CNC Incremental Forming Research Articles

Research on the multi-stage CNC incremental forming of unequal height sheet metal part with large forming angle

Research on the multi-stage CNC incremental forming of unequal height sheet metal part with large forming angle

Design of a CNC Incremental Forming Machine with a tiltable structure

In view of the existing incremental forming machine, there is a problem that the tool needs to be replaced when machining parts with different degrees of sidewall concavity. The incremental forming machine with a tiltable cutter was designed, and the feasibility of a cutter tilting structure was discussed. The forming results show that the tiltable structure meets the design requirements.

Numerical Simulation of CNC Incremental Forming of Straight Wall Parts Based on Model Partition and Non-Steep Surface

In order to realize the CNC incremental forming of the straight wall parts, a CNC incremental forming method with the sheet metal posture adjustment in multiple directions based on the model partition and the non-steep surface was proposed in this paper. With the help of the non-steep surface, the sheet metal posture is adjusted to reduce the forming angle of the straight wall; to ensure the straight wall to be formed without breaking. The results of numerical simulation shows that the method proposed in this paper can form the straight wall parts that cannot be formed by the traditional multi-pass incremental forming, and the straight wall parts of the formed parts have better contour accuracy, uniform thickness distribution and applicability.

The Influence of Sheet Tilting on Forming Quality in Single Point Incremental Forming.

In the CNC incremental forming process, the sheet tilting method can be used to realize the non-fracture forming of a surface with large forming angles. However, the forming effect of the formed part will have big differences when the inclined angle of the sheet is different. Therefore, four different tilted sheets with inclined angles of 15°, 20°, 25°, and 30° were used to study the influence of sheet tilting on forming quality by using 1060 Aluminum sheet as the forming sheet in single point CNC incremental forming. First, the influence of four different inclined angles of the sheet on the overall thickness distribution, plastic strain, and material flow of the formed part was studied by using numerical simulation. Then, the influence of four different inclined angles of sheets on the profile accuracy and thickness thinning rate of the formed part was studied through single point incremental forming experiments. The research results show that sheet tilting has little effect on the profile accuracy of the formed part, but has a great influence on the material flow, plastic strain, and thickness distribution.

The effect of extrusion direction on the forming quality in CNC incremental forming with multidirectional adjustment of sheet posture

In the CNC incremental forming, the forming quality will be different with the different extrusion direction. The effects of the different extrusion directions on the forming quality in the CNC incremental forming with the multidirectional adjustment of sheet postures were studied by using three extrusion directions: parallel to the Z-axis, perpendicular to sheet surface and perpendicular to the surface to be formed. The algorithm for calculating the inclination angle of the extrusion tool and determining the extrusion direction vector in the multidirectional adjustment environment of sheet postures was presented. The feasibility of the algorithm was verified by an application example. The equivalent plastic strains under the three extrusion directions were analyzed through the numerical simulation. At the same time, the contour accuracy, thickness reduction and thickness distribution were compared and analyzed through the CNC incremental forming experiment with the multidirectional adjustment of sheet postures under the three extrusion directions.

Research on combinatorial optimization of multidirectional sheet postures for forming thickness uniformity

To solve the problem of the uneven thickness distribution of a formed part caused by a large difference between the forming angles and the different curvatures of the surfaces in CNC incremental forming, a combinatorial optimization method of multidirectional sheet postures was proposed based on particle swarm optimization. In this method, an infinite number of optional sheet postures at each point in the forming area are taken as the combined object. The optimization goal is to make the forming angles of the entire sheet part be smaller than the forming limit angle and to minimize the difference between them; then find the optimal combination of the multidirectional sheet postures that can be selected at each point in the forming area. Case studies of the algorithm and the actual forming experiment show that not only can the optimized multidirectional sheet metal postures determined by the proposed method realize the non-fracture forming of the sheet metal parts with different forming angles and different curvature of the surface, but also obtain a more uniform thickness distribution of the formed parts.

Research the CNC incremental forming of straight-wall parts based on a virtual auxiliary body

In order to realize the CNC incremental forming of straight-wall part, a CNC incremental forming method for multi-directional adjustment of sheet postures based on the virtual auxiliary body was proposed. In the method, the sheet posture was adjusted based on the virtual auxiliary body which was set inside the straight-wall part to establish a gently inclined surface, thereby the forming angle was reduced to successfully form the straight-wall part. To ensure the non-rupture forming of the straight-wall part, a generation algorithm of the virtual auxiliary body based on the desired forming angle determined by the user and the forming limit angle was presented. And, in order to achieve the forming of the straight-wall part with uniform thickness as much as possible, a forming toolpath generation algorithm that could realize the sheet postures adjustment and the sheet parallel downward movement was given. The case studies show that the proposed algorithm can generate the required virtual auxiliary body and the forming toolpath, and achieve the multi-directional adjustment of the sheet postures. The results of the numerical simulation and the forming experiments show that the proposed method is applicable and can be used to form the straight-wall part that cannot be formed by the conventional CNC incremental forming.

Research on point-pressing based double-sided CNC incremental forming

For the problem of the sheet distortion caused by the force of the two extrusion forming tools on the sheet in the double-sided CNC incremental forming, a point-pressing based double-sided CNC incremental forming was proposed in which the consecutive-extrusion of the extrusion forming tool on the sheet was replaced by the point-pressing. A point-pressing based double-sided CNC incremental forming toolpath generation algorithm based on the consecutive-extrusion based double-sided CNC incremental forming toolpath was presented. The double-sided CNC incremental forming processes based on the point-pressing and consecutive-extrusion was simulated by using the ANSYS/LS-DYNA software and the actual forming experiment. The numerical simulation results show that the double-sided CNC incremental forming based on the point-pressing compared with the process based on the consecutive-extrusion can acquire less circumferential displacement, less distortion, more evenly distributed average equivalent strain and less mutagenicity. It can be seen from the actual forming experiment that the sheet metal part formed by the point-pressing method has better geometric anastomosis with the design model than that formed by the consecutive-extrusion method.

Tool path generation for the point-pressing-based 5-axis CNC incremental forming

Considering the residual height of the sheet metal part surface formed by the point-pressing incremental forming method and the efficiency of the forming process, the candidate terminal cutter location points based on the latitudinal/longitudinal residual height were calculated firstly, and then adjusts the candidate terminal cutter location points that are beyond the maximum residual height. Finally, all the terminal cutter location points are obtained. Thus, while satisfying the maximum residual height, the pressing points are sparse as much as possible, which improves the forming efficiency. In addition, for the problem that the ordinary 3-axis CNC incremental forming cannot press the sheet in the different directions according to the surface features, a method for determining the spatial posture of the 5-axis pressing tool by adjusting the front angle and side dip angle was proposed so that the sheet metal can be pressed in different extrusion directions. According to the proposed 5-axis point-pressing incremental forming tool path generation method, the actual forming experiment was carried out, and the sheet metal part was successfully formed, which meets the residual height requirements and shows that the methods for the tool path generation and the spatial posture determination of the forming tool are feasible. In addition, a comparative experiment was conducted with the 5-axis consecutive incremental forming tool path under the same residual height conditions. Through the measurement and analysis of the experimental parts, it is concluded that the profiles of the sheet metal parts obtained under the two forming methods have a good geometrical agreement with the designed parts. However, the profile of the sheet metal part formed by the 5-axis point-pressing incremental forming tool path is closer to the designed part as a whole, and the thickness in the forming region is also slightly higher than that of the sheet metal part formed by the 5-axis consecutive incremental forming tool path.

5-axis CNC incremental forming toolpath planning and generation for the sheet metal part with multi-peaks

The existing studies on the CNC incremental sheet metal forming technology are all for the sheet metal parts with either concave peaks or convex peaks, and rarely involve the sheet metal parts with both concave peaks and convex peaks. However, with the deepening of the research for the CNC incremental sheet metal forming technology, the forming of the multi-peak sheet metal parts with both concave peaks and convex peaks will become a hot research topic. Compared to 3-axis CNC incremental forming, 5-axis CNC incremental forming can extrude the blank in any desired direction because its extruding tool has even more freedom and is more suitable for the forming of the multi-peaks sheet metal parts. In this paper, 5-axis CNC incremental forming path planning and generation method based on STL model has been proposed for the sheet metal parts with both concave peaks and convex peaks. The forming path planning scheme and the algorithms for the cutter location point calculation, forming path planning and extruding tool posture calculation are also given, which are necessary for 5-axis CNC incremental forming path generation for the sheet metal part with both concave peaks and convex peaks. The case study shows that the proposed method can automatically generate smooth and continuous 5-axis CNC incremental toolpath and runs steadily and reliably.

Research on the CNC incremental forming method based on the surface partition and multi-size extrusion tool head

For the problem that a single-size extrusion tool head cannot meet the high-precision and high-efficiency forming requirement in the CNC incremental forming of the complex-shaped sheet metal parts, a new CNC incremental forming method based on the surface partition and multi-size extrusion tool head is proposed. This method divides the inner surface of the sheet metal parts into the different forming regions according to the curvature of the inner surface, thereby to select the extrusion tool heads with different radius for the different forming regions. That is, the extrusion tool head with large radius is used for the forming region with large curvature radius so as to effectively improve the surface quality and formability of the sheet metal parts, and the small radius of the extrusion tool head is used for the forming region with small curvature radius so as to improve the profile accuracy of the sheet metal parts. The results of the numerical simulation and forming experiment showed that the method can partition the surface of the given sheet metal part and ascertain the corresponding multi-sized extrusion tool heads to the partitioned surface, which can effectively form the complex-shaped sheet metal parts and improve the forming quality and forming efficiency of the sheet metal parts.

5-Axis CNC incremental forming toolpath generation based on formability

To the problem of the existing CNC incremental forming that mostly adopts the 3-axis CNC incremental forming method and cannot form the complex sheet metal part containing the surface by one-stage forming, which cannot be visible in the positive and negative directions of the Z-axis and whose forming angle is larger than 90°, a multi-directional slant and multi-directional pressing toolpath generation method for the 5-axis CNC incremental forming was proposed to accomplish the forming of the complex sheet metal parts by fully considering the differences of the forming angles at each position of the surface and the accessibility of the extrusion tool to the surface. In this method, the posture of the forming toolpath is adjusted individually according to the forming angle at each position of the surface so that the posture of the sheet metal is constantly adjusted in the forming process, which ensures all the forming angles of the surface to be less than the forming limit angle. Moreover, the posture of the extrusion tool is also adjusted according to the accessibility of the extrusion tool to the surface and the features of the surface, which makes the extrusion tool to press the sheet metal along the needed directions so as to control the deformation state and material flow efficiently, and then accomplish the forming of the complex sheet metal part. The results of the research show that the 5-axis CNC incremental toolpath generated based on the method mentioned earlier can form the complex sheet metal part containing the surfaces whose forming angle is larger than 90° and that is invisible from the positive and negative directions of Z-axis.

The generation of the forming path with the springback compensation in the CNC incremental forming

Aiming at the problem of the springback in the CNC incremental forming, a method for predicting the springback and generating the compensated forming trajectory was proposed based on the explicit and implicit finite element analysis. First, the middle surface of the simulated sheet metal part was reconstructed after the springback simulation with the coordinates of all nodes obtained from the numerical simulations, and the reconstructed middle surface was compared with the middle surface of the theory model to calculate the normal deviation values. Second, the theory model was offset with the unequal distances of the deviation values to generate the compensated facet and the forming path. Once more, the finite element analysis was done until the compensatory effect met the required precision. Meanwhile, aiming at the roughness of the compensated facet caused by the multi-compensation process, the smoothing method was given to guarantee the smooth of the forming path. According to the predicted result of the numerical simulations, three times compensation meets the required precision and the normal deviation value is decreased from 0.696 mm to 0.194 mm. The forming experiments indicate that the springback of the target part in Z direction is decreased from 1.107 mm to 0.427 mm. Therefore, the predicting and compensating method of the springback proposed in the paper is available, which can improve the forming precision of the sheet metal part.

Generation of the Underdraught Points Uniformly Distributed Contour Tool Path for CNC Incremental Forming

Aiming at the problem that indentation was generated on the forming surface due to the concentration of underdraught points on contour tool path, this paper proposed a method that can obtain a series of uniformly-distributed underdraught points on the contour tool path generated based on STL model in sheet metal CNC incremental forming. In this algorithm the STL model was taken as the input model and the cutting plane through the central rotation axis of model was rotated a certain angle in turn to cut the contour tool path, then the underdraught points distributed uniformly along the workpiece contour can be obtained. The case study shows that the proposed method can effectively generate the contour tool path with the underdraught points uniformly distributed.

Research on the Interference Correction in the CNC Incremental Forming

Aiming at the problem of global interference correction that the extrusion tool is entirely contained within the workpiece in 5-axis CNC incremental forming, a method that can avoid interference by correcting only once based on STL (StereoLithography) model is proposed in this paper. The interference critical point is found by using the plane which is paralleled to the extrusion tool and the Z-axis to cut the extrusion tool and the workpiece model, and then the interference correction angle is calculated through the interference cirtical point. The case study shows that this method is simple, effective and it can correct interference only by one step.

Fabrication of the Sheet-Metal Part with Non-Horizontal End Face Based on the CNC Incremental Forming

Aiming at the problem that current CNC incremental forming technology can’t directly manufacture the sheet-metal part with non-horizontal end face, the method that can manufacture this kind of sheet-metal part by using the equidistant tool path parallel to the sheet metal was proposed in this paper, in which the support and sheet metal was made together and sheet metal was directly fixed on the support. In addition, the equidistant tool path parallel to the sheet metal was generated using UG software and the sheet-metal part was fabricated by using vertical CNC machining center.

Research on the Forming Path for Fabricating the Sheet-Metal Part with Non-Horizontal End Face Using CNC Incremental Forming

For the purpose of the fabrication of the sheet-metal parts with non-horizontal end face using the sheet metal CNC incremental forming technology, two kinds of path generating methods, namely the level path perpendicular to Z axis method and the equidistant path parallel to sheet metal are proposed in this paper. Both of the paths are generated by Visual C++ and OpenGL graphics library, the effect of the two kinds of forming paths to the forming quality of the sheet part with non-horizontal end face is researched using the finite element analysis method in this paper.

A Study on the Interference Detection and Correction in 5-Axis CNC Incremental Forming

A kind of high efficient and accurate method for the interference detection and correction of 5-axis CNC incremental forming tool and sheet part on the basis of STL(Sterolithography) model is proposed considering the detection efficiency, accuracy and correction. STL model of sheet part is discretizated along the edges after the triangular facets have been subdivised according to the minimum edge of the cube obtained by octree division algorithm so that the octree segmentation for the discrete point cloud model are more regularly. And in order to directly detect the interference area without recursive search, the discrete point cloud model is expand to an octree division model with index sequence. Meanwhile the forming tool is surrounded by axis-aligned bounding boxes and the interference location is detected through the octree division model roughly. The interference location is detected in detail through the discrete points in cubes of the octree division model and the forming tool of the cylinder shape. The interference correction is conducted on the section cutting plane which is along the axis direction of forming tool at interference points. The case study shows that the proposed method can quickly find the interference as well as give the correction, and the whole operation process is stable and reliable.

Research on the Simulation for Sheet Metal NC Incremental Forming

In the sheet metal CNC incremental forming, the forming is realized by its tool's step by step and point by point extrusion movements along the pre-programmed contour tool path in the outline of the sheet part. Therefore, the correctness of the forming path used to control the tool's movement has a magnificent impact on the forming quality. And a NC incremental forming process simulation method which is used to verify the correctness is showed in this paper. Meanwhile the simulation software system is developed by using VC++ and OpenGL. The case study shows that the software system can be used in the verification of NC incremental forming path and the motion analysis of forming tool, and the software system runs steadily and reliably.

Research on the Discretization of STL Model in the CNC Incremental Forming

To the demand for the discretization of STL(Stereolithography) model in sheet metal CNC incremental forming, two kinds of discretization algorithms respectively based on unequally divided projection grids and unequally cutting planes were proposed. And the software systems were implemented by using VC++6.0, C++, OpenGL. Meanwhile the comparison of every discrete model with the original test model was done by using RapidForm XOV verification software. The case study shows that both discretization algorithm can generate uniformly distributed discrete points, and compared with the original test model, the average errors are 0.0475 and 0.0036 respectively.