Forging is a widely used metalworking process that shapes metal using compressive force. It is essential in producing high-strength components such as flanges, shafts, gears, bars, and rings across industries like aerospace, automotive, oil and gas, and machinery manufacturing.
Despite its benefits—like refined grain structure, enhanced mechanical properties, and reduced porosity—the forging process is not without challenges. Improper control or poor practices during forging can lead to defects that compromise the quality, strength, and performance of the final product.
This article explores the most common problems encountered in the forging process, their causes, how they impact product quality, and preventive measures. Understanding these issues is vital for engineers, quality control teams, and purchasing managers who work with forged metal products.
Company Logo: sakysteel
Description:
Underfilling occurs when the metal does not completely fill the forging die cavity, resulting in missing shapes or incomplete dimensions.
Causes:
Insufficient forging pressure
Low billet temperature
Poor die design
Incorrect billet size
Impact:
Dimensional inaccuracies
Rework or rejection of parts
Poor mechanical performance
Solutions:
Adjust forging parameters
Preheat billet properly
Use optimized die geometry
Ensure correct billet volume
Description:
Laps are overlapping folds on the surface, while cold shuts are surface discontinuities where two metal flows do not bond correctly.
Causes:
Improper die design
Low forging temperature
Poor lubrication or dirty die surfaces
Impact:
Weak zones in forged parts
Susceptibility to cracking under stress
Reduced fatigue life
Solutions:
Maintain proper die design and temperature
Avoid excessive flow resistance
Apply consistent lubrication
Description:
Cracks may form during or after the forging process due to excessive stress, poor material properties, or rapid cooling.
Types:
Hot cracks: Form at high temperatures due to low ductility
Cold cracks: Form during cooling due to high internal stress
Causes:
Overheating
Poor material ductility
Non-uniform deformation
Improper cooling rate
Impact:
Serious structural failures
Reduced toughness
Scrapping of parts
Solutions:
Monitor heating cycles
Choose materials with good forgeability
Use controlled cooling techniques
Modify die design for uniform stress distribution
Description:
Oxidation of the billet surface at high temperatures creates a scale layer, which can become embedded in the metal during forging.
Causes:
Prolonged exposure to high temperature
Improper furnace atmosphere
Impact:
Surface contamination
Tool wear during machining
Reduced surface finish quality
Solutions:
Use protective atmosphere or inert gas furnaces
Reduce exposure time
Remove scale before final passes or machining
Description:
Internal voids or porosity are often invisible but can drastically reduce the mechanical strength of the forged part.
Causes:
Inadequate pressure
Poor-quality ingots or billets
Gas entrapment
Impact:
Lower fatigue strength
Higher risk of failure under pressure
Difficulty in ultrasonic inspection
Solutions:
Use vacuum-degassed or ESR ingots
Apply sufficient compressive force
Conduct NDT inspections like ultrasonic testing
Description:
Dies deteriorate over time, affecting part accuracy. Misaligned dies can lead to asymmetric parts and dimensional errors.
Causes:
High-frequency usage
Improper die alignment during setup
Lack of maintenance
Impact:
Dimensional deviation
Poor sealing surfaces (for flanges)
Increased rejection rates
Solutions:
Schedule regular die maintenance
Use high-grade die steels
Train operators for proper die setup
Description:
Excessive forging temperature can lead to grain growth or even burning of the metal, compromising its strength and ductility.
Causes:
Poor temperature control
Operator inattention
Overlong soaking time in the furnace
Impact:
Grain coarsening
Brittleness in the final part
Cracking and reduced mechanical properties
Solutions:
Monitor temperature using pyrometers
Use precise time-temperature curves
Train personnel on heating cycles
Description:
Superficial defects such as scratches, pitting, or gouges can occur during billet handling, forging, or transportation.
Causes:
Damaged billets
Poor handling practices
Die contamination
Impact:
Reduced corrosion resistance
Rework or rejection
Aesthetic issues
Solutions:
Inspect and clean billets before use
Use protective handling methods
Clean dies and tools regularly
Description:
Improper forging direction can lead to grain flow misalignment, reducing the strength and performance of critical sections.
Causes:
Incorrect die orientation
Uncontrolled metal flow
Poor design of preform
Impact:
Weak zones in the product
Poor fatigue resistance
Premature failure under load
Solutions:
Optimize die and billet design
Use simulation software to predict grain flow
Align forging direction with stress paths
Description:
Residual stresses remain trapped in the forged part due to non-uniform cooling or deformation.
Causes:
Asymmetric forging
Inconsistent cooling
Rapid quenching
Impact:
Warping during machining
Cracking during heat treatment
Dimensional instability
Solutions:
Apply post-forging heat treatment
Use uniform cooling rates
Optimize deformation steps
To minimize forging defects, sakysteel applies strict quality assurance procedures:
Visual and dimensional inspections
Ultrasonic testing (UT) and magnetic particle inspection (MPI)
Hardness and tensile tests after heat treatment
Microscopic grain analysis for structure integrity
Nondestructive testing to detect internal flaws
These steps ensure every forged product meets mechanical and safety standards.
The forging process is essential in modern metal manufacturing, but it comes with its share of challenges. Defects such as underfilling, cracks, scale formation, or grain misalignment can significantly affect the performance, reliability, and service life of the forged component.
By understanding the causes and adopting preventive measures such as optimized die design, proper heating control, and rigorous quality checks, manufacturers can reduce defect rates and improve product consistency.