Static-Structural Analysis Of Rolling Operation

ABSTRACT

This report presents the Static-Structural analysis of rolling operation using Ansys-Workbench. Rolling is one of the most widely used metal forming process for converting metal ingots into sheet, slabs, billets etc. by reducing their cross-sectional thickness. In the following analysis, a work piece made up of copper NL material is simulated to undergo rolling operation and various mechanical responses thereby generated are recorded.

Simulation result showed the development of high Equivalent stress of magnitude 3317 MPa & showed the deformation of approx. 6mm along the widthwise of the workpiece. A saturation curve trend is observed in almost all of the mechanical responses, however the stress developed is very & is disastrous to both roller & finishing of workpiece.Therefore, it is always recommended to perform rolling process in very stages so as to avoid early failure of equipment & improving final finish of workpiece.

INTRODUCTION

Rolling is a type of metal forming process in which workpiece is made to pass through constricted space between the two rollers rotating in opposite directions. During the process, workpiece is plastically deformed and come out of the machine with reduced uniform thickness. This process is accomplished in rolling mills. A rolling mill is a complex machine having two or more working rollers, supporting rollers, roll stands, drive motor, reducing gear, flywheel, coupling gear etc.

Depending upon the operating temperature there are two types of rolling processes:

1. Hot Rolling: If operating temperature is above re-crystallization temperature.
2. Cold Rolling: If process is carried out below re-crystallization temperature.

Applications

• Hot rolling is used mainly to produce sheet metal or simple cross-sections, such as rail tracks.
• Other typical uses are in producing, Truck frames, Automotive clutch plates, wheels and wheel rims, Pipes and tubes, Water heaters, Agricultural equipment, Strappings, Stampings, Compressor shells, Metal buildings, Railroad hopper cars and railcar components, Doors and shelving, Disc, Guard rails for streets and highways etc.
• Typical uses for cold-rolled steel include metal furniture, desks, filing cabinets, tables, chairs, motorcycle exhaust pipes, computer cabinets and hardware, home appliances and components, shelving, lighting fixtures, hinges, tubing, steel drums, lawn mowers, electronic cabinetry, water heaters, metal containers, fan blades, frying pans, wall and ceiling mount kits, and a variety of construction-related products.

In the following report, workpiece of copper NL material is made to pass through rollers rotating in opposite direction. Fig. shows the geometry of the workpiece

Fig. Roller and Workpiece Geometry

Various Mechanical responses i.e. Equivalent Stress, Equivalent Plastic Strain, deformation occurred in the workpiece are recorded and presented in this report.

OBJECTIVE

To simulate the rolling operation on a workpiece of copper material in 14 steps and ensure the workpiece displacement by 90mm. And figure out,

1. Equivalent stress for the whole setup
2. Equivalent Plastic strain for the workpiece
3. Directional Deformation in the Z axis for the workpiece
4. Prove that the workpiece has displaced by 90mm

ANALYSIS PROCEDURE

1. Material Selection: Copper NL material is assigned to the workpiece while rollers are assigned with Structural Steel.

Properties of Copper NL material

Properties of Structural Steel material

2. Geometry: Geometry of the workpiece is directly imported into the workbench from the available sources.

Fig. Geometry (Rollers and Workpiece) Fig. Thickness of Workpiece

3.Meshing: Program controlled mesh is generated with default element size. However, body sizing for workpiece part is done with mesh element size of 2mm.

Fig. Meshed Geometry

STATISTICS

Total No. of Mesh Elements : 1629

Total No. of Nodes : 9321

Avg. Mesh Element Quality : 0.93

Fig. Mesh Element Quality

*Further mesh refined is not done in order to reduce the computational time and avoid academic version limitation.

4. Boundary Condition or Setup:

• To simulate the rotational motion of rollers, revolute joints are assigned to the rollers thereby allowing only axial-rotation. Rotation (degree) is provided as boundary condition to the rollers in 14 incremental steps.

Fig. Revolute Joint

Fig. Rotation (in degrees) Boundary Condition

• Workpiece is provided with displacement boundary condition incrementing from 0mm to 90mm in 14 steps. Displacement is provided in such a manner that workpiece perpendicularly traverse in the space between the rollers.

Fig. Displacement Boundary Condition

• A frictional contact with frictional coefficient of 0.2 is established between the roller and workpiece interface.

Fig. Frictional contact between Roller & Worpiece interface

In analysis setting, following changes are made in order to support the convergence and reduce the computational time.

Fig. Analysis Settings

RESULTS & DISCUSSION

At the end of 14th step, results are presented in the report.

1.Equivalent stress for the whole setup

Fig. Stress Distribution in the Setup Max. Equivalent Stress = 3317 MPa

Fig. Equivalent Stress Vs Time Steps Graph

Legends : Green – Max. Stress

Blue - Avg. Stress

Red - Min. Stress

From the results, an increasing trend in magnitude of Equivalent Stress is observed which later becomes asymptotic. Some turbulence behaviour in the starting steps of simulation is also observed in the graph between Max. Equivalent stress and Time steps.

The initial increase in the magnitude of Equivalent Stress is attributed to the fact that, in the beginning there is increase in material amount, which get compressed in the gap between the rollers. This causes more material to resist the deformation & hence high values of Stresses develops. In addition, the sliding contact status between the roller-workpiece interfaces during initial steps causes the origination of the turbulence behaviour in the starting & leads to development of unstable high stresses. Later on this geometry becomes uniform & therefore no such abrupt changes occurs, but because of the accumulation of deformed material in uncompressed side (i.e. region just before the rotating rollers) the magnitude of stress developed increases further however this accumulation becomes constant in the later steps.

2.Equivalent Plastic strain for the workpiece

Fig. Equivalent Plastic Strain occured in the workpiece Max. Plastic Strain = 1.9486

Fig. Equivalent Plastic Strain vs Time Steps

Legends : Green – Max. Plastic Strain

Blue - Avg.

Red - Min.

Results showed the similar behaviour of development of Equivalent Plastic Strain as in case of Equivalent Stress. With the increase in the pressure between the gap more & more plastic deformation occurs & the same is observed in the graph.

3.Directional Deformation of the workpiece in Z-axis

Fig. Directional Deformation occured in the workpiece in Z-axis i.e. widthwise

Max. Widthwise deformation = 6.2058 mm

Fig. Deformation vs Time Step graph

Legends : Green – Max. Deformation (i.e. on one side of workpiece)

Blue - Avg. ( center position)

Red - Min. ( other side)

Results showed the deformational increase in the width of the workpiece by a magnitude of approx. 6 mm in both the sides.

Since, workpiece is subjected between the gap of rotating rollers, the only space left to deform because of rolling operation pressure is to deform width wise although lengthwise is also possible but because the workpiece is driven in that direction so only little bit deformation take place in lengthwise direction.

4.Directional Deformation of the workpiece tip in Y-axis

Fig. Directional Deformation of Workpiece tip in Y-axis (length-wise direction)

Result, shows the directional deformation of the workpiece tip along the lengthwise direction. It is observed that the way in which deformation occurs is almost exactly similar to the boundary displacement condition hence confirming the displacment of workpiece by 90 mm.

ANIMATION