Forging is a mainstream forming process for high-strength mechanical components,as it effectively enhances their structural strength,density,and mechanical properties.However,cracking—including surface micro-cracks,edge cracking,catastrophic tearing,and delayed aging cracks—is a frequent defect during production that directly compromises the quality and reliability of the finished parts.Such defects can be effectively prevented through process optimization,parameter control,raw material treatment,and die optimization.
Optimizing raw material pretreatment reduces the likelihood of cracking at the source.Underlying causes of forging cracks include excessive impurities,coarse grains,residual internal stress,and insufficient plasticity.Strict material screening prior to production is essential to control metallurgical defects such as internal slag inclusions,segregation,and porosity.Processes like annealing and spheroidizing are employed to refine metal grains,enhance plastic deformability,and lower the risk of fracture during forging;additionally,removing surface scale,cracks,and burrs prevents surface defects from propagating or enlarging during the forging and extrusion process.
Precise control of the forging temperature range helps avoid temperature-induced cracking.Excessively high temperatures lead to grain coarsening and material embrittlement,resulting in overheating cracks;conversely,excessively low temperatures reduce plasticity and increase deformation resistance,making the material prone to stress-induced tearing.Specific isothermal forging ranges must be established based on the metal material,with strict control over initial and final forging temperatures.Uniform heating processes ensure consistent temperatures throughout the billet,preventing excessive local temperature gradients that could cause uneven deformation,stress concentration,and cracking.
Optimizing the forging process and deformation parameters is also crucial.Excessive deformation in a single stroke or excessively high forging speeds can cause uneven metal flow and sudden localized stress accumulation,exceeding the material's plastic limit and triggering cracks.For forgings with complex geometries and significant deformation requirements,a multi-pass progressive forging process is employed;by utilizing incremental deformation and gradual shaping,the risks associated with massive single-stage deformation are avoided.Furthermore,forging speeds are carefully controlled to ensure smooth metal flow and minimize instantaneous stress shocks.
Die structures are optimized to eliminate points of stress concentration that could lead to cracking.Issues such as excessively small radii,sharp transitions,poor cavity surface finish,and die wear(causing scoring on the workpiece)can all trigger localized stress concentrations,resulting in edge splitting or surface cracking.Optimization measures include enlarging corner radii,polishing cavity surfaces to a smooth finish,and removing sharp stress-inducing points.Regular maintenance to repair worn or scored areas ensures smooth forming,reduces resistance to metal flow,and minimizes localized stress accumulation.
Lubrication and post-forging aging treatments are refined.Insufficient lubrication during forging leads to excessive friction between the workpiece and the die,impeding surface metal flow and causing tearing cracks.High-temperature-compatible lubricants are selected to form a uniform film,ensuring smooth metal rheology.Additionally,stress-relief aging is performed promptly after forging to release internal residual stresses,thereby preventing delayed cracking during subsequent storage or service.
Through comprehensive measures—including raw material control,precise temperature regulation,process parameter optimization,die upgrades,and stress relief—cracking defects in forgings can be effectively prevented,significantly enhancing the yield rate and structural stability of the finished products.
