Solid PCD drills development process

Polycrystalline diamond (PCD) tools are more efficient than traditional tungsten carbide tools when machining parts for power machinery and leading tool manufacturers are developing and producing PCD drills. The cutting edge of these tool products is made of PCD material, and the drill body part is solid carbide material. The Carbide drill body has good rigidity and dimensional accuracy to ensure the processing quality of drilling, and the spiral chip flute can improve the chip removal performance. These characteristics are very necessary for drilling processing. The cutting-edge part is made of PCD material, which has high wear resistance and can improve processing efficiency and service life.

 

Tool development process

① Material selection;

In order to solve the problem that ordinary insert-type drills cannot make large helix angles, we choose front-end cylindrical or conical PCD. For tools with smaller diameters, we can use PCD as shown in Fig. 1 for insert design, and small diameters can also make large helix angles; for large-diameter drills, only cylindrical PCD or conical PCD as shown in Fig. 2 can be used to ensure a large helix angle the design of.

② Welding;

For the selection of different PCD raw materials, we choose different welding technologies. The alloy-free substrate of the insert type drill adopts vacuum brazing technology. The high-efficiency brazing material is usually a high-melting polymer material, so the brazing temperature is very high.

In order to avoid the negative effect of high temperature on diamond oxidation, the welding is selected in a vacuum environment. For large-diameter cylindrical or conical PCD materials, we choose high-frequency welding. During induction high-frequency welding, the high-frequency current generates an induced current in the workpiece through the coupling effect of the external induction coil of the workpiece, thereby heating the workpiece and the welding piece, and the welding piece is melted. After cooling, multiple single parts are welded together.

 

③ Produce;

When drilling CFRP composite laminates, it is very difficult to select the appropriate tool geometry. Drilling of CFRP materials usually requires a large helix angle and a long cutting edge, because the carbon fiber should shear along the cutting edge, which is achieved by a small drill point angle. In addition, the drilling of CFRP materials should also reduce the axial force to avoid spalling of the machined material when the tool is retracted.

In view of the above characteristics, the PCD drill must have a very sharp cutting edge geometry, a large cutting rake angle, and a large helix angle, and the helix angle is about 30°. In order to achieve tight hole tolerances, it is absolutely necessary that the drill tip has excellent self-centering properties.

 

From another point of view, the angle of the drill tip also plays an important role in the formation of burrs. Drill tip angles below 90° or above 150° are known to help reduce burr height at the exit of the drilled hole, but self-centering performance is poor. Therefore, a double point angle design is recommended, where the inner point angle is 130° and the outer point angle is 80°. The PCD drill adopts a double support design to increase the dimensional stability of the machined hole.

 

The PCD material is difficult to process, and making the helix angle on the PCD increases the difficulty. In response to the above problems, we use the electric grinding compound integrated grinding machine for the electrolytic machining of the PCD part and the alloy part for grinding. In this way, we can carry out a variety of geometries and drill tip designs for PCD drills for different working conditions.

 

④ Measure.

The PCD monolithic drill is finished, and its quality control is also critical. The finish of the edge of the drill bit directly affects the processing quality of the workpiece to be processed. After processing, we will first observe the quality of the cutting edge under a stereo microscope. Dimensional measurements are carried out on the tool setter to ensure that the dimensions of the processed product are within the tolerance range.