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1

Inductive heating and quenching of planetary shafts

Kosec B., Karpe B., Licen M., Kosec G.

Journal of Achievements in Materials and Manufacturing Engineering

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2010

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Vol. 39, nr 2

190-196

EN

Purpose: High mechanical and temperature cyclic loading of the final products for automotive, construction, transport and agriculture mechanization industry, demands sufficient mechanical properties of all of their components during its exploitation. Majority of the components is made from steel, by different cold forming processes. Their main demanded characteristics are surface wear resistance and fatigue strength under pulsating stress in combination with cyclic temperature loading, which could be achieved only by appropriate heat treatment. Design/methodology/approach: In the experimental part of our work, the efficiency of the combined inductive heating and water quenching heat treatment and quality of the planetary shafts were analyzed, with the use of thermographic analysis, hardness measurements, and metallographic examination. Findings: Combination of inductive heating and water quenching is the most effective heat treatment process of carbon steel planetary shafts for the diesel engine starters. Research limitations/implications: Long life span of carbon steel planetary shafts it's essential for their economical production. The replacement of starter is expensive from both: money and working time point of view. Practical implications: Surface temperature measurements during the inductive heating process were realized in the industrial environment. The intensity and homogeneity of the planetary shaft surface temperature field was measured by thermographic camera. Originality/value: On the base of theoretical knowledge and measurements, a mathematical model for temperature conditions determination in the shaft during the entire process of heating and quenching was carried out. On the basis of developed mathematical model a computer program was worked out, and used for analyses and optimization of planetary shafts induction hardening process.

2

Heat treatment of cold formed steel forgings for the automotive industry

Kosec B., Brezigar M., Kosec G., Bernetic J., Bizjak M.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 22, nr 2

87-90

EN

Purpose: In the Slovenian company ISKRA Avtoelektrika they manufacture, with the processes of cold forming, a great number of a different steel forgings for the Slovenian and European automotive industry. During their exploitation they are exposed to the high mechanical and temperature loads. Design/methodology/approach: A gas furnaces and devices play important role in the heat treatments of various metal parts for the automotive industry. Their thermotechnical characteristics have a great influence on the product quality and costs. The basic aim of our investigation work is to present the optimization of a device with emphasis on continuous control of working temperature. Findings: The efficiency and quality of the treatment were analysed with the use of: chemical analysis, hardness measurements, measurements of carbon and sulphur content in the surface layer, and metallographic examination methods. Research limitations/implications: For economical production of cold formed steel forgings for the automotive industry it is important that they have a long working life. The corresponding mechanical and thermal properties of the steel forgings are achieved by a heat treatment. Practical implications: As a practical example is presented an optimisation of the heat treatment procedure for typical cold formed steel forging for the automotive industry from the ISKRA Avtoelektrika production program. The practical result of the used heat treatment are the cold formed steel pinions with the surface hardness of approximately 65 HRC, and the case hardened depth of the surface layer approximately 0.7 mm. Originality/value: On the basis of the results of our technical investigation work and corresponding economical studies, the second device (of the same producer, type and capacity) for the heat treatment was installed at the end of last year.

3

Case of temperature field and failure analysis of die-casting die

Kosec B., Kosec G., Soković M.

Journal of Achievements in Materials and Manufacturing Engineering

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2007

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Vol. 20, nr 1-2

471-474

EN

Purpose: For economical production of aluminium and aluminium alloys die-castings it is important that the dies have a long working life. The replacement of a die is expensive in both: money and production time. Design/methodology/approach: Dies for aluminium alloys die-casting fail because of a great number of a different and simultaneously operating factors. Some of them may be controlled to some extent by the die-casting experts. Findings: In the process of the die-casting the primary source of loading is cyclic variation of the temperature; the influence of other loads is relatively insignificant. Research limitations/implications: Beside, the die design, the material selction and the process thermal stress fatigue course, which is the consequence of the working conditions, the inhomogeneous and to low initial temperature of the die, contribute to the cracks formation. Practical implications: In the experimental part of our work the failures on the working surface of the fixed half of the testing die for die-casting of aluminium alloys were observed with the use of non-destructive testing methods: such as thermographic analysis, penetrants and metallographic examination of polymeric replicas. Originality/value: It is clearly seen from the presented thermographs, that the required temperatures and homogeneity of the temperature field of the discussed case are not possible to reach without the changing both: the heating method and the die design. Therefore in the first stage a solution of the problem should be in changing of the position of heating and/or cooling channels, i.e. their closer shifting to the working surface of the die.

4

Temperature field and failure analysis of die-casting die

Kosec B., Kosec G., Soković M.

Archives of Materials Science and Engineering

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2007

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Vol. 28, nr 3

182-187

EN

Purpose: Dies for aluminium alloys die-casting fail because of a great number of a different and simultaneously operating factors. Some of them may be controlled to some extent by the die-casting experts. Design/methodology/approach: In the experimental part of our work the failures on the working surface of the fixed half of the testing die for die-casting of aluminium alloys were observed with the use of non-destructive testing methods: such as thermographic analysis, penetrants, and metallographic examination of polymeric replicas. Findings: In the process of the die-casting the primary source of loading is cyclic variation of the temperature; the influence of other loads is relatively insignificant. Research limitations/implications: For economical production of aluminium and aluminium alloys diecastings it is important that the dies have a long working life. The replacement of a die is expensive in both: money and production time. Practical implications: Beside, the die design, the material selection and the process thermal stress fatigue course, which is the consequence of the working conditions, the inhomogeneous and to low initial temperature of the die, contribute to the cracks formation. Originality/value: It is clearly seen from the presented thermographs, that the required temperatures and homogeneity of the temperature field of the discussed case are not possible to reach without the changing both: the heating method and the die design. Therefore in the first stage a solution of the problem should be in changing of the position of heating and/or cooling channels, i.e. their closer shifting to the working surface of the die.

5

Failure and surface temperature analysis of working surface of die-casting die

Kosec B., Sokovic M., Kosec G., Bernetic J.

Archives of Materials Science

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2007

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Vol. 28, nr 1-4

63-68

EN

Die-casting is the most cost efficient and technical easy method of casting sophisticated and accurate aluminium alloys parts in great-scale series. Aluminium alloys die-castings require little machining prior the final installation. Die-casting dies for casting of aluminium alloys fail because of a great number of different and simultaneously operating factors. Die design, material selection, and thermal stress fatigue generated by the cyclic working process, as well as to low and inhomogeneous initial die temperature contribute to the failures and cracks formation on/in dies for die-casting of aluminium alloys. In the frame of the presented investigation work the intensity and homogeneity of the temperature, fields on the working surface of the testing die were checked through thermo graphic measurements, and failures and cracks on the working surface of the die were analysed with nondestructive metallographic examination methods.