A Universal Pocket Plunge Milling Method to Decrease the Maximum Engagement Angle

Plunge milling has been proven to be an efficient strategy for machining of pockets with deep cavities and difficult-to-cut material. Previous work generates the plunge toolpath mainly by controlling the radial cutting width within the given value. However, uneven tool engagement angles may lead to excessive tool load and tool load fluctuations, which has a negative influence on tool life. In this study, a universal plunge milling toolpath generation method is proposed to improve tool life by decreasing the maximum tool engagement angle. A series of concentric circles with constant radius increment is utilized to generate a toolpath with constant cutting radial depth. Center of the concentric circle is determined based on the pocket contour. New detailed algorithms to generate plunge toolpath for basic cases have been developed. An automatic pocket subdivision algorithm has been developed by dividing the pocket into several subregions that are easy to be machined. Without loss of generality, the method is applicable for both open and closed pockets. It also works for pockets with and without islands inside. The method is implemented and verified successfully by machining experiments. The results provide strong evidence that the proposed method can reduce the maximum engagement angle over the entire toolpath and thus improve the tool life.

Analysis and Prediction of the Machining Force Depending on the Parameters of Trochoidal Milling of Hardened Steel

Current demands on quality are the engine of searching for new progressive materials which should ensure enough durability in real conditions. Due to their mechanical properties, however, they cannot be applied to conventional machining methods. In respect to productivity, one of the methods is the finding of such machining technologies which allow achieving an acceptable lifetime of cutting tools with an acceptable quality of a machined surface. One of the mentioned technologies is trochoidal milling. Based on our previous research, where the effect of changing cutting conditions (cutting speed, feed per tooth, depth of cut) on tool lifetime was analysed, next, we continued with research on the influences of trochoid parameters on total machining force (step and engagement angle) as parameters adjustable in the CAM (computer-aided machining) system. The main contribution of this research was to create a mathematical-statistical model for the prediction of cutting force. This model allows setting up the trochoid parameters to optimize force load and potentially extend the lifetime of the cutting tool.

Time-Efficient Trochoidal Tool Path Generation for Milling Arbitrary Curved Slots

Trochoidal (TR) tool paths have been a popular means in high-speed machining for slot cutting, owing to its unique way of cyclically advancing the tool to avoid the situation of a full tool engagement angle suffered by the conventional type of slot cutting. However, advantageous in lowering the tool engagement angle, they sacrifice in machining efficiency—to limit the tool engagement angle, the step distance has to be carefully controlled, thus resulting in a much longer total machining time. Toward the objective of improving the machining efficiency, in this paper, we propose a new type of TR tool path for milling an arbitrary curved slot. For our new type of TR tool path, within each TR cycle, rather than moving circularly, the tool moves in a particular way such that the material removal rate is maximized while the given maximum engagement angle is fully respected. While this type of TR tool path works perfectly only for circular slots (including straight ones), by means of an adaptive decomposition and then a novel iso-arc-length mapping scheme, it is successfully applied to any general arbitrarily curved slot. Our experiments have confirmed that, when compared with the conventional TR tool paths, the proposed new type of TR tool path is able to significantly reduce the total machining time by as much as 25%, without sacrificing the tool wear.

Geometric accuracy of corners after milling operation of aluminum alloys

The study comparing a geometry of the inner corners after milling operation of aluminum alloy 7075 elements was conducted. The influence of changes of technological parameters and types of treatment on the geometric accuracy of the samples was investigated. The correct process of corner milling involves the need to select the right feed speed as well as the correct engagement angle of the milling tool. Corner milling is problematic due to the increase of engagement angle in their area. This makes it much more difficult to perform stable machining and adversely affects the surface accuracy and geometry of the concave corners. The tests using various strategies and technological parameters for milling corners with variable opening angles were carried out. When analyzing the obtained results, conclusions were formulated indicating the relationship between the change of selected technological parameters of milling in the corners and the geometric accuracy of the samples tested.

Analysis of Corners Milling of Aluminum Alloy Elements

The article presents comparative research on the effects of milling of concave corners of elements made of aluminum alloy 7075. The work focuses on the study of the impact of changes in technological parameters and types of machining on the obtained geometrical state of the machined samples. Correct milling of the corners requires selection of the appropriate feed rate and the proper engagement angle of the milling cutter. At the corners, tool engagement angle increases, which significantly hinders the execution of stable machining and adversely affects the geometric and qualitative characteristics of the surface in the corners. Study with application of various strategies and technological parameters of milling corners with variable opening angles were carried out. The main parameters of surface roughness of the machined elements were examined. When analyzing the results obtained, conclusions were formulated indicating the relationship between the change of selected technological parameters, with the assumed type of treatment, and the obtained quality parameters of the samples made.

MATHEMATICAL MODEL FOR CHIP GEOMETRY CALCULATION IN FIVE-AXIS MILLING

This paper presents the method to calculate the geometries of instantaneous chip in five-axis milling. The inclination angle changes in between two consecutive CC-points were taken into account in the calculation. In the first stage, the engagement angle, the axial depth of cut and cut width were determined through the mapping technique. The engagement point of the Work piece Coordinate System (WCS) was mapped to a Tool Coordinate System (TCS). In the second stage, the engagement angle and depth of cut, which were defined in the first stage were then used as a primary input to obtain the cut thickness and cut width. Two simulation tests have been presented to verify the ability of the proposed model to predict the cut geometry. The first tests revealed that the inclination angle makes the size of the cut thickness and cut width fluctuate. The cut width increased when the tool inclination angle increased. For the cut thickness, its magnitude was influenced by two effects, the orientation effect and the tooth path effect. The final result was a compromise between these two effects. In the second simulation test, the proposed model was successfully implemented to support the feedrate scheduling method.

Preliminary Study: The Effect of Tool Engagement and Cutting Speed on Cutting Temperature during Contour Tool Path Strategy

In pocketing operation for mold and die, the variation of tool engagement angle causes variation in the cutting force and also cutting temperature. The objective of this study is to investigate the effect of tool engagement on cutting temperature when using the contour in tool path strategy for different cutting speeds. Cutting speeds of 150, 200 and 250m/min, feedrate from 0.05, 0.1, 0.15 mm/tooth and depths of cut of 0.1, 0.15 and 0.2 mm were applied for the cutting process. The result shows that by increasing cutting speed, the cutting temperature would rise. Varying the tool engagement also varied the cutting temperature. This can be seen clearly when the tool makes a 90oturn and along the corner region. Along the corner, the engagement angle varies accordingly with the radial depth of cut.

Optimized Steam Turbine Operation by Controlled Clutch Angle Engagement

Some single shaft CCPPs are known to display increased vibrations if engaged at certain angles and a very smooth operational behavior if engaged at other angles. Neither the reason nor a mechanical mitigation for this behavior is known. Roughly, the engagement angles can be clustered into four 90° sectors, one of them is deemed unfavorable and another one is classified as favorable with respect to vibrations of the overall power train shaft. Although the first priority is to have an assembly that runs smoothly at arbitrary engagement angles, an option to engage at a predefined ‘good’ angle provides an I&C back-up solution to avoid undue vibrations. To meet this requirement a control method was developed to run up the steam-turbine thus that it will engage at a pre specified angle. The basic idea of the developed control algorithm is to increase the acceleration of the steam-turbine during run up if a prediction reveals an engagement angle that would be too small to be within the desired area and, conversely, decrease the acceleration if the anticipated angle would be too large. A control algorithm to exploit this idea was developed and tested with the aid of a simulation model. The simulation model comprises a detailed thermodynamic model of the steam-turbine, the control valves and their actuators, the steam-turbine shaft and the shift clutch. I&C was modelled with all details relevant to turbine speed control. The gas-turbine/generator unit, however, is cut down to angular velocity and relative angle, respectively. The performance of the controller was validated to comply with parameter uncertainties, different sampling times and frequency fluctuations of the electrical grid during coupling. In parallel, a high precision angular measurement device was developed and integrated into the existing turbine I&C. Hardware-in-the-loop tests with simulated turbines and a hardware I&C system implementation also revealed a very satisfactory performance. On site implementation of a prototype was successfully accomplished and resulted in the predicted accuracy of the preset engagement angle.