Janez Grum

How to reduce new product development time

Abstract When entering the global market the companies encounter several difficulties, the most important one being excessive time for new product development. This problem can be solved by transition from sequential engineering to concurrent engineering, (Concurrent Engineering Fundamentals, Integrated Product and Process Organization, Vol. I, Prentice Hall PTR, New Jersey, 1996; Concurr. Eng. Res. Appl. 9 (2001) 191). The article presents the principle of concurrent product development process. The market forces small- and medium-size enterprises (SMEs) to a transition from sequential to concurrent engineering and as team work is the basic element of the concurrent engineering, special attention is being paid to team and workgroup forming in the loops of concurrent product development process in an SME. The article does not deal with communication issues within a team and among teams. A survey of published works in the field of designing teams in big companies has revealed that in big companies a three-level team structure is recommended, as well as a workgroup, consisting of four basic teams. Analysis of the three-level team structure has led us to the conclusion that in SMEs a two-level team structure and a workgroup consisting of two basic teams should be preferred. The results of designing a two-level team structure and the project of transition to concurrent development of mini-loader are presented. Time and cost analysis results prove the justification of transition from sequential to concurrent product development.

A review of the influence of grinding conditions on resulting residual stresses after induction surface hardening and grinding

Abstract Internal stresses which are, since the completion of manufacturing, termed residual stresses very much reflect the manufacturing procedures and machining conditions. Residual stresses are analysed in terms of different induction surface hardening conditions and then also after finish grinding in terms of different machining conditions. Induction surface hardening creates very desirable residual stresses in the hardened surface layer. Residual stresses are always of a compressive nature and are usually present to the depth of the induction-hardened layer. By the appropriate selection of grinding wheel and grinding conditions and taking into account the physical and mechanical properties of the workpiece material very favourable compressive residual stresses in the hardened surface layer can be retained. How is it possible to assure a desirable surface and surface layer quality after induction-hardening and fine grinding? Finding an answer to this question requires a very good knowledge of the process of grinding on the micro-level as well as knowledge of mechanical and heat effects acting on the layer of the workpiece including the type and condition of the grinding wheel. An all-inclusive consideration of the numerous influences of the kind and condition of the tool on the changes on the surface and in the surface layer of the workpiece in the given machining conditions is described by the term “surface integrity”.

Concurrent engineering in small companies

Abstract In 1991, attainment of independence in Slovenia caused a drastic decrease in the domestic market for Slovenian companies. The companies which did not adapt to the new market conditions were destined for ruin. In this time several smaller companies were established which could adapt to new market conditions more easily. When these companies entered the world market they encountered several difficulties such as excessive flow times for development of new products. After a survey of available literature had been made it was found that those problems could be solved by transforming sequential engineering to concurrent engineering. The article presents the principles of sequential and concurrent product development processes. The market forces small Slovenian companies to a transition from sequential to concurrent engineering and as team work is the basic element of the concurrent engineering, special attention has been paid to workgroups forming in the loops of concurrent product development process in small companies. A survey of published works in the field of planning teams in big companies has revealed that a three-level team structure is recommended in big companies. Analysis of the three-level structure has led us to the conclusion that a two-level team structure and matrix organisation should be preferred in small companies. Presented are the results of planning a two-level team structure and matrix organisation of a small Slovenian company which produces mini-loaders.

A comparison of tool–repair methods using CO2 laser surfacing and arc surfacing

Abstract The life of loaded machine elements and the vital parts of tools can be successfully extended by systematic maintenance and the timely repair of damaged surfaces. It has been proved that with the regular maintenance of tool parts the cost of the tool in the price of a finished product can be considerably reduced. It is a very economical practise to manufacture certain parts from low-cost, tough structural steel on which a layer of wear-resistant alloy has been surfaced. In such a case the volume fraction of the surfaced layer is usually much lower than 10% of the total volume of the tool or the machine element. In this paper, we report some of our latest results involving comparative studies of repair surfacing on maraging steel and the cladding of common structural steel with a Ni–Co–Mo alloy similar to the maraging steel using a laser process and submerged-arc surfacing. The results are based on micro-structural and micro-chemical analyses of the surfaced layer and are supported by analyses of the micro-hardness and the residual stresses, carried out on suitably adapted flat specimens.

Microstructure analysis of nodular iron 400-12 after laser surface melt hardening

The application of laser surface melt hardening to nodular iron 400-12 causes the material to undergo microstructural changes. A newly created austenite-ledeburite microstructure with the presence of graphite nodules in the melted zone and a martensite-ferrite microstructure with graphite nodules in the hardened zone have been observed. Microscopy of the hardened zone was used to analyze the occurrence of martensite shells around the graphite nodules in ferrite matrix. The size of the shells was later supported by diffusion calculations. The qualitative effects of the changed microstructures were additionally verified by microhardness/depth measurements in the modified layer and microhardness measurements of characteristic microstructures around the graphite nodules in the hardened zone.

Influence of laser surface melt-hardening conditions on residual stresses in thin plates

Abstract Wear resistance of products made of gray cast iron with a ferrite-pearlite microstructure of the matrix may be considerably increased by the process of laser remelting of the surface. Products with comparatively thin walls (up to 5 mm), however, seem to be problematic since the stresses introduced during laser heat treatment may produce deformations of the product. This paper provides the results of research into various methods of laser beam guidance along the workpiece surface with various degrees of overlapping of remended traces and the influence of various machining conditions in laser machining or through thickness variations in residual stresses in the workpiece. Residual internal stresses were measured by a strain gage by means of the relaxation method where the stressed modified surface layer was electro-chemically removed. The size of deformations occurring during heat treatment of rest pieces was assessed. On this basis internal stress intensity was accessed. The efficiency of the process itself of laser remelting of gray cast iron in increasing wear resistance is thoroughly described by an analysis of microstructure and confirmed by through-thickness microhardness measurement of the modified layer.

Comparison of measured and calculated thickness of martensite and ledeburite shells around graphite nodules in the hardened layer of nodular iron after laser surface remelting

Abstract The application of laser surface remelting to nodular iron 400-12 causes the material to undergo microstructural changes. Because of the rapidity of laser beam action on the surface of the specimen material, melting occurs only in a thin surface layer. After the laser beam has passed along the specimen, thanks to very rapid heat transfer from the surface to the interior of the specimen, we can achieve very rapid solidification of the melted pool and self-hardening of the rest of the modified layer. The process of rapid heating above the melting-point temperature and the temperature of the austenitic transformation creates conditions for the formation of metastable microstructures that can offer important technological properties such as high hardness, good wear and corrosion resistance. A newly created austenite–cementite microstructure with the presence of graphite nodules in the remelted layer and a martensite–ferrite microstructure with graphite nodules in the hardened layer have been observed. Microscopy of the hardened layer was used to analyse the occurrence of martensite shells or ledeburite shells around the graphite nodules in the ferrite matrix. The size of the shells was later supported by simple diffusion calculations.

Influence of quenching process parameters on residual stresses in steel

Abstract The paper presents results regarding cooling intensities of quenching oil of domestic production and of polymeric water solutions. Numerous residual stresses measurements on heat-treatment steel specimens with different masses were made. To measure the residual stresses, the relaxation method was used, involving gradual mechanical removal of the hardened layer in which the deformation of the specimen was measured by resistance strain gauges. On the basis of the measured strain at a specific depth of material removal, it is possible to calculate the size or variation of residual stresses depending on the depth of the hardened layer. Numerous residual stresses measurements provided very important data on various steels when using different quenching agents.

Influence of microstructure on surface integrity in turning—part II: the influence of a microstructure of the workpiece material on cutting forces

Abstract Analysis of cutting forces in fine turning is most frequently related to workpiece-material hardness and strength under different machining conditions. Material hardness and strength as well as material machinability, however, can be related to the material microstructure. Consequently, an additional influence exerted by the microstructure was included in the present study to find the relationship between the size of the soft phase described by intercept lengths and the magnitude of the cutting force measured during the fine-turning process. The magnitude of cutting force is usually treated in terms of its static and dynamic components. In our case, both the components are of importance. Because of different types of aluminium–silicon alloys, significant differences occur in the magnitude of the static and dynamic components of the cutting force mainly because of different types of microstructures. The latter can be described by the fraction and quantity of individual microstructure phases. The results obtained are represented by an average magnitude of static and dynamic components of the cutting force in relation to the intercept lengths of the soft phase.

Microstructure, Microhardness, and Residual Stress Analysis of Laser Surface Cladding of Low-Carbon Steel

Abstract This article describes online measurement of thin and flat specimen changes during laser alloying and of the alloyed specimen after treatment. Laser remelting of SiC, Stellite 6, and Stellundum 481 powder was performed on a specimen of low-carbon steel. Experiments were performed with high-temperature resistance-measuring rosettes. Strain was monitored from the beginning to the end of the cladding process (i.e., to a temperature 50°C at the backside of the specimen). Therefore, during the cladding process, the changes in temperature at the backside of the specimen were measured with two Ni-NiCr thermocouples. Other important properties are the size and distribution of residual stresses in the thin cladded specimen (i.e., machine part), because they strongly affect its operational efficiency. Results obtained are analyzed from the viewpoint of minimum final strain of the specimen with the desired variation of residual stresses.