Manufacturing solid carbide coolant-through drills: From powder to finish

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Coolant-fed drills have become increasingly popular despite their higher cost. These tools feature internal channels delivering coolant from the toolholder through the body of the drill to the cutting edge. Directing coolant to the point of cut helps keep the drill cool, reduces wear, provides lubrication, improves chip evacuation, and limits heat buildup in the workpiece.

A carbide blank supplier delivers the rod as a centerless-ground blank with the coolant holes already formed. These internal holes follow a helical path matching the helix angle of the finished drill.

Have you ever wondered how these coolant holes are created? They can’t be drilled or electrical discharge machined (EDM), because the channels are helical. Twisting the rod – either in the green state or after sintering – is also not feasible. Instead, during pressing, a pre-formed core made of helical wires is placed into the mold, and carbide powder is compacted around it to create the green preform. These wires, typically metal (such as nickel) or polymer (such as nylon), act as sacrificial inserts. During sintering, the blank is heated in a furnace, and those wires melt or burn out, leaving behind the coolant channels.

The next stages are completed across three different CNC grinding machines. Centerless grinding is first used to establish a straight, round rod and bring the diameter into a tight tolerance. From there, a CNC pinch/peel grinder is typically used. The ideal setup includes an automatic part flipper, which allows the machine to rotate the blank in the collet so both ends can be ground in a single cycle.

First, the machine grinds features such as the end chamfer, the straight back face, and the coolant slot. The coolant slot at the shank end ties together the coolant inlets for the two internal channels. Its purpose is to ensure coolant can enter the drill’s internal passages regardless of the toolholder being used. A peel grinder typically uses one wheel oriented parallel to the blank to rough grind the outside diameter, and a second wheel mounted on the same arbor to grind the slot. The position of the internal coolant holes is located in-process by a camera.

After the blank is flipped, the pinch/peel grinder finishes the outside profile: grinding the final drill diameter and the required back taper. A pre-point can also be ground in this same setup to reduce wear on the various wheels during the subsequent final point grinding.

A multi-axis CNC tool grinder (typically 5- or 6-axis) is then used to grind the flutes, reliefs, and point geometry. To align the flutes with the internal coolant channels, the machine first locates the two coolant exits at the tip. For most drills, this is done with an electronic touch probe. For very small drills with tiny coolant holes (below 0.040"), a vision system is used instead whereby a camera captures the radial and axial positions of the holes so the CNC control can orient the grinding correctly.

MyGrinding Inc.
https://www.mygrinding.com