Studer offers cylindrical grinding with a shoe grinding fixture to meet the highest precision requirements for grinding of thin-walled workpieces. With this method, the company achieves accuracies which remain unattainable with the conventional grinding process.
The shoe grinding principle
The thin-walled, circular workpiece & the roller bearing ring, must be clamped so that it cannot be deformed and so that absolute concentricity from external diameter to internal diameter is already assured by the clamping system.
These requirements are not met by a jaw chuck (3-, 6-jaw chuck). In addition, the complete external contour and the internal contour should preferably be machined in one clamping. A magnetic chuck clamping generally means that each individual workpiece must be centrically aligned manually using a dial indicator, which not only takes a great deal of time, but also makes automatic loading impossible. This last point in particular proves to be a major obstacle in the mass production required in the roller bearing industry.
The best way to clamp a thin-walled ring is to use a method which completely separates the workpiece support from the rotary drive (workpiece drive):
Shoe grinding fixture, for supporting the workpiece
Electromagnetic chuck for torque introduction (drive) and fixing the workpiece
Design of shoe grinding fixtures
Shoe grinding fixture clamped to workpiece table, movable in Z-direction.
Horizontal supporting shoe in oscillating shoe design, with universal sliding inserts with fine adjustment.
Vertical supporting shoe in fixed shoe design, with universal sliding inserts with fine adjustment.
Electromagnetic chuck for introduction of the workpiece rotary movement and for fixing the workpiece, here with radial pole pitch.
Magnet pole boosters. These are regularly overground in assembled state, to guarantee the flatness and perpendicularity of the magnet contact surface. They are radially adjustable and clamped in the T-slot.
Studer universal shoe grinding fixtures are available in several usefully graded sizes and cover the diameter range from 10 to 460 mm. In parallel to the universal shoe grinding fixtures shown there are also versions for the mass production of part families, which allow quick resetting to a new workpiece using quick-release plates.
Design of the electromagnetic chuck
The electromagnetic chuck drives the workpiece in the direction of rotation, thus, generating the workpiece speed. The chuck also holds the workpiece in its nominal position, as it lies against the front surface of the workpiece. A small relative movement takes place here between chuck (pole booster, pole ring) and workpiece end surface, as the supporting shoes position the workpiece eccentrically: Annular pole or radial pole pitches are selected depending on the workpiece size, with the annular pole pitch tending to be used for smaller workpieces (up to approx 80mm).
Possible grinding head configurations
The top priority is to finish-grind a roller bearing ring externally and internally: perfect concentricity externally/internally; same manufacturing temperature, so more dimensionally stable; reduction of quantity of ‘work in progress’ (working capital) etc. The grinding head should, therefore, be equipped with the grinding tools required for the complete process: external grinding wheel(s), internal grinding wheel(s), measuring probe, and naturally on an infinitely variable, high-precision B-axis with a swivel angle repetition accuracy of < 1" (for STUDER S41).