Light shaping diffusers are optical components that alter the illumination pattern of the beam propagated through them to a desired intensity distribution of the light. This article presents some innovative approaches to additive manufacturing which utilize the advantages of laser beam shaping
Additive manufacturing in a nutshell
Additive Manufacturing (AM) refers to a variety of techniques in which material layers are added on top of one another in a computer-controlled process, to form three-dimensional objects from a CAD or else way produced 3D model, as opposed to traditional “subtractive manufacturing” in which material is typically being removed.
AM processing approach presents some inherent advantages over the traditional methods by enabling the manufacture of lighter and stronger parts and systems. Along with the growing process precision in recent years, AM has become a valuable production approach in many different industrial fields including the food industry, aerospace, automotive, healthcare, and many more.
Other related terms to AM include “3D printing” and “rapid prototyping”, and present subsets of AM, typically referred to in home and product development applications using similar techniques.
There are many different technologies available today for performing the various AM processes, many of them are laser-based where the laser serves as the heating source to enable a selective fusion of materials, either to a melting or sintering state, where different technologies lead to different levels of in-layer material density and can also be appropriate for use with different materials.
Laser beam shaping using a light shaping diffuser
Light shaping diffusers are optical components that alter the illumination pattern of the beam propagated through them to a desired intensity distribution of the light, typically uniform and homogenic, whose design characteristics are determined by the process parameters.
There are various types of light shaping diffusers that are based on different optical concepts:
- A diffractive beam shaping diffuser, which alters the phase of the light in order to generate the desired radiance. The diffractive diffuser is characterized by high uniformity and sharp edges.
- A broadband diffuser, also known as engineered diffuser, is a refractive component much similar to a microlens array which is based on geaometrical optics, whose arrangement and lens heights determine the output shape and qualities. It is characterized by high uniformity and high efficiency.
- A broadband hybrid diffuser, which combines both diffractive and refractive qualities in its design, produces a high-efficiency, high-uniformity sharp shape with distinctive borders. Holo/Or’s broadband diffusers are such hybrid elements.
Other methods for diffusing the light to a more homogenic intensity distribution compared to a standard Gaussian beam are also available, however the above-mentioned methods are the most common ones generating the best output parameters.
AM process optimization using a laser beam diffuser
Generally, different processes are optimized by using different irradiation patterns. Process parameters such as the technique used, input laser beam diameter, optical setup, powder material type and more, will all have an effect on the exact illumination pattern which will yield the best performance for the specific application.
In laser metal deposition (LMD) for example, comparative studies have shown improved process performance when using a ring-shaped beam generated with a light shaping diffuser over a Gaussian beam thanks to its uniform energy and small temperature gradient. Advantages were found in many performance indicators including smaller residual stress in the workpiece, reduction of heat accumulation, avoiding excessive sintering and dilution, refined grain size and improved surface quality of coating. This technology is widely used in industries such as automotive industry, aviation and aerospace, energy technology, petrochemicals, and medical technology.
In selective laser melting (SLM), studies showed that a ring shape with a central spot can improve the melt pool dynamics, resulting in a stabler melt pool compared to a simple, gaussian beam. This enables the elimination of internal stress fractures, allowing production of fully dense material at very high build rates.
