punching tool after the positioning step 101.

[0053] As illustrated in this position, the punch holder 2 is in a rest position at a distance from the part T, which is itself supported against the punching die 4. The punch holder 2, the punch 3, and the punching die 4 are aligned along the axis of movement A.

[0054] There figure 3 illustrates in cross-section the punching tool during the punching step 102 by moving the punch holder 2 from its rest position to its working position along the axis of movement A.

[0055] As illustrated, in this position, the punch holder 2 is in the working position and the punch 3 is in contact with the part T, which is drilled at the point of contact between the punch 3 and the part T on the axis of movement A. In this position, the sheet metal scrap (not visible) has fallen into the punching die. The punch 3 is therefore housed in the hole that has just been drilled in the part T. Note that the punch holder 2 does not pass through the part T, even partially, and therefore does not engage in the hole drilled by the punch 3.

[0056] There figure 4 illustrates in cross-section the punching tool during the withdrawal step 103 of the punch holder 2 by moving the latter from its working position to its rest position along the axis of movement A.

[0057] As illustrated, in this position, the punch holder 2 is between the working position and the rest position. In other words, it has moved from the working position and is moving towards the rest position. The punch 3 is still housed in the hole that has just been drilled in part T and is no longer in contact with the punch holder 2.

[0058] In other words, the punch holder 2 moves back from its working position to its resting position and is moved away from part T, the punch 3 being housed and held in the newly drilled hole in part T.

[0059] It should be noted that punching 102 of part T can, for example, produce a hole with a diameter between 6 and 10 mm. Larger or smaller holes can be made.

[0060] Such a hole can, for example, allow a rivet or other fasteners to pass through.

[0061] There figure 5illustrates step 104 of the release of part T once the latter has been punched.

[0062] As illustrated in this position, the punch holder 2 is in the rest position at a distance from the part T, which itself is free from the gooseneck and is no longer in contact with the punching die 4. The punch holder 2 and the punching die 4 are still aligned along the axis A of movement, while the punch 3 is still housed in the hole that has just been drilled in the part T.

[0063] There figure 6 illustrates the removal step 105 of punch 3 of part T.

[0064] As illustrated, the punch holder 2 is in its rest position, some distance from part T, which is itself free from the gooseneck and no longer resting against the punching die 4. The punch holder 2 and the punching die 4 remain aligned along the axis of movement A. The punch 3 can be freed from part T by passing it through the hole in the direction of drilling part T (i.e., from left to right in the figures).

[0065] In other words, in this embodiment, and as illustrated in figure 6 , the step of removing punch 3 from part T is carried out by pushing the punch through part T in the direction of drilling the hole.

[0066] Therefore, by passing the punch 3 through the hole in the direction of drilling, that is to say by not doing it in the opposite direction of drilling as in the prior art, it is possible to avoid risks of deformation of the edge of the hole, or risks of the punch getting stuck in the hole.

[0067] As illustrated in figure 7 , the punching process may further include a preliminary step 106 of placing the punch 3 in the impression 21 of the punch holder 2.

[0068] It should be noted that, depending on the embodiment, the installation of this punch can be carried out before or after the installation of the punch holder on the gooseneck, i.e. before or after the positioning of the part to be drilled between the punch holder and the die of the punching tool arranged opposite each other.

[0069] Furthermore, and as illustrated in the same figure 7The punching process may additionally include a preliminary step 106 of placing the part against the punching die 4. This part may not be placed against the punching die, but will be pressed against it by the advance of the punch.

[0070] Furthermore, the punch can have a shape other than a cylindrical shape.

Claims

1. Method (100) of punching a part (T) made of a sheet metal or a multi-layer assembly of sheet metals, for example a body part (T) of a vehicle, by means of a punching tool comprising a punch holder (2) holding a single-piece punch (3) for cutting a hole in the part (T) and a punch die (4) arranged in front of said punch holder (2), said cutting punch (3) being housed in a cavity (21) formed in said punch holder (2) with a clearance, without clamping or screwing, said method comprising the following successive steps: - positioning (101) said part (T) to be perforated in position between the punch holder (2) and the die (4) of said punching tool arranged one in front of the other; - punching (102) said part (T) solely by the punch (3) placed on the punch holder (2) by moving the punch holder (2) from its rest position to its work position in which the cutting punch (3) cuts a hole in said part (T) ; and characterised in that the following steps are performed : - removing (103) said punch holder (2) by moving the punch holder (2) from its work position to its rest position, said punch (3) remaining in the hole pierced in said part (T) ; - releasing (104) said part (T) in which the cutting punch (3) is housed; - removing (105) said punch (3) from said part (T) by pushing said cutting punch (3) through the hole pierced in said part (T).

2. Method (100) for punching a part (T) according to claim 1, characterized in that it comprises a prior step (106) for putting said cutting punch (3) in position in said cavity (20) of said punch holder (2) with a clearance, without clamping or screwing.

3. Method (100) for punching a part (T) according to claim 1 or 2, characterized in that the step for withdrawing said cutting punch (3) from said part (T) is performed by pushing said punch (3) through the part (T) in the perforating direction of said hole.

4. Method (100) for punching a part (T) according to one of claims 1 to 3, characterized in that the method comprises a prior step (107) for moving said part (T) to be punched against said die (4).