Background art Progress in machining technology has produced an increasing demand for methods that can provide burr-free machine part surfaces with high abrasion resistance and low surface roughness. Conventional methods aiming at satisfying this demand are deburring, burnishing and roller-burnishing technologies.

Deburring methods can be known from Deburring and Edge Finishing Handbook by La Raux K. Gillespie (ASME Press, New York, 1989) and from Handbuch Entgrattechnik by Hans-Michael Beier (Carl Hauser Verlag, München-Wien, 1999) which describe more than a hundred different manual and machine methods for deburring. The most widely known methods include mechanical machining technologies such as lathing, boring, grinding, abrasive grinding, sandblasting, thermal machining (laser, electron beam, gas jet), chemical and electrochemical technologies.

However, the above sources equivocally put an emphasis on the fact that mechanical machining (cutting) technologies cannot fully succeed in completely removing burrs, especially when working with ductile materials, because after each cutting operation some kind of burr remain there on the surface, even if the remaining burrs are extremely small and can be characterised as micro-burrs. The only place where an "edge rolling"technology is mentioned in the above sources is on page 370 of Deburring and Edge Finishing Handbook by La Raux K. Gillespie, where the process is described as rolling burrs back on the surface of the workpiece, avoiding thereby any further cutting and thus the occurrence of micro-burrs.

Sources that present burnishing and roller-burnishing technologies (e. g. Gépipari megmunkálások by Gribovszky Laszto, Tankönyvkiadó, Budapest, 1977) include both methods in the group of mechanical finishing technologies, their aim being changing

the surface quality, roughness, hardness, or residual stress condition by local (surface) mechanical working, without removing any material. Known methods apply special devices having shaping bodies of spherical shape (rollers, balls) that are sufficiently harder than the material of the workpiece. These bodies are mechanically pressed against the surface of the workpiece, with the tool being moved about the surface of the work while either the tool or the workpiece itself is rotated. These movements result in that the shaping bodies are rolled or, in case of (non-roller) burnishing, slid along the surface.

Existing roller-burnishing technologies that are more closely related to the present invention can be applied for machining inner or outer cylindrical surfaces, flat or spatial surfaces of revolution, and threads.

Such methods can be known from the page www. fette. de. A special method is described on the homepage of Hegenscheidt HFD GmbH, www. heqenscheidt-mfd. de, the method providing that pre-rolling fine cutting and roller-burnishing itself can be carried out in a single step.

The German company mentioned above has been granted several patents and has also filed numerous patent applications in the field.

One of these is patent description HU 267 962, which discloses a tool for smoothing the surface of a workpiece by roller-burnishing comprising a support element having conical surface to provide compression force for roller-burnishing.

Patent description HU 267475 describes a roller-burnishing apparatus comprising hydraulic actuator devices. The force needed for surface smoothing is provided using hydraulic means in patent application EP 146 9972, while patent description EP 145 2272 discloses a process of roller burnishing crankshaft surfaces.

Common characteristics, and common disadvantages, of the above methods are that they can be utilised only for working continuous surfaces of revolution, flat or helicoid surfaces, that they require complicated equipment and precise machine tools, and that they cannot be applied for deburring. Tensioning force of the roller tools is provided using hydraulic means, and there is no possibility for force adjustment/correction during operation.

Disclosure of Invention It is the aim of this invention to provide an apparatus that generates rolling force by a magnetic field that is freely adjustable during operation, and that is capable of roller-

burnishing continuous and non-continuous rotationally symmetrical and asymmetrical surfaces (flat surfaces, general spatial surfaces) as well as rolling edge burrs produced at the edges formed at the connection of these surfaces.

The inventive apparatus should be mountable on conventional and CNC-machine tools, such as turning and milling machines.

The invention is based on the recognition that with suitably configured means it is possible to produce magnetic fields for pressing the magnetisable roller balls against the surface of the workpiece with the desired force, and so mechanical tool tensioning is not needed. The balls are flexibly pressed against the surface so they can follow minor surface irregularities and edge cracks. Compression force can be adjusted during the process if desired.

The inventive aim can be realised by providing an apparatus that can be mounted on conventional or CNC-machine tools (lathes, mills), comprises an electromagnet and a DC power supply for energizing the electromagnet, and further comprises a"tool holder"implemented as a magnetic jaw or magnetic arbour, with the"tools", that is, the roller balls, being directly connected thereto.

The aim of the invention can also be realised by utilising a powerful permanent magnet that is preferably placed over the work to be machined such that the roller balls remain pressed against the surface of the workpiece.

A further aim of the invention is to provide a method that has the steps of pressing the magnetisable roller balls against the surface of the workpiece by means of magnetic field and performing the desired surface smoothing operation by moving the balls along the surface in a way determined by the possibilities of the given machine tool.

The inventive aim is realised by providing an apparatus for working plane and general spatial surfaces by deburring and roller burnishing action that comprises a DC power supply and a magnetic coil and is characterised by having a revolving magnetic arbour disposed inside the magnetic coil, with the magnetic arbour adapted for being fitted on a milling machine, and also having roller balls pressed against the surface of the workpiece to be machined by the uniform magnetic field generated by the magnetic coil and the magnetic arbour.

A preferred embodiment of the inventive apparatus is for machining axial-like workpieces by deburring and roller burnishing action, adapted for being fitted on lathe and magnetic coil for producing uniform magnetic field, characterised in that the

rolling balls are pressed against the surface of the workpiece by magnetic field of magnetic jaws, and the apparatus further comprises a tapered magnetic arbour having at least one.

The inventive aim is further realised by providing an apparatus for deburring and roller-burnishing plane and general spatial surfaces that is characterised by that it can be fitted on a turning machine and that it comprises a permanent magnet disposed inside a tubular extension piece made of non-magnetisable material, a connecting piece having bores for receiving fastening screws securing the tubular extension piece, with the connecting piece being adapted for connecting the permanent magnet and a rotatable arbour; and roller balls that are pressed against the surface of the workpiece to be machined by the magnetic force of the permanent magnet.

In a preferred embodiment of the apparatus according to the invention the tubular extension piece has a groove or grooves and there is an undetachable connection between the connecting piece and the arbour, while in another preferred embodiment the connecting piece and the arbour are detachably connected.

A preferred embodiment of the inventive apparatus comprises roller balls covered with hard coating of a non-magnetisable material and has a minimal-quantity oil lubrication system comprising an air spray nozzle, adapted for decreasing friction and removing contaminants.

The aim of the invention is still further accomplished by providing a method for deburring and roller-burnishing machine parts that comprises the steps of producing adjustable-intensity uniform magnetic field for pressing hard, abrasion-proof rolling balls against the surface to be machined and moving the workpiece while simultaneously rolling the rolling balls along the surface and the burred edges of the workpiece, flexibly tracking the surface irregularities thereof.

In a preferred way of carrying out the inventive method deburring and roller-burnishing are performed in a single run, without there being a need for a subsequent stage of roller-burnishing, and, applying air-spray minimal quantity oil lubrication for lubricating and cleaning the workpiece for decreasing friction and protecting the workpiece from contamination, separated burr pieces are gotten away from the surface of the workpiece.

Brief description of the drawings A preferred embodiment of the inventive apparatus and the inventive method is explained in detail with reference to the attached drawings where Fig. 1 is the side view of the embodiment of the inventive apparatus that comprises an electromagnet and can be applied for roller-burnishing and deburring workpieces with plane or general spatial surfaces, Fig. 2 shows the sectional view of the embodiment comprising a permanent magnet, Fig. 3 shows a magnified view of the working zone of the apparatus shown in Figs. 1 and 2, and Fig. 4 is the front view of the apparatus shown in Fig. 1, taken while machining a cylindrical-surface work.

Fig. 5 is the over-view of the workpiece shown in Fig. 4.

Best made of carrying out the invention The apparatus of Fig. 1 can be utilised for machining a workpiece 2 having plane or general spatial surface, with the workpiece 2 being held on a table of a milling machine and moved in a transverse direction while it is being machined. The inventive apparatus essentially consists of a rotatable magnetic arbour 4 surrounded by a magnetic coil 3 and an adjustable-current DC power supply 5 that is connected to the magnetic coil 3. The apparatus further comprises roller balls 1"sticking"to the magnetic arbour 4 and performing the machining action, and an oil feed nozzle 6.

During the machining operation the roller balls 1 are pressed against the surface of the workpiece 2 by the collective action of the tapered-end magnetic arbour 4 and the magnetic coil 3, and rotate with the same rpm n as the magnetic arbour 4 along the surface of the workpiece 2, providing rolling action. The roller balls 1 are disposed in seats formed in the conically shaped (tapering) surface of the magnetic arbour 4. The number and size of the roller balls 1 depend on the size and degree of complexity of the surface to be machined. For extended surfaces it is recommended to use a greater number of bigger-sized balls, whereas for complex surfaces fewer and smaller-diameter roller balls 1 may be applied. When roller-burnishing complex spatial surfaces, the magnetic arbour 4, being held in the main spindle of a CNC-machine tool, can track the surface (in a manner similar to the cutter of a milling machine), with the distance between the end of the magnetic arbour 4 and the surface of the workpiece 2 being kept at a minimum in order to minimize magnetic resistance.

During the machining operation oil is fed from a nozzle 6 to the working zone in a minimal quantity by means of high-pressurized air, reducing friction and with the oil spray removing material that may have chipped off the surface. The roller balls 1 are preferably hard, magnetisable, polished-surface bearing balls that are coated with TiC-TiN coating to increase abrasion resistance. The non-magnetisable micrometer- thick coating also reduces the adhesivity of magnetisable contaminants, making more effective the operation of the nozzle 6.

Fig. 2 shows the sectional view of another embodiment of the inventive apparatus.

This embodiment contains a permanent magnet 12.

The permanent magnet 12 is disposed inside a tubular extension piece 11 made of non-magnetisable material, together with a connecting piece 9 that is connected to a rotating arbour 8 located above the permanent magnet 12. Bores are disposed in the skirt surface of the tubular extension piece 11 near the end thereof that is proximate to the connecting piece 9, with fastening screws 10 being disposed in the bores securing the tubular extension piece 11 to the connecting piece 9.

The connecting piece 9 and the arbour 8 are connected with detachable or undetachable connection. Fig. 2 shows an embodiment with detachable connection.

The roller balls 1"stick"to the permanent magnet 12 and to the tubular extension piece 11 by virtue of the magnetic force exerted by the permanent magnet 12. The apparatus illustrated in Fig. 2 is placed during the machining operation above the workpiece 2 movably attached to the table of a milling machine (not shown in the drawing) in such a way that the roller balls 1 touch the surface of the workpiece 2. The arbour 8, chucked on a driving apparatus not shown here, is rotated with an rpm n, while the workpiece 2 is moved about the table of the mill in a transverse direction.

The machining process of the workpiece 2 is essentially the same as has been described above referring to Fig. 1. After the machining operation has been completed, the rotation of the arbour 8 and the movement of the table of the milling machine are stopped, and the arbour 8 is withdrawn by lifting it in a direction perpendicular to the plane of the table. Because of the application of permanent magnet 12 the magnetic force exerted on roller balls 1 remains there after the machine has been stopped, and thus the roller balls 1 remain"stuck"to the tubular extension piece 11 and to the permanent magnet 12 and so they can be removed from the workpiece 2 together with the arbour 8.

As it is shown in Fig. 3, roller ball 1 effectively rolls back edge burrs that are about to come off the top surface of the workpiece 2.

Fig. 3 is a magnified view of a portion of Fig. 1, showing unfinished (freshly milled), rolled-burnished and deburred surfaces. It can be easily seen that, due to the roller- burnishing action burrs either get torn off or are transferred to adjacent surface parts that are less important for the future operation of the machined piece, with the relatively rough surface produced by the tearing off of burr pieces by the first ball being roller-burnished by the next roller ball and the torn-off burr piece being removed by the high-pressure spray coming from nozzle 6.

Fig. 4 shows elements of an apparatus that is applied for roller-burnishing a cylindrical surface, at the stage when the roller balls 1, pressed against the surface by magnetic jaws 7 that are moving in a direction parallel with the axis of the workpiece 2, are rolling edge burrs produced at the edge located at the connection of the flat end surface and the cylindrical surface of the workpiece 2. The apparatus can be mounted on a turning machine, the magnetic jaws 7 placed on the saddle can be magnetised by a uniform magnetic field, and the workpiece 2 can be placed in a chuck and rotated with the desired speed, while contaminations that might be produced during roller- burnishing are removed by the high-pressure spray flowing from nozzle 6 that contains a small quantity of oil conforming to the method of minimal-quantity lubrication.

Major advantages of the inventive roller-burnishing, deburring apparatuses are that they can be produced simply, can be adapted to be mounted on conventional machine tools, and can be easily operated.

With the application of the method according to the invention the surfaces and burred edges of machine parts can undergo a single-stage roller-burnishing operation, which increases productivity and reduces per unit costs, while also reducing the environmental load of the operation due to minimal-quantity lubrication used in the inventive method.

List of references 1 roller balls 2 workpiece 3 magnetic coil 4 magnetic arbour 5 power supply 6 nozzle 7 magnetic jaws 8 arbour 9 connecting piece 10 fastening screw 11 tubular extension piece 12 permanent magnet