Glass Bottle Mold Gun Drilling: Precision Cooling Hole Machining

Customer Background

The customer is a mold manufacturer specializing in glass container molds for the beverage and cosmetics industries. Each bottle mold — typically a split-mold set with a body half and a bottom plate — requires a network of cooling holes drilled around the cavity to regulate glass temperature during blow molding. Accurate cooling directly determines glass distribution, cycle time, and mold service life.

The Challenge

Glass bottle mold cooling holes combine several demanding requirements that conventional gun drilling equipment struggles to meet:

Curved cavity contours. The cooling holes must follow the curved profile of the bottle cavity at a consistent standoff distance. In large molds this produces drilled holes at multiple angles relative to the parting line, requiring precise indexing rather than simple straight-line positioning.

Thin-wall risk. If a cooling hole breaks through to the cavity wall, the mold is scrapped and hot glass can leak into the cooling channel during production. Uniform wall thickness between the hole and the cavity surface is the single most important quality criterion.

Small diameter, deep aspect ratio. Cooling holes range from Ø3mm to Ø10mm with drilled lengths around 350mm — depth-to-diameter ratios above 35:1. Chip evacuation and tool stability become critical at these aspect ratios.

Hardened mold materials. Glass bottle molds are commonly made from cast iron, H13, or 420 stainless steel, often heat-treated to 30–40 HRC. Drilling through the hardened skin without work-hardening the hole wall requires rigid machine construction and controlled cutting parameters.

Multi-step process. Optimal cooling holes are produced in sequence — twist drilling a pilot hole, then gun drilling to final depth, then milling and tapping any threaded ports. Previously this required multiple machine transfers between dedicated drill, mill, and tap machines.

The Solution

RuidCNC supplied a Gun Drilling on Glass Bottle Mold machine — a specialized dual-spindle configuration engineered for this application:

• Dual independent spindles — two gun drilling spindles for simultaneous or sequential drilling, effectively halving per-mold drilling time
• Dual automatic tool changers — two ATCs carry gun drills, end mills, and taps, enabling pilot drilling, gun drilling, milling, and tapping in a single setup
• Rotary worktable — the mold rotates between operations so both the cavity side and the parting side can be machined without re-clamping
• Stainless steel machine bed — designed for easy chip evacuation and corrosion resistance in mold shop environments
• Programmable indexing — precise angular positioning lets each cooling hole follow the cavity contour at a controlled standoff

Key Machine Specifications

Parameter	Specification
Gun drilling spindles	2 (independent)
Auto tool changers	2 (gun drills, mills, taps)
Drilling diameter	Ø2 – Ø12 mm
Max drilling length	~350 mm
Machining processes	Pilot drill, gun drill, mill, tap
Worktable	Rotating, multi-position

Results

Metric	Previous Process	Specialized Machine	Improvement
Setups per mold half	3 (drill, mill, tap)	1	67% fewer
Cycle time per mold set	6.5 hours	3.6 hours	45% reduction
Wall-thickness deviation	±0.30 mm	±0.12 mm	60% better
Hole surface finish (Ra)	1.8 µm	0.8 µm	56% better
Scrap from thin-wall breakouts	6%	0.8%	87% reduction
Tool life (holes per gun drill)	120	210	75% improvement

Process Validation

The drilling process was validated through:

• Cut-section inspection of sample molds to confirm wall-thickness uniformity
• Dimensional inspection of hole position and depth against the cavity model
• Surface roughness measurement of drilled holes on a representative mold half
• Pilot production run of 10 mold sets before full ramp-up

Conclusion

The specialized dual-spindle glass bottle mold gun drilling machine addresses the specific demands of curved-contour cooling hole production. By combining pilot drilling, gun drilling, milling, and tapping in a single setup with rotating worktable indexing, the customer eliminated machine transfers, improved wall-thickness control, and reduced cooling hole cycle time by nearly half.

Figures are representative of typical applications.