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Common knowledge of flanged pipe fittings: how to control the folding and cracking of aluminium flanges?

Jul 13, 2018

Aluminum alloy flange forgings are widely used for medium and high strength parts with certain requirements due to their advantages of small proportion, good thermal conductivity, high electrical conductivity and corrosion resistance. The process features of aluminium alloy forging heating is poor liquidity, low plasticity, good thermal conductivity, narrow forging temperature range, strict beginning, finish forging temperature, heating the performance characteristics of die forging is aluminum alloy does not produce with heterogeneous change, mainly rely on the correct control forging mechanical parameters to improve metal organization, uniform metal flow continuously along the forging shape distribution in order to improve the mechanical properties; The quality characteristics of hot die forging are that aluminum alloy is easy to produce two major quality defects of fold and crack.

Among them, folding can reduce the bearing area of parts, and it is easy to generate stress concentration during service and become a fatigue failure source, which is very harmful. The crack damage is greater, and the crack waste accounts for 5% ~ 10% of the total forging waste.

The reasons for the folding are the large cross-section size of the blank, unreasonable shape of the blank, the forming of local pressing type, the small radius of the circular Angle at the transition point of mold and bore, and the large amount of pressing at one time during operation.

Cracks are mainly caused by the obvious anisotropy of extruded aluminum bars, in which the longitudinal mechanical properties are significantly higher than the transverse mechanical properties (the longitudinal toughness is the largest while the transverse toughness is the smallest). At the beginning of finish forging ranging from three to stress or under the condition of the three-way under the action of compressive stress and maximum shear stress, easy contact between billet grain damage, is not conducive to the development of the slip deformation, deformation ability is poor and oblique crack generation.

At the same time caused by uneven deformation of additional stress and thermal stress produced by the uneven temperature, deformation of large parts and small deformation of interaction, tensile stress cracking occurs beyond the part strength.

Aluminium alloy forging in the actual production of folding and crack defects in quality control, should be prevention first, technology and production management, the combination of specific should do the following several aspects:

(1) the necessary analysis should be made on the technical conditions of the forging equipment, technological equipment and blank, so as to make the forging process in line with the production reality and achieve advanced, reasonable, complete and accurate results.

(2) in the forging die design, should consider forging the forming force and equipment tonnage required, reasonable distribution of blocking or intermediate billet size, choose the right way of packing, increasing the die mould chamber transition radius or draft Angle, the lower mold chamber (including flash bridge) of the surface roughness value.

(3) the aluminum alloy used shall be ensured free from defects such as folding, cracking and coarse crystal rings. For the heating of billets, the amount of charging should be strictly controlled, and the billets should be turned over within half of heating time, so as to minimize the time from discharging to forging.

(4) in the forging operation, should be based on the principles of the operation of the first light after heavy, properly control the deformation degree of blank or hammer force, reasonable use of extruding the anisotropy of raw materials, preheating forging die and operating tools correctly, and reasonable lubrication forging die (especially the upper die die chamber).

(5) in forging production, the production monitor unified command, first article inspection shall be competent technical personnel to cooperate, work instruction of shift production when necessary, at the same time, the first production of the first article, should be as much as possible to arrange in day shift production, to detect the quality of forgings defects, after confirmation no folding and defects such as cracks, but within the prescribed time interval with rhythm, the uniform and balanced production.

(6) forging test, you must do first article inspection, strictly implement the "three inspection system", but should also do process inspection tour, intermediate inspection, inspection and final inspection, prevent systemic defects into the next process.

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