PCD FLUTED HELICAL DRILL FOR COMPOSITE MATERIAL

We have seen a progressive broadening of the application of new exotic materials such as: 

-  plastics synthetically reinforced with carbon fiber (CF.R.P.), 

- M.M.C, composites containing green silicon carbide,  

- synthetic materials containing fortified ceramics, carbon and carbon   carbon fibres,  

- aluminium and various reinforced carbon fibre sandwiches,   

- glass fibre, plexiglass, agglomerated panels containing wood, carbon, glass fibre or refractory alloys, 

developed in the aircraft, space and nuclear industries.   

Previously, the use of these materials was reserved only for very high technology applications but they are now finding their way into mass production in automotive applications. The objective remains the same in the use of these materials: to improve the mechanical performances of components, to reduce the weight and thereby, fuel consumption and to reduce the cost of maintenance.   

The replacement of the carbide-tipped tools by tools using polycrystalline diamond (PCD) has lead to significant increases in depth of cut and tool advance rates. These cutting tool materials have made it possible to obtain improved surface quality thereby eliminating the need for subsequent machining operations.  They allow the complete machining of the component in one operation.  

In milling synthetic reinforced materials, surface speeds are about 200 to 3500 mm/min in Vc with advances of around 0.1 to 1mm/tooth, in turning 180 to 1100m/mn with advances of 0.05 to 0.25mm/tr.  However, there has been a certain field of application with no satisfactory solution: drilling. Indeed, there are PCD drills on the market but a large number of the tools offered are with stepped material, without the helical cut in the PCD. This configuration induces high cutting pressures resulting delamination of the materials being drilled.

 In addition, these drills are designed based on standard drills, often with the important helix angles fixed between 25 to 30°. This results in difficulties in the removal of swarf and clogging of the flutes by the removed material. This leads to deterioration of the component being drilled and a reduction in the lifespan of the drill.   

Today not a lot of company produces PCD drills with helical flutes in the PCD and the helix angle optimised according to the workpiece material requirements. 

In 1994 Diamoutils filed its first patent n° 89 15445 on rotary tools with diamond and the process for production. At the time, further development was not made due to the high cost of production.  

 Today, technologies have evolved and have moved forward and Diamoutils can produce helical PCD drills which are far more technically advanced and more economical to implement. These latest PCD drills have a far superior cutting edge which considerably reduces the problem of delamination of the workpiece material around the drilled hole. Their positive cutting angles produce a significant improvement of the material structure around length of the drilled hole. These PCD drills also produce greater accuracy compared with tungsten carbide drills.  Significantly, three major properties of polycrystalline diamond (PCD) are exploited for optimum performance: wear resistance, compressive strength and the excellent thermal conductivity which is released in the body of the tool.  

 During operation, a majority of heat is generated at the point of drilling, where a drill can carburize in synthetic composite materials. In materials reinforced with carbon fibre, this limits the drilling performance to around 25m/min Vc with an advance of approximately 0.02mm/tr and a lifespan lower than 70 holes.  Helical PCD drills operate at more than 100m/min Vc with advances of 0.02/tr which results in a time saving of around 90%. In addition the tool life is increased about 40 to 100 times compared with that of a drill which carburizes in materials discussed here.  Finally the very high wear resistance of the PCD provides the possibility to regrind the drill, if it is carried out prior major to damage to PCD material. 

Diamoutils remains at your disposal for all development of helical PCD drills. These drills are available from 4 mm to 13 mm diameter with a point angle of 120° but are also available with certain diameters with reversed point.  

These drills complement the product line which can be viewed on www.diamoutils.com                                   

 La le 2 juillet 2007 – JF BUCOURT.