Kamran Mumtaz

• BEng (Hons) MSc PhD
• Professor at The University of Sheffield

This study investigates the use of Diode Area Melting (DAM) to process 316L stainless steel (SS316L), an alternative to Laser Powder Bed Fusion (LPBF), utilising independently addressable, low-power (~ 3.5 W) 450 nm blue lasers to address key limitations of LPBF, including thermal control, scalability, and efficiency. A normalised energy density (N...

Laser powder bed fusion (L-PBF) presents a promising technique for producing neodymium–iron–boron (NdFeB) magnets. However, the magnetic properties of L-PBF-generated magnets remain inferior to those of their sintered counterparts. To address this, post-processing techniques, such as heat treatment, could enhance the magnetic properties of L-PBF-fa...

Laser Powder Bed Fusion (LPBF) is a commonly used Additive Manufacturing (AM) method for the production of geometrically complex metal components that are used in high-value sectors. It uses high power fibre lasers directed by a galvanometric scanner to rapidly melt powdered feedstock. LPBF systems are expensive, making them inaccessible to many se...

Diode Area Melting (DAM) is a novel additive manufacturing technology that contains low optical power (~3.5W) output and lower wavelength (450 nm) lasers compared to traditional laser powder bed fusion (LPBF) with 1064 nm. DAM enables the processing of materials with independently addressable 450 nm blue diode lasers, which are integrated into a mu...

Due to its inherent high reflectivity, the processing of copper and its alloys is challenging using low power lasers. Literature reviews indicate that using a 450 nm blue laser for processing copper increases absorptivity dramatically from 5% to 65% (x13 higher) compared to traditional laser powder bed fusion (LPBF). Therefore, this study aims to d...

Binders used in binder jetting often pose health and environmental risks during processing and post processing operations. The print-heads which are used to deposit binder selectively on the feedstock are prone to clogging, despite the trend of print-heads being highly customised to suit different kinds of binders. These factors often hide the adva...

Laser powder bed fusion (L-PBF) is an additive manufacturing technique that provides an opportunity to create complex NdFeB magnets, potentially enhancing their performance. L-PBF possesses its own processing challenges, such as porosity/cracks and thermal stresses due to rapid cooling. This study focused on optimizing the parameters and the use of...

Titanium alloys are particularly sensitive to temperature during additive manufacturing processes, due to their dual phase microstructure and sensitivity to oxygen uptake. In this paper, laser powder bed fusion (LPBF) was used in conjunction with a heated substrate bed at 100 °C, 570 °C and 770 °C to produce specimens of Ti–6Al–4V, to investigate t...

Additive manufacturing (AM) of carbon fibre reinforced thermoplastic composites can offer advantages over traditional carbon fibre manufacturing through improved design freedom and reduction in production time and cost. However, the carbon fibre composites produced using current state-of-the-art AM approaches generally possess high porosity (18-25%...

This paper presents an alternative to traditional laser powder bed fusion (LPBF), using an efficient, highly scalable multi-laser additive manufacturing methodology known as Diode Area Melting (DAM). DAM integrates multiple individually addressable low power fibre coupled diode lasers into a laser head, these traverse across a powder bed to melt po...

Inkjet-printing technology enables the contactless deposition of functional materials such as conductive inks on surfaces, hence reducing contamination and the risk of substrate damage. In printed electronics, inkjet technology offers the significant advantage of controlling the volume of material deposited, and therefore the fine-tuning of the pri...

The 3D printing thixo-forming process is a method that utilizes semisolid thixotropic feedstock for layer extrusion by controlling feedstock viscosity below the complete melting temperature of metallic alloys to form a 3D structure. The process of producing metallic feedstock has a significant impact on alloy microstructure, which is critical for t...

The 3D printing thixo-forming process is a method that utilizes semisolid thixotropic feedstock for layer extrusion by controlling feedstock viscosity below the complete melting temperature of metallic alloys to form a 3D structure. The process of producing metallic feedstock has a significant impact on alloy microstructure, which is critical for t...

The additive manufacturing process selective laser melting (SLM) uses a powder bed fusion approach to fully melt layers of powdered metal and create 3D components. Current SLM systems are equipped with either single or multiple (up to four) high-power galvo-scanning infrared fibre laser sources operating at a fixed wavelength of 1064 nm. At this wa...

Advanced characterisation techniques were used on LPBF Ti-6Al-4V samples produced on a heated base plate. When the substrate temperature is 100{\deg}C the elongation is 6\%, which increases and peaks at 10\% at 570{\deg}C, then sharply decreases to zero ductility at 770{\deg}C. At 100{\deg}C, a heavily strained and twinned microstructure, primarily...

Advanced characterisation techniques were used on LPBF Ti-6Al-4V samples produced on a heated base plate. When the substrate temperature is 100°C the elongation is 6\%, which increases and peaks at 10\% at 570°C, then sharply decreases to zero ductility at 770°C. At 100°C, a heavily strained and twinned microstructure, primarily composed of {\alpha...

The effect of thermally induced residual stresses is not dynamically considered during a selective laser melting (SLM) build; instead, it processes using invariable parameters across the entire component’s cross-section. This lack of pre-emptive in situ parameter adjustment to reduce residual stresses during processing is a lost opportunity for the...

The ability of high-speed sintering to fabricate fully functional polymer parts at higher production rates as compared to other alternative additive manufacturing processes makes it prudent to further investigate its capability in processing different materials. The preferential deposition of a radiation absorbing material, which is often presented...

This investigation developed selective laser melting (SLM) processing parameters for the in situ fabrication of an Al-Cu12 alloy from pure elemental blends of aluminium and copper powders. Use of elevated pre-heat temperatures (400°C) created a coarser dendritic cell microstructure consisting of supersaturated Al-rich with a uniform Al2Cu phase gra...

Microstructural variations affect deformation response of materials and it is not presented in most of plastic flow prediction models. This work presents a unified description for the deformation response of Ti-6Al-4V (Ti-64) that successfully captures the differences in strength between microstructures produced by conventional cast & wrought route...

Diode area melting (DAM) is a new additive manufacturing process that utilises customised architectural arrays of low-power laser diode emitters for high-speed parallel processing ofmetallic feedstock. The laser diodes operate at shorter laser wavelengths (808 nm) than conventional SLM fibre lasers (1064 nm) theoretically enabling more efficient en...

High cooling rates within the Selective Laser Melting (SLM) process can generate large residual stresses within fabricated components. Understanding residual stress development in the process and devising methods for in-situ reduction continues to be a challenge for industrial users of this technology. Computationally efficient FEA models represent...

Selective laser melting (SLM) process is characterized by large temperature gradients resulting in high levels of residual stress within the additively manufactured metallic structure. SLM-processed Ti6Al4V yields a martensitic microstructure due to the rapid solidification and results in a ductility generally lower than a hot working equivalent. P...

Diode Area Melting (DAM) is a novel additive manufacturing process that utilises customised architectural arrays of low power laser diode emitters for high speed parallel processing of metallic powdered feedstock. The laser diodes operate at shorter laser wavelengths (808nm) than conventional SLM fibre lasers (1064nm) theoretically enabling more ef...

During the Selective Laser Melting (SLM) process large temperature gradients can form, generating a mismatch in elastic deformation that can lead to high levels of residual stress within the additively manufactured metallic structure. Rapid melt pool solidification causes SLM processed Ti6Al4V to form a martensitic microstructure with a ductility g...

This work investigates whether the unique low thermal expansion property of Invar (64Fe–36Ni) is retained after processing using the additive manufacturing process selective laser melting (SLM). Using this process, near-full-density components (99.96%) were formed by melting thin (20 μm) layers of powdered Invar (15–45 μm particle size). The mechan...

The additive manufacturing process Selective Laser Melting (SLM) can generate large thermal gradients during the processing of metallic powder; this can in turn lead to increased residual stress formation within a component. Metal anchors or support structures are required to be built during the process and forcibly hold SLM components to a substra...

This work investigates whether the unique low thermal expansion property of Invar (64Fe–36Ni) is retained after processing using the additive manufacturing process selective laser melting (SLM). Using this process, near-full-density components (99.96%) were formed by melting thin (20 μm) layers of powdered Invar (15–45 μm particle size). The mechan...

During the Selective Laser Melting (SLM) process large temperature gradients can form, generating a mismatch in elastic deformation that can lead to high levels of residual stress within the additively manufactured metallic structure. Rapid melt pool solidification causes SLM processed Ti6Al4V to form a martensitic microstructure with a ductility g...

Additive manufacturing processes have been developed to a stage where they can now be routinely used to manufacture net-shape high-value components. Selective Laser Melting (SLM) comprises of either a single or multiple deflected high energy fibre laser source(s) to raster scan, melt and fuse layers of metallic powdered feedstock. However this defl...

The layer-by-layer building methodology used within the powder bed process of Selective Laser Melting facilitates control over the degree of melting achieved at every layer. This control can be used to manipulate levels of porosity within each layer, effecting resultant mechanical properties. If specifically controlled, it has the potential to enab...

Additive manufacturing processes have been developed to a stage where they can now be routinely used to manufacture net-shape high-value components. Selective Laser Melting (SLM) comprises of either a single or multiple deflected high energy fibre laser source(s) to raster scan, melt and fuse layers of metallic powdered feedstock. However this defl...

In contrast to subtractive manufacturing techniques, additive manufacturing processes are known for their high efficiency in regards to utilisation of feedstock. However the various polymer, metallic and composite feedstocks used within additive manufacturing are mainly derived from energy consuming, inefficient methods, often originating from non-...

A two-dimensional Cellular Automata (CA) – Finite Element (FE) (CA-FE) coupled model has been developed to predict the microstructures formed during the laser melting of a powdered AA-2024 feedstock using the Additive Manufacturing (AM) process Selective Laser Melting (SLM). The presented CA model is coupled with a thermal FE model, which computes...

A two-dimensional Cellular Automata (CA) – Finite Element (FE) (CA-FE) coupled model has been developed to predict the microstructures formed during the laser melting of a powdered AA-2024 feedstock using the Additive Manufacturing (AM) process Selective Laser Melting (SLM). The presented CA model is coupled with a thermal FE model, which computes...

A two-dimensional Cellular Automata (CA) – Finite Element (FE) (CAFE) coupled model has been developed in order to predict the microstructure formed during melting of a powdered AA-2024 feedstock using the Additive Manufacturing (AM) process Selective Laser Melting (SLM). The presented CA model is coupled with a detailed thermal FE model computing...

The Selective Laser Melting (SLM) process generates large thermal gradients during rapid melting of metallic powdered feedstock. During solidification certain alloys suffer from thermally induced micro-cracking which cannot be eliminated by process optimisation. An alloy’s crack susceptibility may reduce by increasing its Thermal Shock Resistance (...

Rapid melt pool formation and solidification during the metal powder bed process Selective Laser Melting (SLM) generates large thermal gradients that can in turn lead to increased residual stress formation within a component. Metal anchors or supports are required to be built in-situ and forcibly hold SLM structures in place and minimise geometric...

The work reported investigates in-situ alloying using a semi-solid processing technique with metal powder bed Additive Manufacturing (AM); in this instance Selective Laser Melting (SLM) and Electron Beam Melting (EBM) were employed. This technique utilised customised powder blends that were processed at elevated temperatures. The selection of proce...

Metal powder Additive Manufacturing (AM) allows complex parts to be build from commercial materials. Several industries such as automotive, aerospace and medical have interests in using these technologies. However in metal powder AM, supports/ anchors are required to be melted in place to avoid process failure due to upward warping of flat overhang...

Metal powder bed AM processes have a significant drawback in that they require anchors/supports to hold overhanging features down during laser processing. This severely restricts the geometries that the processes can make, adds significant time and cost to production and reduces throughput as parts cannot be easily stacked in the build bed. A metho...

Purpose – The purpose of this paper is to investigate the selective laser melting (SLM) of Inconel 625 using pulse shape control to vary the energy distribution within a single laser pulse. It aims to discuss the effectiveness of pulse shaping, including potential benefits for use within SLM. Design/methodology/approach – Laser parameters were var...

Journal of Materials Processing Technology j o u r n a l h o m e p a g e : w w w . e l s e v i e r . c o m / l o c a t e / j m a t p r o t e c a b s t r a c t Pulse shaping is a technique used to temporally distribute energy within a single laser pulse. This provides the user an added degree of control over the heat delivered to the laser material...

Purpose – Obtaining the required part top surface roughness and side roughness is critical in some applications. Each of these part properties can often be improved to the detriment of the other during selective laser melting (SLM). The purpose of this paper is to investigate the selective laser melting of Inconel 625 using an Nd:YAG pulsed laser t...

In this work, high density Waspaloy® specimens were produced using selective laser melting (SLM). SLM of Waspaloy® powder was performed using a high power pulsed Nd:YAG laser. The laser parameters pulse energy (J), pulse width (ms), repetition rate (Hz) and scan speed (mm/min) were varied. Process parameter optimization was achieved using factorial...

Pulse shaping is a technique used to temporally distribute energy within a single laser pulse. This allows the user to have an added degree of control over the heat delivered to the laser material interaction zone. Pulses that induce a gradual heating or a prolonged cooling effect can be generated with peak power/pulse energy combinations specifica...

This is a journal article. It was published in the journal, Journal of materials science [©Springer] and the original publication is available at www.springerlink.com An approach for fabricating functionally graded specimens of supernickel alloy and ceramic compositions via Selective Laser Melting (SLM) is presented. The focus aimed at using the Fu...

In this work, high density Waspaloy® specimens were produced using specially assembled laboratory equipment by Selective Laser Melting (SLM). SLM of Waspaloy® powder was performed using a high power pulsed Nd:YAG laser. The laser parameters pulse energy (J), pulse width (ms), repetition rate (Hz) and scan speed (mm/min) were varied. Process paramet...