Studies based on CAE
Final Report: Reverse Engineering
Wheel Bearing Hub
May 16, 2019
OBJECTIVE
As a part of the class project I chose to design a hub assembly of Mazda 3 car of mass 1600 kg or 16000 N and a maximum speed of 200 mi /hr and average speed of 60 mi /hr. The assembly must give stability during rotation of the wheels. The weight and the dimension of the hub must be as small as possible because of the unsprung weight which further reduces the rotational mass. Also, it is to be noted that each of the wheels will exert a force of 16000/4= 4000 N.
INTRODUCTION
Reverse Engineering has been defined in many different ways. The aim of reverse engineering is to use a physical part to gather complete knowledge about the part, which enables its replication. This knowledge can be anything from general appearance and physical dimensions to working methodology and material properties. In the manufacturing world ‘Reverse Engineering’ refers to the creation of engineering design data from the existing parts. It recreates or clones the exiting part by acquiring the CAD (Computer Aided Design) of the existing part. So, my focus on this design project will be the wheel hub assembly of Mazda 3 2016.
This Project is based on analysis of Mazda 3 rear hub for weight reduction and increase the strength of hub by re designing or re-engineering the part itself. A wheel hub assembly also referred to as wheel hub unit or wheel bearinghub is an automotive part used in most cars, passenger vehicles, and light and heavy trucks. It is one of the major and very important components and needs very good material and design in low cost and avoids failure. The three basic elements of a wheel are the hub, the spokes and the rim. Sometimes these components will be one piece, sometimes two or three. The hub is the center portion of the wheel and is the part where the wheel is attached to the suspension through the wheel carrier (or knuckle). The spokes radiate out from the hub and attach to the rim. The rim is the outer part of the wheel that holds the tire. A hub assembly contains the wheel bearing and hub to mount the wheel to vehicle and it is located between the brake rotor and axle. Engineering component with optimum use of material and easy manufacturability is a direction where prior simulation through finite element method is found to be very useful.
Fig: Wheel Assembly Hub with other crucial car components including axle and strut
Fig: Exact replica of the model being modeled with part number and price
INSPIRATION
Fig: Measurements taken in order to design the hub
COMPLETE BENCHMARK
Most of the mechanical systems are subjected to dynamic loading causing crack, noise, fatigue and so on. Lots of work have been done in the field of automobile performance analysis using finite element method rules and various alternatives and improvements have been proposed. Initially I was thinking to carry out a comparative analysis of two materials with the existing steel and second material would be any kind of strong aluminum but the FOS suggested me not to compare with different materials as a medium strength material would have a reasonable FOS on the wheel hub itself. However, the FOS on the bearing would be a lot smaller as compared to the hub itself. Hitting a pothole has a very high impact on the bearing.
In design stage, we estimated all the force acting on hub and disc. The wheel hub was modeled in Solidworks with given parameter acquired from the initial measurement phase. The forces were applied on model using finite element analysis in hyper mesh. The thickness of hub was varied in increment of .02mm till a max factor of safety value was attained. Thus the final design of the wheel hub is complete.
Problem Description: Accurate Speciation of Hub
· Material used: - Chrome Stainless Steel
· Type – 2016 Mazda 3 Wheel Bearing Hub
· Application for case study – Automobile
· Computational approach- Solidworks Simulation for modelling and analysis
· Steps for the proposed work
· Creation of modelling of hub
· Importing the geometry for meshing
· Solving for the meshed model to identify mode shapes
· Modifying the CFL factor for accuracy and stability of the hub
· Comparison / Interpretation of the results
· Recommendations
MECHANICAL PROPERTIES
ANALYTICAL LOADING: DROP TEST
Based on the class notes, a drop test was carried out for the hub for analysis. This is to just use the knowledge acquired in the class and is not related to the FEM test. This test try to replicate stress produced when the vehicle falls from a certain height. To obtain the impact load on the hubs
Assuming the vehicle falls from the height (h), h=1𝑚
The impact velocity (v) of the vehicle is, From kinematic relation for rectilinear motion
𝑣 =√(2∗𝑔∗h)−𝑢2
whereas,
g ꞊ acceleration due to gravity (9.8 m/s2 )
u ꞊ initial velocity of the vehicle before the fall ( 0 m/s) Substituting the above value,
𝑣 =4.42𝑚/𝑠
And now for calculating the impact force (F)
From Work-Energy Principle,
Change in Kinetic Energy of the object ꞊ Work done on the object
.5 * 𝑚 ( 𝑣 2 − 𝑢 2 ) = 𝐹 ∗ 𝑑
whereas,
d ꞊ the compression of the shock springs ( 0.15 m) Thus,
F ꞊ 22,800 𝑁
GENERAL DESIGN CONSIDERATION
The bolt pattern is determined the by the number of bolt on the wheel hub. Selection of material strong enough to take the weight of the car. Wheel bearing in the hub depending on ID and OD of spindle coming out of hub. Type of lug nuts or bolts.
Wheel hub is highly stressed but a safety component which must not fail under the applied loading condition. The main parameters for design of wheel hub assembly are loading condition, manufacturing process and material behavior. The influence of these parameters are interactive so material fatigue behavior will be change depending upon the wheel hub design and loading condition.
· Selection of material: Any engineering component has one or more functions (to support a load, to contain a pressure, to transmit heat, etc.).The designer has an objective (to make it as cheap as possible, or as light as possible, or as safe as possible or some combination of these).The component must carry the given load without failure, it should function in a certain temperature range, etc. he objective must be achieved subject to constraints.
· Material property: Cost, density, modulus, strength, endurance limit, thermal conductivity, expansion coefficient ,Mechanical property- Hardness, Elastic constants, Yield strength, Ultimate strength, Fatigue, Fracture Toughness, Creep, Damping, Wear resistance, Spalling, Ballistic performance
· Material selection methodology: Translate the design requirements into materials specifications. It should take into consideration the design objectives, constraints and free variables.
INITIAL PHASE: MEASUREMENTS
With the help of digital readout caliper and a few tricks, we can reverse engineer a thing accurately. I started off by figuring out just exactly which measurements I needed to take: where the outer plate and the hub units are in relation to the lock in mechanism to the wheel motor. I have attached some pictures taken during the measurements of the important units that were required in the second phase of my project- designing the hub in solidworks.
Fig: Measurements taken in order to design the hub
Fig: Measurements taken in order to design the hub
MODELLING
A literature survey was undertaken before modelling of the component began. Initially as a reference the stock Mazda hub was taken. The model was loaded in the Solid-works. Initially it was decided to use it but due to its weight idea was soon dropped. Also component was analyzed to develop a lighter and stronger equivalent in Chrome Steel.
Fig: Extrusion of the redesigned disc
Fig: Solid Modelling of the redesigned disc
Fig: Final Hub Assembly design infested with smart dimensioning
Fig: Wireframe view of the final design with all pins located
Fig: Pin Extrusion model and circular pattern feature was applied at equal spacing
Fig: Final Meshing with maximum nodes (839987)
FEM Results:
The Finite Element Analysis (FEA) has been widely implemented by automotive companies and is used by design engineers as a tool during the product development process. When used properly the FEA becomes a tremendous productivity tool, helping design engineers reduce product development time and cost.
Following is a FEM report produced that contains the crucial Numerical Methodology information:
CONCLUSION
Wheel Hub has been re-designed for MAZDA 3 car of mass about 1600 kg. The designed assembly gives stability during rotation of the wheels. The design project enabled us to understand the various forces that act on the wheel hub. The design project helped me better under the uses of software in real scenario.
ANALYSIS
The hub is the crucial component as every force experienced by the car is passed on through it. Also analyzing every effect of this complex ever changing moment and forces becomes complicated. A worst case scenario’s is therefore recommended where forces are scaled and restrains are applied in view of real time. I performed various finite element computational analysis to match approximately with the actual conditions that will be experienced by the component so as to avoid failure in real-time.
There are many different types of analysis that must be completed to ensure that the part in question is able to withstand the applied loads. In addition, there are other factors that must be included in each analysis to ensure that the analysis itself is correct. In order to analyze the part correctly, the restraints must be an accurate representation of the real world scenario and the loads must be calculated for different loading scenarios. Finally, the mesh must be as homogenous as possible. This would include minimizing the difference in aspect ratio between elements, as well as maximize element mapping quality. We must ensure that all of the meshes we use for the different components in our assembly are set up to be compatible with one another.
The main objective behind analysis was to check the maximum stress induced, predict the life of component and establish a suitable factor of safety in design. Since most of suspension component used were steel and it must be noted forth that it does exhibit a fixed fatigue limit unlike major aluminum categories. All of the analysis were done in student package of Solid works 2018 Simulation module. The meshing package utilizes the tetrahedral mesh on the component. To give better accuracy the mesh size was made finer until the results became stagnant. Any more decrease in mesh size would just waste computer resource without marginally increasing any solution accuracy.
Modal analysis was also done on the component to determine how the system behaves in its displacement dynamic response. It was done to check how different frequencies naturally excite the system to a degree where resonance fluctuates through the component resulting in dropping of life expectancy of the system. For this study no external load is applied to the component, while it is known that external loads do not affect the natural frequency. The component was however restrained. Note that in all the analysis, self-weight of the component was considered.
The fundamental task is make small weight hub and strength is to be increased. That is why the hub has been reengineered to smaller size without affecting the functionality of the hub. Re designed hub cuts the safe portion of the plate (colored blue from the FEM analysis) and hence the reverse engineering is partially attained.
FUTURE STUDIES
The impact force on the hub itself is less effective as suggested by the FEM analysis, so my future studies will focus on the effect of the impact force on the bearing.
REFERENCES
1. https://www.diva-portal.org/smash/get/diva2:1221239/FULLTEXT01.pdf
2. Slides from the lecture notes provided by Prof. Sadegh, CCNY