S. Mateos

Automatic determination of bending sequences for sheet metal parts with parallel bends

A method for solving the problem of bend sequencing in sheet metal manufacturing is presented. The algorithm developed divides the part into basic shapes (channels and spirals) and determines the partial sequences associated with them. The complete bending sequences associated with the complete part were obtained from the combination of these partial sequences. To make this combination possible, several strategies were defined to reduce the number of solutions and, therefore, the searching time. All sequences (partial and complete) were checked considering possible part-tool collisions and tolerance constraints. The last stage was to order the sequences by taking into account the total process time. To attain the required process time accuracy, a robot was used for the handling operations. Finally, the sequence associated with the lower process time was selected as the optimal solution.

Influence of Surface Position along the Working Range of Conoscopic Holography Sensors on Dimensional Verification of AISI 316 Wire EDM Machined Surfaces

Conoscopic holography (CH) is a non-contact interferometric technique used for surface digitization which presents several advantages over other optical techniques such as laser triangulation. Among others, the ability for the reconstruction of high-sloped surfaces stands out, and so does its lower dependence on surface optical properties. Nevertheless, similarly to other optical systems, adjustment of CH sensors requires an adequate selection of configuration parameters for ensuring a high quality surface digitizing. This should be done on a surface located as close as possible to the stand-off distance by tuning frequency (F) and power (P) until the quality indicators Signal-to-Noise Ratio (SNR) and signal envelope (Total) meet proper values. However, not all the points of an actual surface are located at the stand-off distance, but they could be located throughout the whole working range (WR). Thus, the quality of a digitized surface may not be uniform. The present work analyses how the quality of a reconstructed surface is affected by its relative position within the WR under different combinations of the parameters F and P. Experiments have been conducted on AISI 316 wire EDM machined flat surfaces. The number of high-quality points digitized as well as distance measurements between different surfaces throughout the WR allowed for comparing the metrological behaviour of the CH sensor with respect to a touch probe (TP) on a CMM.

Parametric and associative design of cartridges for special tools

Presents work on the design of special rotary tools using CAD systems. Special tools are used for the simultaneous machining of several parts in the same workpiece, with only one feed motion. The reduction in the number of tool-changes is the main advantage using them. Special rotary tools have a modular feature, and the cutting edges are assembled onto small holders called cartridges. Taking into account the importance of defining the cartridge geometry, it seems to be necessary to point out all the steps followed in the design process as well as those concerning their suitable location and orientation. On the one hand, one needs to make a parametric design of the ISO standard cartridges so that all the sizes and types of cartridges can be obtained from a few basic models. Each cartridge is built joining several solids together: an insert, the cartridge body and the axial adjusting screw. On the other hand, it is necessary to have in mind the location and orientation of the cartridge. With this aim, the cartridge geometry is attached to three points, two of these represent the tool axis direction and the third one is a point on the work surface profile. These three points define the tool reference plane from which all the whole cartridge geometry is generated.

Methodology for set-up planning automation of turned parts

This paper presents an automatic set-up planning module integrated in a CAPP system for rotational parts to be machined on a lathe. The developed system determines the possible set-up combinations that are necessary for a complete machining of the part as well as the order of each set-up and the surfaces to be used for clamping the part. The applied methodology takes into consideration constraints such as the geometry of both the stock and the final part, the geometry and the capacity of the chuck, and the part tolerances. In general, these constraints allow the system to obtain several valid solutions for clamping the part. Some criteria based on the clamping force and the value of tolerances have been considered in order to establish a preference order among these solutions. Finally, the analysis of linked tolerances and the tool approach direction to each surface determine the sets of surfaces to be machined within each set-up. An example part is used in the course of the paper to illustrate conveniently the methodology, and two additional case studies prove that this methodology is adequate for the solution of real cases.

Accessibility analysis for automatic inspection in CMMs by using bounding volume hierarchies

Accessibility analysis represents one of the most critical tasks in inspection planning. This analysis determines those probe orientations that can touch an inspection point without collision. This paper presents a methodology based on part discretization and the application of space partitioning techniques (kd-tree) in order to reduce the number of intersection tests between probe and part. A STL model has been used for discretizing the inspection part in a set of triangles, which permits the application of the developed system to any type of part, regardless of its shape and its complexity. Likewise, a recursive ray traversal algorithm has been used in order to speed up the traversal of the kd-tree hierarchical structure and to calculate exclusively the intersection of each probe orientation with those part triangles that can potentially interfere with it. In a further step of the analysis, the real geometry of the probe has been considered. Hence, a simplified model has been developed for each probe component (column, head, touch probe, stylus and tip) using different basic geometrical shapes. Finally, collision-free probe orientations are clustered for minimizing the orientation changes during the inspection process. Furthermore, the applied algorithm allows for determining different valid combinations of clusters. The developed system was applied to two example parts in order to prove that this methodology is adequate for the solution of real cases.

Influence of surface material on the quality of laser triangulation digitized point clouds for reverse engineering tasks

Laser triangulation systems (LTS) are one of the most popular non-contact inspection techniques. These systems are widely used in reverse engineering tasks as they allow for a fast acquisition of thousands of points that represent the geometry of the part in a virtual 3D model. The accuracy and repeatability of these systems are lower than the traditional contact inspection techniques, as they depend on the surface properties, the illumination conditions and the LTS configuration. Present work deals with the influence of surface material on the quality of the virtual model. The objective is to evaluate the behaviour of different materials and their suitability for being digitized.

Accessibility analysis for star probes in automatic inspection of rotational parts

This article describes a method of accessibility analysis based on the geometrical study of all possible interferences between the probe and the part to be inspected. The parts considered in the analysis are rotational parts and their recognition is automatically made from a feature-based design. The probe considered is a star type, defined by adjustable parameters that allow for the adaptation to different types and sizes. The system analyses the possible collision with the machine column, touch probe and probe stylus. Apart from determining the conditions of collision, the system also calculates any collision-free positions on each surface to be probed. These positions can be used to obtain inspection paths for communication to a CMM or to a global inspection planning system. The collision conditions calculated have been checked and validated using different rotational parts.

An automatic CAPP system for rotational parts

This paper describes a turning process planning of rotational parts. It also reports general aspects to develop an automatic planning system, from the part geometrical identification to the NC program generation. The minimum number of grippings (based on the part shape), the blank type, the boring operations and the geometrical tolerance presence are established in order to determine the machining operations. The proposed method used to recognize the part geometry is based on a combination between an automatic identification of 2D profiles and a feature-based method. By this way, the developed CAPP system could use geometrical information given by any CAD system.

Development of a Virtual Machine for the Sheet Metal Bending Process Simulation for Educational Purposes

In this work the development of a virtual machine for the simulation of the sheet metal bending process is presented. The developed software is based on SolidEdge® as commercial CAD base, and allows the student to design the whole sheet metal part in a 3D environment. The application guides the student during all process, including the selection of the press brake and the tools (dies and punches) by means of a graphical interface. Finally, the bending sequence is introduced and the application simulates the bending process. This way the student can see the problems during the manufacturing process, in particular collisions, that arise from the design of the part, from the tools selected or, in most cases, from the bending sequence. Finally, the student should fix these problems in order to manufacture the part.

Accessibility Analysis for Automatic Inspection Using Bounding Volume Hierarchies

The accessibility analysis presented in this paper is based on part discretization and the application of space partitioning techniques (kd-tree) in order to reduce the number of intersection tests between probe and part. The discretization of the part in a set of triangles (STL model) allows the developed algorithms to be applied to whatever part or environment obstacle, independently of their geometry. A recursive ray traversal algorithm has been used in order to speed up the traversal of the hierarchical structure of the kd-tree and to calculate exclusively the intersection of each probe orientation with those part triangles that potentially can interfere with it. In a further step of the analysis, the real geometry of the probe has been considered. For this, a simplified model has been developed for each probe component (column, head, touch probe, stylus and tip) using different basic geometrical shapes. Different models for each probe component have been tested to calculate their intersection with the part, and several algorithms have been implemented to accelerate the computation. Finally, collision-free probe orientations are clustered for minimizing the orientation changes during the inspection process. Furthermore, the applied algorithm allows for determining different valid combinations of clusters.