Analysis of Processing Methods for Titanium Alloy Parts
Analysis of Titanium Alloy Parts Processing Technology
Titanium alloys have excellent mechanical properties but poor processability, leading to a contradiction where their application prospects are promising but processing is quite difficult. This article discusses various aspects of titanium alloy machining, including the selection of cutting tools, determination of cutting speeds, characteristics of different cutting methods, machining allowances, and processing precautions, based on an analysis of the metal cutting performance of titanium alloy materials and years of practical work experience, clarifying my insights and suggestions on titanium alloy machining.
Titanium alloys have low density, high specific strength (strength/density), good corrosion resistance, high heat resistance, and good toughness, plasticity, and weldability. They are widely used in many fields such as aerospace, automotive, medicine, sports equipment, and electrolysis industries. However, their poor thermal conductivity, high hardness, and low elastic modulus make titanium alloys difficult to process. This article summarizes some process measures in titanium alloy cutting based on their processing characteristics.
1 Main Advantages of Titanium Alloy Materials
(1) Titanium alloys have high strength and low density (4.4kg/dm3), providing a solution for reducing the weight of large structural components.
(2) High thermal strength. Titanium alloys can maintain high strength at temperatures between 400 and 500°C, allowing stable operation, while aluminum alloys can only operate below 200°C.
(3) Compared to steel, the inherent high corrosion resistance of titanium alloys can save costs in the daily operation and maintenance of aircraft.
2 Analysis of Titanium Alloy Processing Characteristics
(1) Low thermal conductivity. TC4 has a thermal conductivity of l=16.8W/m at 200°C, and its thermal conductivity coefficient is 0.036 cal/cm, which is only 1/4 of steel, 1/13 of aluminum, and 1/25 of copper. The poor heat dissipation and cooling effect during cutting processing shorten tool life.
(2) Low elastic modulus, resulting in significant rebound of the machined surface, which increases the contact area between the machined surface and the tool's clearance face, affecting the dimensional accuracy of the part and reducing tool durability.
(3) Hardness factors. Titanium alloys with low hardness values tend to stick during processing, causing chips to adhere near the cutting edge of the tool, affecting processing results; titanium alloys with high hardness values can easily cause tool chipping and wear. These characteristics lead to a low metal removal rate for titanium alloys, only 1/4 that of steel parts, and significantly longer processing times for parts of the same size.
(4) Strong chemical affinity. Titanium can react chemically with nitrogen, oxygen, carbon monoxide, and other major components in the air, forming TiC and TiN hardened layers on the alloy surface, and can also react with tool materials under the high-temperature conditions generated during cutting, reducing tool durability.
(5) Poor safety performance during the cutting process. Titanium is a flammable metal, and the high temperatures and sparks generated during micro-cutting may ignite titanium chips.
3 Titanium Alloy Processing Technology Methods
(1) Use carbide tools as much as possible. Tungsten-cobalt carbide has high strength and good thermal conductivity, and it is less likely to react chemically with titanium at high temperatures, making it suitable for processing titanium alloys.
(2) Reasonably select tool geometric parameters. To reduce cutting temperature and minimize tool adhesion, the tool's rake angle can be appropriately reduced to increase the contact area between the chip and the cutting face for heat dissipation; simultaneously, increase the tool's clearance angle to reduce tool adhesion and the reduction of machined surface accuracy caused by rebound and friction contact with the tool's clearance face; the tool tip should adopt a rounded transition to enhance tool strength. Tools should be regularly sharpened to ensure sharp cutting edges and smooth chip removal.
(3) Suitable cutting parameters. The following scheme can be referenced for determining cutting parameters: lower cutting speed—high cutting speeds can lead to a sharp increase in cutting temperature; moderate feed rate—a large feed rate increases cutting temperature, while a small feed rate accelerates tool wear due to prolonged cutting time in the hardened layer; larger cutting depth—cutting beyond the hardened layer of the titanium alloy can improve tool life.
(4) The flow rate and pressure of the cutting fluid during processing should be high, providing sufficient continuous cooling to reduce cutting temperature.
(5) When selecting machine tools, always pay attention to improving stability to avoid vibration trends. Vibration can lead to chipping of the cutting edge and damage to the tool. Additionally, the rigidity of the titanium alloy processing system should be good to ensure larger cutting depths, but the significant rebound during titanium alloy processing and the large clamping force can exacerbate workpiece deformation, so auxiliary supports such as assembled fixtures can be considered during finishing to meet the rigidity requirements of the process system.
(6) Milling is generally done using conventional milling. The chip adhesion and chipping caused by climb milling in titanium alloy processing are much more severe than those caused by conventional milling.
(7) Common issues in grinding include chip adhesion causing wheel clogging and burning of the part surface. Therefore, during grinding, it is advisable to use green silicon carbide wheels with sharp grains, high hardness, and good thermal conductivity; depending on the surface finish requirements, wheel grit can be F36 to F80; the wheel hardness should be relatively soft to reduce the adhesion of grains and chips, lowering grinding heat; the grinding feed rate should be small, with a lower speed and sufficient emulsion.
(8) When drilling titanium alloys, standard drill bits need to be sharpened to reduce burning and breakage. Sharpening methods include appropriately increasing the point angle, reducing the rake angle of the cutting part, increasing the clearance angle of the cutting part, and doubling the taper of the cylindrical edge. During processing, increase the number of retractions, do not let the drill stay in the hole, promptly remove chips, ensure sufficient cooling with emulsion, and observe the drill bit for dullness to replace or sharpen it in a timely manner.
(9) Standard reamers also need to be modified for reaming titanium alloys: the width of the reamer cutting edge should be less than 0.15mm, and the cutting part should transition to the calibration part with a rounded arc to avoid sharp points. When reaming, a set of reamers can be used for multiple reamings, increasing the reamer diameter by less than 0.1mm each time, with the spindle speed slightly slower and no stopping during retraction. This method can achieve high surface finish requirements.
Threading is an extremely difficult aspect of titanium alloy processing. Due to excessive torque, the teeth of the tap can wear out quickly, and the rebound of the processed area can even cause the tap to break inside the hole. When using a standard tap, the number of teeth should be appropriately reduced based on the diameter to increase chip space. After leaving a 0.15mm wide cutting edge on the calibrated teeth, the back angle should be increased to about 30°, removing 1/2 to 1/3 of the tooth back, and after retaining 3 threads on the calibrated teeth, the taper angle should be increased. It is recommended to use a skip-tooth tap, which can effectively reduce the contact area between the tool and the workpiece, resulting in better processing effects.
4 Processing Precautions
1. Tools should be frequently sharpened and kept sharp to ensure minimal cutting heat is generated during processing.
2. Equipment, tools, workpieces, and fixtures should be kept clean, and chips should be removed in a timely manner.
3. Use non-combustible or difficult-to-burn tools to transfer titanium chips. Store the discarded chips in a non-combustible container and cover them well.
4. When handling cleaned titanium alloy parts, wear clean gloves to avoid causing sodium chloride stress corrosion later.
5. There are fire prevention facilities in the cutting area.
6. When cutting in small quantities, if the titanium chips catch fire, they can be extinguished with dry powder extinguishers or dry soil/sand.
Compared to most other metal materials, titanium alloy processing not only requires higher standards but also has more restrictions. However, if the appropriate tools are used correctly and the machine tools and configurations are optimized to an excellent state according to processing requirements, satisfactory titanium alloy processing results can also be achieved.
More information
What are the five main characteristics of titanium plates?
Features: 1. The titanium seed plate has a surface oxide film that acts as a good, durable release agent, saving the use of release agents and making the peeling of the plates easier, eliminating the need for pre-treatment of the seed plates. The titanium seed plate is half the weight of the copper seed plate. 2. The lifespan of the titanium seed plate is more than three times that of the copper seed plate, and can reach 10 to 20 years depending on operating conditions. 3. The electrolytic copper produced using titanium seed plates has a dense crystalline structure, a smooth and flat surface, and high quality. 4. Since titanium seed plates do not require the application of release agents, they can avoid contamination of the copper electrolyte. 5. Increased production capacity reduces the production costs of electrolytic copper, resulting in better economic benefits.
What are the technical requirements for titanium pipes?
Titanium pipes are lightweight, have high strength, and excellent mechanical properties. They are widely used in heat exchange equipment, such as shell-and-tube heat exchangers, coil heat exchangers, serpentine tube heat exchangers, condensers, evaporators, and transport pipelines. Many nuclear power industries use titanium pipes as standard pipes for their units.
Technical requirements:
1. The chemical composition of titanium and titanium alloy pipes should comply with the provisions of GB/T3620.1. When the buyer conducts re-inspection, the allowable deviation of the chemical composition from Mingkun Titanium Industry should comply with the provisions of GB/T3620.2.
2. The allowable deviation of the outer diameter of the pipe should comply with the specifications in Table 1.
3. The allowable deviation of the wall thickness of the pipe should not exceed its nominal wall.
What should be noted when filtering materials with titanium pipes?
Precautions: 1. If using titanium plate as a filtering material, it must not exceed its maximum working capacity. 2. When using titanium plates as filtering materials, be sure to prevent the plates from being bumped or scratched, and keep them clean to avoid contamination. 3. After using the titanium plate material, it must be cleaned and stored properly. 4. Before starting work, the titanium plate filtering material must be activated before adjusting to the normal working environment.
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