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The purpose of this paper is to establish a general method for achievable speed and accuracy evaluation of additive manufacturing (AM) machines and an objective comparison among them.

First, a general schematic is defined that enables description of all currently available AM machines. This schematic is used to define two influential factors describing certain parts' properties regarding the machines' yield during manufacturing. A test part is defined, that will enable testing the influence of these factors on the speed and accuracy of manufacturing. A method for implementing and adapting test parts is established for individual machine's testing. This method was used to test four different machines that are predominantly used in Slovenia at the moment.

Research has proven that the machine's yield had a predominant influence on the achievable manufacturing speeds of all the tested machines. In addition, the results have shown different ranges of achievable manufacturing speeds for individually tested machines. Test parts' measurement results have shown comparable achievable accuracies for all the tested machines.

Speed evaluation is based on a 2^k factorial design that assumes the linearity among individual points of the experiment. This design was chosen to keep the method as simple and quick as possible, in order to perform testing on those machines otherwise used in industrial environments. Accuracy evaluation was limited by a rather small sample size of ten fabricated test parts per machine.

The presented evaluation method can be used on any existing or future type of AM machine, and their comparative placement regarding achievable manufacturing speed and accuracy.

The presented method can be used to evaluate a machine regardless of the AM technology on which it is based.

Among the different methodologies used for performance control in precision manufacturing, the measurement of metrological test artefacts becomes very important for the characterization, optimization and performance evaluation of additive manufacturing (AM) systems. The purpose of this study is to design and manufacture several benchmark artefacts to evaluate the accuracy of the selective laser melting (SLM) manufacturing process.

Artefacts consist of different primitive features (planes, cylinders and hemispheres) on sloped planes (0°, 15°, 30°, 45°) and stair-shaped and sloped planes (from 0° to 90°, at 5° intervals), manufactured in 17-4PH stainless steel. The artefacts were measured optically by a structured light scanner to verify the geometric dimensioning and tolerancing of SLM manufacturing.

The results provide design recommendations for precision SLM manufacturing of 17-4PH parts. Regarding geometrical accuracy, it is recommended to avoid surfaces with 45° negative slopes or higher. On the other hand, the material shrinkage effect can be compensated by resizing features according to X and Y direction.

No previous work has been found that evaluates accuracy when printing inwards (pockets) and outwards (pads) geometries at different manufacturing angles using SLM. The proposed artefacts can be used to determine the manufacturing accuracy of different AM systems by resizing to fit the build envelope of the system to evaluate. Analysis of manufactured benchmark artefacts allows to determine rules for the most suitable design of the desired parts.

This paper aims to present a survey concerning the accuracy of thermoplastic polymeric parts fabricated by additive manufacturing (AM). Based on the scientific literature, the aim is to provide an updated map of trends and gaps in this relevant research field. Several technologies and investigation methods are examined, thus giving an overview and analysis of the growing body of research.

Permutations of keywords, which concern materials, technologies and the accuracy of thermoplastic polymeric parts fabricated by AM, are used for a systematic search in peer-review databases. The selected articles are screened and ranked to identify those that are more relevant. A bibliometric analysis is performed based on investigated materials and applied technologies of published papers. Finally, each paper is categorised and discussed by considering the implemented research methods.

The interest in the accuracy of additively manufactured thermoplastics is increasing. The principal sources of inaccuracies are those shrinkages occurring during part solidification. The analysis of the research methods shows a predominance of empirical approaches. Due to the experimental context, those achievements have consequently limited applicability. Analytical and numerical models, which generally require huge computational costs when applied to complex products, are also numerous and are investigated in detail. Several articles deal with artificial intelligence tools and are gaining more and more attention.

The cross-technology survey on the accuracy issue highlights the common critical aspects of thermoplastics transformed by AM. An updated map of the recent research literature is achieved. The analysis shows the advantages and limitations of different research methods in this field, providing an overview of research trends and gaps.

The purpose of this paper is to report a new direct metal manufacturing method which integrates freeform deposition process and micro rolling process, introduce the manufacturing principle and show the advantages of this method.

This paper introduces the hybrid manufacturing principle and devices first. Then, the key parameters of hybrid manufacturing process are studied by contrast experiments. The results of comparisons of manufacturing accuracy, microstructure and tensile test between freeform fabricated parts and hybrid manufactured parts show the advantages of this new direct manufacturing method.

The experiments results show that the accuracy of hybrid manufacturing method is improved obviously comparing with arc-based freeform deposition manufacturing method; the microstructure of the hybrid manufacturing part turns into cellular crystal instead of dendrite; the tensile strength of the part increases by 33 percent and the tensile deformation improved more than two times.

The paper presents a new hybrid direct metal manufacturing method for the first time. The hybrid manufacturing devices are developed. The experiments results show that the hybrid manufacturing method can be used on directly fabricating large metal components with outstanding quality, efficiency and low cost. The application prospect is great.

This paper aims to improve the alignment accuracy of large components in aircraft assembly and an evaluation algorithm, which is based on manufacture accuracy and coordination accuracy, is proposed.

With relative deviations of manufacturing feature points and coordinate feature points, an evaluation function of assembly error is constructed. Then the optimization model of large aircraft digital alignment is established to minimize the synthesis assembly error with tolerance requirements, which consist of three-dimensional (3D) tolerance of manufacturing feature points and relative tolerance between coordination feature points. The non-linear constrained optimization problem is solved by Lagrange multiplier method and quasi-Newton method with its initial value provided by the singular value decomposition method.

The optimized postures of large components are obtained, which makes the tolerance of both manufacturing and coordination requirements be met. Concurrently, the synthesis assembly error is minimized. Compared to the result of the singular value decomposition method, the algorithm is validated in three typical cases with practical data.

The proposed method has been used in several aircraft assembly projects and gained a good effect.

This paper proposes a method to optimize the manufacturing and coordination accuracy with tolerance constraints when the postures of several components are adjusted at the same time. The results of this paper will help to improve the quality of component assemblies.

The purpose of this paper is to present the results of theoretical considerations and experimental tests concerning microscaffold fabrication by selective laser melting (SLM). Also described are manufacturing technologies for regular lattice microstructure with the smallest possible pore sizes and fullest possible order of geometric accuracy retained. Process parameters of SLM greatly affect the properties of the fabricated structures not only in regards to their material characteristics but also in their geometric representation accuracy.

The paper discusses technological relationships between different laser micrometallurgy strategies and the accuracy of the manufactured microstructures.

With technological possibilities evaluated, regular porous structure was created composed of cubic pores with cylindrical struts as their boundaries. Strut diameters are up to 180 μm, and the distance between neighboring strut axes was reduced to 600 μm, which gives a hollow channels clearance of approximately 420 μm.

Presented results show possibilities of manufacturing small high-strength lattice microstructures by SLM using Ti-6Al-7Nb titanium alloy powders for tissue engineering.

The amount of radiated energy is known to be a crucial parameter in powder-bed additive manufacturing (AM) processes. The role of irradiance in the multijet fusion (MJF) process has not been addressed by any previous research, despite the key role of this process in the AM industry. The aim of this paper is to explore the relationship between irradiance and dimensional accuracy in MJF.

An experimental activity was carried out to map the relationship between irradiance and dimensional accuracy in the MJF transformation of polyamide 12. Two specimens were used to measure the dimensional accuracy on medium and small sizes. The experiment was run using six different levels of irradiance. For each, the crystallinity degree and part density were measured.

Irradiance was found to be directly proportional to part density and inversely proportional to crystallinity degree. Higher irradiance leads to an increase in the measured dimensions of parts. This highlights a predominant role of the crystallisation degree and uncontrolled peripherical sintering, in line with the previous literature on other powder-bed AM processes. The results demonstrate that different trends can be observed according to the range of sizes.

The body of the literature on the Arburg Plastic Freeforming process is still very limited despite the increasing industrial importance of this technology. This paper aims to contribute to a better understanding of this technology by investigating relations between characteristic process parameters and part features. Particularly, the effects of nominal dimension, drop aspect ratio, build chamber temperature and part position on accuracy are investigated. The density of manufactured parts is also measured to understand its relation with dimensional error.

A benchmark part was designed and manufactured in Polycarbonate on an Arburg Plastic Freeformer 2K-3A. The process was repeated with two levels of drop aspect ratio (1.2125 and 1.2150) and two build chamber temperatures (90°C and 120°C). Each build job included five parts in different positions of the chamber. The dimensional accuracy of benchmarks was measured by using a digital caliper, while Archimede’s principle was used for density measurements. All the acquired results were processed through an analysis of variance to investigate the role of experimental factors.

Results demonstrate that the linear shrinkage occurring at the end of the 3D printing process is the main source of inaccuracy. The higher the building chamber temperature, the most the part accuracy is influenced by the nominal dimension. The drop aspect ratio affects the dimensional error in the XY plane by increasing the overlap of adjacent droplets. On the other hand, this parameter does not influence the accuracy along the Z direction. The position of the parts inside the building chamber exhibited an influence on results, arguably due to the hot airflows.

This research did not allow for a complete understanding of the role of part positioning on part accuracy. Further study is needed to understand the detail of this phenomenon.

The results of this study can aid the users of Arburg Plastic Freeforming technology by uncovering the role of the main process parameters.

This paper expands the body of knowledge on the Arburg Plastic Freeforming process by providing new information on the role of the main process parameters on dimensional accuracy and density. Particularly, the results answer a research question on the role of the drop aspect ratio, demonstrating that its main effect is to vary the droplets overlap, which, in turn, affects the thermal shrinkage.

This paper aims to illustrate the tolerance optimization method based on the assembly accuracy constrain, precession constrain and the cost of production of the assembly product.

A tolerance optimization method is an excellent way to perform product assembly performance. The tolerance optimization method is adapted to the process analysis of the hatch and skin of an aircraft. In this paper, the tolerance optimization techniques are applied to the tolerance allocation for step difference analysis (example: step difference between aircraft cabin door and fuselage outer skin). First, a mathematical model is described to understand the relationship between manufacturing cost and tolerance cost. Second, the penalty function method is applied to form a new equation for tolerance optimization. Finally, MATLAB software is used to calculate 170 loops iteration to understand the efficiency of the new equation for tolerance optimization.

The tolerance optimization method is based on the assembly accuracy constrain, machinery constrain and the cost of production of the assembly product. The main finding of this paper is the lowest assembly and lowest production costs that met the product tolerance specification.

This paper illustrated an efficient method of tolerance allocation for products assembly. After 170 loops iterations, it founds that the results very close to the original required tolerance. But it can easily say that the different number of loops iterations may have a different result. But optimization result must be approximate to the original tolerance requirements.

It is evident from Table 4 that the tolerance of the closed loop is 1.3999 after the tolerance distribution is completed, which is less than and very close to the original tolerance of 1.40; the machining precision constraint of the outer skin of the cabin door and the fuselage is satisfied, and the assembly precision constraint of the closed loop is satisfied.

The research may support further research studies to minimize cost tolerance allocation using tolerance cost optimization techniques, which must meet the given constrain accuracy for assembly products.

This study aims to analyze the effect of the different common post-processes on the geometrical and dimensional accuracy of selective laser melting (SLM) parts.

An artefact has been designed including cubic features formed by planar surfaces orientated according to the machine axes, covering all the X-Y area of the working space. The artefact has been analyzed both geometrically (flatness, parallelism) and dimensionally (sizes, distances) from coordinate measuring machine measurement results at three stages, namely, as-built, after sand-blasting and after stress-relieving heat treatment.

Results from the SLM machine used in this study lead to smaller parts than the nominal ones. This effect depends on the direction of the evaluated dimension of the parts, i.e. X, Y or Z direction and is differently affected by the sandblasting post-process (average erosion ratio of 68, 54 and 9 µm, respectively), being practically unaltered by the HT applied after.

This paper shows the influence, from a geometric and dimensional point of view, of two of the most common post-processes used after producing SLM parts, such as sand-blasting and stress-relieving heat treatment, that have not been considered in previous research.