The invention relates to a method for sequentially and continuously machining or shaping sheet parts from continuous strip-like sheet material, such as coiled sheet metal, or sheet material in sheets, by means of an electronically controlled machine tool.
Sheet parts can be machined from sheet material by numerous methods. If we consider the entire chain of work steps, for example, from coiled sheet material to a completed sheet product, which has been machined by applying several working methods, the combinations of methods can at the roughest level be divided into methods for short production runs and those for long production runs.
In short production runs the machining of sheet parts is usually done by first slitting the sheet into strips, whereafter the strips are cut into pieces of suitable length. Thereafter the machining of the pieces is continued, as required, by punching, drilling, notching, etc. When this method is used, the tool costs are moderately low and the delivery time is short. The manufacturing costs are high because the work stages are numerous and there are several transfers from one work station to another. The dimensional precision is poor.
The latest equipment for short production runs consists of so-called sheet-working centers, in which the machining is carried out by punching, nibbling, and laser cutting. The characteristics of sheet-working centers are in general as follows:
One method of handling sheet material in these sheet-working centers is to cut the sheet material coming from a coil first into sheets, which are transferred automatically to the actual working center. At the working center the sheet is machined by one or several of the above-mentioned methods, the tools themselves being fixed and the point to be machined being directed into place by moving the sheet. Such equipment is large in size and also very expensive.
Strip-like sheet material has been handled in short production runs by hot-cutting methods and, fully analogously with this method, also by using a laser cutter. Here the small number of alternative machining methods, i.e. only one work method, restricts the uses, owing either to deficient dimensional precision or to low speed. If the piece requires substantial cutting in proportion to its size and the shapes to be cut are such that they can be done more easily by other machining methods, low speed becomes the problem.
Punching has also been applied to the machining of strip-like sheet material. In this method the sheet is fed forward at indexing intervals corresponding at least to the size of the final product, the cutting of the product and its detaching from the strip being synchronized with this indexing. In addition, the apparatus includes a beam which contains the punching tools and can be moved transversely in relation to the travel direction of the sheet. By means of these tools the punching takes place after the tool or the tools have been brought to the intended point by indexing the sheet forwards over a suitable step in the longitudinal direction and indexing the tool beam over a suitable distance in the transverse direction. In this method, also, there are the following problems: (1) the longitudinal movement is only forwards in steps and only by moving the sheet, and therefore imprecision and detrimental restrictions regarding the shape of the workpiece result; (2) the work method is limited to one type, i.e. punching; (3) all workpieces across the entire width of the sheet are cut out at the same time, in which case either a) only one piece is cut over the entire width, which limits the size of the piece or presupposes previous slitting of the sheet into the correct width, or b) if there are several workpieces in parallel, several similar cutting tools in parallel are needed, aligned both with one another and with the preceding punch, which results in complicated and expensive tools; (4) the interspacing of the patterns of the final product so that the sheet surface is used effectively is successful only in special cases.
A long production run takes place by means of presses and feeding devices from a coiled strip which has been previously slit to the correct width. The machining is by serial tools, the workpiece being completed in one pressing. The advantages of this method include high dimensional precision and low manufacturing costs, if the production run is long enough. The disadvantages include:
The greatest disadvantages of the current machining methods are either that the manufacture of the end product must be divided into several partial work steps on different machines, or that it is necessary to invest in an unreasonably complicated and expensive machine. In both cases the costs are too high.
Furthermore, the difficulties are increased by the fact that, regardless of which alternative has been chosen, it must further be decided whether to choose a setup suitable for short production runs or for long production runs, in which case one of the alternatives suffers. A disadvantage common to all other methods and combinations of methods, with the exception of hot/laser cutting, is the considerable waste of material between the patterns cut or between the cut pattern and the edge of the strip. The disadvantage of hot/laser cutting, for its part, was the use of only one work method, which is not suitable for all pieces.
Let us now set the following requirements for the method for implementing the machining:
All of the above objectives cannot be achieved by any of the known methods described previously.
US-A-4708042 discloses two cylinders having pistons for tool stamps, but there is no indication of the possibility of their being replaced by other kinds of driving mechanisms, or that they could be used separately from one another. There is furthermore no suggestion as to how this could be possible. In US-A-4708042 the tool stamps and slide pistons are stationary relative to one another and it is difficult to change their positions without reassembling the whole machine because they have been irremovably fixed to the punching carriage. Furthermore, US-A-4708042 does not mention the possibility of using several machining methods and does not indicate how this could be possible. The pre-characterising portion of claim 1 is based on US-A-4708042.
By the method according to the invention, which is defined by the combination of features of claim 1, a crucial improvement is achieved regarding all of the disadvantages described above.
The following factors can be considered to be the most essential advantages of the invention:
The invention is described below in detail with reference to the accompanying Figures.
Figure 1 shows an overall representation of an embodiment of the invention. In the embodiment concerned, the machining method is punching, but the use of some other machining method changes only one single tool, and not the way or method of the invention for using them together or separately.
In Figures 1 and 2 the sheet raw material 15 comes from a sheet coil 5, which is standard stored material. The feeding of the sheet forwards is here implemented by means of a drive means 13 and rolls 10, the sheet 15 pressed between them being indexed forwards over the distance necessary at each given time. Indexing devices of other types can also be used. In this case, to the frame 9 of the tool holder there have been attached three hydraulic presses 8 in which the tools are two punching dies 2 and one upper cutter blade 1. Opposite to these there are, attached to the same frame 9 which serves as a single working unit, bolsters 4 and a lower cutter blade 3. This is possible to accomplish for example by making the frame 9 in the shape of a U, and attaching the upper and lower tools to the branches of the U, at mutually corresponding points by means of, for example, mounting plates, not shown in this Figure. The tool-holder frame 9 is, for example, mounted on guides 11 which may be several in number and/or may be positioned in different ways. The frame 9 is indexed transversely in relation to the travel direction 16 of the sheet 15, in direction 17, by an indexing device 12, for example in the form of a screw and ball nut with the aid of a drive means 14.
The machining of the workpieces and their detaching from the sheet 15 is done here transversely relative to the travel direction 16 of the sheet, starting from the first edge 18 of the sheet 15. In the first machining step the foremost of the punching dies 2 makes the hole of the first workpiece in area a of this workpiece. The cutter and the later of the punching dies 2 are at this time outside the edge 18 of the sheet. In the following step the foremost of the punching dies 2 makes the first hole of the second workpiece in area b of this workpiece, and the later of the punching dies 2 at the same time makes the second hole in area a of the first workpiece, detaching both scrap pieces 7. In the third step the punching dies work in areas c and b, as above, while the cutter 3, 4 detaches the first completed workpiece 6 from area a. Thereafter the punching dies move to areas d and c and the cutter to area b, where the above-mentioned work steps are repeated. When the cutter 3, 4 has detached the last completed workpiece in this row, from area m, at which time the punching dies are outside the other edge 19 of the sheet, the entire frame 9 together with the tools returns to the first edge 18 and starts repeating the above-described chain of work steps towards the other edge 19 of the sheet. The procedure continues in this way until the sheet 15 has been used up, or until the required series of workpieces has been made, whereupon the tools are replaced with others and the machining of new workpieces is started, for example further from the same sheet if the material remains the same, or from a fresh material if the sheet coil is replaced with another.
When operating by the method described above, only one set of tools corresponding to the workpiece is needed, and the tools need to be aligned only in relation to one another, in which case the tooling costs remain low and high precision is achieved. The waste material is as small as it can in general theoretically be in the machining method in question, since pre-slitting into strips is not needed. the interval between replacements of material is long, since the coil contains considerably more material than, for example, slit coils corresponding to the width of one product. The savings of material are further increased by the fact that, as the procedure starts from sheet edge 18, machining all the way to edge 19, it is possible in different machining lanes I-II, etc. (Figure 3) to interspace the products 20 in the manner which is considered best, either in the travel direction 16 of the sheet 15 as in Figure 3, or in the travel direction 17 of the frame 9 of the tool holder, or in both directions simultaneously over the entire surface of the sheet 15. In Figure 3, in which the length of the workpiece is A, the saving thus achieved is of the magnitude B (this is only to illustrate the principle, there may be found an even more efficient layout for the pieces concerned). The workpiece 20 can be replaced, in the middle of the sheet, with workpiece 21, the only limiting condition being that the sheet material is the same. Such bi-directional interspacing and replacement is not possible in other combinations of machining methods.
The method described above is perhaps one of the most primitive embodiments according to the invention. However, the method is suitable for use with considerably more complicated equipment. There may be a considerably larger number of tools 2, 4 and 1, 3, they can be easily replaced by means of bolt attachment or automatically; and their positions can for this reason be easily changed. When control logic is added to the method, such as numeric control, a nibbling function may, for example be produced. In this case the punching die can be fitted to make, for example, 50 punchings while the frame 9 moves at an even, small-stepping speed, whereafter the other tools make one punching. This nibbling can be diversified by making in the tool holder frame 9 one or several tool holders 23 guidable in different directions.
Figure 4 depicts such an arrangement, in which the tool holder 23 has been arranged to be movable by means of an indexing device 37 in direction 22, which is transverse or perpendicular to the travel directions 17 of the frame. In this case the nibbling, slotting or laser cutting can be controlled simultaneously in two mutually perpendicular directions 17 and 22, which are at the same time independent of one another. By means of this arrangement, the indexing of the sheet 15 during the machining of one row of workpieces is also avoided; such moving would easily cause flaws in the piece. In terms of control the most advantageous manner of moving the tool holder frame 9 and for transferring the tool holders relative to the frame is to use a machine element producing a linear indexing; there exist several types of such machine elements.
In the tool holder frame 9 there may be several tool holders 23, 25, and 27, of which all, some, or one, can be controllable during work, such as the holder 23, or adjustable only in connection with the replacement of the tools, and there may be attached to each of them several tool sets 24, 26, and 27. In an individual tool set there may be several tools, for example several punching dies in a hydraulic press. Each of these tool sets may be of any type of machining method with its control devices and power sources. When necessary, it is of course also possible to use a common power source. The tool holders, or some of them, may be positioned below the sheet 15, for example, in the lower branch of the frame 9, or there may be tool holders on both sides of the sheet 15 and simultaneously in use. In this case it is possible to take into account the asymmetry of the machining trace in the direction of sheet thickness and its effect on the completed workpiece. It is, for example, possible to punch or to cut the different holes of one and the same workpiece from different directions. The tools to be attached to the tool holders may carry out any machining methods allowed by the limiting conditions of an individual machine construction, such as drilling, punching, cutting, nibbling, plasma cutting, slotting, etc., and also shaping methods such as chamfering, for example from the side edge or front edge of the sheet, flanging, compression molding, etc. In the present patent application and its claims, the term machining is deemed to include also shaping.
(a) The tool holder frame 9 indexable and guidable transversely to the travel direction 16 of the sheet 15, or in general the entity made up of the tool holders; (b) the tool holders 23, 25, 27, etc., indexable and guidable in relation to this, which can be transferred by a linear movement or by means of eccentrics, etc. relative to the frame; and (c) the tools attached to each tool holder and usable independently of one another, constitute a hierarchical entity (cf. decision tree, etc.). Such an entity is suitable for control by using microprocessors or complete computers, and particularly microcomputers, in which case their programming can be carried out simply by following the machining-technique hierarchy with the main program-subprogram hierarchy. Although the frame, the tool holders, and the tools with their actuating devices are as such independent of one another, their operation in relation to one another must, of course, be sequenced correctly, i.e. they must be mutually synchronized.
When using tool holders 23, 25, 27, etc. adjustable or controllable in a sufficiently versatile manner, and when using a logic control device sufficiently versatile and flexible, for example a microcomputer, the workpieces can for example be positioned on the sheet 15 in a manner which greatly saves material. For example, in Figure 5, every other row of workpieces is a mirror image of the adjoining rows. In reality the workpieces can be positioned on the sheet arbitrarily, even every individual workpiece 29-36 in a different position, provided that the coverage of the sheet 15 surface is effective and the machining itself takes place in a direction transverse to the sheet 15.
Effective control and the versatile possibility to move the tools in accordance with the invention also allow standardization of the tools. This means that each opening, hole combination and piece outline does not require a separate tool made specifically for it. For example, the piece in Figure 6
As regards the details of the tool holder frame 9 and the machining technique, it must be taken into account that if the frame is of the shape U presented, in the machine the tool traveling last in the travel direction 17 on each row must carry out the cutting step, in order that the result should be a removed area of the sheet 15 corresponding to the removed workpiece, to provide room for the central part of the U-shape. If the upper tool holders are guided without a U-shaped frame, for example numerically, into alignment with the lower bolsters concerned, or if the machining methods are such that lower bolsters are not needed, the waste material can be left in strip form because, in this case, the route along which it is removed is always free. Usually it is, however, most advantageous to cut off the waste material, because then the front edge of the sheet 15 in its travel direction 16 remains neat, which makes it easy to continue the work. The transfer of the remaining coil of the sheet and its handling, if the work is discontinued at such a stage, is then also possible without additional work steps.
The invention is not limited to the examples described above; the method can be modified and various machining methods and machine elements not mentioned here, as well as computer technology, can be used in carrying out the method within the scope of the appended claims.