These are the main factors that affect the price for anodising and therefore should be taken into account when you are asking for a quote.
Alloy Grade and Surface Condition
The anodising cost is directly affected by the alloy grade. As an example, high-silicon casting alloys produce a duller and less consistent oxide layer. In general, the anodising cost for these alloys is higher as they require additional pre-treatment in order to achieve the desired surface finish. This can result in higher rejection rates during the pre-treatment process. Arriving with a clean, machined surface helps to reduce pre-treatment costs and rejects.
Bath Type Selected
The process of anodising is an electrochemical process. This process is used to convert the surface of aluminium to a hard wearing aluminium oxide surface. Typically anodizing is carried out in a sulfuric acid anodizing tank. However there are many alternative anodizing baths available that can be used to anodize aluminium. These alternative anodizing baths can sometimes produce a more suitable anodized finish for specific requirements.
Coating Thickness Specified
Although each thicker oxide layer will require longer tank time and more strict process control, there is a large price difference between a standard 25-micron thick sulphuric acid anodized part and a hard anodized part to 50-micron thickness. As mentioned before, thicker coatings grow mostly inward but also outward. Therefore, close-tolerance parts, after anodizing, will require some post-anodizing machining in order to achieve proper mating surface. This additional feature will, of course, cost more.
Part Geometry and Racking
More complex parts with for example deep holes, sharp corners or small surfaces for contact will be processed longer and most probably will not fit into a big batch of simple parts like flat plates. These parts will be processed in smaller batches and thus cost more per part.
Dyeing and Sealing Add-Ons
Dyeing and sealing are additional processes which are charged as separate stages to the finishing process. Natural clear or grey finish is included in the quote for finishing. Each colour has its own tank for dyes and hot or cold sealing can be applied to complete the process. The cost for these processes on small orders can be double the cost for normal finishing processes. A line by line breakdown for costs on these processes can be requested from suppliers. Anodising is covered in more detail at https://www.poeton.co.uk/surface-treatments/anodising/.
Batch Size and One-Off Pricing
Cost per unit decreases as a batch is filled up to the point where the parts are racked. The cost of a single prototype can be 5 to 10 times the cost of a single part in a run of 50 identical parts, due to setup, chemistry verification, and handling of a single part. Discussing grouping of similar parts from different jobs into one batch order can often save significant costs.
Knowing the factors that determine costs before you ask for a quote means you can have a much better conversation with your supplier and have fewer surprises.
