Application and Development Trend of Multi-Station Forging Forming Technology

A single-station press makes one blow and one shape. A multi-station machine carries the workpiece through a series of dies inside the same cycle: upsetting, preform, blocking, and finishing. The transfer mechanism moves the part station to station, so the metal is never reheated between steps and never leaves the tool set. For a stepped shaft or a long shaft forging, that sequence is what holds concentricity between diameters.

The reason shops move to this layout is not speed alone. Each intermediate shape controls how the material flows into the next. A preform die that is slightly under-filled will push too much metal into the finisher and overload the corner radii. Get the preform right and the finishing die only has to calibrate, which keeps die wear low and dimensional scatter tight.

For cold and warm forming, the billet is usually sheared or sawn bar. For hot forming, induction coils sit between stations to hold the temperature band. That temperature band matters more than most people expect. A 40 °C drop across the transfer can change flow stress enough to shift the fill line on the next die.

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  Upsetting stationGathers volume for the largest diameter before any shaft is formed.
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  Preform stationDistributes metal; this is where short shots and laps are prevented.
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  Finishing stationCalibrates the profile and sets the final tolerance band.
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  Piercing or trimmingRemoves flash or punches a bore in the same cycle when the design allows.

A conventional hydraulic press follows a fixed stroke and speed curve. A servo-driven press lets you program the ram velocity at each point of the stroke. Slow the ram as the die contacts the billet, then accelerate through the bulk deformation, then hold at the bottom. That profile reduces impact load on the die and improves fill in thin ribs.

The practical result is that near-net shapes with thin webs and tall ribs become feasible in one machine. On a fixed-curve press, those features tend to tear or short-fill. On a servo press, the same feature can be formed with a slower contact phase and a short dwell. Die life typically improves because the peak load spike is gone.

Servo control also makes the transfer easier to synchronize. The ram position and the transfer gripper position are both known at any moment, so the part can be released and gripped at a programmed point rather than a mechanical cam point. That is what allows shorter transfer distances and less temperature loss on hot parts.

None of this removes the need for a good die design. Servo control gives you a wider window. It does not fix a preform that is volumetrically wrong.

The clearest pull is from automotive and EV drivetrain parts: motor shafts, output shafts, and stepped transmission shafts. These parts used to be turned from bar and then splined. Forging them near-net shortens the chip volume and puts the grain flow along the torque path. That is a fatigue argument, not just a cost argument.

A second group is hydraulic and pneumatic rod stock. Long shafts with a flange or a step benefit because the forging holds the step concentric to the rod diameter. Downstream turning becomes a light cleanup pass instead of a full profile cut.

The newer direction is integration. Instead of forging a shaft and then welding or pressing on a flange, the die sequence forms the flange in the same cycle. Fewer joints means fewer inspection points and less chance of a hidden defect at the joint. It also means the blank arriving at the CNC has fewer setups.

Tooling is following the same path. Die inserts are now made as separate modules so a worn finishing insert can be swapped without scrapping the whole block. That lowers the cost of a geometry change and makes the process more viable for mid-volume programs.

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  EV motor shaftsNear-net forming reduces turning stock on long, slender profiles.
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  Hydraulic rodsStep and flange formed concentric to the rod diameter.
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  Integrated flangesRemoves a weld or press joint from the finished part.
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  Modular die insertsSingle insert change instead of full die replacement.

A forged blank is not a finished part. It arrives with draft, flash line, and a scale or decarb layer on hot-formed surfaces. The first machining operation usually removes 0.3–0.8 mm from formed diameters to get under that layer. If the forging is near-net, that cleanup pass is all you need on the formed diameters.

The setup you should plan for is a two-op sequence: hold on a formed diameter for the first side, then flip and hold on a machined diameter for the second. Forging gives you a reliable holding feature that a rough casting often does not.

Concentricity between a forged step and a machined bore is where the process earns its keep. If the forging holds the step within 0.2 mm of true position, the CNC only has to correct the rest. If the forging drifts, you are cutting the whole tolerance band out of the machined feature, and cycle time climbs.

At GreatLight we machine forged and cast blanks on 3-axis, 4-axis, and simultaneous 5-axis centers, with 16 five-axis machines and a 4,000 mm maximum processing size. Formed blanks in 4140, 4340, and 1045 are common here, along with stainless 17-4PH and 316L. Tolerances run to ±0.005 mm on machined features when the drawing calls for it.

One practical note on inspection. Forged surfaces can hide laps or seams that only show after the cleanup cut. We check incoming blanks, monitor in process, and inspect before shipment, and we will flag a suspect lot rather than run it through. Reports are available on request.