METAL ADDITIVE

  1. Introduction
  2. Advantages of metal AM
  3. A comparison of metal AM media
  4. Common metal AM considerations

INTRODUCTION

Industry watchers know that metal 3D printing has seen a meteoric rise in profile. Hardly a day ends without a newsfeed hit about one industry leader or another announcing how it has achieved a performance or cost advantage through the production of redesigned or produced parts using AM, and about how it is reshaping our future.

Why is metal AM so popular? 

ADVANTAGES OF METAL AM

The net benefit of its use is becoming increasingly evident. One of the most touted benefits of additive manufacturing is design freedom. Whether your organization can benefit from a conformal cooling mold, a crystal lattice structure for an orthopedic implant, or an optimized aileron brace, AM can not only upgrade your end product but also redefine how that product is created.

If you haven’t already, check out our AM Basics page,

The above page goes into more detail; however, to recap quickly, benefits of additive manufacturing include:

  • RAPID PROTOTYPING: One of the most well documented benefits of AM, additive manufacturing facilitates and removes many of the costs associated with the production of a high fidelity prototype by cutting out many of the additional steps involved in more historical methods.

  • GREATER DESIGN COMPLEXITY: Since components are constructed one layer at a time, traditional manufacturing restrictions and design requirements like draft angles, undercuts and tool access typically do not apply to additive manufacturing.

  • SUPPLY CHAIN MANAGEMENT: In much the same way as additive shortcuts the production of prototypes, AM adopters can rethink and shorten their supply chain to reduce reliance on 3rd parties and shorten lead times.

  • REDUCED ASSEMBLY REQUIREMENTS: Redesigned parts can simplify assembly by removing fasteners like flanges or hinges, both reducing labor requirements and the net weight of the final component

  • REDUCED WASTE: Even when accounting for possible support structures, 3D printed parts produce less waste than traditional methods like CNC milling that can result in 50% or more material weight.

  • CONTROL OVER INTELLECTUAL PROPERTY: Implicit in the capacity to manage an organization’s supply chain is the ability to limit access to proprietary intellectual property.

  • GREATER CUSTOMIZATION: Changes to a design whether for iterative prototypes or to enhance end-user satisfaction can be produced without incurring capital and set up costs associated with traditional methods.

  • REDUCED INVENTORY RELIANCE: Approved designs can be produced on demand rather than require an exhaustive and capital intensive inventory process.

  • NETWORKED DIGITAL PRODUCTION AND INVENTORY: Approved designs can be stored as digital files that can be forwarded to producers as needed for production.

A COMPARISON OF METAL AM MEDIA

Several metal 3D printing media are available and although there are commonalities among them, each process will yield somewhat different results. We will focus here on explaining and contrasting three of the more popular metal printing media: Selective Laster Melting (SLM), Directed Energy Deposition (DED) and Binder Jetting (BDJ). i3D is available to consult with your organization regarding implementation of any of these technologies.

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If the processes’ differs in the ‘how’, it they also differ in the final product. See the chart below outlining some of the mechanical properties of a commonplace stainless steel: 316L. Printing it using the different 3D printing processes illustrates the comparative results that can be achieved.

[table id=30 /]

  1. Information provided by EPlus
  2. Information provided by Prima Manufacturing
  3. Information provided by Exone

COMMON METAL AM CONSIDERATIONS

For all the advantages offered by metal AM, it is not without challenges, as different variables are in play when 3D printing using metal than plastic. Here is a shortlist of some of the more common considerations.

  • DENSITY:  Industrial applications of metal 3D printed parts typically require consistent and projectable mechanical properties. This punctuates the importance of density as when a part operates under cyclic stress conditions, metal density will determine whether or not the part will fail under load.  In other words, the lower the density of a part, the more likely it is to crack under pressure.

    Some of the factors that affect density include:
    • Porosity:  This adversely affects part density. The more porous a part, the less dense.  Porosity is influenced by the type of 3D printing media being used, the powder atomization process itself, and the degree of heat used to melt the metal.  Powder-bed technologies like SLM and DMLS and EBM can produce parts with densities of 98% and higher; this is crucial for stressful applications.
    • Flowability:  Flowability essentially refers to the supply of raw material used in the 3D printing process.  On a micro-scale, many features that affect material flowability, such as particle size and particle surface morphology.
    • Processes: Different 3D printing processes can result in different part densities.  Current SLM and DED technologies can produce parts that have densities in excess of 98% without post processing.  BDJ can achieve those levels with binder removal and heat treatments.  In addition, post processing steps like hot isostatic pressing (HIP) can be used to enhance part density to 100%.

Stress induced cracking, courtesy of the Swanson School of Engineering at the University of Pittsburg
  • RESIDUAL STRESS:  Sometimes referred to as thermal stress, residual stresses play a role in most conventional AM media. This can have a detrimental impact on the integrity of a part and can be especially acute in metal.  For example, consider the melting point for stainless 316L: between 2,500 and 2,550 °F (1,371 to 1,399 °C).   Using a laser to create a small point of heat to melt stainless at temperatures of between 2500 and 2550 °F (1371 to 1399°C ) is fine, but as the laser moves along, it is important to consider what happens to the residual heat as the metal cools down and the component solidifies. The highest concentration of residual stress will be found at the contact area between the bottom of a printed part and a print bed.
    • Predictive modelling can be used to estimate the appropriate parameters such as heat input and layer thickness in order to build components with low residual stress.  
    • Including support structures and optimizing part orientation can also minimize the occurrence of residual stress.
    • Preheating the print bed and build material before the printing begins reduces temperature gradients (and therefore lowers residual stress). However, since EBM operates at a lower temperature, this technique will be more successful with EBM than with SLM or DED.
    • In powder bed fusion processes, the “island” scanning strategy can help to mitigate the build-up of residual stresses. The exposure area is divided into smaller sections, (the “islands”), to reduce the length of scan vectors. 
  • POST PROCESSING: Metal parts are not ready for their final applications when they are first printed. Post-processing in one form or another will be required in order to achieve an end product. (E.g. powder & supports removal, thermal treatments, surface finish). However, post-processing can involve certain challenges:
    • For example, the operator will need to be careful when removing the support structures, particularly if the metal part has supports in small holes and tubes. These can be difficult to remove without damaging the part and sometimes subsequent machining is needed.
    • Surface roughness is another issue.  Additive-manufactured components for high end applications require an average surface roughness. Because 3D printed parts are often produced with rough surfaces they may require machining, grinding or polishing to achieve the desired finish. (Surface roughness can be mitigated by printing thinner layers. However, such finer layers can significantly increase build time.)
    • Rough surfaces can also result from improper powder melting. This occurs when not enough energy has been applied to melt the metal completely. In this case, surface roughness can be reduced by increasing the power of your laser.

Would your organization like to explore whether metal additive could augment or streamline your operations? Contact us.

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