The recent arrival of all-directional turning and tools has re-written the conventional rules of this age-old machining process, offering tantalising improvements in productivity. By Håkan Ericksson, general turning product manager, Sandvik Coromant
The question for machine shops now is whether they can—or should—make use of this new process in their own operations.
There are many challenges facing modern machine shops looking to achieve competitive gain and increase order levels. Not least among them is productivity. Factors such as inefficient cycle times and bottlenecks have the potential to slow order throughput and damage business reputation through delayed deliveries. Many assume that turning, as a mature machining process, has reached its limit in terms of technological step-changes, leaving machine shops feeling frustrated with slow speeds and feeds.
And yet there is a solution: all-directional turning allows manufacturers to achieve more without any investment in costly capital equipment such as new machine tools. In fact, this radically different approach permits customers to harness the power and capabilities of machines already owned.
Achieve More With Less
So, how does it work? Well, in contrast to conventional turning operations, the new methodology sees the cutting tool enter the component at the chuck and remove material as it travels towards the end of the component. Using specially designed inserts and tool holders, this allows for the application of a small entering angle that promotes increased feed rates and significant productivity gains, typically around 50 percent.
Of course, some machine shops have already tried turning from chuck to part end with small entry angles, but the problem has always been chip control. The small angle produces long, curved chips, forcing manufacturers to apply angles of around 90 deg to reach the shoulder. However, these chip control issues are dissipated when turning from chuck to component end, permitting 25 to 30 deg entering angles to be applied with excellent results.
This advantage is achieved because the small entering angle and higher lead angle create thinner, wider chips that spread the load and heat away from the nose radius, resulting in increased cutting data and/or tool life. Furthermore, as cutting is performed in the direction moving away from the shoulder, there is no danger of chip jamming, a common and unwanted effect of conventional longitudinal turning.
One Insert, Three Functions
As part of its functionality, the process also provides for all-directional turning, which means that conventional turning (from part-end to chuck) can be performed using the same tools. In fact, the inserts have three edges/corners, one for longitudinal turning, one for facing and one for profiling, thus delivering efficient edge utilisation and longer tool life.
Parts made from ISO steel, stainless steel, cast iron, and heat-resistant super alloys and titanium materials will benefit. In fact, almost any general turning operation will achieve gains, including many in the automotive and aerospace industries. The returns will be particularly impressive for high-volume batch sizes (>100-off), or when machining large components where there is a need to reduce set-up time, production stops and tool changes.
The only machine required is a CNC turning centre. To highlight the potential gains on offer, when turning a hub made from cast steel (SAE/AISI 1045) on a Gildemeister CTV 250 turning centre, a machining company in Brazil was able to achieve significant benefits. Using the same cutting speed (300 m/min) as a competitor insert, the adoption of the latest all-directional inserts allowed feed rates to be increased from 0.25 mm/r to 0.4 mm/r, and depth of cut from 1.5 mm to 3 mm. The result was a 59 percent increase in productivity and 55 percent more tool life. With over 120,000 hubs a year being produced, the impact on profitability is considerable.
Increase In Productivity
A further example can be seen at a machine shop in Italy producing parts from forged nickel alloy (ASTM B564) on a Doosan Puma 3100M turning centre. Here, the application of the latest inserts permitted cutting speed to be increased from 150 m/min to 300 m/min, feed rates to be elevated from 0.3 mm/r to 0.8 mm/r, and depth of cut to be doubled from 2 mm to 4 mm. The outcome has seen an 85 percent increase in productivity and 125 percent more tool life. Annual volumes for this particular part are approximately 5,000.
Using a recently introduced twin tool holder, machine shops can also enjoy the benefits of the new process on multi-tasking turn-mill machines. Two inserts can be mounted on the twin tool holders, allowing manufacturers to perform both roughing and finishing operations, and overcoming the often slow tool-changing times (15 to 20 seconds) of multi-task machines. Manufacturers with vertical turning lathes can also apply the new process, using axial tool holders.
Having The Right Mindset
Ultimately, machine shops with the right “mindset”, competence and discipline will enjoy the biggest gains. The manufacturer must be open to change and new ideas in the pursuit of genuine market advantage. As with any process, there are production prerequisites that will help garner success. For instance, the use of stable fixtures, lathes with sufficient torque and rigidity, and CNC units with high-end processors, will help maximise productivity, process flexibility and tool life. An example is the PrimeTurning process from Sandvik Coromant.
Machine shops have the option of two unique inserts: CoroTurn Prime A-types feature three 35 deg corners and are designed for light roughing, finishing and profiling, while CoroTurn Prime B-types with their ultra-strong corners are designed specifically for rough machining. The tools are purpose-designed for use with precision coolant. The Prime A-types come with under- and over-coolant provision, while the Prime B-types offer just under-coolant. As a rule, under-coolant should always be applied for better tool life, with over-coolant is used for chip control.
The inserts are supported by a large number of tool holder variants, including the CoroTurn Capto, QS shank and conventional shank. Complementing the tooling is the PrimeTurning code generator, which supplies programming codes that are compatible with a wide variety of CNC machines. The new code generator not only ensures maximum output, but also process security with suitably adjusted feed rate and entry radius parameters.
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