Machining

DILLIDUR steels are very well suited for machining in spite of their high strength and hardness. However, some basic rules must be observed when machining these hardened steels. Vibrations should be avoided. It is therefore advisable to work on a machine that is as rigid as possible and to keep the gap between the work-piece and the machine (support) to a minimum. Similarly, it is advisable to fix the work-piece firmly to the work-bench.

Depending on the type of machining work, sufficient cooling should be ensured. An interruption of the coolant supply or insufficient coolants and lubricants can lead to overheating of the cutting edge, which can lead to increased wear of the cutting edge and, in extreme cases, to breakage of the tool. Please note the relevant information given by the tool manufacturer. To minimize maintenance costs and increase the service life of the tools, they should regularly be checked for wear (wear band) and ground.

The recommendations given in the following tables for the selection of tools and the machining of DILLIDUR steels are guidelines which may lead to different results for different machines.
The validity of these recommendations should be checked by the processing specialist on site.
Detailed information about machining and tool selection can be obtained by consulting tool manufacturers or DILLIN-GER HTTE GTS.

Drilling: DILLIDUR steels are well suited for drilling in spite of their high hardness. Suitable tools are cobalt-alloyed HSS twist drills, twist drills with brazed carbide cuttings, solid carbide twist drills (with internal cooling where appropriate) and drills with indexable inserts. For stable drills, the feed rate should be set rather higher when machining begins to ensure that the tool engages firmly. This helps to reduce vibrations. Before the drill is completely through the material, feed should be interrupted briefly. This reduces the tension on the machine and the tool and avoids breaking of the cutting edges. Details on the selection of tools, cutting speeds and feed rates can be found in Table 9.

Countersinking: Cylindrical and conical countersinking can best be made in hardened plates if the tool has a pilot. This prevents vibrations. The use of three-edged countersinkers can also contribute to a reduction of vibrations. Recommendations for cutting speed and forward feed are given in Table 10.

Tapping: Screw threads can generally be tapped by machine. Information on the selection of tools, cutting speeds and speeds can be found in Table 11.

Sawing: When using a band saw to saw DILLIDUR steels, we recommend grinding the flame cutting edge 1-2 mm deep in the area to be sawn and sawing the smallest cross-section. In practice, cobalt-alloyed or carbide-tipped saw blades have proved themselves there. We recommend a cutting speed of about 18 m/min with good cooling.

Milling: DILLIDUR steels can be processed with tools made of high-speed steel (HSS, TiN, TiCN-coated) and with tools equipped with indexable inserts. Please note that flame cut edges may show significantly higher hardness values than the rest of the material. Therefore, the first cut should be at least 2 mm deep, i.e. should go far enough below the heat affected zone. To mill DILLIDUR V steels, it is advisable to use round inserts. Experience has shown that this geometry is superior to a planar face milling geometry (i.e. with a 45°angle of incidence). The use of indexable inserts with a broad cutting edge chamfer also minimizes wear. Instead of cooling with emulsion, dry machining is recommended in this case. But the use of compressed air or minimal quantity lubrication can lead to further improvements in the service life. Indexable inserts are sensitive to vibrations. Therefore, all possible measures must be adopted to reduce vibrations, e.g. firm clamping of the work-piece. If large surfaces need to be processed, it is advisable to machine the plate alternately on both sides, as this enables distortion of the work-piece to be avoided. Recommendations for the cutting speed and feed rate for face and edge milling are given in Tables 12 and 13.