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Titanium was first discovered in 1791, but we didn’t begin to realize its industrial potential until 1948 when the U.S. government began funding titanium research for use in aviation, aerospace, and defense applications. Titanium is an abundant mineral—however, the process of transforming titanium ore into pure titanium or its alloys is complex and costly. You’ll pay a premium for new titanium and its alloys compared to other common metals used in machining and fabrication processes.
Titanium Offers a Unique Combination of Properties
Titanium is renowned for its weight-to-strength ratio. It’s 45% lighter than steel but is just as strong, and it’s 60% heavier than aluminum and is twice as strong. Titanium can tolerate extreme temperatures due to its high-cycle fatigue strength and very high melting point (3,034°F or 1,668°C) and also experiences minimal change to dimensions in extreme temperature environments because of its low coefficient of thermal expansion. It’s preferable to aluminum and steel for many applications because of its corrosion resistance, and it’s often utilized in the medical industry because it’s biocompatible and non-magnetic.
This property combination presents some challenges when it comes to transforming commercially pure titanium and its alloys into components for automotive, aerospace, industrial, marine, medical, and recreational equipment. Is titanium machinable? Yes, but you’ll need to understand how its properties affect machining techniques.
Is Titanium Machinable? Yes, but Consider These Factors
Titanium is machinable, but it requires special considerations regarding the machining processes. Because of its unique properties, you’ll need to exercise caution when machining titanium for the following reasons:
- Low thermal conductivity can result in excessive heat build-up in the cutting tools that affect the quality of the finish and shortens tool life.
- Work hardening tendencies and alloy stickiness can create long continuous chips that entangle the tool.
- Low Young’s modulus can cause chatter and spring back that results in poor surface quality.
Experienced titanium machinists deal with these challenges using the proper setup, the right tools, cutting speed and feed balance, and milling techniques.
Titanium Adjustable Mountain Bike Dropout (Image courtesy of Paragon Machine Works)
Tool Selection and Use
Proper tool selection and care are fundamental in producing accurately dimensioned components with high-quality finishes. This can be achieved by observing the following recommendations:
- Maintain sharp tool edges. Dull tools lead to more heat buildup, cause tearing, and produce a poor surface finish.
- Use carbide-grade tools with physical vapor deposition (PVD) coatings. This coating resists alloy stickiness and efficiently breaks up long chips.
- Employ high-speed steel or titanium aluminum nitride-coated carbide tools. These can be optimal for some applications, helping to manage high temperatures generated during cutting, resist alloy “stickiness,” and break up long chips.
- Consider using a fine pitch or corn cob tool. Tool geometry, in this case an increased number of cutting edges, improves the removal rate.
The hardness of titanium can cause tool chatter, which ruins the surface finish. You can prevent this by ensuring a firm grip on the titanium workpiece and rigid machine setup.
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High Feed Rate
Overall, you’ll want to maintain the highest feed rate possible that will produce the required finish quality. Tool manufacturer recommendations, spindle speed, and chip load will factor in calculating the optimal feed rate. Once the tool starts cutting, avoid interruptions. Keep the tool moving to prevent work hardening, seizing, and premature tool wear.
Low Cutting Speeds
Cutting speed affects heat buildup in the tool. A low RPM (revolutions per minute) matched with a larger chip load can help moderate tool temperature. Commercially pure titanium tolerates higher speeds than titanium alloys. Technique also influences the cutting speed. For example, full slotting (180-degree tool engagement) requires a low surface speed. However, by reducing radial engagement, you also reduce the time the cutting edge is generating heat and increase the cooling time. As a result, with less radial engagement, you can increase cutting speed and maintain an acceptable tool temperature.
Coolant Is Critical
Considering the heat issues involved in machining titanium, coolant is critical in producing the desired finish. A wide variety of water-soluble coolants are available to manage temperature, remove chips, protect the tool edge, and extend its life. High-pressure coolant delivery is required for efficient chip removal. Some milling operations can take advantage of tools that deliver coolant directly to the cutting edge via the spindle.
Reduce the Cost of Machining Titanium
In comparison to machining common metals like steel and aluminum, the unique properties of titanium demand a much higher level of skill and knowledge of the interaction between milling tools and metal to achieve the required finish. The extra time and attention required to machine titanium add to the already higher costs of titanium and its alloys.
As an alternative to the expense of new titanium, many machine shops are using verified titanium remnants in their production processes. Industrial Metal Service specializes in supplying usable titanium remnants to machine shops in the San Francisco Bay Area and beyond. Remnants are verified using x-ray fluorescence technology to ensure the titanium grade. We can also arrange to have titanium remnants cut-to-size, making it easier for you to immediately begin the machining process. We provide regular, reliable delivery throughout the San Francisco Bay Area and often ship titanium to machine shops nationwide that don’t have a local metal supplier.
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