Titanium alloy has low density, high specific strength (strength/density), good corrosion resistance, high heat resistance, good toughness, plasticity, and weldability. Titanium alloys have been widely used in many fields, such as in aerospace, automotive, medical, sporting goods, and electrolysis industries, etc. However, poor thermal conductivity, high hardness, and low modulus of elasticity have also resulted in titanium alloy becoming a metal material that is more difficult to process. This article summarizes some technological measures in the cutting of titanium alloys based on their technological characteristics.
- Use cemented carbide tools as much as possible. Tungsten-cobalt cemented carbide has the characteristics of high strength and good thermal conductivity and is not prone to chemical reaction with titanium at high temperatures. It is suitable for processing titanium alloys.
- Reasonably select the geometric parameters of the tool to process titanium alloy parts. Toreduce the cutting temperature and reduce the phenomenon of tool adhesion, we can appropriately reduce the rake angle of the tool, and increase the contact area between the chips and the rake surface to dissipate heat. At the same time, increase the clearance angle of the tool to reduce the phenomenon of tool sticking due to the frictional contact between the machined surface and the flank surface of the tool. The tip of the tool should adopt a circular arc transition to enhance the strength of the tool. When processing titanium alloys, the tools must be sharpened frequently to ensure their sharp edges and smooth chip removal.
- Appropriate cutting parameters. To determine the cutting parameters, please refer to the following scheme: Lower cutting speed. The high cutting speed will cause the cutting temperature to rise sharply. Moderate feed rate. Large feed rate results in higher cutting temperature, and small feed rate results in faster cutting edge wear due to long cutting time in the hardened layer. Larger cutting depth. The tool tip is cutting over the hardened layer of the titanium alloy surface can increase tool life.
- During machining, the flow and pressure of the cutting fluid should be large, and the machining area should be fully and continuously cooled to reduce the cutting temperature.
- When selecting a machine tool, we should always pay attention to improving stability to avoid vibration trends. The vibration will cause the blade to shatter and damage. At the same time, the rigidity of the titanium alloy processing system should be good to ensure that a larger cutting depth is used during cutting. However, titanium alloy processing has a large springback and a large clamping force that will aggravate the deformation of the workpiece. Therefore, auxiliary supports such as assembly fixtures can be considered during finishing to meet the rigidity requirements of the processing
- Down milling is generally used for milling. The chip sticking and chipping of the milling cutter caused by up-milling in titanium alloy processing are much more serious than the damage of the milling cutter caused by down-milling.
- The common problems in grinding are sticky debris causing blockage of the grinding wheel and burns on the surface of the parts. When grinding titanium alloy parts, it is advisable to use green silicon carbide grinding wheels with sharp abrasive grains, high hardness, and good thermal conductivity. According to the surface finish of the machined surface, the grinding wheel size F36～F80 can be used. The hardness of the grinding wheel should be soft to reduce the adhesion of abrasive particles and debris and reduce the grinding heat. The grinding feed rate should be small, and the speed should be low. The emulsion is sufficient.
- When drilling titanium alloys, it is necessary to grind the standard drill bit to reduce the phenomenon of burning knife and drill bit breaking. Titanium alloy parts processing technology grinding method: appropriately increase the apex angle, reduce the rake angle of the cutting part, increase the back angle of the cutting part, and double the inverted taper of the cylindrical edge. During processing, the number of tool withdrawals should be increased, the drill bit must not stay in the hole, and the chips should be removed in time. A sufficient amount of emulsion should be cooled. Pay attention to the drill bit, if it becomes blunt, it should be replaced and reground in time.
- Titanium alloy reaming also needs to be modified to the standard reamer: the width of the reamer blade should be less than 0.15mm, and the cutting part and the calibration part should be arc transitioned to avoid sharp points. When reaming, the reaming tool can be used for multiple reaming, and the diameter of the reaming tool should be increased by 0.1mm or less each time. The spindle speed should be slightly slower, and the tool will not stop when retracting. Reaming in this way can achieve higher finish requirements.
- Thread tapping is the most difficult part in titanium alloy processing. Due to excessive torque, the tap cutter teeth will wear out quickly, and the rebound of the processed part can even make the tap break in the hole. When selecting ordinary taps for processing, the number of teeth should be appropriately reduced according to the diameter to increase the chip space. After leaving a 0.15mm width on the calibration teeth, the clearance angle should be increased to about 30°, and 1/2 to 1/3 tooth backshould be removed, the calibrated tooth retains 3 buckles and increases the inverted taper. It is recommended to use skipping taps, which can effectively reduce the contact area between the tool and the workpiece, and the processing effect is also better.
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