Tool Path Research Articles

Computing smooth preferred feed direction fields with high material removal rates for efficient CNC tool paths

We propose a novel method to compute smooth preferred feed direction fields with high material removal rates to construct CNC tool paths for five-axis machining with ball-end mills. At the core of our method are three new facts about the local maximum feed directions of the material removal rate to facilitate feed direction field optimization. According to these new facts, we develop a practical method to generate desired fields for surfaces with smooth normal directions. Then, the preferred feed direction fields are used to generate tool paths via the existing iso-level method. The experimental results demonstrate the feasibility and advantages of our method. Compared to the state-of-the-art methods, the proposed method achieves a higher efficiency (up to 20.7%).

High-frequency ultrasonic vibration-assisted sculpturing with a smoothed tool path for optical 3D micro-structured surfaces with sharp edges

The fabrication of complex 3D micro-structured surfaces on difficult-to-machine materials such as steel and tungsten carbide is the premise for mass production of glass components with functional surfaces by the glass moulding process. Ultrasonic vibration-assisted cutting (UVAC) is an effective method to machine 3D micro-structured surfaces on these difficult-to-machine materials. However, it is challenging and difficult for UVAC to machine microlens arrays with sharp edges, at which sudden acceleration of the z-axis slide is required to make the cutting tool follow the tool path. This could induce tool vibration and cause relative tool-work displacement, resulting in poor machining accuracy and surface finish of the machined 3D microstructure. In this paper, high-frequency ultrasonic vibration-assisted sculpturing (HFUVAS) with a smoothed tool trajectory is used to machine microlens array on steel mould for fine machining accuracy and surface quality. A comparison is made between the cutting performance of the circular microlens arrays machined by diamond turning and diamond sculpturing. The results found that relative tool-work displacement arising at sharp edge in diamond turning could be eliminated in HFUVAS with a smoothed tool path, demonstrating the effectiveness of a smoothed tool path in reducing relative tool-workpiece displacement in the fabrication of 3D micro-structured surfaces. Furthermore, a quadrilateral microlens array and hexagonal microlens array are also fabricated in order to extend the applications of HFUVAS, with a form error within 1 μm and surface roughness with an arithmetical mean height Sa of below 10 nm achieved.

Effect of FDM Processing Conditions on Snap-Fit Characteristic in Assembly

Snap-fit allows plastic products to have assembly and disassembly capabilities without the use of screws, bolts, or other additional parts. For this reason, snap-fit is used in all kinds of plastic products from stationery to automotive parts. Because the mechanical and other functions of a snap-fit are greatly affected by its shape and material properties, it is desirable to fully evaluate them at the design stage. In addition, as the assembly and disassembly of products by snap-fit is generally performed by people, it is important to evaluate not only virtually but also with actual plastic parts. Therefore, there is a strong need to make a prototype and evaluate the feel of the product during assembling and disassembling, before finalizing on the shape and materials. In the past, making precise prototype required expensive molds, but in recent years, additive manufacturing has made it possible to make prototype efficiently and at low cost. In additive manufacturing, fused deposition modeling (FDM) is considered suitable for snap-fit prototype because it can use the same materials as mass-produced products. Thus, it may be possible to make a snap-fit prototype with rigidity, strength, and other characteristics similar to those of mass-produced products. However, FDM has various processing conditions such as tool path, nozzle temperature, and height of one layer. They are expected to have a significant effect on the snap-fit characteristics. Snap-fit is required to meet various requirements depending on the plastic products. The requirements can be divided into three major categories: in assembly, in disassembly, and when to use. In this study, we investigated the effect of FDM processing conditions on snap-fit characteristic in assembly.

Process Planning with Removal of Melting Penetration and Temper Colors in 5-Axis Hybrid Additive and Subtractive Manufacturing

Hybrid manufacturing (HM), which combines additive manufacturing (AM) and subtractive manufacturing (SM), is effective for the fabrication of thin-walled complex shapes, such as impeller blades. Generally, a process planning for HM is to build a near-net shape through AM and finish its surface through SM. However, in this approach, the cutting tools are limited with long tool lengths and small tool diameters to avoid collisions between the cutting tool and workpiece. In addition, the fabrication shapes are also limited. Therefore, one possible solution is to alternate between AM and SM processes multiple times. In this approach, the workpieces are built gradually as the process progresses. Therefore, the cutting tool can easily avoid collision with the workpiece. However, melting penetration and temper color remain on the finished surfaces using the conventional process planning method with alternate multiple switching. In this process planning, AM and SM processes are alternated. Thus, the finished surfaces are remelted in the subsequent AM process. This heat input causes melting penetration and temper color. These thermal effects must be prevented because these can lead to unfinished part and deterioration of the appearance of the workpieces. Therefore, in this study, a novel process planning method that allows alternate multiple switches without thermal effects is proposed. In addition, a process planning support system that simulates SM process was developed. The SM simulation can detect collision between the cutting tool and workpiece. Using the proposed process planning method, the system plans a process in which thermal effects will not occur. In addition, a case study was conducted using a simulated impeller blade geometry. The results of the case study showed that the developed system could plan by using several cutting tools and parameters of the machining head. The system can estimate the processing time based on the cutting tool path, deposition path, SM process conditions, and AM process conditions. The results validated the developed system and demonstrated its usefulness.

Comparative study on the influence of tool path variation in Fused Deposition Modeling Machine

Additive Manufacturing is one of the recent advancements in the manufacturing sector. It is the process of making three- dimensional solid objects from digital data. Fused Deposition Modelling (FDM) is one of the most commonly known printing types where the material is extruded to print an entity in which feedstock material is pushed through an extruder. It is mainly used for thermoplastics and polymers. In this process, the product is built by printing the tensile specimen in the form of a layer over another layer. This study is based on the comparative analysis of printing ABS specimens in commercial printers (Ultimaker, Stratasys) and a new indigenous printer. The tool path for the new printer is generated manually by using coded data and compared with commercial printers. This paper titled “Comparative Study on the Influence of Tool Path Variation in Fused Deposition Modelling Machines” focuses on the material consumption and the change in production time by varying the raster angles. The time taken for the production and the material consumption by the newly designed printer is lesser than the time taken in the existing ones.

A C3 continuous double circumscribed corner rounding method for five-axis linear tool path with improved kinematics performance

Abstract Corner rounding methods have been widely developed to pursue the smooth motions of machine tools. However, most corner rounding methods, which adopt the double inscribed transitions, still remain an inherent issue of retaining large curvatures of transition curves. Even for those double circumscribed transitions-based methods with relatively small curvatures, they also constrain excessively the transition lengths and are limited to a low-order continuity, deteriorating the feedrate and jerk of machine tools. For addressing these problems, a C3 continuous double circumscribed corner rounding (DCCR) method is proposed for five-axis linear tool path. In this method, the C3 continuous double circumscribed B-splines are specially designed to round the corners of tool position and tool orientation, whose transition lengths are analytically determined by jointly constraining the approximation errors, overlaps elimination, and parameter synchronization. Moreover, the excessive constrains of transition lengths imposed by traditional methods are alleviated by fully considering the effects of overlaps and parameter synchronization, and the jerk of rotary axes is also limited with a high-order continuity. Compared to the existing double inscribed corner rounding (DICR) and DCCR methods, experiment results demonstrate that our method can improve further the feedrate while limiting the jerk of machine tools.

Predicting cutting forces in 5-axis milling of sculptured surfaces directly from a CAM tool path

The present work is motivated by the fact that for predicting the cutting forces which arise under various cutting conditions, workpiece-tool pairs, machining depths and tool orientation, numerical methods are slower and less efficient than analytical methods. In addition, recent developments in Computer Assisted Machining (CAM) techniques have enabled analytical methods to be applied even with complex workpiece geometry. The method developed in this paper is both practical and inexpensive. It is based on an analytical method using only few approximations and uses the toolpath file as the main information source for the machined surface. This method takes into account both tool position and orientation in a 5-axis finishing milling process with ball-end cutter, independent of the machining parameters and the couple of tool-workpiece materials. However, this calculation must be supplemented by a mechanistic approach in order to obtain results equivalent to those of the experiment. The result is a model which is implemented in a program allowing the visualization of the cutting forces along a given path. The program is easy to apply in practical cases with the possibility of implementing it in a machining software.

Iterative Generation Method of Arc Length Parameterized Curve Tool Path for Surface Machining from Short-Line Tool Path

Iterative Generation Method of Arc Length Parameterized Curve Tool Path for Surface Machining from Short-Line Tool Path

Optimisation of the machining time required by insole orthotic shoes for patients with clubfoot using the Taguchi and response surface methodology approach

In this study, the application of the computer-aided reverse engineering system (CARE) to the novel design and manufacture of a comfortable insole for a clubfoot patient is presented. The Taguchi method (TM) and response surface methodology (RMS) were used to predict the machining time of the orthotic boot insole during both computer-aided manufacturing (CAM) simulation and computer numerical control (CNC) machining. Taguchi’s experimental design, presented as a matrix orthogonal array L2736, was acquired for controlling parameters, namely tool path strategy (A), spindle speed (B), step-down (C), step-over of the cutter (D), cutter diameter (E), and dimensional tolerance (F) of the insole size. In this method, the model generated by the RMS method evaluates the six parameters influencing the machining time. The objective of this study is to develop a regression model that demonstrates the relationship between the cutting parameters and insole machining time. The optimal parameters are A1B1C3D2E1F2, where A1 denotes raster finishing, B1 denotes a spindle speed of 10,000 rpm, C3 denotes a step-down of 850 mm, D2 denotes a step-over of 0.25 mm, E1 denotes a cutter diameter of 20–35 mm, and F2 deontes a tolerance of 0.75 mm. The experimental and calculated machining time (tm) results were 236 and 125.4 min, respectively. However, the real machining results were 334 and 152.25 min with error values of 46.86% and 54.42%, respectively. Meanwhile, with the tm RMS method, the simulated and calculated machining time results were 189.22 and 236.35 min, whereas the real tm values were 236.52 and 334.86 min with error values of 19.94% and 29.37%, respectively. This research obtains improvements of 19.82% (simulation time) and 29.19% (real-time).

Modeling of the Variation Propagation for Complex-Shaped Workpieces in Multi-Stage Machining Processes

Variation prediction and quality control for complex-shaped workpieces in automotive and aerospace fields with multi-stage machining processes have drawn significant attention because of the widespread application and increasing diversity of these kinds of workpieces. To finish the final workpieces with complex shapes, multiple setups and operations are often applied in machining processes. However, sources of geometric error, such as fixture error, datum error, machine tool path error, and the dimensional quality of the product, interact complicatedly at different stages. These complex interactions pose significant challenges to final product error prediction and reduction. Manufacturing error prediction based on stream of variation is an effective way to control the machining quality. However, there are few integrated models that can describe the interactions among types of geometric error sources from different stages for different kinds of complex workpieces. This paper proposes a modified error prediction model to systematically capture the interactions of different error sources among different operations for complex-shaped workpieces in multi-stage machining processes. Using differential motion vectors, the connection of all key variations from machine, fixture, and workpiece is established. This modified model can not only handle general fixture layouts for complex workpieces, but also introduce machining-induced variations. Based on this model, the main error sources identification method and error compensation method are proposed. In order to evaluate the effectiveness of the proposed method, engine blocks are used to be machined as an example. Compared with a machining process without a compensating strategy, the average machining error of the key feature is reduced by 80.5% after compensating for the main error sources.

Deformation Prediction of Titanium Alloy in Incremental Sheet Forming with Anisotropic and Asymmetric Yield Function

The present study is concerned with the prediction of deformation in incremental sheet forming (ISF) for a Ti6Al4V sheet. To investigate anisotropic and asymmetric behaviors, uniaxial tension and compression tests were conducted along the rolling direction (RD), diagonal direction (DD), and transverse direction (TD). A representative yield function for a HCP material, the Cazacu–Plunkett–Barlat (CPB06) yield criterion, was selected for constitutive modeling to take into account anisotropy/asymmetry-induced distortional yielding of the titanium alloy. The chord modulus degradation was confirmed through uniaxial loading–unloading tests. The ISF tests were carried out using a single contact-point tool following a truncated pyramid tool path. To predict the deformation during the ISF, finite element analyses were conducted with the ABAQUS explicit and the vectorized user-subroutine (VUMAT). The performance of various constitutive models was evaluated based on the comparison of deformed shapes and distribution of thickness from the experiment and the FEA.

Band-stop-filter-based repetitive control of fast tool servos for diamond turning of micro-structured functional surfaces

Fast tool servo (FTS) is a promising technique for the high-speed diamond turning of micro-structured functional surfaces due to its fast response capacity. However, the inherent actuator non-linearity, the lightly damped vibration mode and the external disturbance of the FTS would degrade its tracking performance severely and thus restrict its machining ability. To overcome this limitation, a band-stop-filter-based repetitive control (BSF-RC) scheme is proposed in this article to improve the operating performance of the FTS. Firstly, the spectra of the FTS tool paths (FTS-TPs) for machining typical micro-structured functional surfaces with the cylindrical coordinate machining method are analyzed in detail. The results reveal that the frequency components concentrate on the tiny neighborhoods of the rotational frequency of the spindle and its harmonic frequencies. Afterwards, the comb-like band-stop filter used by the BSF-RC is elaborately designed via the cascade of three comb-like notch filters to generate a comb-like band-stop loop shape for covering main spectral components of the FTS-TPs. The analytical expression of the comb-like band-stop filter amplitude as well as the stability condition of the closed-loop control system are derived to provide effective criteria for the parameter selection of the BSF-RC. The experimental validation of the developed BSF-RC scheme is conducted on a five-axis ultra-precision lathe equipped with a self-developed FTS via the diamond turning of three typical micro-structured functional surfaces. The experimental results show that good surface qualities with the maximal form error of a few hundred nanometers and the surface roughness of a several nanometers are achieved for all the obtained micro-structured surfaces by using the BSF-RC scheme under a high spindle speed.

Investigation on Tool Path Planning Algorithm of Propeller Blade Double-Sided Collaborative Machining

The concomitant vibration and deformation produced by propeller blades in single-sided machining seriously affect the surface machining precision. Double-sided symmetrical machining can improve system rigidity through mutual shoring on both sides which abates the concomitant vibration and deformation. However, the actual double-sided symmetrical machining cannot be applied to blade machining due to its shape complexity. The double-sided collaborative machining method combining symmetrical machining and staggered machining is devised in this paper, and its tool path planning algorithm is investigated. Firstly, the algorithm achieves smooth fitting and correspondence of bilateral cutter position points through double-curve interpolation and position data alignment. Secondly, the blade surface is divided into four regions by two partition parameters: tip region, internal region, variable region, and edge region. Then, the conversion between symmetrical machining and staggered machining is completed through the Sigmoid deformation curve in the variable region. Finally, the feasibility and superiority of double-sided collaborative machining are verified through machining experiments.

An analytical local tool path smoothing method with curvature control

In traditional multi-axis machining, the linear tool path generated by computer-aided manufacturing systems is still in a broad tool path format, resulting in discontinuities at the corners, which slow down tool motion, and also trigger tool vibration, reducing machining accuracy and surface quality. In order to ensure the C3 continuity of the tool during the multi-axis machining process, this paper proposes an analytical B-spline local smoothing method with curvature control. The tool position trajectory and tool orientation are both smoothed by a 5th spline curve with 9 control points. Optimal control points are determined for position and orientation splines to achieve C3 continuity at the junctions between the spline and linear segment while preserving the predefined geometric tolerance limits and minimizing the maximum curvature of the inserted B-spline curve. The smoothed tool path is expected to have less curvature fluctuation, which can significantly improve both the kinematic performance of the machine tool and the machining efficiency. Both computer simulations and physical printing experiments are carried out to demonstrate the improvements of our proposed method in motion smoothness and tracking accuracy in multi-axis machining tasks.

A Simple Point-based Iso-Scallop Tool Path Planning Method for Noisy Point Clouds with High Robustness and Controlled Errors

With the rapid advances in 3D scanning and vision technologies, point clouds have seen a significant increase in their application to CNC machining. As an important way to generate tool paths from point clouds, point-based direct planning methods are, however, now restricted to high-quality point clouds. Most existing methods would have robustness issues if a noisy point cloud is given due to their reliance on the noise-sensitive estimation of differential properties from point clouds. Error control under noisy point clouds is also rarely considered. This paper presents a robust and error-controlled point-based iso-scallop tool path planning method for CNC machining with ball-nosed cutters. It casts the problem of searching for scallop/CL points to another problem of finding circle-sphere intersection points and the maximum/minimum among them. Both circle-sphere intersections and max/min comparisons are easy to implement and robust. It has also been theoretically proved that the intersections and comparisons can ensure an error bound of 2ϵ on the final results if two conditions called ϵ-sampling and ϵ-covering are met. The effectiveness of the method has been demonstrated by a series of examples and comparisons.

Roughness Test of Aluminum A5052 before and after Forming by SPIF Process

Single point incremental forming process, which is also known as SPIF, that forms from one direction. SPIF process was used for milling an aluminum metallic sheet. In this paper, an aluminum (A5052) sheet was formed in a conical shape by the SPIF process. The A5052 sheet was deformed by the computer numerical control (CNC) technology in the T60 series milling machine. The conical shape was deformed by the spiral toolpath in the T60 series milling machine. At the surface of the A5052, lubricant grease was continuously applied manually for reducing the friction generated due to milling. Also, for decreasing the tool rotational force friction on the A5052 sheet there was the use of lubricant. Moreover, 0.1mm step-down is used for the tool path because it takes more time for forming a metallic sheet, however, it deformed the sheet smoothly. The 0.5mm step-down g-code was extracted from fusion 360. Then the metallic sheet A5052 surface was compared before and after deformation. For testing a metallic sheet A5052 the formability parameter was analyzed in the experiment part. The experiment was performed to find the optimal smooth surface from the CNC milling machine. The initial roughness value and the microscopic image were presented in the investigational part. Likewise, the comparison of points for the highest and lowest rough point was further discussed and compared throughout the experiment.

“4+2” axis ultra-precision diamond shaping for partially overlapping Fresnel lenses based on an ultra-precision machine tool and two additional rotational axes

Optical surfaces and microstructures with high form accuracy and excellent surface quality are widely utilized nowadays and the diamond machining technology is still preferable for the fabrication of these workpieces. However, when machining surfaces featuring a high aspect ratio or intricate microstructures like monolithic microstructural optics, the machining efficiency is quite low and the cutting tool interference is inevitable for the existing diamond turning techniques. Hence, a novel method is proposed to machine such microstructures by introducing two additional rotational motions into the traditional ultra-precision machine tool. In this way, the arbitrary adjustment of the tool posture may be achieved in the machining process and intricate microstructures like monolithic microstructural optics can also be machined by the side cutting edge with high efficiency. The whole mechanical system and machining principle are presented firstly. Next, the tool path planning and the compensation for the tool tip offset are introduced. Then, the partially overlapping Fresnel lens array consisting of two segmented Fresnel lenses are fabricated and inspected. Finally, the measurement data are analyzed and the proposed method is validated to be able to fabricate such complex microstructures with high profile accuracy and surface quality successfully.

Optimal toolpath planning strategy prediction using machine learning technique

Finding the best toolpath planning strategy for Computer Numerical Control (CNC) machining requires a trial-and-error approach. One needs to follow a number of steps: generating the toolpath, performing simulations/machining, measuring various parameters to quantify the quality of the toolpath, and then selecting the best toolpath. This conventional iterative approach is time-consuming and often error-prone, which is a bottleneck in the current CNC machining industry. This paper presents a novel framework to create a machine learning based system for choosing the best toolpath planning strategy for CNC machining (finishing) of complex freeform surfaces directly from the CAD model. Three tool path planning strategies are considered: Adaptive planar, Iso-scallop, and Hybrid. At first, a novel toolpath analysis module is presented to evaluate the quality of the toolpath considering three performance parameters: surface finish, toolpath length, and smoothness. This quality measurement technique is extensively tested for robustness and accuracy. It is then used to analyze and label a large number of CAD models to create a dataset for supervised learning. Finally, a Convolutional Neural Network (CNN) is designed and trained using this dataset to predict the best toolpath planning strategy. Compared to the conventional approaches, the developed system uses multiple performance parameters and chooses the best strategy directly from the CAD model. Results show that the proposed data-driven model achieved 96.8% test accuracy.

Increasing the Performance of Computer Numerical Control Machine via the Dhouib-Matrix-4 Metaheuristic

The Computer Numerical Control (CNC) machine represents a turning point in today's production which has high requirements for product accuracy. The CNC machine enables a high flexibility in work and time saving and also reduces the time required for product accuracy control. Moreover, the CNC machine are used for several activities, most often for turning, drilling and milling operations. Usually, the productivity of any CNC machine can be increased thanks to the minimization of the non-productive of tool movement. In this paper, the results of a new metaheuristic named Dhouib-Matrix-4 (DM4) with an application on the NP-hard problem based on the Travelling Salesman Problem are presented. DM4 is used for increasing the performance of the CNC Machine by optimizing a tool path length in the drilling process performed on the CNC milling machine. The proposed algorithm (DM4) achieves a solution closed to the optimum, compared with the results obtained with the Ant Colony Optimization algorithm and the results found with the manual programming in G code by using a control unit for the selected CNC milling machine.

The Effect of Tool Path Strategy on Mechanical Properties of Brass (65-35) in Single Point Incremental Sheet Metal Forming (SPIF)

In this paper, three tool paths strategies; iso-planar, helical and adaptive have been implemented to investigates their effect on the mechanical properties of Brass 65-35 formed by single point incremental sheet metal forming process. To response this task, a fully digital integrated system from CAD modeling to finished part (CAD/CAM) for SPIF process has been developed in this paper.The photo-micrographs shows an identical grain formation due to the plastic deformation of the incremental forming process, change in the grain shape and size was observed. It's found that the adaptive tool path play a significant role to increase the hardness of the formed specimen from (48 to 90 HV) and the grain texture of the formed specimen found as round shape, while the hardness is increased in little amount from (48 to 74 HV) in the specimen formed using helical and it’s grain texture was found as needle shape.