Titanium alloy has high strength, low density, corrosion resistance and high temperature resistance characteristics, and is widely used in aerospace products to manufacture pressurised parts, such as impellers, forged titanium fans, pressurised discs and blades, cast titanium pressurised magazines, intermediary magazines, and bearing housings. However, too much dissolved hydrogen in titanium alloys produces hydrides that make the alloy brittle. Chloride in the cutting fluid may also decompose or volatilise toxic gases when used, producing stress corrosion, and the parts should be thoroughly cleaned in a timely manner with a chlorine-free cleaning agent after cutting to remove chlorine-containing residues. Titanium chemical affinity is also large, easy to produce adhesion phenomenon with the friction surface, lead or zinc-based alloys, copper, tin, cadmium produced by the work, fixture and titanium alloy contact will change the state of titanium alloy surface metal properties. Therefore, titanium alloy parts in the parts processing process should be avoided and pollutants in contact, or should be eliminated has been contaminated surface.
At present, with the mass production of titanium alloy parts, the concept of anti-fatigue manufacturing in the aviation enterprise has been gradually applied to engineering practice, and the requirements for the surface state of the parts are getting higher and higher. Since 2010, each aviation enterprise respectively on titanium alloy parts in accordance with the theoretical analysis of some manufacturing process requirements, but in the actual process of the effective control measures used in the level of uneven, not perfect and systematic. For titanium alloy parts in the process of anti-pollution methods used in the research is not systematic and comprehensive.
In this paper, through the study of a typical titanium alloy impeller in the processing of anti-pollution process planning, focusing on cleaning up the sources of pollution in the processing of titanium alloy parts, take anti-pollution measures, elaborating on the anti-pollution technology of titanium alloy parts in the processing of titanium alloy parts.
Remove all burrs on the surface of the parts, using scrapers, rotary files and so on. Considering the material factor, all the abrasive grains such as polishing sandpaper, gauze and oil stone should be made of silicon carbide. The hardness of the polishing wheel is medium-soft, and its grain size must be between 240 and 600.
It is possible to use a combination of oil stone and polishing cotton, with the oil stone polishing repair surface, remove large residual, with polishing cotton to improve the surface roughness. You can also use the sand cloth to complete all the polishing process. Optional wind-powered tools can be used to select the appropriate size of the grinding head handle and grinding head, so that it can enter the impeller channel. The speed of polishing tool is 10000r/min. Firstly, the sand cloth is wrapped around the tool, in which the sand paper is silicon carbide sand paper with the grain size of 150 and 240, which is used for roughing and finishing respectively. Then start throwing repair blade and runner. If the silicon carbide deburring polishing brush is used to carry out, the polishing brush rotates at a high speed of 500r/min, and the parts rotate and move axially relative to each other. To ensure multi-angle, multi-position, each flute edge can be thrown. General operation 2min after checking the chamfer deburring situation, with a finger on the tooth surface touch, should be rounded, no sharp feeling that is qualified. If there is a local scraping sense to throw again. On-demand abrasive flow process to improve surface quality, all surface luminosity is further enhanced. Currently the typical silicon carbide abrasive, after the abrasive flow treatment of the surface removal margin is not more than 0.005mm.
Demagnetisation
In the process of processing directly or indirectly make parts magnetisation, so in the final cleaning before all parts have to be demagnetised, all parts demagnetisation treatment should be at least to achieve a magnetic field strength of not more than 3 gauss (except for the functional requirements of the parts are magnetic). When individual parts require magnetisation, they should be individually processed to meet the requirements. Parts shall be protected by maintaining the specified magnetic properties during processing.
General Cleaning
Titanium parts should not come into contact with methanol solvents or chlorinated solvents (e.g. trichloroethylene, trichloroethane). Remove oil and grease by wiping the surface of the part with a clean gauze moistened with acetone, butanone or isopropyl acetone. Non-interrupted water film condition: This condition is defined as the condition in which a continuous film of water forms on the surface of a part after it has been impregnated with water and in which no small droplets of water form on the surface of the part for at least 10s.
Pressure rinsing
Parts with deep grooves shall be pressure flushed and the solution shall be filtered through a 5μ filter before flushing. Such parts include conduits, fuel manifolds, valve covers and internal pipework in castings.
(1) Parts should be degreased prior to the flushing process.
(2) Corrosion-prone alloys should not be flushed under pressure with water.
(3) Pressurise each internal pipe for a minimum of 30 seconds and, in practice, reverse the flushing process for a minimum of 30 seconds.
(4) Mechanical vibration during rinsing is helpful in cleaning parts with internal cavities and pipework.
Deionised water rinsing of parts
Check that the acid solution is removed from wet parts by placing blue litmus paper over the area where acid may remain. If the paper turns red, residual acid is present and the part should be re-washed. If there is no visible discolouration of the paper, the acid is considered to have been removed.
