Abrading – Precision device or process - or with condition responsive... – Computer controlled
Reexamination Certificate
1998-10-14
2001-04-10
Eley, Timothy V. (Department: 3723)
Abrading
Precision device or process - or with condition responsive...
Computer controlled
C451S008000, C451S021000, C451S053000, C451S056000, C451S072000
Reexamination Certificate
active
06213843
ABSTRACT:
BACKGROUND OF THE INVENTION
This invention relates to a method for grinding surfaces of workpieces using a metal bonded grinding wheel, which is sharpened through an electrochemical conditioning by means of an electrode, which is disposed spaced apart from the grinding wheel so that a gap is formed between the electrode and the grinding wheel, an electrolytic cooling lubricant, introduced into said gap, and a power source, by means of which a current is conducted through the electrode, through the electrolytic cooling lubricant and through the grinding wheel.
In addition, the invention relates to a grinding apparatus for surfaces of workpieces with a metal bonded grinding wheel, which can be sharpened through an electrochemical conditioning.
Growing demands with respect to economic efficiency, obtainable workpiece surface quality and precision are being put on grinding methods of this kind, in particular for grinding indexable inserts. Since the respective workpieces are made of very hard material, this means that conventional grinding wheels are no longer able to meet these demands sufficiently. Conventional grinding wheels of this kind have a bonding system of artificial resin or ceramic, by means of which the grinding grains are held. Grinding wheels of this kind have to be sharpened again through a dressing operation after being used for only a short time. Owing to the strong abrasion of the grinding wheel and the relatively frequent dressing operation, the aforementioned demands cannot be fulfilled.
Metal bonded grinding wheels are better suited for grinding methods of this kind. Compared with grinding wheels having other types of bonding, these grinding wheels have great advantages, evidenced in particular by the very high grain retention of the bonding, an enlarged grain protruding length of 30 to 50% of the grain diameter, a larger chip space and a more abrasion-resistant bonding system. Moreover the heat elimination is also optimal, owing to the metallic bonding material.
This metal bonding, however, also has a big drawback. Because of the increased abrasion resistance of the bonding system, the self-sharpening effect is disturbed. The metal bonding of the grinding wheel can no longer be restored through abrasion of the worn material particles. The dull grinding particles are no longer released from the grinding wheel bonding, the whole grinding wheel becomes blunt, and the grinding process very soon comes to a standstill. Restoration of the optimal grinding wheel topography has to take place through a sharpening process, which has as a consequence high non-productive times, and which therefore reduces the economic efficiency of the entire grinding process.
Known from the European patent EP-A-0 576 937 is a method and a device for grinding a mirror surface with a grinding wheel, which grinding wheel has a metal bonding. Here the grinding wheel is sharpened during the grinding operation in that a current is conducted between an electrode, disposed adjacent to the grinding surface of the grinding wheel and the grinding wheel, so that the grinding wheel can be sharpened electrolytically with the aid of a conductive solution.
With this device and method the quality of the surface of the grinding wheel is improved during the operation of grinding the mirror surface; however, it cannot be ascertained whether the grinding wheel would be sharpened more than the grinding operation would require. This could lead to excessive wear and tear on the grinding wheel. It is also not discernible whether the grinding wheel is in a state allowing it to perform an optimal grinding operation.
At the same time, achieving mirror surface quality is only possible by depositing solid lubricants in the form of oxides, hydroxides and cooling lubrication materials in the chip space of the grinding wheel. The chip space of the grinding wheel is thereby greatly reduced in size, whereby the transport of cooling lubricant into the grinding contact zone and material particles out of the grinding contact zone is only possible in a more limited way. Cool-lubricating, abrasion-intensive grinding processes, characterized by very low process forces and stable sharpness conditions over a very long time period, cannot be achieved with the device and the method according to EP-A-0 576 937.
SUMMARY OF THE INVENTION
One object of the present invention is thus to create a method with which the sharpening operation, and therefore also the grinding operation, can be optimized, whereby the economic efficiency of the machining process, the surface finish quality, the precision of the machined workpieces and the edge life of the grinding wheels are improved.
This object is attained according to the invention in that during the grinding operation at least one dimension is measured of a force exerted by the grinding wheel on the workpiece to be ground, and, on the basis of this at least one measured value, the intensity of the electrochemical conditioning of the grinding wheel is controlled by changing the intensity of said current using a computing and control device.
By measuring indicative values relating to the state of sharpness of the grinding wheel, the electrochemical conditioning can be adjusted in such a way that the sharpness of the grinding wheel is constant over a long period of time.
A grinding wheel delivered by a supplier is preferably subjected to an electrochemical preconditioning before being used for grinding for the first time. The sharpness of the grinding wheel is thus brought to the desired level.
A further advantage is achieved if, during the grinding operation, the magnitude is measured of the normal force exerted by the grinding wheel on the workpiece to be ground in perpendicular direction and the magnitude is measured of the tangential force exerted in tangential direction. By dividing the thus measured normal force by the corresponding tangential force, a value is obtained which is independent of the size of the contact zone. This value is indicative of the state of sharpness of the grinding wheel so that, based on the course of this value, the electrochemical conditioning of the grinding wheel can be controlled by changing the current intensity.
In a further preferred embodiment of the invention, the residual normal force is measured, after termination of the grinding cycle and expiration of the pregiven spark-out time, which measured value is compared with a pre-given normal force. If the measured residual normal force after expiration of the spark-out time is greater than the pre-given residual normal force, then the value obtained by division of the normal force by the tangential force can be reduced. The result is that the electrochemical conditioning is activated longer, and the grinding wheel is sharpened.
If the measured residual normal force before expiration of the pre-given spark-out time is less than the pre-given residual normal force, the operation can be ended prematurely. These steps result in an optimization of the grinding operation.
A further object of the present invention is to create an apparatus for carrying out the method with which the desired grinding operation and the electrochemical conditioning of the grinding wheel can be executed in an optimal way, which is achieved, according to the invention, through an apparatus comprising a grinding device, in which a metal bonded grinding wheel is disposed, which is rotatingly drivable by means of a driving motor, chucking means for holding a workpiece to be ground, an electrode mounting with inserted electrode, which is held in such a way that a gap is formed between electrode and grinding wheel, feed means for supply of the electrolytic cooling lubricant into the area of the gap, a current generation means for generating a current which is conducted by conductor means through the electrode and the grinding wheel, measuring means to measure during the grinding operation the normal force and tangential force acting between the grinding wheel and the workpiece, and a computing and control device for collecting the measure
Agathon AG Maschinenfabrik
Eley Timothy V.
Pearne & Gordon LLP
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