1. Upsetting Presses (The "Upsetter")

An upsetting press (Horizontal Forging Machine) is a specialized mechanical power press designed to provide a two-stage motion: clamping the workpiece and heading (deforming) the material.

A. Kinematic Drive System

Unlike standard vertical presses, an upsetter operates on a synchronized dual-slide system:

• The Main Slide (Heading Slide): Moves horizontally to provide the primary forging blow.
• The Side Slide (Grip Slide): Moves perpendicular to the main slide to lock the bar stock in place.
• Synchronization: These slides are mechanically linked via a single crankshaft. The grip slide must reach "full lock" (clamping position) before the heading tool makes contact with the workpiece to prevent axial slippage.

B. Tonnage Distribution and Force Logic

The machine must balance two distinct forces to maintain part quality:

1. Clamping Force (Fc): The force required to hold the bar.
2. Upsetting Force (Fu): The force required to deform the metal.

Rule of Thumb: To ensure process stability, the machine is engineered so that Fc is approximately 20–30% higher than Fu.

Failure Mode: If Fu > Fc, the dies will "gape" (separate slightly), causing "flash" (excess metal leakage) and dimensional inaccuracy.

C. The Energy Theory (Flywheel Drive)

Most upsetting presses utilize a mechanical Crank-Drive system:

• Energy Storage: Energy is stored in a massive rotating flywheel according to the formula: E = ½ I ω²

• Load Application: Upon engagement of the clutch, kinetic energy is converted into a high-impact load. This high strain rate is ideal for filling complex die cavities before the workpiece cools.

---

2. Extrusion Presses

Extrusion press theory is based on the High-Pressure Vessel principle and Controlled Displacement.

A. Hydraulic Power and Flow Control

Extrusion requires a sustained, long-stroke force, making Hydraulic Systems the industrial standard:

• Constant Velocity: To maintain consistent metallurgical properties and surface finish, the ram must maintain a constant speed .
• Pressure Management: The system must overcome the Breakout Pressure (initial peak force to start flow) and then transition to a lower Running Pressure as the billet length decreases.

B. Pre-Stressed Container Theory

The container must withstand internal radial pressures that exceed the tensile strength of standard tool steel.

• Multi-Layer Construction: Containers use Shrink-fitting theory. An outer "mantle" is heated, slipped over an inner "liner," and cooled.
• Pre-compression: This creates a pre-compressive stress on the liner. During extrusion, internal pressure "unloads" this pre-compression rather than putting the steel into tension, significantly extending tool life and preventing catastrophic failure.

C. The "Stiff-Frame" (Tie-Rod Theory)

To manage forces ranging from 500 to 10,000 tons, the press frame must be exceptionally rigid.

• Tie-Rod Construction: Four massive, pre-stressed tie-rods connect the Platen (die end) to the Main Cylinder (power end).
• Elastic Stretching: The frame must resist stretching. Excessive elastic deformation leads to misalignment, resulting in "eccentric" or lopsided profiles.

---

3. Critical Comparison of presses

Feature	Upsetting Press Theory	Extrusion Press Theory
Drive System	Mechanical (Flywheel/Crank)	Hydraulic (Pumps/Accumulators)
Motion Type	High-speed impact (Cycle-based)	Slow, steady displacement (Stroke-based)
Force Logic	Clamping Force > Heading Force	Ram Pressure > Material Flow Stress
Tooling Stress	Repeated Thermal Shock & Impact	Constant High Pressure & Friction
Orientation	Primarily Horizontal	Horizontal (Standard) or Vertical