Advanced Sheet Metal Design Using NX Cad Challenge_1_Casing Design

Casing Design

Objective

Create a Sheet Metal Casing design using Siemen NX cad software.

Introduction

Sheet Metal - Sheet metal is metal formed into thin, flat pieces, usually by an industrial process.

There is no clear definition for it. As a rule, it is understood to be a flat piece of metal whose width is significantly greater than its thickness.

If the sheet is less than 3 millimeters thick, it is referred to as thin sheet.

If it is 3 millimeters thick or more, it is referred to as heavy sheet.

Manufacturing Process - There are cold-rolled and hot-rolled sheets,

Hot rolled material is typical for thicker plates. The surface is more coarse-pored than cold-rolled material and carries a rolling skin / scale layer. If the mill scale is not removed, these plates do not require oiling to protect them from corrosion.

Thinner plates are usually cold rolled. The tolerances are smaller and the surfaces finer. Steel sheet in particular is protected from corrosion by pickling and oiling before it goes from the steel mill to the sheet processor.

How to Machine Sheet Metal

In order to turn sheet metal into a usable finished product, there are various processing methods.

Punching in punching, the sheet metal is punched out with a manually or automatically operated press, punching machine or punching tool and thus separated. Punching is mainly used in the production of small components from flat metal strips.

Laser cutting in this method of cutting, the heat of a laser beam ensures that the sheet metal is divided. As a very flexible tool, the laser is particularly suitable for processing thin sheets. If fine kerfs and high quality are required, laser cutting is the most common method in flexible sheet metal processing.

Plasma cutting This process belongs to the methods of thermal cutting. A plasma volume flow is used here, the heat of which leads to local material liquefaction. The high kinetic energy of the plasma volume flow blows out the liquefied material. The process is usually used for sheet thicknesses between 10 and 50 millimeters.

Flame cutting (oxyacetylene cutting) In this cutting process, the sheet is heated locally to ignition temperature by a fuel gas-oxygen flame. The supply of oxygen creates a kerf at which the sheet is then cut. If metals with large material thicknesses are to be cut, flame cutting is the most common method.

Bending Press braking or bending describes the forming of sheet metal. In this process, the sheet metal is placed on the die of a so-called press brake. A tool then moves down onto the workpiece from above and bends the desired angles into the component.

Round rolling round rolling is also a frequently used forming process. In this process, the sheet is usually plastically deformed over three rolls in order to bend it round.

Roll forming This process is also one of the methods of forming. In this process, the sheet is unwound from a coil and passed through several pairs of rolls arranged in a row until it is bent into the desired shape. This process is generally used for elongated profiles in high volumes.

Deep drawing in deep drawing, the sheet metal is specifically pressed into the desired shape by a tool. As a rule, tools act on the sheet metal through automatic punching machines or forming presses. As the tooling costs often incur considerable one-off costs in production, the processes are often used for high volumes.

Two or more sheets are to be joined together, hemming, riveting, soldering and welding are the usual methods of joining.

Common Materials

Pretty much all the common engineering metals are also used in the form of sheets. Some of them are carbon steel, stainless steel, copper and aluminum. Choosing the right one for application and requirements of your product.

Sheet Metal Cutting/Shearing Defects & Solutions

Sheet metal cutting refers to the application of a significant force on the sheet which eventually causes it to break into parts. The most common method of cutting is by shearing, in which a shearing force greater than the ultimate shear strength of the material is applied, causing it to fail and separate at that location.

Common defects include

Burred and Deformed Edges

Burred edges are sharp, uneven metal pieces that remain attached to a sheared metal workpiece. They usually arise due to blunt blades, or improper positioning thereof. Too large a clearance between blades will cause them to tear instead of shear, while a smaller clearance will prevent the blades from cutting through the material, producing burrs.

Similarly, deformed edges are formed due to faulty clamp pressures, in addition to the improper positioning of blades.

To prevent this, the shear machine’s manual can be referred to obtain the correct clearance and clamp pressure according to the material type and thickness.

Twisting

After completing a shearing process, the metal may have experienced some twisting along its axis. This is caused by cutting too narrow strips or using the incorrect rake angle. This can be avoided by adjusting the rake angle depending on the sheet metal’s properties, geometry, and cutting parameters.

Cambering

Cambering is observed when the sheet metal workpiece has a varying thickness along its width. This occurs when it moves in a horizontal direction, but without twisting or lifting along its edges. The result is a concave, convex, and triangular-shaped metal. This defect can be minimized early on by shifting the direction of the metal grains, and by changing the rake angle.

Bowing

Bowing occurs when the edges slightly rise from the plane due to inappropriate shearing. It is commonly observed in long, narrow, thin sheets. To overcome this, the rake angle should be decreased as much as possible, and the sheet metal must be held with back support.

Sheet Metal Stamping Defects & Solutions

The sheet metal stamping process is a cold-forming manufacturing process where a die is used on a press machine to punch an impression on a metallic blank shape, thus forming plastic deformation. This process may also be accompanied by other forming tools to obtain a completed piece or as an intermediate step.

Splits

Sometimes when the metal layers are pushed past their workability limits, they start to thin until the flat layer tears along the weakest area. Such defects are known as ‘necking’ or ‘splitting’ in the sheet metal stamping process.

To ensure this does not occur, forming simulation software should be used to analyze the sheet before the operation is started. Furthermore, examining the form radius and depth settings, the type, and thickness of the material, and the heat treatment techniques can also help to avoid these defects.

Wrinkles

When the compressive strain conditions applied by the processing equipment push the sheet metal upon itself, the linear force is crushed inwards until a wrinkled flange is obtained and the internal geometry is damaged.

Such defects can be countered by stretching or drawing the sheets instead of forming them. Moreover, draw beads, draw binders, and pads can be utilized when the sheet has an intricate geometric profile. Furthermore, draw beads help control the flow of metal into the die cavity.

Spring back

When the bend radius falls below the set value imposed by the bending equipment, the desired shape is not achieved. This is known as spring back, or final part deviation due to an incorrect process.

To correct these defects, include an overbend or overcompensation adjustment. However, doing so does not eliminate the elastic deformation error, increasing the stiffness of the part by positive stretching.

Sheet Metal Bending Defects & Solutions

Sheet metal bending is an important sheet metal process due to its ability to draw a variety of part geometries without tooling, as well as fast lead times, high repeatability, and automation. It also allows products to be manufactured from one piece of metal, utilizing plastic deformation, as opposed to multiple pieces joined together via welding or riveting, thus resulting in lower costs, improved strength, and simplified assembly.

Cracks in the bending angle

The two major reasons for cracks in a drawn part are poor metal pliability and having a very small bending radius.

To avoid the occurrence of these defects, use softer metals, or increase their malleability by heating and then cooling them slowly.

Unstable bending angle

Primary causes for such defects are insufficient material pressure and irregular bending pressure causing irregular compressive buckling. Asymmetric convex-concave die fillet may also contribute to this problem.

To solve this, increase the jacking force and balance out the clearance in the convex-concave die fillet.

Hole deformation

The location of the hole can be deformed by the friction between the concave die surface and the outside surface during the bending process.

Such defects can be resolved by raising the pressure of the ejector plate or by adding a hard spot on this plate to increase the friction between the aforementioned surfaces so that they do not slide.

Uneven concave piece bottom

Such defects are usually caused by the use of an ejection device, due to insufficient force or uneven material.

Therefore, ensure that the ejection device is set to the correct measure of force, or removed altogether and that the material is evenly leveled before the start of the bending process.

Non-parallel bend to the middle of the holes

This defect is caused by the bending height being less than the minimum bending height limit, which causes the curve to expand and become distorted.

Simply raising the height of the bending piece or the material will solve these types of defects.

Sheet Metal Welding Defects & Solutions

Welding is commonly used to join two or more pieces of sheet metal together. Be it MIG Welding (Gas Metal Arc Welding), TIG Welding (Gas Tungsten Arc Welding), Shielded Metal Arc Welding (SMAW), or Flux Cored Arc Welding (FCAW), several defects may be faced if the proper technique is not used.

Common defects in the sheet metal welding process include

Spatter

Spatter occurs when molten material droplets are formed near the welding arc. It is usually caused by high currents, wrong polarity, or insufficient gas shielding.

To avoid it, reduce the current and arc length and increase the torch-to-plate angle. Cleaning the gas nozzle can also help.

Porosity

These defects are caused when hydrogen, nitrogen, and oxygen are absorbed in the molten weld pool. Upon solidification, they are trapped in the weld. Grease, moisture, paint, and rust can also cause porosity.

To prevent this issue, ensure the plate edges are clean and dry, use fresh welding materials, and check the welding torch for leakages.

Undercut

Undercut occurs when high voltages or long arc lengths are used. Utilizing an incorrect electrode or one that is too large relative to the thickness, as well as a fast travel speed of the torch, can also cause this problem.

Such defects can be averted by using an electrode that is just the right size, ensuring that the torch is moved slowly, and avoiding holding near the vertical plate if a horizontal fillet weld is being made.

Cracks

Cracks can form on the weld when the internal stresses are greater than the strength of the weld or base metal (or both). They can propagate over time, and therefore, must be addressed immediately.

These defects can be avoided by carefully cleaning, filing, grinding, and deburring the edges of the metal plates so that they fit together well. Ensuring the temperature is right while reheating both sides of the joint also helps.

Other Common Defects in Sheet Metal Surfaces

Apart from sheet metal forming processes, other common defects can occur during the manufacturing process.

For example, some of the common include surface scratches, contamination, dents, and pinholes. Also, non-uniformity could occur due to high tensile stresses or compressive buckling during the sheet metal fabrication process.

Sometimes, controlling these defects can be difficult, and often requires special attention during the process.

 CASHING DESIGN USING NX – CAD

Design methodology / approach

Description

The important tools which used during designing of Casing are as follow:

Sketch - This is used to create a basic sketch of the design on selecting the desired plane, then later it can be modeled for the requirement.

In the sketch 1^st draw rectangle of 60mm long and 50mm wide.

Tab – Use to Create base feature by extruding a sketch along a vector by a thickness value or adds a material to a plane face.

The thickness of the sheet is 1mm.

Normal Cutout - This feature is used to cut the portions of the sheet metal Perpendicular to the sheet metal surface.

By Using normal cutout remove (Cut) one side of sheet as rectangle shape 40mm long and 5 mm wide.

Bend - bend the sheet metal along the sketched curve upon our requirement.

As shown in the figure Both sides of the tab are bended at a length of 10 mm and 1 mm bend radius.

 Flange - A flange feature consists of a face and bend connected to an existing face along a straight edge. To add a flange feature, we select one or more edges, and specify the size and position of the material added.

Four flanges are made on the two sides of the casing Two towards inside and the others towards outside with a length of 5 mm.

Break Corner – Break Corner is use to remove the sharp corner of the sheet metal edges. Basically, we can say it is use to provide fillet (Blend) or chamfer to the sheet.

Unbend – It is a powerful tool basically use for analyzing the sheet metal features, dimensions, and also use for creating some features on sheet which is easily create when sheet is flat.

Hole – Hole is a feature which is use to create holes and standard tapping (Metric, BSW, BSP) on the sheet or solid model.

Dimple - Dimple are used to add strength and rigidity to the flat sheet metal panels. It is an easy way to give strength of sheet.

Beads – Bead is similar feature like dimple the only difference is that by using dimple we lift an area while in bead we lift the contour of the sketch. It also added to strengthen the component. beads are also use to give strength and rigidity to the flat sheet.

Rebend - Rebend is used to restore the unbend feature to its previous bent state along with any features added after the unbend feature. This is done by using rebend feature and selecting all the bends carefully in order they unbended.

Flat Pattern - Flat pattern feature allows us to covert 3D sheet metal component into 2D form in Siemens NX software. By using this flat pattern feature we can easily avoid error like interference or collision.

Different views of Casing

Isometric View

Top View

Front View

Side View

Drafting

Conclusion:

1 - We learn about sheet metal workbench.

2 – Commands of sheet metal and how to use it.

3 – Learn designing process of sheet metal component.

4 – By doing this project understand and develop ideas how to proceed to create a sheet metal part. Improve thinking process for developing sheet metal parts.