I just started working with sheet metal in Inventor () and am currently modeling the baseplate of my circular saw as I intend to design a dust collection shroud for it.
If you want to learn more, please visit our website.
I've been able to model the part with a sketch; I formed a face and changed the gauge of the metal. So far so good. I went to bend up the edges with the flange tool and it seems I cannot flange the corners. The straight edges flange properly but the corners stay flat.
Obviously my design intent is incorrect and I am aware that I'm asking a question here that will likely resolve naturally as I continue my training, but I'd like to ask if there's a known good resource to learn this aspect of sheet metal forming.
I have tried fillets in the sketch and also experimenting with the flange and corner round tools and pretty much just end up with flat, un-flanged corners.
It also occurs to me that since this circular saw baseplate is formed by stamping, the only solution may require a boolean operation with a standard solid part.
Picture attached and thanks to anyone who can steer me in the right direction.
Inventor
Sheet Metal Fabrication is the process of forming parts from a metal sheet by punching, cutting, stamping, and bending.
3D CAD files are converted into machine code, which controls a machine to precisely cut and form the sheets into the final part.
Sheet metal parts are known for their durability, which makes them great for end use applications (e.g. chassis). Parts used for low volume prototypes, and high volume production runs are most cost-effective due to large initial setup and material costs.
Because parts are formed from a single sheet of metal, designs must maintain a uniform thickness. Be sure to follow the design requirements and tolerances to ensure parts fall closer to design intent and cutting sheets of metal
Bend line– The straight line on the surface of the sheet, on either side of the bend, that defines he end of the level flange and the start of the bend.
Bend radius – The distance from the bend axis to the inside surface of the material, between the bend lines.
Bend angle – The angle of the bend, measured between the bent flange and its original position, or as the included angle between perpendicular lines drawn from the bend lines.Sometimes specified as the inside bend radius. The outside bend radius is equal to the inside bend radius plus the sheet thickness.
Neutral axis – The location in the sheet that is neither stretched nor compressed, and therefore remains at a constant length.
K-factor – The location of the neutral axis in the material, calculated as the ratio of the distance of the neutral axis T, to the material thickness t. The K-factor is dependent upon several factors (material, bending operation, bend angle, etc.) and is greater than 0.25, but cannot exceed 0.50. K factor = T/t
Bend allowance – The length of the neutral axis between the bend lines or the arc length of the bend. The bend allowance added to the flange lengths is equal to the total flat length.
The K-factor is the ratio between the the neutral axis to the thickness of the material.
Importance of the K-factor in sheet metal design
The K-factor is used to calculate flat patterns because it is related to how much material is stretched during bending. Therefore it is important to have the value correct in CAD software. The value of the K-factor should range between 0 – 0,5. To be more exact the K-factor can be calculated taking the average of 3 samples from bent parts and plugging the measurements of bend allowance, bend angle, material thickness and inner radius into the following formula:
Some basic K-factor values are shown here. Use these as a guideline.
Springback
When bending a piece of sheet metal, the residual stresses in the material will cause the sheet to springback slightly after the bending operation. Due to this elastic recovery, it is necessary to over-bend the sheet a precise amount to achieve the desired bend radius and bend angle. The final bend radius will be greater than initially formed and the final bend angle will be smaller. The ratio of the final bend angle to the initial bend angle is defined as the springback factor, KS. The amount of springback depends upon several factors, including the material, bending operation, and the initial bend angle and bend radius.
Dimensions:
To prevent parts from fracturing or having distortions, make sure to keep the inside bend radius at least equal to the material thickness
Bend Angles:
A +/- 1 degree tolerance on all bend angles is generally acceptable in the industry. Flange length must be at least 4 times the material thickness.
Rule of thumb
It is recommended to use the same radii across all bends, and flange length must be at least 4 times the material thickness.
Material Thickness, t
The thickness of the material is not proportional to the tonnage like the v opening. Doubling the thickness does not mean doubling the tonnage. Instead the bending force is related by the square of the thickness. What this means is that if the material thickness is doubled the tonnage required increases 4 fold.
Work Piece Length, L
Like the v opening the tonnage required is directly related to the length of the work piece. Doubling the work length means doubling the required tonnage. It should be noted that when bending short pieces, under 3” in length, the tonnage required may be less than that which is proportional to its length. Knowing this can prevent damaging a die.
Air Force Bending Chart
The Air Force Bending chart is a chart showing the tonnage used for bending different thickness sheet metal. It is useful for sheet metal designers as it specifies the bend radius and tooling to be used for different thicknesses. It is shown here for mild steel. Designers can use this as a guide when designing the minimum flange length possible with the tooling for different V blocks as well as the bend radius. The following charts are based on the Armada Air Force bend guide.
When a bend is made too close to a hole the hole may become deformed. Hole 1 shows a hole that has become teardrop shaped because of this problem.
Beiouli contains other products and information you need, so please check it out.
To save the cost of punching or drilling in a secondary operation the following formulas can be used to calculate the minimum distance required:
For a slot or hole < 25mm in diameter the minimum distance to Hole 2 centre:
D = 2t + r
As a rule of thumb the distance from the outside of the material to the bottom of the cutout should be equal to the minimum flange length as prescribed by the air bend force chart
D = 2,5t + r
When using a punch press, or laser cutting, holes should never be less than that of the material thickness.
Laser cutting is a type of production that uses a laser to cut different metals. The laser has a high energy beam which easily burns through the material. Laser cutting can be used on materials such as metal, aluminium, plastic, wood, rubber, etc. Lasers use computer numerically controlled programming (CNC) to determine the shape and position ls of the cutouts. Material thicknesses of up to 20mm can be lasercut. There are advantages and disadvantages in using lasercutting. CO2 lasers are more traditional, and can cut thicker materials but do not deliver such an accurate cut as fibre lasers. Fibre lasers can generally cut thinner materials and have much higher cutting speeds than CO2 .
Advantages and Disadvantages
Advantages of lasercutting over cutting mechanically include better workholding, reduced workpiece contamination, better precision and reduced chance of warping as the heat affected zone is small. Some disadvantages are that lasercutting does not always cut well with some materials (for example not all aluminium) and it is not always consistent. Despite the disadvantages lasercutting is highly efficient and cost effective.
Material Restrictions
Materials that are not suitable for lasercutting include mirrored or reflective materials, Masonite boards, composites containing PVC.
Acceptable Materials
Generally the following materials are suitable for lasercutting: metal, stainless steel, some thicknesses of aluminium, wood and some plastics.
Localized hardening
Localised hardening takes place on the edges where the where the laser has cut. This hardening produces a durable and smooth edge without the need for finishing after using the laser cutter
Distortion
A heat-affected zone (HAZ) is produced during laser cutting . In carbon steel, the higher the hardenability, the greater the HAZ. Distortion from laser processing is a result of the sudden rise in temperature of the material near the cutting zone. Distortion is also created by the rapid solidification of the cutting zone. In addition, distortion also can be attributed to the rapid solidification of material remaining on the sides of the cut.
During laser cutting a portion of the material is burnt away when the laser cuts through, leaving a small gap. This ‘gap’ is known as the laser kerf and ranges from 0.08 – 0.45mm depending on the material type, thickness and other conditional factors. A minimum distance of 1-2mm between parts needs to be left to avoid accidental crossover cutting.
It is also advised to keep parts 2-5mm away from the edge of the material due to some sheets being warped or slightly off in their sizing. One should always cut parts in the boundary of the sheet size and not use the sheet edges as a border.
Curl Feature Guidelines
Curling sheet metal is the process of adding a hollow, circular roll to the edge of the sheet. The curled edge
provides strength to the edge and makes it safe for handling. Curls are most often used to remove a sharp
untreated edge and make it safe for handling. It is recommended that: The outside radius of a curl should not be smaller than 2 times the material thickness.
A size of the hole should be at least the radius of the curl plus material thickness from the curl feature. A bend should be at least the radius of the curl plus 6 times the material thickness from the curl feature
Hemming is nothing but to fold the metal back on itself. In Sheet Metal hems are used to create folds in sheet metal in order to stiffen edges and create an edge safe to touch. Hems are most often used to remove a sharp untreated edge and make it safe for handling. Hems are commonly used to hide imperfections and provide a generally safer edge to handle. A combination of two hems can create strong, tight joints with little or minimal fastening. Hems can even be used to strategically double the thickness of metal in areas of a part which may require extra support. It is recommended that:
For tear drop hems, the inside diameter should be equal to the material thickness.
Keep hole and slot diameters at least as large as material thickness. Higher strength materials require larger diameters.
Clearances
Holes and slots may become deformed when placed near a bend. The minimum distance they should be placed from a bend depends on the material thickness, the bend radius, and their diameter. Be sure to place holes away from bends at a distance of at least 2.5 times the material’s thickness plus the bend radius. Slots should be placed 4 times the material’s thickness plus the bend radius away from the bend. Be sure to place holes and slots at least 2 times the material’s thickness away from an edge to avoid a “bulging” effect. Holes should be placed at least 6 times the material’s thickness apart.
Bend notches
Notching is a shearing operation that removes a section from the outer edge of the metal strip or part. In case, distance between the notches to bend is very small then distortion of sheet metal may take place. To avoid such condition notch should be placed at appropriate distance from bend with respect to sheet thickness. Notching is a low-cost process, particularly for its low tooling costs with a small range of standard punches.
Clearances
Notches must be at least 3.175mm away from each other. For bends, notches must be at least 3 times the material’s thickness plus the bend radius. Tabs must have a minimum distance from each other of 1mm or the material’s thickness, whichever is greater.
Recommendations for Notch Feature:
Notch width should not be narrower than 1.5 * t.
Length of notches can be up to 5 * t. Recommended corner radius for notches should be 0.5 * t.
Notches must be at least the material’s thickness or 0.04”, whichever is greater, and can be no longer than 5 times its width. Tabs must be at least 2 times the material’s thickness or 0.126”, whichever is greater, and can be no longer than 5 times its width.
If you want to learn more, please visit our website flange corner.