Enhanced procedures for quality control in additive manufacturing

Paul Boughton

Additive manufacturing (AM), or 3D printing, is used for rapid production of prototypes, usually in one-offs or small quantities, and increasingly for series manufacture of functional components. Quick time-to-market and a need for manufacturing flexibility are important, and so also is reproducible part quality.

Determining and specifying parameters when using layer-by-layer laser sintering can be complex and time-consuming. To simplify the process, German AM system manufacturer, EOS, has introduced ExposureEditor and start values for its entire material portfolio, allowing parameter sets to be adjusted.

It offers an editing function for optimising the parameter values in the exposure settings, which can then be run on EOSINT plastic or metal laser sintering machines. Factors taken into account include surface quality, mechanical attributes, accuracy, detail resolution and cost targets.

ExposureEditor enables a high level of flexibility and openness so that users can meet their specific requirements and implement customised optimisations. Only process-critical parameters are protected. It is noteworthy that EOS is the first AM technology supplier to provide parameter values for the vertical, Z direction as well as in X and Y.

Customers are granted additional freedoms through EOS custom parameter sets, which allow for tailor-made solutions, based on a user's specifications. The customer's intellectual property is protected through a licensing model that allows use and payments to be controlled.

The latest EOSINT P 7xx and EOSINT P 3xx series systems can be upgraded with significantly improved process modules to optimally support the so-called part property profile (PPP) strategy.

FlashRecoating, available for the EOSINT P 760, is a new X-axis control which further increases productivity by accelerating the recoating speed up to 400 mm/s when TopSpeed and Speed parameter sets are used. Build volumes up to 700 cm³/h are achievable. The recoating unit in the EOSINT P 395 has also been improved. The introduction of PPPs has led to the integration into the EOSINT P 395 of EOS’ successful blade cartridge concept, first introduced in the EOSINT P 730, making it simple to carry out adjustments and change the layer thickness.

The five EOS parameter sets for plastic laser sintering AM applications correspond to five different PPPs. They focus on either cost or quality requirements, or carefully balanced compromises.

TopSpeed is a parameter set using 180μm layer thickness for parts with medium to high quality and mechanical load requirements as well as high cost pressure. It is well suited for parts where top productivity is a priority. Large and relatively thick walled components can usually benefit from the fast build-up rates at this layer thickness. In comparison to today’s usual 120 μm layers, production costs are typically 15 to 20 per cent lower. This layer thickness also enables high levels of accuracy, making it ideal for parts sensitive to warpage.

Speed applies a layer thickness of 150μm, which is popular due to the universal qualities it imparts to components. This parameter set offers slightly higher surface quality than TopSpeed and typically lowers production costs by 10 to 15 per cent in comparison with the 120 μm standard.

Balance. The advantage of this parameter set, based on a120 μm layer thickness, is that it balances production costs, mechanical properties, surface quality and accuracy. It is suitable for parts with varying geometries, dimensions and requirements.

Performance is the parameter set of choice for parts with demanding mechanical properties and fracture behaviour, especially when the part will be subjected to multi-axial loading in all three directions. Performance parts are characterised by a high degree of isotropic strength and rigidity. The choice of 100 μm layer thickness results in fine resolution and also very high surface quality and detail resolution.

TopQuality. This parameter set takes AM to a new level. Very small to medium sized parts with extremely fine, fragile geometries and the strictest requirements in terms of surface quality are best served using these parameters. The 60 μm layer is approximately the thickness of a grain of the plastic powder normally used today, significantly reducing the typical stepped effect on near-vertical geometric elements.

EOS parameter sets are also available for direct metal laser sintering on EOSINT M 270 dual mode and EOSINT M 280 systems. Parts produced are dense and the mechanical and thermal properties are almost identical to those of the solid material.

Each metal is assigned one or more parameter sets with corresponding PPPs which typically include geometric properties such as minimum wall thickness and surface roughness; mechanical properties such as tensile strength, yield strength, elongation at break, modulus of elasticity, hardness and, where applicable, dynamic fatigue life; thermal attributes such as thermal conductivity, specific heat capacity and thermal expansion coefficient, and properties affecting cost such as build-up rates in  mm³/s

The three EOS parameter sets for metal laser sintering AM applications are:

Speed, with 30-60μm layer thickness for high productivity and good surface quality. It represents a good compromise between build speed and surface quality.

Performance, with a 30-40μm layer thickness, is suitable when the focus is on surface finish, yet offers higher productivity than parameter sets involving thinner layers, helping to reduce production costs.

Surface. A 20μm layer is the lowest thickness and is ideal for parts that require fine and high detail resolution and best surface quality.

Advantages of the EOS categorisation system are evident throughout the entire process of bringing a new product to market, be it of metal or plastic. The designer can access standardised property profiles at any time as well as the corresponding material values relevant for dimensioning. Purchasing and sales staff benefit from clearly defined quality levels, making quotes consistent and more efficient and eliminating expensive misunderstandings.

From the manufacturer’s point of view, PPPs increase efficiency and reduce costs for data preparation and production planning. Finally, the quality assurance department benefits from defined standards and improved transparency, which is important both in prototyping and series manufacture. Three software modules within EOSTATE 1.2 (Quality Assurance, Controlling, and Machine Park Management) provide various reports to meet customer requirements with regard to quality assurance and documentation.

For more information, visit www.eos.info

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