What Are The Technical Key Points For Hot Straightening Of Titanium Plates?

Titanium and titanium alloys  has poor plasticity and large springback at room temperature, and are easy to deform during rolling and heat treatment. It impairs precision and assembly. Hot straightening achieves accurate correction by leveraging the improved plasticity of materials in a specific temperature range through precise temperature control, pressurization and heat preservation.

(1) Raw Material and Pre-treatment Requirements
It is necessary to verify the grade, composition and specification of titanium plates to ensure no cracks, inclusions, scratches and qualified dimensions. The surface shall be ground to remove the gas absorption layer, and oil stains, oxide scale and impurities shall be cleaned to prevent indentation, uneven heating and oxidation.

(2) Temperature Control Requirements
Temperature shall be controlled according to plate grades to prevent grain coarsening caused by excessively high temperature and excessive springback due to overly low temperature. Adopt gradient heating to ensure uniform temperature inside and outside the plates. Real-time temperature monitoring shall be conducted with thermocouples or infrared thermal imagers, with the temperature deviation ≤±10℃, to avoid local overheating or insufficient heating.

(3) Pressure Control Requirements
Excessively high pressure is likely to damage the mold and cause secondary deformation, while insufficient pressure fails to eliminate springback. Pressure shall be adjusted according to the thickness, grade, deformation and straightening method of titanium plates; reduce pressure for thin plates, and heavy object pressurization can be adopted for large-specification plates. The flatness error of pressure plates shall be ≤3mm/m and the plates shall fully cover the surface of titanium plates to ensure uniform stress. Pressurization shall be stable and slow to avoid impact; for roll straightening, control the speed and reduction, conduct step-by-step straightening and reduce residual stress.

(4) Heat Preservation and Cooling Requirements
The heat preservation time shall be determined according to plate thickness, temperature and material; the heat preservation time for thick plates at low temperature shall be extended to ensure consistent internal and external temperature difference and stable structure.

Cooling is a key step in hot straightening, and rapid cooling is strictly prohibited. Cool the plates ,then cool them in air before discharging; slow cooling can be adopted for high-precision plates to relieve stress. After roll straightening, water-absorbent cotton combined with cooling medium can be used for cooling and shaping to reduce temperature difference and springback.

(5) Quality Inspection Requirements
Dimensional accuracy: Detect the flatness at room temperature, measure the springback of bent parts, and ensure qualified dimensions and good mold fitting.

Surface quality: No oxide scale indentation, scratches or cracks, and the thickness of oxide scale and gas absorption layer shall not exceed 1/2 of the negative deviation of plate thickness.

Performance and composition: Qualified mechanical properties, hydrogen content ≤150ppm, normal metallographic structure and no grain coarsening.

Residual stress: Nondestructive testing shall confirm that the stress is basically eliminated to prevent subsequent deformation.

(1) Mold Hot Press Straightening Technology
The mold shall be high temperature resistant, high rigidity, with polished surface and accurate fitting. Process: Heat and insulate the titanium plate, quickly put it into the mold, apply and maintain pressure, and cool it with the furnace. For thin-walled multi-rib parts, hot bulging clamps combined with molds can be used for straightening, with the fitting gap ≤0.2mm.

(2) Roll Hot Straightening Technology
Continuous automatic straightening is realized through hot straightening rolling and thermal insulation auxiliary pressing, which solves the problems of springback and large temperature difference at both ends. The key is the matching of roll system, temperature and rolling parameters; adopt a multi-roll structure with high temperature resistant roll surfaces and uniform temperature control. Process: Feed the titanium plate into the machine, fit it with the heating roll, conduct continuous reciprocating rolling, and the auxiliary pressing mechanism shall cool and shape the plate in a timely manner to reduce temperature difference and springback. Parameters shall be adjusted according to plate thickness and deformation to avoid edge waves and center waves.

(3) Vacuum Creep Hot Straightening Technology
Deformation and residual stress are eliminated by creep under vacuum through high temperature, long-time heat preservation and slow pressurization.Process: Place the titanium plate on a ceramic platform with high flatness, cover it with a thin plate, evacuate the air, and conduct heat preservation and pressurization for creep straightening.

(4) Stack Hot Straightening Technology for Large-specification Titanium Plates
Single straightening has limited effect on large-specification titanium plates, and stack hot straightening can be adopted to achieve precise straightening through multi-layer stacking, heavy object pressurization and gradient heating & heat preservation, thus reducing costs.

Ruihang Group mainly produces the titanium raw materials for your precision manufacturing. For more details,please reach us to the email: Sam.Rui@bjrh-titanium.com