Basic Bending Concepts Commonly Discussed

This topic is going to involve some basic bending concepts that we at Baileigh Industrial discuss with our customers and prospective customers on a daily basis. I have collected my information from a variety of resources. The primary one is the day-to-day dealing with customers and their applications and attempting their applications on our machines as they come about. Also there are many great online resources and libraries for bending applications and I will site some of them as I think them. I have started a basic library at ww.bifabuk.com under the NEWS section and will refer to that section on occasion (http://www.bifabuk.co.uk/news.htm).

There are 3 different types of bending that are typically known in industry as a standard. The first is compression bending. The second is Press Bending. And the third is rotary draw bending. Baileigh Industrial offers high quality Rotary Draw Benders.

Most applications involve several die components. The first standard component is the bend die itself. This die component is typically specific to the actual outside diameter of a tube or pipe and it is specific to what radius the material will be bent upon. The other component has many common names; we at Baileigh Industrial call it a Counter-die. Other come names I hear from people is a shoe, bending shoe, wipe shoe, counter shoe, and a wide variety of other terms. How these components interact and how they are driven by a bending machine determines what type of bending is being dealt with.

I have inserted some pictures of a bend die and counter die.
http://www.bifabuk.co.uk/Rotary_draw_tooling.htm

I will give a brief review each type of bending application.

1. Compression bending - Compression bending employs a bend die and counter die. The bend die remains in a static position while the counter die rotates around the bend die. Our model 150 series use a combination of two techniques, rotary draw and compression bending. Our model 150 series and video can be seen at http://www.bifabuk.co.uk/rdb-150.htm. On this model the bend die rotates in one direction while the counter die rotates in the opposite direction.
   


2. Press Bending - Press bending employs typically a hydraulic ram that is fitted with a bend die on the end of the ram. The tube is mounted in front of the ram and the ram moves forwards in to the counter dies. There are two counter dies employed. These counter dies move in opposite directions around the bend die. Our horizontal press brakes are capable of accomplishing this task.
   


3. Rotary Draw Bending - Applications within this category range from very simple to complex. Our electric rotary draw (http://www.bifabuk.co.uk/rdb-300.htm) benders fall within the simple end of these applications and the complex applications are taken on by our mandrel bender model MB-350 (http://www.bifabuk.co.uk/images/Mandrel_Tooling.jpg).
   

Basic Bending Concepts

A very basic and critical concept for any bending application is the center-line radius or as it will be referred to from here on out, CLR (An explanation of center-line radius (CLR) is demonstrated at http://www.bifabuk.co.uk/images/CLR_Drawing.jpg). This is a very common everyday question that people ask when enquiring about our benders. What CLR can be accomplished is a function of the physical properties of the tube or pipe but how the tube bending machine and its respective tooling is engineered and designed has a definite impact and will allow you to bend tighter more clean bends. You will find that our Baileigh Industrial rotary draw benders as a standard will accomplish tighter more clean bends that other benders on the market due to the design of the machine and tooling. What CLR a tube or pipe can be bent to is determined by several factors. The two main factors that determine what CLR a tube or pipe can be bent on is 1) nominal outside diameter of the tube or pipe and the wall thickness. A quick standard to gauge what CLR can be achieved on a particular tube or pipe is 4x’s (or 4D) the nominal outside diameter of the material. So for example, if you had 1 inch schedule 40 pipe, the actual outside diameter of 1 inch pipe is 1.315, so by the quick-standard your could “guestimate” that you could achieve a 5.26 inch (5 ¼ inch) CLR. Please keep in mind this is a “quickie” guideline and most applications can be bent on a tighter CLR with the Baileigh Industrial rotary draw bender than what the quickie guideline would indicate. When making suggestions to customers using 1 inch schedule 40 pipe when they request the “tightest CLR” I will often times suggest a CLR between 2.5 inches and 3 inches. Depending on the application a CLR tighter than 2.5 inches may be achieved.

Another simple analytical tool is to figure out the wall factor. From the standpoint of evaluating an application from the standpoint of using the same outside diameter tube, on the same CLR, but with a different wall thickness and determining the probability of it working, this is a good tool. You can figure the wall factor by dividing the wall thickness of the tube or pipe into the actual outside diameter of the tube or pipe. If you have a 1 inch tube with a 13 gauge wall (.109 inches) your wall factor would be 9.17. A CLR of 1.75 to 2 inches should be a safe application. Now if you want to use the same outside diameter tube but use an 18 gauge wall thickness (.049 inches) you wall factor jumps up to 20.41. So, you know that the 1 x .109 inch on a CLR of two will work and it has a wall factor of 9.17. Taking the same application and applying a tube with a wall factor of 20 plus indicates that there is a very good chance that it will not work in the same CLR as the tube with a wall factor of around 9. So, CLR and wall factor are directly related. The larger the wall factor the larger the CLR that is needed.

Other factors to consider when doing rotary draw bending.

• Springback- the tendency of material to return to its original position once bent.
• Material type and its tensile strength.
• Alloy of Material
• Design of the machine and tooling
  

Common types of material bent on our rotary draw benders

• Mild Steel
• Aluminum
• Stainless Steel
• Chromolly
• Copper (annealed)
• Titanium

Profiles that are most commonly bent on our rotary draw benders.

• Round
• Square
• Rectangle
• Solid Round
• Solid Square
• Solid Rectangle

Some factors to consider when comparing rotary draw bender machine tools.

• How much does the machine weigh?
• How the bend shaft is powered?
• What horsepower motor is driving the machine?
• What material the bend shaft is constructed from?
• What material the head of the machine is constructed from?
• How is the electrical system organized?
• For programmable models what electronic controllers are used?
• What is the footprint of the machine?
• How is the tooling made? Is it cast or is it machined from high quality steel?
• Where is the machine made?

Once again these are some common topics discussed with our customers on a daily basis and some basic bending concepts. Please feel free to contact me with any questions or feel free to add any facts or figures that you feel are missing. I can be contacted at cspaeth@bifabuk.co.uk or feel free to visit our website at http://www.bifabuk.co.uk/ to review our machines and their features or visit our library that is continually growing on a daily basis.

Best Regards,

Chad M. Spaeth