There are many factors that must be taken into account in the actual processing of titanium alloys.
Based on this, the milling process for titanium alloys will be different from the main machining methods used for a long time.
Two new milling tool solutions and the continuous development of applications have opened up new possibilities for titanium alloy milling.
Compared to many other materials, the potential for successful processing of titanium alloys is much smaller and has different processing properties.
As titanium alloys are more variable in terms of machinability, this affects the choice of machining methods and tools as well as the machining process, but as with any other alloy, more careful planning is required – from selecting the machine for the job to programming the cutting details.
Although parts in the aviation manufacturing industry have fairly similar characteristics, they vary in size and shape.
As a result, the choice of machine, fixture, coolant, tool, machining method and cutting parameters also varies.
Due to the limited space in the magazine, the flexibility of the process is the primary condition, and in terms of productivity and capacity, the type of shank and the adjustment of the tool mounting are key factors.
Just as the roughing and finishing operations must be planned according to different parameters, for indexable tools and solid carbide tools, titanium alloy milling associated with different application areas also appears.
The size and shape to be machined and the appropriate tool type are the first determining factors.
Indexable tools have the highest efficiency of material removal and are now regarded as the first choice for roughing.
It is also unmatched in the finishing of large and flat surfaces. Integral carbide tools are widely used in semi-finishing and finishing processes and are also the ideal solution when radii, cavities and grooves are too small for indexable blade tools.
The programming data of the parameters of the part to be machined is the basis for the selection of a dedicated milling tool, and since the maximum metal removal rate should be balanced with an economical tool life, based on this it is possible to determine other tool variables.
In the case of titanium alloys, the basis of the tool includes a carbide material with a sharp and strong cutting edge and a relatively large positive front angle, which meet the special thermal and chemical requirements of titanium alloys.
Indexable insert technology has undergone a long development process in terms of grooves and tool materials and is becoming a more cost-effective solution to replace a large number of existing carbide tools, even for medium and large size tools.
Radial milling of titanium alloy materials
Radial milling is well suited for titanium alloy machining. However, large radial depth of cut will greatly reduce tool life, while a large axial depth of cut will have little effect on cutting temperature and therefore will not affect tool life in the same way.
Therefore, the best way to efficiently remove titanium alloys is to use a long-flute milling cutter with a tight tooth pitch, a radial depth of cut of 30% and the maximum axial depth of cut allowed for the specific application.
As a result, the long-edged cutter is suitable for roughing and finishing the sidewalls of many titanium alloy parts.
The long spiral flute of the long-flute milling cutter is ideal for large amounts of radial milling in titanium alloy machining. The indexable inserts long-edge tools consist of multiple rows of inserts, which are the same as the continuously sharpened integral carbide tool cutting edges.
At present, the indexable inserts rising up from the bottom of the cutter and arranged along the outer periphery have reached the limit of achieving good machining performance and safety in the titanium alloy.
A large chip flute for efficient chip evacuation is necessary and combined with an efficient positive rake angle and a sharp blade, it is combined into an indexable long-edge tool for excellent machining performance.
For titanium alloy milling, the stable clamping of the cutting insert is crucial.
Even in roughing, any movement of the cutting insert will cause uneven wear and put the cutting edge in danger. Slight signs of wear can make the cutting edge dull during the titanium alloy cutting process, thereby accelerating wear and causing tool breakage.
For a row of tightly fixed continuous blades, the axial support of the blade is particularly difficult, which can lead to excessive dependence on the blade screw.
Therefore, when using long-edged milling cutters, the best way to obtain outstanding performance is a strong interface between the blade and the cutter body.
The blade holder must have a definite support and locking device, with special consideration to the axial force and rotation force.
Coolant is critical.
Titanium alloy milling depends on the coolant used-the higher the quality, the better the machining effect.
Facts have proved that high-pressure cooling applications (pressure range of standard 70 × 105 ~ 100 × 105Pa, depending on the system used) has shown its obvious advantages.
Since high-pressure cooling has become standard on many modern machine tools, it is a potential resource for optimizing milling of titanium alloys.
High-pressure cooling will affect the heat distribution, chip formation, cutting edge bonding tendency, tool wear and surface integrity, which will have a very obvious impact on the processing results of titanium alloys.
Because titanium alloys are prone to chemical reactions, it is easy to weld the workpiece material to the cutting-edge during processing, which will affect the tool life and cause secondary cutting of chips and blockage of hard chips.
The coolant sprayed from the nozzle under high pressure plays a key role in temperature control, and therefore affects the processing results and reliability.
The tool nozzle is directly aligned with the part of the blade that is in contact with the finishing surface, so that a so-called “hydraulic wedge” is formed between the chip and the rake face of the blade.
Because these nozzle holes belong to the non-adjustable part of the tool, they have been optimized during assembly and the instability has been eliminated so that a more consistent and safe processing process can be obtained.
For practical reasons, the indexable milling cutter has a lower diameter of 12mm, while the carbide cutter has an upper diameter of 25mm based on cost performance.
The choice of intermediate and overlapping ranges depends on the specific application. For finishing, fine grinding of solid carbide end mills is usually the best solution, while for roughing, the best solution is an indexable tool.
However, tools suitable for this mid-range continue to develop, because the modularity of the tool provides a completely different perspective through this interchangeable head milling cutter.
Applications of small diameter milling cutter
Deep and narrow cavities require long tool reach.
Keeping these cavities from becoming a bottleneck in machining requires a solution that provides good performance, combined with small tool machining capabilities and machining flexibility.
The use of an extended chuck to clamp the solid carbide end mill to penetrate the inside of the cavity does not achieve the best stability, because it will limit the cutting parameters and bring risks to the quality of the parts.
However, the interchangeable head tool has the dual advantages of the indexability and finishability of an integral carbide tool.
In terms of performance and machining results, tool cost and flexibility requirements, changeable head tooling systems have significant advantages in the 10 to 25 mm tool diameter range. Not only does it offer a high degree of flexibility, but it also reduces tool inventory.
Its finishing capabilities are superior to indexable insert tools and the cost of the tool is significantly reduced compared to the overall carbide tool.
In addition, there is no need to worry about the blade size being reduced by resharpening.
A high degree of flexibility and more optimization possibilities are offered thanks to the ability to choose between different head and shank combinations.
The interface between the cutter head and the shank is a key element of such tools.
Its performance depends on strength, stability, accuracy, repeatability and ease of clamping.
The sufficiently large axial support surface, conical radial support surface, specially developed thread profile and screw support together create the unique interface required between the tool head and the tool holder.
This interface is the basis for ensuring good machining performance in large tool overhang conditions.
Successful milling of titanium alloys
In rough machining milling, the axial depth of cut is the main factor to be considered in order to obtain the best metal removal rate, while in finishing milling, the selection of the best feed rate must be considered.
In titanium alloy machining, whether roughing or finishing, it is always limited, although there can be different levels of cutting speed.
With an understanding of these basic principles in titanium alloy processing, much can be done to optimize the process, making titanium alloy processing more competitive and achieving reliable processes.
The 4 key factors to consider are machine capacity, coolant supply, cutting tool and machining method.
For radial milling at lower cutting speeds, the machine needs to have sufficient power and torque and also the right spindle to achieve a satisfactory metal removal rate.
If the machine also uses small diameter tools, the spindle speed range needs to be high enough to achieve excellent machining results.
In general, the spindle interface needs to be evaluated and its coupling stability cannot be too weak.
In order to obtain sufficient tool bending stiffness, good end face and taper contact is a basic requirement; adequate clamping pressure is essential in order to eliminate tension on the tool from spiral or radial milling tools.
Since titanium alloys have become more and more commonly used in machining workshops, whether the corresponding processing technology can be further developed to make the performance and processing results of this material to a new level becomes a crucial factor.
Milling dominates in titanium machining, in part because machining cavities, profiles, slots and edges in aircraft fuselage parts is a very challenging process.
Most of the processing is two-dimensional.
Due to the cavity depth and radius requirements and other challenging factors, the processing requirements are becoming more and more strict.
As for the machines used, they are very outdated for titanium alloy machining, which requires the selection of the best tooling systems and machining methods to achieve excellent machining and maximum machine utilization.
The method and programming of titanium alloy milling is more advanced than normal machining.
Machining fillets and contours according to the recommended method can achieve distinctive results in the production cycle of the machine tool and minimizing scrap.
In general, to ensure the right toolpath is machined from the start, taking a little extra time to optimize programming before machining will do more good than choosing an off-the-shelf process. New developments in milling tools have resulted in performance improvements that directly enhance the performance of titanium alloy materials.
Special tools play a major role in overcoming the challenges of machining titanium alloys and, in the optimization section, in selecting and applying the right tools for the process.
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