In machining aluminium alloys, here is what will help manufacturers reduce unit costs and achieve process reliability. Article by Walter AG.
A few years ago, chassis components made of aluminium were still reserved for the premium segment in the vehicle market. Steering knuckles, suspension arms and wheel carriers for medium-class and small cars were predominantly made of cast iron or forged steel. This has changed in the last few years.
Since then, significantly reducing the CO2 emissions of a vehicle has become a top priority in vehicle construction. One way to do this is reducing the vehicle weight. A reduction in weight of 100 kg means 0.3 l to 0.4 l less fuel consumption.
Even with electromobility as an alternative to the combustion engine, the weight of the vehicle is a key factor—the lighter the car, the higher the battery range. Materials like forged wrought aluminium alloys or ductile cast aluminium alloys with a low silicon content can therefore increasingly be found in all vehicle classes.
With the changeover to other materials, the challenges in machining also change. Machining aluminium alloys requires different machining strategies compared to existing materials in use, especially under the conditions of high cost pressure and strict machining quality and process reliability requirements. The machining tools used are an important factor here. Many automotive suppliers already count on machining specialist Walter AG for this.
“Aluminium alloys are the optimal material for the automotive industry. The alloys are light, with sufficiently high strength, and can be machined at speeds that are very different from those of traditional cast iron or steel materials. However, this does not mean that they are easy to machine. Above all, the long chips are a risk factor when it comes to a stable process. In addition, build-up on the cutting edge can quickly form on the cutting edges of the tools. It then soon becomes difficult to comply with the specified tolerances when it comes to the fit sizes and the surface quality. In this respect, users are dependent on the quality of the machining tool and the right technology,” says Fabian Hübner, Component and Project Manager for Transportation at Walter.
Creating Complex Bores
Above all, the integration of solid bores represents a technical and economic challenge in the production of chassis components made of aluminium alloys. While pre-forged recesses are often bored with larger bores, such as the wheel hub bore on the wheel carrier, smaller bores such as on the suspension arm are, in contrast, created in the solid material. The often high complexity of the contours to be drilled and the very strict requirements of the accuracy of the bore and of the surface quality also need to be considered.
Mostly, the smaller bores act as adaptors for plain bearings and dampers. This requires more than simply setting a bore. For example, defined end faces or chamfers must also be fitted, in order to allow you to fit bearing bushings or damping elements in the next production step. Consequently, up to five machining steps per bore quickly follow.
With the WBK20 and WBK30 CBN grades, Walter is launching two new indexable inserts for turning ISO H and ISO K materials: WBK20 (grain size diameter 3.0 μm) for finishing cast iron; WBK30 (grain size diameter 10.0 μm) for high metal removal rates in ISO H and when finishing with a heavily interrupted cut. Both CBN grades are made from a substrate with a high CBN content and are also suitable for roughing and finishing sintered steel.
The WBK20 indexable inserts are “tipped”. The “CBN tip” is applied to the corners of the insert with high tensile strength by means of vacuum soldering. The WBK30 grade is made from a solid CBN substrate and allows for higher cutting speeds and therefore a higher productivity in cast iron than indexable inserts made from carbide.
In addition to the high-precision manufacturing, a strong microgeometry on the cutting edge also contributes to the high quality, productivity and process reliability of the turning insert. This microgeometry is always matched to the respective application. Walter offers the new WBK20 and WBK30 CBN grades in all of the most popular ISO sizes and radii and thereby completes its extensive CBN turning range. These grades are particularly beneficial for users from the automotive industry, general mechanical engineering and the energy industry.
The trend towards miniaturisation of even complex component geometries is driving the need for highly reliable grooving tools. Article by Walter AG.
Grooving processes play an important role, especially in mass production. The trend towards miniaturisation of even complex component geometries is one of the driving forces, especially in the field of parting off and grooving tools. For several years now, the Tübingen-based machining specialist Walter AG has successfully positioned itself here as a provider with excellent technological expertise.
Markus Stumm, product manager for grooving at Walter, states, “We have significantly expanded our portfolio in recent years. In 2020, we will further strengthen our activities in this field. With the Walter Cut DX18, we are launching a tool with innovative clamping that will set completely new standards.”
Conquering the Conservative Market with Innovative Solutions
Users are particularly conservative when grooving. Stumm explains, “In mass production, when the process is running reasonably well, manufacturers rarely change the tooling system. We have to offer a clear advantage in terms of productivity and cost-efficiency to get to the machine. Problems with process reliability with the existing tools, or when a machining strategy is changed, provide us with an opportunity.”
The parameters, according to which the decision for a parting off process and the corresponding tools is made, are machine run times, tool life and process reliability. Typical problem areas, especially for machining operations in which you are grooving deeper into the workpiece, are the stable fixing of the indexable inserts, chip breaking, and cooling. Users who want to play it safe therefore reduce the cutting data below the recommended values. Who wants to risk stopping the production process due to chip jams, a vibrating tool or even if a cutting edge breaks?
This is exactly where the Walter grooving experts come in: With its portfolio of grooving tools, Walter already covers a wide range of grooving applications. Walter Cut DX18 is a double-edged system for grooving and parting off especially on Swiss type auto lathes or multi-spindle machines.
Walter Cut DX18 – Maximum Stability and Convenient Changeover
The Walter DX18 system is suitable for parting diameters of up to 35 mm. With the innovative, patent-pending positive engagement system, Walter’s developers are addressing the fundamental problems of narrowly dimensioned parting off tools: the stability and handling of the cutting insert.
In conventional screw clamping, the cutting forces act in such a way that the existing clamping forces are not sufficient—with negative effects on machining quality and process reliability. In contrast, the new Walter Cut DX18 cutting insert geometry locks the insert securely via positive engagement.
Another innovation is the SmartLock system, which considerably simplifies insert changeover. With conventional screw-clamped systems, the machine operator has to remove the entire tool for this purpose—and this, in cramped and not always user-friendly “oily” machine conditions. With the Walter SmartLock system, the clamping screw is located on the side of the tool: simply insert the screwdriver, unscrew and change the indexable insert. Thanks to the positive engagement, the new cutting insert adjusts correctly, even with very narrow insert widths.
The potential of the system was successfully proven in a tool life test on a Swiss type auto lathe. An outer diameter of 12 mm was parted off from 1.4057 material. The cutting edge width used was 2 mm. Stumm comments, “With the new double-edged Walter Cut DX system, we were able to more than double the tool life compared to the single-edged competitor—with maximum process reliability and productivity. The customer particularly liked the fact that they no longer had to remove the tool for changing the insert.”
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Drilling and threading work with round tools influences approximately 15 to 50 percent of the total costs per part in the automotive industry—therefore being able to reduce costs here remains a key factor for success. Article by Walter AG.
Not only does the Walter Technology Centre present opportunities for visualisations and simulations, it also allows developers to test new solutions on the machine.
The cost per part (cpp) is the gauge by which process efficiency is measured in the automotive industry. The machining tool represents a not inconsequential cost factor in this regard. This is particularly true of solid carbide tools (round tools), which are primarily used for holemaking, milling and threading.
Estimates calculated by tool specialists Walter AG indicate that these tools already make up around half of the machining applications in the automotive industry today. Depending on the characteristics of the component, drilling and threading work with round tools influences approximately 15 to 50 percent of the total costs per part. Being able to reduce costs once again here remains a key factor for success.
Up to Speed with Automotive Industry Trends
The Walter TC 430 thread former produces tear-resistant threads under the application of dynamic force.
The transition from combustion engines to electric motors or other alternative drives, which is gaining momentum as a result of tighter environmental regulations, touches every area of the automotive industry—right up to every last detail in the production processes. Walter has been on hand to actively accompany the sector through these changes from the very start: The company presents car manufacturers and suppliers around the world with a comprehensive portfolio of tools and services, which is constantly expanding through the addition of innovative new solutions. This means the automotive experts at Walter are always up to speed with the ever-growing number of new materials. What’s more, existing tool solutions for established processes are also optimised, usually to meet customer-specific requirements, or alternative solutions are devised on the basis of new technologies.
Lightweight materials now represent a significant portion of automotive production. For instance, the proportion of engine blocks made from aluminium today is already around 70 percent—in an area of industry that until only recently still favoured traditional materials such as grey cast iron and steel. Aluminium alloys have already become the default materials for transmission cases or oil pump housings, both for chassis elements and in structural components. And with the growing trend for electric drives, we will see more and more of these alloys in use.
Seeing the Bigger Picture to Reduce Costs
Complicated machining tasks, including those involving these new materials, or sophisticated part geometries with a lot of cavities increase the complexity of the machining process and, in turn, put extreme pressure on costs. This is where the Walter machining experts come in.
“As a manufacturer of premium products with 100 years of experience, we already offer highly effective and optimum solutions for a diverse range of applications from our standard range, which comprises more than 25,000 products in the solid carbide segment alone. Walter’s expertise, or ‘Engineering Kompetenz’, however, extends far beyond the individual machining tool. We focus on the overall machining strategy and the customer’s machining process. If our experts are involved in the development of production and tool management processes from an early stage, customers will often experience efficiency gains that are felt via more than just the machining tool,” explains Gerardo Campitiello, Component Manager Transportation at Walter. “Requirements, such as making unmanned production processes safe, ensuring reproducible process reliability and quality across a company’s production sites, or making tools available at all times, can only be met by taking a holistic approach. Whether selecting the right tools from the Walter standard range or developing a special tool to meet process-specific specifications, it takes careful consideration of the full picture.”
A Quick Path to an Instantly Productive Special Tool
In the automotive industry, processes that may seem time-consuming on paper are actually completed in very tight time frames in practice. It is with this in mind that Walter establishes its own processes and structures: For instance, tools from the standard range are with the customer within 24 hours of ordering. The Walter Xpress special tool service ordinarily delivers tools, which are developed and manufactured to customer specifications, within two to four weeks. This is based on an automated 3D process, which can be adapted to suit the project in question. A dedicated in-house department (Business Applications Development) constantly monitors market trends to improve existing application solutions and develop brand new approaches. This team of engineers takes on the role of Component Managers, responsible for individual components such as engine blocks, housings, e-axle drives, turbine casings, or crankshafts. They are among the first to know about the market trends and technological advances, which is reflected in their product development work.
The new Walter solutions can be tested in true-to-life situations at the Technology Center in Tübingen, Germany: the test run on the machine incorporates the very latest visualisation and simulation technologies.
This means Walter customers in all areas of the automotive industry benefit from the in-depth technical expertise of an innovative service provider who is active the world over and is also involved in the relevant fundamental research. The company makes major investments in its own R&D projects, and in the development of its own production capabilities in areas that competitors often contract out to third parties—such as being one of the few providers on the market to have its own coating system.
Greater Pull-out Strength Under More Dynamic Forces: The Walter Thread Former
When forming threads in ISO P materials, the process reliability primarily depends on how susceptible the thread former is to breaking. With its TC430, Walter provides a model that stands out for its durability. The extremely long tool life of the TC430 thread former, which is suitable for blind-hole and through-hole threads, is the result of a new substrate, the geometry with more polygons, and an innovative new kind of pre-treatment and post-treatment. The result is that, despite having more polygons, the TC430 Supreme reduces the torque by around 30 percent. This means that the thread former is also well suited for use in machines with a low power consumption.
Walter is planning to launch another carbide thread former for ISO P materials in early 2020. The new tool has already proven its exceptional properties in ongoing field tests. Designed for blank holes and through holes of up to maximum 3.5xDN, it demonstrates twice the tool life of comparable formers, and enables the reduction of power consumption on the spindle by more than 30 percent.
Walter AG is releasing the new TC620 Supreme thread milling cutter in diameters up to M20.
High cutting pressure and tool deflection are the greatest challenges when it comes to thread milling. This results in restricted cutting parameters, necessary cutting passes and short tool lives or even tool breakage. With the TC620 Supreme universal thread milling cutter, Walter is now transferring the functional principle of its T2711 indexable insert thread milling cutter to smaller diameters too. Tool wear is drastically reduced thanks to minimal cutting forces and the resulting high feeds per tooth. The multi-row concept not only reduces the machining time and wear, but also improves process reliability and handling – even when used with more demanding materials such as stainless steels or Inconel 718.
Reliable chip evacuation, thanks to internal coolant, and simple handling of the TC620 Supreme guarantee maximum process reliability. Radius corrections are seldom necessary, and when they are required, it is often only once competitor tools have already reached the end of their tool life. Walter is launching the TC620 Supreme for thread depths of 2 and 2.5 × DN in the dimension range from M4 to M20 as well as UNC 8 to UNC ¾ – and is therefore seamlessly linking to the Walter T2711 indexable insert thread milling cutter.
What is the next stage in the evolution of ISO turning? Ever smaller, ever lighter – many developments across vastly different industries are driven by the trend towards miniaturisation or lightweight construction. For mechanical engineering and suppliers, this results in entirely new challenges for metal machining. Article by Walter AG.
Application example – impeller: The surfaces produced using the HIPIMS PVD process are extremely smooth. This reduces build-up on the cutting edge and the generation of heat thanks due to reduced friction. (Image Walter AG)
Even though it is most apparent in the field of communication and entertainment electronics, the trend towards miniaturisation is shaping many areas of industry: From the medical industry, to the automotive industry, right through to aircraft construction. For producers, this means that they must adapt their processes to increasing demands for dimensional stability and surface quality or even switch to new materials.
Particularly hard, but also particularly tough, materials (such as Inconel 718DA with 42 HRC in the aerospace industry or Ti-6Al-4V in the medical and food industry) have complex requirements for the indexable inserts during ISO turning. This is because tough materials have a high tendency for adhesion, especially when they have a high nickel content (Ni). This results in the chips sticking to the cutting edge forming a build-up on the cutting edge. The dimensional stability and the surface quality suffer. The fact that cutting edges become worn relatively quickly had to be accepted until now, especially in the case of high-strength materials.
During ISO turning operations with high to medium depths of cut, the CVD-coated indexable inserts which have previously dominated the market offer good to outstanding possibilities. However, they reach their limits in machining applications such as finishing and fine finishing, particularly where precision and tool life are concerned. This is where Walter’s machining specialists identified major potential for optimisation.
Gerd Kußmaul, Senior Turning Product Manager at Walter, describes the concept behind the new HIPIMS PVD-coated indexable inserts as follows: “Even if the fine finishing and finishing of ISO M, ISO S, ISO P and ISO N materials with the highest requirements for surface quality are still special or niche applications at the moment, we see great potential here due to dynamic growth in the market right now. Fine finishing involves turning operations which are designed to achieve a consistently good surface quality. This is in the range from Rz 1.6 µm to Rz 6.3 µm – throughout the entire tool life of the indexable insert. This is why for some time Walter has been looking for geometries and cutting tool materials that achieve this with process reliability. The new PVD HIPIMS coatings demonstrate ideal properties for achieving this with their extremely smooth surface and great layer adhesion on sharp cutting edges.”
Innovative Coating Technology To Ensure Best Performance
Walter is one of few indexable insert manufacturers to perform the new PVD HIPIMS process in-house and continuously expand the application possibilities with a dedicated PVD development team. HIPIMS stands for “High Power Impulse Magnetron Sputtering”. In contrast to conventional DC sputtering processes, the HIPIMS process involves subjecting the targets to short pulses of a few kilowatts of power. This produces a plasma density of 1013 ions per cubic centimetre, which have a high content of target metal ions. The bonding of the layers to the substrate is also excellent.
Indexable inserts with extremely sharp geometries, such as the FN2 or the MN2 “Aluminium geometry”, benefit from this coating process in particular because extremely stable cutting edges are produced. Even under high loads, the layers do not chip off and the cutting edges do not break away. In addition, the high level of edge stability ensures that the cutting edge is not only subjected to less wear, but that this wear also occurs evenly. The even wearing ensures dimensional stability and defined surface quality, even right up to the end of the tool life. Another advantage of the HIPIMS process is that the coatings are extremely smooth making them ideal for machining sticky aluminium alloys, for example; materials which would otherwise stick to the cutting edge during machining now reliably glide over it. Typical forms of wear such as built-up edges or significant flank face wear caused by chemical and physical reactions with the adhering material rarely occur. Walter’s new HIPIMS PVD grades WNN10 and WSM01 also have a long tool life.
Finishing of Inconel 718 DA – 40 HRC with Vc: 80 m/min: With identical cutting data, the new HIPIMS PVD-coated DCGT11T304-FM2 WSM01 indexable insert increased the tool life from nine minutes to 18 minutes compared to the DCGT11T304-PF2 WXN10 indexable insert and consistently achieved a surface quality between Rz 2 and Rz 4 μm throughout the entire tool life. (Image: Walter AG)
Long Tool Life, Increased Machining Volumes
Since the launch in 2017, sales for the HIPIMS PVD indexable inserts has grown consistently. Walter is pleased with the positive response from many customers who have already made the change from the previous WXN10 or WK1 cutting tool materials to the PVD-coated WNN10 or WSM01 indexable inserts. Walter Product Manager Gerd Kußmaul reports: “There must be good reasons to change the cutting tool material in established processes. Among other factors, the outstanding results achieved by the new HIPIMS grades with regard to tool life and surface quality speak in their favour. This is clear to see from the comparative tests. For instance, when performing finishing operations on tool steel X40CRMoV5-1 (DIN1.2344) with 54 HRC, it was possible to increase the tool life by 275 percent. And the surface value of Ra 0.8 µm was achieved throughout the entire tool life with process reliability. Another application was finishing Inconel 718DA at a cutting speed of 80 m/min, with the new grade WSM01 and achieving a cutting time of 18 minutes. In comparison to this, the previous grade WXN10 was only able to achieve nine minutes. In addition, a consistently good surface quality between Rz 2 µm and Rz 4 µm was achieved throughout the entire tool life.”
Process Reliability And Cost Reduction
Walter’s new HIPIMS PVD indexable inserts have potential to be effectively used anywhere that maximum precision, surface quality and process reliability are required. At the same time, these inserts have a positive effect on costs because the HIPIMS PVD coating, in conjunction with a carbide substrate, results in a cutting tool material that offers a long tool life with consistently high machining quality right to the very end. This is especially true for difficult machining steps such as fine finishing and for very sticky materials such as aluminium alloys with a high silicon content. In fact, the tool life and surface quality differences compared to previous indexable inserts are so significant that they result in a noticeable cost reduction in production.
In comparative tests, Walter achieved a 73 percent increase in tool life quantity with the WNN10 indexable inserts (compared with previous cutting tool materials) for machining red bronze. (Image: Walter AG)
Optimal Surface Quality When Finishing And Roughing
Walter developed the new WNN10 grade for finishing and roughing of ISO N materials such as aluminium-, copper- and magnesium-based alloys. The indexable inserts are available in two geometries. The FN2 geometry with 18° rake angle is ideal for finishing operations and for long, thin shafts that tend to vibrate. The MN2 geometry with 25° rake angle can be used universally for medium machining of non-ferrous metals.
The new grade WSM01 is available in the FM2, MM4 and MN2 positive geometries and in the MS3, NMS and NRS negative geometries. Its main area of application is finishing and medium machining of nickel- and cobalt-based high-temperature alloys (ISO S) but it is also used with stainless materials (ISO M) such as austenitic stainless steel 1.4301, 1.4404 or duplex steel 1.4462. It is used, for example, for machining engine components in the aerospace industry or for producing surgical instruments in the medical industry. Its applications also include machining stainless steels or hard turning tool steel such as X40CrMoV5-1 with 54 HRC. To summarise, it can be said that the new HIPIMS PVD grade WSM01 is the ideal solution for fine finishing of hard materials.
For the high requirements in the automotive sector in particular, Walter AG is introducing new boring tools with tangentially arranged indexable inserts. The usually high feeds for tangential systems are therefore transferred from the milling to the holemaking. In contrast to radial tools, tangential tools can work without good chip clearance.
Walter combines the extremely stable tool core that results from this with a separate indexable-insert geometry – and therefore not only improves the surface quality: A second clearance angle reduces the effective clearance angle, which is otherwise high for tangential tools, and reduces “chattering”. The square-shaped indexable insert can be installed at any angle. At 72° and 90°, a face chamfer (wiper) also works. This also guides the tool and keeps it quiet. Boring conditions of 4 × Dc can therefore be achieved. Even small diameters (from 24 mm) can be machined with three teeth (z3).
The objective of combining roughing and finishing in a single roughing/finishing machining process is achieved in many cases thanks to the tangential boring tools. Multiple steps and high feeds shorten the machining time here. Other arguments put forward by Walter in favour of the concept include high precision thanks to stability as well as the cost-effectiveness of the indexable inserts with 4 plus 4 cutting edges. A wide range of inserts make the special tools particularly advantageous for users who manufacture components made of cast iron, chrome-nickel materials or steel and aluminium, such as turbine or gearbox housings, gears, cylinder bores and steering knuckles. This is especially the case if they want large machining allowances of 2 to 7 mm.
With Walter Cut MX, Walter AG brought a grooving system to the market which used proven methods while overcoming the disadvantages of existing competitor systems: With dowel pin location to counter handling errors for a high degree of change and positioning accuracy. With four-edged indexable inserts that can be used even after a cutting-edge breaks for maximum cost efficiency. And with a long tool life thanks to the Walter-specific precision cooling and the Tiger·tec Silver cutting tool materials. A combination of stability, productivity and accuracy unlike anything currently available on the market. Now, Walter is expanding the MX range with Walter CaptoTM toolholders and larger insert widths.
With the new Walter CaptoTM monoblock tools (C3–C6), the MX system can now also be used on machines with Capto interfaces. In addition, there are new parting blades such as those used on automatic lathes and multi-spindle machines. Walter has completed the range with new grooving inserts and toolholders for larger insert widths, for example for pre-grooving large grooves: Where previously only 0.80 mm to a maximum of 3.25 mm were possible, the insert width now ranges up to 5.65 mm – including the very common dimensions of 4 mm and 5 mm (maximum cutting depth 6 mm). The extensions are intended to make new applications possible for users of the MX grooving system: From mass producers, for example in small-parts production where a high degree of precision is paramount, to job shops, where the focus is on fast, precise tool changes and cost efficiency. Indexable inserts with special profiles are available via the Walter Xpress system within four weeks.
Richard Harris will become the new President of the Management Board on 4 February 2019. He follows Mirko Merlo, who has been President of Walter AG since 2012 and decided at the end of 2018 to leave the company at his own request.
Richard Harris brings with him to Tübingen many years of experience in tool production and in strategic supply management. The new Walter President has held various management positions for the parent company Sandvik since 2002. Most recently, Richard Harris led the Powder and Blanks Technology division within Sandvik Machining Solutions, which has been trading under the name SMS Supply since 2018. While there, he has made decisive advances in the strategic and operative development of supply management.
The 49-year-old from Britain said of his new position as President of Walter AG, “Walter has an outstanding reputation in the machining industry: The company is a pioneer for technology in many areas. The digitalisation strategy, started by Mirko Merlo, puts the company in an ideal position for the future. Together with the Walter Team, I want to further develop this successful business strategy so that we can continue to grow globally in a demanding and ever-changing market environment.”
Walter AG would like to thank Mirko Merlo for 35 years of very successful work for the company. In his time as President, he set Walter AG on a path of growth and profitability. “Walter has performed extremely well over the last six years. Now is the right time to enable change at the highest level of management and to lead the company strategically into the future,” Mirko Merlo explained with regards to his decision. “I wish Richard Harris great success in his future tasks and positive challenges.”
With the X·treme Evo solid carbide drill from the Advance product range, Walter AG is launching the new DC160 product type.
Walter AG is releasing an all-rounder for every material, machine and drilling application. This can be used universally in three different ways: In all ISO material groups. It is designed for a wide variety of applications such as inclined entries and exits, drilling holes close to the edge of the workpiece or convex and concave surfaces. Furthermore, it can also be used with all machine concepts: In machining centres, horizontal or vertical, in lathes, rotating with driven tools, axial and radial (with angular head), or stationary. As a first step, Walter is bringing out the X·treme Evo in the variants three and five × Dc without internal coolant and five, eight and 12 × Dc with internal coolant. In addition to the DC160 variant, the drill from the Advance range is also available as the DC260 Advance step drill with and without internal coolant. According to Walter, the greatest strengths of the X·treme Evo lie in its long tool life and high levels of productivity and process reliability.
The WJ30ET (full coating) and WJ30EU (point coating) grades are new to the X·treme Evo: A highly tough micrograin substrate combined with Walter’s own TiSiAlCrN/AlTiN multi-layer coating on an AlTiN base layer. Extremely wear-resistant for a long tool life – even while maintaining high cutting parameters. Another innovation is the thinner web with steep approach angle, along with the fourth land that lies close to the drill tip. The steep approach angle reduces the feed force and increases the positioning accuracy. The deep-seated fourth land is engaged even quicker and consequently optimises drill guidance, particularly for inclined entries and exits. The new type of face geometry on the X·treme Evo creates plenty of room for the chip in the centre and therefore improves chip removal, particularly in soft material.