Topology Optimization of Wing Structure with Manufacturing Constraints

A methodology and a procedure for topology optimization of wing structure based on manufacturing constraints were proposed. By the methodology and procedure proposed, topology of thin-box wing structure which is easier manufactured than traditional topology result can be obtained. The manufacturing constraints of draw direction, member size control and inexcusable initial design were introduced into the optimal procedure and executed in Optistruct. Effect and efficiency were analyzed and compared with traditional topology optimization.

Bi-Directional Evolutionary Structural Optimization Method with Draw Direction Constraints

This paper proposes a new bi-directional evolutionary structural optimization (BESO) method with draw direction constraints. Draw direction constraints, defined by required manufacturing process, are achieved by modifying element removal/addition criteria such that elements are removed from the top surface of the draw direction to the inner design domain. The optimized design with draw direction constraints is free from hollow or closed cavity geometries which are infeasible for manufacturing. A stiffness design of a motor front cover is carried out to show the ability of the proposed method in practical mechanical design problems.

Uniaxial deformation of nylon-6 and nylon-11: changes in orientation and crystal phase

The effect of uniaxial drawing on orientation of the crystalline fraction of two polymers forming hydrogen bonds, nylon-6 and nylon-11, has been investigated using X-ray diffraction. These two polymers have similar crystal phases, although their hydrogen bond density differs. For both polymers, the deformation occurs in two steps, the first being a plastic deformation of the α-phase spherulites. This leads to two popul ations of crystals, one with the chain axis oriented parallel to the draw direction, the second with the a axis (hydrogen bond direction) aligned along the draw direction. In the second step, the a-axis aligned population gradually tilts, leading to a uniaxial orientation of the samples with chain axis aligned along the draw direction. For nylon-11, the onset of this step corresponds to the emergence of crystals of the γ phase, which rapidly becomes the major phase. It reaches a higher orientation than the α phase, and stems from crystallization upon tension of the polymer. For nylon-6, although the γ phase also appears during drawing, at the maximum draw ratio only a small fraction is present. This difference is attributed to the relative stability of the two phases, which is different for nylon-6 than for nylon-11.Key words: orientation, X-ray diffraction, nylon, hydrogen bonds.

Automatic Draw Direction Generation for Die Design

The concept of visibility maps was first used by Woo et al (Woo et al., 1994) to find the draw directions for a die. This paper describes an algorithm that extends this idea by handling free form surfaces, parts requiring multiple draw directions and parts with pockets that have a null visibility map. The algorithm also identifies the core and cavity portions of the die.

Geometric Influence of a Molded Part on the Draw Direction Range and Parting Line Locations

This paper presents a methodology based on the geometry of the injection molded part to identify the draw direction range and parting line locations. These parameters are shown to be a function of the interaction of the outward normals of the surfaces that have been divided into concave and convex regions of the part. This approach can also be applied incrementally to determine these mold parameters for a part as design features are added. The designer can then select from the choices provided to find the optimum parting line location and draw direction using heuristic rules. An absence of an allowable draw direction indicates the presence of an undercut that complicates the mold by requiring a side action so that the mold cost increases. The designer can either redesign the part or accept the undercut by specifying a side core or cavity. Design examples are provided which illustrate the effectiveness of the developed approach.

A Systematic Approach to Support Design for Manufacturability in Injection Molding and Die Casting

In designing a part to be produced by injection molding or die casting, designers need to consider manufacturing characteristics of the part such as filling and ejectability from the dies as well as functional issues. The typical design cycle is iterative, laborious and time-consuming. In this paper, we present a procedure for defining parting information (locations where the mold/die come together), and recognizing the links between part design and die/mold construction. Many decisions and design details, such as draft on surfaces parallel to the draw (die opening) direction, gate and runner locations, vent locations, etc., depend on the parting locations and characteristics. Parting information is normally not part of the geometric model of the part design. Parting design, including draw direction and parting location, is addressed through a custom user interface which contains several options related to different levels of geometric modeling data. The resulting specification is stored in a segment structure which provides a flexible parting description and fits within the B-rep hierarchy. The reasoning about the linking of related surfaces is accomplished by splitting and traversing the extracted geometric entities based on parting definition. The entities covered by the same die/mold component are aggregated as a face group which is a set of complete or partial surfaces with the parting definition as the boundary information and with the draw direction as the moving information. In this approach, manufacturing information can be strongly coupled with geometric data to form a complete part model which supports manufacturability assessment and facilitates any necessary shape transformations to achieve a manufacturable part in a straightforward manner so that design iterations can be controlled and development cost can be reduced.

Mold Tool Configuration to Minimize Undercuts

This paper presents a methodology for obtaining mold configurations, defined by cavity and core geometries, with a minimum number of undercuts in a molded part. The methodology identifies optimal draw directions and associated parting line locations that minimize the number of undercuts thereby obtaining a good mold configuration. The interaction of the allowable draw ranges of the concave regions of the part determines the allowable draw direction range for the part. The allowable draw range for each concave region depends on how the constituent surfaces are grouped. This grouping determines whether the surfaces are formed by one or two mold halves, depending on the draw direction. The grouping also identifies which surfaces, if any, form an undercut regardless of draw direction. This last grouping identifies which surfaces require modification so that either a side core or a mold halves can form the surfaces. The allowable draw direction range for the part and its interaction with surfaces within the convex region defines the parting line location for the part. Once the draw ranges and parting line locations are identified, an algorithm selects the optimum draw direction and parting line location that minimizes the number of undercuts and results in a mold that is easy to make.