In many cases machining of fiber reinforced polymer materials is performed without cooling lubricant, since the coolant can lead to swelling of the polymer as well as inducing chemical reactions with certain functional groups of the macro molecules. This effect can lead to shape and accuracy errors not only of the drilled hole but also of the entire work piece, since a spreading of coolant can not be completely avoided. The latter effect causes a weakening of the composite material by reducing the material strength, which is a result of lower adhesive forces within the polymer material and between polymer and fiber. In contrast, dry machinining offers the risk of a thermal damage induced by high process temperatures. [1±3] Especially, the thermo physical properties of fiber reinforced polymers causes high temperatures at the tool tip, when machined. The thermal conductivity as well as the heat capacity is rather low compared to metal matrix materials, hence the energy balance between tool and workpiece is disturbed. Furthermore, the thermal expansion coefficient is also low, which causes accuracy errors when machining. Another reason which must be considered is the fact, that especially thermoplastic polymers have a glass transition temperature ranging from 150±250 C. This means, that heat formation during the drilling process leads to plastifying of the polymer matrix. In the presented research work, the temperatures which are generated when drilling fiber reinforced plastics are measured and the dependency of cutting parameters is discused. Furthermore, some general aspects are outlined including damages, tool wear and cutting forces, which can be attributed to the process temperatures and thermal overloads.Tool Temperatures: Within the presented work an initial approach was undertaken for measuring the cutting temperatures at the tool tip, in order to estimate the thermal load when drilling fiber reinforced polymers. In Figure 1 (left) the feed force is shown as well as the tool temperature, which was measured with a thermocouple at the drilling tool. It is notable, that the temperature increases instantaneously up to about 180 C at the beginning of drilling. After reaching the initial temperature level it increases through the whole process continuously. The maximum of 387 C is reached, when the tool exits the bore hole. The occuring temperature maximum is possibly caused by stronger friction, as the reinforcement plies are not cutted anymore, but pressed out by the tool tip. Because the temperatures were not directly measured at the cutting edge, it can be assumed, that the temperatures are much higher there. It is also important, that the temperatures are at unexpected high levels, which can be rated as crucial for the machining of plastics. Furthermore, increasing the feed changes the course of the temperature progression (Fig. 1, right). While a definitely progressive rising of the tool temperature is observed at lower feed rates, a nearly constant temperature course is evident when elevated feed rates a...

Within the last decade metal foams have received increasing interest for technical and medicinal applications. These materials are generally manufactured close to their final shape by sintering processes. In some cases, it is necessary to generate the final shape by machining, facing the special problems which result from the porous structure and the outstanding material characteristics. Titanium foams are regarded as potent materials for application in biomedicine, especially concerning bone implants. Therefore, it has become relevant to investigate the machinability of titanium foam materials. Here, studies concerned with face milling and peripheral grinding of titanium foams are presented highlighting principal results.Research and development focused on metal foams has significantly progressed within the last decade regarding new technologies for their applications and their manufacturing. [1,2] The most important benefit of these so-called cellular materials emerge from the very low weight and the high stiffness as well as the sufficient material strength. Besides these fundamental requirements for such state-of-the-art materials, there are additional properties, which attracts interest for innovative construction options. [3] Such properties are for instant the capability for crash energy absorption, heat dissipation or noise control, respectively. However, the most common metal utilized for cellular materials is still aluminum although ferrous and titanious based foams presently attract more and more attention. According to their low specific weight, cellular materials are generally used as structural sandwich panel components. Moreover, metallic foams are exploited in other fields including filter applications, carrier material for catalysts as well as heat exchanger. [4] A further promising aspect is given by biomedical applications. Metallic foams are regarded as potent bone implants, since the porous structure allows the growing in of the body tissue. [5] For this kind of application it is necessary to meet the special demands associated with medical conditions. Due to its excellent biological compatibility titanium is selected for this case. Present investigations are focused on the fabrication of bone implants such as hip joints. Since a rather high porosity is necessary and further more a well defined pore size is required the utilization of the so-called filler process comes into consideration. The manufacturing process is basically carried out close to the final shape of the implant component. Nevertheless, a postprocessing by machining operations frequently has to be carried out. According to the little general knowledge of machining metal foams [6] our research is focused on face milling and peripheral grinding.Manufacturing Titanium Foams: Employing the filler technology the first stage within the manufacturing process is to combine the titanium powder with filler particles. [7,8] The overall porosity as well as the pore size can be determined by choosing the appropriate ratio of titanium powde...

ters after cooling to room temperature. [23] Powder premix: 80 wt% of ultrafine Al (2.5 micron in average) powder, 5 wt% Cu nanopowder (less than 70 nm), and 15 wt% adhesive binder were mixed in 30 ml acetone.Filling: The moulds were filled with the prepared metallic powder paste. When the powder patterns were dry and became solid, the PDMS mould was peeled off.Sintering: The green patterns were placed inside a furnace(Carbolite 2416-tube furnace) filled with Ar gas and heated to 600°C at 5°C/min and then kept for 6 h. The microcomponents were taken out after the furnace was cooled down to room temperature.

Construction parts consisting of modern polymer materials still need to be machined. Thereby special attention has to be paid to the machining quality. The machining quality implies dimensional accuracy as well as a defect-free peripheral zone. Machining defects often occur as a consequence of excessive mechanical loads, which are often caused by unfavorable process conditions. Besides mechanical loads, the thermal influence on the composite material, which is induced by the cutting process itself, has to be considered as crucial. According to the thermo physical material properties of polymer materials the boundary conditions differ from the machining of metals. Especially the drilling of polymer composites is introduced in this article and moreover the influences of the material properties and the process conditions on the process temperatures are presented.

furnace to cool down. This cycle was repeated five times. For comparison, a single heat-and-cool down test with a soaking time of 5 hours was performed.Microstructural characteristics after oxidation test were analysed by X-ray diffraction, scanning electron microscopy (SEM) and energy dispersive spectroscopy (EDS).Mechanical properties: The original flexural strength (r) was measured at room temperature on some of the initial testing bars. The flexural tests were performed on a semi-articulated SiC four-point jig with a lower span of 20 mm and an upper span of 10 mm on a universal screw-type testing machine, Instron mod. 6025, using a crosshead speed of 0.5 mm/min.The high-temperature tests were carried out in laboratory atmosphere at 1200°C, 1300°C and 1500°C. Flexural jig and crosshead speed were the same as for the room-temperature tests. The testing temperature was reached with a heating of 600°C/h and a soaking time of 18 min was allowed to insure thermal equilibrium.For the thermally-treated bars, the retained strength was measured at room temperature as already described. For the calculation of the flexural stress, the initial dimensions of the bars were considered. At least five bars were tested for each condition. In order to identify the fracture origins, most of the fracture surfaces of the broken specimens were inspected by SEM.The acknowledgement of temperature influences onto the cutting edge and workpieces achieves a growing relevance. Particularly with regards to the cutting material, coating, and cooling lubricant selection, the knowledge of appearing temperatures is essential. [1,2] Up to now, the action-close thermo measurement at the cutting edge is conducted by video-thermographic recordings, pyrometers or according to the principle of resistance-measurements. Modern coating technology offers new options. Already established measuring methods allow the detection of temperature and wear following the principle of conductivity variation by close meshed conductor structures plated on the cutting inserts. [3][4][5] An improved method utilizing an alternative physical principle now allows to implicate coatings for temperature measurements by means of the so-called "Seebeck-Effect". Applying the principle of thermo electricity just as in conventional thermo couples, different metals are affiliated with each other and exposed to an temperature gradient, so that a measurable voltage results.Sensor coatings: The principle of detecting measurement parameters during the machining process by using sensor coatings on the rake face and the flank face has successfully been realized. The benefit is to deploy a tool monitoring system, which detects action-close and critical process factors and provides them to the user or a certain control system. [6][7][8] The cutting force, and wear as well as the cutting temperatures are counted among the measurement parameters. [9] When implementing this technology, the cutting inserts are coated with sensor and insulation coating systems. The functional coatings used...