Latest CBN tooling developments set productivity advances and cost savings

Sumitomo Electric Hardmetal CBN tooling

There is an ever-growing need to improve productivity, reduce lead times in production and an ability to respond to increased demands for savings when machining fully hardened steels, hard powder and sintered metals and heat resisting super alloys. Here, the latest advances in cubic boron nitride (CBN) tooling are introducing special compounds, high efficiency coatings and new geometries to withstand heat, further improve surface finish and accommodate greater mechanical shocks such as those generated in interrupted cuts.

For instance, Sumitomo Electric Hardmetal is introducing a ‘hybrid’ series of CBN hard turning inserts, new chipbreaker designs and a new range of micro-boring bars for holes as small as 2.5 mm diameter. The new product launches add to its highly successful SumiBoron range of CBN tooling that now covers milling and end milling cutters, plus tools used for turning, grooving, threading and boring.

Both the SumiBoron hybrids, BNC2010 high precision grade and more general purpose BNC2020 feature multi-layered, heat and wear resistant micro-structured coatings on sintered CBN powder blanks with a substrate that incorporates a carbonitride binder. As a result, these inserts demonstrate high orders of positive application advantages.

To further improve performance and application of the new grade inserts, the company has also developed a totally new series of ‘Break Master’ chipbreakers, N-FV, N-LV for finishing hardened steel and N-SV for improved chip control when removing a carburised layer. In addition, ‘One-Use’ wiper edge inserts: Type WG for low feed turning and WH for higher feed rate applications are now available.

By extending CBN to micro-boring bars, the BSME and SEXC series are designed for ultra-small holes as fine as 2.5 mm diameter in hardened materials which can be finished bored and the also tools used for facing. On recent trials using SumiBoron BSME micro-boring bars on HRC 60 material, tool life was increased from 400 to 3,600 parts on CNC sliding head turn-mill centres and when producing 7.1 mm diameter holes in hardened automotive components, the switch to Sumitomo’s SEXC bore bar recorded the number of parts produced per insert corner increased by over 400 per cent.

Trials against more conventional coated CBN inserts used for hard turning of transmission shafts, BC2010 inserts were able to improve tool life by 230 per cent and when BC2020 was applied for turning automotive constant velocity joints, which featured interrupted cutting in the machining cycle, tool life was increased by 150 per cent.

CBN has excellent hot hardness characteristics second only to diamond allowing it to be used at very high cutting speeds. The SumiBoron material has substantial levels of toughness, resistance to the effects of thermal shock as well as chemicals. Now with Sumitomo firmly entrenched in the second generation of CBN, the material is used to not only machine ferrous materials, but also grey cast irons, challenging heat resisting super alloys and hard powdered metals containing tungsten and titanium carbide where diamond would be unsuitable. Indeed on cast iron, the latest CBN gives distinct advantages in cutting life efficiency with a superior finishing capability than could be achieved with the likes of carbide, cermets or ceramics.

As a result, users are now able to play the higher productivity advantage of single operational strategies on materials over 45 HRC and thus eliminate grinding and EDM processes, hand polishing and other time consuming, highly skill-dependent and difficult to control finishing processes. Indeed, above HRC 55, CBN is the only cutting tool that can effectively replace the traditional grinding process. As a result, single cycle finish machining aids the reduction of lead times, helps control important geometric relationships on a component, lessens the need for tool change interruptions due to the extensions to in-cut life, reduces work handling, and aids costly environmental issues such as disposal of grinding fluids and sludge.

The hybrid, physical vapour deposition coated (PVD) SumiBoron BNC2010 high precision turning grade incorporates no fewer than seven layers of coating. Three are highly secret developments and each is sandwiched between layers of TiCN in order to create high orders of integrity to the cutting edge and resist flank wear of the insert. Finally, in order to help create the superior surface finish, the insert is topped with a layer of TiN.

To differentiate the use of BNC2020, the insert is ideal for more general applications of continuous cutting, light as well as heavier impact type cuts where a higher resistance to chipping around the edge of the insert is needed such as when interrupted cutting. The insert incorporates an adhesive layer to bond its tough CBN substrate to the outer TiAIN layer.
The addition of the newly developed Break Master N-FV, N-LV and N-SV chipbreakers enable chip control to be improved in hardened material production cycles with N-FV ideal for finishing with up to 0.2 mm depth-of-cut. N-LV delivers better performance when depths-of-cut are up to 0.3 mm and N-SV is targeted at the removal of carbonised layers on hardened as well as non-hardened parts.

SumiBoron ‘One-Use’ Type WG and WH wiper inserts are primarily for continuous cutting cycles on hardened steel where comparable finishes to grinding can be achieved. WG is used on low-feed rate turning applications and WH for higher speed continuous cutting conditions.

The move to use CBN on micro-boring tasks opens new opportunities bringing consistency of finish and increased tool life on ultra-small hole machining which can be as fine as 2.5 mm diameter in hardened materials. The same tool can be used to finish bore and face maximising the advantage of the tool material. The BSME tool has a brazed CBN cutting edge on a carbide tool shank, which adds stiffness, for bore sizes between 2.5 mm diameter by up to 5.3 mm deep up to 5 mm by 20.3 mm deep.

Meanwhile, the SEXC version utilises a two-corner, indexable CBN insert able to machine bores from 4 mm diameter by 8 mm in depth, to 6 mm diameter by 18 mm deep. For this insert there are two grades of CBN available, BN2000 and BN7000, each with a 0.2 mm nose radii. BN2000 has a honed preparation to the insert’s sharp edge while BN7000 maintains a normal sharp edge.

Both tool types have through tool coolant and each tool shank across the range can be held in a common 6 mm diameter sleeve with two clamp screws. A location dead-stop pin ensures repeatability when setting depths which can be maintained within 0.02 mm.

Recent trials on the CNC sliding head turn-mill centre involved precision finish turning of a cone in hardened HRC 60 material using neat oil coolant. The brazed SumiBoron BSME tool demonstrated an increase in the number of components produced per tool to 3,600 compared to a competitor tool that had a recorded life that was inconsistent with variations between 400 and 1,500 pieces. The cutting speed was 48 m/min with a feed rate of 0.2 mm/ rev and depths-of-cut between 0.02 to 0.05 mm.

When finish boring the 7.1 mm holes with emulsion coolant in hardened automotive components, the use of Sumitomo’s SEXC indexable insert grade BN2000, increased the number of parts produced per corner by over 400 per cent to 2,700. Cutting speed was 156 m/min (7,000 revs/min) feed rate 0.03 mm/rev with depth-of-cut, 0.10 mm.

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