Hard turning

Hard turning is a high-precision machining process for finishing hardened materials above 45 HRC.

The workpiece rotates in a CNC-controlled clamping device while an extremely wear-resistant cutting material - usually CBN (cubic boron nitride) or ceramic - machines the surface. This results in grinding quality in just one machining step.

In contrast to grinding, hard turning offers significantly greater flexibility for geometries, as flat, internal, external and threaded surfaces can be machined in one clamping operation. The process chain is shortened, energy consumption is reduced and dry machining is also possible. This makes the process particularly economical for complex rotationally symmetrical components with high demands on dimensional accuracy, shape accuracy and surface quality.

Hard turning is used for hardened steels and special alloys with hardness ranges between 45 and 68 HRC. Typical materials are:

• Bearing steels: 100Cr6 (1.3505), 16MnCr5 (1.7131)
  
• Tool steels: X155CrVMo12-1 (1.2379), X38CrMoV5-1 (1.2343)
  
• Quality steels: 42CrMo4 (1.7225), 34CrNiMo6 (1.6582)
  
• Nickel and titanium alloys: Inconel 718, Ti-6Al-4V
  
• Hard-coated surfaces: TiN, CrN, AlTiN
  

CBN cutting inserts are used when hardnesses above 55 HRC are achieved, as well as ceramic cutting materials (Al₂O₃ + TiC) for high-temperature resistant applications.

Optimized cutting values, rake angles and cooling strategies result in low-wear processes with consistent surface qualities. Depending on the material, the cutting speeds are between 100 - 200 m/min, with feed rates of 0.05 - 0.15 mm/rev and cutting depths of 0.1 - 0.3 mm.

Thanks to state-of-the-art CNC hard turning centers with hydrostatic guides, precision-ground clamping technology and temperature-stable machine beds, accuracies can now be achieved that were previously reserved exclusively for grinding processes.

• Dimensional tolerances: up to ± 0.005 mm
  
• Shape and position tolerances: according to ISO 1101
  
• Surface roughness: Ra = 0.2 - 0.4 µm
  

Inline measuring systems and SPC-controlled process monitoring also ensure these values for series production.

Particularly for hardened functional surfaces such as bearing or sealing points, hard turning enables consistent quality over long running times.
Additional advantages are provided by temperature-compensated measuring systems, which automatically correct tool wear and ensure dimensional accuracy across entire batches.

Hard turning is economical wherever high surface quality and dimensional accuracy are required for hardened components, but traditional grinding would be too time-consuming. It reduces process chains, as facing, external turning, thread cutting and fine machining are combined in one clamping process. This eliminates reclamping times, set-up costs and secondary grinding processes - making production faster, more flexible and more energy-efficient.

Typical application industries:

• Automotive & drive technology: valve seats, synchronizer rings, gear wheels
  
• bearing industry: Inner and outer rings, raceways
  
• Tool & mold making: Inserts, guide pins, dies
  
• Mechanical engineering: shafts, coupling parts, piston guides
  
• Energy & turbine technology: highly stressed rotor and bearing components
  

Hard turning combines the precision of grinding with the productivity of machining - ideal for series production of hardened precision parts.

Quality assurance is multi-stage and digitally traceable. Each component is checked in accordance with ISO 4287 (roughness), ISO 1101 (shape & position) and DIN 50150 (hardness testing).

The following are used:

• 3D coordinate measuring machines (e.g. Zeiss Contura)
  
• Optical measuring systems for inline control of contour and concentricity
  
• Roughness and hardness testers with SPC connection
  
• CAQ systems with automatic traceability in accordance with EN 10204-3.1
  

The results are documented live in the production process, ensuring reproducible series quality. In conjunction with IATF 16949-compliant processes, this enables full auditability - crucial for industries with high documentation, safety and traceability requirements.