The diploma thesis deals with the optimization of final position of overlaps on a forged cam. This part is manufactured in Šroubárna Kyjov, spol. s r.o. The cam is made from ČSN 14 109 (100Cr6) steel. The thesis is focused on the optimization of overlaps arising due to pressed burrs on the edges of the semifinished forging. Currently, the final position of these overlaps is very close to the edge of the pre-forged hole of the cam. Undesired chipping of material occurs during machining of the hole to the exact dimension. The final position of the overlaps is optimized by using the numerical simulation in Simufact Forming 15.0, including a verification simulation for optimal parameter settings. Various diameters of semifinished products, turned tools, and modification of shapes of the tools are tested in the thesis to prevent occurrence of the overlaps in undesired positions.

The thesis is focussed on improving the material yield in closed-die forging and rolling. The former is restricted to the manufacturing of heavy crown wheels and front axle beams and the latter to the hot rolling of steel slabs. To enhance the yield the commercial FE-codes Form2D and Dyna3D are used. Results from forging simulations are strengthened by full scale experiments. The research is carried out in near contact with the Swedish steel and engineering industry. In closed die forging, two bulk forming problems are treated: How to improve the tool design and how to change the pre-form geometry for decreasing the amount of material exiting the flash gap? In slab rolling, two problems related to material defects are considered: How to eliminate existing surface cracks and how to prevent the formation of voids around macro-inclusions embedded in the steel matrix? Internal voids might be the reason for scrapping the whole workpiece. Considering the forging of crown wheels, a new concept is proposed. For making the central hole of the product, the traditional method was forging a thin circular plate which was then sheared off and scrapped. Using the new technique this operation is replaced by forging a conical tap in the centre, which is then discarded. Doing so, the inner scrap material decreased with about 15%. The idea has been used in production for seven years. – Regarding the forging of front axle beams, a quasi-3D method is used comprising full scale measurements of the axial material flow. Here the theoretical material yield increased 2-7%. Regarding rolling, the initial surface cracks in the simulations are V-shaped with a crack angle of 6o and of depth 5-20 mm. The inclusions are cylindrical and either three times harder or three times softer than the matrix. The behaviour of the cracks and the inclusions are studied as influenced by process parameters. Current industrial input data are used as a reference. – It is concluded that longitudinal cracks cannot be totally eliminated. During rolling their V-shape gradually changes to Y-shape and a remaining oxide flake separates the crack bottom surfaces. For minimizing the detrimental influence of the entrapped oxide, an early closure of the crack bottom is important. Throughout the remaining rolling schedule the entrapped oxide is then torn to pieces with large areas of virgin metal in between ensuring a strong bond. The following recommendations are given for the longitudinal cracks: Light drafts/pass at the beginning of the rolling schedule followed by heavy ones. – Contradictory to longitudinal cracks it is concluded that transversal cracks are possible to eliminate. When eliminated, the initial bottom of the crack coincides with the slab surface. No folds are formed. For the transversal cracks light drafts/pass are proposed together with reversal rolling, the latter for avoiding crack folding. – Voids are easiest formed around hard macro-inclusions in the centre of the slab. Large rolls and heavy drafts are recommended to avoid this. / QC 20100720

Forging temperature is one of the basic considerations in forging processes. In warm forging, the metals are forged at temperatures about the recrystallization temperature and below the traditional hot forging temperature. Warm forging has many advantages when compared to hot and cold forging. Accuracy and surface finish of the parts is improved compared to hot forging while ductility is increased and forming loads are reduced when compared to cold forging. In this study, forging process of a part which is currently produced at the hot forging temperature range and which needs some improvements in accuracy, material usage and energy concepts, is analyzed. The forging process sequence design with a new preform design for the particular part is proposed in warm forging temperature range and the proposed process is simulated using Finite Element Method. In the simulations, coupled thermal mechanical analyses are performed and the dies are modeled as deformable bodies to execute die stress analysis. Experimental study is also carried out in METU-BILTIR Center Forging Research and Application Laboratory and it has been observed that numerical and experimental results are in good agreement. In the study, material wastage is reduced by proposing using of a square cross section billet instead of a circular one, energy saving and better accuracy in part dimensions is achieved by reducing the forging temperature from the hot forging to the warm forging temperature range.

Forging is a manufacturing process which is preferred among the others in that, the final product shows more enhanced properties. The properties of the final product are directly related with the material used in the forging process. Main parameters such as forging temperature, number of stages, preform design, dimensions of the billet, etc. may be affected by the forging material. Alloys are one of the main areas of interest in the forging industry. The use of alloy steels may bring superior properties, especially in terms of strength and forgeability. In this study, three different alloy steels, which are hot forged in industry have been examined. The flow of the material, stress distribution, die filling and the effects of the process parameters on the forging have been investigated. Three industrial forging parts / M20 and M30 eye bolts and a runner block have been studied. Finite Volume Analysis of the forging process has been performed for carbon steels / C45 and C60 and alloy steels / a stainless steel X20Cr13, a heattreatable alloy steel, 42CrMo4 and a bearing steel, 100Cr6. The results of the simulations have been compared with the findings of the experiments carried out in a forging company. It has been observed that numerical and experimental results are in good agreement.

WEAR ANALYSIS OF HOT FORGING DIES ABACHI, Siamak M. S., Department of Mechanical Engineering Supervisor: Prof. Dr. Metin AKK&Ouml / K Co-Supervisor: Prof. Dr. Mustafa lhan G&Ouml / KLER December 2004, 94 pages The service lives of dies in forging processes are to a large extent limited by wear, fatigue fracture and plastic deformation, etc. In hot forging processes, wear is the predominant factor in the operating lives of dies. In this study, the wear analysis of a closed die at the final stage of a hot forging process has been realized. The preform geometry of the part to be forged was measured by Coordinate Measuring Machine (CMM), and the CAD model of the die and the worn die were provided by the particular forging company. The hot forging operation was carried out at a workpiece temperature of 1100&deg / C and die temperature of 300&deg / C for a batch of 678 on a 1600-ton mechanical press. The die and the workpiece materials were AISI L6 tool steel and DIN 1.4021, respectively. The simulation of forging process for the die and the workpiece was carried out by Finite Volume Method using MSC.SuperForge. The flow of the material in the die, die filling, contact pressure distribution, sliding velocities and temperature distribution of the die have been investigated. In a single stroke, the depth of wear was evaluated using Archard&rsquo / s wear equation with a constant wear coefficient of 1&yen / 10-12 Pa-1 as an initial value. The depth of wear on the die surface in every step has been evaluated using the Finite Volume simulation results and then the total depth of wear was determined. To be able to compare the wear analysis results with the experimental worn die, the surface measurement of the worn die has been done on CMM. By comparing the numerical results of the die wear analysis with the worn die measurement, the dimensional wear coefficient has been evaluated for different points of the die surface and finally a value of dimensional wear coefficient is suggested. As a result, the wear coefficient was evaluated as 6.5&yen / 10-13 Pa-1 and considered as a good approximation to obtain the wear depth and the die life in hot forging processes under similar conditions.

In automotive industry, forgings are widely used especially in safety related applications, typically suspension, brake and steering systems. In this study, forging process of a steering joint used in heavy vehicles has been examined. This particular part has a non-planar parting surface and requires a series of operations, which includes fullering, bending and piercing on a forging press. Forging companies generally use trial-and-error methods during the design stage. Also to ensure complete die filling at the final stage, extra material is added to the billet geometry. However, the forging industry is becoming more competitive finding a way to improve the quality of the product while reducing the production costs. For this purpose, a method is proposed for the design of the preform dies to reduce the material wastage, number of applied strokes and production costs. The designed operations were examined by using a commercially available finite volume analysis software. The necessary dies have been manufactured in METU-BILTIR CAD/CAM Center. The designed process has been verified by the experimental work in a forging company. As a result of this study, remarkable reduction in the flash, i.e. waste of material, has been achieved with a reasonable number of forging operations. In addition to forging of the steering joint, forging of a chain bracket, which has bent sections with planar parting surface, has also been observed and analyzed during the study. An intermediate bending stage has been proposed to replace the manual hammering stage and satisfactory results have been observed in simulations.

Tato diplomová práce se zabývá výpočtovým modelováním zápustkového kování, které patří do metod objemového tváření zatepla. Cílem je změnit běžnou praxi tvorby výpočtových modelů ve specializovaných softwarech na bázi metody konečných prvků (MKP) a sestavit výpočtový model v MKP softwaru Abaqus. Pro výpočet jsou zde použity deformační varianta MKP a explicitní algoritmus. Řešenou součástí je ozubené kolo automobilové převodovky. V rámci práce je vytvořena rešerše z oblasti objemového tváření včetně specializovaných programů pro simulace procesů tváření. Dále jsou v práci uvedeny všechny konstitutivní vztahy pro popis elasto-plastického modelu materiálu s tvárným porušením. Následuje teorie přenosu tepla, jsou popsány všechny způsoby jeho realizace s jejich matematickými formulacemi včetně metod řešení. Klíčovou je kapitola popisující postup tvorby výpočtového modelu v softwaru Abaqus od tvorby geometrie až po okrajové podmínky. Následuje analýza dosažených výsledků a práce je zakončena výhledem na možné pokračování v tomto tématu.