Title :An electro permanent magnetic apparatus. with monolithic working face for holding work pieces magnetically and/ or mechanically.

The present invention relates to an electro permanent magnetic work holding apparatus for holding work pieces magnetically and/ or mechanically. This invention more particularly relates to an electro permanent magnetic (hereinafter abbreviated as ¹ EPM' in this specification for the Bake of brevity and convenience) work holding apparatus having a monolithic ferrous working face with slots of desired shape and configuration separating the magnetic poles, thereby rendering the apparatus suitable for holding the work pieces both magnetically and/ or mechanically in the course of working/ machining/ anchoring. Usually such slots are made around the perimeter of the poles, thereby minimising reduction in active magnetic area of the working face. The subject invention also pertains to a work holding apparatus with at least one nonreversible permanent magnet, and at least another reversible permanent magnet suitably placed, which may be commissioned for work holding by switching electrically, whereby a work piece material is held in place without the use of additional pole separators.

In metal working machines such as CKC machining center, milling machines, electrical discharge machines (EDM) , grinding machine, etc., a magnetic work holding apparatus is often used as a worktable, whereby a work piece to be machined can be held securely on the worktable by magnetic force, and then machining operation may be performed on the work piece.

The principal property of a magnet ia ita capability to attract ferromagnetic materials resulting from flow of magnetic energy called "flux" between magnetic north and south poles. When a ferromagnetic work piece is placed across the poles of a magnet, the "flux" passes through and the work piece gets attracted. The intensity of attraction or pull becomes stronger with the decrease in the distance of separation between the work piece and the magnet. Moreover, strength of attraction of a magnet is the function of the quantum of induction of magnetic flux into the work piece, .t has also been observed that smooth surfaces are better attracted and held in position in comparison to uneven or rough surface.

in the prior art, Electro permanent magnetic (EPM) work holding apparatuses of flux reversal type are known in which a magnetic circuit is activated or deactivated by reversing the poles of the permanent magnets of the device. This ia a combination of permanent magnetic and electro magnetic devices: it presents the advantages of the latter without the disadvantages of the former. These devices uses intrinsic energy of the permanent magnetic device but instead of being switched "ON" or "OFF" mechanically, it requires electrical pulse similar to electro magnetic devices but only momentarily delivered by an electrical winding. Once switched "ON", these devices provide magnetic force for infinite duration of time independent of any

external energy source. For instance, US Patent No. 4507635 granted to Michele Cardone of Milan, Italy, pertains to a magnetic anchoring apparatus, comprising in combination: an external ferromagnetic crown provided with a base plate and lateral walls; at least one group of four pole pieces defining pairs of corresponding poles of an anchoring surface, said pole pieces presenting their longitudinal axes at right angles to the base place and in correspondence with the apexes of a square. Moreover, the apparatus comprises a plurality of permanent magnets for feeding the aforesaid poles, Interposed between the pole pieces, and between the latter and said ferromagnetic crown.

Types of magnets presently available have magnetic poles (north and south) which are separated by non-magnetic insulators between the individual poles. The magnetic insulating material generally used may be selected from the group of epoxy, aluminum, brass, stainless steel, etc.

As the coefficient of thermal expansion of each material is different, the working surface αf the existing magnetic work holding device is not stable when there is a rise in temperature during machining operation. This difference causes unstable surface and often creates small opening (ε) for coolant (sometimes flooded coolant fluid is used during machining) to

enter inside the work holding device and short circuit the winding/ joints or hamper with the insulation resistance of the winding.

Normally in this conventional work holding device, all poleε are individually machined and assembled, which gives rise to a possibility of the presence of weak points on the top working face. Moreover as multiple numbers of pieces are to be handled, it makes the manufacturing process difficult and time consuming.

It is impractical to repair these chucks as any process of repair cannot begin without destroying the chuck.

Moreover, another drawback of the conventional magnetic work holding apparatus is that it cannot be used for holding diamagnetiσ or paramagnetic work pieces, as a result of which they normally had to be removed from the working bed of the machine or a holding means such as a clamp or vice had to be mounted on top of the apparatus to hold diamagnetlc or paramagnetic jobs. Any other provision for clamping the work piece also significantly reduces the active magnetic area of the working face. .

Present invention aims at circumventing and finding an effective solution to the difficulties mentioned above.

The principal object of this invention is to provide a novel dual purpose magnetic and/or mechanical work holding apparatus for machining/ working/ anchoring the work pieces which may be ferromagnetic, diamagnetic or even paramagnetic.

A further object of this Invention is to provide a work holding apparatus having a monolithic ferrous working face with slots separating the magnetic poles.

A still further object of this invention is to provide a work holding apparatus having a monolithic ferrous working face having *τ" slots for insertion of . clamping-cum-holding device to hold diamagnetic or paramagnetic work pieces for being worked upon.

Another object of this invention is to provide an EPM work holding apparatus having a monolithic working face wherein there are provided a plurality of slots resembling inverted "T" (tee- slots) or a truncated dumb-bell across the entire length and/ or width of the said apparatus which separate the magnetic poles and simultaneously can be used to clamp jobs mechanically for being worked upon.

Yet another object of this invention is to provide a magnetic work holding apparatus with a ferrous monolithic working face

capable of being used for anchoring of ferrous metal parts, components or entire apparatus magnetically.

1. The foregoing objects are achieved by the invention which relates to an EPM work holding apparatus for holding work pieces magnetically and/ or mechanically, comprising of a base plate and a ferrous monolithic working face, the said base plate having a pocket or recess which houses the reversible permanent magnets and electrical windings, the said working face having magnetic poles which are deraarked by slots, and on the opposite side of the said working face recesses are provided beneath the said slots for housing the non-reversible permanent magnets.

The work holding device is usually provided with tee-slots, resembling an inverted Tee, running across the length and/ or width of the work holding apparatus, which not only separate the magnetic poles but also enables work pieces or jobs to be held either magnetically and/ or mechanically.

The slots may also be made in the shape of a truncated dumbbell in lieu of a tee-slot, or any other suitable shape for convenience of operation/ anchoring, the latter being preferred for convenience of operation and easy availability of clamping equipments .

Usually such slots are made around the perimeter of the poles, thereby minimizing reduction in active magnetic area of the poles. Tee-slots enable diaraagnetlc or paramagnetic materials like brass, aluminum, stainless steel, copper, etc. to be clamped and worked upon.

This invention will now be described by means of the illustrative drawings accompanying this specification, in whlσh-

Fig.l. shows the longitudinal cross-sectional view of the work holding apparatus ^' ;

Fig.2. gives a view of the electro permanent work holding apparatus holding magnetically a ferromagnetic job, and

Fig.3. depicts a view of the electro permanent work holding apparatus holding a job with the help of mechanical clamps.

Referring to the aforementioned figures of the drawings, xn Fig.l work holding face of the apparatus is (1), the base plate is (2), <3) shows the electrical windings, demarked magnetic poles are (4) , first set of permanent, but reversible magnets are denoted by (6) and the second set of permanent, rion-

reversible, magnets are represented by (5). The work holding face (1) also shows the tee-slots (7) running across the length and/ or width of the work holding apparatus, which are brought into play while dealing with a diamagnetic or paramagnetic job.

Fig.2. shows the assembly holding ferrous job (8) magnetically, obviating the need to deploy additional holding means.

In Fig.3. There is shown a view of the apparatus of the subject invention (Ii ..oiuing a job (8), usually diamagnetic or paramagnetic, with the help of mechanical clamps (9) .

. From the foregoing it may be seen that the magnetic bed of this invention could also be used as a machine bed, thereby enhancing the life of the original machine bed.

The working face of the holding apparatus is obtained from a monolithic block of ferromagnetic material, wherein the poles are demarkεd by making slots in the said block, obviating the need to use filler material (s) .

Moreover, instead of using numerous pole pieces depending on the number of poles as was being used earlier, only a single

θ -

block of ferromagnetic material needs to be handled in the present instance, rendering its manufacture relatively simple/ yet sturdy and stable.

Another embodiment of the present invention resides in a magnetic work holding apparatus, which is a variant of the electro permanent magnetic work holding apparatus as described and illustrated hereinabove, equipped with a monolithic working face of a ferromagnetic material capable of being used for anchoring/ foisting of ferrous metal carts, components or whole machine. The said variant electro permanent magnetic work holder suitable for holding ferromagnetic objects, having at least two poles, each one of which has a non-reversible permanent magnet and a reversible permanent magnet surrounded by. an electrical winding which is used for effecting reversal of the magnetic poles of the reversible magnet.

This apparatus is obtained from two pieces of ferromagnetic material, one serving as the top working face and the other as base plate, wherein poles are demarcated in the top working face of the work holder by making recesses in the monolithic block and cavities are made on the opposite side of the poles for locating/ positioning reversible and non-reversible permanent magnets, the former being placed on the backside of the pole surrounded by an electrical winding and the latter are placed on

the surface nearest the top working face. The top working face provides a stable and leak-proof working surface.

A second monolithic ferrous surface may be introduced in such a manner that it holds the reversible permanent magnets _' between the poles and base plate in a sandwiched manner and on the base plate pockets are made for housing the non-reversible permanent magnets directly below the demarcated poles.

As pointed out earlier, structural stability of the conventional equipments was not satisfactory/, particularly while carrying on heavy machining applications. The filler material, usually epoxy compound, also was a source of problems, as it led to unequal heating of the work holding surface posing accuracy problems. Leakage/ seepage of the coolant into the magnets affected the performance of the apparatus.

The present invention successfully tackled the above problems by recasting the design of the work holding equipment by machining out the top working face and the side walls from a monolithic ferrous block, which rendered the structure quite rigid .

The monolithic structure of the subject invention also has recesses for demarking the magnetic poles, which eliminates the need to use any filler material. Furthermore , instead of plurality of pole pieces required in conventional equipments depending on the number of poles, only a single ferrous block needs to be handled, which makes the manufacture quite easy.

The main advantages of the present invention may be briefly laid down as follows:

Presence of "T" slots enable secure handling of work pieces even for diamagnetic or paramagnetic substances, holding them mechanically.

2. All poles and sidewalls are well-connected being made from a monolithic ferrous block, which adds stability to the structure.

3. The Working face is entirely leak-proof and no liquid/ coolant can seep in from the top working face.

4. The need to use filler material on top is diapended with as the working face is fabricated from a monolithic block of ferromagnetic material, on which magnetic poles are well-marked.

5. As the working face of the subject apparatus is fabricated

from a single block of ferromagnetic material, the heat generated during machining operation like milling, shearing, grinding, etc. is evenly distributed throughout the work holding surface, thereby substantially reducing any possibility of unequal deformation.

6. The slots are made around the perimeter of the poles which ensures minimum reduction of active magnetic area.

7. Repairing of electrical winding pose no problem or difficulty as the winding can be easily accessed by meriv separation of the base and the top working face.

8. This ensures a simplified manufacturing of magnetic circuit which normally separate adjacent magnetic poles of different polaritieε resulting in a considerable reduction of manufacturing costs and with better performance.

Additional modifications and improvements of the present invention may also be apparent to those skilled in the art. Thus the particular combination of parts described and illustrated herein is intended to represent only one embodiment of this invention with a variation and is not intended tα serve as limitation of alternative devices or features within the spirit and scope of the invention.

Having described the inventions in detail with particular reference to the illustrative drawings accompanying both provisional and complete specifications/ it will now be made more specifically defined by the claims appended hereafter.