Improvement of the Technology of Precision Forging of Connecting Rod-Type Forgings in a Multiple System, in the Aspect of the Possibilities of Process Robotization by Means of Numerical Modeling

The study refers to the application of numerical modeling for the improvement of the currently realized precision forging technology performed on a hammer to produce connecting rod forgings in a triple system through the development of an additional rolling pass to be used before the roughing operation as well as preparation of the charge to be held by the robot's grippers in order to implement future process robotization. The studies included an analysis of the present forging technology together with the dimension-shape requirements for the forgings, which constituted the basis for the construction and development of a thermo-mechanical numerical model as well as the design of the tool construction with the consideration of the additional rolling pass with the use of the calculation package Forge 3.0 NxT. The following stage of research was the realization of multi-variant numerical simulations of the newly developed forging process with the consideration of robotization, as a result of which the following were obtained: proper filling of the tool impressions (including the roller's impression) by the deformed material, the temperature distributions for the forging and the tools as well as plastic deformations (considering the thermally activated phenomena), changes in the grain size as well as the forging force and energy courses. The obtained results were verified under industrial conditions and correlated with respect to the forgings obtained in the technology applied so far. The achieved results of technological tests confirmed that the changes introduced into the tool construction and the preform geometry reduced the diameter, and thus also the volume, of the charge as well as provided a possibility of implementing robotization and automatization of the forging process in the future. The obtained results showed that the introduction of an additional rolling blank resulted in a reduction in forging forces and energy by 30% while reducing the hammer blow by one. Attempts to implement robotization into the process were successful and did not adversely affect the geometry or quality of forgings, increasing production efficiency.

Possibilities of Increasing the Durability of Punches Used in the Forging Process in Closed Dies of Valve Forgings by Using Alternative Materials from Tool Steels and Sintered Carbides

This study refers to an analysis of the durability of forging tools applied in the second operation of producing a valve forging from the chromium-nickel steel, NC3015. Due to the extreme working conditions of the tools, caused by cyclic thermo-mechanical loads, the average durability of tools made from tool steel WLV (1.2365) equals about 1500 forgings. An in-depth, complex analysis was performed on the technology, using macroscopic tests combined with a measurement of the wear/allowance on the tool working surface through 3D scanning; microstructural tests by means of light microscopy; observations of the changes taking place on the working surface with a scanning electron microscope; microhardness measurements; and multi-variant numerical simulations. It was established that the key issue is the proper selection of the process technological parameters, such as the input material and tool temperature, friction, lubrication, tribological parameters, type of tool material, or punch design, because even small changes made to them significantly affect the service life of forging punches. Therefore, to increase the durability of the forging dies, alternative materials made of W360, as well as two high speed steels, S600 and S705, were applied. However, the implemented punch materials did not bring the assumed effect of increased durability, as the highest average durability of steel W60 equaled only 1500 forgings, whereas in the case of the tool steels, this was below 900 forgings. For this reason, at the further stage, punches with sintered carbide inserts were introduced, which made it possible to significantly improve the durability up to the level of as many as 20,000 forgings, which, at the same time, points to a promising direction of further studies on the use of materials and solutions of this type.

Possibilities of Increasing the Durability of Dies Used in the Extrusion Process of Valve Forgings from Chrome-Nickel Steel by Using Alternative Materials from Hot-Work Tool Steels

This study refers to an analysis of the dies used in the first operation of producing a valve forging from chromium-nickel steel NC3015. The analyzed process of manufacturing forgings of exhaust valves is realized in the co-extrusion technology, followed by forging in closed dies. This type of technology is difficult to master, mainly due to the increased adhesion of the charge material to the tool substrate as well as the complex conditions of the tools' operations, which are caused by the cyclic thermo-mechanical loads and also the hard tribological conditions. The average durability of tools made from tool steel WLV (1.2365), subjected to thermal treatment and nitriding, equals about 1000 forgings. In order to perform an in-depth analysis, a complex analysis of the presently realized technology was conducted in combination with multi-variant numerical simulations. The obtained results showed numerous cracks on the tools, especially in the cross-section reduction area, as well as sticking of the forging material, which, with insufficient control of the tribological conditions, can cause premature wear of the dies. In order to increase the durability of forging dies, alternative materials made of hot work tool steels were used: QRO90 Supreme, W360, and Unimax. The preliminary tests showed that the best results were obtained for QRO90, as the average durability for the tools made of this steel equaled about 1200 forgings (with an increase in both the minimal and maximal values), with reference to the 1000 forgings for the material applied so far.

Possibilities of Measuring and Detecting Defects of Forged Parts in Die Hot-Forging Processes

This paper presents research results in the field of industrial die forging, mostly related to the use of advanced measuring techniques and tools, numerical simulations, and other IT tools and methods for a geometrical analysis of the forged items as well as detection of forging flaws and their prevention, and optimization of the hot-forging processes. The results of the conducted investigations were divided into three main areas. The first area refers to the application of, e.g., optical scanners and programs related to their operation, data analysis, including the construction of virtual gauges, measurements of selected geometrical features of both the manufactured forgings and their physical and virtual models, as well as an analysis of the durability of the forging tools based on the proprietary reverse scanning method. The second area presents the results of measurements and analyses performed with the use of finite element modeling and by means of some special functions in the calculation packages, such as contact, flow lines, trap, or fold, for the detection of forging defects and an analysis of the force parameters. In turn, the third area presents a combination of different methods of measurement and analysis, both FEM and scanning, as well as other IT methods (physical modeling, image analysis, etc.) for the analysis of the geometry and defects of the forgings. The presented results point to the great potential of these types of tools and techniques in forging industry applications as they significantly shorten the time and increase the accuracy of the measurement, as well as providing a lot of valuable information, physical variables, and technological parameters that are difficult or impossible to determine either analytically or through experimental means. The use and development of these techniques and methods are fully justified, both in the aspect of science and the increased effectiveness and efficiency of production.

Metallographic Evaluation of Increased Susceptibility to Intermediate Embrittlement of Engine Valve Forgings Made of NCF 3015 High Nickel and Chromium Steel

This paper focused on determining the increased tendency of cracking after the die forging process of high nickel and chromium steel. The increase in carbon content in austenitic nickel-chromium steel promoted the tendency of valve forgings to forging intergranular crack on the valve head. Attention was paid to issues related to the chemical composition of the material to be considered when hot forming nickel-chromium steel components. Optical and scanning electron microscopies were used to examine the microstructure and fracture features of the samples removed from a fractured valve head. The embrittlement was due to microcavity formation at grain boundaries. Creep theory at grain boundaries was used to explain crack formation. The tensile behavior was interpreted from the evolution of the microstructure during deformation and referred to intermediate brittleness to explain the effect of carbon. It was found that the increased carbon content of the nickel-chromium steel and the strong undercooling observed at the edges of the valve head are factors that promote a reduction in grain boundary cohesion and enhance intermediate temperature embrittlement. Finally, it was found that the formation of a heterogeneous structure manifested by the presence of grain boundary M23C6-type carbides in the austenitic matrix was most likely related to the occurring brittleness.

Structural Features of Fatigue Crack Propagation of a Forging Die Made of Chromium-Molybdenum-Vanadium Tool Steel on Its Durability

The paper presents the results of tests on a die insert made of non-standardised chrome-molybdenum-vanadium tool steel used during pre-forging, the life of which was 6000 forgings, while the average life for such tools is 8000 forgings. It was withdrawn from production due to intensive wear and premature breakage. In order to determine the causes of increased tool wear, a comprehensive analysis was carried out, including 3D scanning of the working surface; numerical simulations, with particular emphasis on cracking (according to the C-L criterion); and fractographic and microstructural tests. The results of numerical modelling in conjunction with the obtained results of structural tests allowed us to determine the causes of cracks in the working area of the die, which were caused by high cyclical thermal and mechanical loads and abrasive wear due to intensive flow of the forging material. It was found that the resulting fracture initiated as a multi-centric fatigue fracture continued to develop as a multifaceted brittle fracture with numerous secondary faults. Microscopic examinations allowed us to evaluate the wear mechanisms of the insert, which included plastic deformation and abrasive wear, as well as thermo-mechanical fatigue. As part of the work carried out, directions for further research were also proposed to improve the durability of the tested tool. In addition, the observed high tendency to cracking of the tool material used, based on impact tests and determination of the K_1C fracture toughness factor, led to the proposal of an alternative material characterised by higher impact strength.

Development of Preliminary Precision Forging Technology and Concept for Tools Used to Reforge 60E1A6 Profile Needle Rails with the Use of Numerical and Physical Modeling

This study examines the possibilities of applying numerical and physical modeling to the elaboration of technology and design of tools used in the hot forging of needle rails for railroad turnouts. First, a numerical model of a three-stage process for forging a needle from lead was built in order to develop a proper geometry of the tools' working impressions for physical modeling. Based on preliminary results of the force parameters, a decision was made to verify the numerical modeling at 1:4 scale due to forging force values as well as agreement of the numerical and physical modeling results, which was confirmed by the similar courses of forging forces and a comparison of the 3D scan image of the forged lead rail with the CAD model obtained from FEM. The final stage of our research was modeling an industrial forging process in order to determine the preliminary assumptions of this newly developed method of precision forging using a hydraulic press as well as preparing tools to reforge a needle rail from the target material, i.e., 350HT steel with a 60E1A6 profile to the 60E1 profile used in railroad turnouts.

Assessment of the Possibility of Reducing Energy Consumption and Environmental Pollution in the Steel Wire Manufacturing Process

This paper describes research on the influence the technology of zinc-coated steel wire manufacturing has on the energy and force parameters of the drawing process, energy consumption and zinc expenditure. In the theoretical part of the paper, the theoretical work and drawing power were calculated. Calculations of the electric energy consumption have shown that usage of the optimal wire drawing technology results in a 37% drop in energy consumption, which in the course of a single year translates to savings equal to 13 TJ. This, in turn, results in the decrease of CO₂ emissions by tons and a total decrease of the eco-costs by approximately EUR 0.5 mln. Drawing technology also influences the losses of the zinc coating and CO₂ emissions. Properly adjusted parameters of the wire drawing technology allow obtaining a zinc-coating that is 100% thicker, translating to 265 tons of zinc, whose production generates 900 tons of CO₂ and incurs eco-costs equal to EUR 0.6 mln. Optimal parameters for drawing, from the perspective of decreased CO₂ emissions during the zinc-coated steel wire manufacturing, are as follows: usage of the hydrodynamic drawing dies, angle of the die reducing zone α = 5°, and drawing speed of 15 m/s.

Wear Mechanisms of the Forging Tool Used in Pre-Forming in a Double Forging System of Truck Parts

Tool life in plastic forming processes is a problem of the utmost importance as it significantly affects the cost of production. Hot forging with hammers and mechanical presses is an example of the technological process in which the load on tools is extremely high and, consequently, the lifetime of tools is short. Considering, additionally, that this applies to large-scale production, from an economic point of view, the key issue will be to extend the tool life, make an accurate prediction of the number of parts that can be forged before the replacement of dies is necessary, and develop a system for quick tool changeover. Initially, however, it is necessary to understand the causes of excessive tool wear, which may lie in phenomena occurring at the level of microstructure. The aim of this article was to outline an example of the coexistence of multiple wear mechanisms in hot forging dies. For the modified chemical composition, the microstructure examinations were performed in selected areas of the tool. The research has revealed the causes of cracks in tools and some irregularities in the preparation of tools for production process.

Comparative Analysis of the Wear of NC11LV and Hardox 600 Steel Used in Tools for Extrusion of Clay Strands in the Process of Producing Ceramic Roof Tiles

This article presents the results of a comparative analysis performed with respect to the wear of tools used for the extrusion of a clay strand (for ceramic roof tile) made from two materials: steel NC11LV and steel Hardox 600. The aim of the studies was to determine the causes and mechanisms of wear as well as to evaluate the possibility of choosing the optimal material, mostly in respect to its resistance to intensive wear as well as an increase in the operation time. The results of the conducted investigations included: an analysis of the technology, thermovision measurements of the forming process, a macroscopic analysis combined with 3D scanning of the worn tools, ball-on-disc tests of the sliding wear resistance and hardness measurements. The obtained results demonstrated that the tools made of steel NC11LV were much less worn than those made of steel Hardox 600, as the operation time for the NC11LV steel tools was almost three times longer. The results of the ball-on-disc tests showed a similar manner of wear for both materials (with the working temperature of about 50 °C). The higher durability of the tools made from steel NC11LV can be an effect of a slightly lower coefficient of friction in the initial period of operation as well as the presence of hard carbides, which means increased hardness and thus also higher wear resistance at working temperatures.

The Effect of Drawing in Conventional and Hydrodynamic Dies on Structure and Corrosion Resistance of Hot-Dip Galvanized Zinc Coatings on Medium-Carbon Steel Wire

The paper presents the impact of the drawing method on the microstructure and corrosion resistance of galvanized steel wires. The microstructural tests confirmed that, in the drawing speed range v = 5-20 m/s, the use of hydrodynamic dies creates more favorable conditions for the deformation of the soft zinc coating on the hard steel core. The increase in friction at the wire/die interface in the conventional method, as compared to the hydrodynamic method, contributed to the decrease in coating thickness and the increase in the diffusion layer, and the higher the drawing speed, the greater the differences between the analyzed drawing methods. In the conventional method, while drawing at high speeds v = 20 m/s, there was a two-way diffusion and complete remodeling of the ζ phase in δ₁. In the hydrodynamic method, at the speed of 20 m/s, in the analyzed micro-areas, places showing the presence of the ζ phase, partially dispersed in the layer with pure zinc, were observed. A corrosion tests comparison between conventionally and hydrodynamically drawn wires showed an improved behavior of the latter. The greater mass in the surface layer of pure zinc, a substrate for the corrosion product in hydrodynamically drawn wires, reacted, creating insulation from the white corrosion produced. The compressive stresses in the hydrodynamic dies caused by the high pressure of the lubricant on the circumference of the wire closed the microcracks on its surface, which additionally sealed the zinc coating.

Development of Induction Heating System Ensuring Increased Heating Efficiency of the Charge Material in a Forging

This study performs a complex analysis and review of the currently applied methods of inductively heating the charge material in hot die forging processes, as well as elaborates and verifies a more effective heating method. On this basis, a device for inductive heating using variable frequency inductors was designed and constructed, which made it possible to reduce the scale and decarburization with respect to the heater used so far. In the first place, the temperature distributions in the heater in the function of time were modeled with the use of the CEDRAT FLUX software. The aim of the research was to analyze the temperature gradient and value diversification on the surface and in the material core, as well as to determine the process stability. The following stage was designing and constructing a heater with an automatic system of loading and positioning of the charge on the exit, as well as with a possibility of working in a fully automated system adjusted to the work center. The last stage of investigations was the verification of the elaborated effective heating method on the basis of a short production series and a continuous work for the period of 8 h, both in the quantitative and qualitative aspect (reduced oxidation and decarburization as well as a gradient between the core and the surface). The obtained results confirm the effectiveness of the proposed solution referring to heating the charge material, especially in the aspect of stability and repeatability of the process, as well as a significant reduction in oxidation and decarburization of the material surface.

Wear Analysis of Forging Tools Used in an Industrial Production Process-Hot Forging in Closed Dies of the "Head-Disk" of an Engine Valve Forging

The article performs an analysis of the durability of punches applied in the process of producing a valve forging from chromium-nickel steel. A forging of this type is made in two operations: coextrusion of a long shank, followed by finishing forging in closed dies of the valve head. The product obtained in this way (after other additional finishing procedures) constitutes the key element of the combustion engine (resistant to high pressures and temperatures) in motor trucks. Unfortunately, a significant problem in this production process is a relatively low durability of the forging tools, especially the punch used in the second forging operation. The key element at this stage, deciding about the punch’s further operation, is the area of the so-called “calotte”. The short-term life of the tools results from very hard performance conditions present during the forging process (periodical high mechanical and thermal loads, long path of friction). The latter cause intensive abrasive wear as well as high adhesion of the forging material to the tool surface. Based on the performed studies, including the following: technology analysis, numerical modelling, macro analyses combined with 3D scanning of tool sections as well as microstructural tests and hardness measurements, it was established that it is crucial to properly select the process parameters (charge and tool temperature, tribological conditions), as even slight changes introduced into them significantly affect the operation time of the forging tools. Mastering and proper implementation of the analyzed forging technology requires numerous further studies and tests, which will enable its perfection and thus increase the durability of the tools as well as the quality of the produced items.

The Impact of the Lubricant Dose on the Reduction of Wear Dies Used in the Forging Process of the Valve Forging

The paper presents the results of research on the influence of the settings of lubrication and cooling system parameters (solenoid valve opening time and lubricant feed pressure in terms of its quantity) in order to select the optimal lubricating conditions and thus reduce the wear of the dies used in the first forging operation of the valve forging made of high-nickel steel. Based on the observation of lubrication in the industrial process, it was found that a significant part of the lubricant fails to reach the die cavity, reaching the outside of it, which causes die wear due to seizure resulting from adhesion of the forging material to the tool surface as well as high lubricant consumption and dirt in the press chamber. The authors proposed their own mobile lubricating and cooling system, which allows for a wide range of adjustments and provided with automatic cleaning procedures of the entire system, unlike the fixed lubrication system used so far in the industrial process. First, tests were carried out in laboratory conditions to determine the highest wettability and the lubricant remaining inside the tool cavity. These tests determined the lubrication system parameter settings that ensured that the greatest amount of lubricant remains in the cold die cavity without the forging process. Then, to verify the obtained results, tests were carried out in the industrial process of hot die forging of valve forgings for short production runs of up to 500 forgings. The results were compared with the measurement of changes in the geometry of tools and forgings based on 3D scanning and surface topography analysis with the use of SEM (Scanning Electron Microscope). For the best results (the variant of the setting of the dose and the time of exposure to lubricant), the forging process was carried out with the use of a new tool up to the maximum service life.

The Multi-Stage Drawing Process of Zinc-Coated Medium-Carbon Steel Wires in Conventional and Hydrodynamic Dies

This paper discusses experimental studies aiming to determine the effect of the drawing method on the lubrication conditions, zinc coating mass and mechanical properties of medium-carbon steel wires. The test material was 5.5 mm-diameter galvanized wire rod which was drawn into 2.2 mm-diameter wire in seven draws at a drawing speed of 5, 10, 15, 20 and 20 m/s, respectively. Conventional and hydrodynamic dies with a working portion angle of α = 5° were used for the drawing process. It has been shown that using hydrodynamic dies in the process of multi-stage drawing of zinc-coated wire improves the lubrication conditions, which leads to a reduction in friction at the wire/die interface. As a consequence, wires drawn hydrodynamically, as compared to wires drawn conventionally, are distinguished by a thicker zinc coating and better mechanical and technological properties.

Application of a Prototype Thermoplastic Treatment Line in Order to Design a Thermal Treatment Process of Forgings with the Use of the Heat from the Forging Process

The global production of die forgings is an important branch of the motor industry for obvious reasons, resulting from the very good mechanical properties of the forged products. The expectations of the recipients, beside the implementation of the forging process, include also a range of supplementary procedures, such as finishing treatment including shot blasting, thermal treatment, and machining, in order to ensure the proper quality of the provided semi-product or the ready detail for the assembly line. Especially important in the aspect of the operational properties of the products is the thermal treatment of the forgings, which can be implemented in many variants, depending on the expected results. Unfortunately, a treatment of this type, realized separately after the forging process, is very time and energy-consuming; additionally, it significantly raises the production costs due to the increased energy consumption resulting from the necessity of repeated heating of the forgings for such thermal treatment. The article reviews the most frequently applied (separately, after the forging process) thermal treatments for die forgings together with the devices/lines assigned for them, as well as presents an alternative (thermoplastic) method of forging production with the use of the forging heat. The paper also presents a prototype semi-industrial controlled cooling line developed by the authors, which allows the development of the assumed heat treatment of forgings directly after forging with the use of forging heat, together with sample results of conducted tests.

Support Possibilities for 3D Scanning of Forging Tools with Deep and Slim Impressions for an Evaluation of Wear by Means of Replication Methods

This article discusses the problems related to the use of non-contact 3D scanning techniques and their support by means of replication methods for the analysis of the geometrical changes in deep tool impressions used for the forward extrusion of valve-type elements assigned for motor truck engines. The 3D scanning method, despite its unquestionable advantages, also has certain limitations, such as scanning the inner surfaces of deep cavities. This is caused by the fact that the larger the angle between the reflected laser light and the normal direction to the measured surface, the larger the area covered for the analysis, yet at the same time, the higher the measurement error. The authors performed an analysis of the geometrical loss of the tools as well as the corresponding replication masses, together with a discussion of the results related to minimization of the measuring errors. For the analyzed tool, the maximum angle during direct scanning was 40 degrees, which unfortunately does not enable an analysis of the entire pattern, while for larger angles, it is necessary to make the measurement by indirect scanning, i.e., by replicating the cavity imprint of the tool. Therefore, for a given geometry, the reflection angle should be determined individually.