GB2176720A

GB2176720A - Manufacturing a punching or cutting tools and tools thus obtained

Info

Publication number: GB2176720A
Application number: GB08610411A
Authority: GB
Inventors: Pierre-Claude Jaquier
Original assignee: Bobst SA
Current assignee: Bobst Mex SA
Priority date: 1985-06-19
Filing date: 1986-04-29
Publication date: 1987-01-07
Also published as: GB2176720B; FR2583669A1; GB8610411D0; ES556295A0; DE3619765A1; DE3619765C2; ES296527U; JPS61293730A; CA1267074A; SE8602711L; CH666219A5; ES296527Y; SE8602711D0; ES8800094A1

Abstract

A punching tool (6) is made by depositing, e.g. by means of ultra-fine spraying, a bead of material onto the side surface of a metal cylinder (7) in accordance with an arrangement forming a meshed network of punching fillets (10) and pressing fillets (11). The bead of material is then machined e.g. by means of electroerosion using a flat graphite electrode, the remainder of the side surface of the cylinder being excluded. The method can be used for manufacturing tools used in the field of rotary punching of paper and cardboard. <IMAGE>

Description

SPECIFICATION Method of Manufacturing a Punching or Cutting Tools and Tools Thus Obtained The present invention relates to punching or cutting tools. The invention is particularly applicable to the manufacture of rotary punching dies for material in sheet form or strip form and to dies thus obtained.

The kind of rotary punching die in question generally comprises two cylinders, i.e. a male cylinder, which represents the punching tool, and a female cylinder, which represents the counter-cylinder or die block. The punching tool is mounted on top of the counter-cylinder or block, and the material to be cut, for example paper or cardboard, passes between these tools in the manner of a sheet of metal in a rolling mill, for example. The theoretical longitudinal axis of each tool is located in the same vertical plane.

The punching tool is made from a metal cylinder in the side surface of which a network of cutting and pressing fillets are machined. The developed pattern of the side surface of the cylinder represents the arrangement of the objects to be cut.

As for the side surface of the counter-cylinder, it has a network of grooves, the arrangement of which matches the arrangement of only the pressing fillets of the punching tool. In some cases, the counter-cylinder may be smooth and it is then preferably referred to as a "block".

Such a die may be manufactured in several ways, e.g. the network of fillets or grooves may be obtained either by means of milling or by means of electroerosion. The milling machines or electroerosion machines used are numerically controlled machines which allow operations to be performed precisely and automatically. Most frequently, the dies are obtained by means of electroerosion using, for example, a graphite electrode which is precut depending on the punching operation to be performed. U.S. Patent No.

3,796,851 describes a device of this type.

It should be noted that, as regards the manufacture of this kind of die, the counter-cylinder is always easier to machine, since it is merely required to form grooves in the side surface of the cylinder. The machining time is therefore relatively short and this operation does not even have to be performed by means of electroerosion, milling alone being sufficient. The same does not apply to the punching tool which, itself, must be provided with fillets and not grooves. This means that a large volume of material must be removed from the side surface of the cylinder. In addition to the considerable time required for milling, it is also necessary to take into account certain problems relating to the fact that the milling cutter has a certain diameter and the angles at the fillet intersections will not be perfect and must be adjusted.The solution which is therefore chosen is that of electroerosion. The problem of the angles at the fillet intersections is resolved, but the machining time still remains considerable. On the other hand, when using either one of the abovementioned methods, the user remains dependent, as regards the mechanical characteristics of the fillets, on the properties of the material used to manufacture the body of the punching tool, i.e. the cylinder.

An object of the present invention is to overcome these drawbacks by using a method which enables the time required for machining a punching tool to be reduced considerably, while making it possible to modify the mechanical characteristics of the machined fillets.

According to the present invention there is provided a method of manufacturing a punching or cutting tool wherein a bead of material is deposited on the surface of a cylinder, said bead of material being deposited in accordance with an arrangement representing a meshed network, each mesh of which corresponds to the shape of an object to be cut or punched, and wherein said bead of material is then machined, the remainder of the surface of the said metal cylinder being excluded.

The invention will be described now by way of example only with particular reference to the accompanying drawings. In the drawings: Figure lisa partial sectional view of a first punching tool.

Figure 2 is a partial sectional view of a second punching tool.

Figure 3 is a sectional view of a punching fillet.

Figure 4 is a sectional view of a pressing fillet.

Figure 5 is a perspective view of a punching tool.

Figure 6 is a plan view of a box cut-out.

Figure 7 is a view of the developed side surface of a punching tool.

Figure lisa partial sectional view of a first punching tool, more precisely a punching tool 3 machined by means of a electroerosion from a metal cylinder 1, only part of which is shown in this Figure. The punching tool 6, as shown in Fiugre 5, has on its side surface a multiplicity of fillets 2 which may be cutting fillets or pressing or creasing fillets. These fillets 2 are arranged in the form of a network so as to make up several meshes each representing the cut-out shape of a box 5 or any other object to be punched (see Figure 6).

In Figure 1, in order to simplify the drawing, only a cutting fillet 2 has been shown. To obtain a punching tool 3 at the end of machining, all the material 4 located in the vicinity of the fillets 2 must be eroded.

The volume V of material which must be removed by means of electroerosion or milling is calculated with the aid of the following formula: V=VringVd Vr in which Vying is the total volume of material represented by the ring from which the fillets are machined, Vd is the total volume of material represented by the cutting fillets and V, is the total volume of material represented by the creasing fillets.

The formula which allows the volumeVring to be calculated is expressed as follows: n Vr1ng=L. [d2-(d-2h)2] 4 in which L is the length of the cylinder, d is the external diameter of the cylinder and h is the height of the fillets. For the configuration shown in Figure 7, the total volume of material represented by the cutting fillets Vd is calculated as follows.

Vd=Sd. Ld In this expression, 5d corresponds to the cross-section of a punching fillet 10 (see Figure 3) and Ld corresponds to the total length of the punching fillets (see Figures 6 and 7).

Figure 6 shows a plan view of the cut-out shape of a box 5 or of an object to be punched, which appears on the side surface of the tool, making up three boxes along the length L of the cylinder and four boxes along its developed edge or circumference (see Figure 7), and which allows us to define the term Ld in the above formula, i.e. a total of twelve boxes in the example chosen.

Ld=12[2. (2A+2B+P)+2. (H+2B)+6Bj -9. (2A+2B)-8H Total cutting length Common cutting length This formula can be simplified as follows: Ld=30. (A+5B)+8. (3P+2H) The term Sd, i.e. the cross-section of the punching fillet (see Figure 3), is calculated using the following formula: TD+PD Sd= .HD 2 The final expression of the formula for calculating the total volume of the cutting fillets will therefore be: TD+PD vd= . Hid). [30 . (A+B)+8 . (3P+2H)] 2 The total volume of material represented by the pressing fillets (V,), for the example chosen, will be defined by the following expression: V,=S,. L, in which S, represents the cross-section of a pressing fillet and L, represents the total length of the pressing fillets.

The cross-section Sr of the pressing fillet 11 (see Figure 4) is calculated by means of the formula: TR+PR S,= . HR 2 Referring again to Figure 6, the total length L, of the pressing fillets will be defined by the following expression: L,=12. [2. (2A+2B)+4H] which can be simplified as follows: L,=48(A+B+H) The total volume Vr will therefore be expressed as: Th+P" V,=( .HR) . 48(A+B+H) 2 These expansions allow us to express the formula necessary for calculating the total volume V of material to be removed, i.e.: TD+ PD L[d2-(d-2h)2j-[( ). HD] . [30 . (A+5B)+8(3P+2H)] 4 2 TR+PR [() . H,] . [48 . (A+B+H)I 2 In the example chosen, we have expressed numerically the values of the different parameters so as to be able, consequently, to make a quantative comparison as regards the volumes of material to be eroded under different machining conditions.

The values considered are as follows: d=301.76 mm P,=1.538 mm h= 1 mm A=116.5mm L=1000 mm B=42 mm Th=0.03mm H=153 mm PD=0.858 mm P=13 mm TR=0.71 mm According to the formula, the total volume V to be eroded will therefore be 922,487 mm3, i.e. about 1 dm3.

Figure 2 is a partial sectional view of a second punching tool 6 made from a metal cylinder 7 which has a diameter d1 and on the side surface of which there is deposited, in a single operation, using a known method of material deposition, a bead of metallic material 8 possessing mechanical characteristics which are different from the characteristics of the cylinder 7 and which can be chosen in accordance with the type of operation performed by the punching tool 6. The material 8 may advantageously be a finely sprayed alloy sold under the name "Eu Tro Loy" by the company CASTOLI N and in the form of a deposition made by means of the 'Eu Tronic GAP" method developed by the same company. This material 8 is deposited so as to cover all the areas which are to form a punching fillet 9 or pressing fillet, according to the pattern shown in Figure 7.The cross-section of this deposited material 8 has the approximate shape of a segment of a circle having a radius R and angle a over a rise f. Since the diameter d1 is relatively large compared to the radius R, it can be assumed that the chord "a" of the circle segment will be more or less a straight line, so as to simplify calculation of the total volume V1 of material deposited. The dimensions which can be measured after deposition of the material 8 will be the distance "a" corresponding to the chord of the circle segment and the distance "f" corresponding to its rising height.It is thus possible to calculate the area of the segment Smat using the following formula: a (R-f) . a Smat=llR2 t - 360 2 in which R is the radius of the fictitious circle inside which the segment of material 8 is inscribed, "f" is the measured rise and "a" the measured chord, a being the angle of the circle segment.The radius R is calculated as follows: a2 f R= + 8f 2 the angle a in degrees being obtained by the formula: a =2 . sin-' . a/2R The total volume Vmatto be added depends on the length of the cutting and pressing fillets already defined above and is expressed by the formula: Vmat=Smat. (Ld+L,), or, ao (R-f) . a Vmat=[TR2. ] . [30. (A+5B)+8. (3P+2H)+48(A+B+H)] 360" 2 The numerical values given in this example to the different factors are: a=6 mm f=2 mm This will mean that, using the appropriate formulae, R will be 3.25 mm and a 134.76 .

The total volume Vmat of material to be deposited will therefore be 238,485 mm3.

In order to make the punching tool 6, it is still required to cut the bead of deposited material in accordance with the fillets to be provided.

During this operation, therefore, the quantity of material Ver will be eroded, this quantity being calculated by means of the formula: Ver=VmatVr Vd V, and Vd having already been calculated in the first example cited above. The value assumed by Ver will therefore be 238,485-1 6,806-5,574=216,105 mm3.

The figures show that, for a same punching tool, the second solution described above requires the removal of a small, amount of material compared to the first solution. If only the machining times of the two examples are taken into account and knowing that the erosion times are proportional to the volume of material to be removed, we are able to state the following ratio ri: Vie,.100 216,105.100 n= = =23.43% V 922,487 ri being the ratio between the two volumes to be eroded, the gain in the machining time G will be expressed thus: G=100-rl=100-23.43=76.57% It is obvious that such a large gain in time will have an appreciable effect on the cost of the manufactured die.The cross-section of a punching fillet 10 such as that shown in Figure 3 has a trapezoidal shape. The reference PD relates to the large base of the trapezium, TD relates to the small base and HD relates to the height. Figure 4 shows a pressing fillet 11 which also has a trapezoidal shape and where the dimension PR is the large base of the trapezium, TR is the small base and HR is the height.

Figure 5 is a perspective view of a punching tool 3. This figure shows the general appearance of such a tool and serves, in particular, to define the dimensions Land d which are the length of the tool and its diameter, respectively, (see also Figures 1 and 2).

Figure 6 is a plan view of a box cut-out 5, the externai edges of which, shown as continuous lines, correspond to the punching fillets 10 and the internal folds of which, shown as broken lines, correspond to the pressing fillets 11. The dimensions A, B and H represent, respectively, the width, thickness and height of the box to be made, while the dimension Prelates to the width of the sticking flap of this box.

Figure 7 is a view of the developed side surface of a punching tool 6. The length, which is shown in dot-dash lines, corresponds to the length of the cylinder from which the punching tool is machined, while the dimension C relates to its circumference. This is also the configuration which the first graphite electrode used for the tool pattern will have. In this Figure, the punching fillets 10 are represented by continuous lines and the pressing fillets 11 by broken lines. As can be seen, a certain number of punching fillets 10 are common to a same box cut-out 5 and this has been taken into consideration in the preceding calculations for determining the total length of the fillets.

The punching tool 6 obtained using this method has several advantages, such as its low manufacturing cost compared to a tool machined in the conventional manner and the special feature which allows the physical characteristics of the material of the fillets to be chosen in accordance with the punching operations to be performed. The user will thus possess a punching tool which is inexpensive and suited to the long-term requirements which he has, depending on the materials which must be punched.

Claims

1. A method of manufacturing a punching or cutting tool wherein a bead of material is deposited on the surface of a cylinder, said bead of material being deposited in accordance with an arrangement representing a meshed network, each mesh of which corresponds to the shape of an object to be cut or punched, and wherein said bead of material is then machined, the remainder of the surface of the said metal cylinder being excluded.

2. A method according to Claim 1, wherein the material is deposited in a single operation, by means of ultra-fine spraying, and said material is then machined, by means of electroerosion, using a flat graphite electrode.

3. A method as claimed in Claim 1 or Claim 2 wherein the tool is a rotary punching die for material in sheet form or strip form.

4. A punching tool obtained using a method according to any preceding claim, wherein during a first manufacturing stage, it is in the form of a metal cylinder, the curved surface of which is provided with a meshed network of beads of material having a cross-section similar to that of a segment of a circle.

5. A punching tool according to Claim 4, wherein during a second manufacturing stage, it is in the form of a metal cylinder, the curved surface of which has punching fillets and pressing or creasing fillets machined from the said bead of material.

6. A punching tool according to Claim 4, wherein the mechanical characteristics of the bead of material are different from the mechanical characteristics of the metal cylinder.

7. A punching tool according to Claim 6, wherein said bead of material comprises a metal alloy deposited by means of ultra-fine spraying.

8. A method of manufacturing a punching or cutting tool substantially as hereinbefore described.

9. A punching or cutting tool substantially as hereinbefore described with reference to and as shown in the accompanying drawings.