⚙ STS · VDI 3209 Blatt 1 (2024)

BTA Drilling Process

Single Tube System (STS) — coolant flows outside the tube, chips exit through the center. Round tube = maximum torsional rigidity. Feed rates 5–10× higher than gundrilling. Ideal for medium to large diameters and high-volume production.

6–2000mmDiameterOptimal 20–250mm

Up to 200:1L/DDeep hole capability

5–10×Feed vs GundrillHighest productivity

15–100 barCoolant50–500+ L/min flow

PRINCIPLE

How BTA Drilling Works

💡 Key difference vs gundrilling: Coolant is injected through the pressure head (BOZA) into the annular gap outside the drill tube. Chips exit through the center of the tube. The round tube cross-section provides maximum torsional rigidity — no V-groove weakness. The drill head employs a multi-edge design (2–3 step configuration) with carbide guide pads.

Component	Function
Pressure head (BOZA)	Seals against workpiece face, injects coolant at 15–100 bar
Drill tube	Transmits torque, round section for maximum rigidity
Drill head (Heller design)	Single or staggered multi-edge, chip-splitting geometry
Guide pads	Main at 178°, secondary at 276°, burnish hole wall

TOOLING

Head Configurations

Type	Diameter	Best For
Brazed carbide	8–65 mm	Low volume, regrindable, proven geometry
Spade drill type	10–114 mm	Replaceable blade, economical, good chip splitting
Indexable single insert	16–28 mm	No regrinding, quick change, consistent geometry
Indexable multi-insert	25 mm+	Staggered tooth, highest performance, chip splitting

💡 Geometry: Rake angle 6–10°, clearance 6–10°, guide pad angle 40–60° (optimal 45–55°). Guide pads: cemented carbide standard, PCD-coated for friction reduction. Chip breaker width and height must be matched to feed rate for optimal C-shape chip formation.

CUTTING DATA

Cutting Parameters

Material	Vc (m/min)	Feed D=20mm	Feed D=50mm	Feed D=100mm	Pressure
Low-carbon steel	80–120	0.08–0.18	0.20–0.40	0.30–0.60	15–40 bar
Alloy steel (annealed)	50–80	0.06–0.15	0.15–0.35	0.25–0.50	20–60 bar
Alloy steel (hardened)	30–50	0.05–0.12	0.12–0.28	0.20–0.40	30–80 bar
Stainless steel	30–70	0.05–0.15	0.12–0.35	0.20–0.50	20–80 bar
Aluminum	80–160	0.15–0.30	0.30–0.60	0.50–0.90	15–40 bar
Titanium	15–30	0.03–0.08	0.08–0.18	0.12–0.28	60–100 bar
Cast iron	60–90	0.10–0.25	0.25–0.50	0.40–0.75	15–40 bar
Copper alloys	60–120	0.12–0.28	0.25–0.55	0.40–0.80	15–40 bar

⚠️ Chip shape is critical: Ideal = tight C-shape or figure-6. Long helical = feed too low. Bird's nest = coolant insufficient. Needle chips = material too hard for chip breaker. Feed rate has a greater impact on chip breaking than cutting speed. Start at lower feed, increase while monitoring chip morphology.

💡 Engage gradually (2025 machine practice): start the cut at a moderate ~200 RPM and ~500 mm/min, and only ramp speed/feed up after coolant is fully established and the head is seated in the pilot — abrupt engagement is the classic cause of head deflection and a spiral start in the first few diameters.

PROS & CONS

Strengths & Limitations

✅ Advantages

Feed rate 5–10× higher than gundrilling
Round drill tube = maximum torsional rigidity
Suitable for large diameters (20–200+ mm)
Internal chip evacuation protects bore surface
Staggered tooth designs enable chip splitting
Deep holes up to 200:1 L/D achievable

⚠ Limitations

Requires dedicated machine with pressure head
Workpiece face must be flat for seal
Higher machine investment ($200k–$800k+)
Longer setup time (pressure head alignment)
BTA drill heads cost more than gundrills
Coolant filtration to 20μm recommended

APPLICATIONS

Where BTA Is Used

✈ AerospaceLanding gear cylinders, engine shafts, airframe structures. High-strength alloys, Ra ≤0.8μm as-drilled

🚗 AutomotiveEngine blocks, transmission shafts, suspension tubes, hydraulic cylinders. High-volume, large diameters

📝 Oil & GasDrill collars, valves, manifolds, pump bodies. Deep holes in tough alloys at 2–8m depth

🏭 Power GenerationTurbine housings, wind turbine shafts, heat exchanger tubes. Large diameters, extreme depth

🗡 Mold & DieCooling channels, ejector pin holes. Medium diameters, high positioning accuracy

⚖ DefenseCannons, ballistic tubes, naval components. Large diameters, high straightness requirements

CASE STUDIES

Real-World Performance

⚙ Turbine Housing

Ø38mm × 2080mm, SC450 steel. Vc 64 m/min, feed 0.11 mm/rev

5× cycle time reduction — one pass vs 3 spade drills (Tungaloy Success Report)

🔧 Hydraulic Cylinder

Ø34.9mm blind hole, 1045 steel. Allied BT-A drill

Feed +59%, tool life +20%, cost -15% per hole vs competitor (Allied Machine)

✈ Landing Gear Steel

Ø60mm, AISI 4140+QT, Vc 60–120 m/min, feed 0.150–0.300 mm/rev

White etching layer control via thermomechanical optimization. MBN non-destructive testing validated (Strodick et al., 2024)

🏭 Oil & Gas Drill Collar

Stainless steel, 70:1 L/D, internal features at 2–8m depth

BTA drilling + pull boring. 400kg metal removed (Sandvik / Nuclear AMRC)

TROUBLESHOOTING

Common Issues

Problem	Likely Cause	Solution
Poor chip breaking	Feed too low; chip breaker geometry inadequate	Increase feed; check chip breaker width/height
Chip jamming / blockage	Coolant pressure or flow insufficient; wrong chip shape	Check pump pressure and filter; increase flow; adjust feed
Poor surface finish	Worn guide pads; incorrect clearance angle; vibration	Replace guide pads; check alignment; reduce Vc
Chatter / vibration marks	Insufficient rigidity; worn support pads; speed too high	Check steady rest alignment; reduce speed; check tube straightness
Hole deviation / drift	Bushing worn or misaligned; uneven guide pad wear	Check bushing clearance <0.02mm; inspect pads for asymmetric wear
Overheating / burn marks	Coolant flow blocked; Vc too high; feed too low	Check coolant passages; reduce Vc; increase feed
Excessive tool wear	Speed too high; coolant insufficient; wrong carbide grade	Reduce Vc; verify coolant flow; consult manufacturer for grade selection

QUICK PICK

BTA vs Other Methods

Criteria	BTA	Gundrilling	Ejector
Diameter	6–2000mm	0.5–50mm	18–250mm
Productivity	5–10×	1×	3–5×
Best cost/hole	High volume	Low volume	Medium volume
Machine investment	$$$	$$	$ (retrofit)

💡 When to choose BTA: Best for diameters >30mm, L/D up to 200:1, and production volumes >500–1000 pieces/month. Machine investment $200k–$800k+. For smaller diameters or batches, consider gundrilling. For existing machine retrofits, consider ejector drilling.

RESEARCH

Recent Developments (2024)

💡 Tilting pads research (Chen et al., Journal of Manufacturing Processes, 2024): A novel BTA connector with piezoelectric-actuated tilting pads enables real-time pad angle adjustment to counteract radial cutting forces. Experimental results showed radial force reduction of 3.2%–47.5% and roundness error improvement of 28%–50% vs conventional fixed-pad designs. Currently research phase — points toward future adaptive BTA tooling.

SAFETY

Equipment & Safety

⚠️ Pressure head safety: The BOZA seals at 15–100 bar. Ensure workpiece face is flat and seal is intact before pressurizing. A seal failure can eject coolant at lethal velocity. Use protective shielding.

💡 Requirements: Spindle power ~11 hp/inch bore (3.2 kW/25mm). Coolant filtration to 50μm min, 20μm recommended. Flow 50–500+ L/min depending on diameter. Workpiece face must be flat and square to spindle axis. AI-integrated BTA systems (Hartmetall, 2025) report 20–30% cost reduction in automotive/aerospace applications.

BTA Drilling Process

How BTA Drilling Works

Technical Data

Head Configurations

Cutting Parameters

Strengths & Limitations

✅ Advantages

⚠ Limitations

Where BTA Is Used

Real-World Performance

Common Issues

BTA vs Other Methods

Recent Developments (2024)

Equipment & Safety

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