All about Reaming Technology
A reamer is a type of rotating cutting tool used in metalworking designed to enlarge the size of a previously formed hole by a small amount but with a high degree of accuracy and to generate smooth surface.
Initially, Reamers were made of tool steel and hand operated similar to hand tapping. Later on the reamers were used on drilling machines and were made out of High Speed Steel. Again the process of reaming remained a low speed time consuming operation.
With advent of CNC machines came the need for faster operation. With development in cutting materials like carbides and improved manufacturing technologies have led to development of modern day High Precision High Speed Reamers with carbide cutting edges. With High Precision and High Speed reamers we can typically achieve size tolerance of IT 5 to IT 8. Surface Quality of Ra 0.2 Microns to Ra 1.2 Microns.
Reamers based on the arrangement of cutting edges can be widely classified are Single blade reamer and Multi blade reamer.
The single blade reamers derived their design from Gun drill / BTA geometry and commercially available single blade reamers have exchangeable cutting edges and 2-3 large brazed guide pads.
Advantage of Single blade reamers are highly accurate and provide excellent surface quality and size consistency. The limitations are they are highly expansive and require expansive setting systems. Single blade reamers are therefore chosen for very special applications in cast iron work pieces.
The Multi blade reamers are derived from the classic HSS tool design. The reamer has multiple carbide cutting edges brazed on to steel body. In New developments the Bigger size reamers (typically > 40 mm) could be with indexable inserts as well. In the multi blade reamers each of the cutting edge will have CIRCULAR LAND that provide the burnishing action.
Reaming Process
In the Reaming process basically two actions take place. The first is the metal cutting process by the Bevel similar to the Wedge action of a single point tool. All of the actual cutting is done by the bevel. Therefore the bevel angle is of great importance. The chip cross section and thereby the cutting condition and the bore size are influenced by the bevel shape and characteristics.
The cutting action is followed by the Burnishing action done by the circular land. In addition to the burnishing process in the space between the circular land and the work piece surface the coolant forms a thin film lubrication to ensure that work piece material is not burnt and the life of the cutting edge is enhanced as well.