Deep Hole Drilling for the Lighting Industry: LED Heatsink Liquid Cooling Channels, Stage Lighting Yoke Bores, and Fibre Optic Connector Alignment Bores

A manufacturer of stadium LED lighting (AL6063 heatsink, 200 x 150 x 100 mm, 8 liquid cooling channels of 10 mm x 200 mm deep, cross-drilled and plugged serpentine circuit) used PCD-tipped gun drilling (10 mm, Vc = 250 m/min, f = 0.08 mm/rev, emulsified oil at 40 bar). Pressure tested at 10 bar water (zero leakage). LED junction temperature at 1000 W was 85 C with liquid cooling vs 145 C with passive, enabling 50% higher power output.

Lighting Industry Drilling ​

High-power LED lighting fixtures (100-2000 W total power for stadium, high-bay, and architectural lighting) generate significant heat that must be removed to maintain the LED junction temperature below 85-100 C (the maximum for rated lifetime of 50 000+ hours). Gun-drilled liquid cooling channels in aluminium or copper heatsink blocks provide the thermal performance required for these high-power fixtures. The heatsink block (AL6063 or AL1070 aluminium, or C1100 copper) is gun-drilled with a set of parallel channels (3-30 mm diameter, 100-500 mm length, pitched at 2-3x the channel diameter). The channels are connected into a serpentine circuit by cross-drilling and plugging the channel ends.

The gun drilling parameters for aluminium: PCD-tipped gun drill (the PCD tip provides the best surface finish and longest tool life for aluminium), Vc = 200-300 m/min, feed f = 0.06-0.12 mm/rev, emulsified oil coolant at 30-50 bar. For copper heatsinks: PCD-tipped gun drill, Vc = 80-120 m/min, feed f = 0.03-0.06 mm/rev, low-sulphur oil coolant at 40-60 bar. The surface finish inside the channels should be Ra < 0.8 microns to minimise flow resistance and maximise heat transfer. Stage lighting yoke trunnion bores are gun-drilled in aluminium or steel trunnions. The trunnion bore (10-30 mm diameter, 50-150 mm length) must be straight within 0.05 mm over its length and must have a surface finish of Ra < 0.8 microns for the bearing fit.

Gun Drilling Parameters for LED Heatsink Materials ​

The table below compares the drilling parameters for common heatsink materials.

Thermal Performance Comparison: Liquid vs Passive Cooling ​

The table below compares the thermal performance of liquid-cooled and passive-cooled LED fixtures.

FAQ ​

Why is a serpentine channel circuit used instead of straight-through channels? ​

The serpentine circuit forces the coolant to travel back and forth across the full width of the heatsink, ensuring that all LED modules mounted on the heatsink surface receive the same coolant temperature. If straight-through parallel channels were used, the coolant would enter the first channel at 20 C and exit at 40 C (after absorbing heat from the LEDs), while the last channel would receive coolant that had already been heated by the upstream channels. The serpentine circuit provides a more uniform temperature distribution across the heatsink surface, reducing the temperature difference between the hottest and coolest LEDs to less than 2 C.

How are the channel ends plugged to form the serpentine circuit? ​

The channel ends are plugged by pressing a brass or aluminium plug (coated with anaerobic sealant) into the open end of the channel, followed by a TIG welding pass to seal the plug permanently. The plug is pressed to a depth of 5-10 mm from the heatsink face, providing a mechanical lock before welding. The weld is ground flush with the heatsink surface and inspected by dye penetrant testing to verify the seal. The cross-drilled connecting channels between the parallel channels are plugged in the same manner at the heatsink sides.

What pump and coolant system is required for a liquid-cooled LED fixture? ​

A liquid-cooled LED fixture requires a closed-loop coolant system with a pump (typically a magnetically coupled centrifugal pump with a 50 000 h MTBF), a reservoir/expansion tank, and a radiator or heat exchanger. The coolant is typically a 30% glycol/70% deionised water mixture with corrosion inhibitors, circulated at 5-15 L/min at 1-3 bar pressure drop across the heatsink. The coolant temperature rise across the heatsink is typically 10-20 C at full power. The pump power consumption is 15-50 W, representing 1-5% of the fixture's total power consumption.

What is the fibre optic ferrule alignment bore drilling requirement? ​

Fibre optic connector ferrules (the cylindrical tips that hold the fibre end) require a precision micro-bore for the fibre alignment. The ferrule bore diameter is 0.125-0.126 mm (for 125 micron cladding diameter fibre), drilled to a depth of 5-10 mm in the ferrule material (zirconia ceramic, stainless steel, or nickel-silver). The bore must be concentric with the ferrule outer diameter within 0.001 mm TIR to ensure that the fibre is centred in the connector. The bore is gun-drilled using a PCD-tipped micro gun drill at Vc = 10-20 m/min, f = 0.0005-0.001 mm/rev, with the ferrule held in a precision collet on a CNC micro-drilling machine.

How does the channel surface finish affect heat transfer performance? ​

The surface finish of the cooling channel directly affects the convective heat transfer coefficient. A smooth channel surface (Ra < 0.8 microns) provides a 5-10% improvement in the heat transfer coefficient compared to a rough channel surface (Ra > 3.2 microns) at the same flow rate. The improvement is due to the reduced boundary layer thickness at the smooth surface, which allows the coolant to flow more efficiently and absorb heat more effectively. The gun drilling process with a PCD-tipped drill naturally produces a smooth surface (Ra 0.4-0.8 microns in aluminium), eliminating the need for a separate honing or polishing operation for the cooling channels.

Data are based on published research and industry experience as of 2026.