Cast Iron Machining

DEK provides cast iron machining for gray, ductile and malleable iron, from your castings or our continuous-cast bar, to ±0.005 mm on finished features. No MOQ, engineer-reviewed quotes within 6 hours.

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±0.005mm
Finished Features
5
Iron Grades
6 hrs
Engineer-Reviewed

CNC milling a gray cast iron machine tool base surface

ISO 9001:2015 Certified AS9100D and ISO 13485 certified

Cast Iron Parts Machining: Castings or Bar

Most cast iron parts machining at DEK starts with customer-supplied castings: your foundry ships rough castings to Shenzhen, we fixture off the casting datums, finish-machine, inspect and ship. We machine the casting; we do not pour it.

For prototypes and low volumes, we machine continuous-cast gray or ductile iron bar (Class 40 and 65-45-12) in rounds to about 300 mm, with no chilled skin. Still choosing between a casting and a billet? See cast iron vs steel or our full metal machining range.

20+ years of precision machining since 2002
100+ CNC machines set up for dry cast iron
CMM checks on bore positions and flatness
Prototypes in 3–5 days from bar, no MOQ

Cnc machined cast iron bracket on white background

Cast Iron Grades We Machine

Gray, ductile and malleable grades, rated against AISI 1212 free-machining steel (100%). Ratings apply to the base metal, not the casting skin.

Gray iron Class 30
207 MPa min, 180–220 HB
A48 Class 30 / EN-GJL-200 / GG-20 / FC200. Machinability ~80–100%: the fast-cutting choice for damped bases and housings.
Gray iron Class 40
276 MPa min, 210–260 HB
A48 Class 40 / EN-GJL-300 / GG-30 / FC300. Machinability ~70–80%, common bar stock for stronger gray iron parts.
Ductile iron 65-45-12
448 MPa (yield 310)
A536 65-45-12 / EN-GJS-450-10 / GGG-40 / FCD450. 156–217 HB, ~70–80% machinability; stocked as bar for shock-loaded parts.
Ductile iron 80-55-06
552 MPa (yield 379)
A536 80-55-06 / EN-GJS-500-7 / GGG-50 / FCD500. 187–255 HB, ~55–65% machinability, for gears and higher loads.
Malleable iron 32510
345 MPa (yield 224)
A47 32510 / EN-GJMB-350-10 / GTS-35 / FCMB340. 110–156 HB, ~90–100% machinability, used in pipe fittings and agricultural hardware.
Ductile iron
6–18% elongation
Treated with 0.03–0.06% magnesium so graphite forms spheres; gray iron, with graphite flakes, has almost no elongation.

CNC boring a ductile iron pump body bore

±0.005mm
On request, from bar stock
H7
Bored bearing seats
1000 mm
Large part envelope

CNC Machining Cast Iron: Capabilities

Castings and bar are milled, bored, turned and ground on 3-, 4- and 5-axis equipment, from one part to 10,000+, with tolerances set per feature.

1

Milling Faces & Pockets

CNC milling on 3-, 4- and 5-axis machines for mounting faces, bolt patterns, gasket surfaces and pockets, ±0.025 mm standard from bar.
2

Boring to H7

CNC boring and jig boring for bearing and cylinder bores to H7, typically ±0.01 mm at 50–100 mm, Ra 0.8–1.6 µm.
3

Surface Grinding

Surface grinding for machine bases, ways and sealing faces: flatness 0.005–0.01 mm over 300 mm, Ra 0.4–0.8 µm.
4

Large Part Machining

Large part machining to about 1000 mm for bases, frames and gearbox housings, with sea freight for heavy bases.

What Makes Machining Cast Iron Different

Graphite, chilled skin and low stiffness drive our approach to gray iron machining and ductile iron machining.

1

Graphite Lubricity & Dust

Graphite lubricates the cut and breaks chips into short segments or powder, so gray iron machines faster than steel of the same hardness, but its abrasive dust attacks ways and spindle bearings.
2

Dry Machining by Default

Gray iron runs dry: coolant plus graphite dust becomes an abrasive slurry. Ductile iron makes a hotter, continuous chip, so deep bores and threading in 80-55-06 may get mist coolant.
3

Cutting Under the Skin

The chilled as-cast layer reaches 350–450 HB over a 200 HB core. The first cut must go under it in one pass, typically 1.5–3 mm, so castings need 3–5 mm stock per face.
4

Datums & Thin Walls

If castings vary by 1 mm, the fixture locates on a machined datum after the first operation. With a 100–120 GPa modulus, thin-walled housings are clamped lightly on machined pads.

When Cast Iron Is (and Isn't) the Right Choice

Cast iron wins on damping, complex cavities and volume pricing; a machined alloy or carbon steel billet wins on weldability, strength and very short runs.

Criteria	This MaterialCast iron	Alloy steel	Carbon steel
Choose it for	Housings with cavities	Strength, welds	Short runs, welds
Vibration damping	10–20× steel (gray)	–	–
Tensile strength	207–552 MPa	Above ~700 MPa	–
Thin walls	4 mm and up	Under 4 mm	Under 4 mm
Best quantity	Volume pricing	1–20 pcs (4140)	1–20 pcs (1045)

Typical Cast Iron Parts We Machine

Gray iron for damping and stable wear surfaces, ductile iron for shock and bending, malleable iron for fittings and farm hardware.

Heat Treatment and Finishing for Cast Iron

CNC machining + finish: hardening, coatings and corrosion protection applied to the cast iron parts we machine.

Finishing Options

Quench and temper
Austempering
Powder coating
Zinc plating

Need another finish? See all surface finish options

Cast Iron Machining FAQ

Common questions from engineers sourcing gray and ductile iron parts.

Can you cast the part as well as machine it?

No. DEK machines cast iron; we do not operate a foundry. Ship rough castings from your own foundry to us for finish machining, or we can machine prototypes and small parts from the continuous-cast gray and ductile iron bar we stock.

Is cast iron machined dry or with coolant?

Gray iron is machined dry. Graphite lubricates the cut and produces powdery chips that would form an abrasive slurry with flood coolant. Ductile iron sometimes gets mist coolant on deep bores or threading because its chip is more continuous and hotter.

What tolerances are realistic on CNC machining cast iron parts?

±0.025 mm standard and ±0.005 mm on request from bar stock. On customer castings, ±0.01–0.025 mm is typical because the fixture must first establish a machined datum. H7 bores and flatness of 0.005–0.01 mm over 300 mm are routine.