Grinding is the machining process of removing material from a work piece to get the desired size and shape by feeding the work piece against a rotating grinding wheel. In precision surface grinding machines normally the work piece is clamped on the bed of the machine and is fed against the precision grinding wheel which is rotating at very high rpm. In case of precision cylindrical grinding machines the work piece which is clamped on to the spindle at head stock side rotates and the grinding wheel which is rotating at very high speed is fed against the work piece.
Grinding Wheels
The grinding wheel may be compared to a cutting tool with thousands of minute cutting teeth which are firmly held by a bonding material. The cutting element in all grinding wheels is the abrasive grains. These abrasive grains on a grinding wheel actually cut chips out of the work and when cutting edge become loaded (blunt), the abrasive grains on the surface of the grinding wheel are released by the bonding material and new abrasive grains start acting as cutting teeth. When abrasive grinding wheels were first made, the abrasives used in these grinding wheels where hard, natural minerals like emery and corundum. Later artificial abrasives with uniform grain size replaces materials like emery. This resulted in high quality grinding wheels with uniform grin sizes through out the grinding wheel which are used for precision grinding.
Type of Grinding Machines
In metal working, grinding could be precision grinding or tool and cutter grinding. Precision grinding is done on a surface or cylindrical grinding machines where the size tolerance of the work is exceedingly small and the surface finish required is high. Grinding is also preferred when the work piece is hard and removing material by conventional machining processes like turning or milling is not effective. Tool and cutter grinding is the operation of sharpening the cutting tools like drills, milling cutters etc by grinding. I will be mainly discussing about precision grinding than tool cutter grinding.
Precision Surface Grinding
Surface grinding is one of the most commonly used precision grinding process. Precision surface grinding produces flat surfaces on work pieces with very good dimensional accuracy and high surface finish. It is also possible to grind angular surfaces and radius on a precision surface grinding machine using various attachments. In sheet metal stamping die manufacturing, precision surface grinding machines are very much essential to machine stamping die components with high accuracy.
Precision Cylindrical Grinding
Cylindrical grinding is a precision grinding operation by which round work pieces of high dimensional accuracy and surface finish are produced. Precision cylindrical grinding is often done on a cylindrical part which is pre-machines using a lathe machine to get the required size tolerance and surface finish. The work piece is held on the head stock spindle using a chuck or collet and draw bar. Cylindrical grinding can also be done by holding the work between centers and transferring the spindle motion to the work piece with the help of a grinding dog. The grinding wheel which is rotating at a high rpm is fed against the work piece which is running at a lower speed.