Tech Focus: Additive Manufacturing Metal AM for mould and die: What is the status?
The advantages of metal 3D printing for the mould and die world have been known for several years.
While the benefits of metal AM are well documented and have been presented multiple times, its widespread adoption remains slow. This is most likely due to initial concerns about material properties, a lack of understanding on the specific costs related to the technology, but even more important, a lack of expertise in how to apply the technology and integrate it in the factory. This is especially true in a market segment which is often seen as quite risk-averse and conservative.
It is also important to emphasise that mould makers are generally under tremendous pressure from their customers to manufacture moulds at the lowest prices. Further, while it is correct that 3D-printed inserts can offer tremendous gains in term of lead-time, quality, and productivity, they also often lead to additional manufacturing costs per 3D-printed insert. Therefore, the value of the additional investment must be precisely calculated and demonstrated to the end customer.
Another last factor limiting the adoption of the technology lies in the lack of solutions for its seamless integration into conventional production lines. On that specific topic is market players’ strong expectation for supports in terms of both optimised products and expertise from their AM partner. GF Machining Solutions has targeted this barrier in order to support and convince the market of the great advantages of AM technology while working to eliminate the challenges. In fact, the GF Division has years of AM expertise and has developed a complete solution — from software to final machining — for mould makers.
The laser powder bed fusion process (LPBF): How does it work?
There are a number of different metal additive technologies, however tooling mainly makes use of LPBF. This process works by applying incremental layers of metal powder which are subsequently melted by a laser beam. The end part is be achieved after the scanning of hundreds if not thousands of powder layers. The powder around the part is then removed, revealing the printed part.
Metal 3D-printed inserts: What are the current challenges?
Tooling applications are often classified as simple AM applications mainly because the needs in terms of documentation and certification are much lower than those for aerospace or medical implant production, for example.
However, the requirements, particularly in terms of surface finish of the end mould, are of utmost importance as they will dictate the aspect of the final injected part. For this reason, it is critical when printing mould inserts to have a very stable printing process in order to produce the high-density parts that enable perfect surface finish after post- machining. These requirements are some of the most challenging to achieve in 3D printing, especially for bulky mould components produced by scanning large sections of material.
Another challenge for tooling applications is linked to the materials that can be processed by AM. Materials commonly used in mould and die that achieve their hardened state through quenching are, for the most part, not adapted to AM due to their poor welding properties; LPBF is, in essence, a welding process. This has led to the use of steels which are not normally used in mould and die but that can meet the needs of tooling; the most common one being Maraging steel.
Research on new materials is being carried out by powder suppliers in order to cover the specific needs of tooling (hardness, corrosion resistance, etc.) while still being printable with high quality.
While many players are already reaping the benefits of efficiency gains from conformal cooling, the economic viability of many other applications requires other approaches, especially for parts requiring large amounts of material. The latter are often more expensive to manufacture, since the AM price is intrinsically linked to the volume of material to be printed. To overcome these challenges and find ways to cost-effectively integrate this new technology into their operations, manufacturers can optimise the manufacturing of these inserts by pre-machining a "preform" and then using AM technology to produce a part for which the characteristics are the most complex. This combination of subtractive and additive technologies results in what are now commonly called “hybrid parts.” On this subject, GF Machining Solutions and its partner 3D Systems have developed a unique approach that enables printing with great precision on the preform in an automated manner.
Another advantage in the creation of hybrid parts is the elimination of the need to separate the printed part from the printing plate, with a wire-cutting EDM machine for example.
Finally, as described in the introduction, one of the biggest challenges in using this technology is its integration into well-established and mature manufacturing processes. This is all the more costly as, in the mould making segment, additively manufactured inserts require — almost necessarily — post-process steps with additional subtractive machining operations. This is necessary to achieve the very high surface quality required on the mould surface. Therefore, it is important to offer not only software suites that take into account all the manufacturing stages, but also solutions (3D printers, materials, subtractive technologies like GF Machining Solutions’ AgieCharmilles Cut AM 500, automation solutions, and clamping) allowing, when combined, comprise an efficient ecosystem that reduces costs and complexity. This is GF Machining Solutions’ daily target.
Metal AM for mould and die: Why does it make so much sense?
Many promotional efforts and case studies in the last few years have focused on the advantages that conformal cooling channels bring, including reducing the cycle time of injection moulding. Today, there is a common understanding that optimised designs enabled by AM unlock the potential to compress the cooling time, which in most cases represents the lion's share of the cycle time. However, it important to emphasise that this is not the only advantage of improved cooling.
Quality of a plastic part and particularly its propensity to distort are closely linked to homogeneous cooling and elimination of hotspots. The primary goal when designing conformal cooling channels is to achieve a constant temperature gradient and therefore avoid uneven shrinkage. This allows for a more repeatable process and more predictable distortion of parts after the injection process while also reducing the need for the mechanical tooling adjustments often required to compensate for deformation. Removing the need for the mechanical adjustments that are typical in the development phase, thereby reducing prototyping iterations and accelerating the time to market.
Although the use of conformal cooling channels has often been demonstrated for plastic injection moulding and the vast majority of the technology's users are in this field, over the past couple of years an extremely strong interest has emerged from companies actives in high-pressure die casting, where AM’s benefits can be even greater than for plastic parts, especially with regard to easier maintenance and die lifetime.
Less well-established and discussed than plastic injection, improved cooling in these applications has been a big driver to reduce the need for spraying.
Spraying in high-pressure die casting is done with two main goals: lubrication for improved unmoulding and the fact that the spraying medium serves cooling purposes. The trend in the industry is to try to reduce and/or eliminate this spraying phase which leads to more rapid degradation of the mould.
In this case, the conformal cooling designs are used in order to reduce the need for spraying, increase the tool lifetime, and maintain the quality of the cast part, the surface quality of which normally degrades together with that of the mould.
Whether in plastic injection or high-pressure die-casting, conformal cooling designs and AM often result in mould design simplification. In particular, the number of components to be assembled can be reduced (referred to as assembly consolidation), removing or reducing the need for seals. All injection shops have witnessed the consequences of seal failure and know all too well the associated downtime linked to a cooling leakage, whether it be water or, even worse, oil.
It is true that the world of mould and die is not the one where the AM adoption is the most prevalent. The biggest buyers of metal 3D-printing machines are in the aerospace, medical, and automotive industries. But it is important to note that, within plastic injection and high-pressure die casting companies using the technology, they consider it as mature. Indeed, metal AM inserts are no longer only for prototyping departments but are used in the production environment.
Nevertheless, investment decisions in these industrial segments are long and are based on thorough thinking. This is why GF Machining Solutions develops solutions that improve the metal AM ecosystem and supports its customers with a solid technical expertise.
As a conclusion, it is noteworthy to say that companies that have thought carefully before investing in and acquiring a 3D metal printer have quickly benefited from a return on investment and have continuously discovered new applications for the technology. But it also true, that the companies that fully understand the value of AM are often those that produce both plastic part and injection moulds.