To increase productivity, the non-cutting time must be shortened. This allows more components to be produced per shift. © Sandvik Coromant

Each grade from these areas must therefore fulfill numerous requirements: For example, fracture resistance is of the utmost importance, as the cutting edge must be hard enough to withstand plastic deformation caused by the extreme temperatures in the cutting zone. In addition, the indexable insert coating must prevent flank wear, crater wear and built-up edge formation. Furthermore, the quality of the coating adhesion is crucial, as otherwise the substrate is exposed and there is a risk of premature tool failure.

To avoid such problems, delaying continuous, controllable wear and eliminating discontinuous, often uncontrollable wear are the keys to success. Predictable tool wear is therefore the goal. Given the trend towards machining with limited or even no monitoring, this is not easy to achieve.

In any case, the optimum wear pattern for any indexable insert is controlled flank wear, as this leads to a predictable service life of the cutting edges. The ideal grade for this is one that limits the development of undesirable types of wear or even prevents them from occurring in the first place.

It all depends on the right variety

To maximize the number of components produced, it is crucial to choose the right carbide insert. For this reason, Sandvik Coromant has developed the new ISO P turning grades GC4415 and GC4425 for machining steel alloys in the ISO P15 and P25 ranges. While GC4425 offers improved wear resistance, heat resistance and toughness, GC4415 has been developed to complement it for all machining operations that require higher performance and even greater heat resistance.

Both grades are suitable for machining low-alloy and unalloyed steel. They can machine a larger number of components within large and small series production and help to extend tool life. They also prevent unexpected tool breakage and reduce reworking and scrap rates.

Both grades feature second-generation Inveio technology with a unidirectional crystal orientation in the aluminum oxide coating. Its properties become clear on a microscopic level: each crystal in the aluminum oxide coating is lined up in the same direction, which creates a strong barrier to the cutting zone. The crystal orientation of the second-generation Inveio coating has been significantly improved once again. Inveio gives the indexable insert high wear resistance and ensures a longer tool life, which helps to reduce the cost per component.

Other parameters must also be taken into account, in particular the geometry of an indexable insert and how this influences chip control and machining performance.

Improved geometry

The geometry refers to the design of the insert, which is designed according to the type of machining. Finishing, medium machining and roughing each have specific effects on the cutting speed and their own working range in terms of acceptable chip breaking in relation to feed and depth of cut.

In turning, the three most important cutting parameters - cutting speed, feed rate and cutting depth - have a significant influence on tool life and therefore on the cost per component. After all, a 20 percent increase in cutting data can reduce the cost of a component by 10 percent.

The ISO P turning grades GC4415 and GC4425 have been specially developed for machining steel alloys in the ISO P15 and P25 ranges. © Sandvik Coromant

To help users select the best inserts and grades for their application, Sandvik Coromant offers the free online application CoroPlus Tool Guide.

Holistic approach to turning

A model developed by the American mechanical engineer Frederick Winslow Taylor at the beginning of the 20th century establishes a relationship between cutting speed, tool wear and tool life. Taylor came to the conclusion that using the greatest possible cutting depth reduces the number of machining passes required and therefore the machining time. At the same time, he pointed out that optimized turning of steel depends on the stability of tool clamping, workpiece fixturing and coolant application as well as the performance of the machine tool. Taylor's model shows that optimized steel turning goes beyond the choice of grades and geometries. Manufacturers should consider the entire tool concept. Everything from the insert grade to the clamping design to the tool holder helps to increase output, reduce costs and achieve a higher level of process reliability.

This holistic approach was put to the test by a general engineering company. It used the GC4425 carbide indexable insert to manufacture a drive shaft from heat-treated, low-alloy steel 42CrMo4 (material no. 1.7225) with a hardness of 40 HRC. The wear-resistant, heat-resistant and tough grade is capable of working with higher cutting data and is commonly used for machining gears and pumps as well as for various applications in the automotive and plant industries.

The workpiece was subjected to multidirectional external roughing. The performance of the GC4425 was compared with that of a competitor's ISO indexable insert. As a result, the GC4425 was clearly ahead, as the cutting speed vc could be increased and the feed rate fn multiplied. While the competitor's indexable insert was only able to cut at vc = 183 m/min and fn = 0.33 mm/rev, GC4425 achieved vc = 244 m/min and fn = 0.51 mm/rev.

Ultimately, the use of the GC4425 carbide indexable insert enabled a 100 percent increase in productivity with a 50 percent reduction in cycle time. Overall, the customer achieved a cost reduction of 30 percent.

This result shows that manufacturing companies that consider the entire tooling concept can achieve more profitable production and lower costs per part. And this holistic approach to insert grades, geometry and the overall economics of the machining process is crucial if companies are to remain competitive in the face of the ongoing impact of COVID-19.

Rolf Olofsson, Product Manager at Sandvik Coromant / ag