Semi-finishing Operations Research Articles

Analysis of Face Milling of Hard Steel 55NiCrMoV7 by Studying Rough and Semi-Finished Machining and the Influence of Cutting Parameters on Macroscopic Chip Dimensions.

Hard milling is being increasingly used as an alternative to EDM due to its high productivity. The present paper presents the results of theoretical-experimental research on the face milling of hard steel 55NiCrMoV7. A comprehensive analysis of cutting temperatures and forces during single-tooth milling and a morphological examination of the resulting chips are conducted for roughing and semi-finishing operations. The temperature is analyzed in the chip formation area, and the detached chips and the cutting force are analyzed through their tangential, radial, and penetration components, depending on the contact angle of the cutter tooth with the workpiece. The analysis of chip morphology is carried out based on the dimensional and angular parameters of chip segmentation and their degree of segmentation. Based on the central composite design and the response surface method, it is shown that it is possible to mathematically model the dependence of the macroscopic dimensions of the detached chips on the cutting parameters. The determined process functions, the maximum chip curling diameter, and the maximum chip height allow for establishing the influence of the cutting parameters' values on the chips' macroscopic dimensions and, thus, guiding the cutting process in the desired direction.

Cryogenic CO2 assisted hard turning of AISI 52100 with robust CO2 delivery

Cryogenic-assisted hard turning arises a promising sustainable manufacturing technology, emerging as an interesting alternative to conventional grinding. The replacement of traditional metalworking fluids for cryogenic CO2 cooling presents significant environmental benefits as well as the potential process performance improvement. In this paper, a novel cryogenic CO2 delivery system which enables CO2 mass flow and phase control is introduced. In this way, more stable and localized cooling of the cutting zone is obtained in comparison to direct connection delivery systems reported in literature. Finally, this system is employed to perform hard turning tests of hardened bearing steel 52100, where tool wear and surface integrity results are compared to dry air blow and conventional cooling conditions. The application of the cryogenic cooling was found to improve conventional cooling and dry cutting conditions for semi-finishing operations at elevated cutting speeds.

COMPARISON OF PREPARATION METHODS IN TERMS OF TOOL LIFE AND SURFACE ROUGHNESS

The article compares two cutting edge preparation methods and their influence on the machined surface roughness of the difficult to cut nickel alloy Inconel 718 and the tool wear of cutting inserts made of cemented carbide. The manufacturing and preparation process of cutting inserts used in the experiment were made by Dormer Pramet. The preparation methods used in the experiment were drag finishing and brushing. Cutting parameters did not change during the whole turning process to maintain the same conditions in each step of the process and were determined based on tests for a semi-finishing operation of the turning process. To obtain durability of 25 to 30 minutes with controlled development of the tool wear the cutting parameters were determined with cooperation with the cutting inserts manufacturer.

Tool axis adjustment for 5-axis roughing operations

The increased accessibility of the tool achieved by using 5-axis roughing reduces the overall machining time of complex parts by reducing or eliminating the re-roughing and semi-finishing operations thereby decreasing the volume of remaining material before finishing operations. However, 5-axis milling generates significant variations in tool orientation which, combined with the high tool engagement in the material required by the roughing conditions, can be penalizing. Controlling these variations is therefore mandatory to guarantee the tool life, the productivity and the quality of the roughing operation. Thus, a multi-objective optimization is proposed to define the successive orientations of the tool axis along the path that minimize the feedrate slowdowns and thus the machining time, balance the pushing or pulling machining configurations and respect the programmed scallops heights of the machined surface. In this work, the tool path is defined by two curves, one constraining the position of the tool and the other its orientation allowing for a parametric synchronization to conduct the optimization. From the definition of the weights of each of the minimization objective functions, it is possible to find a tool axis orientation solution that satisfies the given constraints all along the path. The application on a test part by simulation and machining highlights the effectiveness of the proposed approach and the advantages of controlling the evolution of the tool axis orientation in 5-axis roughing.

Study of a Novel Ceramic Tool Performance in the Machining of Ti-6Al-7Nb Alloys

ABSTRACTConsidering their distinctive properties, titanium alloys are used in foremost industries, including the aeronautic, automotive and biomedical industries. The reduced machinability of titanium alloys is due to their low thermal conductivity and high plasticity behavior. In the biomedical sector, one of the most studied alloys is Ti-6Al-4V. In the case of the Ti-6Al-7Nb alloy, scarce investigations are identified, related to machinability studies. The machining of Ti-6Al-7Nb alloy requires the development of new tools with higher properties, which provide better performance. The objective of this study is to present the experimental results related to a novel ceramic cutting tool, in terms of cutting tool life and productivity, in the machining of Ti-6Al-7Nb alloy. A turning operation of a 25 mm diameter bar was performed; the cutting speed was varied in three levels. The results showed the high performance of this type of tools, from the point of view of machinability. The values of the obtained cutting forces are found in the ranges reported by the consulted literature using ceramic tools. The surface roughness values were considered appropriate, taking into account that the tool is recommended for roughing and semi-finishing operations. The most relevant results were obtained in terms of productivity, considering that the performance is 2.53 times higher than the presented in similar works.

Investigation of surface roughness and tool wear length with varying combination of depth of cut and feed rate of Aluminium alloy and P20 steel machining.

High-speed milling technique is often used in many industries to boost productivity of the manufacturing of high-technology components. The occurrence of wear highly limits the efficiency and accuracy of high- speed milling operations. In this paper, analysis of high-speed milling process parameters such as material removal rate, cutting speed, feed rate and depth of cut carried out by implemented to conventional milling. This experiment investigate the effects of varying combination of depth of cut and feed rate to tool wear rate length using metallurgical microscope and surface roughness using portable surface roughness tester after end milling of Aluminium and P20 steel. Results showed that feed rate significantly influences the surface roughness value while depth of cut does not as the surface roughness value keep increasing with the increase of feed rate and decreasing depth of cut. Whereas, tool wear rate almost remain unchanged indicates that material removal rate strongly contribute the wear rate. It believe that with no significant tool wear rate the results of this experiment are useful by showing that HSM technique is possible to be applied in conventional machine with extra benefits of high productivity, eliminating semi-finishing operation and reducing tool load for finishing.

Experimental Study on Unsynchronized Ultrasonic Assistance of Electro Discharge Machining Process

The paper deals with experimental study on unsynchronised (out of phase) ultrasonic assistance (US) of electrical discharge machining (EDM) process, considering finishing and semi-finishing operations. The main output technological parameters at classic EDM are not as good as they are expected due to instability of material removal process and long duration of gas bubble formed around plasma channel. The US longitudinal oscillations of electrode-tool produce cavitation within frontal working gap leading to collective implosion of gas bubbles. This hydraulic phenomenon can remove the workpiece material in solid or plastic state or even in liquid state. The goal of our study is to emphasize and quantify the influence of US assistance into EDM process and also to determine a correlation between EDM and US parameters, considering an unsynchronised condition. Nevertheless some optimization conditions of working parameters are needed to attain notable expected performances. From experimental data analysis, it can be noticed that significant growth in process productivity is achieved when EDM process frequency is equal with the ultrasonic assistance frequency.

Multi-disciplinary design optimisation of mechanical parts with freeform surfaces: Case study encompassing manufacturing criteria

Designing parts with freeform surfaces, as typically applied in dies and moulds, is currently dealt with through designer experience, if design intent is to be maintained and if, at the same time, the manufacturing process is to be facilitated. This work puts forward a solution to these issues which is based on computational intelligence. A library of freeform surface morphological features is defined using parametric wireframe models that include constraints. The part is constructed using wireframe features from this library and these are subsequently converted to solid models. The effect of changes of feature parameter values is linked to part functional characteristics in standard design environment. Regarding the effect on manufacturing process characteristics, various models may be employed. As an example, a fuzzy system that decides tool diameter and the necessity of a semi-finishing operation is employed in this work. Artificial neural networks are trained with a number of workpiece variations corresponding to different feature parameter values and the pertinent outputs from functional and manufacturing assessment. Next, a standard genetic algorithm is set up to find the best values of the feature parameters based on both functionality and manufacturing criteria with suitable weighing. The evaluation function of the genetic algorithm employs the artificial neural networks constructed as metamodels. The methodology is demonstrated through an illustrative case study, but may encompass further Design-for-X disciplines.

Influences of Varying Combination of Feed Rate and Depth of Cut to Tool Wear Rate and Surface Roughness: High Speed Machining Technique in Non-High Speed Milling Machine

Machining technique using high spindle speed, high feed rate and shallow depth of cut utilize in High Speed Milling (HSM) machines offer several benefits such as increase of productivity, elimination of secondary and semi-finishing process, reduce tool load and small chips produced. By adjusting some of the machining parameters, non-HSM machine having lower spindle speed and feed rate could also take advantages some of the benefits mentioned above when applying the HSM technique. This experiment investigate the effects of varying combination of depth of cut and feed rate to tool wear rate and surface roughness during end milling of Aluminum and P20 tool steel in dry condition. The criterion for tool wear before it gets rejected is based on maximum flank wear, Vb of 0.6mm. Material removal rate, spindle speed and radial depth of cut are constant in this experiment. After preliminary machining trials, the combination starts with depth of cut of 2mm and feed rate of 45mm/min until the smallest depth of cut and highest feed rate of 0.03mm and 3000mm/min respectively. The obtained result shows that for both materials, feed rate significantly influences the surface roughness value while depth of cut does not as the surface roughness value keep increasing with the increase of feed rate and decreasing depth of cut. Whereas, tool wear rate almost remain unchanged indicates that material removal rate strongly contribute the wear rate. With no significant tool wear rate, this study demonstrates that HSM technique is possible to be applied in non-HSM machine with extra benefits of eliminating semi-finishing operation, reducing tool load for finishing, machining without coolant and producing smaller chip for ease of cleaning.

Improvement of Surface Roughness of Inner Hole for Grinding Machine Using Adaptive Fuzzy Sliding Mode Controller

In industry, grinding is commonly used as a finishing or semi-finishing operation. The surface roughness is a variable often used to describe the quality of the overall grinding system. However, the traverse and longitudinal waviness are produced by the random nature of the grinding process and by machine vibration in surface. This paper presents an adaptive fuzzy sliding mode control (AFSMC) to improve surface roughness in inner hole machining using diamond grinding bar. The experimental results show that the AFSMC can reduce surface roughness (Ra).

Recording of real cutting forces along the milling of complex parts

In this paper, a data acquisition system that simultaneously allows the recording of cutting forces and cutting tool position (coordinates X, Y and Z) is presented. Thus, the geometry of the surface being machined and the values of the cutting forces generated during the surface milling can be correlated. In this manner, two usual problems in milling experimentation are solved. First, those derive from the continuous changes in the feed rate value due to the special look ahead functions (being on-line applied by the numerical control in all high-speed milling centres), which affects the correlation between part geometry and forces. Second, those originate by the presence of unexpected stocks coming from previous semi-finishing operations, which changes the value of cutting forces respect to those calculated taking into account the theoretical tool engagement into the part. The objective of this work is the development of a diagnostics tool for allowing the detection of potential milling problems by researchers, making more profitable the performance of machining test on real complex parts. This tool can be used in the optimization of the milling of test-parts, machining real geometries that incorporate problems different from those observed in the linear tests at constant linear feeds (in end-milling conditions). The final goal of the system is the generation of cutting forces maps as a function of the geometry of real workpieces, which is an advance respect the usual forces recording in function of time or tool rotation typical of linear machining tests. In order to do that, the system incorporates a dynamometric plate for the measurement of the three components of the cutting force, as well as an acquisition card connected to the analog output of the position control loops. After machining, the file containing position and force data is post-processed and chromatic and vector maps are generated. The force analysis utility has been applied to three cases, in order to assess its feasibility in machining research projects. The first example shows a reduction of the number of tests and therefore machining time (even by 18 times) in the validation of a mechanistic cutting force model. Second example is focused on the detection of unexpected tool engagement conditions in complex parts. And the last one addresses to the milling of thin walls, for investigation of static and dynamic milling problems.

Toroidal milling of hardened SAE H13 steel

It is estimated that around 65% of the cost of a die or mould is related to the machining processes. Moreover, the literature says that 70% of the time spent in the machining processes of this kind of parts is used in finishing and semi-finishing operations. The high complexity of the machined surfaces makes mandatory the use of ball nose tools, with large overhang, what increases vibration in the process. These problems have to be minimized, since dies and moulds demand a very good surface finish and tight dimensional tolerances. A frequently used strategy to attenuate these problems is to carry out semi-finishing operations with cutters containing circular inserts, because these inserts produce smooth transitions among the passes and a smaller and more uniform stock material for the finishing operation. The main goal of this work is to evaluate the performance of rounded inserts of carbide and cermet in the semi-finishing milling (called toroidal milling) of H13 steel with hardness of 50 HRc. The influence of radial depth of cut, cutting speed and feed per tooth on tool life will also be considered. It also intends to test the feasibility of using minimum quantity of lubricant (MQL) technique instead of dry cutting in this kind of machining operation.

Geometric Simulation of Ball-End Milling Operations

In this paper, B-rep solid modeling techniques are used to deal with geometric modeling issues encountered in ball-end milling simulation. The precise B-rep model of the cutter swept volume is developed using advanced sweeping/skinning techniques. Semi-finishing operations are simulated by performing consecutive Boolean operations between the updated part and swept volume. The instantaneous chip geometry is accurately and reliably extracted from the B-rep model of the updated part. Also, the material removal in ball-end milling is precisely simulated for finishing operations, in order to construct the feed-mark and scallop geometries. The validity of the final model is confirmed by comparing the predicted feed-mark profile with experimental measurements. The system developed can be used to verify and optimize NC codes, thus contributing to improving reliability, accuracy, and productivity in CNC machining.

On the dynamics of ball end milling: modeling of cutting forces and stability analysis

This paper presents a dynamic force model and a stability analysis for ball end milling. The concept of the equivalent orthogonal cutting conditions, applied to modeling of the mechanics of ball end milling, is extended to include the dynamics of cutting forces. The tool is divided into very thin slices and the cutting force applied to each slice is calculated and summed for all the teeth engaged. To calculate the instantaneous chip thickness of each tooth slice, the method of regenerative chip load calculation which accounts for the effects of both the surface undulations and the instantaneous deflection is used. To include the effect of the interference of the flank face of the tool with the finished surface of the work, the plowing force is also considered in the developed model. Experimental cutting forces are obtained using a five-axis milling machine with a rotary dynamometer. The developed dynamic model is capable of generating force and torque patterns with very good agreement with the experimental data. Stability of the ball end milling in the semi-finishing operation of die cavities is also studied in this paper. The tangential and radial forces predicted by the method of equivalent orthogonal condition are fitted by the equations F t= K t( Z) bh av and F r= K r( Z) F t, where b is the depth of cut and h av is the average chip thickness along the cutting edge and Z is the tool axis coordinate. The polynomial functions K t( Z) and K r( Z) are the cutting force constants. The interdependency of the axial and radial depths of cut in ball end milling results in an iterative solution of the characteristic equation for the critical width of cut and spindle speed. In addition, due to different cutting characteristics of the cutting edge at different heights of the ball nose, stability lobes are represented by surfaces. Comparison of the time domain simulation for the shoulder removal process in die cavity machining with the analytical predictions shows that the proposed method is capable of accurate prediction of the stability lobes.