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Titanium alloy deep hole thread processing technology
Deep hole threading of special material parts is quite difficult. For example
Deep hole threading of special material parts is quite challenging.For example,tapping deep holes in a titanium alloy part is very demanding.If a part is scrapped due to the scraping effect caused by a broken tap on a nearly finished part,it is very uneconomical.Therefore,to avoid scraping,it is essential to use the correct tools and tapping techniques.
First,it is necessary to define what a deep hole is and why it requires special consideration.In drilling,holes that are deeper than three times their diameter are referred to as deep holes.Deep hole tapping means that the tapping depth exceeds 1.5 times the diameter of the tap.For instance,when tapping a thread to a depth of 3/8"with a 1/4"diameter tap,this situation is typically referred to as deep hole tapping.
Processing a deep hole thread means that the tool is in contact with the workpiece for an extended period.At the same time,more cutting heat and greater cutting force are generated during the process.Therefore,tapping in small deep holes of special materials(such as titanium metal parts)can easily lead to tool breakage and inconsistencies in the threads.
To solve this problem,two solutions can be adopted:(1)increase the diameter of the hole before tapping;(2)use taps specifically designed for deep hole tapping.
1.Increase the diameter of the hole before tapping
A suitable thread bottom hole is crucial for thread processing.A slightly larger thread bottom hole can effectively reduce the cutting heat and cutting force generated during tapping.However,it will also reduce the thread contact rate.
The National Standards and Technology Committee stipulates that in deep holes,it is permissible to tap only 50%of the full height of the thread on the hole wall.This is particularly important when tapping small holes in special and difficult-to-process materials.Although the reduction in thread height on the hole wall leads to a decrease in thread contact rate,the increase in thread length can still maintain a reliable connection.
The increase in the diameter of the thread bottom hole mainly depends on the required thread contact rate and the number of threads per inch.Based on these two values,the correct diameter of the thread bottom hole can be calculated using empirical formulas.
2.Cutting parameters
Due to the difficulty of processing titanium metal parts,careful consideration must be given to cutting parameters and tool geometry.
Cutting speed
Due to the high elasticity and deformation rate of titanium alloys,a relatively low cutting speed is required.When processing small holes in titanium alloy parts,a recommended circumferential cutting speed is 10 to 14 inches per minute.We do not recommend using a lower speed,as it can lead to workpiece cold hardening.Additionally,attention must be paid to cutting heat caused by tool breakage.
Chip flutes
When tapping deep holes,the number of flutes on the tap should be reduced to increase the chip space in each flute.This way,when the tap is retracted,it can carry away more chips,reducing the chance of tool breakage due to chip clogging.However,on the other hand,increasing the chip flute size reduces the core diameter,thus affecting the strength of the tap.This also impacts the cutting speed.Additionally,spiral fluted taps are more effective at chip removal than straight fluted taps.
Front angle and back angle
A small front angle can enhance the strength of the cutting edge,thereby increasing tool life;while a large front angle is beneficial for cutting long chips of metal.Therefore,when processing titanium alloys,it is necessary to consider both aspects and choose an appropriate front angle.
A large back angle can reduce friction between the tool and the chips.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.Additionally,fully ground taps and those with ground backs are also advantageous for tapping.
Coolant
When processing special materials,it is essential to ensure that the cutting fluid reaches the cutting edge.To improve the flow of coolant,it is recommended to create cooling grooves on the back of the tap.If the diameter is large enough,consider using internal cooling taps.
3.Application examples
A manufacturer of aircraft parts needs to perform deep hole tapping on a part made of grade 7 titanium alloy.During processing,the circumferential cutting speed is 13 inches per minute,and coolant is used.
To ensure the accuracy of the part,the operator must replace the tap in a timely manner before it becomes dull.When the tap wears,the sound produced during the cutting process changes.By listening to these sounds,the operator can determine the number of threaded holes that can be processed before the tap wears out.
The factory has two tapping stations on each tapping machine,equipped with the same tap.When one tap wears out,it can be conveniently and promptly replaced.
Parts,Thread,Titanium alloy
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