Can Thread Forming Taps Be Used on Aluminum?
Yes—aluminum is one of the best materials in the world for thread forming taps. In fact, for high-volume 6061, 7075, ADC12, or wrought aluminum parts, a forming tap (also called roll tap or extrusion tap) usually beats a cutting tap on tool life, thread strength, and chip control. But it only works if the pilot hole, speed, and lube are set correctly
A forming tap has no flutes and no cutting edges. It pushes into a pre-drilled hole and cold-displaces the ductile aluminum into the thread profile. The metal grain flows continuously around the thread root instead of being severed, which work-hardens the surface and preserves material.
Measured results in aluminum alloys:
- Tensile / strip-out strength: formed threads run 10–30% higher than cut threads of the same size
- Fatigue life: 2–3× longer under cyclic load
- Surface finish: Ra ≤ 1.6 µm, burnished, no burrs
- Chips: zero—so blind-hole chip packing disappears
Recommended surface speed for HSS-E forming taps in aluminum: 20–50 m/min (80–120 SFM), roughly 1.5–2× the Vc of a cutting tap.
Worked examples (RPM = Vc×1000 ÷ πD):
- M6 × 1.0 at 30 m/min → ~1,590 RPM, feed 1.0 mm/rev
- M8 × 1.25 at 40 m/min → ~1,590 RPM
- M10 × 1.5 at 50 m/min → ~1,590 RPM
Tool life on a rigid CNC with correct pilot hole:
- Spiral flute cutting tap in 6061: 1,500–2,500 holes
- Forming tap in 6061: 5,000–15,000 holes
- VÖLKEL field case in die-cast ADC12, M6 TiCN forming tap: >50,000 holes on one tool, pilot hole held at 5.55 mm
Pilot Hole Is Everything
Forming needs a larger pilot hole than cutting—because no metal is removed, only displaced.
Thread | Cutting tap drill | Forming tap drill |
|---|---|---|
M6 × 1.0 | 5.0 mm | 5.25–5.55 mm |
M8 × 1.25 | 6.8 mm | 7.0 mm |
M10 × 1.5 | 8.5 mm | 8.9–9.35 mm |
Too small → torque spikes 30–50% above already-high forming torque → tap snaps. Too large → thread % drops, weak engagement.
Real Shop Case
A CNC shop ran M6 × 1.0 blind holes in 6061-T6 electronics housings. Spiral flute tap: ~1,800 holes, 0.8% scrap from chip packing. Switched to HSS-E TiCN forming tap, pilot 5.55 mm, Vc 35 m/min, light EP aluminum fluid:
- Tool life 9,200 holes
- Scrap 0.04%
- Thread pull-out on QA test +23% vs cut thread
- Tap changes per shift: 5 → 1
When Not to Use Forming on Aluminum
- Thin-wall sections where displacement bulges the wall
- Very hard anodized or Si-heavy die-cast with low ductility (check elongation >5%)
- Manual machines without rigid sync (forming needs higher torque and tight control)
- Mixed job-shop runs where pilot-hole discipline isn’t enforced
If the part is ductile aluminum, blind or through, volume 5k+, specify a forming tap with the correct oversized pilot drill and EP lube. Cost per hole typically drops to 1/3–1/5 of a cutting tap, threads are stronger, and chips never jam the hole. Just never drop a forming tap into a cast-iron or hardened steel hole—and never reuse a cutting-tap drill size.
Need an M3–M20 aluminum forming-tap pilot-hole chart? Contact our technical desk for a printable spec sheet matched to 6061 / 7075 / ADC12.