Machining design tips for marine technology

23rd Mar 2023
by Sam Brown

When developing products for subsea or ocean technology applications, there are two very obvious criteria that must be met: corrosion resistance and suitable waterproofing.

Achieving this should be as simple as it is obvious, but there are some areas that can cause slip ups, particularly when it comes to the manufacture of watertight, corrosion-resistant components. In this blog I’ll take you through some of the key decisions that need to be made when designing your subsea component for manufacture, and when choosing a CNC machining supplier to provide it.

 

Which material should I use for subsea components?

Depending on the application and function of the end product, there are multiple materials that could be chosen. For example, marine autonomous systems will have different needs to underwater sensing technology or surveying technology, and systems operating in saltwater will need different corrosion resistance to those operating in fresh water. These are just some of the many considerations that face a designer of ocean technology systems.

 

Naval brass – the obvious choice for marine applications

Naval brass (C46400) is the classic material used in marine environments. It’s strong, hard and corrosion-resistant. It’s an alloy of copper, zinc and tin, and, incidentally,  very easy to machine. However, it’s heavy, and that may not be appropriate for some technical or electronic systems designed for subsea environments. It’s more commonly used for marine hardware such as propellers, shafts and decorative fittings.

Brass boss used for marine applications

What about aluminium for subsea components?

The 5000 series of aluminium is a lighter alternative to brass. Consider aluminium 5083 for marine applications – it’s a medium strength manganese-chromium-aluminium alloy that’s highly resistant to seawater and can be anodised to provide further protection. 

 

Plastics have a place in subsea technology too

Other lightweight alternatives to brass include a range of plastics. Acetal (POM) is commonly used, thanks to having good corrosion resistance, low water absorption, high strength and rigidity and good compressive strength. This is particularly important when operating in harsh environments: if your system gets knocked or dropped, an acetal housing will keep any electronics inside safe from damage.

Acetal component used for marine applications

Note: there are two types of acetal – copolymer and homopolymer. Delrin is a brand name for a specific acetal homopolymer. You can read more about the difference between Acetal and Delrin in our LinkedIn blog here.

For more information about materials commonly specified for underwater environments, take a look at our materials resources

 

How can I ensure a marine housing will be watertight?

If you’re designing a system that will be housed in some kind of enclosure, any underwater housing must of course be watertight. It’s not just the material choice that’s relevant – getting the design right is imperative. 

There are a number of ways that a watertight enclosure can be designed, and they all rely on the machining company achieving tight tolerances and a good machined finish. Sometimes it’s cleverly designed mating parts, perfectly executed. Alternatively, a design may make use of a series of channels or recesses that will house O-rings, or use nitrile or neoprene gaskets to   achieve the failsafe seal. 

Component with groove for gasket

In theory, these methods are straightforward. And they are, at design stage! It’s when it comes to realising the design through manufacture that the theory can become problematic. 

Usually, injection moulded components will not have the level of repeatable quality that is required to ensure a faultless seal for underwater applications. CNC machining however, is able to achieve the necessary precision, tolerances and repeatability that will guarantee a watertight seal, every time. 

 

Look for robust procedures

It’s worth noting that while CNC machining is the best manufacturing method to create watertight marine housings or enclosures, achieving them in reality relies on the CNC machining company having robust procedures that are consistently followed.  

Brass cylinder on machine

Manufacturing precisely mating components for marine applications takes skilled, experienced machinists, backed up by a series of processes that will ensure repeatable quality. If you’re looking for a CNC machining company that’s up to the job, make sure you ask what methodology, processes, or procedures they use to reassure you that your components are in safe hands. 

One of the main areas of risk when it comes to CNC machining for ocean technology is the interface between humans and machines. Human error happens, but robust processes provide checks and solutions to stop errors before they are made.

Enclosure on pyramid fixture

For example, machining complex shapes with a single set up is one way of reducing human error in machining, as it reduces human intervention. 

 

The trouble with 3- and 4-axis machining for subsea components

3- or 4-axis machines can only access certain surfaces, and so components such as a marine technology housing or subsea enclosure will undergo multiple machining ops (operations) – and multiple human interactions. Setting up multiple ops needs exacting precision from the machinist to ensure the component is in the correct position before cutting. This can be achieved through clever fixturing, but there are other ways. 

 

5-axis machining is the best match for ocean technology

The most reliable way of machining for subsea technology is through the use of 5-axis machines, programmed by highly skilled engineers, sometimes alongside clever fixturing. This way a machine can access every surface of a component, eliminating the need for multiple set ups and taking human error out of the picture. 

Fixture and billet on 5-axis machine

When dealing with exacting quality standards, even a micrometre can make a difference to an underwater housing being successfully water tight, or gradually starting to leak.

 

Essential quality procedures for any company that machines marine components

Quality procedures are also critical to achieve the pinpoint accuracy that a truly watertight seal needs. First-off inspection by skilled machinists or inspectors checks that a machining programme is running correctly, the material is loaded properly, and everything is working as it should. Once the first off has been checked and signed off, the remainder can then be manufactured. 

First off inspection

For long runners, checking a set quantity at agreed batch numbers ensures that any tool-wear or other fluctuations within a machining process are being managed, and the machine continues to run within tolerances. 

Final inspection of manufacturing then gives the assurance that each component is fully water-tight. Certification is usually available for proof of inspection.

Look for a company that has documented machining and inspection procedures that are followed consistently. This will give you the guarantee that every component will achieve the exacting standards required to be corrosion-proof and watertight within marine applications.

 

What finishing processes can be used for marine technology?

Depending on the material selected, there will be different finishing processes that are possible. Some will help to improve properties such as corrosion resistance, while others will be primarily around aesthetics.

Base ring with black sulphuric anodising

If your design includes a finishing process, such as anodising, powder coating or iriditing, it’s important to ensure that you consider the necessary machining allowance for all surfaces where marine components meet or join together. A layer of material is added in these processes, and it can push a perfectly-fitting set of components into the scrap pile. 

Consider too that some finishing processes are more ‘artisanal’ than precision, so it’s best to work with a company with expertise in both CNC machining and finishing to ensure the desired finish is achievable and appropriate for the application. 


How can we help?

If you need a reliable CNC machining company to manufacture components for your subsea or underwater technology product, get in touch with Penta. 

Find out more about our marine technology machining service.

Our company is built on core processes, with each area of the business responsible for examining, improving and following their particular processes. We have put these in place to ensure every customer has a consistent, high quality experience. 

We often work with designs that have tight tolerances and exacting machining requirements, including those within the marine technology industry, and collaborate closely with a small number of trusted suppliers who provide coatings, anodising or iriditing services that won’t jeopardise seal effectiveness. 

Closely fitting components used in marine technology industry

Penta’s customers benefit from our innovative manufacturing techniques, advanced machinery and our committed, highly-skilled estimation, preparation and shopfloor engineers who truly care about the work they do. 

If you’re looking for a quality and experienced supplier for your marine application, get in touch with my team on 02392 668 334, or email us at