English Views: 0 Author: Site Editor Publish Time: 2026-08-28 Origin: Site
Open die forging is a metal forming process used to produce custom forgings by pressing heated ingots or billets between flat or simple-shaped dies. During forging, the work piece is repeatedly pressed, moved, and turned to achieve the required shape and size.
Compared with casting or machining from solid stock, open die forging can improve the internal grain structure, reduce pores and voids, and improve strength, toughness, and fatigue resistance. It is widely used for large shafts, turbine rotors, marine crankshafts, pressure vessel components, and other heavy-duty parts.
This guide explains the main open die forging steps, key process controls, materials, inspection methods, and common OEM applications.
Open die forging produces custom metal forgings by pressing a heated billet between dies without fully enclosing the material. The workpiece is gradually shaped through operations such as upsetting, drawing, bending, and punching.
This process is suitable for large, heavy, and non-standard components where flexibility and high mechanical performance are required.
The open die forging process typically includes eight stages:
1.Material Preparation
2.Billet Heating
3.Upsetting
4.Drawing Out
5.Forming
6.Heat Treatment
7.Rough Machining
8.Final Inspection
Each step affects the final dimensions, internal structure, and performance of the forging.
Material is selected based on the required strength, toughness, wear resistance, heat treatment, and service conditions.
The raw material is then cut into billets. The billet size must provide enough material for the following upsetting, drawing, forming, and machining processes.
The billet is heated to the proper forging temperature according to the material grade. Uniform heating helps maintain stable metal flow during forging.
Overheating or uneven heating may affect the surface quality, grain structure, and forming stability of the forging.
The heated billet is compressed along its axis, reducing its height and increasing its cross-sectional area.
This step prepares the billet for subsequent drawing and forming operations. It also helps improve the cast structure and reduce internal defects.
The upset billet is repeatedly compressed between flat dies and moved along its length. This increases the length and reduces the cross-sectional area.
Drawing out is one of the most common open die forging operations. By controlling the reduction and feed rate, the billet can be gradually forged into the required shaft or bar shape.
Depending on the final shape of the forging, different operations such as upsetting, drawing out, bending, punching, and cutting are combined to gradually form the billet.
During forming, the operator continuously adjusts the position and angle of the billet and repeats the forging operations until the required shape and dimensions are achieved. Extra material is left for subsequent machining.
After forming, heat treatment may be used to achieve the required mechanical properties and improve the internal structure of the forging.
Common heat treatment processes include solution annealing, normalizing, annealing, quenching and tempering, and stress relieving. The appropriate process depends on the material grade and its intended application.f
Open die forgings are usually rough machined after heat treatment to remove surface scale and achieve the required basic shape and dimensions.
Typical operations include turning, milling, drilling, and boring, depending on the forging design. Machining allowances are left for final machining when required.
Final inspection verifies that the forging meets the drawing, material specification, and quality requirements.
Typical checks include dimensional inspection, hardness testing, mechanical testing, and ultrasonic testing (UT). Mechanical tests such as tensile strength, yield strength, and elongation are performed when required. UT is used to check for internal defects such as cracks, inclusions, and voids.
Open die forging controls the final shape through repeated local pressing and turning of the billet. Upsetting reduces the height and increases the cross-section, while drawing out increases the length and reduces the cross-section. During forming, operations such as bending, punching, and cutting are used to achieve the required shape and dimensions.
Key process parameters include:
Forging temperature
Reduction per pass
Total forging ratio
Feed rate
Finishing temperature
Cooling method
Machining allowance
These parameters are adjusted according to the forging size, material grade, and final application.
Forging ratio shows how much the metal is reduced and elongated during forging. A sufficient forging ratio helps break up coarse cast structures, reduce segregation, close internal pores and voids, and refine the grain structure. It can improve the density, strength, ductility, and toughness of the forging.
Full-section deformation means that the entire cross-section of the billet receives enough deformation, rather than only the surface. This helps improve the internal structure and reduce internal defects, especially in large shafts, rotors, and other thick-section forgings.
Alloy steel and stainless steel are the main materials used for ETERNAL open die forgings.
Material | Typical Grades |
Alloy Steel | 4140, 4340, 42CrMo4, 34CrNiMo6, 4130, 4145, 4330, 4340M, H13 |
Stainless Steel | 304, 304L, 316, 316L, 321, 347, 347H, 410, 420, 17-4 PH |
Alloy steel is commonly selected for its high strength, toughness, and fatigue resistance, while stainless steel is widely used where corrosion resistance and durability are required.
The material grade is selected based on the required mechanical properties, service conditions, heat treatment, and application of the forging.
Forgings and castings are both widely used in industrial applications, but their manufacturing processes result in significant differences in mechanical properties and service reliability.
Factor | Open die Forging | Casting |
Grain structure | Dense, with directional grain flow along the main load direction | Coarse dendritic structure |
Internal defects | Pores and voids are compressed, resulting in fewer internal defects | More likely to have pores, shrinkage, and segregation |
Mechanical properties | Higher strength, ductility, and toughness | Generally lower overall mechanical performance |
Fatigue resistance | High | Lower |
Impact resistance | Excellent | Generally lower |
Internal quality | Full-section deformation helps produce a more uniform internal structure | The center may contain shrinkage or segregation |
Applications | Large, heavy-duty, and critical load-bearing components | Complex-shaped, thin-wall, small, or non-load-bearing parts |
For rotating parts, heavy-duty components, and critical parts used under severe service conditions, open die forgings are often the better choice when fatigue strength, material density, impact resistance, and long-term reliability are key requirements.
Open die forgings are inspected at different stages to ensure they meet the required quality and performance standards.
Common inspection methods include:
Dimensional Inspection – checks dimensions, tolerances, and geometry.
Hardness Testing – verifies the required hardness.
Mechanical Testing – checks tensile strength, yield strength, elongation, and impact toughness.
Ultrasonic Testing (UT) – detects internal defects such as cracks, inclusions, pores, and voids.
Magnetic Particle Testing (MT) – detects surface and near-surface defects in magnetic materials.
Dye Penetrant Testing (PT) – detects surface cracks and other open defects.
Chemical Composition Analysis – confirms that the material meets the required grade.
UT,MT and PT are used to detect surface and internal defects such as cracks, inclusions, pores, and voids without damaging the forging.
Mechanical testing verifies key properties such as tensile strength, yield strength, elongation, and impact toughness to ensure the forging meets the required specifications.
The inspection plan should follow the customer drawing, material specification, and applicable standards.
Open die forgings are widely used in industries where high strength and reliability are required:
Aerospace:Turbine discs, landing gear, load-bearing beams, engine casings
Power Generation:Turbine rotors, hydro turbine shafts, nuclear pressure vessel shells, tube sheets
Oil & Gas and Petrochemical:Pressure vessel shells, flanges, tube sheets, compressor shafts
Marine:Marine crankshafts, rudder stocks, propeller shafts
Heavy Machinery:Large gears, drive shafts, mill rolls, mining equipment shafts
General Equipment:Large flanges, valve bodies, hydraulic cylinder barrels, wheel forgings
Open die forgings have a dense structure, refined grains, and excellent mechanical properties. They are well suited for high-temperature, high-pressure, heavy-load, cyclic-load, and corrosive environments. These forgings provide goodfatigue resistance, impact resistance, and long-term reliability, making them an important choice for critical components in heavy industrial equipment.
Open die forging is a flexible manufacturing process for producing large, heavy, and critical components. Proper control of forging temperature, forging ratio, deformation, heat treatment, machining, and inspection helps achieve the required strength and internal quality.
With experience in alloy steel and stainless steel forgings, ETERNAL provides open die forgings with forging, heat treatment, machining, and inspection capabilities to meet different customer requirements and applications.
