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Copper/iron/Stainless Steel Machining
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How to mill in different materials
Milling steel
The machinability of steel differs depending on alloying elements, heat treatment and manufacturing process (forged, cast, etc.).
In soft, low-carbon steels, built-up edge and burr formation on the workpiece are the main issues. In harder steels, the positioning of the cutter becomes more important for avoiding edge chipping.
When milling steel, always follow our recommendations, such as the positioning of the cutter to avoid a large chip thickness upon exit, and always consider running dry without cutting fluid, especially in roughing operations.

Milling stainless steel
Stainless steels can be categorized as ferritic/martensitic, austenitic and duplex (austenitic/ferritic), each with its own machining recommendations for milling.
Milling ferritic/martensitic stainless steel
Material classification: P5.x
Ferritic stainless steel have a machinability that is comparable to low-alloyed steel, and therefore, the recommendations for steel milling can be used.
Martensitic stainless steel has a higher work-hardening property and exerts very high cutting forces when entering the cut. Apply the correct tool path
and roll-in method for best results and use a higher cutting speed, vc, to overcome the work-hardening effect. Higher cutting speed an a tougher grade
ith a reinforced cutting edge gives higher security.
Milling austenitic and duplex stainless steel
Material classification: M1.x, M2.x and M3.x
The dominant wear criteria when milling austenitic and duplex stainless steels are chipping on the edges due to thermal cracks,
notch wear and built-up edges/smearing. On the component, burr formation and surface finish problems are the main issues.

Thermal cracks

Edge chipping on the insert

Burr formation and bad surface finish

Recommendations for roughing

Recommendations for finishing
Milling cast iron
There are five main types of cast iron:

Gray cast iron
Material classification: K2.x
The dominant wear criteria when milling gray cast iron are abrasive flank wear and thermal cracks. On the component, frittering at the cutter exit side of the workpiece and surface finish problems are the main issues.

Typical insert wear​

Frittering on the component​​
Recommendations for roughing

Recommendations for finishing

Nodular cast iron
Material classification: K3.x
The machinability of ferritic and ferritic/perlitic nodular cast iron is very similar to that of low alloyed steel. Therefore, the milling recommendations provided for steel materials should be used regarding the selection of tools, insert geometries and grades.
Perlitic nodular cast iron is more abrasive; therefore, cast iron grades are recommended.​
Use PVD coated grades and wet machining for best machining capabilities.
Compact graphite iron (CGI)
Material classification: K4.x
Perlitic content less than 90%
This type of CGI, which often has a perlitic structure of around 80%, is the most common being milled. Typical components are engine blocks, cylinder heads and exhaust manifolds.
Cutter recommendations are the same as for gray cast iron; however, sharper, more positive insert geometries should be selected to minimize burr formation on the component.
Circular milling can be a very good alternative method to conventional cylinder boring in CGI.​
Austempered ductile iron (ADI)
Material classification: K5.x
Roughing is normally carried out in the non-hardened condition and can be compared to milling a high alloyed steel.
The finishing operation, however, is performed in the hardened material, which is very abrasive. This can be compared to milling hardened steels, ISO H. Grades with high resistance against abrasive wear are preferred.
Compared to NCI, the tool life in ADI is reduced to approx. 40%, and cutting forces are approx. 40% higher.​
Read more about cast iron materials
Milling non-ferrous materials
Non-ferrous materials include not only aluminum, but also magnesium-, copper- and zinc-based alloys.​ The machinability differs primarily depending on the Si-content. Hypo-euthectic aluminum is the most common type, with a Si-content below 13%.
Aluminum with a Si-content below 13%
Material classification: N1.1-3
The dominant wear criteria is built-up edges/smearing on the edges, leading to burr formation and surface finish problems. Good chip formation and chip evacuation are crucial for avoiding scratch marks on the component surface.
PCD-tipped insert


Warning: Make sure that the maximum rpm for the cutter is not exceeded

Read more about non-ferrous materials
Milling heat resistant superalloys (HRSA)
Heat resistant super alloys (HRSA) fall into three material groups; nickel-based, iron-based and cobalt-based alloys. Titanium can be pure or alloyed. The machinability of both HRSA and titanium is poor, especially in an aged condition, requiring particular demands on the cutting tools.
HRSA and titanium alloys
Milling HRSA and titanium often requires machines with high rigidity and high power and torque at low rpm. Notch wear and edge chipping are the most common wear types. The high heat generation limits the cutting speed.

Use round insert cutters to minimize notch wear

Changes have varying impacts on tool life; the cutting speed, vc, has the greatest impact, followed by ae, etc.
Cutting fluid/coolant
Unlike milling in most other materials, coolant is always recommended to assist in chip removal, to control heat at the cutting edge and to prevent the re-cutting of chips. High-pressure coolant (70 bar (1,015 psi)) applied through the spindle/tools is always to be preferred instead of an external supply and low pressure.
Exception: Cutting fluid should not be applied when milling with ceramic inserts, due to the thermal shock.

Cutting fluid supplied through the
cutters is advantageous when
using carbide inserts

Insert/tool wear
The most common causes of tool failure and poor surface finishing are notch wear, excessive flank wear and edge line frittering.
The best practice is to index the cutting edges at frequent intervals, to ensure a reliable process. Flank wear around the cutting edge should not exceed 0.2 mm (0.0078 inch) for a cutter with a 90-degree entering angle, or a maximum of 0.3 mm (0.0118 inch) for round inserts.

Typical insert wear​
Ceramic inserts cutter for roughing HRSA
Ceramic milling typically runs at 20 to 30 times the speed of carbide, although at lower feed rates (~0.1 mm/z (0.0039 in/z)), which results in high productivity gains. Due to intermittent cutting, it is a much cooler operation than turning. For this reason, speeds of 700–1,000 m/min (2,297–3,280 ft/min) are adopted for milling, compared to 200–300 m/min (656–984 ft/min) for turning.

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