Electric heating – Metal heating – By arc
Reexamination Certificate
2000-11-08
2002-11-26
Dunn, Tom (Department: 1725)
Electric heating
Metal heating
By arc
C219S161000
Reexamination Certificate
active
06486436
ABSTRACT:
FIELD OF THE INVENTION
The present invention relates generally to tooling systems for clamping and holding a workpiece within a machining system and in particular to workpiece tooling systems for clamping and holding a non-magnetic workpiece within a machine tool using magnetic means.
BACKGROUND OF THE INVENTION
Numerous machining systems exist for milling, drilling and cutting a workpiece. In such systems suitable tooling is used to hold the workpiece within the system in order for it to be machined. Conventionally the workpiece is held or clamped within the machining system by mechanical tooling means which grip and press against the workpiece to hold it in position. The tooling must secure the workpiece in place during the machining operation and must be able to prevent the workpiece from moving when subjected to the machining loads. The tooling should also not cause damage to the workpiece and must allow for easy access to the workpiece to allow for machining of the workpiece to occur. Furthermore the tooling should be arranged such that the workpiece can be rapidly installed and removed from the tooling and machining system in order to improve overall processing efficiency.
Laser machining systems for drilling, cutting, or machining present particular difficulties in the design of suitable tooling to hold the workpiece. In laser machining systems a laser beam is directed at the workpiece where it removes material from the workpiece to either drill a hole in the workpiece or, as the beam is traversed along a predetermined path, it cuts or machines the workpiece along that path to shape the workpiece. In such systems a clear line of sight for the laser beam to the portion of the workpiece to be machined, cut, or drilled is required. Conventional mechanical tooling and clamping arrangements for holding a workpiece within such a laser machining system are often not ideal since the tooling in order to provide the required clamping often encloses a portion of the workpiece and thereby obstructs portions of the workpiece. There is also a danger with laser machining that the beam will penetrate beyond the workpiece once the laser beam has machined or drilled a portion of the workpiece with the result that the laser beam may machine and damage a part of the tooling. Consequently the tooling has to be carefully designed and positioned relative to the areas of the workpiece to be machined. This complicates the design of the conventional tooling and makes any such tooling very specific to a particular workpiece with the result that there is little flexibility in the use of the tooling. This negates one of the advantages of laser machining systems which are extremely flexible in their application to producing different components. It is also often time consuming to set up such tooling and to install and remove the workpiece from the tooling. Although desirable to reduce such set up time in any operation, with laser machining since the actual machining process is relatively rapid reducing the set up time becomes even more important.
Magnetic clamping of a workpiece within a machining system has been proposed as an alternative tooling method and system. In such a magnetic clamping system a magnet, usually an electromagnet, is disposed on or within a worktable upon which the workpiece is placed within the machining system. The magnet then holds the workpiece in place using an attractive magnetic force that exists between the magnet and the workpiece. Such systems are effective in holding the workpiece in position, provide very little obstruction of the workpiece, are flexible and are also easy to set up to hold the workpiece. The use of such magnetic clamping systems is therefore desirable.
Unfortunately such conventional magnetic tooling and clamping systems are limited to holding metallic components and in particular workpieces of a magnetic material for example steel which are themselves attracted to the magnets. Workpieces of non-magnetic materials, for example plastics, aluminium or titanium, cannot be held with conventional magnetic tooling or clamping systems since a magnetic force between the workpiece and the magnet is not present to hold the component in place within the tooling and machining system. Electromagnets are also conventionally used in such systems generate a sufficient magnetic field to clamp the workpiece. The required control systems for the electromagnets add to the complexity of the resultant tooling system. The use of permanent magnets has been proposed however due to their lower magnetic strength, in particular when used to hold only weakly magnetic workpieces, the magnetic force generated by such permanent magnets is often not sufficient to adequately and securely hold the workpiece during the machining operation.
It is therefore desirable to provide a magnetic clamping system for holding a non-magnetic workpiece within a machining system which address the above mentioned problems and is simple, effective, easy to set up and which can be easily adapted to be used with a variety of different workpieces and/or which offers improvements generally.
SUMMARY OF THE INVENTION
According to a first aspect of the present invention there is provided a magnetic clamping system for locating and holding a workpiece within a machine tool, the system comprising at least one magnet, and a fixture structure, attached to the machine tool, which co-operates with and in use engages and supports a portion of the workpiece mounted upon and within the fixture structure; characterised in that, in use, at least one clamp member made of a magnetic material is disposed opposite and facing the at least one magnet with the magnet and clamp member on opposite faces of a portion of the workpiece so that the portion of the workpiece is sandwiched between a clamp member and a magnet, and a magnetic attractive force between the clamp member and magnet provides a clamping force to hold the workpiece upon and within the fixture.
The workpiece may be non-magnetic.
Preferably the magnet is mounted and fixed to the fixture structure. Alternatively the clamp member is part of the fixture structure.
The clamp member is preferably fabricated from mild steel. The at least one magnet is preferably a permanent magnet. In particular the at least one permanent magnet is a neodymium magnet. The clamp member may also be a magnet.
Preferably the fixture structure comprises a plurality of interconnected frame elements and support members, the frame elements joined to the support members. Furthermore the individual frame elements and support members are preferably substantially planar and are fabricated from sheet material. The frame elements and support members may be joined together by means of twist tabs which engage in a slot hole.
A magnetic clamping system described above maybe part of a laser machine tool. Preferably such a laser machine tool is a numerically controlled multi-axis laser cutting and drilling machine tool.
The workpiece may be of a substantially frusto conical shape and the fixture of an annular configuration with portions which correspond to the profile of a portion of the workpiece and which in use engage and bear against one part of a surface of the workpiece.
According to a second aspect of the present invention there is provided a magnetic clamping method for holding a non-magnetic workpiece within a machine tool using a clamping system comprising a separate magnet and a magnetic clamp member with either the magnet or clamp member attached to the machine tool, the method comprising sandwiching a portion of the workpiece between the said separate magnet and clamp member with a magnetic attractive force between the magnet and clamp member clamping the portion of the workpiece therebetween.
According to a yet further aspect of the present invention there is provided a laser machining system incorporating a magnetic clamping system as described above for holding a non-magnetic workpiece within the machining system.
REFERENCES:
patent: 1449369 (1923-03-01), Anderson
patent: 2367582 (194
Corners Stephen
Herrero Alvaro
Shah Kaval
Szeki Janos AF
Williams Paul S
Dunn Tom
Johnson Jonathan
Manelli Denison & Selter PLLC
Rolls-Royce plc
Taltavull Warren
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