From 10 to 700 – mixed machining at an unprecedented level

The lightweight construction and downsizing of the motor with ever-increasing requirements for power affect the material used. A few years ago, many automotive manufacturers produced the top half shell of the crankshaft bearing out of aluminium instead of out of cast iron that was used before – this was due to the lightweight construction. For this purpose, MAPAL had developed ISO indexable inserts for boring the aluminium cast combination that was successfully in use. Today the development has moved a step further due to downsizing. Together with the top half shell made of aluminium, today manufacturers increasingly rely on sintered steel instead of cast iron for the bottom half shell. This steel features a higher strength than cast iron and is therefore more suited for the increased mechanical loads.

Here the challenges for machining are changing. With the advent of sintered steel in engine production, no ISO indexable inserts were available on the market that met the high demands for machining the aluminium/sintered steel combination.

This is mainly due to the chemical reaction that takes place between the iron alloy and the cast aluminium. Tool manufacturers had to deal with a completely new form of wear. During machining, a solid phase was applied on the insert and caused it to break after a few applications. To counteract this wear and to prevent the chemical reaction, MAPAL developed a completely new cutting material. Using this, mixed machining – for the aluminium/cast iron combination as well as the aluminium/sintered steel combination – is reliably performed. The ISO indexable inserts reliably work in the cast iron or steel part of the crankshaft bearings as well as in the aluminium part.

On the one hand, this leap in development was achieved with modified carbide substrates and optimised micro-and macro-geometries of the insert with adjusted rake angles. On the other hand, it was achieved with a newly developed PVD coating. This is based on a TiAlN alloy with a special dopant. As a result, not only the formation of a built-up edge in the aluminium is prevented, but the cutting material is so resistant to wear and heat that high quality machining of the cast iron/steel part can be achieved.

Depending on the application, customers can choose between ISO indexable inserts available as standard. MAPAL offers four geometries each for the aluminium/cast iron and aluminium/sintered steel combination. In addition, special indexing inserts are available with the new cutting material. The results using the new cutting material are impressive in practice. Previously only ten bearing journal bores were machined from the combination of sintered steel and aluminium with one insert. Now an impressive 700 bores are machined with the new cutting material.

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