Generic vs. proprietary: new approach to turning needed as demands for complexity rise.
It has been a considerably different story for turning applications.
For parting, grooving, and threading processes, the use of proprietary tools has become somewhat common. However, for indexable turning tools, ANSI/ISO platforms maintain a near monopoly. Predominantly, this has resulted from the high flexibility of the system, which allows it to cover a variety of processes ranging from roughing to extreme finishing.
Typically, proprietary turning systems only apply to a small range of the substantial application area covered by the ANSI/ISO platform.
While the longstanding ANSI/ISO systems continue to provide a highly flexible solution, changes in manufacturing demands are beginning to highlight the need for suitable alternatives. The requirements for quality, accuracy, and precision have risen sharply in the past several years and the trend shows no signs of slowing.
Additionally, parts have become much more complex, changing the demands placed on the cutting tool. Unfortunately, the ANSI/ISO standard is becoming inadequate for these higher levels of precision and complexity.
With ANSI/ISO turning systems, VBMT and DCMT inserts are located with a screw that makes line contact with the insert hole and pulls the insert back toward the walls of the toolholder. A significant problem arises when this approach is used for profiling or turning in multiple directions. As the direction of the tool path changes from a facing cut to a longitudinal cut, the insert moves slightly.
This small effect results in pocket wear, which in turn allows for a greater degree of insert movement. Of course, increased insert movement leads to a higher rate of wear and the cycle quickly accelerates, leading to multiple problems.
The issue of pocket wear is even more apparent when using more advanced processes. Many of today's multitask machining centers allow operators to change the angle of the B-axis to match a complex part's unique features. As a result, the insert and toolholder in the B-axis are exposed to variable forces both in magnitude and direction. This added strain amplifies the potential weakness of ANSI/ISO systems.
As pocket wear and insert movement occur, the most noticeable result is reduced accuracy of the cutting edge location, which in turn detrimentally affects the accuracy of the workpiece. The issue also leads to substantially reduced tool life and the possibility of complete tool failure.
With an ANSI/ISO system, the only solution is to back off cutting feeds and speeds, creating a negative impact on productivity. To offer the levels of performance, manufacturers need to remain globally competitive, new turning systems must be created.
Bill Tisdall is development specialist manager for Sandvik Coromant US.
Rail system keeps location accurate, insert motion nil
Sandvik Coromant's solution to the dilemma of tool life versus productivity comes in the form of the CoroTurn TR, a recently introduced proprietary turning product.
The CoroTurn TR system addresses the issue of insert stability by introducing locating rails in the pocket of the tool and surface of the insert. Female rails on the insert match with male rails ground into the insert pockets. The mating surfaces are so accurate that insert movement is virtually eliminated.
While ANSI/ISO systems rely on pressing the insert flank against the wall of the holder pocket, the CoroTurn TR maintains accuracy of location solely through the rail system.
The insert used in the CoroTurn TR platform are direct pressed to an ANSI/ISO H-tolerance. An H-tolerance is extremely accurate, with a tolerance of [+ or -] 0.0005" on the iC and A- dimensions and tolerance of [+ or -] 0.001" on insert thickness.
Due to the tighter tolerance of the insert, total indexability of the system is less than 0.002". With no movement between insert and toolholder, accuracy is increased, tool life is extended, and more aggressive cutting data can be implemented.
The flexibility of the ANSI/ ISO platform will allow it to remain a leader for quite some time, but manufacturers, producing complex, high precision parts are quickly discovering its limitations.
Over the next several years, proprietary turning products such as the CoroTurn TR will take on a more visible role, allowing many shops to maintain an advantage in an increasingly competitive world.
Sandvik Coromant, www.rsleads.com/901tp-150
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|Title Annotation:||turning solutions|
|Publication:||Tooling & Production|
|Date:||Jan 1, 2009|
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