Lapping & Polishing Injector Parts
Lapping is a precision machining process used to achieve extremely fine surface finishes and tight tolerances. In this case study, we outline the process employed to lap 12 injector parts (14.58mm in diameter) to an Ra better than 0.007 µm, an Rz of 0.04 µm, and to mirror polish another 6 parts. The required flatness specification was better than 1 micron.
Equipment and Materials Used
To achieve these stringent requirements, the following equipment and consumables were utilised:
- Lapping Machine: Kemet 15” lapping/polishing machine
- Lapping Plate: Kemet PR3 lapping plate
- Diamond Slurry:
- Kemet liquid diamond 6-micron type K
- Kemet liquid diamond 3-micron type K
- Work Holder: Profiled work holder
- Measurement Tool: Kemet Flatness gauge
- Pressure Weight: Silk-faced pressure weight
- Cleaning Fluid: CO-42 cleaning fluid
Process Breakdown
Step 1: Initial Lapping
Six injector parts were placed into a profiled work holder inside a control ring, with a silk-faced pressure weight on top to ensure even force distribution. The Kemet 15” lapping machine, fitted with a flat PR3 lapping plate, was set to run with Kemet liquid diamond 6-micron type K. The diamond slurry was dispensed at a ratio of 2 seconds of spray every 40 seconds until the parts had cleaned up. After achieving the desired initial surface finish, the parts were cleaned using CO-42 cleaning fluid.
Step 2: Pad Polishing for Mirror Finish
The six previously lapped parts were repositioned in the work holder inside a plastic-faced control ring, with a silk-faced pressure weight placed on top. The Kemet 15” machine, now fitted with an ASFL polishing cloth, was used with Kemet liquid diamond 3-micron type K, dispensed at a ratio of 2 seconds of spray every 50 seconds. Once the mirror finish was achieved, the parts were cleaned again using CO-42 cleaning fluid.
Results and Conclusion
The lapping and polishing process successfully met and exceeded the surface finish requirements: Single-stage process (PR3 plate with 6-micron diamond slurry): Ra: 0.0068 µm, Rz: 0.0409 µm Two-stage process (PR3 plate with 6-micron slurry, followed by ASFL pad with 3-micron slurry): Ra: 0.0048 µm, Rz: 0.0212 µm
The combination of the Kemet PR3 lapping plate and ASFL polishing cloth, along with precise application of diamond slurry, enabled us to achieve an ultra-smooth, mirror-like surface finish. This demonstrates the effectiveness of a controlled lapping and polishing process for high-precision injector components.
Before Processing
After Lapping
After Polishing
Flatness Measurement After Processing
