1. Edge cutting

The cutting edge of titanium alloy forgings must meet the following requirements:

(1) The incision should be smooth, and the metal on the blank should not collapse.

(2) There shall be no cracks or uneven grain size caused by uneven deformation of the cutting edge adjacent to the cutting surface of the blank.

(3) There should be no punch marks left on the trimmed blank, and the punch and the part should be completely identical in appearance.

For batch production, milling machines can be used to cut edges or band saws and specially designed friction plates can be used to remove burrs. For large forgings and thick burrs, regardless of the size or batch of the parts, flame cutting is an effective method as it is not convenient for hot cutting edges. The use of oxygen gas, plasma and other technologies can successfully and economically cut burrs of 50mm or thicker. After flame cutting, heat treatment should be carried out to enable mechanical processing of the heat affected zone. For large quantities of small and medium-sized titanium alloy forgings, the hot cutting edge is usually done on a crank press using a mold, and the edge cutting is carried out at 600-800 ℃. If correction must be carried out immediately after trimming, the trimming temperature should be close to the upper limit. Titanium alloys are rarely cut with molds in the cold state, as the burrs are hard and brittle, which can easily cause uneven cuts and even pose a risk of metal cracking and debris splashing; For certain alloys with a high degree of alloying, cold cutting can cause cracks on the shear surface, which can sometimes propagate into the interior of the metal.

2 Correction

Titanium alloys tend to bend under their own weight at high temperatures, which increases the tendency for products to twist during forging, cooling, and heat treatment. The lifting and trimming of complex die forgings are often important factors leading to twisting deformation. The distortion is particularly evident in products with severe cross-sectional changes or particularly thin cross-sections, therefore, it is often necessary to correct titanium alloy forgings to meet dimensional requirements. Unlike aluminum alloys, titanium alloys are not easily subjected to cold forming due to their high yield strength and elastic coefficient, resulting in significant rebound. Therefore, the forming of titanium alloy forgings mainly relies on creep forming and hot forming, with the former being more common. The creep deformation correction of most titanium alloys can be completed during annealing and aging processes, with the temperature being the annealing and aging temperature. However, if the annealing and aging temperature is below 540 ℃, the time required for creep correction to be completed may be extended for different alloys. Creep correction requires simple or complex fixtures and molds. Hot forming in molds is commonly used for medium-sized forgings. The forgings are heated to annealing or aging temperatures for hot forming, and then stress relief is carried out below the hot forming temperature.

3 Surface Purification Treatment

The oxide rust scale and alpha shell formed during the heating process of titanium alloy forgings are very brittle, and can induce cracks during subsequent forging or final forging, or cause tool wear during subsequent mechanical processing. Therefore, it is best to clean the rust scale and alpha shell layer between continuous forging. The oxide scale of forgings often covers surface defects, so surface purification treatment must be carried out before final verification of forgings. Rust scale and alpha shell layer must be removed before delivering forgings to users.

The surface purification treatment technology for titanium alloy forgings first requires the removal of oxide scale, and rust scale can be removed by mechanical methods such as sandblasting; Alternatively, chemical methods such as molten salt rust removal can be used. The choice of rust removal method depends on the size, complexity, and cost of the parts.

The parts that do not require acid washing should be painted in advance for protection. However, it should be noted that the hanger holding the parts can only come into contact with the painted part of the forging. Any titanium alloy forging with an alpha layer surface is not allowed to be installed on engines or aircraft.