Parallel Milling Research Articles

INCREASING THE EFFICIENCY OF MECHANICAL PROCESSING OF PARTS VEHICLES

The work theoretically substantiates the conditions for reducing the conditional cutting stress (energy intensity of processing) during grinding and blade processing of parts of transport machines, taking into account the angle of entry of the cutting tool into the processed material. It is shown that under the conditions of grinding, they consist in the change of the shape of microsections by cutting grains: the transition from counter grinding by the periphery of the wheel to the kinematic schemes of end and parallel grinding by the periphery of the wheel, the reduction of the intensity of friction of the cutting grain with the processed material and the negative front angle of the cutting material. In terms of blade processing, they consist in the application of tangential turning, parallel milling, especially with an end mill. The existence of the extremum (maximum) of the conditional cutting stress from the sum of the conditional friction angle of the cutting grain with the processed material and the negative front angle of the cutting grain has been proved. The ranges of change of this amount are determined, at which the conditional cutting stress becomes the smallest. It is shown that the nature of the change in the conditional cutting stress is determined by the change in the conditional shear angle of the processed material. It was established that infinite values of conditional cutting stress are achieved under the condition of equality of the conditional shear angle of the processed material and the angle of entry of the cutting tool into the processed material. Therefore, it is necessary to increase the conditional shear angle of the processed material by reducing the intensity of friction in the cutting zone and the negative front angle of the cutting tool. The conditions for increasing the efficiency of blade processing by increasing the ratio of the tangential and radial components of the cutting force, as well as the ratio of the slice thickness to the radius of rounding of the cutting tool tip, which consist in reducing the friction in the cutting zone and the front angle of the cutting tool, have been theoretically determined. The introduction at the machine-building enterprise of high-speed cutting technologies with progressive cutting carbide tools with wear-resistant coatings of the TaeguTec company with the use of high-speed CNC metal cutting machines of the "machining center" type made it possible to increase the efficiency of processing the complex profile surfaces of the "Cup of the wheel differential".

Novel Tool Path Generation Method for Pocket Machining Using Sound Field Synthesis Theory

Contour parallel tool paths have been proved to be a preferred machining strategy for their advantage of less tool retractions and less sharp turns. The traditional geometrical algorithm-based tool path generation method often makes it hard to simply and simultaneously solve the problems of self-intersection, no residual, and smoothness at the same time due to their contradictions. To address this issue, a contoured parallel tool path generation method for pocket machining is developed in this study. It is based on sound field synthesis theory inspired by the phenomenon of sound wave propagation. Firstly, the simplified medial axis (SMA) tree of the pocket is extracted and the propagation direction of each SMA segment is calculated on account of the geometric characteristics of the pocket boundary. Secondly, the final tool path is obtained through the synthesis of the sound field. Finally, the novel method is verified on five different pockets to generate a contoured parallel milling tool path. After machining these pockets and measuring the machining time, roughness, and cutting force, the experimental results demonstrate that the tool path obtained by the novel method has advantages in improving machining quality and efficiency.

Experimental and analytical evaluation of tool path error using computer integrated nonlinear kinematical modeling for a 4DOF parallel milling machine

ABSTRACT Machining errors in parallel kinematic machines primarily depend on their extent of kinematic nonlinearity. In this paper, a computer integrated model of the kinematic nonlinearity and trajectory interpolation method for a 4DOF parallel milling machine is developed. The nonlinear errors prompted during various trajectory modes are analyzed. It is proved that in order to avoid significant non-linearity, the actuator and the end-effector space must possess identical order of trajectory. The effects of tool path length, its spatial location, and the Jacobian matrix properties on the kinematic nonlinearity error, are studied. Results showed that the path length is the governing factor for the nonlinear behavior of the mechanism. Moreover, the kinematic error is illustrated to have a reverse relationship with maximum singular values of the inverse Jacobian matrix. Experiments are conducted using digital dial indicators. Experimental results verified the accuracy of the proposed mathematical approach and confirmed its applicability in actual machining processes. Moreover, the proposed interpolation algorithm successfully limits the kinematic error under the machining tolerance by minimal segmentation. Finally, it is demonstrated that the proposed method is superior in terms of accuracy, to the median osculating circle (MOC) method.

Development of Automatic Chatter Suppression System in Parallel Milling by Real-Time Spindle Speed Control with Observer-Based Chatter Monitoring

To maximize the potential for high material removal rates in simultaneous processes such as parallel milling, developing strategies for successful chatter suppression/avoidance is an important concern for manufacturers. In this study, the effectiveness of the spindle speed difference method (SDM) for chatter suppression is discussed in a parallel end-milling process where a flexible workpiece is machined by two tools rotating in opposite direction. The process model is developed, considering that the dynamic variation due to the regenerative effect occurs on a plane perpendicular to the tool axis direction. Through the process simulations and the experiments, this study provides informative discussion for comprehending the process behavior. Additionally, a real-time active chatter suppression system with adaptive SDM, where the spindle speed difference is sequentially optimized during the process according to the tracked chatter frequency, is developed by integrating a chatter monitoring system based on sensorless cutting force estimation with sliding discrete Fourier transform. The results show that the developed real-time adaptive system of spindle speed suppresses chatter vibrations more effectively than non-adaptive SDM system; hence, the integrated system can contribute self-optimizing machining systems oriented to Industry 4.0.

Simulation Analysis of Surface Roughness for Milling Process

Surface roughness is one of the most important evaluation indexes in machine cutting. In order to analyze how the tool path affects the roughness of the surface after milling, series of simulations are implemented in MasterCAM. We set up the same processing conditions with same parameters such as speed, material and feed rate etc. in these simulations, but different processing paths are used. We choose three paths: the parallel milling along the X-Y axis direction, the parallel milling along the Z-X or Z-Y axis direction and the streamline processing in the simulations. At the same time, end miller, arc miller and ball miller are respectively selected in the software. So there are totally 9 simulations of the milling process that are performed. Then the experimental cutting processes are performed correspondingly and the surface roughness and the accuracy are measured. The results show that the milling effect of the arc is better and the waste is minimal in the parallel milling along the Z-X or Z-Y axis direction with the end mills.

Tool path length optimisation of contour parallel milling based on modified ant colony optimisation

Reducing machining time in a milling process is one of the important criteria to improve the overall efficiency of the machining process. This paper presents a study on the reduction of machining time, focusing on contour parallel machining to increase the efficiency and performance during the machining process. One method to enhance the performance of contour parallel machining is by defining a tool path interval that is larger than the radius of the cutting tool in a roughing operation because of its capability of reducing the tool path length and machining time. However, this causes the occurrence of an uncut region at the corner and at the centre of a contour parallel. This uncut region can be removed through an additional tool path known as the clear tool path. Therefore, in this paper, a new method based on an optimisation technique is introduced to generate a clear tool path that removes the entire uncut region in contour parallel machining at minimum cutting time. Ant colony algorithm (ACO) is used to optimise the clear tool path length in contour parallel machining time by minimising the movement of cutting tool in removing the entire uncut regions. A new transition rule has been established from the conventional ACO, which adapted the uncut region occurring at the corner of the contour parallel. Then, to validate the optimisation result, a cutting experiment was carried out using computer numerical control (CNC) milling machine. It can be ascertained from this study that the optimisation of the clear tool path gives optimal tool path length whilst reducing the cutting time in the roughing process.

Parallel Machining Dynamics with Multiple Time Delays

Abstract Machining process is a time delay system. In general machining applications, there is usually one delay in operation. However, in parallel machining operations such as parallel turning, milling there can be multiple delays. This paper focuses on the dynamics of parallel turning and parallel milling processes. Many models have been developed for machining processes with single delay. There are only a few studies on multiple delay systems. This paper presents some interesting results on parallel turning and milling. Several example cases are presented and ongoing and future work in the area is detailed.

Four-Dimensional Changes of Nasolabial Positions in Unilateral Cleft Lip and Palate

The aim of this study was to analyze the accurate three-dimensional positions and positional changes of the lip and nose in patients with unilateral cleft lip and palate. Sixty-three patients with unilateral complete cleft lip and palate (UCLP) and 96 patients with isolated cleft palate were retrospectively enrolled. Facial casts of all subjects taken immediately before and after cheiloplasty and before palatoplasty were used. Three-dimensional values of 12 landmarks were measured by electronic caliper and parallel milling machine. Independent-samples t test was used in analyzing positional differences between UCLP and control, and 2-way analysis of variance was selected in analyzing positional changes among UCLP groups. The threshold of significance was set at 0.05. Superiorly dislocated christa philtri (Cph) (P < 0.001), subalae (Sa) (P < 0.001), and nostril tip (Nt) (P < 0.001) were partially corrected and still dislocated (P < 0.05, P < 0.001, P < 0.001) immediately after operation, but Cph (P = 0.322) and Cph' (P = 0.081) developed caudally to normal about 10 months after primary surgery. In sagittal dimension, lip and nose, especially Cph' (P < 0.001), Sa' (P < 0.001), and Nt' (P < 0.001) on the cleft side, dislocated dorsally before operation. Immediately after operation, Sa' (P = 0.456) and Nt' (P = 0.067) were normal in sagittal projection, but Cph' was corrected partially and still insufficient (P < 0.001). Unfortunately, sagittal projections of all nasolabial structures, Cph (P < 0.001), Sa' (P < 0.001), Nt (P < 0.001), Cph' (P < 0.001), Sa' (P < 0.05), and Nt' (P < 0.001), decreased significantly and were insufficient after operation. In vertical dimension, nasolabial displacements were corrected partially by primary surgery, and catching-up growth happened since then. Insufficient sagittal projections of the lip and nose were corrected successfully by lip repair, but lip repair itself had adverse effects on nasolabial sagittal growth.

Stability and high performance machining conditions in simultaneous milling

Parallel milling offers the advantage of simultaneous machining of a workpiece with two milling tools. Higher material removal rates and machining with fewer fixtures are possible due to the second tool. These advantages make parallel milling an ideal technology for machining of near net shape structures. However, parameter selection is quite challenging due to the dynamic interaction between the tools. In this study, time and frequency domain stability models are developed to aid the process planner. Effects of process parameters are also investigated and high performance machining conditions are identified. The experimental cuts are made to verify the presented methodology.

Accuracy of a plastic facial cast fabricated with a custom tray in comparison with cone beam computed tomography

The aim of this study was to test the accuracy of a plaster cast fabricated with a facial custom tray. Sixteen patients with unilateral cleft lip and palate were enrolled in this study. Cone beam computed tomography (CBCT) scanning and facial plaster cast were obtained before surgery. Three-dimensional (3D) coordinates of 6 selected landmarks were recorded directly in CBCT by Mimics and indirectly on the plaster cast by using an electronic caliper and parallel milling machine. The accuracy of the plaster cast was compared with that of CBCT by using the t test and Lin's concordance correlation coefficient. P values less than 0.05 were considered statistically significant. Horizontal and vertical measurements were larger and sagittal measurements were smaller in plaster cast measurements, but none of these differences was statistically significant (P values ranged from 0.063 to 0.774). Lin's agreement test also showed that the plaster cast had high agreement with CBCT measurements (concordance correlation coefficients ranged from 0.6319 to 0.9599). Plaster cast fabricated with a custom tray is an accurate method in facial 3D analysis.

Generating STEP-NC Files for a Circuit Board Milling System

Since G-codes have been proved limiting the modern manufacturing industry, ISO14649 was put forward. This paper presents a solution to generate ISO14649 files for circuit board milling. The process planning is given, and all the processes needed are contained in the ISO14649 file. Features and machining operations are identified for each process, such as the closed pocket having a “General_closed_profile” attribute and bosses, round holes, slots, the planar face, contour parallel strategy, contour bidirectional strategy and etc. The scenario of one feature with multi tools are put forward to promote the milling efficiency and an entity “Combined_Machining_workingsteps” is proposed. Besides, some other extensions are made, such as entities for representing circuit geometries in machining features. Algorithms for tool paths generation are demonstrated for contour parallel milling and bidirectional milling, where a new algorithm based on pixels is used. The new algorithm can be used in other functions such as detecting uncut regions.

The Influence of Process Machine Interactions on the Stability of Parallel Milling

The double spindle machining centres are widely employed in industry in order to increase the manufacturing capacity. Such a machine tool configuration is economically advantageous, for it allows to increase the productivity at the same shop floor area and at moderate investment. Practically the cutting productivity is often limited due to a dynamic instability in milling. The reason for the instability lies in interactions between a double spindle machine tool and a parallel milling process. This paper presents a simulation model that allows to predict stability charts for parallel milling and to investigate specific influences onto the process stability. For the simulation the real dynamic machine behaviour was used, which had been ascertained by means of an innovative multiple excitation technique. The simulation results revealed that the process stability is influenced greatly by the temporal relationship of the parallel milling processes. The simulation results were verified on a double spindle milling machine.

Holistic modelling of process machine interactions in parallel milling

Abstract Parallel milling allows to increase the manufacturing capacity in industry due to a higher cutting productivity. The latter is often negatively influenced by dynamical instabilities of the parallel milling process entailing a reduced profitability. In this paper a holistic model of interactions between a double spindle machine and a parallel milling process is presented that enables an identification of the dynamic compliance of parallel milling machines and a simulation of their stability behaviour. With that an investigation of stability optimization means is possible. A significant improvement of the process stability and, thus, the effective cutting productivity was observed in the parallel milling processes, optimized with help of the holistic model.

Tool path generation and modification for constant cutting forces in direction parallel milling

This paper presents an optimized path generation algorithm for direction parallel milling, which is commonly used in the roughing and finishing stages. First, a geometrically efficient tool path generation algorithm using an intersection points graph is introduced. Second, the generated tool path is modified as an optimized tool path that maintains a constant material removal rate to achieve a constant cutting force and avoid chatter vibration, and the results are verified. Additional tool path segments are appended to the basic tool path through a pixel-based simulation technique. The algorithm is implemented for two-dimensional contiguous end milling operations with flat end mills, and cutting tests are conducted by measuring the spindle current, which reflects the changing machining situations, to verify the performance of the proposed method.

Contour parallel milling tool path generation for arbitrary pocket shape using a fast marching method

Contour parallel tool paths are among the most widely used tool paths for planer milling operations. A number of exact as well as approximate methods are available for offsetting a closed boundary in order to generate a contour parallel tool path; however, the applicability of various offsetting methods is restricted because of limitations in dealing with pocket geometry with and without islands, the high computational costs, and numerical errors. Generation of cusps, segmentation of rarefied corners, and self-intersection during the offsetting operations and finding a unique offsetting solution for pocket with islands are among the associated problems in contour tool path generation. Most of methods are inherently incapable of dealing with such problems and use complex computational routines to identify and rectify these problems. Also, these rectifying techniques are heavily dependent on the type of geometry, and hence, the application of these techniques for arbitrary boundary conditions is limited and prone to errors. In this paper, a new mathematical method for generation of contour parallel tool paths is proposed which is inherently capable of dealing with the aforementioned problems. The method is based on a boundary value formulation of the offsetting problem and a fast marching method based solution for tool path generation. This method handles the topological changes during offsetting naturally and deals with the generation of discontinuities in the slopes by including an “entropy condition” in its numerical implementation. The appropriate modifications are carried out to achieve higher accuracy for milling operations. A number of examples are presented, and computational issues are discussed for tool path generation.

Tool path generation for contour parallel milling with incomplete mesh model

In this paper, a tool path generation method for contour parallel milling based on an incomplete two-manifold mesh model, namely, an inexact polyhedron which is widely used in recent commercialized computer-aided manufacturing software systems is presented. The method consists of three major steps: machining area detection, 2D offset, and path linking. Machining areas obtained from a mesh model are closed 2D lines. Thus, offsetting closed lines is essential to generate mesh-based contour parallel tool path. For contour parallel path elements, a new offset algorithm for closed 2D lines with islands is introduced and the result is illustrated. The main point of the proposed algorithm is that every point is set to be an offset using bisectors, and then invalid offset lines, which are not to be participated in offsets, are detected in advance and handled with an invalid offset edge handling algorithm in order to generate raw offset lines without local invalid loops. As a result, the proposed offset method is proved to be robust and simple, moreover, has a near O(n) time complexity, where n denotes the number of input lines. The proposed algorithm has been implemented and tested with 2D lines of various shapes. Finally, contour parallel path is made through linking offset path elements.

황삭 가공을 위한 최적 직선 평행 공구경로 생성

The majority of mechanical parts are manufactured by milling machines. Hence, geometrically efficient algorithms for tool path generation and physical considerations for better machining productivity with guarantee of machining safety are the most important issues in milling tasks. In this paper, an optimized path generation algorithm for direction parallel milling which is commonly used in the roughing stage is presented. First of all, a geometrically efficient tool path generation algorithm using an intersection points-graph is introduced. Although the direction parallel tool path obtained from geometric information have been successful to make desirable shape, it seldom consider physical process concerns like cutting forces and chatters. In order to cope with these problems, an optimized tool path, which maintains constant MRR in order to achieve constant cutting forces and to avoid chatter vibrations at all time, is introduced and the result is verified. Additional tool path segments are appended to the basic tool path by using a pixel based simulation technique. The algorithm has been implemented for two dimensional contiguous end milling operations, and cutting tests are conducted by measuring spindle current, which reflects machining situations, to verify the significance of the proposed method.

Effect of ball size on the performance of grinding and flotation circuits: the Sarcheshmeh copper mine case

At the Sarcheshmeh copper mine, 41 000 t ore per day with an average grade of 0·9%Cu is ground to 70% passing 75 μm. Grinding is effected in eight parallel lines of 8 × 5 m ball mills in a closed circuit with cyclones. The makeup balls are 80 mm forged alloy steel balls and the average ball consumption is 750 g t−1 ore ground. In order to optimise ball size distribution inside the mill, based on the previous investigation, instead of using only 80 mm makeup balls, a combination of 80 and 60 mm (75 and 25 wt-%) ball charge was used in one of the grinding lines. To evaluate the performance of three ball types, namely, forged alloy steel balls (A), ductile cast iron (C), high chromium cast iron (D) and also a combined (80 and 60 mm) charge of forged alloy steel balls (B), four identical parallel mills were charged accordingly. These four mills were sampled during a period of 1 year. The amount of material finer than 75 μm cyclone overflows was selected as a criterion for the performance evaluation. It was observed that in a mill with the combined makeup balls, the amount of fines (<75 μm) produced was 4% higher than that of the other mills. The consumption of ball types A, C and D were 730, 710 and 534 g t−1 respectively. The results of laboratory flotation tests showed that owing to an improvement in the production of fines, an increase of 1·4% in the overall copper recovery is obtainable. Owing to the promising results, the new makeup ball regime was implemented in all mills in the plant.

《補綴治療におけるオーラルデザイン‐技工サイドと臨床サイドのチームコミュニケーション‐》義歯治療に必要なチームコミュニケーション ２）歯科技工士の立場から

As for the team communication between clinical and technological sides in the denture treatment,a smooth cooperative teamwork must be established in its target treatment through individual adequate recognitions concerning the main points of sequential procedures from examination, diagnosis, therapeutic designing, impression taking and bite registration and then setting performed by a dentist on the clinical side as well as concerning the main points of technical procedures indirectly performed by a dental technician on the technological side in order to achieve the most improved preservation of remained tissues with an increased rate of functional restoration, being the final target of treatment. At present when an ultra-aged society is coming, the demand of denture treatment has been enhanced more and more. In response to the enhanced patient's demand, various modes of denture treatment have been introduced and the dental technology has advanced remarkably. In particular, a technical procedure by means of partial parallel milling representative of rigid support or of Konuskronen requires very complicated working processes. In addition, the elasticity is also required including such an occlusal construction as being harmonious with the jaw function or such tooth crown morphology as being prepared in consideration of periodontal tissues together with a lot of information from the clinical side required as well in the denture treatment. In this study, therefore, the dental technical procedures presently performed by referring to varied individual information are newly arranged and summarized so as that these complicated technical processes and working steps could be performed more easily and accurately.

Stochastic modelling of an integrated pulp and paper factory with intermediate storage

Abstract Stochastic models are developed to determine the production rate and efficiency of an integrated pulp and paper factory, which consists of a pulp mill, a storage tank and two parallel paper mills or pulp dryers. The effects of storage tank capacity and random stoppages in the mills on line efficiency and line output rate are investigated. The models are general and can be used for any continuous process system