Deep Hole Drilling for Railway Axle Center Bores

Customer Background

The customer is a railway component manufacturer producing forged axles for freight wagons and locomotives. Each axle — a long, heavy forged bar up to 2.6 meters and several hundred kilograms — carries a central axial bore drilled from both ends. The bore provides access for ultrasonic inspection of the forging and reduces unsprung weight.

The Challenge

Axle center bores are deep, straight, and drilled in a workpiece that is difficult to handle:

Long, heavy axles. An axle laid on a machine table can weigh hundreds of kilograms and run the length of the table. Positioning it once and keeping it stable through the whole drilling program is essential — every re-clamp adds risk.

Bilateral bores must meet in the middle. The bore is drilled from each end and must meet within tolerance at the axle’s center. Any drift means the two halves misalign, leaving a step that blocks inspection access and creates a stress concentration.

Forged material. Axles are forged from medium-carbon alloy steel. Hard spots, scale, and grain-structure variations punish tooling and demand torque and rigidity — a flexible machine lets the bore wander.

Inspection-clean bore. The bore surface must be clean and concentric for ultrasonic inspection probes to run reliably down its length. Tears, steps, or accumulated cutting marks compromise the inspection the bore exists to enable.

Deep holes in one axis. Axle bores run Ø25–45mm to roughly half the axle length from each end. Straightness and chip evacuation over that depth require gun drilling or BTA technique, not twist drilling.

The Solution

RuidCNC supplied the Horizontal Deep Hole Drilling Machine (RD2515-16H) configured for axle center bore production:

• 18-ton worktable capacity, 2700 × 1500mm surface — long, heavy axles held in a single setup
• Ø3–50mm drilling to 1,600mm — bores to half the axle length from each end in continuous passes
• 157 N·m spindle torque with 15/18.5 kW — sustained cutting through forged axle steel
• 6,000 rpm spindle — speeds matched to the drilling range and material
• 3–10 MPa high-pressure coolant at 110 L/min — reliable chip evacuation from deep bores
• Syntec 21MA-E CNC — programmable bilateral bore cycle with consistent depth control

Key Machine Specifications

Parameter	Specification
Drilling diameter range	Ø3 – Ø50 mm
Max drilling depth	1,600 mm
Worktable	2700 × 1500 mm
Max load capacity	18 tons
Spindle max speed	6,000 rpm
Spindle motor power	15 / 18.5 kW
Spindle max output torque	157 N·m
Coolant pressure / flow	3 – 10 MPa / 110 L/min

Results

Metric	Conventional Boring Process	RD2515-16H	Improvement
Axle handling / setups	2–3	1	Eliminated
Bore straightness	0.3 mm/m	0.09 mm/m	70% better
Bilateral bore alignment	±0.25 mm	±0.08 mm	68% better
Cycle time per axle (two bores)	2.4 hours	1.3 hours	46% reduction
Bore surface finish (Ra)	3.2 µm	1.6 µm	50% better
Scrap from bore deviation	3.5%	0.6%	83% reduction

Process Validation

The process was validated through:

• Bore straightness and concentricity measurement along each drilled half
• Bilateral bore alignment check at the axle center
• Ultrasonic inspection run-through to verify probe access
• Dimensional and surface inspection against the axle drawing

Conclusion

The RD2515-16H turns railway axle center boring into a single-clamping operation. With an 18-ton table that holds long axles in one setup, Ø3–50mm drilling to 1,600mm, and 157 N·m of torque for forged steel, the customer improved bore straightness by 70%, cut cycle time per axle by 46%, and made the bilateral bores meet reliably at the axle center. For railway manufacturers who need inspection-clean axial bores in heavy forged axles, the machine delivers them in one pass from each end.

Figures are representative of typical applications.