Micro Gun Drilling Solution for Titanium Orthopedic Bone Screws

Customer Background

The customer is an established orthopedic implant manufacturer producing cannulated bone screws for trauma and spinal surgery applications. Cannulated screws — screws with a hollow center that allows insertion over a guide wire — require extremely precise micro-drilling through the entire length of the screw.

The Challenge

Drilling cannulated holes in titanium bone screws presents some of the most demanding micro-machining challenges in medical device manufacturing:

Extreme aspect ratio. Bone screws require a through-hole of Ø1.5mm with a length of 80–120mm, representing a depth-to-diameter ratio approaching 80:1. At this aspect ratio, tool deflection and chip evacuation become critical issues.

Titanium machinability. Ti-6Al-4V ELI (Extra Low Interstitials) is the standard material for implant-grade bone screws. Its low thermal conductivity causes cutting heat to concentrate at the drill tip, while its work-hardening behavior means any interruption in feed rate can cause immediate tool breakage.

Micro-drill fragility. At Ø1.5mm diameter, the gun drill is extremely delicate. Standard micro-drills were lasting only 5–7 holes before breaking — an unacceptable failure rate for production manufacturing.

Surface integrity. The cannulated hole surface must be free of burrs, cracks, and contamination. Any surface defect could compromise the screw’s fatigue life or serve as a corrosion initiation site.

Straightness tolerance. The guide wire hole must remain within 0.02mm of the screw’s center axis over the full length. Deviation can cause the screw to track incorrectly during surgical insertion.

The Solution

RuidCNC engineered the RD150-C2 Medical Components CNC Gun Drilling Machine specifically for medical cannulation applications:

• High-speed precision spindle — 12,000 rpm spindle with ≤0.002mm runout for micro-drilling stability
• Counter-rotation capability — workpiece and tool rotate in opposite directions, reducing effective runout to near zero
• High-pressure coolant — 150 bar through-spindle coolant ensures chip evacuation from deep micro-holes
• Sub-micron carbide tooling — custom gun drills with sub-micron grain carbide substrate, optimized web thickness, and polished flute surfaces
• In-process monitoring — real-time spindle load monitoring with automatic feed hold on load spikes to prevent tool breakage

Key Machine Specifications

Parameter	Specification
Drilling diameter	Ø0.8 – Ø6 mm
Max drilling depth	300 mm
Spindle speed	0 – 12,000 rpm
Spindle runout	≤0.002 mm
Coolant pressure	Up to 150 bar
Counter-rotation	Standard
Straightness	≤0.01 mm per 100mm depth

Results

Metric	Previous Process	RD150-C2	Improvement
Tool life (holes per drill)	5–7	120+	17× longer
Cycle time per part	4.5 minutes	2.3 minutes	49% faster
Straightness over 100mm	±0.03 mm	±0.01 mm	67% better
Scrap rate	12%	1.5%	87% reduction
Surface finish (Ra)	1.2 µm	0.6 µm	50% better
Monthly output	2,800	5,000	79% increase

Process Validation

The manufacturing process was validated per FDA requirements with:

• IQ/OQ/PQ documentation
• Full dimensional inspection per ASTM F543 (Standard Specification for Metallic Medical Bone Screws)
• Mechanical testing including torsional strength and drive system compatibility
• Surface integrity analysis per ASTM F86

Conclusion

The RD150-C2 demonstrates that specialized machine design, combined with optimized micro-drill geometry and process monitoring, can overcome the extreme challenges of medical-grade titanium cannulation. The solution enabled the customer to more than double production output while dramatically reducing scrap and tooling costs.