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Paul Williams, turning and tooling product manager at Sandvik Coromant, has considered best practice for parting and grooving.

Such are the demands of modern machining operations that in recent years parting and grooving has grown to become a specialist area of turning in its own right, with a range of applications requiring dedicated tooling systems and solutions.

To obtain the optimum performance from parting and grooving tools there are some important factors that demand consideration.

Sandvik Coromant has extended its parting and grooving programme as the result of ongoing research into grade substrates and insert geometries that help control swarf more effectively.

With a range of parting and grooving tools, inserts and tool holders now available Sandvik Coromant is working with its customers to help select the right tool and high-performance insert grade for each application, and provide the ideal cutting data start values.

Sandvik Coromant can also provide optimised programming strategies to help avoid machining problems.

Parting and grooving sounds straightforward enough but within its remit lay a number of similar operations that all demand different machining and tooling strategies.

These include bar parting, tube parting, single-cut grooving, circlip grooving, undercutting, internal grooving and profiling, as well as more conventional operations such as groove turning and face grooving, which involve both radial and axial feed.

Corocut 1- and Corocut 2-edge systems are for all grooving, face grooving, turning, profiling and undercutting operations, along with medium (up to 40mm workpiece diameter) parting-off.

This system is based on a patented rail and V-shaped design, which together with a long insert, gives stability to enable running at higher cutting data.

The inserts are available in widths from 1.5-8.0mm and come in a variety of geometries to suit different applications, materials and feed rates.

Corocut 3 with its economical triangular-shaped inserts (widths 1.0-2.0mm) is intended for shallow parting in the high-volume bearing industry, while for deep parting operations the Q-Cut 151.2 V-clamped, single-edge insert is recommended.

More specialised operations, such as small-diameter internal grooving and small-diameter face grooving, are catered for using the thinner insert design of Q-Cut 151.3.

Other Sandvik Coromant offerings in this area include: Corocut XS, a tangentially mounted system suited to machining micro components on sliding head lathes; Corocut MB, which features a front mounted exchangeable insert for internal grooving, threading and turning in 10-25mm holes; and U-Lock 154.0 three-edge inserts for economical circlip grooving.

All of these solutions come in a range of insert widths.

Most of the Sandvik Coromant offerings in this technology field can be categorised under the headings of parting, grooving and profiling, and each has its own factors to consider regarding appropriate machining strategies.

For instance, when parting bars a narrow insert is recommended in order to save material and minimise cutting forces.

Similarly, insert tool overhang should not be greater than 8x insert width in order to avoid instability, which can lead to tool failure and poor component quality.

Other practical hints to increase tool life and prevent inconsistent performance when parting bars include: reduce the feed rate by 50 per cent around 2mm prior to the part falling off to avoid edge damage; and deploy dwelling (in microsteps) to help chip breaking in long chipping materials.

With regard to grooving, single-cut grooving is an economical and productive method of producing grooves using insert widths up to 8mm.

However, when generating wider grooves, the user has a choice of strategies that include multiple grooving, plunge turning or ramping.

All are roughing operations and each has to be followed by a separate finishing operation.

The rule of thumb is that if the width of the groove is smaller than the depth, multiple grooving should be used – with the converse true for plunge turning – while for slender components ramping may be applied.

Profiling is a strategy used when turning components with complex shapes, and using profiling inserts is a good way to achieve high metal removal rates.

However, wraparound is a problem that can occur with round inserts when profiling into corners.

In this situation, a large area of the insert is in continuous contact with the workpiece, creating high cutting pressure, so the feed needs to be reduced.

If reduced too much, vibration can occur.

To minimise the problem, the insert diameter should be as small as possible compared with the radius being generated.

A good starting point is to use 50 per cent feed into radius plunging compared with parallel cuts.

Sandvik Coromant has developed a number of grades and geometries to suit all parting, grooving and profiling applications, although workpiece material must also be considered before making any selection.

For instance, for hardened steels (50-65 HRc), Corocut inserts with geometries GE for grooving and RE for profiling are available in 3-8mm widths, while Sandvik Coromant’s CB7015 CBN grade is recommended at 130m/min cutting speed and 0.05mm/rev feed rate.

For machining aluminium and other non-ferrous materials including copper, brass, bronze and plastic, a sharp edge and open chip breaker is needed to be successful.

Grade GC1005 is recommended for roughing operations while the sharp-edged H10 or H13A are ideal for finishing.

Feed rates of 0.2mm/rev and cutting speeds of 300m/min and higher can be achieved.

Customers machining heat-resistant super alloys (HRSAs) such as nickel-, iron- or cobalt-based alloys will know that machineability is generally poor compared with steel and stainless steels.

HRSAs typically call for the use of Corocut 1- and 2- edged inserts with PVD coating, such as GC1105 for medium finishing and MTCVD grade S0F5 for roughing.

For higher cutting speed, ceramic inserts in grade CC670 in the 150.23 system will improve productivity when roughing.

Regarding grade selection it is crucial to detect if the grade is too wear resistant (hard) or too tough (soft) by inspecting the edge line behaviour.

Edge lines exhibiting early plastic deformation indicate that the grade is too tough and that a more wear-resistant alternative should be used.

Conversely, edge lines showing early signs of chipping indicate that the grade is too wear resistant, requiring a tougher grade instead.

Parting and grooving also set high demands on accessibility since the inserts are often fed deep into the material.

This means narrow machining and therefore the length of the tool increases as the diameter increases.

Tool holders with high stability are very important and here the Coromant Capto system is recommended along with its full programme of clamping units, cutting units and adaptors.

Naturally a full range of conventional toolholders is also offered.

Additionally, the new modular blade system, Corocut SL, offers a large variety of blades so users can build their own holder.

Corocut SL consists of straight and face-grooving blades for external and internal use.

Adaptors are available in 0deg, 90deg and 45deg angle styles, as well as in Coromant Capto and shank holder versions.

The common sense tip here is to always mount blades with the shortest possible overhang to avoid vibration and deflection.

Effects such as these will not only have a visible impact on the workpiece, but also on the insert.

In all cases, achieving the best possible economy regarding insert life, workpiece quality and optimised cutting data, means careful observation of the insert edge is required.

For instance, at low speed, built-up edge (BUE) and chipping are common problems, while at high speeds plastic deformation, flank wear and crater wear are the main unwanted pitfalls.

Addressing the cutting speed, along with factors such as centre height and overhang, along with correct feed rate, insert geometry and coolant supply ensure Sandvik Coromant customers can rest assured that advice based on decades of experience will lead to optimised and highly economic parting and grooving processes.

Sandvik Coromant

Part of global industrial engineering group Sandvik, Sandvik Coromant is at the forefront of manufacturing tools, machining solutions and knowledge that drive industry standards and innovations demanded by the metalworking industry now and into the next industrial era.

Part of global industrial engineering group Sandvik, Sandvik Coromant is at the forefront of manufacturing tools, machining solutions and knowledge that drive industry standards and innovations demanded by the metalworking industry now and into the next industrial era.

Educational support, extensive R&D investment and strong customer partnerships ensure the development of machining technologies that change, lead and drive the future of manufacturing. Sandvik Coromant owns over 3100 patents worldwide, employs over 8,500 staff, and is represented in 150 countries.

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