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General turning

How to do turning in different materials

How to do turning in different materials
 
 

Turning steel

Steels can be categorized as unalloyed, low-alloyed and high-alloyed, all of which affect the machining recommendations for turning.

Turning unalloyed steel

Material Classification: P1.1

Unalloyed steel has a carbon content of up to 0.55%. Low-carbon steels (carbon content < 0.25%) require special attention, due to the difficult chip breaking and the tendency to smear (built-up edge).

In order to break and steer the chip, aim for the highest feed possible. A wiper insert is highly recommended.

Use high cutting speeds to avoid built-up edge on the insert, which can negatively influence the surface. Sharp edges and light cutting geometries will decrease the smearing tendencies and prevent edge deterioration.

​Turning low-alloyed steel

Material Classification: P2.x

The machinability for low-alloyed steels is dependent upon alloy content and heat treatment (hardness). For all materials in this group, the most common wear mechanisms are crater and flank wear. For hardened materials, plastic deformation is also a common wear mechanism due to higher heat in the cutting zone.

For low-alloyed steels in a non-hardened condition, the First Choice is the steel series of grades and geometries. In hardened materials, it is beneficial to use a harder grade (cast iron grades, ceramics and CBN).

Turning high-alloyed steel

Material Classification: P3.x

High-alloyed steels include carbon steels with a total alloy content over 5%. The group includes both soft and hardened materials. Machinability decreases at higher alloy contents and hardness.

As for low-alloyed steels, the First Choice is the steel series of grades and geometries.

Steels with more than 5% alloying elements, and with hardness over 450 HB, require extra demands on plastic deformation resistance and edge strength. Consider using a harder grade (cast iron grades, ceramics and CBN).

Read more about steel materials

 

Turning stainless steel

Stainless steels can be categorized as ferritic/martensitic, austenitic and duplex (austenitic/ferritic), each with its own machining recommendations for turning.

Turning ferritic and martensitic stainless steels

Material Classification: P5.1

This stainless steel is classified as a steel material, therefore with material classification P5.x. The general machining recommendations for this type of steels are our stainless steel grades and geometries.

Martensitic steels can be machined in hardened conditions, requiring extra demands on the plastic deformation resistance of the insert. Consider using CBN grades, HRC = 55 and higher.

Turning austenitic stainless steels

Material Classification: M1.x and M2.x

Austenitic stainless steel is the most common type of stainless steel. This group also includes super-austenitic stainless steels, defined as stainless steels with a Ni-content over 20%.

Recommended grades and geometries are our stainless steel offer of CVD and PVD grades.

For intermittent cuts, or where chip hammering or chip jamming is the main wear mechanism, consider using PVD grades.

Other considerations:

  • Always use coolant to decrease crater wear and plastic deformation, and select the largest possible nose radius. Read more about coolant
  • Use round inserts or small entering angles in order to prevent notch wear
  • Smearing tendencies or built-up edge are common. They both negatively influence surface finish and tool life. Use sharp edges and/or geometries with a positive rake face

Turning duplex (austenitic/ferritic) stainless steels

Material Classification: M3.4

For higher-alloyed duplex stainless steels, designations such as super-, or even hyper-duplex stainless steels are used. The higher mechanical strength makes these materials more difficult to machine, especially when it comes to heat generation, cutting forces and chip control.

Recommended grades and geometries are our stainless steel offer of CVD and PVD grades.

Other considerations:

  • Use coolant to improve chip control and avoid plastic deformation. Use tools with internal coolant supply, preferably precision coolant. Read more about coolant
  • Use small entering angles to avoid notch wear and burr formation

Read more about stainless steel materials

 

Turning cast iron

There are five main types of cast iron:

  • Gray Cast Iron (GCI)
  • Nodular Cast Iron (NCI)
  • Malleable Cast Iron (MCI)
  • Compacted Graphite Iron (CGI)
  • Austempered Ductile Iron (ADI)

Cast iron is a Fe-C composition of Si-content (1–3%) and C-content over 2%. It is a short-chipping material with good chip control in most conditions.

For the majority of cast iron materials, it is recommended to use our cast iron grades and geometries. It is recommended to use ceramic and CBN grades for gray cast iron at higher cutting speeds.

Read more about cast iron materials

Turning heat resistant superalloys (HRSA)

A superalloy has excellent mechanical strength and resistance to creep (the tendency for solids to slowly move or deform under stress) at high temperatures. It also offers good corrosion/oxidation resistance. HRSA can be divided into four material groups:

  • Nickel-based (for example Inconel)
  • Iron-based
  • Cobalt-based
  • Titanium alloys (titanium can be pure or with alpha and beta structures)

The machinability of both HRSA and titanium is poor, especially in aged conditions, requiring particular demands on the cutting tools. It is important to use sharp edges to prevent the formation of so-called white layers with different hardness and residual stress.

HRSA material: PVD and ceramic grades are commonly used when turning HRSA materials. It is recommended to use geometries optimized for HRSA.

Titanium alloys: Mainly use uncoated and PVD grades. It is recommended to use geometries optimized for HRSA.

A common wear criteria in both titanium and HRSA is notch wear. Follow these guidelines for optimal performance:

  • It is recommended to use an entering angle less than 45°
  • Use the correct relationship between the insert diameter/nose radius and depth of cut
  • When using ramping or multiple passes, it is recommended to use a depth of cut higher than 0.25 mm (0.0098 inch)
  • Coolant should always be applied when turning HRSA and titanium alloys, regardless of whether carbide or ceramic inserts are used. The coolant volume should be high and well-directed. Read more about coolant
  • When using ceramics, pre-chamfering is recommended to minimize the risk of burr when the insert enters and exits the cut, and to obtain optimal performance

HRSA application guide

Read more about HRSA and titanium

 

Turning non-ferrous materials (aluminum)

This group contains non-ferrous soft metals, for example, aluminum, copper, bronze, brass, metal matrix composite (MMC) and magnesium. The machinability differs depending on alloying elements, heat treatments and manufacturing processes (forged, cast, etc.).

Turning aluminum alloys

Material Classification: N1.2

Inserts with a positive basic shape and sharp edges should always be used. Uncoated and PCD grades are the First Choices.

For aluminum alloys with an Si-content above 13%, PCD should be used, as the tool life of cemented carbide grades is drastically reduced.

Coolant in aluminum machining is mostly used for chip evacuation.

Read more about non-ferrous materials

Turning hardened steel

Turning steel with a hardness of typically 55–65 HRC is defined as hard part turning, and is a cost-efficient alternative to grinding. Hard part turning offers improved flexibility, better lead times and higher quality.

Cubic Boron Nitride (CBN) grades are the ultimate cutting tool material for the hard part turning of case and induction hardened steels. For steels softer than approximately 55 HRC, use ceramics or cemented carbide inserts.

Use optimized CBN grades for hard part turning.

  • Ensure good machine and clamping stability
  • Use as small depths of cut as possible to achieve a low entering angle, and correct edge preparation to improve tool life
  • Use wipers to achieve best surface finish

Application tips for hard part turning

Read more about hardened steel materials

 
 
 
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