AIR BENDING
Air Bending is a bending process in which the punch touches the work piece and the work piece does not bottom in the lower cavity. As the punch is released, the workpiece springs back a little and ends up with less bend than that on the punch (greater included angle). This is called spring-back.
The amount of spring back depends on the material, thickness, grain and temper.The spring back will usually range from 5 to 10 degrees. The same angle is usually used in both the punch and the die to minimize set-up time. The inner radius of the bend is the same as the radius on the punch.
In air bending, there is no need to change any equipment or dies to obtain different bending angles because the bend angles are determined by the punch stroke. The forces required to form the parts are relatively small, but accurate control of the punch stroke is necessary to obtain the desired bend angle.
Total Fabrication Solution under one roof.
Phone: +91 22 2764 1236 / 63
Email: info@jjelectrofab.com
Web: www.jjelectrofab.com
Address: Plot No. R-885, M.I.D.C, Rabale
Navi Mumbai – 400701. India
BOTTOMING
Bottoming is a bending process where the punch and the work piece bottom on the die. This makes for a controlled angle with very little spring back. The tonnage required on this type of press is more than in air bending. The inner radius of the work piece should be a minimum of 1 material thickness.
In bottom bending, spring-back is reduced by setting the final position of the punch such that the clearance between the punch and die surface is less than the blank thickness. As a result, the material yields slightly and reduces the spring-back.Bottom bending requires considerably more force (about 50%~60% more) than air bending.
COINING
Coining is a bending process in which the punch and the work piece bottom on the die and compressive stress is applied to the bending region to increase the amount of plastic deformation. This reduces the amount of spring-back. The inner radius of the work piece should be up to 0.75 of the material thickness.
Total Fabrication Solution under one roof.
Phone: +91 22 2764 1236 / 63
Email: info@jjelectrofab.com
Web: www.jjelectrofab.com
Address: Plot No. R-885, M.I.D.C, Rabale
Navi Mumbai – 400701. India
Sunday, June 28, 2009
Thursday, June 25, 2009
Sheet Metal Bending: The fine-art
Bending is a manufacturing process by which metal can be deformed by plastically deforming the material and changing its shape. The material is stressed beyond its yield strength but below its ultimate tensile strength. There is little change to the materials surface area. Bending generally refers to deformation about one axis only.
Bending is a flexible process by which a variety of different shapes can be produced though the use of standard die sets or bend brakes. The material is placed on the die, and positioned in place with stops and/or gages. It is held in place with hold- downs. The upper part of the press, the ram with the appropriately shaped punch descends and forms the v-shaped bend.
Bending is done using Press Brakes. Press Brakes can normally have a capacity of 20 to 200 tons to accommodate stock from 1m to 4.5m (3 feet to 15 feet). Larger and smaller presses are used for diverse specialized applications. Programmable back gages, and multiple die sets currently available can make bending a very economical process.
BENDING ALLOWANCES
When sheet metal is bent, the inside surface of the bend is compressed and the outer surface of the bend is stretched. Somewhere within the thickness of the metallies its Neutral Axis, which is a line in the metal that is neither compressed nor stretched.
What this means in practical terms is that if we want a work piece with a 90 degree bend in which one leg measures A, and the other measures B, then the total length of the flat piece is NOT A + B as one might first assume. To work out what the length of the flat piece of metal needs to be, we need to calculate the Bend Allowance or Bend Deduction that tells us how much we need to add or subtract to our leg lengths to get exactly what we want.
The location of the neutral line varies depending on the material itself, the radius of the bend, the ambient temperature, direction of material grain, and the method by which it is being bent, etc. The location of this line is often referred to as the K factor.
K-factor is a ratio that represents the location of the neutral sheet with respect to the thickness of the sheet metal part.
REVERSE ENGINEERING THE K-FACTOR
First, cut a strip of material and measure its length and thickness as accurately as possible. The width of the strip is not that critical but generally somewhere around100mm (4 inches) or so usually does the trick.
Then, bend the strip to 90 degrees, and measure its Length X and Length Y as shown in the diagram below.
NOTE: that it is very important to bend the sample piece in exactly the same manner as you plan to bend your real pieces, so that whatever you measure now becomes reproducible later.
The bend radius can be extremely difficult to measure accurately but, in this case, is not critical (within reasonable limits, of course!). The reason it is not critical is that what we are interested in is a number to use in our CAD program that, with the bend radius used in our CAD program, will produce the results you are measuring in real life.
In other words the K-factor you calculate now will take into account any small inaccuracies in the bend radius measurement and compensate for it. If, for example,we are using a Bend radius of 0.5 in our CAD program, it does not matter if our real tooling radius is actually 0.4, as the K-factor, which was worked out from our real tooling, corrects for this. The only implication of this is that we may occasionally get a K-factor that seems odd (higher than 0.5, for example) if our real radius is very different from our CAD program radius. Remember though that most CAD programs such as Solidworks only accept K-factor values from 0 to 1, so if the calculated K-factor is outside these limits, then you may need to double-check your numbers.
The correct K-factor to use in your CAD program can now be calculated as follows:
BendDeduction = Length X + Length Y - Total Flat Length
OutSideSetBback = (Tan(BendAngle / 2)) * (thickness + BendRadius)
BendAllowance = (2 * OutSideSetBback) BendDeduction
K-Factor = (-BendRadius + (BendAllowance / (ลก * BendAngle / 180))) / thickness
Using this method will produce the most acceptable results other than by using a bend table.There are however also some general rules of thumb that can be used for K-factors that will generally give results that are within acceptable tolerances for non-precision sheet metal work. Some of these sample K-factors are given in the methods of bending section below.
Total Fabrication Solution under one roof
CONTACT
Phone: +91 22 2764 1236 / 2764 1263
Email: sales@jjelectrofab.com
Web: www.jjelectrofab.com
Address: Plot No. R-885, M.I.D.C, Rabale
Navi Mumbai – 400701. India
Bending is a flexible process by which a variety of different shapes can be produced though the use of standard die sets or bend brakes. The material is placed on the die, and positioned in place with stops and/or gages. It is held in place with hold- downs. The upper part of the press, the ram with the appropriately shaped punch descends and forms the v-shaped bend.
Bending is done using Press Brakes. Press Brakes can normally have a capacity of 20 to 200 tons to accommodate stock from 1m to 4.5m (3 feet to 15 feet). Larger and smaller presses are used for diverse specialized applications. Programmable back gages, and multiple die sets currently available can make bending a very economical process.
BENDING ALLOWANCES
When sheet metal is bent, the inside surface of the bend is compressed and the outer surface of the bend is stretched. Somewhere within the thickness of the metallies its Neutral Axis, which is a line in the metal that is neither compressed nor stretched.
What this means in practical terms is that if we want a work piece with a 90 degree bend in which one leg measures A, and the other measures B, then the total length of the flat piece is NOT A + B as one might first assume. To work out what the length of the flat piece of metal needs to be, we need to calculate the Bend Allowance or Bend Deduction that tells us how much we need to add or subtract to our leg lengths to get exactly what we want.
The location of the neutral line varies depending on the material itself, the radius of the bend, the ambient temperature, direction of material grain, and the method by which it is being bent, etc. The location of this line is often referred to as the K factor.
K-factor is a ratio that represents the location of the neutral sheet with respect to the thickness of the sheet metal part.
REVERSE ENGINEERING THE K-FACTOR
First, cut a strip of material and measure its length and thickness as accurately as possible. The width of the strip is not that critical but generally somewhere around100mm (4 inches) or so usually does the trick.
Then, bend the strip to 90 degrees, and measure its Length X and Length Y as shown in the diagram below.
NOTE: that it is very important to bend the sample piece in exactly the same manner as you plan to bend your real pieces, so that whatever you measure now becomes reproducible later.
The bend radius can be extremely difficult to measure accurately but, in this case, is not critical (within reasonable limits, of course!). The reason it is not critical is that what we are interested in is a number to use in our CAD program that, with the bend radius used in our CAD program, will produce the results you are measuring in real life.
In other words the K-factor you calculate now will take into account any small inaccuracies in the bend radius measurement and compensate for it. If, for example,we are using a Bend radius of 0.5 in our CAD program, it does not matter if our real tooling radius is actually 0.4, as the K-factor, which was worked out from our real tooling, corrects for this. The only implication of this is that we may occasionally get a K-factor that seems odd (higher than 0.5, for example) if our real radius is very different from our CAD program radius. Remember though that most CAD programs such as Solidworks only accept K-factor values from 0 to 1, so if the calculated K-factor is outside these limits, then you may need to double-check your numbers.
The correct K-factor to use in your CAD program can now be calculated as follows:
BendDeduction = Length X + Length Y - Total Flat Length
OutSideSetBback = (Tan(BendAngle / 2)) * (thickness + BendRadius)
BendAllowance = (2 * OutSideSetBback) BendDeduction
K-Factor = (-BendRadius + (BendAllowance / (ลก * BendAngle / 180))) / thickness
Using this method will produce the most acceptable results other than by using a bend table.There are however also some general rules of thumb that can be used for K-factors that will generally give results that are within acceptable tolerances for non-precision sheet metal work. Some of these sample K-factors are given in the methods of bending section below.
Total Fabrication Solution under one roof
CONTACT
Phone: +91 22 2764 1236 / 2764 1263
Email: sales@jjelectrofab.com
Web: www.jjelectrofab.com
Address: Plot No. R-885, M.I.D.C, Rabale
Navi Mumbai – 400701. India
Tuesday, June 23, 2009
Total Fabrication Solution under one roof
Total Fabrication Solution under one roof.
CONTACT
Phone: +91 22 2764 1236 / 2764 1263
Email: sales@jjelectrofab.com
Web: www.jjelectrofab.com
Address: Plot No. R-885, M.I.D.C, Rabale
Navi Mumbai – 400701. India
CONTACT
Phone: +91 22 2764 1236 / 2764 1263
Email: sales@jjelectrofab.com
Web: www.jjelectrofab.com
Address: Plot No. R-885, M.I.D.C, Rabale
Navi Mumbai – 400701. India
How to develop a Square to Round
A true understanding of what "True Length" means and how to find and see true lengths is everything in pattern development by means of triangulation. Here we take you step by step in developing a Square to Round, just keep in mind "Practice makes perfect"
Take a look at how we got started, before you can begin to layout your pattern you have to find all your true lengths. The only way you can see a true length line is perpendicular to its plane, the best way to see the true lengths in a square to round fitting is to draw a top view of the fitting as we did above.
You need to develop a true length bar. Using your dividers or trammel points, transfer from your top view points A1, A2, A3, A4, A5, A6, B6 and B1. Making sure to mark each one.
Draw a line from the top of your True length bar (which must be the total height of your fitting) down to each reference mark on the base of your true length bar .
The two illustrations above are all you need to start your pattern.
Take the dimension A to A from your top view and draw a straight line.
Set you dividers to dimension A to B and draw a small arch as a reference point. Once your dividers are set, place one end on A and make a reference mark as we did in Fig.1 (you will need to do this with each side.
* Set your dividers on points 6,5 in your top view and transfer this dimension to your drawing as we did in Fig.2
* Set your dividers to the A5 length from your true length bar and make a reference mark that intersects with 6,5 reference mark
* Reset your dividers to the distance of 5,4 from your top view and transfer this to your drawing.
Determining line B1. We know from our top view that B is half the distance from A to A and we referenced this with an arch. Now we need to transfer line B1 from our true length bar by setting your dividers to that distance and transferring it by placing one end on point 1 and drawing an arch across the arch we labeled B. The intersection of these two arch's becomes point B.
Draw a line from point 1 down to point B and draw another line from point A to point B 2 pieces required to make one fitting.
One last thing to do is to connect the points 1 through 6. We did not add allowance for any seams or overlaps.
Total Fabrication Solution under one roof.
Phone: +91 22 2764 1236 / 63
Email: sales@jjelectrofab.com
Web: www.jjelectrofab.com
Address: Plot No. R-885, M.I.D.C, Rabale
Navi Mumbai – 400701. India
Take a look at how we got started, before you can begin to layout your pattern you have to find all your true lengths. The only way you can see a true length line is perpendicular to its plane, the best way to see the true lengths in a square to round fitting is to draw a top view of the fitting as we did above.
You need to develop a true length bar. Using your dividers or trammel points, transfer from your top view points A1, A2, A3, A4, A5, A6, B6 and B1. Making sure to mark each one.
Draw a line from the top of your True length bar (which must be the total height of your fitting) down to each reference mark on the base of your true length bar .
The two illustrations above are all you need to start your pattern.
Take the dimension A to A from your top view and draw a straight line.
Set you dividers to dimension A to B and draw a small arch as a reference point. Once your dividers are set, place one end on A and make a reference mark as we did in Fig.1 (you will need to do this with each side.
* Set your dividers on points 6,5 in your top view and transfer this dimension to your drawing as we did in Fig.2
* Set your dividers to the A5 length from your true length bar and make a reference mark that intersects with 6,5 reference mark
* Reset your dividers to the distance of 5,4 from your top view and transfer this to your drawing.
Determining line B1. We know from our top view that B is half the distance from A to A and we referenced this with an arch. Now we need to transfer line B1 from our true length bar by setting your dividers to that distance and transferring it by placing one end on point 1 and drawing an arch across the arch we labeled B. The intersection of these two arch's becomes point B.
Draw a line from point 1 down to point B and draw another line from point A to point B 2 pieces required to make one fitting.
One last thing to do is to connect the points 1 through 6. We did not add allowance for any seams or overlaps.
Total Fabrication Solution under one roof.
Phone: +91 22 2764 1236 / 63
Email: sales@jjelectrofab.com
Web: www.jjelectrofab.com
Address: Plot No. R-885, M.I.D.C, Rabale
Navi Mumbai – 400701. India
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