Tungsten Heavy Alloy Deep Hole Drilling: Parameters and Tooling for Dense Materials

A manufacturer of radiation shielding collimators for medical linear accelerators was drilling Ø12 mm × 300 mm (L/D 25:1) bores in WHA (93% W, 5.25% Ni, 1.75% Fe, density 17.6 g/cm³, 32 HRC) using gun drilling. Standard K10 carbide TiAlN-coated gun drills lasted only 8–15 mm per drill (20–38 tool changes per 300 mm bore), with witness marks at each restart. Investigation revealed abrasive wear from tungsten grains (1,000–1,800 HV) being displaced from the binder matrix and dragged along the cutting edge. The solution: PCD-tipped gun drills (5,000–8,000 HV, 10× carbide wear resistance), cutting speed reduced from 25 to 15 m/min (preventing diamond graphitization), and 200 bar oil coolant. Tool life increased to 300–500 mm per PCD drill (30–50× improvement), the full 300 mm bore was completed in a single pass, and the PCD drill cost (€600 vs €120 for carbide) was offset by eliminating tool change downtime and reaming, yielding a net 40% cost reduction per bore.

Tungsten Heavy Alloy Metallurgy ​

WHA Grades and Drilling Characteristics ​

Abrasive Wear Mechanisms in WHA Drilling ​

Drilling Parameters and Tooling ​

Gun Drilling Parameters for WHA ​

BTA Drilling Parameters for Large-Diameter WHA Bores ​

FAQ ​

Why are tungsten heavy alloys so difficult to deep hole drill? ​

Tungsten heavy alloys are among the most difficult materials to deep hole drill because of their unique two-phase composite microstructure. The material consists of hard tungsten grains (1,000–1,800 HV, 20–50 µm diameter) embedded in a softer nickel-iron or nickel-copper binder matrix (200–400 HV). During drilling, the cutting edge must traverse through alternating hard and soft phases — the hard tungsten grains resist cutting and abrade the tool, while the softer binder erodes preferentially, exposing the tungsten grains. This creates a self-sustaining wear cycle: binder erosion exposes tungsten grains, the exposed grains abrade the cutting edge, the abraded tool surface becomes rough, the rough surface increases friction and cutting forces, which accelerates binder erosion further. The abrasive wear rate in WHA is 20–50× higher than in steel, meaning a carbide gun drill that lasts 100 m in steel may last only 2–5 m in WHA. The high density of WHA (17–18.5 g/cm³, more than twice that of steel) also creates challenges: the chips are heavy and dense, requiring higher coolant velocity to evacuate them from the bore; the workpiece weight (a WHA collimator block may weigh 50–200 kg) requires robust workholding; and the high inertia of the material means that cutting vibrations are amplified rather than damped. Additionally, the thermal conductivity of WHA (80–120 W/mK for 90–93% W) is actually higher than steel (45 W/mK), which means that heat conducts away from the cutting zone rapidly — this is beneficial for tool temperature but causes thermal expansion of the workpiece that can affect bore diameter control. The practical implication is that deep hole drilling in WHA requires PCD or PCBN tooling for any production application, cutting speeds must be kept low (8–25 m/min), coolant pressure must be high (150–350 bar) to evacuate the dense chips, and the tool design must account for the higher cutting forces (1.5–2× those in steel) and the abrasive wear mechanism.

What tool material is best for gun drilling tungsten heavy alloys? ​

PCD (polycrystalline diamond) is the best tool material for gun drilling tungsten heavy alloys, offering 10–30× the tool life of carbide under equivalent conditions. The extreme hardness of PCD (5,000–8,000 HV compared to 1,500–1,800 HV for carbide) provides the abrasion resistance needed to withstand the tungsten grain cutting without significant wear. PCD also has high thermal conductivity (500–600 W/mK compared to 80–120 W/mK for carbide), which draws heat away from the cutting edge and reduces the temperature at the tool-chip interface. The limitations of PCD for WHA gun drilling are: edge preparation — PCD requires a specialized grinding process to produce the sharp cutting edge needed for gun drilling. The PCD layer (typically 0.3–0.7 mm thick on a carbide substrate) must be ground to a < 1 µm edge radius, which is more difficult than grinding carbide. Cost — a PCD-tipped gun drill costs €400–1,200 compared to €80–300 for a carbide gun drill, but the 10–30× longer tool life and reduced machine downtime usually provide a net cost benefit. Brittleness — PCD is more brittle than carbide and cannot survive interrupted cuts, vibration, or feed rate spikes. The gun drilling machine must be in good condition and the process must be stable. PCBN (polycrystalline cubic boron nitride) is a secondary choice for WHA drilling, particularly for higher-tungsten grades (95–97%) where the high cutting temperatures (> 600 °C) may cause diamond graphitization. PCBN has lower hardness (3,500–4,500 HV) than PCD but higher thermal stability (1,200 °C vs 700 °C for PCD). PCBN is also 10–30% lower cost than PCD. For carbide tooling (K10 with AlCrN coating), the tool life is so short (5–40 mm of bore per drill) that it is only viable for prototype or very low-volume work. For production applications, PCD gun drills are the standard recommendation, with PCBN as a backup for the highest tungsten content grades.

What coolant type and pressure are optimal for WHA deep hole drilling? ​

The optimal coolant for tungsten heavy alloy deep hole drilling is straight oil (synthetic or mineral) at 150–350 bar pressure, depending on the bore diameter and L/D ratio. Oil coolant is strongly preferred over water-miscible emulsion for WHA because: lubrication — oil provides superior boundary lubrication at the tool-chip interface, which is critical for reducing the abrasive wear from tungsten grains. The oil film between the tool and the tungsten grains reduces the coefficient of friction from approximately 0.4–0.6 (dry or water-miscible) to 0.1–0.2 (oil), reducing cutting forces and heat generation. Cooling — although oil has lower specific heat capacity than water, the high thermal conductivity of PCD tooling compensates, and the oil's lubricity allows lower cutting forces that generate less heat. Chip evacuation — the dense WHA chips (17–18.5 g/cm³) settle rapidly in still fluid. Oil's higher viscosity (10–30 cSt at 40 °C vs 1 cSt for water) provides better chip suspension and transport, reducing the risk of chip settling in the bore. The coolant pressure requirement for WHA deep hole drilling is 150–350 bar, with the higher end for smaller diameters and higher L/D ratios. The high pressure is needed because: the dense chips require higher fluid velocity to maintain suspension; the small annulus between the drill shank and the bore wall creates a significant pressure drop; and the high cutting forces generate more frictional heat that must be removed. Coolant temperature control is also important — the coolant should be maintained at 25–35 °C. Below 20 °C, the oil viscosity becomes too high, reducing flow rate; above 40 °C, the viscosity drops too low, reducing the lubricating film thickness. Coolant filtration for WHA drilling requires a magnetic separator followed by a 10–20 µm cartridge filter. The tungsten particles in the coolant are highly abrasive and will rapidly damage coolant pump seals and guide bushings if not removed.

What surface finish and bore quality can be expected in WHA? ​

The surface finish achievable in gun-drilled tungsten heavy alloys depends strongly on the tool material and cutting parameters. With PCD gun drills at optimal parameters (Vc = 12–20 m/min, f = 0.015–0.035 mm/rev, oil coolant), the achievable surface finish is Ra 0.4–1.4 µm, with Rz 3–10 µm. The surface profile is characterized by uniform feed marks with occasional pits (0.5–2 µm deep) where tungsten grains have been pulled out rather than cleanly cut. These pull-out pits are a characteristic feature of WHA drilling and are difficult to eliminate completely because they result from the fundamental composite structure of the material — the binder erodes preferentially, and individual tungsten grains can be dislodged before they are cut. The frequency and depth of pull-out pits depend on: the tungsten grain size (smaller grains = fewer and shallower pits), the binder content (higher binder = more grain support = fewer pits), and the cutting edge sharpness (sharper edge = cleaner grain cutting = fewer pits). Bore diameter tolerance in WHA gun drilling is typically IT8–IT10, which is 1–2 IT grades wider than in steel because: thermal effects — the high thermal conductivity of WHA causes the workpiece to heat and expand during drilling, and the bore contracts when the workpiece cools, creating a diameter variation of 0.01–0.03 mm between hot and cold conditions; and tool wear — the rapid abrasive wear in WHA causes the effective cutting diameter to decrease during the bore, creating a tapered bore (larger at entry, smaller at exit). The taper can be 0.01–0.05 mm over a 300 mm bore with carbide tools, but is reduced to < 0.01 mm with PCD tools. Bore straightness in WHA gun drilling is typically 0.02–0.08 mm/m, which is comparable to steel at equivalent L/D ratios.

What are the main applications of deep hole drilling in tungsten heavy alloys? ​

The main applications of deep hole drilling in tungsten heavy alloys are in radiation shielding, aerospace, defense, and precision engineering. (1) Medical radiation shielding — the largest application by value. Medical linear accelerators for cancer treatment use WHA collimators (multi-leaf collimators and primary collimators) that require precision bores for radiation beam passage. A typical collimator block (93% W, 50–200 kg) may have 4–80 bores ranging from Ø5–30 mm × 200–400 mm, each positioned with ±0.05 mm accuracy. The bores must be clean, straight, and free of burrs to prevent radiation scattering. (2) Aerospace counterweights — WHA counterweights in helicopter rotor systems, control surfaces, and turbine engines require drilled bores for attachment bolts. These bores must meet aerospace quality standards (AS9100) and are typically Ø5–25 mm × 50–300 mm. (3) Defense kinetic energy penetrators — armor-piercing projectiles (95–97% W) may require a central bore for pyrotechnic initiation or tracer material. The bores are typically Ø3–10 mm × 100–400 mm and must be concentric within 0.05 mm. (4) Vibration damping — WHA components in high-speed machinery and precision instruments may require drilled bores for mounting or tuning. (5) Electrical discharge machining electrodes — WHA electrodes used in EDM may require coolant through-bores. (6) Sporting goods — WHA weights and balance components in golf clubs, tennis rackets, and racing vehicles may require drilled mounting bores. The common thread across all applications is that the bores must be produced without cracking or damaging the WHA material, and the high tool wear rate means that PCD tooling is the only economical choice for production volumes above a few bores per year.

Disclaimer: The tungsten heavy alloy drilling parameters, tooling recommendations, and material data presented in this article are based on published technical literature and industry-reported experience with machining tungsten-based materials. Actual drilling results depend on the specific WHA grade, tungsten grain size and distribution, binder composition, and processing history (sintered vs wrought vs heat-treated). The interaction between PCD tooling and WHA is sensitive to cutting temperature — excessive temperature (> 700 °C) can cause diamond graphitization and rapid tool failure. WHA materials are subject to export controls in some jurisdictions (ITAR, Wassenaar Arrangement) when used in defense applications. No guarantee of specific tool life, bore quality, or process capability is expressed or implied. All data is provided for informational purposes and reflects industry practices as of 2026.