Gun Drilling in Tool Steel

For several years now there has been a trend among mold and die makers to try and avoid heat treatments on their products if possible. There are several benefits in doing this: the obvious lower costs, shorter delivery times, and a controlled consistency of the properties, as the risk involved with heat treatment can be avoided.

This trend has become even more critical during these difficult economical conditions. Mold and die makers must be even more competitive with their costs, but it is also crucial to be able to deliver the products in as short time as possible, especially with the end customers placing the orders as late as possible. At the same time, long production runs are not as common as before, making it even less important to heat treat the molds and dies to the highest hardness possible.

To meet this increasing interest in avoiding heat treatments, steel makers are manufacturing more wear resistant and harder mold and die steels. Currently, the prehardened steel with the highest toughness and hardness in the market is the tool steel Toolox, manufactured by Swedish steel maker SSAB Oxelösund AB (Oxelösund, Sweden).

Toolox 44 has a high hardness of 45 HRC and an excellent machinability thanks to its low carbon content and high homogenity. However, mold and die sometimes have machining difficulties the first time they use this steel. The most critical operation has been found to be long hole drilling (i.e., gun drilling). Long hole drilling is typically carried out in mold and die making when cooling channels are required in the tool.

To develop procedures and recommendations that successfully perform this gun drilling process in Toolox, SSAB found it beneficial to cooperate technically with tool supplier Botek GmbH (Riederich, Germany) and the French long hole drilling specialist René Devaux (Montreal Lacluse, France).

Optimizing the drilling parameters and the tooling, René Devaux did not find the long hole drilling operation too difficult to make. In one test, five 12 mm diameter holes were drilled to a depth of 650 mm, giving a combined total depth of 3250 mm without any complications, no re-sharpening of the drill was needed.

Based on the tests that were carried out, Botek shares the following comments on long hole drilling in 45 HRC Toolox steels:

• Long hole drilling in Toolox 44 is totally possible, but parameters need to be individually adapted for each application
• No vibrations can be accepted
• Coated tools with the correct carbide type are extremely important
• It is crucial to have the recommended angle on the drill tip (not to sharp)
• 100 percent drilling oil is needed (no mixture can be accepted)
• For holes longer than 40X diameter, support of the drill is needed

The development of special steels, along with new parameters in tooling, are the way forward, but the important technical know-how of how to capitalize on these innovative developments, and to take advantage of the major benefits they offer, are crucial to the success of the relevant industries. The successful cooperation and commitment of SSAB-Botek-René Devaux is a good example of how a total solution can be achieved and offered to the end customers.

Botek GmbH, 61380 Oxelösund, Sweden, +39 521 618823, Fax: +39 521 618816, www.botek.de.

www.toolox.com