IN a growing number of operations today it is the toughness property of an indexable insert which is playing an increasingly decisive role in providing productivity increases. The main reasons are higher security, larger application areas in combination with cutting data increases.
In both turning and milling, the ability of the insert to withstand new operational demands often determines how competitive the machining is.
Sandvik Coromant is currently introducing three new insert grades to provide improved performance in the toughness demanding operations in steel machining.
Steel milling - demands have changed
As a process, milling is a series of interrupted cuts, which means that entering and leaving the workpiece always demands certain toughness in the grade. The tool concepts used in milling today have in most cases positive geometries, with sharp and positive-angle edges. This emphasizes the demand for added toughness to be provided by the grade - the tool-material - compared with turning, where negative basic-shape inserts still dominate.
Several trends that have affected the demands made on milling insert-grades:
* The growing use of smaller, low-powered machines, ISO 40 and HSK 63, with higher spindle speeds and table feeds.
* Multi-task machines and turn-mill centres are increasing at about 35% per year. In these machines the tool has to reach into the workpiece or past the chuck, making additional demands on the tools. When tools are longer by design this leads to less stability at the cutting edge which in turn makes demands on the insert-grade toughness. The main tool-concept in these machines is the CoroMill 390 endmill, size 11 and 18 with Coromant Capto size C6 as the dominating tool/spindle interface.
* The growing use of 5-axis machining also affects tool development and the way insert-grades are positioned.
There is considerable difference between demands on grades according to the type of milling cutter the insert is used in. A square-shoulder cutter (90-degree entering angle) needs tougher inserts than a facemilling cutter (45-degree entering angle or round-inserts).
Previous tough insert-grades have needed to be optimized for today's more toughness-demanding tool-concepts. This is the reason the new GC1030 and GC4240 are focused on the CoroMill 390 cutter. But at the same time, the tough grades are needed as back-ups in very severe conditions for facemills like the CoroMill 245. In fact, even if the focus has been on square-shoulder machining, the new grades have also achieved better results in other operations.
Potential to optimise the new positive-cutter concepts
Modern tool-concept development has to some extent been directed towards the growing number of weaker machining centres and that this has changed the way milling inserts are designed. With a strong focus on a positive cutting action with more teeth, but with each cutter-tooth taking less material, there has been a need for new developments of insert grades. CoroMill 390 endmills and round insert cutters such as the CoroMill 300 are examples of these with dedicated inserts. Since most insert-grades for milling were developed for tools employing ISO-standard inserts, there is an interesting potential for which to develop a new platform of grades to optimise the new positive-cutter concepts.
Today, it is not a question of trying to initiate a new machining-era as actually optimising new grades for an era that has already begun. Compared to the existing grades for this area of steel milling, the new grades GC4240 and GC1030 are considerably better adapted for use in CoroMill cutter-concepts for steel milling. The most obvious benefit is the marked improvement in reliability during machining. This enables more un-manned machining and in batch-production and the potential to increase cutting speed leads to increased productivity.
All machine shops, irrespective of size, machine types and production batches will benefit from these new grades primarily through enhanced security against sudden insert breakdowns, resulting in more predictable insert behaviour.
For example, when it comes to demanding steel-milling operations - in large- or small-batch production - there has always been a need for almost constant supervision. The new insert-grades will provide a new perspective on this by coping with the operational demands in a better way.
The new grades are also ideal for milling in mixed-production machining, with small batch sizes of different components and materials, because of the greater flexibility that they provide. They are more capable than comparable grades and provide a good tool-rationalization potential for machine shops.
Steel turning - many expectations
A broad insert-grade for turning operations requires a lot of creative grade-development. The challenge lies in providing a high performing multi-functional insert-grade, such as the new GC4225, with the ability to satisfy the individual requirements of tens-of-thousands of users. Each one has expectations on how such a grade should perform on their components, and in their machines.
The challenge therefore lies in making the grade the best for most users` needs, while not compromising on the performance in peripheral operations. It is much more straightforward to develop a high-performing insert-grade for a narrow band of turning-operations than a field-leading, mid-range grade.
The ISO-P25 mid-range area dominates as regards the share of performed turning operations in that it represents around forty percent (40%), well above finishing which asses to thirty percent. Especially in what is called general steel turning, the breadth of the previous mid-range grade has grown to dominate the area and it is expected the new GC4225 to exceed this. In mass-production industries, the tendency has been to prefer P15 grades because of their ability to optimize cutting data through higher wear resistance. Machining has often been carried out in stable machines suited to the task as well as components designed more specifically for production in question. But also in this area, a new-generation, mid-range grade such as GC4225 has the ability to play an important role in increasing machining speeds. Consequently, the right, flexible and optimised P25 grade goes a long way today.
Higher productivity is the main advantage provided through the new steel-turning insert-grade GC4225. Such are the capabilities of this new grade that the user will be offered a very broad application area, with no compromises in performance. Shorter machining times, improved machining security, higher cutting data, longer predictable tool-lives and fewer tools needed to cope with different operations have also been achieved. These are improvements vital for staying competitive.