Benchmark

After acquiring good results from synthesizing and printing copper in the earlier methods, it is always necessary to test the machine with the parameters such that it can be able to print all kinds of shapes and structures. One such method to testify our results is the state of art benchmarking. Since there is no readily available source of methods to create parts made from copper, carefully evaluated models have been created using the evaluation methods defined by Moylan et al.

• Have a significant number of small, medium, and large features.

• Not consume large quantities of material.

• Have many features of the real-world parts.

• Have simple geometric shapes that can have perfect definition and easy control of the geometry.

• Allow repeatability measurements.

• Requires no post-treatment and manual intervention (support structures)

• Not take long to build.

It is noted that the last point is entirely dependent on the layer thickness and machine speed, so it is not considered as an issue for this benchmarking. Printing a benchmark considering all the features and shapes is easy, but the most important task is to make sure that the benchmark can be evaluated with proper testing equipment. Thus, making the benchmark considering the fifth point is important for the test to be successful.

The proposed benchmark is designed to fit into the current testing setup with its overall dimension of 70 x 70 x 12 mm with the provision to stick to the baseplate. Further, the part is designed in such a way that it doesn’t need support structures, but the powder layer provides enough support compared to other printing technologies. As the major concern is dimensional evaluation, inheriting simple geometry with varying sizes would be able to synthesize the 50mm, 50 to 80mm and 80 to 120mm. Further, the parts are printed above the baseplate, there is no need for a separate copper base as the plate is not affecting the parts and left along with the parts for measurement. The parts that are considered for printing are explained with a model and listed below.

Figure 16. Isometric view of Benchmark CAD drawing

• A set of six cuboids (R): the blocks have a 15mm length and 11mm height as common which vary with different thicknesses such as 0.5mm, 1mm, 1.5mm, 2mm, 2.5mm and 3mm. Further, the blocks are separated by 2mm between them.

• A set of seven tilted cuboids (TC): The cuboids be inclined to the base plate with an increasing angle of 15 degrees per step. The length and breadth of 15mm x 5mm remain common for all the inclined parts starting from 0 degrees and ending with 90 degrees.

• A set of five slotted rectangular cuboids (SR): the parts are designed with the purpose of checking the capability of producing internal slots as well as the thin wall feature.

Each block is a unique thickness and has dimensions but with a constant length and height of 20mm x 11mm. The change in thickness is as follows:

o 1^st cuboid with 8mm total breadth and has a slot of 14mm x 2mm o 2^nd cuboid with 6mm total breadth and has a slot of 16mm x 2mm o 3^rd cuboid with 4mm total breadth and has a slot of 19mm x 3mm o 4^th cuboid with 4mm total breadth and has a slot of 17mm x 1mm o 5^th cuboid with 4mm total breadth and has a slot of 18mm x 2mm

• An overhanging bridge with 5 different gaps (OB): 6 square blocks of dimensions 10mm x 2mm x 10mm separated by distances of 1mm, 2mm, 3mm, 5mm and 10mm and the blocks have a common horizontally placed rectangular block of the dimension 33mm x 10mm x 2mm which is placed on top of the blocks.

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• A set of 6 semi cylinders with different radii (SC): An array of closely packed semi cylinders of radii 6mm, 5mm, 4mm, 3mm, 2mm and 1mm. All the semi cylinders have the same length of 4mm.

• A set of 8 horizontal holes (HH): A hole of different radii are placed in a direction parallel to the base plate. The holes are arranged in a wall of thickness 5mm. The holes have a diameter ranging from 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm and 6mm.

• A set of 8 vertical holes (VH): A hole of different radii are placed in a direction perpendicular to the base plate. The holes are arranged in a cuboid of thickness 5mm.

The holes have a diameter ranging from 1mm, 1.5mm, 2mm, 2.5mm, 3mm, 4mm, 5mm and 6mm.

• A set of 5 Straight cylinders (CY1): Five cylinders of the varying diameters of 5mm, 4mm, 3mm, 2mm and 1mm placed perpendicular to the base plate.

• A set of 5 inclined cylinders (CY2): Five cylinders of the varying diameters of 5mm, 4mm, 3mm, 2mm and 1mm placed at an inclination of 60degrees to the base plate.

• A set of 5 inclined cylinders (CY3): Five cylinders of the varying diameters of 5mm, 4mm, 3mm, 2mm and 1mm placed at an inclination of 45degrees to the base plate.

The parts are organized and aligned rationally to be representative for the evaluation of geometrical tolerances during the inspection. The common additive manufacturing defects such as the staircase effect which is typical in processes that involve layer by layer manufacturing can also be evaluated for straightness and curvatures in the model.

In short, more than sixty geometrical features have been found on the references part. The parts are printed with carefully selected parameters from the experiments carried out for the optimal processing parameters for printing copper. The processing parameters for printing this benchmark are listed below. The outcomes of the print are discussed in the results section in detail.

Table 5. Process Parameters for the Benchmark Models

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