Search

Injection molding is an advantageous technology for the mass production of plastic parts without the necessity for additional procedures. The applicability of this method is still partially limited by the required properties of the manufactured parts. Especially in the field of optics, there is a need to produce thick-walled parts while maintaining their transparency. This paper reports on how various shapes of gating systems affected the process parameters and cavity filling during the injection molding of polycarbonate thick-walled specimens. These outcomes demonstrated that film gates and their alternatives are more suitable for the standard injection molding of thick-walled optical products than the triple-edge gating systems. Favorable results were observed particularly in the uniformity of cavity filling, size of shrinkage, and in the occurrence of defects such as voids or sink marks.

Fused Filament Fabrication (FFF) printers are usually designed to create a product with one single material. Some of them allow fabricating items in multiple colours but creating a single product consisting of two different materials remains an advantage of industrial 3D printers only. The aim of this research was to develop a design of a device with two printheads which enables to print products with two different materials, compatible with a cheap and commonly available FFF device Prusa i3MK2S, and the subsequent production of a prototype. A key aspect of the design was the hardware compatibility of the device with the given printer while maintaining the maximum possible printing area., IGA/FT/2023/005, Internal Grant Agency of TBU in Zlin [IGA/FT/2023/005]

Cross-linking is a process in which polymer chains are associated through chemical bonds. Radiation, which penetrated through specimens and reacted with the cross-linking agent, gradually formed cross-linking (3D net), first in the surface layer and then in the total volume, which resulted in considerable changes in specimen behaviour. Creep value is an important parameter that describes the behaviour of a material for the duration of its exposure to long term stress. Most of the technical parts used in industry are subjected to the long term stress for their whole life cycle. This can lead to material creep, which directly results in the transformation of dimensions. To eliminate this problem, a number of construction materials was chosen and subsequently irradiated by a source of electrons. This created a 3D network within the polymer structure, which led to an increase of the micro-mechanical and micro-creep properties. Evaluation of these modifications was done by state of the art device Micro-combi tester manufactured by Anton Paar. This device lowers the time required to measure the creep by standard technology and it fluently records the changes of indentation depth in relation to applied force. This dependence is then used to calculate the creep values. Due to the electron irradiation, a 40 % increase was reached in creep resistance; therefore the useful properties of selected construction materials were improved. © Czech Technical University in Prague, 2020., European Regional Development Fund under the project CEBIA-Tech Instrumentation [CZ.1.05/2.1.00/19.0376]; Ministry of Education, Youth and Sports of the Czech RepublicMinistry of Education, Youth & Sports - Czech Republic [LO1303 (MSMT-7778/2014)]; Internal Grant Agency of TBU in Zlin [IGA/FT/2020/003], IGA/FT/2020/003; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT: LO1303, MSMT-7778/2014; European Regional Development Fund, FEDER: CZ.1.05/2.1.00/19.0376

Cross-linking is a process in which polymer chains are associated through chemical bonds. The cross-linking level can be adjusted by the irradiation dosage and often by means of a cross-linking booster. The polymer additional cross-linking influences the surface nano and micro layers in the way comparable to metals during the thermal and chemical-thermal treatments. Polybutylene terephthalate (PBT) can be found in a group of structural polymers, which are often used in industry, especially in automotive. Applying the technology of electron radiation induces a creation of 3D network structure, which improves the local mechanical properties. These were later measured by a depth sensing indentation (DSI) test. This state of the art method is based on immediate detection of indentation depth in relation to applied force. The creation of 3D network caused an increase in nano-mechanical properties values, such as indentation hardness and indentation modulus, in comparison to the virgin material. The indentation hardness rose by 80%, while the indentation modulus elevated by 62%. The selected structural materials, e.g. PBT, were modified by the electron irradiation in a positive way and as such could be moved to a group of high performance materials. © Czech Technical University in Prague, 2020., European Regional Development Fund under the project CEBIA-Tech Instrumentation [CZ.1.05/2.1.00/19.0376]; Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Program [LO1303 (MSMT-7778/2014)]; Internal Grant Agency of TBU in Zlin [IGA/FT/2020/003], IGA/FT/2020/003; Ministerstvo Školství, Mládeže a Tělovýchovy, MŠMT: LO1303, MSMT-7778/2014; European Regional Development Fund, FEDER: CZ.1.05/2.1.00/19.0376

New technologies known as unconventional technologies make it possible to cut complex shapes at high speed and with relatively high precision. In many cases, especially in the case of thin sheet, created parts produced do not require any further treatment by post-machining. Knowledge of the accompanying phenomena, such as the heat-affected zone (HAZ) or the surface quality of the cutting edge, is necessary, for example, to assess further machining of material in these areas (e.g. drilling and reaming holes or finishing operations on the cutting edge). In this study, the thermal effect of four unconventional cutting technologies – laser, plasma, wire electrical discharge machining (wire EDM) and waterjet cutting on the cut surface of steel sheets is investigated. Steel 1.7102 (DIN 54SiCr6) was chosen for purpose of this study. The width of the HAZ and the nanohardness beneath the cut surface were analyzed.

Commodity polymers are a common part of everyday life. They consist mainly of polyolefins such as polyethylene, polypropylene. They are primarily used for ease of processing, cost and especially chemical resistance. The disadvantages of these polymers are low mechanical properties as well as temperature resistance. Any improvement in the mechanical properties can extend the application possibilities of the commodity polymers to the areas reserved for the construction polymers. This paper deals with changing two injection moulding process parameters - melt and mould temperature to high-density polyethylene (HDPE) surface hardness. HDPE hardness was measured using the method of Depth-Sensing Indentation (DSI) on three different instruments (ultranano-, nanoand micro-hardness tester). It has been found that as the melt and mould temperature increases, the hardness slightly increases.

Irradiation of polymeric materials is a modern method of modifying their final properties (for example, improvements in mechanical, thermal and chemical properties). The main used types of radiation to modify polymers include ionic and ionizing radiation. Due to its properties, ionization beta (electron) radiation is the most widely used. The interaction of ionizing radiation with polymeric materials manifests as radiation cross-linking, which is a result of recombination of migrating polymer radicals into the amorphous region. In this type of radiation, electrons are generated under high vacuum using a hot cathode. Electrons emitted from the cathode are then accelerated in the electrostatic field that arises between the cathode and the anode. The depth of penetration into the material rises with increasing energy of electrons. This study examines the influence of ionizing beta radiation on the flammability index and ignition temperature of thermoplastic materials.

This study focuses on the problematic of polyamide 6 containing various concentrations of cross-linking agent that was exposed to electron radiation. It is important to improve the material properties of polymers as much as possible. This endeavor can be realized by numerous methods, one of which is radiation exposure. This study investigates the effect of electron beam radiation in doses ranging from 66 to 132 kGy on the micro-mechanical properties of polymers, specifically pol-yamide 6 filled with 1, 3 and 5 wt.% of cross-linking agent triallyl isocyanurate (TAIC). The changes in the material brought by the radiation exposure were quantified by measurements of indentation hardness and modulus, which were the main measured micro-mechanical properties. Furthermore, thermo-mechanical analysis (TMA) was chosen to confirm the results of the material cross-linking, while the effect of degradation was investigated by Fourier-transform infrared spectroscopy (FTIR). In pursuit of complete evaluation, the topography of the test subject’s surface was explored by atomic force microscopy (AFM). The optimal concentration/radiation ratio was found in polyamide 6 enriched by 5 wt.% concentration of TAIC, which was irradiated by 132 kGy. Material treated in such a way had its indentation hardness by 33% and indentation modulus improved by 26% in comparison with the untreated material. These results were subsequently confirmed by the TMA and FTIR methods. © 2021 by the authors. Licensee MDPI, Basel, Switzerland., IGA/FT/2021/005, TBU in Zlin Internal Grant Agency [IGA/FT/2021/005]

In the production of plastics tools, due to the high mould price, high demands are placed on cost reduction or shortening mould production times. The price of the injection mould is reflected not only in the price of used injection material but also in the price of its own production.Mould form cavities were made with different materials and different machining technology (finishing methods). Various polymeric materials were injected into the cavities thus prepared, and the surface quality of the samples was evaluated and compared to the quality of the surface cavities, thereby verifying the copying of the surface of the mould cavity onto the surface of the polymer product. The aim of this article is to determine the impact of technological conditions on the quality of the plastic tool (injection mould) and the future polymer product. In this experiment, they were made by different technological conditions of the shape cavity and their influence on the resulting roughness parameters of tested samples was determined.

The article deals with additive manufacturing technologies especially with ability to create reports on FDM 3D printers. These assemblies are non-disambiguable. Therefore, it is important to choose the optimal magnitude of the deviation between the walls so that the mechanism has the required mobility. These deviations are examined in several materials with different rheological properties. Finally, the dependence of the magnitude of the variance between the walls and the thickness of the layer for the given materials is shown. The result is the recommendation of modelling and printing parameters.

Polymer injection molding is the most used technology of polymer processing nowadays. It enables the manufacture of final products, which do not require any further operations. Working of shaping cavities is the major problem involving not only the cavity of the mold itself, giving the shape and dimensions of the future product, but also the flow pathway (runners) leading the polymer melt to the separate cavities. This paper shows the influence of cavity surface roughness, polymer material (with different flow properties) and technological parameters on the flow length of polymers into mold cavity. Application of the measured results may have significant influence on the production of shaping parts of the injection molds especially in changing the so far used processes and substituting them by less less expensive production processes which might increase the competitiveness of the tool producers and shorten the time between product plan and its implementation.

Modification of polymers by fillers is one of the most used material alterations to improve its required properties. This article is about modification of polymer matrix by fillers with layered particles. Linear low density polyethylene (LLDPE) was used as matrix and it was mixed with different kinds of fillers. Fillers used were: CaPhP – Calcium Phenylphosphonate, double layered hydroxides (ZnAl-DDS, ZnAl-lac and ZnAl-CO3) and natural Talc. Individual fillers were mixed into the matrix by kneading machine with the use of several velocities. The article focuses on influence of the individual filler on mechanical properties measured by tensile strength test. This paper also investigates the problem of process parameters’ influence on final mechanical properties and later confirms positive impact of all fillers that were used, although the size of them differs.

Good quality of surface layer is an important aspect for correct function and longevity of final product. Surface layer was modified by beta radiation with differing intensity. Radiation caused creation of three dimensional spatial network, that directly leads to improvements of the tested polymer’s (PA11, PA12) surface properties. Surface properties (micro-creep) were measured by micro-indentation test on MHT3 machine. Goal of this paper is to modify the surface layer (by using several different intensities of beta radiation) in a way, that causes increase in resistance against long term stress (micro-creep) in the final product, which is an important property that ensures correct function of the product. The changes in micro-creep were compared and afterwards confirmed by the use of gel test, that showed us what percentage of the whole part was crosslinked.

Injection molding is one of the most extended plastic processing technologies. Delivery of polymer melts into the mold cavity is the most important stage of the injection molding process. This paper shows the influence of mold cavity surface roughness and technological parameters on the flow length of thermoplastic elastomers and rubber into mold cavity. The fluidity of polymers is affected by many parameters (mold design, melt temperature, injection rate and pressures) and by the flow properties of polymers. Evaluation of the data obtained by experiments where the testing conditions were widely changed shows that quality of the cavity surface does not affect the length of flow.

Surface properties are important aspect for correct function of construction (technical) parts. By improving mechanical properties of surface, an increase of abrasion resistance and wear resistance is reached. Longevity and economical aspect have an important role in final useful properties of product. Measurement of surface properties was done by ultra-nanoindentation technique (UNHT3), this is the best tool available right now, this technique is based on instrumented testing. Surface properties were modified by ionized radiation, that caused the creation of crosslinked structure in polyethylene. During radiation a three dimensional network is created, that improves final properties of product such as: hardness, elasticity modulus, thermal stability, etc. During ionized radiation there are two actions that take place at the same time, crosslinking and degradation. Goal of this paper is to consider how radiation intensity affects surface properties (indentation hardness, indentation modulus, deformation work, etc.) Another goal of this paper is to find out the optimal dose of radiation, that will cause more three dimensional crosslinking and less degradation as degradation causes decrease in mechanical properties.

The presented article deals with the thermal energy influence on various types of construction steels during laser beam cutting. When the material is cut by a laser, the workpiece is subjected to intensive thermal load. Due to this influence, steels hardness is increased and the structure is changed.The aim of this study is to verify how the thermal energy influences the surface layer of material during laser cutting. The influence was studied on data measured by DSI (depth sensing indentation) micro-hardness method. Each sample was subjected to cross-section from edge to the distance of 20 mm from the edge measurement. To evaluate surface layers during laser cutting, three types of steels with different carbon content 1.0038 (S235JR), 1.1203 (C55) a 1.7131 (16MnCr5) were chosen. The main objective was to determine the distance from the cutting point to the material when cutting with a laser beam, how its micro-mechanical properties and structure change or the distance from the cutting point to the component's hardening.

This publication deals with influence of tool topography (injection mould) on properties of a product. Surface of the mould was machined by various finishing technologies (milling, grinding, polishing and electrical discharge machining) which resulted in varying surface quality of the tool. The tested topography had an effect on the flow length of polymer and topographical and mechanical properties of the specimen. Examined properties (surface topography and mechanical properties) were measured in several places along the length of the product (starting at the gate and finishing at the end of the specimen). The results show that increase of the tool’s surface roughness leads to longer flow length. These findings disprove the necessity for polishing of each and every shaping part of the mould when manufacturing non-visual products. Thus, from economical and manufacturing perspective the milled or grinded tool surfaces are sufficient. Furthermore, replication of the tool’s topography is non-homogenous, which results in varying mechanical properties throughout the product. The discrepancy in mechanical properties along the length of the product is caused by differing cooling speeds in the mould. In practice, guided cooling can be used to achieve varying mechanical properties in desired places of the injected article. For example, highly stressed parts can be manufactured with the goal of having improved mechanical properties in specific places of the product. Future application of these findings poses a significant benefit for industrial practice, as it could lower the manufacturing cost of the injection mould in order of tens of percent.

This study&rsquo, s goal was to describe the influence of a wide range of ionizing beta radiation upon the changes in surface layer mechanical properties and structural modifications of selected types of polymer. Radiation crosslinking is a process whereby the impingement of high-energy electrons adjusts test sample structures, thus enhancing the useful properties of the material, e.g., hardness, wear-resistance, and creep, in order that they may function properly during their technical use. The selected polymers tested were polyolefin polymers like polyethylene (Low-density polyethylene LDPE, High-density polyethylene HDPE). These samples underwent exposure to electron radiation of differing dosages (33, 66, 99, 132, 165, and 198 kGy). After the crosslinking process, the samples underwent testing of the nano-mechanical properties of their surface layers. This was done by means of a state-of-the-art indentation technique, i.e., depth-sensing indentation (DSI), which detects the immediate change in the indentation depth associated with the applied force. Indeed, the results indicated that the optimal radiation dosage increased the mechanical properties by up to 57%, however, the beneficial levels of radiation varied with each material. Furthermore, these modifications faced examination from the structural perspective. For this purpose, a gel test, Raman spectroscopy, and crystalline portion determination by X-ray all confirmed the assumed trends.

This article deals with the influence of the radiation cross-linking of polyamide 11 (PA 11) on the mechanical properties. The aim of this study is to provide more detailed knowledge of the relation between the radiation dosage and the properties of cross-linked PA 11 and its mechanical behaviour. Electron-beam-unmodified and modified PA 11 test samples were exposed to electron radiation with dosages from 0 kGy to 198 kGy, which were graded at 33 kGy. The surface-layer properties of the modified PA 11 were tested using a state-of-the-art indentation technique, which detects the immediate change in the indentation depth, depending on the applied force. The evaluation of the measured mechanical properties (indentation hardness, modulus and creep) was done by the Oliver and Pharr method. A significant influence of the radiation cross-linking on the PA 11's mechanical properties improvement was confirmed by the measurements. This enhancement grows with the increasing radiation dosage. Due to the electron-radiation modification of PA 11, the mechanical properties of the surface layer were increased by up to 59 % compared with the unaltered material. Radiation crosslinking is an important thermoplastic modification method by which the desired properties can be achieved in a relatively short period of time. The main advantage is that the process is executed on the final product., European Regional Development Fund under the project CEBIA-Tech Instrumentation [CZ.1.05/2.1.00/19.0376]; Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Program [LO1303 (MSMT-7778/2014)]; Internal Grant Agency of TBU in Zlin [IGA/2020/003]

In recent years, materials with natural fillers have begun to be used for manufacturing window frames and various linings. These compounds can replace natural materials such as wood and stone. The main reasons to use these fillers are price (which is lower than that of a polymer) and rigidity. The resulting product is strong, hard, light, possesses a long-term resistance to wind abrasion and takes on the appearance of wood and stone. The type of filler has a significant effect on the final properties of the material. In the past, however, insufficient attention was paid to the effect of natural fillers on the injection-molded product's mechanical properties. First, the test samples were measured by depth sensing indentation (DSI), which is a contemporary instrumented hardness test used to determine the micro-mechanical properties. A Micro Combi Tester made by the Anton Paar company was used for these tests. Then, the measurements were evaluated by the Oliver and Pharr method. The goal of this study was to prepare a low-density polyethylene (LDPE) filled with varying natural fillers, e.g., finely ground wood, coarsely ground wood and slate) and its subsequent granulation. The implementation of these fillers led to an increase of the mechanical properties, e.g., indentation hardness and modulus, by up to 100 % in comparison with the virgin material. The goal of this study was to evaluate the effect of natural fillers, such as wood and slate, on the mechanical properties of the tested materials., European Regional Development Fund under the project CEBIA-Tech Instrumentation [CZ.1.05/2.1.00/19.0376]; Ministry of Education, Youth and Sports of the Czech Republic within the National Sustainability Program [LO1303 (MSMT-7778/2014)]; Internal Grant Agency of TBU in Zlin [IGA/FT/2020/003]

Cross-linking is a process in which polymer chains are associated through chemical bonds. Radiation, which penetrated through specimens and reacted with the cross-linking agent, gradually formed cross-linking (3D net), first in the surface layer and then in the total volume, which resulted in considerable changes in specimen behavior. This paper describes the effect of electron beam irradiation on the nanoindentation creep of unfilled and glass fiber filled polypropylene (25%). nanoindentation creep were measured by the DSI (Depth Sensing Indentation) method on samples which were non-irradiated and irradiated by different doses of the β – radiation (0, 30, 45 and 60 kGy). The purpose of the article is to consider to what extent the irradiation process influences the resulting nanoindentation creep measured by the DSI method. The unfilled and filled polypropylene tested showed significant changes of indentation creep. The measured results indicate, that electron beam irradiation is very effective tool for improvement of creep properties of unfilled and filled polypropylene. The nanoindentation creep after irradiated unfilled Polypropylene was decreased up to 16 % (filled polypropylene was decreased up to 9%) compared to non-irradiated surface. These changes were examined and confirmed by Gel content.

Cross-linking is a process in which polymer chains are associated through chemical bonds. Radiation, which penetrated through specimens and reacted with the cross-linking agent, gradually formed cross-linking (3D net), first in the surface layer and then in the total volume, which resulted in considerable changes in specimen behavior. This paper studies the effect of different doses of ionizing beta radiation on the micro-mechanical properties of commercially available polyamide. The measured results indicate, that electron beam irradiation is very effective tool for improvement of surface properties of PA6. In terms of micro-mechanical properties, the values of micro-hardness of surface layer increased by 24% at radiation dose of 132 kGy, stiffness of surface micro layer by 26% (132 kGy) as a result of different loads (0.5N and 2N). Improvement of micro-mechanical properties of radiated polyamide has a great significance also for industry. The modified polyamide shifts to the group of materials that have considerably better properties. Its micro-mechanical properties make polyamide ideal for a wide application in areas where higher resistance to wear, creep are required. Commonly manufactured PA6 can hardly fulfil these criteria.

Nowaday´s trend is the effort to replace metal materials with the polymers, which already have the irreplaceable place in the field of the construction of various applications. Development offices effort is to achieve the best polymer quality for which various ways of modification are used. Besides common fillers and e.g. modification using beta radiation, there is a possibility to modify these properties (creep resistance, hardness, tensile strength) with the nanofillers, which have also the irreplaceable place in the field of development. This article deals with the possibilities of use of the nanofillers in HDPE material and primarily with the influence on creep properties of thus modified matrix. The influence of nanofillers shows a considerable influence in various materials, which should contribute to better resistance during these long-term tests.

This study describes the influence of polymer flow length on mechanical properties of tested polymer, specifically polycarbonate. The flow length was examined in a spiral shaped mould. The mould cavity’s surface was machined by several methods, which led to differing roughness of the surface. The cavity was finished by milling, grinding and polishing. In order to thoroughly understand the influence of the mould surface quality on the flow length, varying processing parameters, specifically the pressure, were used. The polymer part was divided into several segments, in which the micro-mechanical properties, such as hardness and indentation modulus were measured. The results of this study provide interesting data concerning the flow length, which was up to 3% longer for rougher surfaces, but shorter in cavities with polished surface. These results are in disagreement with the commonly practiced theory, which states that better surface quality leads to greater flow length. Furthermore, evaluation of the micro-mechanical properties measured along the flow path demonstrated significant variance in researched properties, which increased by 35% (indentation hardness) and 86% by indentation modulus) in latter segments of the spiral in comparison with the gate. © 2021 by the authors. Licensee MDPI, Basel, Switzerland., project TBU in Zlin Internal Grant Agency [IGA/FT/2021/005], IGA/FT/2021/005

This research paper studies the influence of preparation method of recycled polymer material with glass fibers on the tensile properties of the final product. The recycled material was made from polypropylene, which originally contained 30 % of glass fibers. It was divided into fractions using size of the crushed particles. These fractions ranged from large particles, similar to the original material, to small dust particles. Measurements were performed at various temperatures. It was found that the mixture of dust particles showed a large decrease in measured properties. It is mainly due to shortening of the large glass fibers, so that it no longer fulfills its function as reinforcing filler. Conversely, mixture with larger particles did not show a significant decrease in properties compared to the original material.

This article is focused on a test assesment with a low repeatability, which is typical of its financial and time severity. In the introduction of this work the assessment of the current state of the solved problem concentrated on the creep test assesment is carried out, which is typical of its low repeatability. These results are subsequently graphically confronted with the subjective assessment of the observer and using Mann-Whitney test. This test is there used for finding if measured data come from the same basic file or come from the selected confidence level. The results show the significance of using this test, which is calculated with certain probability.

The presented article deals with the research of micro-mechanical properties in the surface layer of modified linear polyethylene (LLDPE). These micro-mechanical properties were measured by the Depth Sensing Indentation - DSI method on samples which were non-irradiated and irradiated by different doses of the β - radiation (0, 66, 132 and 198 kGy ). Individual radiation doses caused structural and micro-mechanical changes which have a significant effect on the final properties of the LLDPE tested. The highest values of micro-mechanical properties were reached at radiation dose of 132 kGy, when the micro-hardness values increased by about 29%. These results indicate advantage crosslinking of the improved mechanical properties.