Additive manufacturing could bring many benefits to marine and offshore, but it presents challenges too, says ABS metallurgical and materials engineer Alexander Gonzalez
Additive manufacturing (AM), also known as 3D printing, has existed in many forms for decades. The rise of AM is often attributed to a technology called stereolithography developed in the 1980s. Stereolithography builds parts by hardening photosensitive polymers with ultraviolet light.
Today, additive manufacturing processes are divided into seven major categories, and each process can have tens—or even hundreds—of manufacturers that each offer systems capable of building designs from a wide range of materials.
The advantages of additive manufacturing
As AM evolves in the 21st century, it has been hailed as a revolutionary tool and a disruptive technology across multiple industries. Whereas originally AM was consigned to rapid prototyping, used to test models prior to committing them to production, AM is now increasingly used to produce high-performance metal parts intended for end-use in demanding applications.
While the exact details for fabricating parts differ depending on the category of AM process, the general workflow is similar: an object is designed using computer software, split into many individual layers, and sent to a machine that builds it layer-by-layer. Once the machine is finished, the object often looks nearly-complete, but it may still require other processes such as heat treatment or machining before it is ready for use.
In general because of the layer-by-layer construction and other unique process aspects, AM can facilitate building a low number of complex parts quickly with less material waste than ‘traditional’ manufacturing methods such as casting or forging.
For example, aerospace companies are investing in AM technology to redesign parts to reduce weight, increase efficiency, reduce material waste, and combine parts—thereby reducing the number of items in complex assemblies. In the medical sector, AM is used to construct custom orthopedics, implants, and prostheses with a quicker turnaround and better patient compatibility. Both the aerospace and medical sectors have developed initial methods for certifying metal AM parts, further demonstrating these industries’ confidence in the performance of AM parts.
The benefits of AM are not unique to these two industries. The potential to lower marginal cost, reduce material usage, save weight and time, and develop highly complex designs are compelling advantages of AM technology across industry sectors. But given these benefits, what are the barriers to entry for the marine and offshore markets?
Complex barriers to additive manufacturing
The ability to fabricate complex parts quickly has a downside: process complexity.
AM processes often have many process variables acting at once. Changing one parameter can affect many others, and detailed relationships among these parameters are not all well understood. Because of this lack of knowledge, it can be difficult to control processes and verify that the end part will have similar properties of its cast or forged counterpart.
Additionally, AM parts can have a unique metallography, distinct from both castings and forgings, due to the layer-by-layer process conditions. Another way of describing the resistance to additively manufactured parts is with the term variability. In other words, “Yes, the part can be made with AM, but how repeatable is it?” If the same part is made on the same machine with the same computer file twice, the parts can be (and often are) different.
There is a critical distinction between an AM process and an AM part. While an AM machine can build a part, this is only one step in a larger manufacturing process. Confidence in the AM part depends on the whole process. Factors that affect final part confidence may be outside the scope, expertise, or control of the AM part builder. These factors could include the feedstock manufacturing process, heat treatment characteristics, and inspection results. By defining each stage of the overall AM process, it becomes easier to recognise and reduce part variability thereby improving quality.
The future of AM for marine and offshore
These AM challenges make it difficult to establish equivalence in the existing rules, codes, and standards that regulate quality for the marine and offshore industries.
Getting past this barrier is like a chicken-and-egg problem: how can we confirm with a reasonable degree of confidence that an AM part will behave the same as a traditionally manufactured part in service? This uncertainty increases risk and makes it more difficult for manufacturers to adopt the new technology and install parts into service. The lack of in-service data furthers the reluctance to accept the new technology.
There is (and will be) a need for additional fundamental knowledge, rules, codes, and standards for additive manufacturing for many years to come. There is much opportunity for improving industry confidence in AM parts.
One step towards gaining the benefits of AM can come from a standardised method of outlining each AM process in detail, from feedstock through end-application. A template like this would help AM part manufacturers reduce variability in AM parts. This standardisation would give potential AM-part-users more confidence in the final properties of the AM parts, and therefore their performance.
As AM continues to develop, we look towards its future in the marine and offshore sectors. The upsides of cost and time savings remain highly appealing for part replacements, complex items, and other small-production-volume fabrication requests. As always, safety is to be prioritised—reliability and consistency must continue to advance to meet the challenges associated with AM’s new applications.
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