Hollow Radial Forging vs Conventional Open Die Forging: Material Savings, Weight Reduction and Process Selection
Hollow components create one of the most interesting process-selection questions in heavy manufacturing.
Should a supplier forge a solid billet and remove the centre through machining? Should a hollow be produced through open-die punching and mandrel operations? Or can radial forging create a tubular preform closer to finished geometry?
There is no universal answer.
The economics depend on material price, component dimensions, quantity, wall thickness, final tolerances and qualification requirements.
The Hidden Cost of Starting Solid
A simple purchase price comparison can make solid stock look attractive.
But the raw material bill is only the beginning.
If a large finished component contains a substantial central bore, a solid starting billet requires machining time to remove that entire volume. Tool wear, machine capacity, handling and chip management all add cost.
For expensive titanium and nickel alloys, the discarded central material may represent a significant portion of total raw-material purchase value.
How Hollow Radial Forging Works Conceptually
Radial forging can form tubular components using a mandrel where geometry permits.
The external dies progressively reduce the outside diameter while the mandrel supports or defines the internal region.
Academic research confirms that radial forging of tubes can be performed with a mandrel to size or profile the internal diameter and, in some applications, without one when geometry or internal surface requirements permit.
The result can be a hollow preform requiring much less internal machining.
Open Die Hollow Forging
Open die forging also has established methods for manufacturing hollow components.
A billet can be pierced or punched and subsequently worked over a mandrel.
This route offers enormous flexibility and can be applied to very large components outside the range of many radial forging machines.
The real comparison is therefore not “new process versus old process.” It is a geometry-and-economics decision.
Radial vs Open Die Hollow Forging
| Consideration | Radial forging | Open die forging |
| Best geometry | Long axial tubes/shafts | Wide range of large hollows |
| Diameter variation | Highly suitable for stepped profiles | Also possible with manipulation |
| Very large sizes | Machine-envelope limited | Strong advantage |
| Internal mandrel use | Well suited for long tubular forms | Established mandrel forging route |
| Automation | High on suitable equipment | Varies by forge |
| Low-volume flexibility | Good for suitable shapes | Excellent |
| Near-net axial profile | Strong advantage | Geometry dependent |
Material Utilisation Can Be Dramatic
An early technical paper on radial forging reported more than 95% material utilisation for certain precision-finished rod and tube products, demonstrating the process’s potential for near-net manufacture.
That should not be turned into a blanket marketing claim.
Aerospace or heavy industrial components that require substantial machining allowance, NDT surfaces and heat-treatment cleanup will not necessarily reach that figure.
The useful fact is that radial forging has demonstrated very high material efficiency when component geometry and process conditions permit it.
Hollow Design and Structural Efficiency
A hollow shaft can reduce weight because material near the centre contributes less to bending and torsional section properties than material located farther from the axis.
This does not mean designers should simply drill out every shaft.
Local stresses, buckling, interfaces, fatigue, impact and manufacturing requirements may make a solid section preferable.
Hollowing is a design decision;op hollow forging is a manufacturing solution for an already approved design.
