Forging Press: How to Calculate Tonnage for Optimal Results

Calculating tonnage correctly

Forging hammer, screw press and hot forging press are the three main forging equipment in the forging industry.

Although the respective technologies have been developed over many years, they have different capabilities due to their unique performance characteristics.

Forging tonnage calculation

Forging tonnage refers to the maximum force (usually measured in tons) that a forging machine can withstand. This force is sufficient to plastically deform the metals, thus producing the necessary forgings.

According to the definition of the China Forging Association, large forgings are freely forged products produced by hydraulic machines of more than 1,000 tons and free forging hammers of more than 5 tons, as well as forgings produced by hot forging equipment of more than 6,000 tons and forging hammer dies of more than 10 tons.

In practical applications, selecting the appropriate tonnage for forging involves consideration of several factors, including the size, shape and degree of deformation required of the forgings.

For example, the tonnage of a screw press can be calculated using the formula P= p/q= (64~73)F/q, where P is the tonnage of the screw press (KN), p is the deformation force required for die forging (KN), and F is the forging projection area together with the burr (cm ² ).

In addition, theoretical calculation methods and empirical formulas are also used to determine the tonnage of the equipment.

Performance characteristics and selection of forging equipment

1. Forging hammer

1 . 1 Performance characteristics

The forging hammer is a forging equipment used to produce various forgings under medium to large batch production conditions.

It is versatile and can be used for various types of forging.

Due to its simple structure, high productivity, low cost and adaptability to the forging process, it is widely used as forging equipment.

The role of the forging hammer in the modern forging industry depends on the following factors:

• Simple structure and low maintenance cost;
• Easy to operate and flexible;
• The forging hammer can be used for multiple die forging, without the need for pre-forging equipment and with great versatility;
• The forming speed is fast, adaptability to different types of forgings;
• Investment in equipment is low (only 1/4 of the investment in hot forging presses).

The main advantage of the forging hammer is its fast striking speed, which results in a short contact time with the mold and makes it ideal for situations that require high-speed deformation to fill the mold.

This includes forgings with thin ribbed plates, complex shapes and strict weight tolerance requirements.

Due to its fast and flexible operating characteristics, it has strong adaptability and is sometimes called “universal” equipment.

Therefore, it is particularly suitable for multi-type and small batch production.

In terms of cost-benefit, the forging hammer is the most advantageous forming equipment.

1 . 2 How to select forging hammer

The maximum impact energy of the forging hammer is the most critical parameter in determining its work capacity.

When choosing the required hammering impact energy, the following formula can be used as a reference:

E=25（3.5～6.3） _total KF

In the formula:

• E—Attack energy required for forgings (J);
• K — Steel type coefficient (0.9 for low carbon steel; 1 for medium carbon steel and low carbon alloy steel; 1.1 for medium carbon and low alloy steel; 1.25 for structural steel of high alloy);
• _Total F —Total deformation area of ​​the forging plane (including coating and burr) (㎝ ² )

When high productivity is required in batch production, the formula uses the upper limit value of 6.3. In cases where the final forging step can be performed and productivity is not a concern, the lower limit of 3.5 is used.

2. Screw press

two . 1 Performance characteristics

The screw press is suitable for forging, upsetting, precision pressing, correcting, cutting and bending processes.

However, its average eccentric load capacity is significantly lower compared to hot forging press and forging hammer.

As a result, it is not suitable for multi-process heating operations (such as descaling, pre-forging and cutting).

Therefore, when using a screw press for final forging, additional equipment is required to carry out auxiliary processes.

The forging characteristics of the screw press are determined by the performance of the equipment.

As the screw press has the dual working characteristics of hammer forging and hot forging press, it has the following characteristics:

• Have a certain impact during the work process;
• The slider's travel is not fixed; the device is equipped with an ejection device;
• The force received between the slider and the table during forging formation is received by the press structure.

Therefore, screw press forging has the following characteristics:

1. The screw press slider has a slow travel speed and minimal impact, allowing multiple deformations in a single groove. As a result, it can provide ample strain energy for large deformation processes (such as upsetting and extrusion) and can also produce significant strain force for smaller deformation processes (such as precision pressing and stamping).
2. Because the slider stroke is not fixed and has an ejection device, it is suitable for upsetting for burr-free die forging and long-shank forgings. For the extrusion and cutting process, a stroke limit device must be added to the mold.
3. The screw press has limited ability to handle eccentric loads and is generally used for single-slot die forging. The blank is normally produced on other auxiliary equipment. In cases of small eccentric forces, it is possible to have two grooves, as in the process of press bending followed by final forging or upsetting followed by final forging.

The use of a screw press for forging is limited by unfavorable factors, including equipment tonnage, low operating speed and the need for auxiliary equipment for stamping. It is typically used for small and medium-sized batch production of small and medium-sized forgings.

two . 2 Adaptability to other forging dies press

The screw press operates using impact energy and has similar working characteristics to a forging hammer. The pressure slider travel is adjustable and can return to any position before reaching its lowest point. The amount of impact energy and number of blows can be controlled based on the deformation work required for forging.

However, during forging, the deformation resistance of the forging is balanced by the elastic deformation of the bed closure system. The screw press has a similar structure to a hot forging press, which makes it a forging device with a certain overload capacity.

The average eccentric load capacity of screw press is lower compared to that of hot forging press and CNC forging hammer, making it only suitable for single-slot die forging. Additional equipment may be required to complete the auxiliary process when using a screw press for final forging.

The screw press slider has a slower stroke speed and a lower operating frequency, and can only perform single-stroke deformation in a groove. During single impact deformation, the central part of the blank undergoes significant deformation, causing it to flow horizontally and form a large scalloped edge, making it difficult to fill metal in deep grooves and increasing the likelihood of bending compared to forging with hammer. This is particularly pronounced for forgings with complex cross-sectional shapes.

Furthermore, the screw press has poor flexibility and a shorter die life compared to a CNC forging hammer. It is suitable for forging parts with relatively simple shape, low precision requirements and high deformation energy. Impact energy and frequency are generally determined by the operator based on the deformation work required for forging.

However, the screw press has poor control performance compared with a CNC forging hammer, leading to unstable forging quality and difficulties in automation. It is generally used for small to medium batch production of small to medium sized forgings.

two . 3 How to select Screw press

The calculation formula for selecting screw press tonnage is as follows:

1）P= p/q=（64～73）F/q

In the formula:

• P—Screw press tonnage (KN);
• p—Deformation force required for die forging (KN)；
• F—Forged part along with flash projected area (㎝ ²⁾ ；
• (64~73)—The coefficient of complex forgings is 73, and that of simple forgings is 64；
• q—q is a deformation coefficient, which can be divided into stroke and deformation work in forging a screw press:

1. For forgings that require a large deformation stroke, deformation and deformation work for die forging, the value of q should be between 0.9 and 1.1.
2. For forgings that require a smaller deformation stroke and deformation work for die forging, the value of q is 1.3.
3. For forgings that require only a small deformation stroke but require a large deformation force for precision pressing, the value of q is 1.6.

2） P=（17.5～28） _total K·F (KN)

In the formula:

• _Total F —Total projected area of ​​forgings together with flash (㎝ ² )；
• K — Steel type coefficient (0.9 for low carbon steel; 1 for medium carbon steel and low carbon alloy steel; 1.1 for medium carbon and low alloy steel; 1.25 for structural steel of high alloy);
• (17.5~28)—Coefficient 28 is used for deformation difficulties (such as extrusion deformation, flash edge deformation, etc.) and high productivity. Otherwise, the coefficient is taken as 17.5.

The above formula applies to calculating the equipment tonnage required for double to triple forging strokes. If a single forging stroke is required, the calculation must be multiplied by two.

3. Hot forging press

3 . 1 Performance characteristics

The characteristics of forging in hot forging presses are determined by the structural design of the press. It has the following notable features:

The rigidity of the hot forging press structure and crank linkage mechanism is high, resulting in minimal elastic deformation during operation, leading to greater precision in the forged parts produced.

The slider features an additional nose-like structure, improving guide length and improving guide accuracy. With precise guidance and the use of a die combined with a guiding device, hot forging presses are capable of producing forged parts with greater precision. The grooves for each step are made into a practical insert and fixed to the universal formwork using fixing screws, eliminating kickbacks during operation.

The working stroke of the press is fixed, with one step completed in one stroke and an automatic ejection device included.

3 . two Adaptability to other forging equipment:

The hot forging press has a certain stroke and operates at a slow speed, which allows the blank to undergo the predetermined deformation in a single stroke. However, this results in significant deformation in the middle of the billet, causing it to flow easily in the horizontal direction and form a large burr, which prevents metal in deep grooves from being filled effectively.

Additionally, bending of forgings is more likely than hammering, especially for those with complex cross-sectional shapes.

To overcome these challenges, it is necessary to use a molding step to bring the blank closer to the desired forging shape, which requires careful design of the die forging step. On the other hand, forging hammers have a large number of blows per minute and can control the weight of the hammer to meet the deformation requirements of the blank. This makes it easier to operate and forge forgings such as stretching and rolling.

However, the long rolling and rolling processes are difficult to carry out in a hot forging press. For long rod-type blanks with large differences in cross-section, other equipment such as pneumatic hammers, roller forging machines or flat forging machines should be used for stamping and stretching/rolling.

The hot forging press also faces difficulties in removing the oxide scale on the surface of the blank, especially at its ends, which is easily pressed onto the forging surface.

To avoid this, electric heating and other non-oxidation heating methods must be used. The hot forging press adopts a die combined with a guiding device, and the grooves of each step are made into convenient inserts.

This design makes the size of insertion dies much smaller than that of hammers, effectively saving mold material and making the manufacturing, use and repair of insertion dies much more convenient.

3 .3 How to select hot forging press

The tonnage of the hot forging press is determined based on the maximum resistance to deformation at the end of the forging process. Forging pressure (P) can be calculated using the following empirical formula:

P=（64～73）KF

In the formula:

• F —Projection area of ​​forgings, including flash bridges (cm ² )；
• K — Steel type coefficient (0.9 for low carbon steel; 1 for medium carbon steel and low carbon alloy steel; 1.1 for medium carbon and low alloy steel; 1.25 for structural steel of high alloy);

For forgings with a simple shape, large round surface, low thick ribs and thick wall, the complexity coefficient has a small value, and the opposite is true.

Three Die Forging Press Performance Comparison Table

Item	Steam hammer	screw press	hand crank	Die forging hammer
Attack speed (m/s)	4~7	0.6~0.8	0.3~0.7	4~6
Cold attack time (ms)	2~3	30~60	30~60	2~3
Formation time (ms)	5~15	30~150	80~120	5~15
Attack frequency	80~100	6~15	40~80	80~110
Flexibility	Good	Bad	Bad	Good
Investment ratio	1	1~2	4	two
Adaptability	Small batch multi-variety	Single piece in large quantities	Single piece in large quantities	Small batch multi-variety
Complexity of the structure	Simpler	Average	More complicated	Simple
Degree of automation	Bad	Bad	Good	Good
Forging principle	Formation of multiple hammers	An impact forming	Static pressure formation	Formation of multiple hammers
Working precision	Bad	Bad	High	High
Power consumption comparison	15	2~3	3	1

Equivalent ratio of three die forging equipment

When selecting forging equipment with similar capacities, the conversion relationship between the capacities of the forging equipment is as follows: a 25KJ forging hammer (1 ton double-action hammer) is equivalent to a 10,000 hot forging press KN, which in turn is equivalent to a screw press of 3,500 to 4,000 KN.

How to choose the appropriate forging press tonnage based on different types of forgings?

Selecting the appropriate forging tonnage requires initial consideration of the size and deformation of the forgings. For different types of forgings, the required forging equipment, unit fuel consumption, mold consumption and more vary, which means that the choice of tonnage must be based on the specific circumstances of the forgings.

For example, titanium alloys have high resistance to deformation during the forging process, so when choosing forging tonnage equipment, special attention should be paid to the size and deformation of parts.

Additionally, the grade of forging is an important consideration.

Generally speaking, forgings with greater strength and hardness can withstand greater loads and pressures, which means that the grade of the forging must also be taken into consideration when selecting the forging tonnage. For example, grade 3 steel has greater strength and hardness than grade 2 steel, so choosing forging tonnage may require larger equipment to meet your processing needs.

Choosing the correct forging tonnage requires comprehensive consideration of the size and deformation of forgings, material quality, and production costs.

In practice, this can be achieved by calculating the forging pressure tonnage and arranging the position of the mold cavity in conjunction with the working space and equipment structure, enabling the overall design of forging mold components. This guarantees not only the quality of the forged parts, but also effective control over production costs.