What Problems Will Be Encountered in the Forging Process

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

1. Incomplete Filling of Die (Underfilling)

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

2. Laps and Cold Shuts

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

3. Cracks (Hot and Cold Cracks)

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

4. Scale Formation

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

5. Internal Porosity and Cavities

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

6. Die Wear and Misalignment

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

7. Overheating or Burning of Material

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

8. Surface Cracks and Defects

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

9. Grain Flow Misalignment

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

10. Residual Stresses

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

Quality Control Measures

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.

Conclusion

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.