Jason Allen* examines the kind of tools needed to drill the perfect hole.
HOLE making operations are always considered to be a demanding task and require several factors for creating a perfect hole.
The quality of the hole can be affected by the depth, workpiece setup, coolant qualities and chip evacuation methods.
The pocket design of a drill must take good advantage of the cutting forces, which are mechanically exerted upon the tool. These forces are then converted into gripping forces that are used for tightening the insert towards the back of the pocket. In that sense, the more the cutting forces applied the better gripping forces are obtained.
The clamping forces around the connection area generate little strain, preventing any potential plastic deformation and by that providing at least triple the amount of head indexes. The most important attribute of the new clamping design is therefore a 50% increase in productivity.
Deep hole drilling
Deep hole drilling is very popular in the automotive, die and mold and aerospace industries.
Standard applications are normally undertaken by a solid carbide drill with a length to diameter ratio of 13X D. However for high productivity, repeatability and accuracy the gundrill technology is most recommended for deep hole drilling applications.
Iscar has developed a gundrill that enables the replacement of drilling heads while the driver is still connected to the machine. The ‘No Setup Time’ concept enables quick head changes without the need to remove the drill from the spindle while indexing.
The end result is excellent straightness and concentricity inside the hole with high hole precision centre alignment. In addition, surface roughness is easily obtained within the range of 0.4-1.6 Ra.
Drilling composite materials
Drilling composite materials is perhaps one of the most challenging tasks that industry is facing these days, particularly in the aerospace industry.
In the past, drilling composite materials was associated with flaking, delaminating layers, burn marks, poor surface finish and inadequate concentricity. The extent of these faults appeared to be even worse when attempting to drill sandwich or stacked materials, comprising a layer of titanium on top of carbon fibre reinforced plastics and a final layer of aluminium.
Drilling composite materials is considered a very crucial operation for the aerospace industry and drilling riveting holes have to be made with a high level of accuracy in terms of diameter, surface finish on the walls, roundness and concentricity. Iscar’s solution lies in a tool, mounted on a Multi-Master shank, which by using interpellation movement inside the material generates the perfect hole.
The tool operates in a sequence of performing roughing, semi-finishing and finishing – producing a perfect hole, of the right accuracy in terms of diameter, surface finish, roundness and concentricity, without any undesirable phenomenon of flaking, delaminating layers or burn marks.
Another common way to deal with this demanding drilling operation in composite or sandwich materials is by using orbital drilling. However, this technique has its own limitation and involves much invested capital in machinery.
*Jason Allen is the Managing Director of Iscar Australia. For more information phone 02 9722 4500 or visit the website at www.iscar.com.au.