Operability, functionality and maintenance of LB-PBFAM

[2] laser based powder bed fusion AM

There are no fundamental processing differences between laser-based powder bed fusion systems, yet not all machines are created equal. So how do choose and invest in the right equipment? In the first part, we listed what you should be looking for in the hardware equipment. In this second part of a 3-part series, we review different functional and maintenance aspects.

​There are four components to using an SLM machine:

• Hardware operability, maintenance facility and the ease to retrofit optional add-ons;
• Software usability and upgrades frequency;
• Processing parameters development;
• Health and safety.

Again, not all SLM machines are created equal in these respects.

​With  simplicity of operation come process efficiency, safety and repeatability even with various operators.

As more and more solutions centre are opening to let customers try before they buy, it is easy to think manufacturers have nothing to prove or to hide as they let you try-before-you-buy. Realistically, very few clients have the time and human resources to go through the on-site test-and-try process for different machines. Manufacturers bet on you getting used to the idiosyncracies of their machines and their processes. Once you have committed your workforce and your time, it is very unlikely you’ll want to invest additional resources to run through a similar process with their competitors’ equipment.

​Before choosing the AM centres and equipment you may want to test, here are a few points you may want to keep in mind.

​How user friendly is it to operate? 

How many operators do you need to run one machine? Do they need to take up body building to lift the substrates platforms, to replace filters units? Do they need to crawl under cables, tubes or climb precarious ladders to refill powder tanks to carry out daily operations? ( just check...)

How much time does it take to turn the machine around? How easy and safe is it to ‘debuild’ (= remove) a heavy component that entirely fills the build chamber? Are there ancillaries planned and tested for this scenario? How many operators do you need? Is this a process that has been thought through?

Are the powder reservoirs big enough to enable a complete full-volume build? If not, how easy is it to top it up during process? Will your engineers need to come back at 2am to add some powder and nurse the jobs to completion? Can you do it at all or do you have to stop the process altogether and open the build chamber to access powder reservoir and build? Hence contaminating the working environment with ambient air? Is it really something you can afford to do with your products?

Do you have to stand by each machine to monitor the manufacturing of various components or can one engineer easily monitor the vitals of the machine in real time, from their office? 

​How easy is it to learn how to use it?

​A one-week training is usually common once the purchase has been agreed upon and the machine installed in you premises. Is that enough? How is the training structured? There are four components to using an SLM machine: Hardware training, software, parameters development training, maintenance training, health and safety training. What are key aspects (hardware, software, maintenance, parameters development, health and safety) included in the training? Are they on hand to answer questions once the field engineer has left? Is there/who is the main point of contact for these queries? How fast do they plan to get back to you? Can they specific response times? Or will you be left in the lurch if something happens?

​How easy and safe is it to change material?

The vast majority of LB-PBF machines are production machines. This means a single material composition will be used of the production chain. For instance, you’re are planning a manufacturing chain that will exclusively output aluminium components of a certain compositional grade, such as A307 or A7075 for instance, with no motivation to switch grades. That’s just as well because the vast majority of SLM machines are not well designed for easy swap of feedstock composition. They are cumbersome to clean properly, especially if you consider the nooks and crannies and various tubes, filters and various hidden tubes used to transport powders easily prone to end up everywhere you don’t want it to be.
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Now, don’t get me wrong, it can be done to a sensible extent. But it takes time to clean properly and to prevent cross batches contamination. Assume a certain – minimal – amount of powder will remain in the system and accept it will dilute itself in the next batch anyway. If you are happy with that, brilliant.

​Open parameters and parameters development process

When it comes to parameters, machines suppliers provide three main options:

• fully open option with full access to all the parameters (up to 150 of them); this gives you complete freedom to tailor the process features;
• fixed parameters for given compositions, typically hidden and locked to prevent meddling and errors;
• or both, where you have access to standard parameters for a given composition and where you can also tweak these parameters (or create from scratch) to vary properties for your specific components.

Fixed parameter sets may come in few variants defined as ‘performance’, ‘speed’ etc… As the names suggest, outputs characteristics will vary in parallels with the parameters. For instance, ‘performance’ parameters may focus on producing high surface quality or high mechanical properties whereas ‘speed’ may be more suited for quick manufacturing, like prototyping, to assess designs manufacturability.
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Provided with the machine or bought as add-ons, it is worth asking what the guarantees surrounding these parameters are in terms of production performance and products quality

[1] - parameters development is complex.

​Health & safety

Is using the machine safe? That’s a big one, right? How do you handle powder? How do you remove the fully built component out of the build chamber? Is it easy and straight forward? Are there procedures in place? You are responsible for the H&S of your team. Will you need to kit them up with bomb proof suits (don't laugh...) or are you satisfied H&S is taken seriously? How do manufacturers go about neutralising powder residue? What procedures do they advise to safely remove builds and recycle powders? Do these procedures minimise contact with the environment to minimise contamination? Are these H&S procedures easy to follow? What's their advised procedure to contain and store condensate and waste powders?

What are the procedure in place to contain powder leakage? Has the supplier ‘fool-proofed’ powder handling? What are the risks? Are there clear procedure in place to change filters full of inflammable condensate, to sieve or compartmentalise pure condensate coming out as a sieving by-product. How do you go about cleaning the chamber of the soot, reactive condensates and spatter produced during the process? How much waste is there ?

​Upgrades and retrofits

​As technology matures, there will be software upgrades and hardware changes. For instance, results show that high-temperature (~600/800°C) platforms in LB-PBF technology might reduce cracking in hard-to-weld materials such as nickel-based alloys. Conventionally, platform temperature sin SLM reaches up to 200°C. As technology develops, options appear that will offer high-temperatures modules. This type of module may (or may not) be engineered to be potentially retrofitted. Other retrofits could include monitoring modules and their onboard processing capabilities enabling processing feedback loops. It is worth inquiring. Could these be retrofitted?  

​Running costs and consumables costs?

How efficient is the machine? What quality of inert gas do you require? What typical amount are required. Will you need individual gas bottles or tanks? Will you need to store these gas bottles or will you need to install a tank near your buildings?
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What about the ancillaries such as recoating blades, filters units, sieving stations? Are they proprietary, expensive, easily accessible, customisable and/or included as part of optional packages?

​After sale and customer service

​That’s a big one. As much as everything should run smoothly, they won’t. And that will have a critical impact on your production yield, productivity and revenues. You want to know in advance how to deal with the worst-case scenario. What’s the typical response time? Is there a dedicated service, team member, phone number? What’s the quality and diligence of the service? Can you ask current customers? If you can, do so.

In the 3rd part, we'll have a look at the quality assurance and guarantees you may want to discuss with your provider. Stay tuned!

References
[1] M.M. Francois et al. Current Opinion in Solid State and Materials Science 21 (2017) 198–206
[2] T. DebRoy et al. Progress in Materials Science 92 (2018) 112–224