Papers by Keyword: Cryogenic Machining

Abstract: Composite structures, such as glass fiber reinforced polyether-ether-ketone (PEEK) and polyamide (PA66), usually undergo drilling operations for subsequent assembly. A typical problem with these composites is damage around the drilled surface due to a possible non-homogeneous cutting of the fibers. In this context, the delamination is evaluated after a cryogenic drilling. Thus, the objective of this paper is to determine the feasibility of cryogenic drilling considering surface damage after cryogenic machining, at hole the entry and exit. Experimental test were carried out in a machining center at a temperature close to -130 °C using liquid nitrogen, LN₂, as cooling environment. The diameter of the drill is 6 mm and the drill tip is polycrystalline diamond (PCD). The plate material is PEEK-GF30 and PA66-GF30. The delamination factor was obtained using a three-dimensional measurement device with an optical sensor and a focus-variation device. The results obtained are favorable regarding the potential use of cryogenic machining.

Abstract: Cryogenic machining offers advantages compared to conventional cooling lubrication strategies particularly for difficult-to-cut and high-temperature-resistant materials such as titanium and nickel alloys. For implementation purposes environmental and cost factors are crucial for this new machining approach in series production. In order to facilitate investments it is mandatory to evaluate the technology’s potential prior to the final implementation decision. In the field of machining, in particular machining with cryogenic process cooling, there is no standardized and uniform procedure to assess this potential. In this paper a systematic approach and underlying analysis tool will be introduced to determine the potential of cryogenic processing in terms of resources and energy efficiency of the manufacturing operation. This approach satisfies the general conditions in a reasonable assessment effort as well as in the detail level. With this analysis tool, real production and process data are compared with results from scientific cryogenic tests and research and examined with regards to their applicability. Thus, it is possible in an early stage of the production to identify potentials in manufacturing and to take measures to realize these effects. In case cryogenic processing of a specific material has not been carried out so far, the similarity of this material to existing research results is determined. If positively assessed, the surrogates’ potential is transferred with a specific safety factor to the material. The analysis tool has been applied and refined in a real large-scale series production as well as in a complex component manufacturing and the holistic potential for e. g. durability, material removal rate (MRR) or savings regarding the use of metal working fluids (MWF) have been identified.

Abstract: Chemical cleaning methods are under strict restrictions due to the legislator, as they are often harmful to environment and health. Therefore, environmentally neutral cleaning methods will gain importance in the future. Alternative cleaning processes like blasting with solid carbon dioxide can substitute such harmful chemicals without residues of blasting media. CO₂ snow blasting has a minor technical complexity with a possible high degree of automation, but is limited in its cleaning performance. Basic knowledge of CO₂ formation must be gained in order to increase the cleaning performance. The basic dependencies of ambient pressure and temperature as well as the possibility of their manipulation regarding the produced CO₂ particles were investigated. The investigations were conducted using design of experiments and lead to a model describing the CO₂ snow formation and its properties. The goal was to manipulate the properties of the generated CO₂ snow in order to optimise the technology regarding the cleaning task.

Abstract: Metastable austenitic steels offer the opportunity of a surface hardening during machining due to a deformation induced martensite formation, substituting downstream hardening-processes. To maintain the necessary low process and workpiece temperatures for a phase transformation from austenite to martensite, cryogenic cooling using CO₂-snow was examined in this study. The influence of workpiece diameter, coolant flow rate as well as pre-cooling and pre-surface hardening on the obtainable phase content of martensite in the surface layer was investigated.

Abstract: The major challenge of the Mg alloys has been their unsatisfactory corrosion resistance, which can be enhanced by improving the surface integrity. Cryogenic machining, where liquid nitrogen was used during machining, has been reported to improve the surface integrity of machined components, including compressive residual stresses. This paper analyses the influence of several cutting parameters, tool geometry and cryogenic conditions on the surface and subsurface residual stresses distribution.

Abstract: Application of cutting fluid that provides both coolant and lubrication properties in manufacturing operations such as turning, milling, grinding and other processes has been proven to improve the machining output in many aspects. In cryogenic machining, liquid nitrogen (LN₂) is used as cutting fluid to reduce the temperature generated at the cutting zone. However, there is still an issue being raised on whether LN₂ also functions as a good lubricant as it does as an excellent coolant. Therefore, an intensive study on the chip formation during dry and cryogenic turning of AISI 4340 alloy steel has been conducted to examine the effect of LN₂ cutting fluid on the reduction of friction between the chip and the tool. Results from calculation of coefficient of friction indicate that application of LN₂ during turning is able to help the friction reduction up to 73%. Smaller value of coefficient of friction indicates that the shear angle is larger which results in smaller shear plane area that provides benefits of lower cutting force needed to shear off the chips and lower cutting temperature being generated during the machining process.

Abstract: Machining of Carbon Fibre Composites (CFCs) particularly drilling, is frequently employed in industry especially when dealing with joining, assembly and structural repair of the parts. However, the nature and heterogeneous structure of CFCs often results in rapid wear of the cutting tool. This research studied the relationship and compared the effect of drilling a CFC plaque without cutting fluid, with conventional cutting fluid and with cryogenic cooling at constant cutting speed of 94 m/min and feed rate of 0.065 mm/revolution using tungsten carbide twist drill. The conventional cutting fluid was supplied continuously to the drill and the CFC plaque during the drilling cycle; while for the cryogenic cooling tests, the drill tip was immersed in liquid nitrogen for 10 and 30 seconds prior to drilling the CFC. It was found that the tool wear increased with the increasing number of drilled holes at all machining conditions. After drilling of 325 holes, the largest tool wear observed was 181 μm which was produced when drilling the CFC plaque with conventional cutting fluid. The corresponding tool wear for drilling with cryogenic cooling was 164 μm and the smallest tool wear of 155 μm was observed during dry drilling. Dry drilling produced the smallest tool wear because the heat generated reduced the strength of the CFC, particularly polymer matrix. Therefore, this situation led to easier machining of CFC materials; consequently reduced the wear of the tool.

Abstract: Cryogenic cooling is an environmental friendly and effective cooling technology. The present work investigates the role of cryogenic cooling on tool wear at various cutting conditions. An indigenous method of applying cryogenic coolant was developed. Different methods of circulating the liquid nitrogen and vaporizing it inside the tool holder were tried with the objective of lowering down the temperature at the cutting zone. This was achieved through more efficient heat transfer. As-rolled AISI 4340 steel shafts were turned using coated cemented carbide inserts. Results of tool wear show improvement of tool life during cryo-machining as compared to dry machining especially when heavy depths of cut, high feed values and high cutting speeds are employed. The effect of cryogenic cooling was not pronounced at low speeds, small feed and depths of cut.

Abstract: This paper presents experimental investigations on influences of cooling air temperature, as well as cutting velocity, on performance in milling of the 1Cr18Ni9Ti alloy with coated cemented carbide inserts. Cutting force, tool wear and surface roughness are experimentally studied to compare the effects of different cooling air temperatures. The results showed that minimum quantity lubrication (MQL) with cooling air significantly reduces cutting force, tool wear. Three different cooling air temperatures are used to investigate the effects of cooling air temperature on the machinability characteristics of 1Cr18Ni9Ti alloy. Based on the experimental results, MQL with cooling air of −50°C provides more favorable effects compared to the other two cooling air temperatures (−10°C, −30°C). However, different cooling air temperatures have a slight effect on cutting force under the same MQL condition.

Abstract: Cryogenic machining is considered as an eco-friendly machining process in manufacturing industry. In order to study the influence of cryogenic gas mixture of nitrogen gas and compressed air on machining performance, the experiments of turning 0Cr18Ni9 stainless steel were performed . The experimental results show that cryogenic machining technology can remarkably improve the surface integrity, cutting tool life and chip-breaking performance. Its advantages of improving machinability are especially obvious at higher cutting speeds.