Flat Tool Research Articles

An Innovative Method for Forming Balls by Cross Rolling.

The paper describes an innovative cross rolling method that enables the production of six balls at the same time, each ball with a diameter of 100 mm. The principle of the proposed rolling technique is discussed and the tools used in this forming process are described. Two variations of the proposed method for producing balls were investigated, one performed with the use of flat tools and the other with the use of two rolls. Results of the numerical modelling are discussed. They clearly demonstrate that the proposed method can be used to produce balls with large diameters. Rolling experiments were performed under laboratory conditions to produce 40 mm diameter balls, i.e., in the 1:2.5 scale. The experimental findings show a good qualitative agreement with the numerical results.

Cavity formation in cross-wedge rolling processes

The problem of end-face cavity formation in parts produced by cross-wedge rolling was studied in order to reduce material consumption. The cavity depth was measured by the displacement method. Twenty-one different cases of rolling were analysed by finite element method to determine the effects of process parameters such as the wedge tool angle, the temperature of material, the tool velocity and the reduction ratio on the depth of end-face cavities. Relationships between these parameters are examined in order to establish dependencies enabling quick and simple selection of a concavity allowance in order to remove the cavities. The equations for calculating the concavity allowance were verified in an experimental process for manufacturing ball pins with the use of flat tools. Rolling tests were performed using a billet with its length selected in compliance with the established dependencies. The experimental results demonstrate that the proposed solution is a viable method for end-face cavity removal.

Multi-shaped tool wear study during rotary ultrasonic drilling and conventional drilling for amorphous solid

Float glass, which is a hard and brittle material, is generally machined and drilled using rotary ultrasonic machining and conventional drilling to create products such as solar panels, metrological instruments, etc. But researchers are facing serious issues with regard to tool wear and opting for best shape of tool for the drilling purpose. In this study, blind holes are made on float glass specimen using rotary ultrasonic drilling and CNC conventional drilling process with the aid of multi-shaped tools. The opted tools are namely hollow abrasive tool, pin-pointed conical tool, flat cylindrical tools, and concave circular tool. The entire experimental work is accomplished by considering industrial conditions. Multi-shaped tool’s weight is computed at three stages i.e. (a) fresh tool, (b) after rotary ultrasonic drilling, and (c) after conventional drilling to analyze the overall tool wear. Apparently, micro-studies are used to investigate the phenomena of lateral and end face tool wear while creating blind holes at these three stages. It is revealed that the concave circular tool achieved a minimum percentage of weight loss i.e. 4.92% after conventional drilling and 1.96% after rotary ultrasonic drilling process, which could be preferred for drilling purpose followed by the hollow abrasive tool.

Improving process robustness in ultrasonic metal welding of lithium-ion batteries

Ultrasonic metal welding is a solid-state joining method popularly adopted in the assembly of lithium-ion battery cells, modules, and packs for electrical vehicles due to its numerous advantages over traditional fusion welding techniques. Ultrasonic metal welding process yields quality welds under optimal conditions, but can result in poor welds when there are disturbances, such as the presence of oil contamination. State-of-the-art controllers cannot detect those disturbances or control the welding process accordingly. In this research, two methods are proposed to improve the process robustness, namely, a real-time controller and a new tool geometry design for the sonotrode. The developed controller monitors the on-line power signal and adjusts the weld clamping pressure through a calibrated step function accordingly. Experimental results show that with oil contaminated workpieces, the new controller yielded an average improvement of 14.5–440% in the T-peel strength over the current controller, depending on the level of oil contamination. Additionally, the process robustness was shown to be improved by the use of a spherical tool in place of a flat tool. Improvements are achieved for all tested clamping pressures, especially when the pressure is outside the optimal range for the flat tool.

Effects of Process Parameters on Surface Roughness in Incremental Sheet Forming

Incremental Sheet Forming (ISF) process significantly reduces the tooling costs as compared to other conventional sheet metal processes where expensive dies are used to produce any product. Hence, multi-variety components in small batches can be manufactured at lower cost with ISF technology which prevents limitations of traditional sheet metal forming processes. This paper represents effects of process parameters on surface roughness of formed components on AA2024-O sheets. Surface roughness has been measured by a roughness tester. Average roughness was found to increase with decrease in tool diameter. Hemispherical ended tools produced better surface quality of formed components as compared to that produced by flat end tools

Effect of temperatures during forming in single point incremental forming

In this article, the temperatures at sheet-tool interface are observed with non-contact temperature sensors in single point incremental forming at high relative tool velocities. A flat-ended tool was used to form AA5754-H32 sheets, and the results were recorded to study the heat generation from relative tool motion over the sheet metal surface. This paper proposes a new geometry to study the effects of temperature on formability and resulting geometrical errors. The regions of large geometrical errors are presented in cross-sectional and isometric views in colour contrasts. As the tool moves along a prescribed path, a moving comet type temperature structure is observed with two heat generation zones for the first few step downs. The resulting microstructures are observed for each of the following cases and the disparities are reported. Generally, the blankholder is assumed to be at a constant temperature. Results show this is not true; the actual temperature rises with a heat loss to the blankholder via backing plate. High rotation speeds are used, with an upper limit being observed, before forming of sheet metal becomes untenable. At this limit, high wear followed by lubricant fuming is observed. The result at higher rotational speeds is similar to friction stir welding, which are explained in detail by the microstructures. Surface roughness of the formed components as a response to the high tool linear speeds with flat tools is also presented.

Comparison Between Cemented Carbide and PCD Tools on Machinability of a High Silicon Aluminum Alloy

The high content of silicon of aluminum casting alloys challenges the tool life of conventional cemented carbide inserts, and polycrystalline diamond (PCD) tools appear as an interesting material to machine these alloys because they improve substantially the durability of cutting tools and consequently the productivity of machining. However, the surface roughness, cutting forces and chip morphology are equally important factors in machining evaluation. Therefore, an experimental study is performed aiming at comparing the performance of cemented carbide and PCD tools taking into account cutting forces, surface roughness and chip morphology, under dry longitudinal turning, performed for the AlSi9Cu3 alloy produced by permanent mold casting process. Different chip breaker geometries were also considered, and their influence on the referred parameters was also investigated. Analysis of variance was employed to study the different contributions of inserts, cutting speed, feed rate, depth of cut and their interactions in machinability performance. The results show low cutting forces and better results for surface roughness for uncoated cemented carbide tools, with simpler chip breakers and flat rake face PCD tool, but an efficient chip control was obtained for inserts with small grooves with high cutting forces and power consumption. Nevertheless, the feed rate and depth of cut have the highest influence on the machinability performance of the alloy under investigation.

A rotating core-based magnetorheological nano-finishing process for external cylindrical surfaces

ABSTRACTA rotating core-based magnetorheological finishing process has been developed to finish the external cylindrical surfaces at the nano-level more efficiently. The existing MR finishing process based on the stationary curved core tool tip is found to be comparatively less effective than the present process based on a rotating flat core tool tip for finishing the external cylindrical surfaces. This is due to the fact that in the present process both the workpiece and the tool rotating rather than giving rotation to the workpiece alone as in the existing process. The carbonyl iron particle (CIP) chains are rotated along with the rotation of the tool. This results in an increase in the kinetic energy of the active abrasive particles gripped by CIP chains which causes for the better finishing performance. Finishing is done by both the processes and their corresponding results are compared. The Ra, Rq, and Rz values are reduced to 71.62%, 72.53%, and 70.73% with a stationary curved core tool tip, and 94.59%, 94.51%, and 92.68% with a rotating flat core tool tip in 90 minutes of MR finishing. The overall results revealed that the present developed process using the rotating flat tool tip is more useful in finishing the external cylindrical surfaces as compared to the stationary curved tool tip.

Numerical Investigation of Microtexture Cutting Tool on Hydrodynamic Lubrication

The aim of this technical brief is to provide a numerical approach to investigate the lubricity enhancement effect of microgrooves texture on tools' rake face. The key parameters related to cutting condition and grooves morphology were considered in the analytical model of tool–chip friction pair. The fully textured surfaces with the periodic microgrooves were systematically studied by solving the nondimensional Reynolds equation with the multigrid method. The results indicated that the microgrooves texture generates extra carrying capacity comparing to the flat tool and the optimum grooves direction is vertical to the chip sliding. Higher area density and optimum grooves width can further promote hydrodynamic lubrication. By modifying the tool rake face geometry to restrict the tool–chip slope angle, efficiency of surface texture could be greatly extended. In addition, the film's average pressure was nearly proportional to the chip velocity. Hence, the textured tool is more effective in high-speed cutting.

Modeling of heat generations for different tool profiles in friction stir welding: study of tool geometry and contact conditions

In this work, improved heat generation models are developed for straight and tapered shoulder geometries with different tool pin profiles in friction stir welding. The models are developed considering the welding process as a combination of the pure sliding and the pure sticking conditions. From the results, the amount of heat generation is directly proportional to the number of edges in the pin profiles in such a way that the heat generated in the profiles increases from the triangular pin profile to hexagonal pin profile. Also, increase in the tool rotational speed under constant weld speed increases the heat input while increase in the weld speed under constant tool rotational speed decreases the heat input and the rate of heat generation at the shoulder in a flat shoulder tool is more than that of conical/tapered shoulder tool. The predicted results show good agreements with the experimental results in literature.

Successive Forming of Multi-thickness Plates by Using Wedge-shaped Tool

Abstract A new forming process has been studied for manufacturing sheet metal blanks with multi-thickness profiles, referred to as “tailor-formed blanks”. The thickness variations will be effective in achieving load-optimized profiles, which further reduce weight of structural parts in automotive, aerospace, electronics metal components and etc. Unlike tailor-welded blanks, these tailor-formed blanks offer smooth and continuous thickness transitions, preferable for subsequent forming operations. In this new process, a multi-thickness plate is formed from a uniform thickness plate by a successive forming operation using a wedge-shaped tool and flat tool. The wedge-shaped tool features three different zones – knifing, spreading and sizing zone with two key defining parameters – forming angle (α) and spreading angle (β). These three zones progressively cause metal to flow transversely creating a distinct thinner portion of predefined width and transition walls in the plate. The thin portion in the workpiece can then be extended to the plate’s full length by the successive forming under a relatively small forming force in each forming step. This paper discusses the basic concept of this new forming process, tool design, deformation characteristics, and process limits through experimental and numerical studies. It was found that inner crack and edge crack were the dominant defects in this forming method. Based on the experimental results, forming process windows were established, describing relationships between the defects, workpiece thickness reduction and feed rate. The numerical study showed effects of the forming angle (α) and spreading angle (β) on maximum damage value induced and forming load. The tailor-formed blanks of 50mm by 500mm were successfully fabricated from three kinds of aluminum alloy, i.e. Al5052, Al6061 and Al7075 of 2-4 mm thickness with maximum thickness reduction of 35%-45%. Subsequently, the aluminum tailor-formed blanks were stamped to produce lightweight part demonstrators with thickness variations.

Observations on Heat Generated in Single Point Incremental Forming

The forming tool in single point incremental forming (SPIF) follows a path prescribed by CAM software. As the tool follows this path, thereby deforming the sheet, both friction and deformation occur generating heat. The effect of increasing feed rates and tool rotation speed on resulting temperatures has been studied for AA 5754-H32. A flat tool was used to form a variable wall angle geometry and the temperatures were recorded using an infrared camera. The infrared camera was able to give a temperature gradient at the tool-sheet interface. It was found that along with geometry, lubricant and rig design also have an impact on the net heat within the system. In addition, beyond a certain limit, the high relative velocity can cause wear at the tool-sheet metal interface. The observations on temperature distribution are new and novel.

Enhancing Performances of Micro-Grinding of BK-7 Glass through Modification of PCD Micro-Tool

This paper focuses on the performance enhancement of micro-grinding of BK-7 glass through modification of polycrystalline diamond (PCD) micro-grinding tools. A single groove and double perpendicular grooves were created on the flat end of the PCD tools using wire EDM process. The performance of single-groove and double-groove PCD tools with flat end wascompared based on grinding forces and surface roughness values. Modified PCD tools allowed for the significant decrease of grinding forces as well as surface roughness compared to those obtained with flat end tool.

Development of magnetorheological finishing process for external cylindrical surfaces

ABSTRACTThe recent increase in demand for functional and technological requirements of the component results in the development of complex geometrical shapes and that too with close tolerances and fine surface quality. To fulfill the needs for finishing the external cylindrical surfaces such as groove, taper, step surfaces, and threads, an advanced finishing process based on magnetorheological (MR) fluid has been developed. The developed process can finish the external cylindrical surfaces with controlled magnetic field as likely similar to turning operation. Fine finishing of external cylindrical surfaces is a significant requirement in many functional applications. The wide applications of this present process can be valuable in automotive, machine tool production, valves manufacturing, and aerospace. A modified new MR finishing tool with flat and curved tip surface has been made to perform finishing on external cylindrical surfaces. The present cylindrical finished workpiece is useful in macaroni manufacturing machine. The surface roughness values Ra, Rq, and Rz are reduced to 54.41%, 51.65%, and 40% with flat tool tip surface and 80.88%, 81.32%, and 82.5% with curved tool tip surface in 90 min of finishing time. The overall results reported that the present process with curved tool tip surface is comparatively more useful in finishing the external cylindrical surfaces.

Modeling and optimization of CNC milling of AISI 1050 steel by a regression based differential evolution algorithm (DEA)

Abstract The present study is aimed at finding an optimization strategy for the CNC pocket milling process based on regression analysis including differential evolution algorithm (DEA). Milling parameters such as cutting speed, feed rate and depth of cut have been designed using rotatable central composite design (CCD). The AISI 1050 medium carbon steel has been machined by a high speed steel (HSS) flat end cutter tool with 8 mm diameter using the zig-zag cutting path strategy under air flow condition. The influence of milling parameters has been examined. The model for the surface roughness, as a function of milling parameters, has been obtained using the response surface methodology (RSM). Also, the power and adequacy of the quadratic mathematical model have been proved by analysis of variance (ANOVA) method. Finally, the process design parameters have been optimized based on surface roughness using bio-inspired optimization algorithm, called differential evolution algorithm (DEA). The enhanced method proposed in this study can be readily applied to different metal cutting processes with greater and faster reliability.

Prediction and control of pillow defect in single point incremental forming using numerical simulations

Pillows formed at the center of sheets in Single point incremental forming (SPIF) are fabrication defects which adversely affect the geometrical accuracy and formability of manufactured parts. This study is focused on using FEA as a tool to predict and control pillowing in SPIF by varying tool size and shape. 3D Finite element analysis (FEA) and experiments are carried out using annealed Aluminum 1050. From FEA, it is found out that the stress/strain state in the immediate vicinity of the forming tool in the transverse direction plays a determinant role on sheet pillowing. Furthermore, pillow height increases as compression in the sheet-plane increases. The nature of in-plane stresses in the transverse direction varies from compressive to tensile as the tool-end geometry is changed from spherical to flat. Additionally, the magnitude of corresponding in-plane stresses decreases as the tool radius increases. According to measurements from the FEA model, flat end tools and large radii both retard pillow formation. However, the influence of changing tool end shape from hemispherical to flat is observed to be more important than the effect of varying tool radius, because the deformation zone remains in tension in the transverse direction while forming with flat end tools. These findings are verified by conducting a set of experiments. A fair agreement between the FEM and empirical results show that FEM can be employed as a tool to predict and control the pillow defect in SPIF.

Investigation on the profile of microhole generated by electrochemical micromachining using retracted tip tool

Electrochemical micromachining (EMM) is becoming an effective technology to manufacture microparts due to its multiple advantages of almost no tool wear, almost forceless machining, no heat effect and relatively high removal rate, etc. However, accuracy controlling is the key issue which limits the industrial application of EMM. From the current theory and industrial practice, traditional side-insulated flat tip tool often causes bell-mouth profile at entrance and exit, rough surface on the top and bottom of workpiece, and excess radial overcut due to the dispersed distribution of electrical field. To improve the machining accuracy, a novel tool structure with retracted electrode tip is proposed for EMM of microhole in the present work. The effect of the novel tool structure on machining accuracy was studied with both simulation and experiments. Simulation results show that electrical field distribution with retracted tip tool is increasingly confined to the electrode region compared to the flat tip tool throughout the EMM process. Experiments were carried out to verify the advantages of the retracted tip tool and investigate the effect of tip retracted depth on machining accuracy. The critical criterions, including depth average radial overcut (DAROC), entrance profile, exit profile, and surface quality at the entrance and exit were measured to evaluate the machining accuracy. The experimental results show that high-quality microhole with sharp entrance and exit profile, smooth surface, and small DAROC can be successfully manufactured using a retracted tip tool with the optimum tip retracted depth of 71 μm.

Cutting performance of nano-crystalline diamond (NCD) coating in micro-milling of Ti6Al4V alloy

Hard coatings are an important factor affecting the cutting performance of tools. In particular, they directly affect tool life, cutting forces, surface quality and burr formation in the micro-milling process. In this study, the performance of nano-crystalline diamond (NCD) coated tools was evaluated by comparing it with TiN-coated, AlCrN-coated and uncoated carbide tools in micro-milling of Ti6Al4V alloy. A series of micro-milling tests was carried out to determine the effects of coating type and machining conditions on tool wear, cutting force, surface roughness and burr size. Flat end-mill tools with two flutes and a diameter of 0.5mm were used in the micro-milling process. The minimum chip thickness depending on both the cutting force and the surface roughness were determined. The results showed that the minimum chip thickness is about 0.3 times that of the cutter corner radius for Ti6Al4V alloy and changes very little with coating type. It was observed from wear tests that the dominant wear mechanism was abrasion. Maximum wear occurred on NCD-coated and uncoated tools. In addition, maximum burr size was obtained in the cutting process with the uncoated tool.

Investigation of material transfer in sliding friction-topography or surface chemistry?

To differentiate between the roles of surface topography and chemical composition on influencing friction and transfer in sliding contact, a series of tests were performed in situ in an SEM. The initial sliding during metal forming was investigated, using an aluminum tip representing the work material, put into sliding contact with a polished flat tool material. Both DLC-coated and uncoated tool steel was used. By varying the final polishing step of the tool material, different surface topographies were obtained.The study demonstrates the strong influence from nano topography of an unpolished DLC coated surface on both coefficient of friction and material transfer. The influence of tool surface chemistry is also discussed.

Establishing Relationship between Mechanical Properties and Process Parameters of Friction Stir Spot Welded Dissimilar Al Alloy/Cu Joints

Friction stir spot welding, a linear variant of friction stir welding is a solid state material joining technique which is widely used in for joining dissimilar materials and different metal alloys which are difficult to join by using conventional fusion welding processes. In this paper, friction stir spot joining technique has been used for joining aluminium (Al) commercial alloy (Al 5083 – ‘0’ - H111) and oxygen free copper (C10100) using probe pinned tool and a pin less flat tool. Within feasible limits, the effect of friction stir spot welding process parameters such as tool rotational speed, plunge depth and dwell time on variation of tensile shear failure load and hardness of the dissimilar joints were evaluated.