Igor Drstvenšek

Speed and accuracy evaluation of additive manufacturing machines

Purpose – 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.Design/methodology/approach – 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 machines testing. This method was used to test four different machines that are predominantly used in Slovenia at the moment.Findings – Research has proven that the machines 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 ...

A multi-level rapid prototyping drill guide template reduces the perforation risk of pedicle screw placement in the lumbar and sacral spine.

IntroductionThe method of free-hand pedicle screw placement is generally safe although it carries potential risks. For this reason, several highly accurate computer-assisted systems were developed and are currently on the market. However, these devices have certain disadvantages. We have developed a method of pedicle screw placement in the lumbar and sacral region using a multi-level drill guide template, created with the rapid prototyping technology and have validated it in a clinical study. The aim of the study was to manufacture and evaluate the accuracy of a multi-level drill guide template for lumbar and first sacral pedicle screw placement and to compare it with the free-hand technique under fluoroscopy supervision.Materials and methodsIn 2011 and 2012, a randomized clinical trial was performed on 20 patients. 54 screws were implanted in the trial group using templates and 54 in the control group using the fluoroscopy-supervised free-hand technique. Furthermore, applicability for the first sacral level was tested. Preoperative CT-scans were taken and templates were designed using the selective laser sintering method. Postoperative evaluation and statistical analysis of pedicle violation, displacement, screw length and deviation were performed for both groups.ResultsThe incidence of cortex perforation was significantly reduced in the template group; likewise, the deviation and displacement level of screws in the sagittal plane. In both groups there was no significantly important difference in deviation and displacement level in the transversal plane as not in pedicle screw length. The results for the first sacral level resembled the main investigated group.ConclusionsThe method significantly lowers the incidence of cortex perforation and is therefore potentially applicable in clinical practice, especially in some selected cases. The applied method, however, carries a potential for errors during manufacturing and practical usage and therefore still requires further improvements.

Mathematical model for the selection of processing parameters in selective laser sintering of polymer products

Additive manufacturing (AM) is increasingly applied in the development projects from the initial idea to the finished product. The reasons are multiple, but what should be emphasised is the possibility of relatively rapid manufacturing of the products of complicated geometry based on the computer 3D model of the product. There are numerous limitations primarily in the number of available materials and their properties, which may be quite different from the properties of the material of the finished product. Therefore, it is necessary to know the properties of the product materials. In AM procedures the mechanical properties of materials are affected by the manufacturing procedure and the production parameters. During SLS procedures it is possible to adjust various manufacturing parameters which are used to influence the improvement of various mechanical and other properties of the products. The paper sets a new mathematical model to determine the influence of individual manufacturing parameters on the polymer product made by selective laser sintering. Old mathematical model is checked by statistical method with central composite plan and it is established that old mathematical model must be expanded with new parameter beam overlay ratio. Verification of new mathematical model and optimization of the processing parameters are made on SLS machine.

Responding ability in dynamic production circumstances

Abstract The information flow in production environments mainly depends on the structure of a production database. A connection between the database and the production process is established using an interface based on the idea of a process matrix. The interface equipped with the genetic algorithms search technique gathers functions of process planning and scheduling into a common decision-making environment. Decisions usually consist of production scenario changes caused by disturbances of the production process. The reactions are mainly influenced by costs caused by momentary decisions. To keep these costs under the profitable border a condition criterion named the point of no return is introduced.

Influence of Injection Molding Process Parameters on Part Quality

A case study to determine the influence of injection molding process parameters on part quality is performed. Part quality is evaluated based on deflection rate, volumetric shrinkage, and sink mark depth results. Considered process parameters are mold temperature, melt temperature, injection time, pack time, pack pressure and cooling time. A thin walled butterfly valve flap and a thick walled butterfly valve shaft are analyzed separately. Polypropylene is used as molding material. A design of experiment based on the Taguchi method is generated for both parts and a computer simulation to solve the case matrixes is executed. Relative process parameter influence on each individual quality criteria is determined by analysis of variance. Importance of process temperatures as well as parameter impact dependence on characteristic part shape is reveled.

Study of the complementary usages of selective laser sintering during the high volume production of plastic parts

Purpose n n n n nThis paper aims to present a comparison between selective laser sintering and injection moulding technology for the production of small batches of plastic products. n n n n nDesign/methodology/approach n n n n nThe comparison is based on analysing the time–cost efficiencies of each manufacturing process regarding the size of the series for the selected product sample. Both technologies are described and the times and costs of those individual processes needed to create a final product are assessed when using each of the manufacturing processes. n n n n nFindings n n n n nThe study shows that the time-cost efficiency of the selected laser sintering technology increases according to the complexity of the product and decreases with increasing series size and product volume. n n n n nResearch limitations/implications n n n n nThe study and absolute values of the presented results are limited to a selected plastic product, but the series size-focused efficiency analysis could be expanded to general cases. n n n n nOriginality/value n n n n nThe presented analysis could be used as a general guideline for a decision-making process regarding the more efficient manufacturing method. In addition, the results show the viability of using selective laser sintering during the early stages of production when fast product availability is required, regardless of the series size. Also, some complementary effects of using both technologies in the serial production of the same part are discussed.

Influence of Laser Speed on Average Manufacturing Speed of Selective Laser Sintering

With the technology of Additive manufacturing (AM) still developing and more and more AM machines and technologies becoming available, it is very important to know accurate data about every machine to make the right choice for your product. This paper will focus on selective laser sintering (SLS) and more specifically the influence of the laser speed on the average manufacturing speed.

Treatment of movement disorders using deep brain stimulation – illustrative case reports and technical notes

Operative neuromodulation is the field of electrically or chemically altering the signal transmission in the nervous system by implanted devices in order to excite, inhibit or tune the activities of neurons or neural networks to produce therapeutic effects. Deep brain stimulation (DBS) is an important component of the therapy of movement disorders and has almost completely replaced high-frequency coagulation of brain tissue in stereotactic neurosurgery. This article presents the first DBS cases in Slovenia. In the article the technical features and adjustments of magnetic resonance (MR) imaging and development of a new microdrive, which was clinically successfully tested, are described and discussed.

Layered additive manufacturing in clinical medicine

The use of contemporary technologies of Computer Assisted Design (CAD), combined with latest rapid prototyping, tooling and manufacturing, with traditional CT scanning techniques and high medical skills are used as instruments for better diagnostic visualization, simulation of procedures and treatment of patients with craniofacial deformities. They also improve the overall performances of medical and nursing staff thus influencing the quality of medical service. Patients with congenital defects, orthognathic deformities, deformities after malignancy treatment or after craniofacial traumatic injuries of different severities are of particular interests due to both aesthetic and functional alterations. The paper presents two clinical cases - a patient with scull bone defect after brain hemorrhage and brain edema as well as a patient with hemifacial microsomia treated by surgery followed by implantation of titanium angular implant prepared by means of computer tomography scans, Computer Aided Design and Rapid Manufacturing technologies.