Turning of crushing cones in austenitic manganese steel
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The two main application areas for CBN are:
  • machining of hardened steel
  • machining of grey cast iron
There are several types of hardened steels including case hardened steels (in gears, shafts etc), through hardened steels (in bearings etc) and tool steels (in moulds, dies, rolls etc).Grey cast iron is not hardened, but highly abrasive, and can be found in automotive brake components (brake discs, brake drums etc).

Normally CBN only works when the steel component is hardened, with a hardness above 50 HRC. One exception are the so called austenitic high manganese steels. These are steels with a manganese content of 11% or more, originally invented by Sir Robert Hadfield. In its original state, the material is usually around 250 HB, but the hardness is increased significantly through deformation hardening when used, without any loss of toughness. The hardness is also very difficult to measure with high accuracy due to the high level of work hardening.

The application areas for these materials are in the mining industry, such as in components for cement mixers, rock crushers, railway switches and crossings, crawler treads for tractors, teeth for excavators and other high impact and abrasive environments.

The deformation hardening will affect the material also during machining, and this impacts the selection of materials that can be used for machining.

Cutting data when using carbide has to be very low, cutting speeds in the range of 20 to 30 m/min is normal. By instead using CBN, cutting speeds can be increase to 200 m/min, which significantly improves productivity.

One typical application where Seco Tools has a long experience and has been very successful is turning of crushing cones.


 These components are usually cast, and machining include one or more roughing cuts depending on the stock allowance, and one finishing cut. Seco Tools’ grade CBN500 has been developed to meet the challenges when machining these materials.

CBN500 is a high cBN-content grade with high wear resistance and high toughness. Other application areas for CBN500 include machining of hardened chrome irons and rough machining of hardened steel components.

Crushing cones are usually machined with round inserts or large nose radii inserts. A round insert has the advantage of multiple “edges”. At a depth of cut of 2 mm, there are six usable edges per side (twelve edges in total) on a round R...12-insert.

A typical example is shown below, where they were using carbide. The cutting speed is low, and they have to do several insert changes during the cut. The much higher cutting speed with CBN reduces significantly the machining time and the machining down time due to tool change. Due to the high wear resistance of CBN500, typical tool lives in these materials are up to 60 minutes time-in-cut.

What used to require 20 pcs of carbide inserts, can now be done with one single CBN insert. This means that not only are the components machined much faster, the insert cost per part is also lower. By using CBN, the productivity is increased, and the tooling cost is reduced.


 
For more information, please contact your local Seco representative, or our Advanced material (PCBN/PCD/CERAMIC) team.

Author:
Henrik Sandqvist
Product Specialist SECOMAX PCBN/PCD/CERAMIC
SECO TOOLS Shanghai CO., Ltd. Level 2, Building 8, 456 HongCao Rd., Shanghai 200233, China
Office: +86 21 5426 5849
Mobile: +86 186 167 90063
e-mail: henrik.sandqvist@secotools.com

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