Alloy Stee CNC Machining Services

These grades are carbon steel with chromium, molybdenum, nickel or manganese added to raise hardenability and fatigue life. In our shop the common five are 1018, 1045, 4130, 4140 and 4340, plus A36 and tool steel. They machine very differently. 1018 is soft and forgiving. 4140 in the annealed state at 28–32 HRC cuts cleanly and holds a good thread. 4340 is tougher in the same condition and will work-harden if you dwell.

The practical question is not which grade is strongest. It is whether the part needs through-hardening, case hardening or no heat treatment at all. A shaft that will be induction hardened to 55 HRC can be turned and ground from 1045 and cost less than 4340. A landing gear fitting that must survive 1,000 MPa and cyclic load usually justifies the nickel-chrome-moly cost.

We ask three things before quoting: final hardness, section thickness and whether the drawing calls out a specific condition like normalized or Q&T. Get those right and the grade picks itself. Get them wrong and you pay twice, once for the wrong bar and once for the rework.

Carbide grades for steel run at 150–250 m/min surface speed with flood coolant. Push 4340 past 200 m/min and the insert edge breaks down within minutes; drop to 120–150 m/min and tool life climbs sharply. Depth of cut matters too. A 2 mm radial engagement with a 12 mm end mill keeps heat in the chip instead of the part.

Work hardening is the main trap. 4130 and 4340 are prone to it when the tool rubs instead of cuts. If your insert is dull or your feed is too light, the surface hardens to 45 HRC and the next pass destroys the cutter. We keep feed per tooth above 0.05 mm for roughing and never let the tool dwell in a corner.

Thermal growth is the second issue. A 300 mm 4140 shaft can grow 0.03 mm during a long roughing cycle. We rough, let the part cool, then finish. On tight bores we leave 0.15 mm and take it in a single finishing pass after the part reaches room temperature.

Our standard alloy steel tolerance is ±0.005 mm (±0.0002 in) on critical features, measured on a CMM with temperature compensation. That number only holds on features we can reach in one setup or re-datum accurately. A 400 mm bore referenced to a face machined in a different operation will drift. We call that out during DFM instead of after delivery.

Surface finish sits in three bands. As-machined runs Ra 1.6–3.2 μm and suits most structural faces. Ra 0.8–1.6 μm comes from a controlled finishing pass and works for sealing surfaces. Ra 0.2–0.8 μm needs grinding or fine boring, and we quote it only on features where the geometry allows.

Hardened parts change the sequence. If the drawing calls for 50 HRC, we rough machine at 20% oversize, send the part out for heat treatment, then finish by hard turning or grinding. Skip that step and the part moves 0.02–0.05 mm during the quench. That is normal, not a defect.

We run 127 high-precision CNC machines across three plants in Dongguan and Singapore. For this work the relevant ones are 16 simultaneous 5-axis machining centers, 16 mill-turn centers, 12 four-axis mills and 27 three-axis machines. Maximum processing size is 4,000 mm, with travels of 4,000 × 400 × 150 mm on the large platform.

Five-axis setups cut the number of operations on parts with angled faces or deep pockets. A steering knuckle that needs four sides machined can be done in two setups instead of five, and every re-clamp is a chance to lose 0.01 mm. Mill-turn centers handle shaft-type parts up to Ø400 mm with a rotary table.

We machine from bar, plate or near-net forgings depending on volume. One prototype and a 10,000-part run both work here. There is no minimum order quantity. For castings or forgings we ask for the raw part drawing so we can plan stock allowance before quoting.

Every alloy steel job gets a raw material certificate check on arrival. We verify grade and condition against the drawing, because a bar marked 4140 that shows up as 1045 will fail after hardening. In-process checks run at each setup change, and a full final inspection happens before shipment. Reports are available on request.

Heat treatment is a separate supplier we qualify, not something we improvise. We specify the process, the target hardness range and the test coupons in the purchase order. Parts come back with a hardness report and we re-check critical dimensions after the part stabilizes.

Our quality system holds ISO 9001:2015, IATF 16949:2016, ISO 13485:2016 and ISO 27001:2022. The first three cover process control for industrial, automotive and medical work. The fourth covers how we handle your drawings and models. Uploads stay confidential and we sign an NDA on request.