Titanium is considered difficult to machine. What the challenges of the material are and which strategies and tools can still be used to process them.
In the aerospace industry, in particular, the demand for the most efficient machining solutions possible for machining titanium has been increasing for years. Also in the manufacture of medical devices or lightweight components. The possible uses of titanium are varied and the material brings many advantages, but the processing of the very special material is often a special challenge.
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What are the challenges in titanium machining?
Titanium is characterized by its remarkably high strength and low density. It reacts quickly with the oxygen in the air, creating a very durable oxide layer that protects against corrosion. These properties are at the same time the advantages of using titanium, but also the disadvantages of machining.
"The strong reactivity with oxygen can cause tool wear through diffusion, especially at high temperatures," explains Moritz König, co-founder and CEO of Facture, which also offers titanium machining as an online manufacturer.
High temperatures often occur when machining titanium, because the thermal conductivity of the light metal is very low, which is why the tools are subject to high thermal loads. König explains exactly why: "The low thermal conductivity combined with high heat resistance leads to a high-temperature load on the cutting edge, since the heat dissipation - unlike steel, for example - only takes place to a small extent via the workpiece and chips."
Philipp Dahlhaus, Head of Product Management at Paul Horn GmbH, adds: "In the case of steel, around 80 per cent of the temperature generated during the machining process is dissipated via the chips, while in the case of titanium it is only 20 per cent."
Further limitations arise from the low weight of titanium, which according to Dahlhaus is approximately 40 per cent less than steel. This requires a yield point of up to 900 N/mm².
König sees further challenges in the rigidity of titanium: "Properties such as the relatively low modulus of elasticity, which can cause vibrations during processing, further increase the complexity of the requirements."
Besides, titanium is not titanium, as Dahlhaus explains: "A distinction is made between the rather hard grade 5 (Ti-6AI-4V), which is used in the aerospace industry, for example, and the softer grade 2, which consists of 99.7 per cent pure titanium The technical pure titanium is particularly corrosion-resistant and is therefore mainly used in medical technology and implantology." Special machining strategies and tools are therefore required for the various titanium materials.
Which strategies and technologies can be used to overcome the challenges?
If you are aware of the properties of titanium, the challenges can be solved with adapted machining strategies and adequate tools.
"When machining titanium, for example, high cutting speeds should be avoided and work should be carried out with a relatively large, uniform feed rate," König explains with regard to the machining strategy. "The use of sufficient coolant is essential in most cases."
According to the Facturee CEO, if you outsource titanium processing, you should make sure that the processing company has the appropriate equipment and know-how for this activity. "As an online manufacturer with a network of more than 1,000 manufacturing partners, Facture offers the right solution for every need," reports König. "For the production of titanium parts, we only select highly specialized manufacturing companies that have sufficient experience with the material."
The appropriate equipment also includes the tools. König: "When machining titanium, tools that are specially optimized for the machining of the material, often made of hard metal, with sharp cutting edges should be used.to prevent tool failure."
Dahlhaus emphasizes that with the tools used, it is particularly important to minimize friction on the cutting edge since titanium tends to work hard. "Sharp tools are a must for this," says the horn expert. "The substrate and the coating have to be precisely matched to one another. The right carbide substrate ensures that the tool has a high heat resistance and toughness with high dynamic cutting forces, while the appropriate coating is responsible for good sliding properties, high temperatures and good insulation."
Horn takes these special challenges into account, for example, when optimizing the DS milling system for productive and economical machining of titanium and titanium alloys. But other manufacturers are also bringing special tools for machining titanium onto the market.
What special tools are there for machining titanium?
Ceratizit: Monstermill TCR
The Monstermill TCR solid carbide milling cutter was specially developed for machining titanium. Above all, the geometry has been optimized, but the material has also been adapted to the circumstances of titanium machining.
The solid carbide milling cutter has a variable helix pitch and an unequal spacing of the cutting edges. The latter should enable optimized chip formation. The high-performance substrate used gives the tool high toughness and strong transverse rupture strength. The Dragonskin coating technology helps the TCR to withstand thermal loads well.
Guhring: Titan milling cutter RF 100 Ti Aircraft
The 100 Ti Aircraft ratio milling cutter from Guhring is particularly suitable for machining structural components made of titanium for aviation. The cutter is adapted to aviation standards and works among conventional, but also modern HPC milling strategies.
A specially adapted corner radius promotes chip formation and improves wear behaviour. In addition, a modified core adapted to the cutting behaviour prevents the chips from being pulled through in the next cut. This enables clean component surfaces and long tool lives.
Hoffmann Group: Garant Master Titan
The Hoffmann Group's Garant Master Titan product family consists of roughing cutters, finishing cutters, torus cutters, face torus cutters and full radius cutters. Milling cutters for HPC (High-Performance Cutting) and TPC (Troichoidal Performance Cutting) are also available. All are matched to the respective type of machining in titanium.
Here, too, the cutting edge geometry was adapted and a special substrate was used. According to the manufacturer, the latter is so resilient that the milling cutters remain productive even when the coating is already completely worn out. With some tools, such as the HPC solid carbide finishing cutter, for example, it was even possible to dispense with coatings entirely.
Horn: milling system DS
When optimizing tools for titanium machining, tool manufacturer Horn relies primarily on a special substrate: the IG3I. The homogeneous wear behaviour makes it possible to increase the service life. An additional coating also contributes to this. It also supports cutting edge stability.
The geometry of the DS milling system is specially adapted: the sharp micro-geometry on the cutting edges, positive rake angles, large clearance angles and polished gullets are intended to prevent strain hardening of the workpiece edge zone and built-up edges on the rake faces when machining titanium. Variable twist angles and different Tooth pitches make the milling process smoother.
Iscar: Multi-Master solid carbide milling heads
Iscar's Multi-Master tools are designed for semi-finishing, finishing or 3D profiling in the aerospace, die and mould and medical industries.
With regard to the geometry, users can choose between a droplet or lens shape. The tools consist of the TiAIN-PVD-coated finest-grain cutting material grade IC908. In addition to titanium, Inconel and stainless steel can also be machined with the milling heads.
Kennametal: FBX Drills
The FBX drill is part of a tooling concept developed by Kennametal to maximize metal removal and reduce cycle times when machining aerospace structural components. Four effective cutting edges on the outer diameter contribute to this.
The flat-bottom geometry of the drill directs the cutting forces towards the spindle. This reduces lateral tool deflection, which can increase tool life and material removal rates.
The tool concept also includes the Harvi Ultra 8X shell end mill and the Harvi solid carbide milling cutter.
Mapal: NeoMill XPTK milling program
Among other things, Mapal offers a family of tools with indexable inserts that are tailored to machining titanium. Also in the portfolio: shoulder milling cutters and shell end milling cutters as attachment and shank variants.
The topography of the indexable inserts in the NeoMill XPTK range of milling cutters has been completely redeveloped in order to optimally shape and remove the chips from the demanding material. The tool body was also newly developed. The coolant is transported to each cutting edge via a chamber inside the milling cutter. Thanks to the flowing shapes, the chip flutes transport the chip out of the shearing zone.
Seco: solid carbide barrel cutter with HXT coating
High surface quality in difficult-to-machine materials such as titanium was the goal that Seco had in mind when developing the solid carbide barrel cutters. The resulting tools enable now also larger stepovers at the same cutting speed and reduce the time required.
The tool paths required for barrel milling technology are generated using special CAM programming modules. These tools are also typically used in the aviation industry, medical technology and tool and mould-making.
Walter: MD377 Supreme and MC377 Advance solid carbide milling cutters
Walter has developed two milling cutters that are precisely tailored to the production of titanium components. The MD377 Supreme is a high-end specialist for the aerospace industry, while the MC377 Advance is more universal.
Both milling cutters are suitable for a wide range of applications: roughing, finishing, semi-finishing, full slots, ramps, shoulder milling and plunging. Dynamic milling is also possible with the MD377.
Zecha: Kingfisher tools
Zecha's Kingfisher series relies on a special VHM substrate and a particularly stable, easy-cutting geometry with three cutting edges.
What is special about the tools: an ingenious cooling system: An internal cooling system is combined with a power chamber so that the cooling medium in the core area is guided close to the tooltip and exits through one or more bores in the chip chamber. The power chamber in the chip area increases the flow rate of the coolant. In this way, the temperature in the process can be reduced in a targeted manner.
