Titanium alloy processing In many aerospace applications, titanium and its alloys are replacing traditional aluminum alloys. Today, the aerospace industry consumes about 42% of global production of titanium materials, and from now to 2010, it is expected that the demand for titanium materials will continue to grow at a double-digit rate. The new generation of aircraft needs to make full use of the performance provided by titanium alloys. Both commercial and military aircraft markets are driving the demand for titanium alloys. New models such as Boeing 787, Airbus A380, F-22 Raptor fighter, and F-35 Joint Strike Fighter (also known as Lightning II) all use a lot of titanium alloy materials.
Advantages of titanium alloy materials
Machining titanium alloy has high strength, high fracture toughness, good corrosion resistance and weldability. As aircraft fuselages increasingly adopt composite structures, the proportion of titanium-based materials used in the fuselages will also increase, because the bonding properties of titanium and composite materials are far superior to aluminum alloys. For example: Compared with aluminum alloy, titanium alloy can increase the life of the fuselage structure by 60%. The extremely high strength/density ratio of titanium alloys (up to 20:1, which means that the weight can be reduced by 20%) provides a solution for reducing the weight of large components (this is the main challenge for aircraft designers). In addition, the inherent high corrosion resistance of titanium alloys (compared to steel) can save the cost of daily operation and maintenance of aircraft.
Need more processing capacity
Titanium alloy processing is more difficult than ordinary alloy steel processing, so it is generally considered that titanium alloy is a difficult-to-process material. The metal removal rate of a typical titanium alloy is only about 25% of that of most ordinary steels or stainless steels, so the time required to process a titanium alloy workpiece is about that of processing steel
Pieces 4 times.
In order to meet the increasing demand for titanium alloy processing in the aerospace industry, the Dongguan cnc processing plant requires manufacturers to increase production capacity and therefore need to better understand the effectiveness of titanium alloy processing strategies. The processing of a typical titanium alloy workpiece starts from forging until 80% of the material is removed to obtain the final shape of the workpiece.
With the rapid growth of the aerospace parts market, manufacturers have felt powerless, coupled with the increased processing demand due to the low processing efficiency of titanium alloy workpieces, resulting in obvious tension in the processing capacity of titanium alloys. Some leading companies in the aviation manufacturing industry even openly questioned whether the existing machining capabilities can complete the processing tasks of all new titanium alloy workpieces. Since these workpieces are usually made of new alloys, the processing methods and tool materials need to be changed.
Titanium alloy Ti-6Al-4V
Titanium alloys have three different structural forms: α titanium alloy, α-β titanium alloy and β titanium alloy. Commercial pure titanium and alpha titanium alloys cannot be heat treated, but they usually have good weldability; alpha-beta titanium alloys can be heat treated, and most of them are also weldable; beta and quasi-beta titanium alloys can be heat treated, and generally It is also weldable. Most common α-β titanium alloys used in turbine engines and airframe components are Ti-6Al-4V (Allvac Ti-6-4, Ti-6-4 for short). In this article, Ti-6-4 is used to represent ATI Allvac. The company is a major supplier of titanium alloys (recently signed a 2.5 billion dollar long-term supply contract for titanium alloys with Boeing). In addition, ATI Stellram, which cooperates with ATI Allvac to develop processing solutions, also uses these titanium alloy codes to describe processing requirements. Ti-6-4 has excellent comprehensive properties of strength, fracture toughness and fatigue resistance, and can be made into various product forms. The annealed Ti-6-4 can be widely used in structural parts. Through small changes in chemical composition and different thermomechanical treatment processes, Ti-6-4 can be used to produce parts for various purposes. Titanium alloy Ti-5Al-5V-5Mo-3CrTi-5Al-5V-5Mo-3Cr (Ti-5-5-5-3 for short) is a new type of titanium alloy with considerable market influence. Compared with β titanium alloy and α-β titanium alloy, this quasi-β titanium alloy can provide the fatigue fracture toughness required in aircraft component applications that require higher tensile strength. Compared with traditional titanium alloys (such as Ti-6-4 and Ti-10-2-3), Ti-5-5-5-3 has complex shapes that can be forged, and the final tensile strength after heat treatment can reach 180ksi ( Thousands of pounds per square inch) and other properties make it the most promising material for the manufacture of advanced aircraft components and landing gear.
By performing dissolution heat treatment below the β transformation temperature or annealing treatment above the β transformation temperature, while appropriately controlling the grain size and precipitation in the microstructure, Ti-5-5-5-3 can obtain excellent mechanical properties. The beta transition temperature is the specific temperature of the composite at which the alloy transforms from an alpha-beta microstructure to a full beta microstructure. Changes in chemical properties and microstructures allow titanium alloys to obtain a wide range of performance combinations, and therefore are widely used in aerospace components. The processing difficulty of Ti-5-5-5-3 is about 30% higher than that of Ti-6-4. Therefore, parts manufacturers using this new alloy are working to develop products that do not shorten tool life and extend production cycles. The corresponding processing technology.
When processing titanium alloys, material hardness is a key factor. If the hardness value is too low (<38HRC, the titanium alloy will be sticky and the cutting edge is prone to build-up edge. Titanium alloy with a higher hardness value (>38HRC) will have an abrasive effect on the tool material and wear the cutting edge. Therefore, The correct choice of processing speed, feed rate and cutting tool is very important.
Requirements for cutting tools
In order to meet the requirements of production cost, processing quality and on-time delivery, the Dongguan cnc processing plant has put more pressure on aerospace parts manufacturers with new workpiece materials and part designs. The machining of these new materials has changed the requirements for cutting tools. Improving the metal removal rate, tool life, product quality and predictable tool life without damage is essential for efficient and safe machining. "Difficult to machine" is a relative concept. Through the correct combination of cutting tools and machining parameters, efficient productivity can also be obtained.
When processing aviation-grade titanium alloy workpieces, cutting tool manufacturers control the cutting heat generated by the tool-work interface by increasing the matrix density, designing special tool geometry, adopting precise cutting edge grinding technology, and developing new coating technologies. The method greatly improves the performance of the tool.
In milling, an important characteristic of titanium alloys is extremely poor thermal conductivity. Due to the high strength and low thermal conductivity of titanium alloy materials, extremely high cutting heat (up to 1200°C if not controlled) is generated during processing. The heat is not discharged with the chips or absorbed by the workpiece, but is concentrated on the cutting edge. Such high heat will greatly shorten the tool life.
Using special processing technology, it is possible to improve the performance and life of the tool (using the correct processing technology to control the temperature, the temperature can be reduced to 250 ~ 300 ℃). Reducing heat generation reduces the radial and axial engagement of the tool and the workpiece to control the generation of cutting heat. For titanium alloys, the adjustment period for speed, feed rate, and radial and axial joints is very short before the build-up due to overheating. In order to achieve proper tool life, the maximum "joining arc length" of 15% is required for machining titanium alloys, compared with 50% to 100% when machining ordinary steel. Reducing the contact arc length can increase the cutting speed and increase the metal removal rate without losing tool life.
Using a tool with an entry angle of 45° or chip thinning can increase the contact length between the cutting edge of the tool and the chip, thereby reducing local high temperature, extending the life of the cutting edge, and allowing higher cutting speeds.
Blade geometry design:
When cutting titanium alloys, the use of peripheral grinding inserts is essential to minimize the cutting pressure and friction with the machined surface. The blade geometry must be positive, but this is not enough to ensure optimal performance. If a small initial angle with higher strength is used in order to strengthen the first part of the cutting edge, then a larger secondary angle (to obtain a larger front chamfer) is the best for enhancing the compression resistance of the insert and prolonging the tool life. Geometric design. In addition, slight passivation also helps to protect the cutting edge, but the size of the passivation must be coordinated with the cutting process and maintain tight tolerances. When processing titanium alloys, it is necessary to use a sharp cutting edge to cut the material, but the cutting edge is too sharp to easily cause chipping and shorten the tool life. Proper passivation can protect the cutting edge and avoid premature chipping. The correct blade geometry parameters can reduce the stress and pressure on the tool material, make the tool longer life and improve processing efficiency. The cutting angle of the cutter body and the blade must be a positive angle to obtain a progressive cutting effect, and to avoid impact on the entire cutting edge during cutting and failing to obtain the desired shearing effect. If this is not done, the structure of the workpiece may be deformed, making processing impossible.
Cavity milling and spiral interpolation milling
When the Dongguan cnc processing plant performs cavity milling and spiral interpolation milling, internal cooling tools must be used. If possible, constant pressure coolant should be used. This is especially important for deep cavity or deep hole machining. When processing deep cavities, the use of high-density cemented carbide extension tools with modular cutting heads can increase rigidity and reduce flexural deformation to obtain the best processing results. The function of the coolant is to remove chips from the cutting area and avoid secondary cutting that may cause early tool failure. At the same time, the coolant also helps to reduce the temperature of the cutting edge, reduce geometric deformation of the workpiece, and extend the life of the tool. Spiral interpolation milling holes with milling cutters can reduce the use of other tools (such as drills, etc.) in the tool magazine. A milling cutter with one diameter can be used to process different sizes of apertures.
As the application of titanium alloys in the aerospace industry continues to grow, cutting technologies that support efficient processing of titanium alloys are also evolving. Due to the large demand for the processing capacity of titanium alloy parts, those workshops or manufacturers that use the most effective processing technology will benefit first. Internal integration produces new solutions. Allegheny Technologies is a multi-field manufacturer whose business units include both metal smelting and metal cutting. The combination of these two fields enables the company to develop new methods for processing advanced materials (such as titanium alloys) Has advantages.
ATI Stellram is a business unit of ATI Metalworking Products, a subsidiary of llegheny Technologies. It is responsible for processing performance tests on all new materials developed by ATI Allvac to determine the best insert design, tool geometry, substrate and coating structure As well as cutting parameters, these new materials can be processed cost-effectively before they are publicly marketed. In addition, as a representative of Allvac, Stellram is a major aerospace manufacturing company and a first-class supplier of aerospace machinery parts, which can meet the common needs of workpiece materials and cutting tools.
The comprehensive understanding of the inherent structure of the material gives ATI Stellram an advantage in the design of the unique formula of the tool matrix. One of its achievements is the X-Grade technology. According to ATI Stellram, this technology has been proven to be a reliable tool for processing difficult-to-process materials. Program. Through research and development of X-Grade technology, a new cemented carbide grade has been produced, which can effectively cut difficult-to-machine materials with extremely high metal removal rates under unstable processing conditions. X-Grade blade technology (substrate and coating) X-Grade blade adopts a ruthenium/cobalt alloy matrix, which can resist the generation and expansion of thermal cracks, and can obtain a higher metal removal rate. The matrix has a strong crystal bonding matrix structure, thereby improving the toughness of the cutting edge. According to ATI Stellram, the matrix material combined with new tool geometries and coatings can provide an excellent tool combination for machining aerospace alloys. The use of X-Grade blades can achieve: ①The metal removal rate is increased by 1 time; ②The tool life is increased by 3 times; ③The surface finish of the processing is increased by 30%. Available X-Grade inserts include 3 grades (X400, X500 and X700), each of which is designed for specific difficult-to-cut machining. They can use standard blade types, and most of them can be installed in the blade groove of the standard blade body. But ATI Stellram said that the best solution is to use specially designed tools to optimize the performance of X-Grade blades.
The groove design of these tools allows maximum chip evacuation, enhanced geometry and optimal cooling. The two tools in this series include: ①7710VR anti-rotation button milling cutter: equipped with round inserts and with a patented locking indexing system to prevent the insert from shifting at high feedrate cutting; ②7792VX high-feed milling cutter: similar to traditional cutters Compared with, the metal removal rate can be increased by 1 times. In addition to high-feed surface milling, the 7792VX series tools can also be used for cavity milling, slot milling and plunge milling. Since the cutting force is directly transmitted to the spindle in the axial direction, it can reduce spindle friction and improve cutting stability.
A case study of aerospace titanium alloy parts processing
The following are two examples of machining aerospace titanium alloy parts using ATI Stellram cutters and X-Grade blades.
(1) Processing example 1
Part to be processed: Titanium alloy outer cover (military) Workpiece material: Ti-6Al-4V (Allvac Ti-6-4 alloy) Workpiece size: 110"×18"
Processing description: ATI Stellram 7792VX high-feed milling cutter with XDLT-D41 indexable insert is used for processing, and the tool life of rough milling reaches 156 minutes. Milling cutter: C7792VXD12-A3.00Z5R; number of slots: 5 pieces: XDLT120508ER-D41; grade: X500 (designed with X-Grade technology) axial cutting depth ap: 0.080" radial cutting width ae: 2.100" cutting speed vc : 131sfm feed per tooth fz: 0.023ipt feed rate: 19.2ipm tool life: 156 minutes/per indexing (each blade can index 4 times)
(2) Processing example 2
Parts to be processed: Turbine blades of military aircraft (new application) Workpiece material: All titanium alloy Blade size: 23.6"×11.8"
Processing description: The ATI Stellram 7710VR milling cutter with anti-rotation blade is used to process the propeller blades. The tool life of rough milling processing reaches 110 minutes. Milling cutter: C7710VR12-A2.00Z5R; number of slots: 5 inserts: RPHT1204MOE-421-X4; grade: X700 (designed with X-Grade technology) axial cutting depth ap: 0.080"～0.100" radial cutting width ae: 0.800"～1.37" cutting speed vc: 265sfm feed per tooth fz: 0.0086ipt feed rate: 21.8ipmTool life: 110 minutes per indexing (each blade can index 4 times)