Titanium castings are subsequently processed with key process steps

Necessity: The surface oxide film formed during the casting process can hinder subsequent processing and treatment results.

Common methods:

Mechanical method: grinding, sanding, or polishing using grinding wheels, abrasive belts, sandpaper, polishing wheels, etc., to physically remove oxide layers and surface defects.

Chemical method (pickling): A mixed solution of nitric acid (HNO₃), hydrofluoric acid (HF), hydrochloric acid (HCl) or sulfuric acid (H₂SO₄) is used to dissolve and remove the oxide film. Strict control of acid concentration, temperature, and soaking time is key.

Objective: To adjust the microstructure to obtain the desired combination of mechanical properties (strength, hardness, toughness, plasticity).

Main processes:

Annealing: Heating to an appropriate temperature below the phase transition point, controlled cooling after heat preservation (usually furnace cooling). The purpose is to eliminate stress, improve plastic toughness, stabilize the structure, and obtain uniform fine grains.

Solution treatment + aging (STA): Heating above the β phase change point (solution), rapid cooling (quenching, such as water quenching or air cooling), and then holding at a lower temperature (aging). During the aging process, a reinforced phase is precipitated, which significantly improves strength and hardness.

Stress relief annealing: Insulation at lower temperatures, mainly used to eliminate residual stress caused by machining or welding, stabilizing the dimensions.

Purpose: to achieve precise final dimensions, shapes, and surface roughness requirements.

Machining methods: milling, turning, drilling, reaming, boring, grinding, etc.

Key Control Points:

Tool Selection: Use carbide or diamond-coated tools to resist titanium's high strength and work hardening tendencies.

Cutting parameters: strictly control the cutting speed, feed rate, and cutting depth. Typically with lower speeds, moderate feeds, and smaller depths of cut.

Cooling and lubrication: A large amount of high-efficiency coolant (special titanium alloy cutting fluid or emulsion) must be used to effectively reduce the cutting temperature and prevent tool overheating, workpiece burns, and material sticking.

Rigidity: Ensure that the machine, workpiece, and fixture system are sufficiently rigid to reduce vibration.

Purpose: To improve appearance, remove machining marks, improve surface integrity, and enhance corrosion and wear resistance.

Common methods:

Sandblasting: Using a high-pressure gas (air/inert gas) to spray abrasives of a specific particle size (e.g., alumina, glass beads) to clean the surface, remove tiny burrs, obtain a uniform and consistent matte texture, or clean the activated surface in preparation for subsequent processing.

Polishing: Mechanical polishing (cloth wheel + polishing paste) or chemical/electrolytic polishing to obtain a smooth surface with a high finish, mirror or specific roughness, reducing stress concentration points.

Anodizing: In an acidic electrolyte (such as chromate), titanium castings are energized as anodes. A dense, adhesive colored or colorless oxide film (TiO₂) is formed on the surface.

Main functions: greatly improve corrosion resistance, increase surface hardness and wear resistance, improve lubricity (as a dry film lubrication substrate), provide a decorative appearance or mark substrate.

Purpose: To ensure that the processed castings are 100% compliant with design specifications, technical standards and customer requirements.

Test items:

Visual inspection: Visual inspection of surface defects (cracks, porosity, inclusions, scratches, contamination, color uniformity of oxide film, etc.) visually or with the help of magnifying equipment.

Dimensional and geometric accuracy inspection: Use tools such as calipers, micrometers, coordinate measuring machines (CMMs), optical projectors, and other tools for precise measurements.

Mechanical property test: Sampling for tensile test (measurement of tensile strength, yield strength, elongation), hardness test (Brinell Rockwell, Vickers), impact toughness test, etc.

Non-destructive testing (NDT): Penetrant testing (PT), ultrasonic testing (UT), radiographic testing (RT), etc., to detect internal defects (porosity, shrinkage, cracks).

Chemical composition analysis: verify that the material composition meets the standards (usually done by the foundry and re-tested if necessary).

Metallographic analysis: Check whether the microstructure (grain size, phase composition, defects) meets the heat treatment requirements.

Purpose: To prevent damage or secondary contamination/oxidation of treated high-quality surfaces prior to delivery.

Request:

Environment: Clean, dry (low humidity), dust-free, non-corrosive atmosphere warehouse.

Protection:

Avoid friction between castings or in direct contact with other hard materials (use isolation pads, foam, special station appliances).

Clean and dry glove operation to prevent sweat contamination from the hands.

For delicate or vulnerable surfaces, use protective films, protective caps or special packaging.

The packaging should be moisture-proof, shock-proof, and collision-proof (using a sturdy wooden case lined with foam or a custom box).

Handling: Handle it gently and use appropriate lifting/handling tools to avoid violent vibration and shock.