Alan C. Lin

Automatic generation of mold-piece regions and parting curves for complex CAD models in multi-piece mold design☆

Abstract Multi-piece molding technology is an important tool in producing complex-shaped parts that cannot be made by traditional two-piece molds. However, designing multi-piece molds is also a time-consuming task. This paper proposes an approach for automatic recognition of mold-piece regions and parting curves for free-form CAD models. Based on the geometric properties of objects and mathematical conditions of moldability, a collection of feasible parting directions is formed from which the sets of visible-moldable surfaces are identified for each parting direction. Moldable surfaces that are partially visible to a particular parting direction are recognized and divided into fragments by silhouette detection and edge extrusion. A set of criteria is proposed to arrange tentative fragments, which can be simultaneously visible to several parting directions, into appropriate regions for mold pieces. Finally, the parting curves for mold pieces are extracted from the corresponding mold-piece regions. The proposed algorithm overcomes the problems found in previous multi-piece molds and at the same time achieves high accuracy and high performance. Examples of industrially complex models are used to demonstrate the performance and robustness of the proposed algorithm. The approach is generic in nature, allowing its application to be extended to any complex geometry in 3-D mold design.

Parting curve selection and evaluation using an extension of fuzzy MCDM approach

Parting curve selection and evaluation plays an important role in mold design. Multiple criteria decision-making (MCDM) is an effective tool for evaluating and ranking problems involving multiple criteria. In order to select suitable parting curve, several criteria need to be taken into account. Therefore, this paper proposes an extension of fuzzy MCDM approach to solve parting curve selection problem. In the proposed model, the ratings of alternatives and importance weights of criteria for parting curve selection are expressed in linguistic terms. The membership functions of the final fuzzy evaluation value in the proposed model are developed based on the linguistic expressions. To make the procedure easier and more practical, the normalized weighted ratings are defuzzified into crisp values by using a new maximizing set and minimizing set ranking approach to determine the ranking order of alternatives. An example of parting curve evaluation and selection is given. The results show that the proposed approach is very effective in selecting the optimal parting curve for the molded part. Finally, this paper compares the proposed approach with another fuzzy MCDM approach to demonstrate its advantages and applicability.

A multiple slicing approach to automatic generation of parting curves

A new slicing algorithm that uses multiple sets of cutting planes to automatically determine parting curves for three-dimensional parts is proposed. In this algorithm, one set of cutting planes is used to generate the slicing profiles, and two others are used to determine the intersection points with the inner and outer loops of the parting curves. The algorithm provides a highly effective solution for handling complicated models that contain free-form surfaces. The features of the algorithm are highlighted in three case studies using tessellated geometry in STL file format as the input. The resultant parting curves overcome many problems inherent in the current methods and can be used by various downstream computer-aided design systems for three-dimensional mold design.

Determining Side-Cores of Plastic Moldings

The determination of side-core for plastic moldings plays an important part in design process. Numerous studies have been investigated for side-cores recognition in literature. However, most of the existing methods have been developed based on the side-core surfaces of one region are known. In fact, it is difficult to identify relevant surfaces of one region. This study proposes a new algorithm of relevant surface attribution (RSA) based on topological relationship and V-map to automatically identify relevant surfaces of a side-core region. Then, the proposed approach defines the shape of side-core region as bounding surfaces and side-core direction. Finally, case studies are used demonstrating the applicability and usage of proposed approach.

Automatic Side-Cores Construction in Injection Plastic Mold Design for Free-Form NURBS Surface Models

In computer-aided design for moldings, automatic generation of side-cores is a crucial design task that has an influence on the entire mold structure and manufacturing cost. This paper proposes a synthetic approach for creating the side-cores of free-form NURBS surface models. Based on the geometric properties of entities, surfaces of undercut features which are molded for side-cores are identified. After determining the withdrawal directions for each group of undercut’s surface features, the number of side-cores is optimized. The heads and the bodies of side-cores are finally obtained through the combination of the Boolean operation and 3D oriented extrusion. The algorithm is efficiently for both protruded and indented portions of undercut features. A complex industrial part is used to demonstrate the performance and robustness of the proposed algorithm. Since the approach is generic in nature, it is easy to be applied to any complex geometry in 3D mold design.

A hybrid approach to automatically generate parting curves of free-form surfaces

In computer-aided design for moldings, automatic generation of parting curves is a crucial design task that has an influence on the entire mold structure. This article proposes a hybrid approach for determining the parting curves of free-form computer-aided design models. Based on the analysis of the geometric properties of specific entities and mathematical conditions, different sets of moldable surfaces for two-half molds and side cores are identified. All surfaces that do not contribute to the parting curves can be subtracted from these surface sets. The proposed parting curve is generated based on the combination of both the outermost boundary edges and the visible silhouette segments of the relevant surfaces. By the techniques of silhouette detecting, edge projecting, and ray testing, the proposed algorithm overcomes the problems found in conventional research that cannot guarantee that the outermost curves generated are the actual silhouette of a free-form surface. In addition, by eliminating all irrelevant surfaces and without using the surface approximation method, the proposed approach achieves the goals of obtaining high accuracy coupled with high performance. Two examples of industrial models are used to demonstrate the performance and robustness of the proposed algorithm. The approach is generic in nature, which allows it to be applied to any complex geometry in three-dimensional mold design.

Using Interpolation Points to Rectify Cutter Paths of Five-Axis Machining

When operating a 5-axis linear cutting command G01, the controller automatically inserts point data between two NC blocks in a linear distribution fashion, and then drives the cutter along these inserted points. If a simultaneous 5-axis machining is initiated, and CL data is directly transformed one-to-one into NC data, and then cutting is performed directly without having the 5-axis controller inserting any points between NC blocks, its processing path will deviate from the original plotted path. In fact, the processing path is no longer a straight line, but a curve line. This study proposes a method to increase CL interpolation points to automatically rectify the path deviation. The extent of research of this study comprises: (1) Transforming CL data into NC data (2) Programming tool orientations (3) Obtaining all CL interpolation points and their tool orientations (4) Generating NC data.

Conversion CL Data to NC Data Using an Instinctive Method for Non-Orthogonal Table-Type 5 Axis Machines

Since different types of 5-axis milling machines have their own unique rotation mechanisms, the solutions developed to generate numerical control (NC) data are traditionally targeted toward specific mechanisms and are obtained via specific methods, normally resulting in complex algorithms. In order to resolve this problem, this paper proposes an instinctive method to convert cutter location (CL) data to NC data for non-orthogonal table-type 5 axis machines. The rotational angles of the two rotational axes can be easily derived from the tool-orientation vector, and the coordinates of the three linear axes in the NC data can be easily derived from the rotational angles and coordinates of tool position. Even more, this method enables the development of a generic algorithm for the rotation mechanism of any 5-axis CNC milling machine.

Tool Orientation Planning for Four-Axis CNC Machines

Improper tool orientation planning often causes four typical types of inappropriate four-axis tool paths. They are included: 1. Severe changes of tool orientations occur, 2. Reversions of tool orientations exist, 3. Discontinuous tool paths occur, 4. Gouging. After explore the common methods of the present four-axis machining and their restrictions, the research proposes a hybrid tool orientation planning (HTOP) method to improve the above shortcomings and to get smoother rotary tool paths. An example is done in the last to verify its feasibility.

Determination of Parting Lines and Multiple-Undercut Boundaries for Complex CAD Parts with Application to Multi-Piece Molds Design

This paper proposes a new slicing approach that uses multiple sets of cutting planes to automatic determine parting lines and boundaries of undercuts of complex CAD parts for the multi-piece molds design. In this algorithm, the group of feasible parting directions is first collected and three sets of cutting planes are then formed based on the primary parting direction. One set of cutting planes is used to generate slicing profiles, and two others are used to extract intersection points passed through by parting loops and boundaries of undercuts. The result shows that the proposed parting lines are suitable to obtain parting surfaces and construct the entire mold-pieces. The algorithm provides a highly effective solution for handling many complex industrial parts.