Titanium Alloy Deep Hole Thread Processing Technology

It is quite difficult to process deep hole threads on special material parts.For example,deep hole tapping on a titanium alloy part can be very challenging.If the scraping effect caused by a damaged tap on a nearly completed part results in the part being scrapped,it is very uneconomical.Therefore,in order to avoid scraping,it is required to use the correct cutting tools and tapping techniques.

Firstly,it is necessary to define what a deep hole is and why it requires special consideration.In drilling,holes with a depth greater than three times the aperture are called deep holes.Deep hole tapping means that the tapping depth is greater than 1.5 times the diameter of the tap.When using a 1/4"diameter tap to process threads with a depth of 3/8",this situation is usually referred to as deep hole tapping.

Processing a deep hole thread means that there needs to be long-term contact between the tool and the workpiece.At the same time,more cutting heat and greater cutting force will be generated during the machining process.Therefore,tapping in small deep holes of special materials(such as titanium metal parts)is prone to tool damage and thread inconsistency.

To solve this problem,two solutions can be adopted:(1)increasing the diameter of the pre tapping hole;(2)Use a tap designed specifically for deep hole tapping.

1.Increase the diameter of the pre tapping hole

Suitable threaded bottom holes are crucial for thread machining.A slightly larger threaded bottom hole can effectively reduce the cutting heat and force generated during the tapping process.But it also reduces the contact rate of threads.

The National Standards and Technical Committee stipulates that in deep holes,only 50%of the full height of the thread is allowed to be tapped on the hole wall.This is particularly important when tapping small holes on special and difficult to machine materials.Although the decrease in thread height on the hole wall leads to a decrease in thread contact rate,due to the increase in thread length,reliable thread connection can still be maintained.

The diameter increment of the threaded bottom hole mainly depends on the required thread contact rate and the number of threads per inch.Based on the above two values,the correct diameter of the threaded bottom hole can be calculated using empirical formulas.

2.Cutting parameters

Due to the difficulty of machining titanium metal parts,it is necessary to fully consider cutting parameters and tool geometric dimensions.

cutting speed

Due to the high elasticity and deformation rate of titanium alloys,relatively small cutting speeds are required.When machining small holes in titanium alloy parts,the recommended circumferential cutting speed is 10-14 inches/minute.We do not recommend using a smaller speed as it can lead to cold work hardening of the workpiece.In addition,it is also important to pay attention to cutting heat caused by tool damage.

Debris storage tank

When tapping deep holes,it is necessary to reduce the number of tap slots to increase the chip holding space of each slot.In this way,when the tap retracts,more iron chips can be taken away,reducing the chance of tool damage caused by iron chip blockage.On the other hand,the increase in the chip holding groove of the tap reduces the diameter of the core,thus affecting the strength of the tap.So this also affects the cutting speed.In addition,spiral groove taps are easier to remove chips than straight groove taps.

Front and rear corners

A small rake angle can improve the cutting edge strength,thereby increasing the tool life;A large rake angle is beneficial for cutting metal with long chips.Therefore,when processing titanium alloys,it is necessary to comprehensively consider these two factors and choose a suitable front angle.

A large back angle can reduce the friction between the tool and the chip.Therefore,sometimes it is required that the back angle of the tap be 40°.When processing titanium metal,grinding a large back angle on the tap is beneficial for chip removal.In addition,fully ground tap and blade back shovel ground tap are also beneficial for tapping.

Coolant

When processing special materials,it is necessary to ensure that the cutting fluid reaches the cutting edge.To improve the coolant flow rate,it is recommended to open a cooling groove on the back of the tap blade.If the diameter is large enough,internal cooling tap can be considered.

3.Application examples

A certain aircraft parts manufacturer needs to perform deep hole tapping on a part.The material of this part is grade 7 titanium alloy.During machining,the circumferential cutting speed is 13 inches/minute,while using coolant.

To ensure the accuracy of the parts,the operator should replace the tap in a timely manner before it becomes dull.When the tap wears out,the sound generated during the cutting process will change.By listening to these sounds,the operator can determine the number of threaded holes that can be processed before the tap wears out before processing.

The factory has 2 tapping stations on each tapping equipment,equipped with the same tap.When one of the taps is worn,it can be easily and promptly replaced.