Selections of working conditions for creep feed grinding. Part(II): workpiece temperature and critical grinding energy for burning

In this study, the workpiece temperature is predicted by the thermal model presented in the previous paper. Also, the grinding energy when the fluid begins to cause boiling is defined as the critical grinding energy for the workpiece burning. Thus, a sequence of experiments are performed. The results show that the predicted workpiece temperatures have great agreement with experimental and published data. Hence, the validity of the thermal model is proved. From the measured signals of grinding force and workpiece temperature, the occurrence of workpiece burning is accompanied with the abrupt rise of both signals. At the moment, the experimental grinding energy is also greater than the critical grinding energy. Thus, the workpiece burning can be predicted or evaluated so as to avoid the working conditions of burning occurrence.     

凯芙拉防弹复合材料的孔加工试验研究

分析了凯芙拉防弹复合材料的纤维增强聚合物的组织结构特点和力学性能,立足于传统加工方法,从加工的经济性和实用性考虑,针对其在加工过程中产生各种加工缺陷的关键原因设计了专用夹具,并采用最新出现的单层高温钎焊金刚石刀具对其进行钻孔加工试验,取得了满意的结果,具有实用和推广价值。     

Machinability study on composite (polyetheretherketone reinforced with 30% glass fibre–PEEK GF 30) using polycrystalline diamond (PCD) and cemented carbide (K20) tools

Polyetheretherketone (PEEK) is a relatively new technical thermoplastic material, which has excellent physical properties. By this reason exits a strong need to understand the issues associated with the machining of this thermoplastic. The major concern of this paper is the study of the cutting parameters (cutting velocity and feed rate) under power (Pc), specific cutting pressure (Ks), surface roughness (Ra) and International dimensional precision (IT) in PEEK reinforced with 30% of glass fibre (PEEK GF30). A plan of experiments, based on the methodology of Taguchi, was established considering turning with prefixed cutting parameters in the PEEK GF30 workpiece. The analysis of variance (ANOVA) was preformed to investigate the cutting characteristics of PEEK GF30 using a polycrystalline diamond (PCD) and a cemented carbide (K20) cutting tool.     

On the interdependence between kinetics of friction-released thermal energy and the transition in wear mechanisms during sliding of metallic pairs

Sliding of complying solids is often associated with the release of thermal energy. This energy accumulates within the mechanically affected zone (MAZ) of the rubbing pair. The accumulation of thermal energy within the MAZ tends to maximize the potential energy at the interface. Now, since a maximized potential energy renders the sliding system unstable, one (or both) materials will respond in a manner that consumes (dissipates) part or all of the accumulated energy in order to re-establish system stability or at least equilibrium. The material response may be in many forms: oxidation, crack initiation, wear debris generation, transition in wear mechanism, etc. As such, one may consider that these processes are intrinsic responses by the material to dissipate energy. Moreover, many of these responses are triggered at different stages of rubbing according to the balance between the rate of external thermal energy release (which is a factor of the nominal operation parameters) and the rate of thermal energy accumulation—RTEA (which is mainly a function of thermal transport properties of the rubbing pair). An interesting feature of this view is that the later quantity—RTEA—is directly related to the ability of the particular solid to dissipate thermal loads. This quantity, which is termed here as the heat dissipation capacity (HDC), is directly related to the state of blockage of energy dissipation paths within the rubbing solid. The objective of this paper is therefore to study the relation between the change in the HDC of a sliding solid and the transition in the mechanism of wear. It is shown that there exists an inverse correlation between the change in the HDC and the transition in the mechanism of wear. Moreover, it is also shown that a so-called ratio of residual heat (RRH, representing the ratio between the actual thermal load and the part of that load that is not dissipated by the solid) is a significant parameter that influences the magnitude and mechanism of wear. The findings are applied to explain the wear behavior of two tribo systems: a titanium (Ti-6Al-4V) sliding on itself and sliding on a steel (AISI M2) counterpart.