Potential customers often ask how our technology produces complicated geometries with little to no supports, so for this article, we’re pulling back the curtain a little to explain how we accomplish this feat with our unique non-contact recoater technology.
We will also provide a high-level overview of the laser powder bed fusion (LPBF) metal additive manufacturing (AM) process, explain how conventional metal AM systems are limited in their ability to successfully print complex geometric features, and dive into the Velo3D approach, which allows for true design freedom when printing parts with our fully integrated metal additive manufacturing solution.
A story of layers: the conventional path to LPBF
Powder bed-based metal-additive manufacturing works on the principle that a solid geometry is built up layer by layer from finely atomized powder. Each layer is created by spreading a thin, homogenous (uniformly thick and consistently packed) amount of powder across the bed with a typical layer height of 20 – 100 µm.
In conventional powder bed AM systems, a layer is created by removing excessive amounts of powder in front of a recoater blade and dragging the blade across the powder bed where the clearance between the blade and bed is defined by the desired layer thickness.
A focused heat source then melts the powder particles together to form a solid layer.
By scanning the cross-section of the desired part geometry at a specific height, the scanning area is outlined. Once the current slice is scanned entirely, the powder bed is lowered by the specified layer thickness and the process repeats, starting with a fresh layer of powder.
In LPBF, at least one CNC-controlled laser beam creates the required heat energy. The galvanometer-actuated mirrors, which steer the laser, can tilt in a very dynamic and precise fashion. The focusing and defocusing of the laser beam on top of the powder bed is achieved through a set of lenses: a stationary object lens and a moving focusing lens.
To create and maintain a fully liquid phase within the rapidly moving (up to 3000 mm/sec) melt pool, high heat input and liquefication, followed by rapid cooling rates and solidification, can induce large amounts of residual stress within the resulting part geometry.
While bulky, non-overhanging geometry has a high bending stiffness and can withstand the residual stress without excessive warping, thin, overhanging geometry tends to warp upwards and can protrude into the next layer.
If this protrusion is greater than the specified layer-thickness, a collision between the solidified material and the blade is inevitable when recoating the next layer. Naturally, a collision like this can result in a catastrophic and non-recoverable build-failure.
Designing around the limitations of conventional systems
Working around the physics of LPBF, conventional processes utilize strategies that either adjust part design to avoid complex, low-overhanging geometric features altogether or introducing anchor geometry to counteract warpage and protrusion (support structures).
This approach is questionable, and undesirable, when the underlying business case requires a design that is highly optimized to perform a certain way, such as controlling fluid with maximum efficiency.
Introducing additional design constraints often compromise part performance (sacrificing optimized designs), increase manufacturing cost (adding more material, complicate post-processing), or even prohibit manufacturability altogether.
In many cases this will disqualify LPBF as a viable means of manufacturing.
The advantages of a contact-free recoater blade
Velo3D’s proprietary contact-free recoating process introduces a new level of process robustness and manufacturing capability by increasing the clearance between the recoater blade and the powder bed to a multiple of the specified layer thickness while still achieving a thin, homogenous “working layer (50 µm)” after each recoat.
The contact-free recoater consists of three components that work in parallel during a recoating stroke. The leading component is a powder dispenser, which lays down a thick layer of powder. Trailing the dispenser is a recoating blade that creates a uniform layer. The final layer thickness of 50 µm is created by removing excessive powder from the blade layer via a proprietary vacuum process.
Watch the short video of the recoater process below:
There are several technical advantages of using a contact-free recoater.
The additional recoating-clearance allows for some level of part-protrusion, which increases the manufacturability of low-angle overhanging geometry (in some cases down to 0° relative to the horizontal) by significantly reducing or eliminating anchor-geometry without surface-breakdown.
Using a contact-free recoater also allows for “high aspect ratio features”, such as thin walls/pins. The large clearance between the doctor blade and the powder bed reduces the magnitude of shearing forces exerted during the recoating process. This makes the resulting shearing forces too weak to deflect, deform, or even break delicate, free-standing geometry.
The last advantage that the contact free recoater offers, is an expansion of the known LPBF-processing window by enabling new ways to scan and supply powder within each layer, thus further pushing the limits of design limitations.
Velo3D’s contact-free recoater process helps free engineers from the constraints of conventional LPBF rules by allowing them to evade traditional AM design limitations. These limitations hinder innovation through restrictive design for additive manufacturing (DfAM) rules, which prioritize manufacturability over optimization.
With the Velo3D fully integrated metal additive manufacturing solution, the focus is instead on maximizing part performance; not design compromises to achieve manufacturability.
Interested in learning more about Velo3D metal AM? Get in touch with our team of experts today.
Author
Michael Harsch – Technical Sales Engineer – Velo3D
