Deep hole drilling
[2][3][4] With large diameters, the l/D ratio is usually limited by the travel or the bed length of the deep hole drilling machine.
The mentioned tool types differ with regard to the realizable diameter range, the achievable l/D ratios, the surface quality and their productivity.
The advantage of the symmetrically designed tools compared to the "classical" deep hole drilling tools in the small diameter range is the feasibility of significantly higher feeds f, which can be 6 times higher compared to the usual values for single-lip deep hole drilling.
Important for the good surface quality is the asymmetrical design of the deep hole drilling tools.
Due to this design features, a certain amount of the cutting forces during the process is transferred via the guide pads to the bore hole wall.
Due to this forming process the surface roughness caused by the engagement of the cutting edges during drilling can be decreases by about 70%.
Subsequent steps to improve the surface quality of the bore hole can often be reduced or eliminated completely.
[1][12] Characteristic for single-lip deep hole drilling is the internal coolant supply through one kidney-shaped or two circular cooling channels.
The general structure of single-lip tools is divided into three parts: the drill head, the shank and the clamping sleeve.
The drill head is usually made of carbides of the ISO cutting application group K 10 to K 20 and is coated if required.
In this respect, a distinction is made between different cutting edge angles and the circumferential shape of the guide pads.
The choice of the circumferential shape, i.e. the number and arrangement of the guide pads on the circumference of the single-lip drill, is also important.
In addition, single-lip drilling achieves comparatively high bore hole qualities, which can reduce the need for post-processing.
It can also be seen that approximately 1/4 of the shank consists of a grove, in which the coolant flow flushes the chips out of the bore hole.
BTA stands for "Boring and Trepanning Association" which was dominated by the now liquidated company Gebrüder Heller in Bremen Germany.
Burgsmüller used a double-edged tool and an air-oil mixture, which is nowadays used in production with minimum quantity lubrication.
In most cases, the rear side of the BOZA is sealed by a stuffing box, which also guides the drill tube.
In the BOZA, the tapping bush is usually integrated, which means that working with a pilot bore hole in the BTA process is rarely necessary.
Tools The chips are removed through the openings integrated in the drilling head with the aid of the cutting oil flow.
This creates a negative pressure (ejector effect) at the chip mouth, which facilitates the backflow in the inner tube.
As the pipe cross-section through which the chips are to be removed is reduced by the double tube system, the cutting capacity is lower than with the BTA process.
For this reason, lower cutting speeds are usually selected for ejector deep hole drilling.
[1][14][13][7] A prerequisite for the implementation of the process is the use of a connecting piece which is inserted into the turret holder of the lathe or the spindle of the machining centre.
The hole can be post-processed with regard to their surface finish or can serve as a basis for machining complex and non-cylindrical contours.
If the radially extendable cutting tool holder is controlled via an NC axis and connected to the NC bore slide of the deep hole drilling machine, it is almost possible to produce any bore hole wall contour in one cut over the entire contour length.
[19][20][21][22][23][24][25][26] Another machining process to increase the surface quality and dimensional accuracy of a bore hole is the use of single-bladed reamers.
The difference to single-lip deep hole drilling with low cutting depth is the usually missing circumferential chamfer, a long side cutting edge parallel to the milling axis and the low coolant volumes and pressures.
