Metal deforming – Tool and/or tool holder – Having unitary tool-face
Reexamination Certificate
2002-05-30
2003-11-11
Jones, David (Department: 3725)
Metal deforming
Tool and/or tool holder
Having unitary tool-face
C072S482100, C072S481200, C072S481100
Reexamination Certificate
active
06644090
ABSTRACT:
FIELD OF THE INVENTION
The object of the invention contained herein is a safety tool for supporting and holding a punch in a clamping system, used on the upper beam of a press-bending machine.
The invention has particular, but not necessarily exclusive, application in the press-bending machines sector.
BACKGROUND OF THE INVENTION
There are various types of press-bending machines. They are used in the mechanical engineering industry, particularly for processing sheets of metal in order to obtain, for example, longitudinal sections with various profiles that can be re-worked with a press-bending cycle.
A press-bending cycle consists basically of a bending tool moving down vertically until it presses on a sheet of metal that is positioned on a work-bed, carries out the bending of the sheet, and returns to its original position. To carry out the aforementioned phases, the machine is made up of two parts. The first part, which is usually the upper part of the machine, is mobile, and a second part, which is usually a lower part, is static and positioned perpendicular to the upper part. Regarding the mobile part, during a typical work cycle, a punch, which is made with an interchangeable blade shaped according to the work to be carried out, carries out a vertical return movement by means of a hydraulic cylinder that lowers an upper beam which carries the punch (held in a clamping system) towards a lower beam, on which an interchangeable mould is positioned, followed by a pause and then its return upwards to the original position.
State of the Art
Generally speaking, most press-bending machines currently available on the market have interchangeable punches that make the machine more flexible in order to meet the wide range of requirements for the companies that use them.
According to the type of work to be carried out on the sheet of metal, there are two types of punches. The first one is made up of a single punch, that is, a single monolithic body with a linear blade, which is held longitudinally along the entire length of the upper beam by means of a single clamping system. The second type is made up of a divided or multiple punch, with various elements held by clamping systems to the upper beam. Each element is a single punch, and these punches may even be different from each other. While, with the first type, a single, continuous type of clamping system along the length of the upper beam is required to hold the punch, with the second type, a number of intermediate clamping systems are required according to the number of single punches to be held and clamped.
Regarding the punch itself, it is usually made up of a one-piece metallic body, with a square upper part called the shank, and a lower part that can be any of various shapes, which actually does the bending, perforating, or cutting. The shank is for attaching the punch to the upper beam, and it is the part on which the clamping systems operate. The clamping systems, operated by pneumatic or hydraulic cylinders, or other means of electro-mechanical systems, close one or more plates with a large surface area, thereby clamping and holding the shank of the punch.
The punch or punches have to be replaced more or less frequently, according to the type of work being carried out on the sheet of metal in question. This operation has to be carried out with the machine in a temporary state of arrest, and preferably with the upper beam at an accessible working height for the operator, to make the operation simpler.
To sum up, (see
FIGS. 3
,
3
A and
3
B that represent typical applications), whatever the shape of punch or punches used, there are three types of shanks available on the market that are clamped by one or more clamping means to the upper beam:
FIG. 3A
shows the original type of shank, indicated as C
1
. This solution has been abandoned by all the manufacturers because of its lack of safety features. This type of shank has only one tooth that is square and has smooth walls. There is a support surface for the punch adjacent to the tooth, such as, for example, on the head of an clamping device on which the pushing force is distributed perpendicularly.
FIG. 3
shows the Standard-type shank, indicated as C
2
. This type, for punches with a pressing axis that is not in line with the support shank, has been standardised by all constructors of press-bending machines and punches and, compared to the first type, is characterised by the fact that it has a certain safety feature. This feature is made up of a seat or “C”-shaped continuous groove which runs transversally to the punch at the base and on one side of the shank, into which a holding tooth of the clamping device enters. The main function of this feature is to avoid the utensil dropping from its seat when the clamping means of the clamping device is released. A variation of the standard shank has a double safety groove. In this case, on each of the two sides of the shank, there is a groove which runs transversally, similar to the groove used for a single-type safety shank.
FIG. 3B
shows the third type, indicated as C
3
. This type is not as common as the second type, and is only produced by some manufacturers. These “personalised” shanks are designed to be used exclusively on certain makes of press-bending machines and are not interchangeable with other machines. A typical example is the GASPARINI® shank which, compared with the previous examples, is characterised by the fact that it has a wedge-shaped groove, into which the tooth of the clamping means enters and that, when released, allows the shank to be suspended from the upper beam in complete safety until it is manually removed by the operator.
Drawbacks
From the brief description above, it easy to imagine the main problems that the producers are trying to solve. First of all, there is the problem of the time required and the difficulties encountered when carrying out the operation of replacing the punch. This especially true when using the punch C
2
, which is the type most widely used, because the operator has to withdraw the utensil along one side. This operation is relatively simple if there is enough space at the side of the machine and if there is only one punch to be drawn out from the upper beam. The punch may be quite heavy, thus requiring more than one operator to withdraw it, or may require suitable lifting means such as a winch. The operation becomes much more difficult if the punch is divided. In this case, when the distance between the intermediate devices is less than the length of the punch, it is necessary to draw it out by withdrawing all the punches that precede it, with all the problems that are inherent with this type of operation.
All these operations have to be carried out with the machine in a rest position, which obviously implies that the cost involved will be proportional to the number of interventions that have to be carried out.
A second aspect that cannot be overlooked is the fact that the punches with safety features currently used are not automatically aligned. This problem is quite serious when high-precision components are being manufactured and where the split punches have to be perfectly aligned with each other. With the current technology, such alignment is almost impossible, resulting in operations carried out on the sheets of metal positioned below the punch that are not satisfactory according to current standards.
Amongst the solutions commonly used in order to resolve the first of the problems mentioned above, that is, withdrawing the punch sideways with respect to the upper beam, the insertion of the punch from below, and vice versa for its removal, is becoming common practice. In this case, in order to hold the groove of the safety feature that runs transversally to the standard-type shank, a wedge is used that is pressed into position in the groove by a spiral spring. This solution requires a considerable amount of effort by the operator to overcome the force of the spring, both when inserting or withdrawing the shank of the punch from the clamping means on the upper beam. The
Jones David
St. Onge. Steward Johnston & Reens
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