New Mixed Machining Formula For Automotive Engine Applications

The lightweight construction and continual downsizing of the motor with an ever increasing power demand has consequences on the material selection process. A few years ago, many automotive manufacturers produced the top half of the crankshaft bearing out of aluminium instead of the previous cast iron construction for weight reduction purposes. 

For this purpose, MAPAL successfully developed its ISO indexable inserts for boring the aluminium and cast combination. Today the development has moved a step further due to downsizing. Together with the top half shell made of aluminium, now manufacturers are increasingly relying 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 to meet the high demands for machining the aluminium and 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 prevent chemical reaction, MAPAL developed a completely new cutting material. Using this, mixed machining for the aluminium and cast iron combination as well as the aluminium and sintered steel combination can now be 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. 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 and steel part can be achieved.

Depending on the application, customers can choose between ISO indexable inserts that are available as standard. MAPAL offers four geometries for the aluminium/cast iron and aluminium/sintered steel combinations. In addition, special indexing inserts are available with the new cutting material. The results using the new cutting material are impressive. 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.