Forging Press

Chapter One – What is a Forging Press?

A forging press is a process that uses a vertical ram to apply gradual controlled pressure to a die holding a workpiece. The process is similar to drop forging but uses slow pressure instead of a series of blows. The slow movement of the ram penetrates deeper into the workpiece so that the workpiece undergoes uniform plastic deformation.

Press forging uses an open or closed die. In open die forging, the die does not completely enclose the work piece. In the closed die method, also known as impression die forging, the die completely surrounds the workpiece.

A forging press applies force using hydraulic or mechanical force. Mechanical is produced by a flywheel that stores energy, which is used to move a ram attached to a crank mechanism. It can apply 12,000 tons of pressure.

A hydraulic forging press, unlike the mechanical flywheel type, creates force through the use of a high pressure fluid. Large hydraulic presses can create 75,000 tons of force.

The types of forging presses vary according to their size and the amount of force they use for plastic deformation of the workpiece.

Chapter Two – Types of Forging Presses

There are several methods for creating force using a forging press. The four main methods are mechanical, hydraulic, servo, and pneumatic. Each method is used depending on the type of final product and the required speed of the operation. The names of each of the different types describes how they create force.

The types of forging presses can be further divided by their frame design, which can be straight sided or C frame. Straight side presses have two sides, while C frames have one open side.

The parts of hydraulic and mechanical presses vary though they all perform the same function. Pneumatic presses are similar to hydraulic presses but apply force using air pressure instead of a fluid. Servo forging presses produce high torque using a low rpm motor. The basic difference between a hydraulic press and mechanical one is the flywheel on a mechanical press.

Parts of a Mechanical Forging Press

• Flywheel: The flywheel supplies the power to the forging press and is driven by an engine or motor.
• Board: The board converts the rotary motion of the flywheel into vertical motion.
• Ram: The ram is the connection between the board and upper half of the die.
• Die: The die has two halves with one half connected to the ram with the bottom half setting on the ram.
• Anvil: The anvil holds the bottom half of the die.

Parts of a Hydraulic Forging Press

• Safety Door: Safety door is a correction gate.
• Limit switch: The limit switch limits the amount of movement past a certain point.
• Manual control Valve: The manual control valve allows for control of the operation.
• Relief valve: The relief valve controls hydraulic pressure.
• Pressure gauge: The pressure gauge gives a reading of the pressure.
• Hydraulic cylinder: The hydraulic cylinder applies unidirectional stroke force.
• Oil tank: The oil tank stores the hydraulic fluid.
• Pressing Plate: The pressing plate applies pressure to the workpiece.
• Bailing Compartment: The bailing compartment is where the workpiece is placed to be shaped.

Types of Forging Presses

Hydraulic:

Hydraulic presses create their force through hydraulic pressure from a fluid using Pascal’s Law. A small amount of force is applied to the fluid, which moves a larger amount of fluid to create the force that moves the ram to shape the workpiece. They operate slower than other forging presses and have longer contact with the workpiece.

Mechanical:

Mechanical presses are powered by a flywheel that stores energy from a motor or engine. The released energy from the flywheel forces the ram down onto the workpiece.

Screw:

A screw press, like a hydraulic press, works slowly. A motor turns a screw that pushes the ram down onto the workpiece with a constant pressure with a long stroke. Screw presses can produce up to 31,000 tons of force.

Servo:

A servo press uses a servo motor to directly drive the crankshaft. The rotational motion of the servo motor is changed into linear motion by a belt or pair of gears and ball screws. The motion of the ram is like that of a hydraulic press but has less tonnage force.

Pneumatic:

The force of a pneumatic press comes from compressed air or a gas, which is forced into a cylinder connected to the ram. When the cylinder is filled, the pressure from it forces the downward movement of the ram. The ram releases when the air or gas is released through an escape valve.

Chapter Three – Advantages of a Forging Press

The process of a forging press is quicker and less expensive than other methods. It produces a grain flow that makes the final piece stronger. The diagram below compares the grain flow for casting, machining, and forging. In casting, there is no grain flow, while the grain flow with machining remains straight. With forging, the grain flow follows the contour of the piece.

The texture of the piece is continuous creating improved strength for the final piece.

Advantages of the Forging Press Process

Strength to Weight Ratio:

During the forging process, the grain structure of the piece becomes compressed, which creates reduced stress on the corners and fillets increasing the strength of the piece.

Reduced Defects:

Forging reduces metallurgical defects such as porosity and alloy segregation, which reduces the time for machining the completed piece and a positive response to heat treatment.

Post Forging Treatments:

With the absence of voids and porosity, pieces can be machined after forging without a loss to dimensional accuracy or quality. Tolerances are within 0.01 to 0.02 inches.

Cost Savings:

The saving factors for forging include raw material usage, reduced machining time, and reclamation of die material.

Die Life Span:

The number of cycles for a die varies depending on types of materials being shaped, the strength of the material, the need for close tolerances, sharp corners, and intricate designs.

Higher Productivity:

Forging presses have a wide range of tonnage from several hundred to several thousand with working strokes per minute as high as 40 or 50, which is 40 to 50 parts per minute. Parts are completed in a single squeeze, which can be slowed by complex and intricate designs. The forging press process can be used for mass production of nuts, bolts, rivets, screws, break levers, bearing races, valves, and many other parts.

Produces Complex Designs:

Dies in press forging have less draft, which makes them able to produce complex and complicated shapes with excellent dimensional accuracy. Forging can create deep protrusions, up to six times the thickness of the material. Draft angles are made less or eliminated by designing.

Materials:

Some ferrous metals can be forged including stainless steel. Non-ferrous metals are highly suited for press forging.

Process Control:

The speed, travel distance, and pressure of a press forging die is automatically controlled for accuracy and efficiency.

CNC Automation:

The forging press process has the same options as any other manufacturing method and can use CNC programming to enter designs, which can include blank feeding and forged piece removal.

Plastic Deformation:

Plastic deformation goes deep into the workpiece creating a uniform deformation throughout the metal.

Operators:

As with any form of manufacturing and production, safety is an initial concern. The positive side of press forging is that it does not require any form of special training for the operator except concerns for safety.

Mechanical Properties:

Due to the uninterrupted grain structure of forged parts, they are tougher and stronger as well as defect free. Press forging improves the elasticity of completed pieces making them more ductile. Parts produced from forging are anisotropic and, due to the grain structure, have different properties in traverse and axial directions.

Consistency:

Each forged part has exactly the same structure from the first to the last. Parts are made by a controlled and monitored production process, which creates uniformity of composition and structure as well as minimal variations in machinability and the elimination of transfer distortion.

Chapter Four – Forging Press Metals

Most metals can be press forged though some metals are more adaptable to the process. The range of metals includes carbon steel, stainless steel, tool steel, aluminum, titanium, brass, and copper. High temperature metals containing cobalt, nickel, and molybdenum can also be press forged. Since every metal has its individual strength, endurance, and weight, the type of metal chosen for a process depends on the needs of the person who will use the completed piece.

Bar medium is used for its grain structure, mechanical properties, shape, dimensions, quality of its surface, and the ability to be mass produced.

Metals Used in a Forging Press

Steel:

Steel needs to be heated to 1200o C or 2200o F to be able to press forged. The heating process makes steel more ductile and malleable for shaping under pressure. A billet of steel can be permanently formed without cracking because of its plasticity.

Aluminum:

Aluminum is ideal for forging because it is lightweight, corrosion resistant, and durable. Forgings of aluminum are used in applications requiring performance and the ability to endure excessive stress. Aluminum has high thermal conductivity, design flexibility, and fracture toughness. It can be forged using open or closed dies and does not require preheating before being forged.

Titanium:

Titanium has an excellent weight to strength and strength to density ratios and corrosion resistance. Prior to press forging, titanium is heat treated to improve its natural toughness and strength.

Stainless Steel:

As with several other metals, stainless steel is corrosion resistant, has excellent strength, and can be forged into multiple shapes. Of the many grades of stainless steel, 304(L) and 316(L) are used for press forging. Stainless steel requires greater pressure due to its strength and is forged at temperatures of 930o C to 1260o C.

Brass:

After being cut to lengths, brass is heated to 815o C and is forged using a closed or open die. Brass can be shaped into any type of form in sizes from a few ounces to several tons. Forged brass is stronger and durable.

Copper:

Copper bars are heated prior to the forging process. After heating, the bars are pressed into the desired shape. Forged copper has excellent electrical and thermal conductivity. Copper forgings are divided by high conductivity and non-electrical, which is an engineering grade.

Magnesium:

Magnesium has a low density with strength and stiffness that is greater than steel or aluminum but costs more and is difficult to forge. The different magnesium alloys that are best for forging are AZ31B, AZ61A, AZ80A, ZK60A, M1A, AND HM21A. The problem with pure magnesium is its tendency to ignite, which is why it is used in combination with other metals.

Chapter Five – Disadvantages of a Forging Press

The press forging process has many qualities that has made it an excellent means for producing high volumes of parts at low cost. Regardless of its wide use, there are drawbacks, limitations, and disadvantages to the process.

Disadvantages of Press Forging

Cost:

Cost is the major factor regarding press forging. The equipment for the process is very large and has to be durable to be able to create the necessary force. Tools and dies for the process have to be specially made using a select number of metals.

Complex Parts:

Highly complex parts and designs cannot be produced using press forging. Though parts with exterior complex designs can be manufactured using the process, parts that have internal cavities and intricacies cannot be forged.

Types of Parts:

Only parts that can be formed by pressing two dies together can be produced. Delicate features, overhangs, or special add ons cannot be forged.

Dies:

Forging press dies are very expensive and difficult to make for complicated parts. A special type of steel is used to make the dies, which has to be heat treated, rough machined, and have special finishing.

Amount of Force:

Tons of pressure is necessary to form a part in a forging press, which requires very large and expensive equipment.

Heated Metals:

If a metal has to be heated before being press forged, it will require after processing finishing.

Size:

Only parts of a certain size can be produced by press forging, which eliminates any large designs.

Metals:

Press forging is restricted by the types of metals that can be forged. Cast iron, chromium, and tungsten cannot be press forged because they are too brittle.

Defects:

Though press forging eliminates shrinkage and porousness, there are still defects that can occur in the final product, such as laps, piping, and die failure.

Tolerances:

Tolerances in a forging press cannot be forged down to a millimeter.

Residual Stress:

Residual stress takes place in metals that have to be heated before being pressed. If the parts are not cooled properly, residual stress occurs.

Scale Pits:

Scale pit happens when the surface to be forged has not been properly cleaned and is common when forging is done in an open environment.

Flakes:

Flakes happen when heated pressed forged metals are cooling. They are internal cracks that reduce the strength of the product.

Time Consuming:

Press forging slowly applies pressure to the workpiece. The die has to remain in contact for an extended period of time. The length of this part of the process slows down production.

Chapter Six – Parts Produced by a Forging Press

Forging presses are an essential part of the manufacturing processes of several industries, which include automotive, aerospace, agricultural equipment, oilfield parts, tools and hardware, and military ordnance.

Automotive:

Press forged parts in automobiles are found at points of shock and stress. There can be over 200 press forged parts in a car or truck. Some of them can be seen in the diagram below.

Aerospace:

Ferrous and nonferrous forgings are used in helicopters, piston-engine planes, commercial jets, and supersonic military aircraft. Aircraft is designed using press forged parts and can contain over 400 different forged parts. Some can be seen in the diagram below.

Tractors and Earthmovers:

Engine and transmission parts, gears, sprockets, levers, shafts, spindles, ball joints, wheel hubs, rollers, yokes, axle beams, bearing holders, and links are produced using forged parts for farm tractors and earthmovers.

Tanks:

Tanks have over five hundred forged parts.

Oil Platform Valves and Fittings:

Forging press parts are an essential part of the construction of oil platforms due to their lack of porosity and ability to withstand high pressure conditions.

Chapter Seven – Forging Press Safety Requirements

The Occupational Safety and Health Administration (OSHA) has developed practices and standards that manufacturers must follow regarding the safe use of a forging press.

The regulations for the operation of a forging press are contained in OSHA standard 29 CFR Part 1910.

Required Inspections:

• Clutch
• Brake
• Linkages
• Counterbalances
• Air lines
• Worn or damaged parts

Important Safety Considerations:

1. Electrical: Presses must have a disconnect switch, motor starter, and a transformer for reducing voltage
2. Covers: Shafts, crankshafts, pulleys, sprockets, rolls, flywheels, gears, and couplings must be covered.
3. Side Barriers: Side barriers include light curtains to prevent standing near the point of operation.
4. Guards: If light curtains are not being used between the operator and point of operation then guards should be installed.
5. Danger Signs: Warning signs should be mounted on the device and must be clearly visible.
6. Hand Tools: Hand tools should be used when feeding or retrieving pieces from the equipment.
7. Mirrors: Mirrors should be mounted on the sides and back of the machine.
8. Two Hand Controls: Two hand controls are necessary for single stroke devices.
9. Pullback or Pullout Devices: Pullbacks, attached to the operator’s hands, pull the operator’s hands away from the machine when it begins its stroke.
10. Restraints: Restraints operate on the same principle as pullbacks and are adjusted so the operator can never reach the point of operation.
11. Gates: Gates can be types A or types B. A gates are used in full revolution presses, while B gates are used in partial revolution presses. A gates must be closed before press operation begins and must remain closed. B gates protect the operator on the down stroke.

Conclusion

• The forging press process uses a vertical ram to apply gradual controlled pressure to a die holding a workpiece.
• There are several methods for creating force for a forging press, which include mechanical, hydraulic, servo, and pneumatic.
• The process of a forging press is quicker and less expensive than other production methods.
• Regardless of the wide use of press forging, there are drawbacks, limitations, and disadvantages to the process.
• Forging presses are an essential part of the manufacturing processes of several industries, which include automotive, aerospace, agricultural equipment, oilfield parts, tools and hardware, and military ordnance.