Manufacturing engineers in the automotive industry have tried almost everything to extract the last drops of productivity from their conventional turning processes. Although these processes are evolving by making small gains on an almost constant basis, a different approach looks set to help turning shops take a step forward.
With a different take on turning conventions, PrimeTurning from Sandvik Coromant offers opportunities for manufacturers tasked with the external turning of steel parts in high volumes. The methodology can not only address many of the common challenges faced by automotive original equipment manufacturers (OEMs) and suppliers, but also provide potential gains.
The specialised insert is designed for light
roughing, finishing and profiling
Steel turning dominates many automotive applications, including the production of transmission shafts and shift sleeves, and flange and post ends on engine crankshafts, for instance. Hub units, constant-velocity joint components and drive pinions are among further examples. In a market as notoriously competitive as automotive, all of these parts share a common requirement: To maximise productivity without compromising quality.
The question is how can this still be achieved? Turning is a mature process that has been edging forwards for a number of decades but without a major step-change of note. Sure enough, more rigid machines have been matched with ever-improving workholding and cutting tool solutions, but the methodology of turning itself has not evolved.
The upshot is that turning has become a bottleneck in comparison with many other manufacturing processes which have advanced at a faster rate.
Turning On Its Head
In contrast to conventional longitudinal turning, the new turning methodology allows the tool to enter the component at the chuck and removes material in the opposite direction. Turning “backwards” in this manner allows a small entering angle to be applied, which in turn can provide productivity gains.
Experienced operators are aware that small entry angles permit increased feeds, but in conventional turning are restricted to around 90 deg in order to reach the shoulder and avoid the long, curved chips that small entering angles characteristically generate. In contrast, the new process provides reach at the shoulder and allows for entry angles of 25-30 deg, with chip control and maintained tolerances.
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. With the new methodology, however, there are chip breakers, edge preparation and a machining strategy that can account for chip thickness and a gradual release of cutting forces when entering the workpiece. As a result, speed and feed rates can effectively be up to doubled.
The small entry 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 unwanted effect of conventional longitudinal turning.
This is good news for automotive manufacturing engineers under pressure to reduce cycle times and cost per part in order to stay competitive. The methodology also has additional benefits to offer, such as reducing downtime through fewer set-ups. This is because the new process allows for all-directional turning, which means that turning conventionally from component end to chuck can be performed using the same tools. This is supported by newly developed inserts that have three edges/corners: one for longitudinal turning, one for facing and one for profiling.
Efficient Edge Utilisation
As cutting is performed in the direction moving away
from the shoulder,there is no danger of chip jamming.
Conventional longitudinal turning uses the corner radius and a small part of the insert side to create the chip, whereas the new methodology uses just the side to create a thin and wide chip. For facing operations, conventional methods continue to rely on the corner radius, thus further increasing wear. In contrast, the new methodology uses the other side of the insert, delivering edge utilisation and longer tool life.
Traditional turning methods always use the corner radius when turning, which leads to concentrated heat, excessive wear and unfavourable chip forms that are difficult to break, while the new methodology generates the heat in a wider and different area so that heat can move away from the cutting zone. The chip is also straight and easier to form.
All-directional turning presents possibilities for automotive shops to perform existing operations in a more optimised manner. Tests show that the new turning process is typically best suited to short and compact components, although all-directional turning inserts mean that slender parts can also be processed (conventionally) using a tail stock. With specialised Coroturn inserts, feed rates up to 1.2 mm per revolution and depths of cut up to 4 mm can be achieved, depending on the application.
Turning Code Generator
To highlight the potential gains on offer to automotive manufacturers through a combination of the new methodology, specialised inserts and a new code generator. Numerical control code changes can be viewed as problematic to many machine shops. With the aim of simplifying adoption of the new process, the specially-developed code generator facilitates changing from conventional toolpath programs to the new methodology.
Furthermore, it helps to maximise output through the application of optimised parameters and variables, and ensures process security with suitably adjusted feed rate and entry radius data.
The new methodology is suitable for use on CNC turning centres and multi-tasking turn-mill machines, and early customer tests have yielded results. For instance, when turning a hub made from cast steel (SAE/AISI 1045) on a Gildemeister CTV 250 CNC turning centre, a machining company in Brazil was able to achieve significant benefits.
Using the same cutting speed (300 m per min), the adoption of the specialised inserts allowed feed rates to be increased from 0.25 mm per revolution to 0.4 mm per revolution, 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 overall impact on profitability is expected to be considerable.
The new methodology will thus appeal to automotive OEMs and their tier 1, 2 and 3 suppliers that know their cutting data and its current limitations.
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