Tips for Tapping Titanium
Best results occur when using rigid tap holders, proper speeds and feeds
The unique physical and chemical properties of titanium make it difficult to tap.
Machinists typically find it much more difficult to tap titanium alloys, such as the popular 6Al-4V, than other alloyed materials. However, with the appropriate taps, holders, and techniques, the operation still can be performed productively and accurately.
Titanium is both lightweight and strong, which makes it very appealing for many industries, such as aerospace and medical. It is, however, the material’s unique physical and chemical properties that make it a challenging material for manufacturers.
Titanium is not a good conductor of heat. Because of this, tools such as taps hold much of the generated heat directly on the cutting edge and tool face, rather than dissipating it through the workpiece, chips, and machine. Very high temperatures are reached during the tapping process, resulting in the chipping of cutting edges and, therefore, reduced tap life.
Also, titanium’s low modulus of elasticity makes the material “springy,” and the workpiece tends to close in on the tap.
Experts offer the following tips for successfully tapping titanium alloys:
1. Use the Proper Speed
Using the proper tapping speed is critical for cutting threads in titanium alloys. Improper speeds can shorten tap life and even cause tap failure.
“We recommend a tapping speed of 10 to 13 SFM [surface feet per minute], both turning into the tapped hole and exiting out of the tapped hole,” explained Mark Hatch, product director - taps and thread mills for Emuge Corp., West Boylston, Mass.
2. Use Tapping Fluid
Tapping fluid (coolant or lubricant) will affect tap life. You can use machine tool tank fluid, which is designed for all machining operations, but this may not necessarily produce the desired thread quality and tap life.
“For the best results, we recommend quality emulsions with a higher percentage of oil and tapping oil,” said Hatch. “Performance of your threading applications can be improved by adding coolant through the tap. Taps with through-coolant can be run much faster without the fear of generating too much heat.”
3. Consider Tapping Paste
Sometimes a tapping paste, which contains extreme-pressure additives, can be useful for very difficult-to-machine titanium alloys. The high machining pressure generated in the tool and component interface can be challenging, and the additives enable the paste to stick to cutting surfaces. Applying tapping paste is a manual process, however; it is not applied through the machine’s coolant system.
4. Use a Modern CNC Machine
Even though all machines are capable of tapping and threading titanium alloys, modern CNC machines have the best controls for tapping.
5. Choose the Correct Taps
Taps designed for cutting threads in titanium alloys should have through-coolant capability.
Also, taps should be chosen for the type of hole that has been created. For example, taps with 8- to 10-degree, left-hand spiral flutes are suitable for right-hand cutting in through-holes. When combined with a 4-5 thread chamfer and proper face rake and relief characteristics, these taps enable productive cutting in even the toughest alloy materials.
Blind-hole applications should use a tap with a 10- to 15-degree, right-hand spiral flute, designed for right-hand threads. They are combined with a 2-3 thread chamfer, in addition to face rake and relief characteristics specifically designed for cutting titanium.
6. Use a Rigid Tap Holder
Because the tapping process is susceptible to vibration, for best results rigid holders should be used. Vibrations will result in decreased thread quality and will reduce the life of a tap.
“All things being perfect, we recommend the use of rigid/synchronous tapping cycles with Softsynchro® collet-type tap holders,” said Hatch. “When using CNC machines without a rigid tap cycle, or a manual tapping machine, a quality tap holder with an initial hard-start feature and proper feed control programming will yield the best results.”
7. Hold on to Your Work
For the highest accuracy and repeatability, examine your clamping application to ensure your workholding system can adequately hold on to the part.
“Low-volume job shops and high-volume automotive production environments both should stay close to their workholding system provider so they learn about any unique challenges. Doing so will help avoid potential miscommunication, minimizing additional project costs,” said Hatch.
8. Plan Ahead for Tap Requirements
Estimating tap life depends on many factors, such as machine capability, machine feed controls, tap holders, grade of titanium alloy, and coolant/lubricants. A good rule of thumb is that for 2xD holes, 250 to 500 holes should be realized from each tap. Also, it is always important to start a new job with new taps.
