Additive full cycle production at an aviation enterprise is a matter for the near future

SLM Solutions (Germany) is one of the world's leading manufacturers of industrial 3D printers using the technology of selective laser melting . In February 2016, an SLM office was opened in Moscow. We spoke with Pavel Ladnov, a leading technical expert at SLM Solutions RUS. The conversation touched upon the introduction of additive technologies in domestic aerospace enterprises, as well as solutions offered by SLM Solutions.

- If we are talking about 3D technologies, what are the challenges facing aerospace enterprises, what problems are most relevant for them?

- First, this is the problem of certification of the production process on the basis of additive technologies. Secondly, the lack of experience in working with difficult titanium and nickel alloys on the installations of selective laser melting (SLP). And finally, the absence of powder compositions, aluminum and magnesium alloys widely used in our country, steels, etc.
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- Please tell us about the solutions offered by SLM Solutions.

- Our company represents a wide range of various equipment options and configurations, allowing to fully satisfy all customer requirements. In the SLM 280HL and SLM 500HL models, multi-laser systems with a power of 700 W of each laser are used - this is interesting just for aviation topics . This option provides (for example, on a SLM 280HL installation) an increase in productivity of up to 30 percent on aluminum alloys compared to a similar installation, but with two 400 W lasers. To solve the problems associated with the certification of parts manufacturing technology, systems of monitoring the working real laser power and the system for monitoring the emission of thermal radiation from the molten bath are optionally installed on the company's equipment. It should be noted that the quality control system of the deposited and fused layer and the system of streaming log files of the installation operation process are included in the basic equipment. SLM Solutions is also constantly working to expand the range of metal powders supplied by the company.



- What are the specifics of the use of 3D technology in the aerospace industry?

- First of all, this is a strict certification procedure. The quality of the part obtained by selective laser melting is determined by four main factors.

1. Quality 3D printer.

Provided by: carrying out and analyzing test work before shipment of equipment to the client, and then on the client’s territory after installing the equipment, and regulating calibration and maintenance procedures.

2. The quality of the process of building parts.

Provided by: the regulation of process parameters and equipment settings.

3. Quality of work with the equipment.

Provided by: regulation of procedures for working with equipment and the external conditions of the premises for the operation of equipment; level of training of operators of additive installation.

4. The quality of the material used.

Provided by: input control and testing of the material, regulation of procedures for storage, transportation, work with the material.

Based on this, one can imagine how time-consuming the certification process for all these four parameters can be to obtain a certified part.

Another important feature of the application of selective laser melting technology, in the aerospace sector in particular, is the work with technologically difficult materials such as alloys of titanium and nickel. These alloys are prone to the formation of residual stresses, leading to distortion of parts and even cracks.

The geometry of aerospace parts is sometimes replete with thin walls, complex complex shapes, and cellular structures, while the standard parameters for the material provided by the manufacturer of the equipment refer to the “average” part, which is not too large and not too thin-walled. There is an obvious need to pre-work out the parameters of the construction process, not only for the material in general, but also for parts with a characteristic geometry. Failure to understand this feature sometimes confuses people who believe that a 3D printer should produce high-quality parts by pressing the Start button without any preliminary work on the process.



- At what level is it possible to use additive technologies in aviation - laboratory tests, the manufacture of individual parts, small-scale production or high-grade additive production in the chain of the overall technological process in an enterprise?

- Additive technologies in aviation make it possible to drastically reduce the Buy-to-Fly ratio, that is, the ratio between the amount of material purchased and the amount of material in the finished part that “flies”. They also make it possible to achieve previously unattainable functionality of individual parts and components, to make lightweight and durable parts, thereby increasing the payload of the aircraft. However, as I have already said, serious issues related to certification and ensuring the stability of the production process remain unresolved.

SLM Solutions has a large portfolio of customers from the aviation industry. All of them first tested the parts in the laboratory, after which some customers were able to apply 3D technologies for the manufacture of single and small-scale parts. Additive full cycle production at an aviation enterprise is a matter for the near future.

- Is the SLM equipment the final solution? Or do you need separate software for preparing for printing, for post-processing, etc.? What advice do you have for customers?

- Equipment of the SLM company is first of all a tool, a combine, if you will, for solving various production problems in the field of 3D printing with metals. You can draw an analogy with the software Photoshop, which has a huge number of settings options and use cases, and each user chooses exactly what he needs to solve a particular problem. Yes, definitely, SLM equipment is Photoshop on the market for selective laser melting machines.

Depending on the task, the tool can be either a final or intermediate solution. Of course, problems related to the design of parts, topological optimization and generative design require the use of third-party software to obtain the final original model details. Preparation of parts for printing is carried out using the software supplied with the equipment and the postprocessor; no additional software is required.

Due to the characteristics of the selective laser melting process, parts made of materials such as nickel, titanium alloys, tool steels may require additional heat treatment or HIP processing.

The process of selective laser melting cannot be attributed to high-precision processes, and the surface quality of parts is comparable to casting on burned and smelted models . Therefore, the structural elements of parts with higher requirements for roughness and flatness of the surface must be subjected to subsequent finishing machining.



- What is the technical superiority of SLM Solutions?

“The main advantage of SLM Solutions equipment is the highest performance in its class due to the patented multi-laser system, the use of 700-watt lasers and the application of layers in two directions.

Other advantages include an open system of equipment parameter settings, ease of maintenance, a powerful postprocessor and the availability of systems for monitoring the parameters of the construction process with the ability to store data, a wide range of plant configurations and peripheral equipment.



- What metal powders are used for 3D printing? Can metal powders from other manufacturers be used in SLM 3D printers?

- Installations SLM Solutions are adapted to work with almost all materials. The range of metal powders of the company includes not only alloys widely used in the SLP process, such as TiAl6V4, 316L, IN718, AlSi10Mg, but also quite rare in the market for 3D printing services, such as Invar36 with a low coefficient of linear thermal expansion and tin bronze CuSn10 .

In general, powders for an SLP process are obtained by gas or plasma atomization. An important condition is the spherical shape of the particles and the absence of satellites. From the point of view of work, the SLP installations impose the most stringent requirements on the fluidity of the powder. To achieve good fluidity allows both spherical shape of particles, and a certain fractional composition. In general, powders for an SLP process have a particle size in the range of 10–63 μm and a unimodal distribution.

- What can you say about the quality of Russian-made powders (if they are already on the market)?

- It is difficult for me to judge the quality of Russian powders, since I did not specifically deal with this topic. However, I want to note that we have customers who use domestic powders and, in principle, provide the necessary quality of parts. Sometimes the problem is not so much in the powder as in the correct work to optimize the parameters of the construction process for a particular material. The key condition for the possibility of using powder on SLM Solutions installations is good fluidity of the powder, and the rest can be worked on.

- Let's talk about the prospects of developing in your company new technologies, equipment and materials for solving problems in the aerospace industry.

- First of all, SLM Solutions, as a manufacturer of equipment, seeks to improve the design of plants for PSL, to make them more convenient and productive. Work is underway to improve the monitoring systems of the building process - this is important just for the certification of technology in aviation - and the improvement of peripheral equipment. Another area of ​​work is related to the development of the parameters of the PSL process for new groups of alloys - the expansion of the range of powders used. SLP technology is very flexible and variable, there are many promising areas.



- What else could you share with the readers of our blog?

- I would like to say such an important thing. Of course, for the additive technology of the future, but do not take them as a panacea, a universal method of manufacturing parts. Journalists sometimes like to greatly exaggerate existing opportunities, but engineers need to understand: each method has its own limitations in terms of applicability - technological, economic, technical, and others.

Selective laser melting, indeed, allows you to look beyond the usual approach to the design of parts, offers certain advantages, but they are realized only when the user of the technology understands the limits of its applicability - by materials, design, economics of the production process.

3D printing should be taken as another variant of the technology for producing products along with mechanical and plastic processing, casting, welding. When selecting options for the production process, carefully weigh all the pros and cons.