The Complete Anodising Process Part 1: The Foundation of Superior Anodising

Anodising is one of the most durable surface finishes available. Anodising protects against corrosion, enhances aesthetic qualities, and ultimately increases the durability and longevity of components and products. When it comes to aluminium anodising, a successful finish begins long before the anodising tanks are fired up and extends to post anodising processes which aren’t always top of mind like product packaging and handling.

We’ve put together an informative three-part series in which we explore the complete anodising process to provide you with valuable insight into this fascinating process. In part one, we address surface preparation and the importance of proper jigging. We also touch on masking – all things to consider before anodising begins. In part two we look at the magic of anodising and its colourful possibilities – the actual anodising process. This includes anodising for a clear (natural) finish, the range of available colours, and we look at industry specificity. The third and final article in the three part series focuses on the importance of sealing after the anodising process, quality inspection as well as value add services such as packaging and handling.

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The Complete Anodising Process Part 1: The Foundation of Superior Anodising

While anodising serves as a cost-effective surface finish solution for components used in general industrial OEM equipment as well as bespoke aluminium products, achieving a consistently high-quality aesthetic finish demands a close partnership with a capable anodising company. It’s essential to recognise that, as the emphasis shifts toward top-notch quality, there may be corresponding increases in processing costs.

For achieving optimal performance, consistency, and efficiency it is highly advisable for customers to take into account the factors that can influence the anodising process. While designers and engineers often select a particular surface treatment for its desired properties, having a deeper understanding of the steps involved can significantly inform design and planning decisions, leading to cost savings and ultimately, better end results.

Pretreatment for Aluminium

Customers should ensure that the parts they provide for anodising are clean and free from any contaminants. Even small particles or residues on the parts can lead to marks. Pretreatment services such as sandblasting (bead blasting), soda blasting (vapour blasting), and vibratory polishing / finishing can be used to remove any unwanted material like paint from the surface, providing a smooth finish and improve the overall quality (appearance) of the material before anodising takes place. At Astro Anodising we offer a range of Pretreatment Services in-house. These pretreatment services also extend to products and parts which need to be powder coated.

Optimising Jigging for a Smooth Anodising Process

In anodising, it’s imperative to securely hold all parts. This dual function provides essential support for the components while establishing the necessary electrical contact during the anodising process. One of the most important steps in the preparation process is proper jigging, specifically to minimise the issue of jig marks. Jig marks typically refer to marks or blemishes on the surface of the anodised aluminium that is caused by the contact of the aluminium with the jig used during the anodising process.

There are several proactive steps that can be taken to minimise the issue of jig marks. While much of the responsibility for managing jig marks falls on the anodiser, the customer’s input and collaboration is vital for best results.

It is important to note that an anodic film still forms in the contact area to ensure corrosion resistance, so only the product’s aesthetics are potentially affected by jig marks.

The Challenge of “Cut-to-size”

When customers provide parts that have not been precisely cut to their final dimensions (cut-to-size), it allows us, as the anodising company, more flexibility in the jigging process. This approach minimises the potential for jig marks because there is more room for the jigging elements to secure parts without affecting the finished surfaces. The slight increase in excess material costs can often be offset by simpler and more cost effective jigging, speeding up the surface finishing process and leading to cost savings further down the line.

Minimising the risk of jig marks results in a higher likelihood of achieving the desired finish quality, which is often a primary concern for customers.

Specialised Jigging

When customers provide aluminium parts with limited clearance or space for jigging, we may need to employ specialised jigging techniques and use different jig materials to ensure precise anodising while protecting specific areas of the parts. These techniques, while effective, can be more labour-intensive and time-consuming, potentially increasing the cost of the anodising process.

If there are specific areas where jig/contact marks cannot be tolerated for functional or decorative reasons, it is important to communicate this during the initial project briefing so that project specific requirements can be taken into account. In some cases the part design can include tooling holes for proper jig contact. We are also able to offer specialised jigging design, but once again, this often leads to increased costs for the anodising process.

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Types of Jigs

Each jigging method has its own potential for causing jig marks, and it’s essential to understand and manage this issue for a successful anodising project. Let’s explore how jig marks relate to each of the jigging methods:

1. Wire Jigs:

Wire jigging is one of the most common methods for holding and suspending parts and involves the use of wires, hooks, or hangers to suspend and hold the aluminium parts during anodising. It has the potential to create jig marks where the wire makes contact with the part. These marks can vary in size and shape, depending on the wire diameter and how tightly the parts are secured.

• Parts are often hung individually or in rows
• This allows for more exposure in the anodising bath/tank and even coating
• Well-suited for smaller or irregularly shaped parts
• Provides good electrical contact and stability
• May require more labour-intensive setup

2. Pin Jigs:

Pin jigging uses pins or small posts that are inserted into holes or recesses on the aluminium parts to hold them in place. Pin jigging is generally more precise than wire jigging, but there is still a risk of jig marks where the pins or pegs make contact with the part. The size and shape of the marks depend on the pin’s design and tightness. Careful selection of pin materials and precise setup can help minimise jig marks.

• Allows for vertical or angular positioning of the parts.
• Ideal for parts with existing holes or recesses that can accommodate pins
• Provides stability and precision but may be less secure than clamp jigging
• Generally faster to set up compared to wire and clamp jigging

3. Clamp Jigs:

Clamp jigging has the potential to leave marks on parts where the clamps make contact. These marks can vary in size and shape and may be more significant when using heavy-duty clamps. Careful selection of clamps and precise adjustment can reduce the risk of jig marks.

• Utilises clamps or fixtures to secure the aluminium parts in a fixed position during anodising
• Suitable for larger or flat parts with regular shapes
• May require custom fixtures or clamps for each part type
• Offers excellent stability but may require more complex setup

4. Titanium Jigs:

Anodising jigs are typically made from aluminium or titanium. Aluminium jigs get anodised after serving a certain period and have to be chemically cleaned, the constant anodising and stripping results in a shorter lifespan. Titanium jigs are less likely to leave marks compared to aluminium wires, pins or clamps due to their chemical resistance and smoother surfaces. However, if the contact points on a titanium jig are not properly designed or maintained, they can still result in jig marks. The higher initial cost of titanium jigs is more than offset by the in-process savings, better consistency and longer life advantages of titanium, but this is a project specific decision which requires special consideration.

• Typically holds parts horizontally, parallel to each other, and in a flat position
• Provides excellent stability and consistent positioning for all parts in the rack
• Efficient for mass production but may require custom racks for different part types
• Not cost effective for smaller orders, batches and projects

There are other types of jigging like frame jigging, vacuum jigging and even magnetic jigging, each with its own advantages and disadvantages. The risk of jig marks is present in every jig setup and so it is vital that customers work closely with their anodising partner, even from the early stages during product design and development, to ensure the best possible results.

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Masking for Functional or Aesthetic Purposes

Masking involves covering or protecting specific areas of an aluminium part to prevent them from being anodised. This is done by applying a masking material, typically a resistive substance like wax, paint, or tape, to the areas that you want to keep unanodised. Masking is used when you want to create patterns, designs, or specific surface finishes on a part. By masking certain areas, you can ensure that the anodising process only affects the exposed areas. The masking material is applied to the part before it goes through the anodising process. After anodising, the masking material is removed, revealing the desired contrast between the anodised and unanodised areas.

Conclusion

Achieving a consistently high-quality finish in the anodising process, whether for industrial equipment or bespoke aluminium products, demands a close partnership with a capable anodising partner. To optimise costs, consistency, and efficiency, customers must consider several key factors, including proper design and project planning, pretreatment and setup for the anodising process. At Astro Group, our anodising capability and capacity, coupled with more than twenty five years of experience across the aluminium value chain, provide the most efficient and effective anodising results for our clients in a diverse range of industries.

Look out for Part 2 in our series – The Complete Anodising Process, as we explore the magic of anodising and its colourful possibilities – the actual anodising process. This includes anodising for a clear (natural) finish, the range of available colours, and we address industry specificity.