The Xstep® cnc honing tool technology allows conventional path-controlled (SME) honing in a machining centre with any machine side available push/pull rod or with exchangeable U-axis-systems (such as a KomTronic® by KOMET). The machining is done with regular honing kinematics (expansion during machining), thus generating the classic cross hash pattern in a defined honing angle.
Enormous advantages result by this kind of honing operations on the machining centre by the arrangement of both system parts (tool and workpiece) in a fixed clamping:
Process control is integrated by the path-control of the feed. The measurement of the bore size can be done downstream off the machines main machining time. The following bore sizes can be adjusted in diameter and cylindricity via a closed feedback loop based on the measurement.
The Xstep®2 tool system is a double expansion system (pre-honing and finish honing) in a single tool. It is implemented by the push and pull movement of the expansion rod in the tool. Both machining steps can thus be controlled with the same high precision.
Xstep® honing tools use a push/pull rod for expansion of the cutting stones. Cooling lubricant is diverted directly to the contact point honing stone/bore for process cooling. This ensures optimum cooling and chip removal. The finish diameter is set via control of the end position of the push/pull rod and can can compensate the wear on the honing stone. By changing the specification (bond, grit size and concentration) of the honing stones, the required parameters (e.g., roughness, cycle time or cylindricity) can be achieved to meet the requirements.
Depending on the requirement and hole geometry, Xstep® honing tools can be supplied in different types:
The use of post-process air measuring devices with an interface to evaluation systems and feedback into the controls of the machining centre allows full size control identical to conventional honing machines.
Prerequisites for the successful use of the technology:
The task was the prove of concept of a 2-stage honing of a V8 engine block in an existing machining center with KomTronic® U-axis system of KOMET®. The solution a combination of coolEX®- and Xstep ®-honing tools to utilize the advantages of both honing systems.
Requirements: Rz=8±3µm, Rpc>170 peaks per cm, honing angle 40-50°, diameter 41.00 +12µm roundness lt. 5μm, parallelism lt. 8μm, straightness lt. 8μm, reversing wiper free hash pattern
The machining is done on pre-machined parts (after fine spindle operation), which are inserted into a floating fixture (allows the center of the eye to move and center itself towards the tool axis). This fixture applies no clamping force into the part and reduces common roundness problems. Big advantages are the ease in loading and the avoidance of clamping forces...
2-stage plateau honing of a grey cast iron bore: