Radial Forging Machine

Overview

A radial forging machine, also called a rotary forging machine, reduces and shapes a round bar or tube by striking it from several sides at once. Four hammers spaced 90 degrees apart around the work axis drive hardened dies inward in short fast strokes, up to about 1000 strokes per minute, while two chuck heads grip the workpiece, rotate it in indexed steps, and feed it through the die aperture. Because the blows are radial and synchronized, the metal is worked symmetrically and flows mainly along the axis, so a thick bar is drawn down into a longer thinner shaft, a stepped axle, or a tube of controlled wall thickness. The process is used both hot for large alloy-steel shafts and cold for precision parts such as gun barrels, axle shafts, and stepped transmission shafts, where the cold work raises strength and leaves a fine surface that needs little machining.

How it works

The bar is held at one or both ends by a Chuck Head and pushed into the Forging Box, the central housing that carries the hammers and dies. Each Forging Hammer drives a Forging Die mounted on a Die Saddle toward the axis. The four dies together form a closing aperture, so when they strike they squeeze the section down by a small amount. Between blows the dies retract a few millimeters, the chuck rotates the bar a fraction of a turn, and the bar feeds forward a step. The next blow then works fresh metal at a new angle, and over many cycles the whole length is reduced to a clean round. The final diameter is set by the Adjusting Wedge under each saddle, which fixes the inner stroke end and so the bore the four dies leave.

Drive and hammers

The short fast stroke is the defining feature of the machine, and two drive schemes produce it. On a hydraulic machine each hammer has its own Stroke Cylinder fed from the Hydraulic Power Unit, and a fast Valve Manifold fires the four cylinders together so the blows land at the same instant. Blow force then comes from oil pressure and is set independent of speed. On a mechanical machine the Eccentric Hammer Drive uses a single Eccentric Shaft whose offset throws drive four Connecting Rod links, one per hammer, so one shaft revolution gives every hammer one stroke. A Drive Motor of 75 to 315 kW turns the shaft through a Helical Gear Pair in a Gearbox Housing, and a Flywheel stores energy between blows because each strike draws heavy peak power for only a few milliseconds. The eccentric runs in Ball Bearing sets sealed by Oil Seal elements, and an Encoder reports shaft angle so the control can hold stroke timing.

Chuck and manipulator

Two chuck heads do the gripping, rotating, and feeding. The infeed head pushes the workpiece in while both heads turn it in step, so the bar stays straight and the dies forge a round free of flats. Each head carries a Gripping Chuck closed by a Chuck Cylinder hard enough to hold the bar against the axial push-back from the blows. A Rotary Drive indexes the Work Spindle a small angle between strokes, and a Axial Feed Unit unit advances the Feed Carriage along the bed in controlled steps. The carriage rides a Linear Guide Rail pair and is driven by a Ball Screw under a Servo Motor, with an Encoder reporting position and a Pressure Sensor confirming clamp force. By varying feed and rotation against the stroke, the CNC can forge plain shafts, tapers, shoulders, and tube walls along one bar.

Lubrication and hydraulics

Forging is hard on dies, so the Die Lubrication and Cooling system sprays a graphite or water-based release agent from four Spray Nozzle units onto the die faces between strokes, metered by the Lubricant Pump from an agitated Lubricant Mix Tank. A Die Coolant Circuit circuit pulls heat from the dies so the H13 faces keep their hardness, and on hot work a Scale Blow-Off clears furnace scale off the bar before the dies press it into the surface. The hydraulics carry the highest loads on the machine: the Hydraulic Pump supplies 250 to 350 bar, a Accumulator supplies the burst of flow each blow needs, and the Oil Cooler with its Coolant Pump holds oil temperature down despite the heat the fast cycle adds.

Control and frame

The Control Cabinet cabinet houses a CNC Control that ties hammer stroke timing to chuck rotation and axial feed, so the bar is forged to a programmed profile along its length. The Operator HMI holds forging recipes and diameter targets per part number, and a Drive Module feeds the rotary and feed servos through a Power Supply, an IGBT Power Module stage, and a Relay bank, all wired by a Wire Bundle to a Connector panel. The whole machine sits on the Machine Bed and Frame, where a Forging Box Mount reacts the recoil from the blows, a Bed Rail pair keeps the chuck heads in line, and Guard Panels shield operators from spray and the rotating bar.

Materials and use

Dies are hot-work tool steel such as H13 hardened to resist the heat and abrasion of repeated impact, and the eccentric shaft and connecting rods are tough alloy steel like 42CrMo4 to carry the blow reaction in fatigue. Workpieces range from carbon and alloy steels such as 42CrMo4 to stainless and tool steels, forged hot at up to about 1100 deg C for large shafts or cold for precision parts. Radial forging suits long axisymmetric parts where the symmetric blows give a uniform grain flow and a near-net diameter, so it is common for stepped axle and transmission shafts, gun and artillery barrels, seamless tube of varying wall, and preforms drawn down before a finishing step. Cold radial forging in particular raises yield strength through work hardening and leaves a fine surface that often needs only light grinding, which is why it is used for high-volume shaft work where downstream machining would otherwise dominate cost.