WO2013167232A1

WO2013167232A1 - Method and device for cutting a workpiece

Info

Publication number: WO2013167232A1
Application number: PCT/EP2013/001146
Authority: WO
Inventors: Wolfram Volk; Peter DEMMEL
Original assignee: Technische Universität München
Priority date: 2012-05-10
Filing date: 2013-04-18
Publication date: 2013-11-14
Also published as: DE102012011767A1

Abstract

Disclosed is a method for cutting a workpiece (2) and a device (22) suitable therefor. In the method, a notch geometry (12), which terminates in the workpiece (2), is introduced into the workpiece (2) to be cut at least at one side along a separation line (10) causing plastic deformation, and the workpiece (2) is cut by shearing along the separation line (10). A burr-free cut or separation surface can thus be immediately produced.

Description

description

METHOD AND DEVICE FOR DIVIDING A WORKPIECE

The invention relates to a method for cutting a workpiece and to a device arranged for cutting a workpiece. In this case, the invention is particularly concerned with the desire for a burr-free cutting of workpieces, so that necessary processing steps for burr removal can be avoided.

A cutting of a workpiece according to DIN 8588 is understood to mean a mechanical separation of a workpiece without the formation of shapeless material, that is to say, in particular, without chips. The most commonly used in industry for cutting a workpiece is the so-called shear cutting, the workpiece is divided between two moving blades that move past each other while maintaining a defined cutting gap. In particular, shear cutting is one of the most commonly used separation processes in sheet metal working. When shearing, which is also referred to as normal cutting, the material is deformed by the two penetrating cutting until its formability is exhausted and the material is lost through breakage.

Due to the material deformation during the shear cutting process, there is a characteristic formation of the cutting surface on the workpiece.

Due to the process, shear-cut workpieces have a tendency to cut or fracture surface and always a burr. However, such a burr is usually undesirable on the workpiece. Thus, loosening or chipped burrs can cause workpieces to malfunction. For example, this can result in short circuits in electrical and electronic components. Furthermore, in the case of downstream coating processes, the wetting thickness decreases in the area of burr formation. This can for example lead to a reduced corrosion protection of the finished workpiece. In general, burrs on the workpiece are adjusted during manual further processing or during assembly

CONFIRMATION COPY In addition, a burr on the workpiece can lead to a reduced positioning accuracy when positioning the workpiece or when mounting in an assembly. In addition, burrs on the workpiece in subsequent manufacturing steps can also lead to damage or increased wear on the tools.

Very often, therefore, burrs on the parted workpiece must be removed by additional post-processing steps or at least reduced in size. This leads to increased workpiece costs and overall to a reduction in cost-effectiveness.

In particular, in the metal and electrical industry, there is a desire for a flashless production of workpieces, since without post-processing steps to remove the burr worse corrosion protection at the cut surfaces or the risk of short circuit exists. In addition, the problems of increased tool wear due to a burr formation, especially when trimming of structural components made of soft sheet materials, as they are often used in particular in the automotive sector. The burr formation and thus the effort for a post-processing are greatest for soft materials. In the electrical industry in particular electrical connectors must meet high quality standards due to their field of application. Post-processing processes for burr removal are often unavoidable.

As a burr-free method for cutting a workpiece so far only the so-called counter-cutting is known. Reference is made, for example, to DE 393 13 320 C1. The counter cutting comprises at least two counter-rotating cutting stages. The workpiece is first cut on and then cut in opposite directions. However, counter-cutting has not become established industrially, since a triple-acting press is required for this process. In addition to the cutting force, an opposite counterforce and a hold-down force must always be applied. According to DE 393 13 320 C1 The opposite cutting and cutting is achieved by a complex press with a ram stroke.

According to VDI guideline 2906, page 6: Cut surface quality at

Cutting, trimming and punching of metal workpieces: counter-cutting, Verein Deutscher Ingenieure, 1994, the resulting cutting surfaces during counter cutting also have two edge indentations on the upper and lower edge of the workpiece, as well as two smooth-cut zones, due to the cutting in opposite directions which are usually separated in the middle by a rupture zone. This is also evident from DE 39 31 320 C1. These stepped cut surfaces can again lead to problems in painting due to sharp transitions between the smooth cut portion and the fracture surface.

The object of the invention is therefore to provide an alternative method for cutting a workpiece, wherein the fracture or cut surface after the cutting is as free of burrs as possible. Another object of the invention is to provide a device with which a workpiece can be cut as free of burrs as possible.

According to the invention, the first object is achieved by a method for cutting a workpiece, wherein a notch geometry ending in the workpiece is introduced into the workpiece to be cut along a parting line with plastic deformation at least on one side and the workpiece is sheared along the parting line.

In a first step, the invention proceeds from the consideration of producing a predetermined breaking point in the workpiece by a targeted introduction of a material deformation, which results in a burr-free cutting or fracture surface in a subsequent cutting of the workpiece. It has been found that a suitable material deformation can be generated by introducing a notch geometry, wherein the material of the workpiece is plastically deformed. By introducing a notch geometry under plastic deformation of the material, the structure of a particularly ductile material in the compressed or stretched, which leads to a local work hardening in the material. In the area of the notch impression, the hardness of the material thus increases, in particular in the case of metallic materials.

In a second step, the invention recognizes that a burr-free cut or fracture surface can be produced by dividing the material in the region of the microstructure change effected by the notch impression. This is achieved by cutting the workpiece in the region of the local pre-deformation. In this case, the cutting edge of a cutting tool penetrates into the area pre-deformed by the notch impression. It can not come to a burr formation, since in the last separation phase due to the introduced notch indentation of the material can not take place in the cutting tool.

By localizing the shear cutting process also small dimensional tolerances can be achieved. In addition, due to the targeted local pre-deformation and in particular the resulting increased hardness in the material during shearing, a directed crack propagation occurs at the location of the notch impression. The latter leads to a nearly vertical cutting or fracture surface, which can be a great advantage in a further processing of the divided workpiece by joining.

Furthermore, stress peaks occur in the material at the bottom of the notch geometry during the shearing process. Due to the locally increased stresses an early break in the material is initiated, whereby the cutting force maximum is reduced. A reduction of the cutting force maximum leads to a reduction of the wear of the active elements and to a lower machine load. The invention also offers an advantage in the division of high and very high-strength workpieces, as they must be increasingly processed due to the increased requirements in the field of lightweight construction.

The specified method is particularly suitable for cutting metallic sheet metal parts. In principle, however, other materials, for example a ductile polymer, can also be made free from burrs and chips by the stated method be parted. Due to the introduced notch geometry, the cutting force required for cutting during shear cutting is reduced even with hard and brittle materials. The method is thus also suitable for cutting a fiber-reinforced plastic or ceramic.

For the purposes of the invention, the term notch geometry is not necessarily understood to mean only the shape of a notch in the actual sense, which is often described as a wedge shape. Such a wedge or actual notch shape is generally advantageous for generating a predetermined breaking point in conjunction with resulting voltage peaks. However, it may also be advantageous in individual cases to generate the local deformation on the workpiece with a soft or rather round, not directly wedge-shaped notch geometry. The advantage of this is a lower wear of the deformation tool under the assumption that the voltage increase does not occur to the same extent as in a wedge-shaped notch geometry with sharp radii. Since the actual notch or wedge shape is thus not immediately essential to the invention, the described forms of local deformation are summarized under the term of a notch geometry.

When introducing the plastic deformation in the form of a notch geometry as well as in the following dicing process, the workpiece can basically be in a warm, semi-warm or cold state.

In a preferred embodiment, the workpiece for introducing the notch geometry is moved with a holding-down device against a notching tool and the workpiece for this purpose rectified sheared with a first cutting tool against a second cutting tool. By the rectified movement of both steps, the required pressing tool can be further simplified. In addition, the Zerteilprozess the workpiece is thereby significantly shortened, which increases the production throughput considerably.

In an advantageous embodiment, the notch geometry is introduced by a bite or knife cutting. The kerf geometry along the dividing line introduced by means of a wedge-shaped cutting edge in the workpiece. For the purposes of the invention, however, this is not a dicing method in accordance with the DIN 8588 standard, since in the present case the notch geometry in the component ends and the workpiece is not divided by the introduction of the notch geometry. Rather, it is therefore an incomplete dicing process that results in separation of the workpiece only in combination with another dicing process.

The invention is not limited to the fact that the notch geometry is introduced on one side into the workpiece. Rather, the notch geometry along the dividing line can also be introduced into the workpiece on both sides. In this case, the two notch geometries are introduced in such a way that a material connection remains in the workpiece between the notch geometries. Also, the two-sided introduction of a notch geometry, the workpiece is not completely divided. Preferably, the two-sided notch geometry with wedge cutters in the manner of the so-called Teissschneidens according to the standard DIN 8588 introduced. In the present case, this is an incomplete bite-cutting because the workpiece is not broken after the notch geometries have been introduced.

The process steps of introducing a kerf geometry ending in the component and shearing cutting can be carried out both in two separate working steps and combined in a common working step. From a procedural economic point of view, the introduction of the notch geometry in a joint step with the shear cutting is to be preferred. In this case, for example, penetrates a notching tool against a hold-down in the workpiece while a cutting tool is moved against the notching tool, the notching tool acts as a second cutting tool of the shear cutting.

In a preferred embodiment, the component to be divided is deformed by a forming process, in particular by deep drawing. The dividing line for dividing the workpiece is provided in particular in an edge region of the workpiece, so that the edges are cut off or separated outside the shaping. Particularly advantageous is the introduction of the notch geometry in one step with the Umformverfahreri. For this purpose, for example, a shaping die or a punch forming the workpiece in the die at the same time be configured as a notching tool, so that in particular during deep drawing along the desired parting line, for example at the edge of the die, the corresponding notch geometry is introduced into the workpiece.

In a further preferred embodiment, the workpiece is sheared in one step with the forming process. In this case, the introduction of the notch geometry can take place before or during the forming process. The latter embodiment is made possible in particular by the fact that, for example, the notching tool is at the same time designed as a cutting tool for the shear cutting. In a particularly preferred embodiment, the deep-drawing and the cutting of the workpiece thus take place in a single combined operation. A separate machining process for separating edges of the formed by deep drawing workpiece can thus be completely eliminated. The formed by deep drawing workpiece is generated directly burr-free and freed from its edges.

Our own investigations have further shown that to achieve burr-free and as vertical as possible cutting or fracture surfaces on the workpiece, the depth of the impression of the notch geometry should be selected in the material of the workpiece to be divided depending on its ductility. For a soft deep-drawing steel, the notch geometry, for example, should preferably be introduced at least to a depth of 10%, based on the thickness of the workpiece, at least to a depth of 10%. The specified method is particularly suitable for cutting workpieces having a thickness between 0.3 mm and 3 mm. The method is also suitable for cutting workpieces with thicknesses over 10 mm. In general, the method is not limited to a specific workpiece thickness. The second object is achieved according to the invention by a device for dividing a workpiece, which comprises a first and a second cutting tool, which are movable relative to each other with the interposition of the workpiece, a blank holder and a movable against the workpiece notching tool. In this case, the notching tool for introducing a kerf geometry ending in the workpiece along a parting line and the cutting tools for shearing the workpiece along the parting line are arranged.

The notching tool has, for example, a wedge or knife edge formed in accordance with the desired parting line, which can be introduced into the workpiece under plastic deformation of the material. The wedge cutting edge or another active element for introducing the notch geometry can be made, for example, from a hardened steel.

Advantageously, the device is adapted to move the workpiece for introducing the notch geometry with the hold-down device against the notch tool and the same time scissors cut the workpiece with the first cutting tool against the second cutting tool. As a result, the device can be made simpler and cheaper and the dicing process can be carried out more quickly.

The notching tool preferably comprises a first wedge cutting edge and a second wedge cutting edge, which are movable relative to one another and arranged to incomplete cutting teeth. This makes it possible to introduce a notch geometry on both sides along the dividing line into the workpiece.

In an advantageous embodiment of the device comprises a die and a punch, and wherein the die and / or the punch is additionally designed as a notching tool / are. In other words, the device is designed as a deep-drawing tool with a shaping die and a punch for molding the workpiece into the die. In this case, the die and / or the punch are at the same time designed to introduce the notch geometry into the workpiece to be treated. During deep drawing, the notching tool penetrates the die or on the stamp at the same time in the workpiece, so that the desired notch geometry in the workpiece in one step with the deep drawing takes place.

Further advantageous is / are the die and / or the stamp additionally as

Cutting tool formed. As a result, it can be achieved that the workpiece can be processed in one step with a forming process, such as thermoforming, is parted. Particularly advantageously, the die and / or the punch are designed both as a notching tool and as a cutting tool. In a one-step work step, the workpiece can thus be cut both shaped and burr-free. In particular, the notching tool is designed as a second cutting tool against which the first cutting tool is guided during shear cutting.

Vorteihafterweise the device comprises a control device for actuating the movable tools, which is arranged to perform the division of the workpiece according to the method described above.

Embodiments of the invention will be explained in more detail with reference to a drawing. Showing:

1 shows schematically the cutting of a workpiece by notching and shearing in a two-stage two-sided process,

Fig. 2: schematically dividing a workpiece by notching and shear cutting in a two-stage unilateral process and

3 shows schematically the cutting of a workpiece by notching and shear cutting in a single-stage one-sided process.

In Fig. 1, the cutting of a workpiece 2 by notching and shearing is shown schematically in a two-stage two-sided process. The process is divided into a total of four phases, wherein the phases a) and b) are assigned to the method step of introducing a notch geometry and the phases c) and d) to the method step of shearing.

In phase a), a sheet-like workpiece 2 is introduced between a first notch part 4 and a second notch part 5. The two notching parts 4, 5 comprehensive notching tool 6 is this purpose in an open state. The two notch parts 4, 5 each comprise a cutting edge 7 for introducing a notch geometry 12. The work piece 2 is positioned in the notching tool 6 such that the desired parting line 10 at which the work piece 2 is to be cut is arranged between the cutters 7.

In phase b) the notch part 4 is moved with the interposition of the workpiece 2 against the notch part 5. Under an embossing force, the cutting edges 7 penetrate into the material of the workpiece 2 on both sides, forming the respective notch geometry 12. In this case, the material of the workpiece 2 is locally plastically deformed. The blades 7 are dimensioned so that after completion of the phase b) between the resulting notch geometries 12 a material connection 13 remains. The workpiece 2 is not divided. The notch introduction according to phases a) and b) corresponds to an incomplete Teissschneiden.

In the next step, the workpiece 2 is sheared along the introduced notch geometries 12. For this purpose, the workpiece 2 is pressed in phase c) by means of a blank holder 14 against a die 16. The die 16 may be formed, for example, for shaping the workpiece 2 by deep drawing. In this case, the hold-down 14 may be formed in particular as a stamp 15. Or it is a separate, not marked stamp provided. At the same time a first cutting tool 18 moves against the workpiece 2. The workpiece 2 is positioned so that the dividing line 10 and the introduced Kerbgeometrien 12 between the die 16 and the first cutting tool 18 is arranged. Subsequently, the first cutting tool 18 is moved further against the workpiece 2. In this case, the die 16 also acts as a second cutting tool 19. While maintaining a predetermined cutting gap, the workpiece 2 is sheared by counter-moving the two cutting tools 18, 19 along the parting line 10. The local deformation of the material due to the introduced notch geometries 12 leads to crack formation in the material connection 13. Because of the introduced notch impression 12, the material can not flow to a cutting tool 18, 19 during shear cutting. The result is a burr-free cut or fracture surface, which is aligned approximately perpendicular to the workpiece surface.

FIG. 2 schematically shows the cutting of a workpiece 2 by notching and shearing in a two-stage one-sided method. The sequence is identical to FIG. 1. However, a notch part 4 is omitted. This notch part 4 is replaced by the hold-down 14. In phase b), the holding-down device 14 moves against the notch part 5 of the notching tool 6. The result is a notched geometry 12 introduced on one side into the workpiece 2, which ends in the workpiece 2 and has led to a local plastic deformation of the workpiece 2.

In Fig. 3, the cutting of a workpiece 2 by notching and shear cutting is shown schematically in a one-stage unilateral process. In contrast to FIGS. 1 and 2, the introduction of the notch geometry and the shear cutting take place in one work step. For this purpose, the notch part 5 of the notching train 6 at the same time acts as a die 16, for example, for a deep drawing and as a second cutting tool 19th

In phase a), the workpiece 2 is positioned between a holding-down device 14, a first cutting tool 18 and a notching part 5. In phase b), the hold-down 14 is moved with the interposition of the workpiece 2 against the die 16 and the second cutting tool 19. The cutting edge 7 penetrates under plastic deformation along the parting line 10 on one side into the workpiece 2. At the same time, the first cutting tool 18 moves against the workpiece 2. In phase c), the first cutting tool 18 is moved further against the workpiece 2 or against the die 16 acting as the second cutting tool 19. The workpiece 2 is sheared along the parting line 10 at which the one-sided notch geometry 12 is introduced.

The wedge 7 of the die 16 is shaped so that in phase c) the first cutting tool 18 can be moved against the die 16 under shear cutting of the workpiece 2.

In all three figures, an edge 20 of the workpiece 2 is separated along a parting line 10 from the workpiece. For actuating the tools of a device 22 shown in the figures, a control device 24 is provided according to FIG. 1.

It is further apparent that the specified method can be configured so that only a single-acting press is required to cut the workpiece 2. The active tools are, as indicated by the arrows drawn, moved to divide the workpiece 2 with force only in one direction. In each case, the workpiece 2 for introducing the notch geometry 12 with the hold-down 14 against the notch part 4, 5 of a notching tool 6 is moved and the workpiece 2 with the first cutting tool 18 rectified sheared against the second cutting tool 19.

LIST OF REFERENCE NUMBERS

2 workpiece

4 first notch part

5 second notch part

6 notching tool

7 cutting edge

10 dividing line

12 notch geometry

14 hold downs

16 matrix

18 first cutting tool

19 second cutting tool

20 waste, edge

22 Device for cutting

24 control device

Claims

claims

1. A method for cutting a workpiece (2), wherein introduced into the workpiece to be divided (2) along a parting line (10) under plastic deformation at least one side in the workpiece (2) notch geometry (12) and the workpiece (2) along the dividing line (10) is sheared.

2. The method according to claim 1,

wherein the workpiece (2) for introducing the notch geometry with a hold-down (14) against a notching tool (6) is moved and the workpiece (2) for this purpose rectified with a first cutting tool (18) against a second cutting tool (19) is sheared.

3. The method according to claim 1 or 2,

wherein the notch geometry (12) is introduced by wedge cutting.

4. The method according to any one of the preceding claims,

wherein a notch geometry (12) is introduced on both sides into the workpiece (2) along the parting line (10) in the manner of the bit-cutting, but with a material connection (13) being obtained.

5. The method according to any one of the preceding claims,

wherein the introduction of the notch geometry (12) takes place in one step with the shear cutting.

6. The method according to any one of the preceding claims, wherein the workpiece (2) to be cut is deformed by a forming process, in particular by deep drawing.

7. The method according to claim 6,

wherein the introduction of the notch geometry (12) takes place in one step with the forming process.

8. The method according to claim 6 or 7,

wherein the workpiece (2) is shear-cut in one step with the forming process.

9. The method according to any one of the preceding claims,

wherein a sheet-like workpiece (2) is divided.

10. The method according to any one of the preceding claims,

wherein as a workpiece (2) a metal, a polymer or a fiber-reinforced plastic is divided.

11. Device (22) for dividing a workpiece (2), comprising a first cutting tool (18) and a second cutting tool (19), the interposition of the workpiece (2) are mutually movable, a hold-down (14) and a relative to Workpiece (2) movable notching tool (6), wherein the notching tool (6) for introducing a notch in the workpiece (2) geometry (12) along a parting line (10) and the cutting tools (18, 19) to a shear cutting of the workpiece (2 ) are arranged along the parting line (10).

12. Device (22) according to claim 11,

which is adapted to move the workpiece (2) for introducing the notch geometry with the hold-down (14) against the notching tool (6) and the workpiece (2) for this purpose rectified with the first

Shear cutting tool (18) against the second cutting tool (19).

13. Device (22) according to claim 11 or 12,

wherein the notching tool (6) comprises a wedge cutting edge (7).

14. Device (22) according to one of claims 11 to 13,

wherein the notching tool (6) comprises a first wedge cutting edge (4, 7) and a second wedge cutting edge (5, 7) which are movable relative to each other and adapted to incomplete biting cutting.

15. Device (22) according to one of claims 11 to 4,

wherein a die (16) and a punch (15) are included, and wherein the die (16) and / or the punch (15) is additionally formed as a notching tool (6) / are.

16. Device (22) according to claim 15,

wherein the die (16) and / or the punch (15) is additionally designed as a cutting tool (18, 19) / are.

17. Device (22) according to one of claims 11 to 16,

wherein a control device (24) for actuating the movable tools, which is arranged to perform the division of the workpiece (2) according to one of claims 1 to 10.