The Ø48.5 mm bore of a hardened gear is honed after hard turning. The machining concept combines face and bore machining with honing and grinding the synchroniser cone in one setup. The remaining honing allowance is approximately 0.02 mm on diameter.

In addition to the Ø48.5 G6 size, the bore requires different roughness limits in the axial and circumferential directions, together with low circumferential waviness. Ultimately, K046 was identified as a honing stone specification that enabled efficient machining while meeting the specified requirements.

The original tool concept uses a 6-stone Xstep® honing tool with mechanical expansion through the existing NC expansion unit. The 6LM48,5/33S-80/110 version is designed with internal coolant supply and air gauging and is connected to the machine through HSK-C63S.

The gauging nozzles are positioned to measure the diameter in two axial planes. This allows a taper deviation to be assessed in addition to the diameter. The required tool overtravel must be coordinated with the fixture and gauging positions.

During further development, two tools were converted to hydraulic coolEX® technology. Alongside mechanical expansion, hydraulic expansion was therefore also tested for machining the hardened bore.

Clamping: The gear is located using its teeth. The setup provides a common basis for machining the faces, bore and synchroniser cone.

Hard turning: The bore is prepared with a small remaining allowance that is as uniform as possible. Dimensional coordination of pre-machining limits the amount of material to be removed during honing.

Honing: The expandable honing tool performs the final size and surface machining of the bore. The honing stone specification, contact geometry and coolant are matched to the hardened material.

Gauging: The planned air gauging in two planes supports the assessment of diameter and taper. The gauging positions are coordinated with the stroke end positions and available overtravel.

Tool development showed that low roughness alone does not ensure efficient machining: some tested specifications produced a fine surface but removed too little material. Other variants achieved effective stock removal, but their roughness was still close to the limit.

In addition to the honing stone specification, the contact geometry of the honing stones and the coolant supply were therefore adjusted. The aim was a free-cutting tool that removes the small honing allowance while meeting the directional surface requirements.

Ultimately, the K046 specification was identified. It enabled efficient machining while meeting the specified requirements, resolving the previous challenge of balancing stock removal and surface quality.

Why is honing performed after hard turning? Hard turning prepares the bore with a small remaining allowance. Honing then finishes the bore and matches the surface to the axial and circumferential requirements.

Why is roughness assessed in two directions? The drawing specifies Rz ≤ 4 µm axially and Rz ≤ 2.5 µm circumferentially. The surface must therefore be assessed in the specified measurement directions.

What is the purpose of air gauging in two planes? It measures the diameter at two axial positions. Comparing the readings supports the assessment of bore taper.

Which specification was ultimately suitable? K046 enabled efficient machining while meeting the specified requirements. The decisive factor was the combination of effective stock removal and suitable surface quality.

The application concept integrates honing of the hardened Ø48.5 G6 gear bore into complete machining on an EMAG machine. Development included mechanically expanded Xstep® tools, a hydraulic coolEX® version and targeted honing stone adjustment. K046 was ultimately identified as a specification that enabled efficient machining while meeting the specified requirements.

Related DIAHON sections: Xstep® tool system and coolEX® tool system.