Investigation of the Applicability of Topological Methods

Abstract

In many areas of the industry, continuous and rapid changes can be observed, which are setting a unified direction for product design and creation of the product. Classic examples include the spread of modern production equipment, the consecutive research and development of material technology, computer support and development that allows the extension or supplement of traditional manufacturing technologies. The latter includes additive manufacturing technology, which provides a new opportunity to produce everyday products that have a significant impact on serving market demand. Integrated CAD systems have taken their place in the process of product design and development for decades, partially reforming classical design methods and its steps. The optimization processes have emerged in recent years and are becoming more widespread in integrated CAD systems; these include shape optimization, topology optimization, and the new generative design process, all of which provide an effective solution for design engineers in an increasing number of industrial applications, meaning that these methods can be used in numerous areas of industry. Until now, it was not possible to test the designed products during long-term operation in case of the classic rapid prototyping procedures. However, the appearance of metal powder printing and additive technology already allows the long-term testing of designed prototypes and even the production of final products if the deviation from the required properties of the product is negligible. As a result, using the generative design process, design engineers also have the opportunity to create products that seem to be unfeasible. The following article seeks to prove the facts mentioned above based on a case study. The study describes the product or part that has been traditionally designed and manufactured to replace it with new design methods. And finally details and summarizes the steps required to create a new product or solution.

1 Introduction

Engineering design is intended to create an adequate solution to a formulated problem both technically and economically. Product design and development require a great deal of experience and a unique vision. A long time ago, it was accepted that this science is an internal ability that cannot be mechanized. It has been recognized that the quality of a product is greatly influenced by the series of decisions that arise during the design process. Accordingly, design tasks need to be transformed into a task that can be completed by many and in which each stage and step can be well followed and achieved [1].

Methodical design is a monotonously advanced process, the first step of which is to define the task precisely, and based on existing technical solutions or intuitions, conceptual and construction plans can be drawn up. The developed solutions are checked on the basis of the formulated requirements. Before manufacturing a physical prototype, the part is pre-inspected in a virtual environment, the aim of which is to reduce time and costs. During the test carried out, each solution is evaluated based on different aspects, such as geometric collision testing, internal stress distribution, degree and nature of deformation, natural-frequency testing, the effect of temperature, and inspection of assembly and manufacturing processes. These steps are called virtual prototyping, which can be related to the parallelization of methodical design [1,2,3,4]. Furthermore, additive manufacturing today is an emerging technology that can be considered the next industrial revolution. In fact, the use of this technology is projected to expand steadily [5, 12, 13].

Compared to traditional manufacturing technologies, additive technology offers greater design freedom for both prototype and finished products and also does not require expensive tools and molds. Furthermore, computer-aided design CAD technologies, such as generative design, can further increase the relevance of additive manufacturing. Generative design tools are similarly showing growth and expansion in many areas of the industry. The main CAD system providers have also developed their own generative design systems, adapting to the trends [6, 7, 11]. The interactive design seems to connect with different engineering cultures [8]. Considering the novelty of additive manufacturing and generative design technologies, the methodology is currently thought to be incomplete. This article seeks to answer the following research question (RQ): how effectively can the generative design method be applied to a properly designed part based on the methods explored?

2 The Basis of the Case Study

The case study in this article is based on a previous 2019 competition development proposal. The main theme of it is an experiment in the development of chassis components for a racing car participating in student competitions, which is concentrated on the wheel hubs located on the front axle. The main objective of the study is to reduce the weight of the components in the wheel suspension. The automotive and aerospace industry is characterized by the desire to reduce the weight of the vehicle while, of course, maintaining adequate performance and safety. In the case of vehicles designed for racing, this demand is even more emphasized as increasing the acceleration potential of the vehicle can be understood by an increase of the traction force and/or reduction of the mass. Furthermore, the unsprung mass of the wheels is also important for acceleration and braking performance, as, with more weight, more force must be overcome against inertia during acceleration and deceleration. The chosen topic may be appropriate for several reasons to examine the applicability of the given design method, as the role of mass reduction, especially the reduction of unsprung masses, is particularly important in the case of vehicles designed for racing. In addition, parts should be sufficiently rigid that the chassis can provide the expected properties. The individual connection points were determined during the entire chassis design, which are located on different planes and axes capable of each other, which can generate complex and spectacular results.

3 Design of the Components of the Landing Gear

The wheel hub, also known as the stump stand, is one of the most important and most functional components of a wheel suspension. The main task of this is to connect the wheel and the chassis. Accordingly, it includes bearing points, fixing points of brakes, rocking-arms and connecting rods. It can also include optional features such as mechanical interfaces for temperature and speed sensors. The current design also provides the ability to set basic chassis parameters.

Fig. 1.

The traditionally designed model of the wheel hub.

Figure 1 shows a 3D model of the part under consideration, which was designed on the basis of traditional design methods. The raw material of the component is 6061 aluminium with a density of 2.7 [g / cm³], a yield point of 275 [MPa] and tensile strength of 310 [MPa]. The overall size of the stump stand is 275x147x55 [mm], and the weight of the current design is 1.05 kg. The indicated hub can be manufactured using conventional cutting operations. The entire component features cuts, breakthroughs and pockets, which are said to be the tools of traditional design and manufacturing methods.

4 The Generative Design Process in iCAD System

Generative design is a design process in which an algorithm optimizes the shape of the component for a particular boundary condition. The design of the shape is not a manual design task. The designer determines the functional boundary conditions of the part and adds them to the software, which calculates the shape of the optimized part according to the specified criteria during iteration processes [7, 11]. Recently, several articles have been devoted to the description of generative design processes [9, 10], on the basis of which the outlined task is solved (Fig. 2).

Fig. 2.

Steps of the generative design process [10].

It is advisable to carry out the design process step by step based on the indicated flowchart because this is the only way to get an effective solution based on preliminary research. The case study in this article is solved in the Generative Design Support module of the Fusion 360 Integrated Design System. Examination of the installation environment of the chassis components is examined in the Design Module, the mass optimization task is performed using the Generative Design Module, and the check of the results is carried out in the Simulation Module.

4.1 Determination of Design Space

In accordance with the recommended design process, the installation environment of the part should be examined and then the necessary and limiting volumes using a method should be constructed.

Fig. 3.

“Preserve geometries” Volumes to be preserved.

Figure 3 presents the partial assembly model of the chassis, which has been used to determine the volumes that must be retained. It can be seen that the chassis is a complex structure consisting of many parts to create a suitable interface. In this case, these models are formed through traditional modelling, which is not an automatic process. This process can serve as the creative part of the design, as the designer can significantly interfere with the specificities of emerging geometry (Fig. 4).

Fig. 4.

“Obstacle geometries.“ Portion of space occupied by related adjacent components.

Tt the current design stage, it is necessary to perform the inverse of the previous process, so it is essential to define volumes that limit the design space of the program. Care must be taken in the process, as with these constraints, the maximum or even the smallest material thickness of a critical section can be limited, which can hinder the optimal design. In the case of the complete assembly, the best solution is to define the limitations using the results of a kinematic simulation parameterized with real movements.

4.2 Definition of Loads and Constraints

Loads and constraints are specified on the volume parts to be retained with the following functions.

Fig. 5.

Definition of constraints and loads.

In the next step, as Fig. 5 represents, the individual constraints and load forces were placed on the connection points. The individual forces and force components are of the same magnitude as those for which the original part was inspected. These forces have been determined by experience, it always depends on the mass and engine power of the construction of a particular age, so these parameters can vary from year to year. The loads for the design are summarized in the below table, which can be considered to be maximum values (Table 1).

Table 1. Loads affecting wheel hub

During the test, the moment with the highest load is taken into account when the forces summarized in the table occur simultaneously. The generative design module creates the optimal geometry based on the von Mises voltage formed in the material of the part. It is not possible to take dynamic effects into account.

4.3 Definition of Design Objective Functions

In the applied program, the “Objectives” function can be used to define optimization goals and limits. When specifying the design objective function, there are two choices that seek to maximize rigidity or minimize mass. Throughout the design process, a target function is selected to maximize rigidity, with a mass target of 0.7 [kg], taking into account the current design of the component and the minimum required safety factor, which is 2. By prescribing different production technologies, the certain system of conditions on the basis of which the results are developed can be further tightened. At least one raw material must be assigned to the solution in the program. The design module can only handle a linearly flexible material model. In the case of the design of the wheel hub, the “SLM” (Stereo Lithography) and EBM (Electron Beam Melting) processes were selected from the additive manufacturing technologies, for which the chosen materials are Aluminum (AlSi10Mg) and Titanium (6Al-4V), as these can be applied in case of milling.

4.4 Evaluation and Selection of Solutions

Various filters and diagrams are available to review and compare solution variants. The tabular view helps the sorting of solutions by different criteria. The weighting of each aspect can be modified, such as weight, price, and degree of deformation.

Fig. 6.

Evaluation of different production technology solutions depending on mass and maximum displacement.

Fig. 7.

Evaluation of solutions based on different raw materials as a function of mass and maximum displacement.

Comparing Fig. 6 and Fig. 7, it can be stated that the lowest weight solutions can be achieved with additive manufacturing technology and the application of Titanium as the raw material, but in this case, the material suffers relatively large deformations under load. In the case of additive manufacturing, the most massive but rigid solution is obtained by using aluminium raw materials (Fig. 8 and Table 2).

Fig. 8.

Selected solution I, solution II, solution III.

Table 2. Analysis of solutions.

The three versions indicated in the table reflect the characteristics of the solutions. The lightest and heaviest parts have been selected, and an ideal solution has also been selected from the middle field. The selected parts made of aluminium show well that traditional cutting technologies do not have a negative impact on individual solutions. The raw material of solution number two from the middle field is inexpensive, and the production technology is widely used in five-axis milling. It achieves the desired weight reduction and meets the strength requirements well. In the case of the lowest weight solution, it is necessary to work with expensive raw materials, which are accompanied by expensive and limited production equipment (Fig. 9).

Fig. 9.

Preliminary FEM analysis results for stress and deformation test.

The program provides an opportunity to show the results of preliminary FEM analysis, based on which the critical points of the component are revealed, from the aspects of solidity.

5 Summary

The article reviewed traditional design procedures and the classical method, as well as the motivation for the development of the discipline, which forms the basis of Generative Design, the defining stages of which were introduced. The factors influencing the spread of the process and the development of the necessary technological processes are described. The article revealed the steps of the design process currently being explored in generative design, the accuracy and applicability of which were examined in the framework of a case study. The study presented the workflows of each step in a popular integrated CAD system. By going through all the necessary steps, the article could present effective solutions for the formulated design needs.