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Development of innovative manufacturing technologies for reducing process chain


Laser assisted turning procedures after hardening were developed for the part selected in the project. The very high hardness of the surface could be softened by heating and maybe by tempering effects preceding the use of the cutting tool. The material thus becomes soft and can be turned using cheap cutting tools as used in soft turning.
Dry turn-milling processing implements the turning, drilling and milling processing on a machine tool. This will optimise the process parameters such as machine tool specifications, tool specifications and machining conditions on dry turn-milling technology. It enables the conventional process chain before hardening, carried out with several machines, to be completed with one machine by increasing the material removal rate and reducing tool wear. Moreover, it helps to establish an environmentally friendly process chain.
A peal grinding strategy was developed for CVT components at high cutting speeds (up to vc = 200 m/s), preferably using Minimum Quantity Lubrication. For this purpose, adapted specifications of CBN grinding wheels are selected for high-speed peal grinding procedures. A process strategy for the most efficient grinding of automotive components was developed (with reference to the defined workpiece material). During the investigations, different coolant strategies like Minimum Quantity Lubrication were tested for the process applied. In view of the fact that hard turning in combination with hard roller burnishing and laser assisted hard turning is also used to work the hardened parts, evaluation criteria were set up in order to compare the different manufacturing processes. This is important information for the end user. Though the technology explored is mainly developed for machining CVT components, it can be applied to almost every cylindrical part where a grinding process is demanded. Thus, an optimised traverse grinding technology can be applied not only by the automobile industry, but by large variety of producers to increase their quality and productivity. Using the aimed Minimum Quantity Lubrication technology, significantly reduces the amount of coolant employed for machining processes, which results in more ecological production procedures.
The target surface roughness of Ra 10 nm or lower can be readily achieved by UPG on the Tetraform'C' machine, with good surface integrity, for simple workpiece geometries. A surface finish of Ra 30 nm or lower roughness can be consistently achieved using a D15 resin bond wheel on the friction discs of CVT material (steel). The cutting time with a slow cross feed of 3mm/min for a CVT component will be 33 minutes, including 26.7 minutes grinding time and dwells for spark out. The cutting time will be greatly reduced to 15-20 minutes if a higher roughness in the order of Ra 40-50 nm is allowed which can use a higher cross feed and eliminate the dwells for spark out. Surface roughness achieved on CVTs by using B91 plated wheel is about Ra0.17-0.24microm with cutting time down to 2.8 minutes. When using a wide cup wheel on the conical part and a form wheel on the toroid of the CVT component, a plunge grinding mode is expected to reduce the cutting time down to 5-10 minutes with surface roughness at about Ra 40 nm.
The result consists in the development of a laser hardening technique for the part selected in the project. A process window was estimated und some trials on round samples were performed. This was done using a line focus and a fibre-coupled diode laser. The effect of shielding gas was also investigated and a theoretical model was developed for the extrapolation of the hardness depth and width, derived from known data on different speeds and laser power.
Studies to drill small holes (few 10microm) with laser sources at high repetition rate (typically 35 000 holes/s) were carried out, resulting in the definition of the process parameters (laser sources, optical system, etc). Tests were made of different hole geometries and of the relevance of micro-machined surface. A laboratory system drilling the holes on prototype parts was also developed.
The induction hardening for the part selected in the project has been optimised in order to minimise distortion while keeping the required hardness profile.
The application of the results of this project is to develop dry machining operations of different difficult to-cut metallic materials with innovative PVD coatings specific for turn-milling and ultra precision machining. The present research project has a very high degree of scientific novelty and a high degree of technological innovation. The medium-sized company Genta is developing such innovative PVD coatings and the necessary coating technology appropriate for these materials on an industrial scale for cutting applications and the first results are already available. The generic nature of the design concept will allow us to develop a new class of materials with high hardness combined with a high toughness, oxidation resistance and chemical inertness towards the materials to be machined (various metallic alloys, wood etc.). This will be possible because of the large variety of materials which can be combined together in order to tailor the desired properties. The presently most promising materials include the TiCN, TiAlN, MoS2 multilayer coatings; other transition metal nitrides instead of TiN (e. g. CrN), carbides and others.
The result consists in the development of a laser-assisted turning process for soft material before hardening for the part selected in the project. This leads to a flexible integration of a laser optic in a lathe, with which the material should be heated and softened before applying the cutting tool. The aim is to reduce cutting forces, increase the lifetime of the tool and achieve higher removal rates.
High efficiency deep grinding (HEDG) of CVT material (steel) has been carried out, using electroplated CBN wheels. The initial tests were conducted in a surface grinding mode over a wide range of grinding conditions, to evaluate the levels of specific grinding energy, workpiece surface integrity and wheel wear. Thermal modelling of the HEDG process has been validated and proved to be very helpful for determining the optimal process conditions. The burn threshold conditions for the ground workpiece surface have been proposed in terms of a critical heat flux which is shown to vary with material removal rate. The predicted upper and lower boundaries for occurrence of workpiece burn show good agreements with the experimental observations. It has shown that the HEDG technology can be transferred successfully to the field of cylindrical grinding to achieve very high stock removal rates in excess of 2400mm3/s. The successful application of HEDG to cylindrical components depends on the appropriate selection of grinding parameters and also the grinding fluid supply strategy. Mineral oil can generally provide better lubrication to the wheel-work contact zone and reduce the net grinding power, but the safety issue concerning the oil mist and potential fire has to be properly addressed. Water based fluids can provide good cooling effect but less lubrication, the material removal rate therefore has to be reduced due to higher grinding energy input and quicker wheel wear.
This result concerns process chain design in metal cutting operations with induction hardened steel and FEM simulation of cutting process operation. The successful implementation of hard machining process will increase production efficiency of the selected part. This potentially leads to significant cost reductions by designing shorter process chains and by more reliable process operations based on process monitoring. FEM simulation is a powerful software tool for setting up cutting processes during ramp-up procedures or in optimising cutting operations with less experimental efforts.