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This paper presents findings from a study examining curing procedures to improve the compressive strength and hardness properties of specimens while maintaining surface quality. All specimens were created from a standard grey, acrylic-based photopolymer and fabricated using stereolithography technology. This paper aims to investigate the effects of printing layer thickness and print orientation on specimen compressive strength, as well as the effects of thermal and light curing methods. In addition, the post-print curing depth was investigated.

The effects of layer thickness and print orientation were investigated on 10 × 20 mm cylinders by determining the ultimate compressive strength once cured. The compressive strength of cylinders subjected to varying thermal and light settings was also investigated to determine the optimal curing settings. The effective depth of curing was investigated on a 25.4-mm cuboidal specimen, which received both thermal and light curing.

To achieve the highest compressive strength, specimens shall be printed with the minimal layer thickness of 25 µm. Increasing temperatures up to 60° C during curing provided a 0.75-MPa increase in compressive strength per degree Celsius. However, increasing temperatures above 60° C only provided a 0.15-MPa increase in compressive strength per degree Celsius. Furthermore, curing temperatures above 110° C resulted in degraded surface quality noted by defects at the layer laminations. Specimens required a minimum light curing exposure time of four hours to reach the maximum cure at which point any increase in exposure time provided no substantial increase in compressive strength.

This study provides recommendations for printing parameters and curing methods to achieve the optimum mechanical properties of cured stereolithography specimens.

3D printing techniques have been widely used for manufacturing complex parts for various dental applications. For achieving suitable mechanical strength, post-cure processing is necessary, where the relative time duration and temperature specification also needs to be defined. The purpose of this study/paper is to assess the effects of post curing conditions and mechanical properties of 3D printed clear dental aligners

Dental long-term clear resin material has been used for 3D printing of dental aligners using a Formlabs 3D printer for direct usage on patients. Post-curing conditions have been varied, all of which have been subjected to mechanical compression loading of 1,000 N to evaluate the curing effects on the mechanical strength of the aligners.

The experimental studies provide significant insight into both temperatures and time durations that could provide sufficient compressive mechanical strength to the 3D printed clear dental aligners. It was observed that uncured aligners deformed plastically with large deformations under the loading conditions, whereas aligners cured between 400°C–800°C for 15–20 min deformed elastically before fragmenting into pieces after safely sustaining higher compressive loads between 495 N and 666 N. The compressive modulus ratio for cured aligners ranged between 4.46 and 5.90 as compared to uncured aligners. For shorter cure time durations and lower temperature conditions, an appropriate elevated compressive strength was also achieved.

Based on initial assessments by dental surgeons, suitable customised clear aligners can be designed, printed and cured to the desired levels based on patient’s requirements. This could result in time, energy and unit production cost savings, which ultimately would help to alleviate the financial burden placed on both the health service and their patients.

The resistivity of cured conductive ink films are dependent on a wide range of process parameters. An early indication of the resistivity that is likely to result following curing can enable these parameters to be optimised and, therefore, improve product quality. This paper aims to report on the use of alternating current (AC) impedance measurement techniques on curing printed ink films as a means of assessing the resistivity likely to be attained following the curing process.

Impedance measurements (100 Hz-10 MHz) were performed on curing conductive carbon ink films printed on polyethylene terephthalate substrates during convective heat curing. A jig was designed to incorporate the test structure in an convection oven such that the effect of cure on the structure impedance could be investigated.

The initial impedance was found to decrease with an increase in the measurement frequency. As the ink films were cured, the impedance magnitude across the 100 Hz-10 MHz range converged with the direct current (DC) resistance value. For a given ink, the ratio of initial AC impedance at 10 MHz to final cured resistance was found to be consistent, thus giving a method where final conductivity can be estimated before cure.

Data from printed ink resistance measurements are required to ensure the optimal conductivity of printed devices. However, after the printed structures are fabricated and cured, it is too late to optimise process parameters, leading to significant wastage. AC impedance measurement can give an indication of the final cured resistivity whilst the structure is freshly printed and still in its curing phase, enabling the printing process parameters to be adjusted to improve the resistivity of subsequently printed devices. Measuring AC impedance of printed ink structures in a production environment can, therefore, improve output.

This paper aims to present a multi-material additive manufacturing (AM) process with a newly developed curing-on-demand method to fabricate a three-dimensional (3D) object with multiple material compositions.

Unlike the deposition-on-demand printing method, the proposed curing-on-demand printheads use a digital light processing (DLP) projector to selectively cure a thin layer of liquid photocurable resin and then clean the residual uncured material effectively using a vacuuming and post-curing device. Each printhead can individually fabricate one type of material using digitally controlled mask image patterns. The proposed AM process can accurately deposit multiple materials in each layer by combining multiple curing-on-demand printheads together. Consequently, a three-dimensional object can be fabricated layer-by-layer using the developed curing-on-demand printing method.

Effective cleaning of uncured resin is realized with reduced coated resin whose height is in the sub-millimeter level and improved vacuum cleaning performance with the uncleaned resin less than 10 µm thick. Also, fast material swapping is achieved using the compact design of multiple printheads.

The proposed multi-material stereolithography (SL) process enables 3D printing components using more viscous materials and can achieve desired manufacturing characteristics, including high feature resolution, fast fabrication speed and low machine cost.

The paper reviews U‐V curable screen‐printable etch plating and solder resists, their basic components, principles of U‐V curing, their performance in the liquid as well as in the solid state and their advantages. Also discussed are the basic construction and performance of U‐V curing equipment.

Techniques of extrude and cure additive manufacturing for thermally cured, high viscosity and medical-grade silicone are investigated by using a small ram extruder and a near-infrared (IR) laser. The purpose of this study is to evaluate the process parameter effects on the stiffness of the final products.

Process parameter effects on axial stiffness values and durometer are explored. Parameters such as extrusion layer height, laser speed, laser current, laser raster spacing and multiple laser passes were investigated and compared to traditional cast and cure methods. Dimensional changes were also recorded and compared.

Tensile and durometer tests show that certain curing parameters give tensile stress and durometers within 10 per cent of bulk material specifications at 200 per cent strain. Parameters that had the highest impact on tensile stress at 200 per cent strain were layer height (0.73 per cent) followed by laser power (0.69 per cent), and then laser raster spacing (0.45 per cent). Parameters that had the highest impact on durometer were laser power (1.00 per cent), followed by layer height, (0.34 per cent) and then laser raster speed (0.32 per cent). Three-dimensional printed samples had about 11.2 per cent more shrinkage than the bulk cast samples in the longest dimension.

This paper is one of the first that demonstrates near IR laser curing parameter effects on three-dimensional printed, commercial off-the-shelf, medical-grade and viscous silicone. The ability to cure very viscous thermosets locally enables interesting technologies such as wire encapsulation, high voltage actuators and drug delivery devices.

The purpose of this paper is to present a hybrid manufacturing system that integrates stereolithography (SL) and direct print (DP) technologies to fabricate three‐dimensional (3D) structures with embedded electronic circuits. A detailed process was developed that enables fabrication of monolithic 3D packages with electronics without removal from the hybrid SL/DP machine during the process. Successful devices are demonstrated consisting of simple 555 timer circuits designed and fabricated in 2D (single layer of routing) and 3D (multiple layers of routing and component placement).

A hybrid SL/DP system was designed and developed using a 3D Systems SL 250/50 machine and an nScrypt micro‐dispensing pump integrated within the SL machine through orthogonally‐aligned linear translation stages. A corresponding manufacturing process was also developed using this system to fabricate 2D and 3D monolithic structures with embedded electronic circuits. The process involved part design, process planning, integrated manufacturing (including multiple starts and stops of both SL and DP and multiple intermediate processes), and post‐processing. SL provided substrate/mechanical structure manufacturing while interconnections were achieved using DP of conductive inks. Simple functional demonstrations involving 2D and 3D circuit designs were accomplished.

The 3D micro‐dispensing DP system provided control over conductive trace deposition and combined with the manufacturing flexibility of the SL machine enabled the fabrication of monolithic 3D electronic structures. To fabricate a 3D electronic device within the hybrid SL/DP machine, a process was developed that required multiple starts and stops of the SL process, removal of uncured resin from the SL substrate, insertion of active and passive electronic components, and DP and laser curing of the conductive traces. Using this process, the hybrid SL/DP technology was capable of successfully fabricating, without removal from the machine during fabrication, functional 2D and 3D 555 timer circuits packaged within SL substrates.

Results indicated that fabrication of 3D embedded electronic systems is possible using the hybrid SL/DP machine. A complete manufacturing process was developed to fabricate complex, monolithic 3D structures with electronics in a single set‐up, advancing the capabilities of additive manufacturing (AM) technologies. Although the process does not require removal of the structure from the machine during fabrication, many of the current sub‐processes are manual. As a result, further research and development on automation and optimization of many of the sub‐processes are required to enhance the overall manufacturing process.

A new methodology is presented for manufacturing non‐traditional electronic systems in arbitrary form, while achieving miniaturization and enabling rugged structure. Advanced applications are demonstrated using a semi‐automated approach to SL/DP integration. Opportunities exist to fully automate the hybrid SL/DP machine and optimize the manufacturing process for enhancing the commercial appeal for fabricating complex systems.

This work broadly demonstrates what can be achieved by integrating multiple AM technologies together for fabricating unique devices and more specifically demonstrates a hybrid SL/DP machine that can produce 3D monolithic structures with embedded electronics and printed interconnects.

The industry standard for applying the identification nomenclature to Printed Circuit Boards (PCBs) is silkscreen legend printing, using white ink. This multi‐step process has minimal flexibility for applying unique legends e.g. serialization numbers to individual boards. This paper describes a new, alternative single step direct legend printing system which uses piezoelectric inkjet technology, the leading digital imaging method for a variety of industrial applications. The advantages that this, inherently clean and efficient, drop‐on‐demand, printing process brings to legend printing include increased flexibility, shorter process times, good legend definition, accurate placement, small footprint equipment and reduced labour and material usage.

In this study, it is aimed to synthesize ultraviolet (UV)-curable water-borne polyurethane acrylate (WPUA) binders using different types of polyols (poly (propylene glycol), PPG₁₀₀₀ and PPG₂₀₀₀ and poly (ethylene glycol), PEG₁₀₀₀ and PEG₂₀₀₀) at different molecular weights, DMPA (2,2-bis(hydroxymethyl) propionic acid) at different amounts and isophorone diisocyanate (IPDI) and use for pigment printing on synthetic leather.

UV-cured films were characterized by Fourier transform infrared spectroscopy (FTIR) and differential scanning calorimeter (DSC). The effect of binder structure on printing performance was determined with hardness, crock fastness, abrasion resistance and color measurements.

The highest abrasion resistance (60,000 cycles) and crock fastness values (dry crock and wet crock: 3/4) were obtained with binder PEG-C synthesized with PEG₂₀₀₀ and lower DMPA amount of 4.89 wt%; however, PEG-C binder showed lower hardness values. Due to lower urethane groups in PEG-C binder, more flexible films were obtained which imparted good adhesion property to printing film. Synthesized binders provided lower crock fastness and abrasion resistance properties than commercial WPUA binder.

Pigmented formulations including UV-curable water-borne synthesized PUA binder were developed and for the first time applied onto synthetic leather using screen printing method. Within this context, a new environmentally friendly printing method was proposed in this study including binder synthesis in the preparation of printing formulations.

The purpose of this paper is to prepare waterborne UV-curable pigment pastes for cotton fabric printing.

O/W (oligomer-in-water) emulsions of polyurethane acrylate (PUA) oligomer in sodium dodecyl benzene sulphonate (SDBS) aqueous solution were prepared by ultrasonic emulsification method.

The present work studies various factors affecting the stability and droplet size of the O/W emulsion stabilised by SDBS. The optimal emulsifier concentration was 2.5 per cent, under which condition the stability of the emulsion increased as the emulsifier content increased, with a subsequent decrease in the droplet size of the emulsion, while above which emulsion agglomeration occurred. Increasing the power and duration of ultrasonic dispersion resulted in increased emulsion stability and decreased droplet size, while increases in the oligomer content reduced the emulsion stability. Darocure 1173 mixed with PUA and then emulsified in the SDBS aqueous solution guaranteed uniform dispersion of the photoinitiator, resulting in faster curing speed.

This paper presents a new method for making waterborne externally emulsified oligomers for UV curing, and finds that it is easy to convert the existing oligomers into waterborne equivalents by this method. Cotton fabrics printed with the oligomer emulsion based pastes were found to have good colour strength and crockfastness.