One of the most common tools found in the automatic tool changer (ATC) stations of machining centres and multi-tasking machines is the light cutting shoulder mill. This is because, apart from shoulder milling being one of the most prevalent machining operations, the cutters are versatile enough to be used for face milling, slot milling, ramping and more.

CoroMill 390 from Sandvik Coromant has for a long time been seen as the state-of-the-art square shoulder end mill, and now the company is extending this successful concept with the addition of the smaller 07 insert size. This becomes the first choice for small diameter, light cutting applications on low-powered machines, where it offers impressive levels of versatility and productivity.

The objective for the Sandvik Coromant design and development team was clear: to create an extremely versatile cutter for productive milling in a wide range of operations and materials. The solution had to offer trouble-free, reliable milling performance, as well as easy-to-use insert clamping to increase process security. The result was CoroMill 390 tools with size 07 inserts, a product that has close synergies with two other Sandvik Coromant innovations: the Coromant EH modular system; and the new steel milling grade GC1130.

Customer input

As with all Sandvik Coromant innovations, each is designed to address genuine machining challenges highlighted through extensive market research and customer feedback. Mixed production machine shops face the daily uncertainty of not knowing what jobs will come through the door next. This scenario, with different components and materials, means that having an optimised tool for each component feature is unfeasible. Instead, a set of tools is required that allows machine shops to produce whatever components are needed. Having the CoroMill 390 family of cutters, particularly with the extended 07 insert size, can be the difference between being able to service the needs of customers and having to turn down a new order due to lack of capability to produce the components.

The concept of ‘producing more with less’ – an increasingly prevalent industry trend – is facilitated further by multi-purpose end milling cutters capable of delivering top level performance. Here, investing in the modular system Coromant EH when choosing the coupling type will result in optimised tool holding options with a limited inventory. The coupling is self-centring and facilitates quick and accurate cutter head exchange, which saves costs in regard to eliminating the need for additional dedicated tool assemblies. This is of course vital for shops using small machining centres with a limited number of stations in the ATC unit.

What’s more, the short tool assembly of an integrated machine adapter and cutter head with Coromant EH coupling gives high productivity when the gauge line is critical. Modular systems, which allow users to achieve the required reach and accessibility with a series of different shanks and adapters, will also help reduce the number of tool changes required. Factors such as these help ensure consistent profitability, which is the bedrock of machine shop operations the world over.

Cylindrical shanks are a flexible solution suitable for numerous toolholding options.

On multi-tasking machines, undersized shanks can be used in different lengths and materials for stability and clearance when milling with long overhangs. The combined modularity of Coromant Capto and Coromant EH offers accessibility for hard-to-reach features. The versatility of CoroMill 390 is also favourable when the number of tool positions is limited on turning centres with driven tool holders.

Of course, there is a common viewpoint that versatile tools are good at many things but not great at specific operations. Aware of this, Sandvik Coromant set about refining the performance of the new CoroMill 390 end mills to ensure they achieve the highest levels in many different machining tasks. The cutters have been designed as the ideal choice for mixed production, as well as when a square shoulder end mill for a specific component feature is required.

Cutting edge innovation

So, what technical features underpin such elevated performance levels? Well, firstly the end mill cutter bodies are produced in a new material with increased heat resistance. Secondly, parts of the range have been optimised with differential pitch for applications that are particularly prone to vibration.

Process security also featured highly on the agenda when developing CoroMill 390 inserts. With this in mind, the light cutting geometries and high performance grades of this cutter concept are designed to give secure milling in all material groups. For steel milling, the new first choice insert grade is GC1130, which is produced with Zertivo technology. GC1130 offers a new level of process security thanks to long and predictable tool life with a clean and intact edge.

The objective for modern machine shops is to deliver secure milling in operations such as pocket milling, where one of the major challenges is ensuring the efficient and secure opening of cavities. Here, the typical solution would be to use helical interpolation and linear ramping to create pockets from a solid workpiece, but this requires strong insert face geometry. As a consequence, inserts are required that can adhere the stress caused by steep ramping or demanding interpolation, giving a low-vibration process with even tool life.

In shoulder milling operations, close-tolerance inserts and an exact insert position help produce shoulders without steps. The smooth cutting action of CoroMill 390 limits radial cutting forces, which provides machining with minimal bending and good wall perpendicularity.

Slot milling offers a set of different challenges, typically centred on chip evacuation and vibration. Indeed, these issues are exacerbated when milling with large engagements as vibration often accelerates tool wear. Here, light cutting geometry in combination with a cutter featuring optimised differential pitch can take care of this issue and offer a low vibration milling process. In a customer example involving slot milling, a subcontractor’s productivity was limited by its end mill as the two-insert cutter could only manage a cutting depth of 2mm. However, when switching to a CoroMill 390 cutter with three size 07 inserts, the cutting depth was increased to 3mm. Furthermore, cutting speed could be increased by 33%, and spindle feed speed by 50%. The upshot was a gain in productivity equal to 225%. As a bonus, the burr formation caused by the previous tool was nowhere to be seen when milling with the new cutter.

For key slot milling, specifically, the CoroMill 390 cutter with size 07 inserts is available in dimensions designed purposely for key slots. With a tool diameter 0.3mm smaller than the slot width, a suitable amount of stock is left for the subsequent finishing operation.

When it comes to face milling, the goal for machine shops is usually high metal removal rates with good surface finish – an ambitious combination that is not easy to achieve. For this reason Sandvik Coromant has designed geometries for milling with low cutting forces, which prove ideal for facing surfaces that demand a shiny finish and close tolerances.

Process security

To further improve process security in all types of milling operations, a new torque key is delivered with each cutter. Its built-in spring functionality makes it easy to mount inserts with correct clamping force, giving reliable and consistent tool life. Maintaining the process security theme, the cutters also offer internal coolant in operations where chips tend to get stuck – for example slots – and for machining of materials where elevated temperatures are undesirable.

In short, the new CoroMill 390 equipped with size 07 inserts for small diameters offers capability that is ideally matched to component features that have a cutting depth of up to 5.8mm. The smaller inserts deliver higher cutter-teeth density, giving superior output in many different milling operations. In combination with the new steel milling grade GC1130, productivity can be optimised.