In this application, four PTWA thermal-sprayed cylinder bores are machined directly on a CNC machining centre. The PTWA coating provides the wear-resistant functional layer. A two-stage equalization-honing process is designed to replace the previously specified fine-boring operation and prepare the bores for subsequent finish honing.
Two matched DIAHON multi-stone honing tools are used. The first stage pre-machines the coated surface, while the second stage moves the bore towards approximately Ø83.92 mm. The documented trial achieved a combined machining time of approximately 39 seconds per bore for both honing stages. Subsequent finish honing produces the nominal Ø84 mm size and the required functional surface.
Initial condition: After thermal spraying, the bore exhibits coating-related variation in stock allowance and geometry. The honing process must machine the functional layer evenly while retaining the required minimum coating thickness.
First equalization-honing stage: A multi-stone honing tool with ten honing stones machines the coated bore. The large number of evenly distributed honing stones supports uniform loading of the coating and stable tool guidance.
Second equalization-honing stage: A second multi-stone honing tool performs further diameter and geometry correction. The target size of this stage is approximately Ø83.92 mm, leaving a defined allowance for subsequent finish honing.
Air gauging and size compensation: Integrated air gauging monitors the bore diameter during the process. The µ-matik adjustment unit provides defined tool adjustment and supports compensation for honing-stone wear.
Machine integration: In addition to the HSK-A100 interface, automated operation requires a torque support for the rotary air transfer and coordinated pneumatic, electrical and control-system integration.
| Process stage | Documented stock removal | Machining time per bore |
|---|---|---|
| First equalization-honing stage | approx. 600 µm | approx. 17 s |
| Second equalization-honing stage | approx. 350 µm | approx. 22 s |
The documented total machining time was approximately 39 seconds per bore, meeting the target of no more than 40 seconds. The initial trial included five components with four bores each, giving a total of 20 bores.
No visible honing-stone wear was identified on the first stage after these 20 bores. For the second stage, calculated wear of approximately 0.5 µm per bore was determined after a total of 40 machined bores. Based on this limited sample, a calculated tool life of approximately 33,000 bores was projected for the developed tool version with ten 100 mm honing stones. This figure is a trial-based projection, not a guaranteed production tool life.
Can fine boring after thermal spraying be replaced by honing? The tooling concept is designed to replace the previously specified fine-boring operation with two equalization-honing stages. Approval depends on the stock allowance, coating variation and results under production conditions.
Why are two honing tools used? The first stage homogenises the coated surface and performs the initial stock removal. The second stage corrects diameter and geometry and produces a defined allowance for finish honing.
What is the purpose of integrated air gauging? It provides process-related monitoring of the bore diameter. Together with automatic size compensation, tool adjustment and wear compensation can be integrated repeatably into the machining sequence.
Why do the tools use ten honing stones? The multi-stone arrangement distributes contact forces around the circumference, supports tool guidance and is therefore suitable for uniform machining of the thermally sprayed functional layer.
What machining time was achieved in the trial? The first honing stage required approximately 17 seconds and the second approximately 22 seconds. The combined time of around 39 seconds per bore met the target of no more than 40 seconds.
How was tool wear evaluated? No visible wear was identified on the first stage after 20 bores. For the second stage, calculated wear of approximately 0.5 µm per bore was determined after 40 machined bores. Tool-life figures derived from this trial are projections and must be confirmed under production conditions.
Which machine requirements must be considered? The process requires an HSK-A100 interface, a stable coolant supply, air transfer to the gauging system and the electrical, pneumatic and control-system integration of the measurement and adjustment functions.
The two-stage DIAHON tooling concept combines equalization honing of a thermally sprayed cylinder bore with process-related air gauging and automatic size compensation. Two matched equalization-honing stages prepare the Ø84 mm bore for final honing directly on the CNC machining centre. The documented trial achieved the cycle-time target at approximately 39 seconds per bore. This allows the specified fine-boring operation to be eliminated while diameter, geometry and remaining coating thickness are considered together.