Manufacturing Elements with Small Cross-Sections of 17-4 PH Steel (1.4542) with the Application of the DMLS Additive Manufacturing Method

The application of direct metal laser sintering renders it possible to manufacture models with complex geometries. However, there are certain limits to the application of this method connected with manufacturing thin-walled cuboidal elements, as well as cylinders and holes with small diameters. The principal objective of the research was to determine the accuracy of manufacturing geometries with small cross-sections and the possibility of application in heat exchangers that are radiators with radially arranged ribs. To that end, four specimens were designed and manufactured; their geometries of representations assumed for the purpose of research (analysis) changed dimensions within the following scope: 10–0.1 mm. The specimens to be applied in the research were manufactured with 17-4 PH stainless steel (1.4542) with the application of 3D-DMLS printing and an EOS M270 printer. The measurement of accuracy was performed with the application of an optical stereomicroscope (KERN OZL-466). In addition to that, research into the chemical composition of the material, as well as the size of spherical agglomerates, was conducted with the application of a scanning electron microscope. The analysis of the chemical composition was conducted as well (after the sintering process). The analysis of the results based on the values received by means of measurements of the manufactured geometries was divided into three parts. Based on this, it is possible to conclude that the representation of models manufactured with the application of DMLS was comparable with the assumptions, and that the deviations between a nominal dimension and that received in the course of the research were within the following scope: 0–0.1 mm. At the final stage of research and based on the received results, two heat exchangers were manufactured.

AUTOMATED DIMENSIONING OF ASSEMBLY STRUCTURES OF MACHINE TOOLS BY USING COMPENSATORS

The article presents the results of the obtained dependencies for determination of the dimensions and the number of compensators in assembling units of machine tools. An algorithm for automated dimensioning with non-adjustable compensators has been developed.The non-adjustable compensators are parts that are pre-fabricated with different dimensions. In the assembly process, that one is used providing the set size of the initial link in the particular configuration of the constituent links. The initial conditions for dimensioning the compensator are the results of the constructive design of the assembly with CAD products. As a result of this design, the nominal dimensions of all the parts of structural consideration are determined and under the condition to achieve the nominal size of the initial link. The tolerances and limiting dimensions of the parts, excluding those of the compensator, are chosen by the designer-constructor according to the functional purpose of the parts and the technological capabilities of the methods for their manufacture. This does not require limitations of the dimensional analysis but functional and cost-effective accuracy of the parts is taken into account. Dimensioning is done by applying a series of procedures, which are discussed in detail in the paper and the number of compensators by groups is determined. Based on the applied procedures is proposed an algorithm for sizing the units of machine with non-adjustable compensators. The tolerance for manufacturing the compensators shall be symmetrical in relation to the nominal dimension. On the basis of the dependencies obtained for the dimensions and the distribution of the compensators in groups, an algorithm and software for automated dimensioning of the structures with non-adjustable compensators can be created.

Tolerance allocation of complex assembly with nominal dimension selection using Artificial Bee Colony algorithm

Optimum tolerance allocation plays a vital role in minimizing the direct manufacturing cost of mechanical assembly. It is very sensitive due to the variations in manufacturing processes of the components. Most of the earlier studies are aiming at optimum tolerance allocation for assemblies without considering the selection of nominal dimensions of components and considering them as discrete values. It is proposed to minimize the manufacturing cost of an assembly with tolerance allocation and alternate nominal dimension selections by considering them in closer decimal intervals. The evolutionary algorithms such as Genetic and Artificial Bee Colony algorithms are developed and proposed to achieve the above objectives. The performance of the algorithms has been enhanced with the seed solution obtained using Lagrange Multiplier method. The complex assembly problems proposed by various authors with the required parameters have been considered for investigating the proposed method. The critical dimensions of the assemblies are fixed and the nominal dimension has been varied with its tolerances. The resultant manufacturing cost by various methods is presented and compared with corresponding nominal dimensions and tolerances. Based on the percentage of improvement of manufacturing cost, it is observed that the Artificial Bee Colony algorithm outperforms.

Optimum tolerance synthesis of simple assemblies with nominal dimension selection using genetic algorithm

Optimum tolerance allocation plays a vital role in minimization of the direct manufacturing cost, and it is sensitive to tolerances related to variations in manufacturing processes. However, optimal adjustment of both nominal dimensions and selection of tolerances may further reduce assembly manufacturing cost and wastage of materials during processing. Most studies in existing literature focus on optimum tolerance allocation for the assemblies without considering nominal dimension selection. The method proposed in this work uses genetic algorithm techniques to allocate tolerances to assembly components, thereby minimizing costs. The component alternate nominal dimensions are predicted based on critical dimensions and its tolerances. The effectiveness of the developed algorithms demonstrated using randomly generated problems as well as sample problems taken from the literature. Test results are compared with those obtained using the Lagrange multiplier method. It is shown that by adjusting the nominal dimensions, the proposed method yields considerable savings in manufacturing costs.

Laser Sinterization Aspects of PA2200 Biocompatible Powder - Spinal Cage Application

The paper presents the dimensional aspects of a generic spinal cage build up from PA2200 powder. The cage was manufactured by means of selective laser sintering (SLS) technology, on Formiga P100 machine. The geometric model of spinal cage was designed in SolidWorks by taking into account the requirements that have to be fulfilled by such an implant. The dimensional aspects refer to geometric dimensions along X, Y and Z axes measured on sample parts, when these were placed on a 4x4 matrix on the building plane. The measurements were conducted using a digital caliper having a precision of 0.01, and were presented together with the nominal dimension of the CAD model. In conclusion, some qualitative aspects regarding the setting of the scaling factors were underlined.

Reynolds Number Effects on the Calibration of a Subminiature Four Hole Three Dimensional Wake Probe

A subminiature four-hole probe is designed and fabricated to be used specifically to measure wakes that occur in turbomachinery and its components. The probe has a nominal measuring area of 0.413 mm2 and has a nominal dimension of 0.254 mm in the direction across the wake downstream the trailing edge of a blade thus minimizing spatial and flow gradient errors in this direction. The non-nulling calibration of the probe is carried out in the pitch and yaw angle range of ±30° at 5° interval. The probe is calibrated at four different velocities, viz., 10 m/s, 20 m/s, 30 m/s and 50 m/s corresponding to the probe thickness Reynolds numbers in the range of 159 to 794 with objective of finding the effect of Reynolds number on the calibration coefficients. In addition to these, for practical importance the actual changes in yaw angle, pitch angle, static pressure, total pressure and velocity magnitude due to Reynolds number variation has been investigated. A method to incorporate the effect of Reynolds number for minimum interpolation errors is described.

Miniature Four Hole Probe for Three Dimensional Boundary Layer Measurements

The design, fabrication and calibration details of a miniature four hole probe for three-dimensional boundary layer measurements are presented in this paper. The probe has a nominal measuring area of 1 mm2 and has a nominal dimension of 0.4 mm in the boundary layer direction thus minimizing pressure and velocity gradient errors and wall vicinity errors. The probe is calibrated in an open jet calibration tunnel at a velocity of 50 m/s in the yaw and pitch angle range of + 40O at 5O interval. The calibration coefficients are defined, calculated and presented. The sensitivity of the calibration coefficients is also calculated and presented.