centerless grinding and centerless grinding machines-overview
How does centerless grinding work?
Centerless grinding is an industrial process to remove material by cutting chips from the workpiece. The workpiece is located between two rotating wheels, supported by a workrest blade.
- The regulating wheel controls the workpiece rpm, supports it and its tilt generates the axial feed rate.
- The grinding wheel is abrasive and removes the material.
The workpiece is not being clamped and rests between the wheels and the workrest blade.
Even very long or delicate workpieces can be machined.
Centerless grinding allows a high precision combined with a high productivity.
It is possible to machine a wide range of round workpieces, from a few grams to several tons within very tight tolerances.
For centerless grinding, two different principles are used.
- Throughfeed grinding
Is used when only the cylindrical area with the largest diameter has to be machined. The rotating workpiece moves axially through the complete grinding gap, on top of the workrest blade, between the grinding and the regulating wheel. The tilt of the regulating wheel generates the axial feed rate.
- Infeed/plunge grinding
Is used when areas smaller than the largest diameter need to be machined, for example cam shafts or gear shafts, or if non-cylindrical contours are needed. Workrest blade, regulating wheel and grinding wheel have an altered negative workpiece profile. Workpieces need to be loaded and unloaded separately. The regulating wheel supports the workpieces, rotates it and moves it against an axial stop. The grinding wheel plunges towards the workpieces radially and removes the material.
Choosing the grinding wheel
The grinding wheel needs to be suitable for the workpiece material, the stock removal, the productivity, the surface quality and other parameters.
Grinding wheel parameters are:
- thermal conductivity
- dressing parameters
The workpiece height, relative to the grinding and regulating wheel, is the basis for good roundness and geometrical tolerances.
Grinding wheel and regulating wheel are usually positioned in the same height. The workpiece is positioned above this height.
This height difference is decisive for the roundness results. Out-of-roundness usually appears in the form of odd number polygons, for example 3, 5, 7 edges. The height, depending on the current wheel and workpiece diameters, results in an improvement or worsening for each edge number. The height needs to be adjusted to improve an existing unroundness and avoid generating a new one.
The coolant is a decisive factor for the grinding result. If the coolant is applied without pressure through a simple nozzle, it will not be able to break through the air cushion surrounding the running grinding wheel. The coolant will still transport chips and heat, but will not support the actual machining. By using properly targeted needle nozzles, the whole grinding process can be improved.
Experience, consulting, training and service are decisive for centerless grinding.
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