Innovations in insert grades that moved machining forward

Metal cutting represents a substantial part of industrial activity and the role of innovations in this area has through higher productivity had a very positive effect on the economy at large, adding to prosperity and quality of life in society.

The role of tool-material grades – especially cemented carbide – has been a major one. This is because the capability of cutting edges in machining metal plays such a huge role in the overall manufacturing productivity.

This has driven grade development at Sandvik Coromant which has been pioneering since the 1950s and marked by numeous innovations.

Enter ready-to-use cutting tools

For the first half of the 1900s, metalworking companies had to fix their own cutting tools or buy special tools for operations. There were no standard programmes of tools and solutions. Tool materials were mainly high-speed-steel and, on the increase, cemented carbide for brazed tools. Since then, machines, equipment, numerical control and tools have developed dramatically to make parts much more efficiently and to higher quality levels.

Since indexable-insert tools were introduce during the 1950s, output in machining has increased many times over. From their idea of introducing ready-to-use, standard tools, Sandvik Coromant have led the way to the high-tech tools and methods of today. Innovations in tool material is as much about developing manufacturing processes as it is about material sciences. It is in the insert-making processes where setting and achieving targets for grades have made in making the best use of tool materials.

Quality and innovation

The year 1942 marks the beginning of metal cutting as we know it today. Sandvik Coromant was formed on the business idea of making better use of the potential held by cemented carbide as a superior tool material. This composite tool-material had been well-known for some fifteen years but its useful properties had only been put to very limited use in relation to its capability, and then mostly in rock-drilling. However, the success of cemented carbide that was to follow was only due to the chain of innovations. Already in 1943, there were six newly-developed grades of cemented carbide available from Sandvik Coromant and ten years later, there were twelve grades that optimized metal cutting over a broad area as brazed tools.

The quality of the cemented-carbide used for cutting tools had been an issue from the outset at Sandvik Coromant, with much being learnt from dialogues with customers. In 1954, a dedicated cemented carbide factory with R&D facilities was built, and the vital step to achieve the tightly-controlled quality that was to become a corner-stone of Coromant-tools globally.

In 1957 Sandvik Coromant introduced the first indexable-insert tools – the T-Max range for turning. Although the market-interest in “throw-away” (indexable) inserts was poor initially, when the domineering manufacturing-companies adopted them, insert tooling took off in use. Machine shops could adopt more efficient, high-volume machining and tool re-grinding shops for brazed tools were not needed any more.

An innovation in un-coated grades from these early days (1956) was the insert-grade called Coromant S1 Premium – the first of the big productivity-boosters. S1P outperformed everything else in turning by a good margin as regards cutting data and tool-life - and thus reducing machining time for finishing and light-roughing. This was in its day a superior grade that was also recommended for turning without any coolant for various steel-types and even alloyed cast-iron. This grade was developed to be particularily suited to indexable inserts and really opened up the eyes of machine shops as to what improvements were to be expected from innovations in tool material.

During the 1960s, inserts and grades were developed to suit additional operations, such as milling, drilling and threading. In 1963, Coromant had introduced eighteen (uncoated) insert-grades that covered broad areas of machining.

Coatings made the difference

The concept of indexable inserts was to be the means for the next huge innovation in 1970. It meant that properties such as brazability and grindability of cemented carbide could be disregarded completely, opening a new door to developing cemented carbides. R&D led to that adding a very thin coating to the insert had a dramatic effect on cutting speed capability and tool-life. The chemical vapour deposition method (CVD) provided a hard titanium-carbide layer of a few microns on an insert substrate. This led to first coated carbide-insert : GC125. It was a ground-breaking innovation, with a giant step forward in machining performance.

The coated-insert grade brought with it a marked reduction of machining time through higher cutting-speed capability and/or providing a longer tool-life. Two more coated grades followed in the early seventies (GC135 and GC315) with different application-areas to that of GC125. These first three coated grades had standard-grade substrates, which was subsequently seen as a limitation. The next step was then to develop specially-designed insert-substrates for specific coatings to be applied on - in that way further increasing the capability of the coated insert. The first grade with a substrate tailored to the coating was GC1025 introduced in 1973 and represented the second generation of coated grades.

The reaction from other tool manufacturers to these innovations was one of disbelief but the new reality of elevated performance soon dawned with a new benchmark having been set.

A stream of innovations

The seventies were a remarkable decade for new approaches in cutting tool technology to lift machining performance. For a turned component of mixed cuts, the typical cutting time in 1969 would have been five-and-a-half minutes. A decade later, the same component was machined in under a-minute-and-a-half. This amazing progress in productivity was due particularily to that of continued coated-grade development. But it was also due to, in parallel, the many innovative tool-solutions, developed during the seventies by Sandvik Coromant. To name a few : the first indexable-insert parting tool, the first double-coated insert grade, the first anti-vibration boring bar, the first positive turning insert, with an open-wavy-type chipbreaker and the first indexable-insert drill.

In the mid-seventies, a major step forward in coated grades took place when inserts could, for the first time, be coated with aluminium oxide – a ceramic material having high chemical stability, that reduces wear at elevated temperatures, and low thermal-conductivity, that protects the insert-substrate from heat. Based on this development, Sandvik Coromant introduced grade GC015 for the area of turning that is dominated by the need for wear resistance – typically finish-turning at high cutting speeds. This grade was based on a Coromant patent using, for the first time, a double-coating solution where the inner layer was titanium carbide.

One of the limitations at this stage was that only thin layers of aluminium oxide could be applied. However,developing tool-material manufacturing processes were since some time back an important part of Sandvik Coromant science-innovations and by 1980, a catalysed, chemical-vapour-deposition method had been put to work - which led to yet another generation of coated grades : GC415, another, improved hard finishing grade. This was in parallel to the development of GC435, a very tough grade for secure, rough turning and broad GC425 grade – to complete the series of grades to cover and optimize steel turning. The development of a process for a stronger bind between titanium-carbide and variable thicknesses of aluminium-oxide led to this series of multi-layer coated inserts with higher performance during the eighties.

New insert generations and new processes

During the 1990s, more than twenty new grades had been developed, most of which were coated and mostly for turning, different workpiece materials and different operational demands. Yet another generation of coated turning grades were developed (GC4000-series) where the chrystal-structure of an even thicker aluminium-carbide coating was provided, with considerably improved strength especially for the GC4015 grade, targeting higher cutting speeds.

On the developments of coating processes, another route was followed to produce a different kind of grade altogether. CVD coatings could not be applied on tools with sharp edges due to the inherent brittleness of the ceramic material. The physical-vapour-deposition (PVD) process of coating solved this with a new line of grades being devloped (GC1025 and GC1125). The PVD coatings provide a very high amount of cutting-edge toughness and, although these coatings cannot reach the level of wear resistance of the thick CVD-coatings, the wear resistance provided is still very much higher when compared to uncoated tools.

Since then, development of CVD and PVD processes have meant that the two types of coated grades have become closer in application and resulted in programmes of insert-grades that complement each other. Changes in applications, conditions, operations, machining-rates, workpiece-materials and component-quality in the manufacturing industry have been all highly influencial in the development of these new grades over time.

A lot more was going on, resulting in groundbreaking innovations for tool material. Diamond coating of inserts was one, which improved turning of aluminium by allowing the the use of chipbreaking insert-geometries by moving away from only compacted, solid polychrystaline diamond tips. Cermet-grade development for finishing, cubic-borin-nitride for hard-part-machining and ceramics for super alloys were additional developments in parallel to cemented carbide. Also ongoing was the important development of grades for indexable inserts for milling, drilling, parting and grooving, thread-turning and solid-carbide tools.

Process development

In the mid-nineties, a medium-temperature (MT) CVD-coating process was developed which provided improved orientation of chrystals for a titanium-carbo-nitride inner coating to be applied. Fine-grain coatings had also been introduced which played a vital role in capability. This gave multi-coated grades much better strength and adherance to the insert-substrate with longer, secure tool-life at high cutting speeds.

Another big advantage of the new MT-CVD coating process was that carbon was not taken from the substrate – resulting in a wider choice when designing insert-substrates. The new substrates became less sensitive to cutting-edge deformation as well as to thermal cracking – two very destructive and hence unwanted wear patterns. The first grade made with this technology was actuaslly a coated grade for milling : GC3020, followed by the turning grade LC25. But it was also the secret of success behind the GC4000-series of turning grades.

Gradient-zone technology became an important source of development by Sandvik Coromant. This is where functionally-graded structures are created, such as cobalt-enriched surface layers to establish desired balancing of properties in the substrate.The compostion in the substrate surface-zones of coated inserts became an important means with which to achieve various coated-insert grades. These advances were mainly used to improve plastic deformation resistance with edge toughness. Basically, the phase containing cubic carbo-nitrides when concentrated in the cutting edge was found to improve the hot-hardness. Beyond the cutting edge, a binder structure rich in tungsten-carbide inhibits crack tendencies and gives resistance to chip-hammering effects.

CVD-coatings came to be regarded as relatively thick and able to combine various combinations with which to provide different effects. As an example, titanium-carbo-nitride gave high hardness and abrasive-wear resistance, along with the excellent aluminium-carbide properties, with titanium-nitride as the golden top-coat for added wear resistance and wear detection. The main aim of the thinner, hard PVD-coatings was to add wear resistance through sequenced and/or lamellar coatings, in numerous layers in the nanometer range.

A range of PVD coatings have evolved, where some examples are titanium nitride with allround properties, titanium carbo-nitride for high wear resistance, titanium-aluminium-nitride with very high hardness and oxidation resistance and PVD-oxide for chemical inertness and crater-wear resistance. In this way, ranges of CVD- and PVD-coated inserts came to form complimentary application ranges where the dominant properties could be used for far-reaching optimization of machining operations – where the edge sharpness was one important factor.

Another important route in insert-grade development was that of post-processes, involving basically such methods as blasting and brushing of coated edges. These were developed into different insert-manufacturing processes which were found to complement the effects provided by coating and to provide distinct positive effects on the insert surface.

For example, by using blasting as a post treatment, compressive stresses are introduced in the coating which provide improved insert toughness

New century – new innovations

This development of cemented carbide grades which commenced with start of the 2000-century demonstrated the enormous potential which was still available with coated inserts – and still is. This potential was recognized through close ties with machine shops and how they wanted to develop their machining. The pin-pointing of the optimum application and recommended application ranges were enhanced through more detailed studies of not only the required toughness and wear resistance of a grade but also the deformation resistance, coating adhesion, thickness and the edge-line reliablity.

For the twenty-first century, a new insert generation was developed, taking the GC4000 series a second, higher step ahead.

In 2005, the introduction of GC4225 marked a marked step in grade improvement for this dominant, intermediate application area in steel turning. Advance was made in considerably reducing the rate of unwanted wear types or even eliminating them completely. Wear mechanisms that were found to interact with each other could be countered with this new grade, giving longer, secure tool-life. Slower, predictable, natural flank-wear - at higher cutting speeds - had been the objective with the new grade and this was reached by a good margin. The newly-developed grade was so successful and broad that it took over operations from both ISO P15 and P35 insert-grades. A completely new coating and post-coating processes had been developed to lift performance and production security.

Continued huge potential of coated cemented-carbide

To arrive at a next step in insert-grade technology, Sandvik Coromant is now in the midst of R&D for new coating technology, powder technology, indexable-insert pressing technology, cutting-edge treatment technology, post-treatment technology and new technology for metrology. Materials for both indexable inserts and solid-carbide tools will form the next generation of cutting tools.

The aim is to yet again bring longer and more predictable tool-life in combination with opportunities for increased output rate. These tool materials will also be solutions for limited-supervision and unmanned machining operations and above all to provide metal cutting that gives users lower machining costs per component.

Since coated cemented carbides were introduced 1970, the basic principle remains the same but the coated insert has evolved to what could then only have been seen as science fiction. The basic sciences involved, as well as processes and development methods and means, have come a long way, as have the knowledge behind actual insert-grade development. Today`s multi-layer coatings on indexable inserts – as well as specialized un-coated grades - have given machining huge reductions in cutting time compared to the pioneering single-coated GC-inserts, let alone the grades before these. Moreover, a huge potential for advances remain for this versatile tool-material.

Sandvik Coromant

Established in 1942, Sandvik Coromant is a part of Sandvik Group with its head office in Sandviken, Sweden. Our Gimo factory is the world’s largest carbide insert manufacturing plant. With more than 8,000 employees worldwide, Sandvik Coromant is represented in more than130 countries, 27 state-of-the art Productivity Centers and 11 Application Centers located around the world. The 4 Central Distribution Centers in the Netherlands, the US, Singapore and China supply our customers directly and rapidly. Sandvik Coromant is a world-leading producer and supplier of cutting tools and over 30,000 products cover all aspects of turning, milling and holemaking in the metal cutting industry. We spend nearly twice as much on R&D as the industry average and own over 600 active patent families. Twice a year, we introduce more than 2,000 new products with our renowned Coropak. Sandvik Coromant opened its first office in China in 1985. The company is registered in Shanghai and the headoffice is in Beijing. Through the development for the past more than20 years, Sandvik Coromant Greater China Region has built a service network with 42 representative offices. Our engineers are providing products and services to our machining customers across China. We have established Productivity Center in Shanghai and Beijing and Application Center in Shanghai. Training Centers are opened in Guangzhou, Xi’an, Chengdu, Shenyang, Wuhan, Nanjing and Hangzhou. Our Advanced Center for Engineering Solutions and special tool manufacturing plant is in Langfang, Hebei.

Contact details for editorial enquiries
Contact: Lianne Mills
Tel: 86-10-65399902
Email: Catherine.li@sandvik.com

www.sandvik.coromant.com