Xstep® cnc honing with mechatronical path-controlled expansion (SME) in machining centres

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: 

  • only a small honing allowance is required, thus very short machining times
  • the axis placement of the bore in pre-machining for honing (e.g., fine spindling with actuating tool on KomTronic® U-axis system) permits the elimination of so-called "position honing"
  • separate honing machines can be eliminated
  • highly scalable to fluctuations in production due to use of standard machining centres
  • no limitations compared to path-controlled honing with regular honing machines
  • process control and availability of advanced measuring equipment allows 100% checking of the bore geometrie
  • no additional costs for additional honing fixtures or gimballed connecting rods for the honing process

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.

Xstep®2 - mechanical double expansion

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.

Technical details - Xstep®

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: 

  • blind or through bore tools
  • tools with double expansion (Xstep®2)
  • exchangeable honing heads with connecting rods

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.

Information for builders of machining centres

Prerequisites for the successful use of the technology:

  • pre-machining of the hole in the same fixture (no reclamping)
  • fine filtration of coolant depending on surface requirements (about 30-50µm or less)
  • positioning accuracy of the bore axis to the tool axis within 5μm (tool changer)
  • high axial acceleration at the stroke end positions depending on the diameter and required honing angle

Selection of projects on various machining centres from different machine manufacturers

Click here to find a selection of successful completed projects on various machining centres from different manufacturers.

2-stage honing operation of a V8-engine block (AlSi17 hypereutectic) in a machining centre

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.

  1. Honing operation with Xstep®-honing tools on KomTronic® u-axis-system for dimensional control of the diameter
  2. Honing operation with coolEX®-honing tools to expose the silicon crystals in the functional surface of the cylinder

Example machining: PV connecting rods - honing of big eyes, allowance of 30µm

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...

Example: Grey cast iron valve block (hydraulic housing)

Complete machining of the bores (after heat treatment) with tools on KomTronic U-axis system: Fine spindling with live actuated fine spindle tools and honing with Xstep honing tool into IT6 tolerance.

Example: PV connecting rod - complete machining of large eyes with honing allowance 20-25µm

Requirements: Rz=8±3µm, Rpc>170 peaks per cm, honing angle 50°-60°, diameter 50.6+12µm, roundness lt. 5µm, parallelism lt. 8µm, straightness lt. 8µm, no reverse wipes in honed surface

Example: 2-stage plateau honing of a grey cast iron bore in a machining centre - Xstep® and coolEX®

2-stage plateau honing of a grey cast iron bore: 

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