EP0916421B1 - Machining a sheet metal without removing material, by compressing - Google Patents

Description

The present invention relates to the machining of sheets, or alternatively of plates (assimilated to sheets in the context of the present invention) in order to modify the geometry of the faces of said sheets. A method according to the preamble of claim 1 is known of document FR-A-1 217 035.

In metallurgy, the raw sheets are conventionally obtained by rolling. An operation of rolling results in a difference in sheet speed between upstream and downstream of the rolling operation, which results in an increase in the length of the sheet after rolling. Basically, by an operation as described above, we change the sheet dimensions, while keeping a profile (section perpendicular to the direction of travel) rectangular. The product obtained is generally with parallel faces.

From a conventional sheet, it is difficult to obtain profiles with non-parallel faces by rolling. If for example the respective axes of the rolling rolls are not parallel, the volume of material treated per unit of width (dimension parallel to the axis of the cylinders) is no longer constant. As a result, the frame rate tends to be higher in places rolled to a lower thickness. This causes, in the rolled sheet, very internal stresses significant, hence a very great difficulty in obtaining a rolling product without curvature.

The objective of the present invention is to modify the geometry of the faces of a raw sheet, to so as to obtain sheets whose faces are not parallel. A special case consists in obtaining sheets with flat faces but not parallel. By convention, in the latter case, we speak in the series of “biased” sheets, that is to say sheets whose faces form inclined planes one by relative to the other, from angles as small as you want to angles worth a few degrees. According to a particular aspect of the present invention, a so-called blank is produced. "Bias", in which it is then possible to cut, by any technique, an object with a predefined contour depending on the intended end application.

• écraser la tôle en pressant sur l'une de ses faces une portée d'outil sensiblement longiligne ayant une petite dimension et une grande dimension, ladite tôle étant supportée par l'autre de ses faces par un organe présentant une surface de support de portée au moins sensiblement équivalente et disposée en regard de ladite portée d'outil, la grande dimension de ladite portée d'outil étant supérieure à la largeur de la tôle à usiner, l'écrasement étant arrêté lorsque le jeu subsistant entre ladite portée d'outil et ladite surface de support atteint une valeur prédéterminée,
• écarter ladite portée de la face de la tôle,
• déplacer ladite tôle, transversalement par rapport à l'orientation de ladite portée, d'un pas de valeur prédéterminée,

reprendre les étapes précédentes tout en faisant varier ladite valeur prédéterminée du jeu d'un pas au pas suivant jusqu'à ce que l'on ait conféré à ladite tôle une section de taille prédéterminée variable en fonction de la localisation de la section considérée.The invention provides a method of machining by deformation of a sheet intended to modify the thickness between the opposite faces of said sheet, comprising the following steps:

• crush the sheet by pressing on one of its faces a substantially elongate tool seat having a small dimension and a large dimension, said sheet being supported on the other of its faces by a member having a support surface of reach to the less substantially equivalent and disposed opposite said tool seat, the large dimension of said tool seat being greater than the width of the sheet metal to be machined, the crushing being stopped when the clearance remaining between said tool seat and said support surface reaches a predetermined value,
• move said span away from the face of the sheet,
• move said sheet, transversely with respect to the orientation of said span, by a predetermined value,

repeat the preceding steps while varying said predetermined value of the play from one step to the next step until said sheet has been given a section of predetermined size which is variable depending on the location of the section considered.

Two variant embodiments are explained below. The invention can be applied to each Once a final product or a semi-finished product is a sheet with a cross section trapezoidal, that is to say has biased faces. By way of nonlimiting example, the making knife blades, or making a certain type of strip mold tire bearing, the basic design of which is defined in patent EP 0 569 909.

La figure 1 est une coupe suivant I-I à la figure 2, montrant une première variante d'un dispositif selon l'invention ;

La figure 2 est une coupe suivant II-II à la figure 1, montrant plus particulièrement une commande d'un mouvement ;

La figure 3 est un agrandissement de la partie délimitée par le cercle III à la figure 2 ;

La figure 4 est une vue du dispositif comparable à celle de la figure 3, montrant la tôle dans une phase ultérieure de l'usinage ;

La figure 5 est une coupe suivant V-V à la figure 6, montrant une deuxième variante du dispositif ;

La figure 6 est une coupe suivant VI-VI à la figure 5, montrant plus particulièrement la commande d'un mouvement ;

La figure 7 est une vue plus détaillée de la partie droite de la figure 6 ;

La figure 8 est un agrandissement de la partie délimitée par le cercle VIII-VIII à la figure 7 ;

La figure 9 illustre l'application à la fabrication d'un moule pour pneumatiques.

The invention will be perfectly understood thanks to the consultation of the following description, illustrating with the aid of the attached figures, and in a nonlimiting manner, two embodiments of the invention.

Figure 1 is a section along II in Figure 2, showing a first variant of a device according to the invention;

Figure 2 is a section along II-II in Figure 1, showing more particularly a control of a movement;

Figure 3 is an enlargement of the part bounded by the circle III in Figure 2;

Figure 4 is a view of the device comparable to that of Figure 3, showing the sheet in a subsequent phase of machining;

Figure 5 is a section along VV in Figure 6, showing a second variant of the device;

Figure 6 is a section along VI-VI in Figure 5, showing more particularly the control of a movement;

Figure 7 is a more detailed view of the right side of Figure 6;

Figure 8 is an enlargement of the part delimited by the circle VIII-VIII in Figure 7;

FIG. 9 illustrates the application to the manufacture of a mold for tires.

The machining device shown in Figures 1 to 4 includes a frame 11 supporting a press 16 comprising a blade 162 movable relative to the frame 11 and a counter blade 161 immobile by relative to the frame 11. The blade 162 is substantially elongated and is provided with a bearing having a large dimension and a small dimension. Blade and counter blade 161 and 162 are mounted in look at each other. Blades and counterblades 161 and 162 leave a predetermined clearance between them and rigorously controlled constituting an orifice 1 receiving the sheet 2. The device comprises means for moving the sheet relative to the blade and counter blade 161 and 162. In the first variant, it is a clamp 15 which can grip the sheet 2. The device further comprises means to move said clamp 15 (therefore the sheet 2) relative to said blade and counter blade 161 and 162, in successive steps, laterally with respect to the large dimension of the blade 162. Preferably, in its movement away from the blade and counter blade 161 and 162, the clamp does not will not stray too far from a plane perpendicular to the plane of the orifice 1, passing through the said orifice.

According to one aspect of the invention, the sheet 2 is crushed located under a span 165 of width W (see FIG. 3), each crushing occurring in offset from the previous one, by preferably with overlapping of the parts subject to crushing. Said scope is for example plane. More generally, if we observe experimentally a difference between the desired shape and the shape of the sheet after deformation, it is corrected by modifying the shape of said bearing so to obtain the shape of the sheet as desired. The sheet will generally bear the footprints successive, by spaced traces of the length P of said pitch (see FIG. 3), P being smaller than W (W being the small dimension of the span 165). We proceed by successive crushing of the sheet 2 by acting perpendicular to the plane of the sheet 2. It is a matter of closing each step a little more (or a little less depending on the direction chosen to vary the thickness) the press 16 on the sheet 2, by slightly advancing said sheet 2 at each step (the arrow F in FIG. 4 recalling the direction movement of the sheet between two steps).

The frame 11 is pierced in the center of a window 101 extended on one side by a clearance 102, receiving press 16 (see Figure 2). The counter blade 161 is mounted on a fixed blade holder 13, and the blade 162 is mounted on a movable blade holder 14, by means of trapezoidal keys 131 and 132 respectively (see more particularly Figure 4). The back 130 of the fixed blade holder 13 is a circular base cylinder, i.e. forms an arc of a very large radius when viewed in the plane of FIG. 1, in order to be able to adjust the parallelism of the blade and counter blade 161 and 162 by moving the fixed blade holder 13 transversely relative to the frame 11.

A corner 181 is interposed between the movable blade holder 14 and a reference surface 17 on the frame 11, with interposition of needle roller tracks 185. This corner 181 is mounted on a nut 183, itself mounted on a screw 180. The translation of the screw 180 along its axis is blocked by suitable arrangement. The translation of the movable blade holder 14 takes place while it remains always parallel to itself, the forces exerted by the mobile tool holder 14 in the direction parallel to the axis of the screw 180 are taken up by the frame 11. The movable blade holder 14 and all of the members cooperating therewith are held in place against the frame 11 by a plate 160.

The corner 181 forms an angle α whose value is chosen to develop an effort on the sheet sufficient to deform it, while providing the possibility that the length of movement of the corner is sufficient to control with relative precision the relative movement of the blade and counter blade. The screw 180 is driven by a motor 186. The rotation of the screw 180 in one direction allows move the corner 181 in one direction (for example from left to right in Figure 1); the rotation of the shaft 180 in the other direction makes it possible to move the corner 181 in the other direction. Given the direction of assembly of corner 181, a displacement of corner 181 from left to right in FIG. 1 will increase the distance between the movable blade holder 14 and the reference surface 17, therefore decrease the distance between the movable blade holder 14 and the fixed blade holder 13, therefore reduce the distance between the blades 161 and 162. The looping of the forces involved passes through the frame 11, dimensioned accordingly. Return springs (not shown) ensure that the fixed blade 13 and movable blade 14 deviate from each other when the corner 181 is moved from right to left in FIG. 1.

In this variant, the blade 162 and counter blade 161 are similar and have a profile symmetrical with respect to their large dimension. Appropriate surface treatment allows give said range 165 a suitable hardness. For example, carbide tipped blades tungsten having undergone a surface treatment based on titanium nitride and bisulphide molybdenum have adequate strength and sliding (coefficient of friction), associated with lubrication.

Hoses 19 make it possible to spray a lubricant, for example machining oil, to cover the faces of the sheet just in front of the hole. We can use for example an oil strongly additive in chlorine.

A clamp 15, with a self-tightening jaw, is arranged in parallel with the jaw 16. This clamp includes clamping wedges 151 of trapezoidal section interposed between the object to be clamped (here the sheet 2) and support surfaces 150 inclined so as to converge on the side of the jaw 16. The clamp 15 makes it possible to grip sheet 2 firmly by one of its ends. The clamp must of course be able to close to grip sheet 2 correctly and open to drop sheet 2. The necessary constructive details will be easily drawn by the skilled person and will not appear not on the drawing so as not to overload it unnecessarily. A traction mechanism (not shown) allows to move away (or to move closer to make the sheet reverse from two passes) the clamp 15 of the jaw 16, clamp and jaw remaining constantly parallel, the movement of the clamp intervening in a plane perpendicular to the plane in which the movement develops blades and counter blade 161 and 162 of the jaw 16. Alternatively, a pliers can be used hydraulic tightening.

The device also comprises means for stopping the movement of the movable blade 162 towards the counter blade 161 so as to leave a clearance of predetermined value between the blade and the counter blade as a function of the pitch considered and of the means for controlling the displacement by pitch of the sheet and the displacement of the movable blade 162 towards the counter blade 161 in successive and alternating sequences, each of the sequences varying said predetermined play value from one step to the next step. In this first variant, this is obtained by judicious control of the motor 186 and of the means of displacement of the clamp 15. In the example of use described, as it is to obtain a rough skew, with flat faces, the variation of the value of the play between blade and against blade is constant for a linear variation of the step value. The sequences are the following: relative approximation of the blade and counter blade 161 and 162 to a first value clearance J, relative spacing of the blade and counter blade 161 and 162, movement of the clamp 15 towards the left (Figures 2 and 4) with a step P, relative approximation of the blade and counter blade 161 and 162 up to a second value of the set J slightly lower than the first, and so on.

Of course, depending on the intended application, the predetermined value of the clearance can vary from one step to the next. according to any law.

A second variant is described below by referring to Figures 5 to 8. We see a blade 261 mounted on the movable plate of the press 26. The counter blade is an anvil 262 which supports the sheet 2 to be machined. Lateral stops 251 limit the descent of the movable plate towards the anvil 262. Said means for controlling the displacement by steps of the sheet metal comprising means for move the anvil laterally with respect to the large dimension of the blade: anvil 262 can slide on the frame 21 of the press, in a direction understood substantially perpendicular to the plane described by the moving blade 261. The range 265 of the blade 261, coming into contact with the sheet 2, is of very small width (FIGS. 6 and 7) and of length corresponding to the width of the sheet to machine (Figure 5). The anvil 262 is driven by a motor 264 acting on a screw 263. The anvil forms or supports a wedge wedge with angle β, said angle β being identical to the angle of bias that we want to give to the sheet 2. The value of the angle β is exaggerated on the drawings, to better highlight this characteristic of the invention.

To machine the sheet, the anvil 262 is, at each step, when the blade 261 is raised, moved transversely to the blade 261 (from right to left in Figures 6 to 8). We start from the end of the sheet to which we want to give the minimum thickness (left side in Figures 6 to 8). The sheet is crushed between the blade 261 and the anvil 262 by lowering the blade 261 until the press meets the stops 251. Gradually, the blade 261 is raised, having each time advanced the sheet of a pitch P slightly less than the width W of the bearing surface 265 of the blade 261, then repeat the crash. In this variant, the trace of successive steps on the surface of the sheet is more dimmed than in the previous variant, because the descent of the blade 161 is stopped each time at the same level, the bias coming from the inclination β of the receiving surface of the sheet 2 on the anvil 262 with respect to the guide surface 210 of the anvil 262 on the frame 21. With each step, the crush varies in importance, for example it gradually decreases when the anvil moves from right to left in Figures 6, 7 and 8.

We have found that, as with many other machining techniques, we obtain the best results if, during a pass, the rate of deformation of the sheet does not exceed certain limits. It depends on the nature of the material. Also take into account the angle of bias and the length machined. In fact, taking into account the fact that the total volume of material is preserved, the parameter to take into account is the quantity of material displaced by machining. The more there are, the bigger will be the number of passes required. From one pass to another, the crushing continues. So, for example, for ductile stainless steel, if one wishes to achieve a bias angle reaching the order of size of 0.1 °, and for a machined length of the order of 10 centimeters, it is preferable to work in at least two successive passes. So, with each pass, we implement a law targeting different thickness values.

The invention allows machining without thermal input. The invention allows machining while having constant deformation rates throughout the worked section. The resulting benefit is the absence or at least the very low impact of parasitic deformations, hence no or very little warping of the sheet after machining.

The proposed machining process fits easily into a more complex installation manufacturing drafts according to a particular application. For example, we start with a metal strip continuous whose width and thickness are chosen according to the width and thickness maximum of the blank bias to manufacture. The strip, for example packaged in the form of coil, is cut into pieces which feed a machining device as described. Yes several passes are required, then the anvil includes a means for adjusting the angle β and the anvil backs up between two passes, or two are used one after the other devices in which the angle β of the anvil is different. During successive passes, the faces of the sheet remain flat, their relative inclination increasing.

The deformation machining as proposed allows a great saving of material compared to material removal machining. The type of material depends on the intended application, the process suitable for all sufficiently ductile materials. In particular, the invention finds a particularly interesting application for machining thick steel sheets between 0.5 millimeter and 3 millimeters.

As mentioned above, the invention advantageously applies to the manufacture of a type of tire tread mold. If we refer to the description of a mold for tire given in patent application EP 0 569 909, it can be seen that said mold is consisting of the stacking in the circumferential direction of a large number of elements, the section, seen in a plane perpendicular to the axis of the mold, is preferably trapezoidal. The invention provides a method which makes it possible to obtain a blank suitable for cutting said blanks. elements. Said elements are then cut to the desired profile so that, on the side of the most thin, part of the wafer is a molding zone of a corresponding wafer of the tread, and so that outside of said molding zone, the additional wafer in the part cited above cooperates with members controlling the opening movements and closing the mold.

The steel thus machined is stainless steel, due to the use of the blanks in a mold for tire. From a continuous strip, blanks are mass produced by applying the process described above, then we chain the production by cutting, according to the desired profile, as and as one or more elements in each blank, and stacking as and when said elements to constitute said mold.

More precisely, from the mathematical definition of the surface of the tread as the tire designer designed it, and from the choice of the number of elements that will include the crown ensuring the molding of said tread, the dimensions of the blank 3. We see in Figure 9 that it is a trapezoid, seen in perpendicular section to the axis of rotation of the tire (see face 30), the width L of the blank being sufficient to cut here a single element such as 31. A starting metal strip is chosen according to the width L and the maximum thickness of the trapezoid. In this draft, each of the elements 31 is then cut using preferably cutting means slaved to the profile 32 of the strip bearing to be molded. Of course, the cutting of the profile 32 will typically be different for each of the elements 31, according to the shape of the sculpture of the tread to be molded. The invention lends itself perfectly well to computer-aided manufacturing. From computer files containing the definition of the sculpture, you can order a cutting cutting of preforms, for example a laser cutting machine. The invention allows therefore the production of molds of the type described in patent application EP 0 569 909 according to a very direct method.

Claims (10)

1. A process of machining by deformation a sheet (2) which is intended to modify the thickness between the opposing faces of said sheet (2), comprising the following stages:

   compressing the sheet (2) by pressing on one of its faces a substantially elongate tool bearing surface (165, 162) having a small dimension and a large dimension, said sheet (2) being supported on its other face by an element having a bearing support surface (165, 161) which is at least substantially equivalent and placed opposite said tool bearing surface (165, 162), the large dimension of said tool bearing surface (165, 162) being greater than the width of the sheet (2) to be machined, compression being stopped when the clearance remaining between said tool bearing surface (165, 162) and said support surface (165, 161) reaches a predetermined value;

   separating said bearing surface (165, 162) from the face of the sheet (2);

   moving said sheet (2) transversely in relation to the orientation of said bearing surface (165) by a step of predetermined value, the process being characterised by the fact that the foregoing stages are repeated while varying said predetermined value of clearance from one step to the following step until said sheet (2) has had imparted to it a section of predetermined size variable depending on the location of the section in question.
2. A process according to Claim 1, characterised in that the variation of the value of the clearance is constant for a linear variation of the value of the step.
3. A process according to one of Claims 1 or 2, characterised in that the value of said step is less than the small dimension of said bearing surface.
4. A process according to one of Claims 1 to 3, characterised in that the machining entails several successive passes so as to continue the compression on each pass.
5. A process for manufacturing a tyre tread mould, said mould being formed by circumferential stacking of a large number of elements, the section of which, seen in a plane perpendicular to the axis of the mould, is trapezoidal, consisting of fabricating blanks (3) by applying the process according to any one of Claims 1 to 4, and cutting one or more elements (31) in each blank (3) to the desired profile (32) so that, on the side of lesser thickness, a part of the section will be a moulding zone of a corresponding section of the tread, and so that outside said moulding zone the section will cooperate with devices controlling the mould opening and closing movements.
6. A device for machining of a sheet (2) which is intended to control the thickness between the opposing faces of said sheet, comprising:

   a press (16, 26) comprising a substantially elongate moving plate (162, 261) having a bearing surface (265) with a large dimension and a small dimension;

   a counter-plate (161, 262) and means for relatively moving the moving plate towards the counter-plate;

   means for locking the sheet (2) relative to the counter-plate (161, 262);

   means for moving the sheet (2) in successive steps, laterally relative to the large dimension of the plate;

   means for limiting the movement of the plate (162, 261) towards the counter-plate (161, 262), so as to leave between the plate and the counter-plate a clearance of predetermined value according to the step in question;

   the device being characterised by the fact that it comprises

   means for controlling the stepped movement of the sheet (2) and the movement of the plate (162, 261) towards the counter-plate (161, 262) in successive, alternating sequences, each of which sequences varying said predetermined value of clearance from one step to the following step.
7. A device according to Claim 6, in which the plate (162, 261), seen in section perpendicular to its large dimension, has a symmetrical profile.
8. A device according to Claim 6 or 7, characterised in that the plate (162, 261) and the counter-plate (161, 262) are similar, the device comprising a clamp (15) for grasping the sheet (2), said means for controlling the stepped movement of the sheet (2) comprising means for moving said clamp (15) relative to said plates.
9. A device according to Claim 6 or 7, characterised in that the counter-plate is an anvil (262) and said means for controlling the stepped displacement of the sheet (2) comprising means for moving the anvil (262) laterally relative to the large dimension of the plate.
10. A device according to one of Claims 6 to 9, characterised in that it comprises means (19) for dispensing a lubricating fluid opposite the plate.

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