Die casting dies and 3D printing – a legal issue

As a forensic expert, I also deal with litigation in the field of the manufacturing and use of die casting dies. In this branch it can be assumed that the recommendations of Nadca 207 are guidelines for usual procedures, and nowadays, especially for the manufacturing of die casting dies for the automotive industry they can also be considered obligatory.

The fact that they are mandatory also follows from the fact that AIAG (Automotive Industry Action Group) has inserted it into CQI-27 Special Process: Casting System Assessment, Table H, Paragraphs H1.6 and H1.7, and therefore dies manufacturers should be able to prove that they proceeded in the manufacturing process of the die casting dies according to Nadca 207.

But all this applies to parts conventionally produced from forged steels, specified in Nadca 207. But how is it for parts produced by AM technologies, especially by the LB-PBF (Laser Beam Powder Bad Fusion) method?

Fig. 1 – Front page of Nadca 207, version 2018

Fig. 2 – Front page of CQI-27

Fig. 3 – Front page of publication Nadca 550

The Nord American Die Casting Association itself has attempted to take a stand on this in a new Nadca 550 publication, entitled “Tooling Certification for Die Casting Die Components Fabricated by Additive Manufacturing“. However, it is more of an assessment of the state of the art in the field of die-casting dies than a document with recommendations comparable to Nadca 207.

When making dies for die casting, we should adhere to the guidelines set out in publication No. 402 entitled “Nadca Product Specification Standard for Die Casting“. Here it is said that each part of the die casting die should be categorized according to the following criteria:

• According to functionality in the die
• According to the required service life

Fig. 4 – Front page of publication No. 402 “Nadca Product Specification Standard for Die Casting”  and die part coding tables from page 2-19.

But since Nadca 207 says that there are Class 1 and Class 2 categories of die parts, differing from each other in the way the material input and output quality is tested, then we have to add a third parameter to the coding of die casting dies. A Class 1 code means that input and output impact tests will be part of the die insert manufacturing, and their results will be in accordance with Nadca 207 recommendations. A Class 2 code says that these input and output impact tests are not performed, however the remaining input parameters steel grades must be respected.

Fig. 5 – Individual test steps for verifying the input quality of steel according to Nadca 207

This coding is important not only for the production of a new dies, and for ensuring the contractual terms of the purchase agreement between the tool manufacturer and the die-cast foundry, but also for recording the lifespan of individual parts in the foundry, including the registration of all costs related to their maintenance and renewal. As a result, the die design should take this form:

Fig. 6 – An example of coding parts in the die bill of materials  for its production and for the mold user

But what to prescribe for die parts manufactured by 3D printing, if we want to order a new die casting die with a minimum lifespan of 100,000 runs?

Currently, there is a minimum of information about the actual lifespan of die inserts produced by 3D printing. E.g. from Bohler published this chart to evaluate the life of die inserts printed from W722 AMPO/1.2709 powder steel, and compared this life to the H11/1.2343 ESR material.

Fig. 7 – Bohler presentation comparing bulk and powder steels heat-checking resistance

From this diagram it is clear that 3D printed die inserts made of W722 AMPO powder material will have a 1/3 of the service life of parts made of classically produced steel 1.2343 ESR. What does this imply? If we want to order a die casting die with contracted lifetime of 100,000 runs, we must contractually ensure that the specified die insert produced by 3D printing technology will be delivered in the amount of 3 pieces. So, the question is, is this really what we want?

Fig. 8 – Illustrative case of 3D printing of an insert to ensure a lifetime of 100,000 pcs

In order to deal with the legal question of what is usual procedure, we must first deal with its definition. In order for this definition to be used, the usual procedure should necessarily correspond to the highest achieved scientific knowledge, and at the same time, according to a fairly common consensus, either the general recognition of the procedure by the professional public or the submission of evidence of the effectiveness of such a procedure needed for the recognition of the usual procedure lege artis.

The situation with Nadca 207 developed in a similar way, when in the beginning it was only a recommendation for steel suppliers, toolmakers or pressure foundries, but these procedures were gradually recognized by the professional public, and this recognition was fulfilled by the implementation of Nadca 207 procedures into CQI-27.

But what about 3D printing? To deal with this term for AM technologies, we must first seek answers to the following questions:

1. What powder steels are suitable for die casting dies? Is it 1.2709, H13, AMPO W360, HEATVAR, DIEVAR, other? Which ones are NADCA approved?
2. If we already choose powder steel, is it described what the quality of this powder should be? Grain size, shape, statistical distribution, powder reuse? Is there any NADCA recommendation?
3. If we print a part from the selected powder steel, is the permissible porosity of the parts defined after 3D printing? And is it even economically possible to print parts with minimal porosity? Is there any NADCA regulation or recommendation for printing parameters?
4. Is a heated printing platform required for all types of martensitic steels? And if so, at what temperature? And if this temperature is above 200 C, is such a printer even available?
5. As with heat treatment, the vacuum furnace must be in a validated according to AMS 2750 G, is there any regulation that says how to validate the printers so that the results are reproducible?
6. If we already print part of the die, under what conditions can HIP (Hot Isostatic Pressing) be omitted and under what conditions must we apply it?
7. If we already print the part, is there a prescription for heat treatment and all other post-operations to maximize material resistance to thermal fatigue?
8. Is there a rule on how to test the print result? It can be assumed that we will need to perform reference impact tests on each printing platform to verify the printing. Do we have information on how to place these samples on the platform and in which direction so that they best represent the state after printing?

We do not know the answer to practically any of the previous questions, and the Nadca 550 publication does not answer these questions either. It is only stated here that today there are already a number of standards for 3D printing issued within the framework of ASTM, ISO, ASWE, AWS, but these standards are oriented towards the aerospace industry or for medical purposes, but none of them address the issue of 3D printing for high pressure die casting dies.

Fig. 9 – Citation of the text in the Nadca 550 publication

From the above, it follows that for the time being, there is no usual procedure for 3D printing of inserts for die-casting dies. What does exist, however, is the risk of hidden defects. The 3D printing technology itself is based on the fact that individual powder grains are fused with an electron (EB-PBF) or laser beam (LB-PBF). The result of this process is a material structure containing pores.

E.g. it follows from the Quintus presentation that even if we print with a high print density, there will still be a significant amount of micron or submicron-sized pores inside the material.

Fig. 10 – Quintus presentation, 6^th of October2022, webinar on “HIP for PVD sputtering targets”

However, each of these pores can be the source of a hidden defect, with a direct impact on the service life of the part. If we project this into a legal expression, the person who manufactures and supplies the tool is responsible for ensuring that the contractual conditions are observed, i.e. for example the lifetime of the tool for 100,000 runs, and at the same time is responsible for hidden defects for a period of 2 years (according to the Czech Civil Code,  §2618).

However, since 3D printed parts are always porous from the principle of the method, there will practically always be a risk of hidden defects with the possibility of claiming product defects, including consequential compensation for damages. Therefore, in my opinion, it is necessary to specify 3D printed parts for high pressure die casting dies as critical parts, and proceed accordingly in their production.

In terms of principle, the die inserts produced in this way can be compared to critical parts for aircraft engines. These are primarily combustion turbine blades. Today, these are produced by the investment casting method, but also recently by 3D printing. Because, despite the perfection of the production methods, there is a certain risk of hidden defects that are also difficult to detect, the parts must mandatory undergo HIP (Hot Isostatic Pressing) technology and subsequent heat treatment processes.

Fig. 11 – Process workflow for investment casting or 3D printing aircraft turbine blades

The reason is not that we would not be able to cast or print perfectly, with maximum density, without visible defects, but mainly because there can be untreated random hidden defects inside the casting or 3D printed part.

Therefore, if we look at parts for die casting die inserts as critical parts, where we want to ensure the same service life as parts produced classically according to Nadca 207, the application of HIP technology must be mandatory.

Conclusion

• If the insert from 3D printing does not reach the contractual service life, then this is a breach of contract
• In order for the contractor (tool shop) to avoid possible fault, he must prove that he followed the usual procedures and that the object of the work had no hidden defects at the time of delivery
• Since the usual procedures do not exist, and the 3D printed part will always have hidden defects, especially if we do not apply HIP, the customer (foundry) is very likely to assert his rights successfully in terms of product hidden defects, except for the case when in the purchase contract for new tool, one of the contracting parties waives its rights in terms of claims arising from hidden defects from 3D printing, and within two years of handing over the die casting die insert or part

December 11, 2022

Jiří Stanislav