Overview
Lapping Operation and Procedures
Specifications
The Kemet 15 is a lapping machine that uses (iron and copper) composite discs to embed diamond, from various sized suspensions, to planarization and lap and then polish samples before testing to ensure they are flat and to the desire roughness. Planarization is important for tribological testing as deviation from flatness in the samples can lead to undesired high and localised contact pressures, much beyond those intended during testing and sometimes beyond the tribological pair to operate without pushing them in destructive adhesive modes.
The machine uses a pneumatic system to periodically dose the lapping disc with diamond suspension and lubricant, while the rotation speed and load can be manually adjusted. The machine also timer to allow long duration processes of hard samples or samples that require a long time to planarize.
To avoid contamination from large diamond particles to lower grade processes nCATS has two iron composite discs for 25 µm (used for planarization) and 14 µm; two copper composite discs for 6 µm and 3 µm, polishing is achieved with an aluminium disc and self-adhesive pad using 1 µm diamond suspension (and no lubricant). Each of these grades has its own ring (where the samples are contained), dispensing bottle and tubing.
Links to external websites
- Link to manufacturer website
- https://www.kemet.co.uk/product-videos/kemet-15-diamond-lapping-machine-set-up-video-instructions
The University cannot accept responsibility for external websites.
The lapping machine is multi-disc system with six lapping discs: two iron composite, two copper composite and two aluminium discs; the latter are designed to take self-adhesive polishing cloths. Each disc takes a different diamond suspension (Kemet Liquid Diamond Type K), from 25 µm to 1 µm. The iron-based is harder and used with 25 and 14 micron diamond suspensions, while the soft copper disc is used with 6 and 3 microns diamond suspensions, while the polishing cloth is used with 1 micron diamond. The discs locate onto a rotating base unit and align and are driven via dowels.
When in position the ring platform is raised to operating position and the ring arms are moved into position. The rings are positioned against the ring arms and the samples placed inside the ring and a load placed onto.
On the left-hand side of the rig are the Liquid Diamond and lubricant (Kemet Lubricating Fluid Type K) filled bottles, the diamond has a magnetic stirrer which maintained the diamond in suspension. Both the diamond and lubricant are connected to the pneumatic system, which sucks the liquids up from the bottles and sprays onto the lapping discs.
Operation is controlled by the start and stop button, in addition the rotation speed of the base unit is controlled by a twisting knob. When the start button is depressed the base unit (and lapping disc) start rotating and will continue to rotate for the duration set by the timer or if the stop button is depressed. The diamond and lubricant feed-rate and interval are set on the feed panel.
Additional operations include re-cutting of the iron and copper discs with an alumina suspension (Kemox Type O-400s). The alumina suspension is pumped from a unit in the back right-side of the base unit. The cloth pads on the aluminium discs need to be replaced periodically due to wear and scoring of the cloth; this is achieved by peeling the pads from the disc and removing any adhesive on the discs with solvent (isopropanol).
At the end of operation, or when lapping plates are changed the machine is thoroughly cleaned with paper and solvent (isopropanol) to remove the residual lapping fluids. The machine has a system where lapping fluids are allowed to drain base the rotating base unit, then into a side chute and collected for disposal (by Hazardous Waste Collection).
Procedure
As with any operation general the first step is planarization and this employs the 25 µm iron-composite disc and two conditioning ring.
- Place the iron-composite disc onto the drive plate, locating by dowel (rotate with hands on top, to prevent finger crushing);
- Raise ring platform so that it level with top of ring;
- Move ring arm in position so that the ring(s) is/are central to the lapping disc and samples do not overlap inner or outer edges;
- Put diamond suspension bottle in and turn on magnetic stirrer (check level and top up as necessary)
- Check lubricant level (and top up as necessary)
- Adjust diamond and fluid interval and durations
- Manually add diamond and lubricant (by pressing the manual button on panel), while rotating the disc with the rings in position. This wets the lapping disc.
- Add samples to be lapped, ensure they are evenly distributed
- Add ring weight(s) to top of samples
- Set rotation speed and duration and press start
- Run until the desire finish is achieve
- Clean (and proceed to next level - repeat as necessary with next diamond suspension)
Note at each lapping stage there is a set of ring(s) and disc and bottle with the diamond suspension and delivery tube, this is minimise the amount of cross-contamination between lapping stages, the numbers are listed in the table below:
| Abrasive | Disc | Rings |
|---|---|---|
| 25 µm | Iron-composite | 2 rings |
| 14 µm | Iron-composite | 2 rings |
| 6 µm | Copper-composite | 1 ring |
| 3 µm | Copper-composite | 1 ring |
| 1 µm | Aluminium with self-adhesive cloth | 2 nylon covered rings |
Technical data
| Specification | |
|---|---|
| Lapping Plate outside Diameter | 381 mm |
| Lapping Plate Speed | up to 70 rpm |
| No. of Conditioning Rings | 2 |
| Max load per Conditioning ring | 39 kg |
| Height of Open Face Machine | 670 mm |
| Working Height | 310 mm |
| Depth of Machine | 660 mm |
| Width of Machine | 760 mm |
| Electrical Supply | 220V single phase |
| Main Drive Motor | 0.37 kW |
| Abrasive pump motor | 0.18 kW |