Design, Study and Analysis of Semi Elepitical Leaf Spring for Front Axle Using Creo Analysis

A leaf spring is a simple form of spring commonly used for suspension in wheeled vehicles. Originally called a laminated or carriage spring, and sometimes referred to as a semi-elliptical spring, elliptical spring, or cart spring, it is one of the oldest forms of vehicle suspension. A leaf spring is one or more narrow, arc-shaped, thin plates that are attached to the axle and chassis in a way that allows the leaf spring to flex vertically in response to irregularities in the road surface. Lateral leaf springs are the most commonly used arrangement, running the length of the vehicle and mounted perpendicular to the wheel axle, but numerous examples transverse leaf spring exist as well. Leaf springs can serve multiple suspension functions: location, springing, and to some extent damping as well, through interleaf friction. However, this friction is not well controlled, resulting in stiction and irregular suspension motions. For this reason, some manufacturers have used mono-leaf springs. Generic diagram of a leaf spring pack, without eyes; leaves are fastened together by the center bolt, midway along the length of the spring, and lateral alignment is enforced by multiple clips A leaf spring takes the form of a slender arc-shaped length of spring steel of a rectangular cross-section. In the most common configuration, the center of the arc provides the location for the axle, while loops formed at either end provide for attaching to the vehicle chassis. For very heavy vehicles, a leaf spring can be made from several leaves stacked on top of each other in several layers, often with progressively shorter leaves. The longest leaf is also known as the main, master, or No. 1 leaf, with leaves numbered in descending order of length. The eyes at the end of the leaf spring are formed into the master leaf.? In general, aside from the main leaf, the other leaves are tapered at each end. Sometimes auxiliary or rebound leaves are part of the main spring pack, in which case the auxiliary leaf closest to the main leaf is No. 1, the next closest is the leaves are attached to each other through the center bolt, which is at or near the midpoint along the length of the leaf spring. ? To ensure that leaves remain aligned laterally, several methods can be used, including notches and grooves between leaves or external

MATERIAL AND METHODOLOGY

Spring steels were discovered to be most efficient at approximately 1% carbon content. Individual leaf thickness is specified by the Stubbs or Birmingham gauge, with typical thicknesses ranging between 0.203 to 0.375 in (5.2 to 9.5 mm) (6 to 3/8 or 00 gauge). 1 The material and dimensions should be selected such that each leaf is capable of being hardened to have a fully martensitic structure throughout the entire section Suitable Spring steel alloys include 55Si7, 60Si7, 65Si7, 50Cr4V2, and 60Cr4V2

Table 1. Chemical composition of Semi elliptical leaf spring

Stress Analysis: Evaluating load distribution and fatigue life using simulation      tools like CREO

• Weight Optimization: Reducing unsprung mass for better fuel efficiency and ride comfort.
• Manufacturing Feasibility: Considering ease of fabrication, cost, and availability.
• Performance Testing: Validating durability through real-world testing and cyclic loading experiments.
  1. Manufacturing of leaf spring

Leaf springs are commonly made from spring steel, a high-carbon steel alloy known for its strength and hardness. It can come in bars or coils and is shaped using machines. For parabolic springs, the steel varies in thickness throughout the leaf. The main leaf’s ends form eyes for attachment purposes and can be reinforced with metal. Subsequent leaves are shaped to match the main ones. To enhance its qualities, spring steel undergoes heat treatment. It’s first heated and then rapidly cooled in a process called quenching, which bolsters durability. Next, it’s reheated to a lower temperature and cooled slowly, a process called tempering, which enhances its flexibility and resilience. Forming the Leaves The formation of the leaves in leaf springs is a crucial process that determines the strength, flexibility, and resilience of the spring. Two primary methods are typically employed in the formation of leaf spring leaves: hot forming and cold forming.

Hot forming: This involves heating metal to a high temperature and then shaping it into the desired configuration using intense pressure, forging, or pressing. It’s suitable for creating complex and precise shapes.

Cold forming: This process shapes metal at room temperature using high-pressure forces. Cold forming increases the strength and durability of the finished leaf springs, making it an essential step in the production process.

Heat Treatment and Annealing Heat treatment is essential for enhancing the strength of materials. It involves controlled heating and cooling processes applied to a material, such as metals, to alter its microstructure and properties. Annealing is a heat treatment process used to relieve stress in materials such as metals or glass. It involves heating the material to a specific temperature and then slowly cooling it down, often in a controlled environment. During annealing, internal stresses within the material are reduced or eliminated, resulting in improved mechanical properties and increased durability. The process allows for the redistribution of atoms, reducing defects and restoring uniformity. Shot Peening and Stressing In the context of manufacture leaf springs, shot peening is employed to prolong the fatigue life of the springs by bombarding the surface with high-velocity metallic particles, creating stresses that prevent cracks. Additionally, stress testing is conducted to ensure the springs can handle the intended loads. This involves applying controlled stress that simulates or even exceeds the expected conditions, allowing for evaluation and necessary adjustments to meet the load capacity requirements.  Assembling the Leaves Assembling the leaves is a core step, crucial for vehicle suspension. Here’s a succinct overview of the process:

Layering: Leaves of spring steel are placed on top of each other, starting with the longest at the bottom, decreasing in size upward. This forms the spring’s characteristic curve.

Stacking: Alignment during stacking is essential for efficiency and durability. The leaves must fit together accurately.

Bolting: In the bolting stage of leaf springs manufacturing, the process begins with the positioning of a center bolt, inserted through pre-drilled holes in the leaves. Once in place, the bolt is then tightened, an action that compresses the leaves and helps to maintain their alignment. After securing, final adjustments are made to the assembled leaves. This careful fine-tuning ensures correct alignment and achieves the desired spring shape, solidifying the integral structure of the leaf spring.

RESULT AND DISCUSSION

The design of the leaf spring is done in CREO software. All the leaves, clamps and bolt are designed separately in the part drawing and are assembled in the assembly drawing section in CREO. The leaves are assembled by giving surface contact between the bottom surfaces of one leaf to the top surface of the other leaf. In this way all the 3 leaves are assembled in the CREO, after that the clamps and bolts are assembled in the Semi Elliptical leaf spring. Computer-aided design (CAD) modelling of a Semi Elliptical leaf spring was performed using CREO in Part Design Workbench. It is essential to use the developed CAD model as a physical specimen prior to the production of a prototype.

2.1. Design parameters for Semi elliptical leaf spring:

Here Weight and initial measurements of Electric Tow Tractor.

Gross vehicle weight = 3550 kg

Front axle weight = 1600 kg

Taking factor of safety (FS) = 1.4

Acceleration due to gravity (g) = 9.8m/s²

There for; Total Weight (W) = 1910*9.8*1.4 = 26740 N

A single leaf spring corresponding to one of the wheels in front axle takes up Weight (F) = 26740/2 = 13370 N 21

Fig 1. Meshing of semi elliptical

Fig 2. Load and constraints

2.2. Geometry and mesh

Geometry refers to the 3D model of the part or assembly you want to analyze. This model can be created within Ansys using tools like Ansys Design Modeler or imported from external CAD software. Preparing the geometry involves simplifying or "defeaturing" the model to remove unnecessary details that don't affect the simulation results but can increase computational time Meshing is the process of dividing the geometry into smaller, finite elements. These elements can be tetrahedral or hexahedral (hex), among other shapes. The quality of the mesh significantly impacts the accuracy and efficiency of the simulation. A good mesh should balance between having enough elements to capture the details of the geometry and keeping the number of elements manageable to reduce computation time2.3. Structural Simulation on Existing Leaf Spring

• Structural simulation of an existing leaf spring in Creo involves using Finite Element Analysis (FEA) to evaluate stress distribution, deflection, and durability under various loads. Creo provides tools for designing, analyzing, and optimizing leaf springs, ensuring better performance and material efficiency.
• A research paper on designing and analyzing leaf spring suspension systems using Creo Parametric, discussing strain energy and optimization techniques.

• A Creo Ansys Simulation guide, explaining how to model stiffness in connections, including spring behavior and constraints.

Table 1. Load Condition on Existing leaf Spring

Fig 3 Stress for 1600 Kg

Fig 4 Stress for 2400 Kg

Fig 5 Stress for 3200 Kg

2.4. Structural Simulation on New Leaf Spring

Table 2 Load Condition on New leaf Spring

Fig 6 Stress for 1600 Kg

Fig 7 Stress for 2400 Kg

Fig 8 Stress for 3200 Kg

Table 3 Comparison of Existing and new leaf spring

Fig 9 Comparison of Existing and new leaf spring