How LR Approaches Certification of Metal Parts Made by Additive Manufacturing

A question commonly asked by our clients is about our approach to the certification of parts made by additive manufacturing. They want to know how that certification is different from more traditional certification requirements. This question is becoming increasingly relevant as additive manufacturing (AM) is growing in attractiveness for many manufacturers.

The current state of standards
Currently there are a few broad standards for AM published by ISO/ASTM, and some detailed standards being jointly developed by ISO and ASTM (with collaboration from Lloyd’s Register’s technical team) – but these don’t yet close the gap between well-established processes (e.g. forging, casting, etc.) and a relatively new technique like AM. In January 2016, our team took a key step forward in closing the gap by producing the first edition of the LR and TWI Guidance Notes for Additive Manufacturing. This document helps outline the steps needed to achieve product certification.

How do we do it?
From research and practical work conducted in the LR TWI Joint Industry Project (JIP), Lloyd’s Register has mapped the requirements in each part of the process that affect the quality and certification of an AM component, from initial design through to final part. The process is more complicated than traditional certification projects due to the lack of AM-specific codes and standards.

Below we have listed some of control measures for each part of the process. Get in touch with LR to understand our full approach to certification.

Some of the major aspects
that affect quality and certification

Materials

Acceptance tolerances

Existing metallic materials standards have not yet expanded to include requirements for the additive manufacturing material form, and the required tests and acceptance tolerances for other material forms cannot be simply adopted due to differences in the resulting properties. Tailored test plans must therefore be carefully designed in order to prove the material suitability.

Design

  • File translation 
  • Support structure

The nature of AM as a layer-by-layer manufacturing method creates some key differences that a designer should be aware of and accommodate for, including:

  • Orientation and position relative to the build platform.
  • Designing support structures (which can affect the integrity of the building and removal of the part).
  • File translation from CAD through to an AM machine readable file.

Powder

  • Control of base characteristics and consistency between batches 
  • Storage and handling

Many of the base characteristics of the powder (e.g. chemical composition, apparent density, particle size distribution) need to be properly tested and controlled – not only when purchasing from a supplier, but also any variations that may occur between batches.

The storage and handling of the powder must also be controlled to an approved procedure (in a similar fashion to welding consumables). This is to avoid the contamination, physical damage, oxidation and ignition/explosion of the powder.

Facilities and Personnel

  • Personnel competence 
  • Powder and part handling 
  • Machine capability

Suitable facilities, including qualified equipment and procedures, must be in place. Personnel, including designers and machine operators, shallbe competent and use appropriate personal protective equipment (PPE) for powder and part handling and to complete other tasks in the process. This level of competence can be demonstrated through training records and experience.
The machine must be qualified (benchmarking exercise) to confirm satisfactory performance.

Build Process

  • Laser power 
  • Speed 
  • Environment

 Reliable build parameters must be determined to produce repeatable parts. Testing of the part and associated test pieces, followed by statistical analysis of the results, shall confirm reliability of the build parameters in producing acceptable and repeatable parts.

Post Processing

  • Removal of supports 
  • Surface finish 
  • Heat treatment

Suitable post processing operations must be defined in order to achieve the required part as it is unlikely that the as-built part will meet the application requirements. Control of these processes must be demonstrated in addition to consistency within the final part and associated test pieces.

Testing

  • Tensile strength 
  • Hardness 
  • Geometrics

The printed test pieces must be built in such a way as to provide test specimens that will accurately represent the characteristics of the final component, without affecting the properties of the build. All testing is carried out after post-processing.

Non-destructive testing (and destructive tests, where required) shall confirm the part and test pieces are free from defects. Where possible, existing standards and techniques are used.

The material properties of the final part are to be confirmed through recognised mechanical and metallurgical testing. Also, the geometry of the final part must be confirmed to be within acceptable tolerance when compared to the original 3D build model. The acceptance of test results is determined from pre-defined criteria.

Certification

  • Third Party Assessment 
  • Accredited and/or Notified Body

This is where things are business as usual – Lloyd’s Register is an accredited Third Party Assurance organisation and Notified Body that awards certification worldwide against many codes,  standards and regulations. Your certification may include caveats to mitigate the risk of variations in the additive manufacturing supply chain (such as machine-specificity and design-specificity).

 

Note: This article was published August 2016, and is a goal-based approach to certification. For current and more detailed, please get in touch via additivemanufacturing@lr.org.