About the prevention of titanium alloy grinding burn
(AVIC Harbin Dongan Engine Company. Harbin, Heilongjiang 150066)
Abstract: This article mainly studies and tests on the grinding burn problem of titanium alloy parts, and summarizes the parameters that inhibit grinding burns, grinding wheels, coolant and other influencing factors to prevent the occurrence of titanium alloy grinding burns.
Keywords: titanium alloy parts; grinding burns; grinding wheels; coolant
The research of titanium alloy grinding has a history of decades abroad. In-depth research has been conducted on the mechanism of titanium alloy grinding and the performance of titanium alloy grinding, forming applicable norms and standards. There are clear regulations on the selection of coolant, processing methods, and grinding process parameters. At present, it is a very mature technology abroad and has been widely used in the aviation field. The accuracy of the products has been greatly improved, making the aerospace manufacturing technology ahead of my company for decades.
Through carrying out titanium alloy grinding experiments, conduct in-depth research on titanium alloy grinding, and find out the grinding parameters that inhibit grinding burns and grinding cracks.
2 Factors affecting grinding burn of titanium alloy
2.1 Titanium alloy material characteristics
(1) High specific strength; (2) Good heat resistance; (3) Good corrosion resistance; (4) Low thermal conductivity; (5) Small modulus of elasticity.
The characteristics of the grinding process caused by the material characteristics of titanium alloy: (1) The grinding force is high, the grinding temperature is high; (2) The deformation during the grinding process is complex; (3) The adhesion of the grinding wheel is serious, and the adhesion of the adhesion can cause the grinding wheel The abrasive particles are broken and falling off.
2.2 Grinding principle
The heat release in the grinding area is the main cause of burns. The result of the heat release changes the metallographic structure of the surface of the workpiece, which greatly changes its mechanical properties and performance.
2.3 machine tool
In order to ensure the dimensional accuracy of parts and the stability of various processing parameters, and to achieve functions such as contour grinding and vibration grinding. The machine tool has a vibration grinding function, an operation panel, a portable operation unit, and the speed of the dressing tool can be set. At the same time, it has the function of correcting the entire workpiece and trimming the shape of the special grinding wheel.
2.4 grinding wheel
According to the general principles of selection of material, particle size and hardness of titanium alloy grinding wheels, the grade of grinding wheel suitable for titanium alloy grinding is determined. The structure of the grinding wheel is relatively loose and has certain pores. When grinding titanium alloy, the efficiency is higher, the grinding temperature is lower, and the grinding wheel is not blocked; the diamond dressing roller is used to complete the dressing of the grinding wheel. The hardness of the grinding wheel is medium to soft, and the grain size of the abrasive is 60-120.
Grinding wheel grade:
Norton GC60-Jl0V02P35M/S produced by Saint-Gobain Abrasives Company
Wheel size: 60
Abrasive material: silicon carbide (GC)
Wheel hardness: soft (J)
Wheel structure: loose (10)
Grinding wheel bond: ceramic bond (V02)
Minimum diameter of grinding wheel available: 350mm
The shape of the grinding wheel for grinding arc-end teeth is shown in Figure 1. It is a cup-shaped grinding wheel and the length of the grinding wheel is H
Figure l The shape of the grinding wheel
According to the selection principle of the coolant composition and combined with the recommendation of the machine tool manufacturer, we selected the internationally commonly used Castrol semi-synthetic cutting fluid as the additional coolant for titanium alloy grinding, and ensured that the direction of the nozzle when pouring the coolant can be directly poured into the parts and the grinding wheel. On the contact surface (Figure 2), the maximum flow is used at the same time to achieve sufficient cooling. The grinding fluid not only has good cooling performance, but also its lubricating performance inhibits the adhesion of the grinding wheel and the titanium alloy and reduces the grinding temperature. The grinding fluid does not contain chlorides or sulfides that pollute the titanium alloy. When grinding titanium alloys, the flow rate of the grinding fluid is not less than 15-20ml/min.
Castrol semi-synthetic cutting fluid HYSOLX related information: It is a high-tech, multi-purpose, biologically stable solvent semi-synthetic cutting fluid with good lubrication and extreme pressure characteristics. The product has a wide range of applications and is suitable for ferrous and non-ferrous metals. A variety of processing has excellent performance. The water quality is highly adaptable, but its low foam characteristics are more prominent in soft water. Can be widely used in the aviation industry. The product does not contain chlorine. (1) Coolant application: suitable for processing a variety of different metals on high-speed machining centers and flexible machining systems that adopt the latest technology. In processing steel, titanium alloy, cast iron and even various difficult-to-machine metals such as stainless steel, nickel silicon aluminum steel. (2) The role of coolant: This product is designed for most metal processing, and is also suitable for large central cooling systems and small cooling devices. Suitable for milling, drilling, boring, reaming, broaching and low-feed grinding. (3) Advantages of coolant: a. The processing brightness is good and the tool life can be extended, even for materials that are difficult to process. b. Applicable materials and processing methods are wide. c. Even at extreme pressures higher than 70 bar, there is little foaming. d. Does not corrode and pollute aluminum. e. Strong water quality adaptability and long service life. Good lubrication characteristics can reduce lubricating fluid residue and ensure the cleanliness of machine tools and parts. g. The operator and the environment are not exposed to the danger of free chlorine, nitrite and phenol. h. Will not damage the paint prints and other markings usually made on the parts.
2.6 Grinding parameters
According to the machine tool manual and related foreign standards, determine the grinding wheel speed 35m/s and the workpiece speed 100r/min. Because the titanium alloy material is easy to adhere to the grinding wheel, it is not easy to dissipate heat. In order to ensure the air permeability of the grinding wheel, before semi-finishing and fine grinding
Each wheel dressing is performed once. After solidifying the basic factors affecting grinding burns, the machine tool, grinding wheel, coolant, and grinding parameters will focus on optimizing the contact area between the grinding wheel and the workpiece, the grinding depth and the feed rate.
3 Titanium alloy grinding burn acid etching inspection
(1) The acid, alkali, and water tank used for acid etching inspection should have enough volume to ensure that the parts can move freely and be completely immersed. (2) The container material and the solution in the container must not react, nor damage the inspected parts. The material of the container is polyvinyl chloride or austenitic stainless steel. (3) All containers should be labeled with the solution they contain, and should be covered with a lid when not in use. (4) The acid etched work site should have good ventilation devices.
Nitric acid, hydrofluoric acid, alcohol, deionized water
3.3 Acid etching procedure
(1) Inspection before acid etching. Before the acid etching inspection, there should be no bumps, scratches, rust spots, etc. on the surface of the parts that may affect the inspection results. (2) Degreasing. Immerse the parts in gasoline for washing, if necessary, use nylon brush dipped in gasoline to scrub until the oil is completely removed. (3) Cleaning. Clean the degreasing parts with alcohol for 2 minutes. Ensure that the parts get a moist, stain-free, uniform gloss and clean surface. (4) Erosion. Immerse the cleaned parts in the prepared acid etching solution and shake the parts. Stay at room temperature for about 90 seconds, and then perform a macro inspection. If the macroscopic inspection finds that the corrosion is not sufficient, it is corroded in the original solution for another 30 seconds. (5) Rinse. Immerse the whole in running water at room temperature and rinse for 3 minutes. (6) Blow dry. Dry the parts with clean, dry compressed air.
3.4.1 Inspection method
Using the OlympusSZX16 solid microscope to inspect all the surfaces to be inspected under the magnification of 10X-30X.
3.4.2 Acceptance criteria
Typical grinding burn judgment photos are shown in Figure 3 to Figure 5.
Figure 3 Standard state (no burn state)
Figure 4 Mild burn state
Figure 5 Severe burn state
Through the analysis of relevant factors in the grinding of titanium alloy parts and the modulus in actual processing, the processing parameters suitable for preventing grinding burns, coolant, grinding wheel, machine tool related parameters, etc., are summarized.