Most of the aviation forgings are die forgings. According to the size and size of the die forgings can be divided into: rough forgings, ordinary die forgings, semi-precision forgings and precision forgings.
According to the standard of China Aviation Industry Ministry HBO-6-67 (dimensional tolerance of die forgings and structural elements of die forgings), die forgings are divided into five grades:
Grade Accuracy - For dimensional tolerances between cold-finished surfaces of die forgings.
Secondary Accuracy - For dimensional tolerances between hot-finished surfaces of die forgings.
Tertiary accuracy - dimensional tolerances for refining die forgings.
Four-level accuracy - for dimensional tolerances of common die forgings.
Five-level accuracy - dimensional tolerances for machining between forged parts, including machining allowances.
According to the above-mentioned precision grade of die forgings, and the structural elements of die forgings and the utilization ratio of forgings, the definitions of various die forgings are as follows:
Rough forgings - Die forgings with large margins and large tolerances. Such die forgings have a thick web, a large radius of convex and concave fillet, a die forging slope of about 7° or more, a dimensional accuracy that meets the requirements of HBO-6-67 five-level precision, all surfaces need to be machined, and the weight is about finished. About 4 times the size of the part or more.
Ordinary die forgings -- Molded parts with general allowance and general tolerances. The forgings have thicker webs, larger radius of the concave and concave fillets, 3-7° forging and forging, and 60-80% of the surface to be machined. The dimensional accuracy of the non-machined surface meets the four-level accuracy of HBO6-67. The requirements and weight are about 3 times that of the finished parts.
Semi-precision forgings - die forgings with small residuals and tolerances. Its convex and concave fillet radius is small, the die forging slope is 1°-5°, and the processed surface accounts for 10-60%. The dimensional accuracy of the non-machined surface satisfies the three-level precision requirement of HBO-6-67, and the weight is about the finished part. 1.7 times or so.
Precision Forgings - Die forgings that are machined with advanced machining and precision molds that require only machining of parts or holes. Its convex and concave fillet radius is small, the die forging slope is 0°?3°, the surface roughness is not more than Ra2.5, the dimensional accuracy is not lower than the three-level precision requirement of HBO-6-67, and the weight is about 1 of the finished part. , about 2 times.
Obviously, precision satin will outperform other forgings in terms of quality and performance of the above four types of forgings, but the production of precision forgings is not economically justified in all cases, but also by production conditions, equipment, batches and technology. Limitations of factors, etc. At present, precision forgings are only used in small structural parts of certain aluminum alloys and titanium alloys, such as precision forgings and other precision forgings called "seamless forgings" produced by combined die and isothermal die forging. .
Determining the type of die forging according to the precision of the forging requires the designer and the producer to make a decision after comprehensively weighing the use requirements of the part, the possibility of production technology, and economics.