Principle methods of manufacture employed by Advanced Ceramic Engineering Ltd –Precision Ceramics UK
Since the information on this site can only be of a general nature, the services of our technical advisory staff should be called upon to aid the early design stages of your production.
The forming method use for a component is determined by it’s shape, size, surface finish and dimensional tolerances.
Alumina isostatic pressing is one of the most popular and consistent types of ceramic pressing. Due to the uniform pressure applied by the pressurised water, isostatic pressing gives a consistent pressure throughout the billets, both length-wise, and radially.
It is therefore very useful when making a number of components from the same billet, as it lends itself to achieving consistent shrinkage, grain size and density throughout a batch of components.
At present we can produce components up to 80 mm in diameter and up to 300 mm in length. We do hope to double our capacity – diameter wise – in the not too distant future.
Machining before firing (Green machining)
After pressing components are machined in their ‘green state’, which refers to the pre-fired condition of the material.
As green machining is much easier and less labour intensive then the ‘post fired’ diamond grinding processes, we try and remove as much material as possible at this stage. Our technical team will equate how much the parts will shrink during the sintering process, and add these figures to the dimensions for green machining. Shrinkage can vary between batches and materials, but usually runs at around 20 %. Therefore the technical team will decide what tolerance can be achieved in green machining, and what can only be achieved by the more accurate diamond grinding processes, after the sintering stage.
In the green state parts can be turned, ground, and drilled / slotted etc. with suitable tooling.
Components are fired in our purpose built kilns, and can reach temperatures in excess of 1700 degrees C.
The ceramics are usually fired over a 48 hour period, with an accurate ramp and dwell time etc. essential to ensure the proper density and grain size of the finished product. These are controlled very closely, and samples are checked from each kiln to make sure they fall within the parameters set for that material.
During the firing process volatiles such as water and organic binders are driven off, leaving an extremely hard, dense and stable material.
When necessary, post-firing processes including grinding, lapping, honing and polishing are carried out using diamond abrasives. These techniques are to obtain exceptionally tight control of the dimensions and surface finish, which would otherwise be impossible to achieve.
At ACE we use many different machines to achieve what can often be intricate and very accurate components. Processes such as surface grinding, centreless and cylindrical grinding, milling (including cnc milling) and diamond drilling are used to machine components to within drawing spec.
Because alumina ceramics are subject to such a rate of shrinkage during firing (up to 20% of their green size), a general tolerance on ‘as fired’ parts of +/- 1% is necessary for economic manufacture, subject to a minimum of +/- 0.10 mm.
Where more accurate tolerances are required, these can be achieved by diamond grinding. This allows the parts to be machined to precision engineering standards. However features which cannot be ground using standard grinding procedures must carry the ‘as fired’ tolerance of +/- 1%.
As a rule of thumb, the more ‘green machining’ which can be implemented on components, rather than ‘diamond grinding’, the less expensive the parts will be to produce.
‘Cutting and feed rates’ are at least 10 times faster in green machining as opposed to diamond grinding. Therefore tolerances are a very important part of pricing, and draughtsmen are encouraged to remember this when producing component drawings. A needless tight tolerance can add a lot of unnecessary expensive to components.
At ACE we regularly grind components to within +/- 5 microns (0.005 mm). If a more accurate tolerance is needed, we can subcontract the parts out for honing or lapping procedures, where tolerances of +/- 1 micron (0.001mm) can be achieved.
Quality control – Precision Ceramics UK
Advanced Ceramic Engineering employ strict quality controls to all their processes. Product traceability is exercised on every single component, with approved procedures ensuring a high degree of control from the raw material intake, right through to the final inspection process and despatch to the customer.
As well as patrol inspection during manufacture, components are inspected for cracks, chips and flaws as well as dimensional accuracy both at the sintered stage and final inspection.
Laboratory checks are also carried out, including tests for stress analysis, electrically resistivity, and vacuum tightness, surface roughness and where appropriate examination using photomicrography and electron microscopy. The latest electronic techniques are used to maintain our reputation for quality.