Although many benders have the ability to generate a tremendous amount of force, specifically with direct pressure-die pressure, it’s important to use only what is required – anything more is counterproductive.

Key Components: Mandrel and Pressure Die

Two key components make low-pressure bending possible:

• The Mandrel: This internal support tool fits inside the tube to prevent the tube from kinking, wrinkles from forming and the wall from collapsing. The further you insert the mandrel past tangency, the less pressure you’ll need from….
• The Pressure Die: This external clamp holds the tube firmly against the bend die throughout the bending process. But here’s the catch: we want the pressure die to be like a friendly hug, not a suffocating squeeze.

Anticipating Pressure

There’s no one-size-fits-all pressure setting. It depends on your:

• Tube Material: Soft metals like aluminum or copper require less pressure than tougher ones like steel, stainless steel or titanium.
• Tube Shape: Round tubes generally need less pressure compared to square or rectangular tubes
• Wall Thickness: Although heavy-walled tubes can handle more pressure before deforming, they generally don’t require much more pressure than thin-walled tubes.
• Bend Radius: Tighter bend radii experience more elongation along the outside of the bend and more compression along the inside of the bend than larger bend radii, so more pressure will be expected with tighter radius applications.

Setting the Mandrel and Pressure-die:

Assuming all relevant tooling components are installed for your application, lets pay close attention to the:

• Mandrel position: For clearance purposes, the mandrel is slightly smaller than the inside diameter of the tube and often has a radius at the leading edge of the nose. This means the mandrel may be positioned past tangent to a position where the tube is drawn over its leading edge.
• Pressure-die pressure: Adjust the pressure-die to the anticipated pressure settings. The primary goal is the keep the back end of the tube from pushing away from the bend die, if a wiper die is being used, the secondary objective is to keep enough pressure on the tube to prevent wrinkles.

Fine-Tuning Your Bends

Tweaking the set-up for perfect results!

• Pressure-die tracking: verify the pressure-die is maintaining constant position against the bend die. If it is pushing away from the bend-die during the bending process then you must increase pressure.
• Inner Wrinkles: If the inside of your bend is wrinkled, move the mandrel deeper into the bend. If the problem persists, you may also need to increase pressure-die pressure.
• Outer Collapse: If the outside of the bend exhibits outlines of the mandrel balls or is collapsing, it’s getting squeezed too much. Reduce pressure-die pressure slightly and see if that fixes the issue.

Remember: It’s always better to start with low pressure and gradually increase it if needed. This way, you minimize the risk of damaging your bender and tooling.

FAQ

1. What is the main advantage of using the low-pressure tube bending method?

The low-pressure method allows you to achieve clean, precise bends without applying excessive force. This minimizes stress on your tube materials, tooling, and the bending machine itself, leading to better quality bends and longer tool life.

2. What are the two most important components for successful low-pressure bending?

The two key components are the mandrel and the pressure die. The mandrel provides internal support to prevent kinking, wrinkling, and wall collapse, while the pressure die externally clamps the tube against the bend die, ensuring consistent contact throughout the bend.

3. How do I determine the correct pressure setting for my bending application?

There’s no universal setting. The ideal pressure depends on several factors, including the tube material (softer metals need less pressure), tube shape (round tubes generally need less), wall thickness, and bend radius (tighter radii often require more pressure). It’s always recommended to start with a lower pressure and gradually increase it if needed.

4. What should I do if I see wrinkles on the inside of my bend?

If you observe wrinkles on the inside of the bend, your first step should be to move the mandrel deeper into the bend. If the wrinkles persist, you may also need to slightly increase the pressure-die pressure.

5. How do I prevent the outside of my tube from collapsing or showing mandrel ball outlines?

If the outside of your bend shows signs of collapse or outlines of the mandrel balls, it indicates that the tube is being squeezed too much by the pressure die. To rectify this, you should reduce the pressure-die pressure slightly and check if the issue is resolved.

The post Bending Tubes Like a Pro: The Forward Mandrel, Low-Pressure Method appeared first on Bend Tooling.

The Bend Tooling Mandrel and Wiper Chart allows for quick and easy evaluation of almost any rotary-draw tube bending application for round tubing. This tool will allow you to determine the mandrel and wiper tooling requirements for your application.

Download Bend Tooling Mandrel and Wiper Selection Chart

The post Bend Tooling Mandrel and Wiper Chart appeared first on Bend Tooling.

1. The Draw Bending Advantage:

The draw bending method, often referred to as “mandrel bending,” distinguishes itself by fixing the line of tangency in space through which the material is formed in a flow parallel to the bend form. Unlike compression or ram bending, draw bending allows the practical and effective use of tooling both inside and outside the tube to control material flow as it becomes plastic at the point of bend. Mandrel and wiper tooling, unique to the draw method, play a central role in ensuring the quality of tube bends.

1.1 Mandrel’s Central Importance:

The draw method is closely associated with the use of a mandrel, making it a key element in achieving high-quality bends. The seminar emphasizes the central importance of the mandrel in draw bending, highlighting its role in controlling material flow and preventing defects.

2. Comparisons to Ram Bending and Compression Bending:

To underscore the advantages of draw bending, it is essential to compare it to other common methods, namely ram bending and compression bending.

2.1 Ram Bending:

Ram bending, also known as vertical or press bending, is a simple yet limited method. The ram die pushes a tube through a pair of wing dies, creating two lines of tangency moving in opposite directions. This limitation restricts its applications to heavy-wall tubes with large-radius bends. The complexity and expense of incorporating tooling such as mandrels and wipers to control bend quality make a ram-bending machine less practical and cost-effective than a draw-bending machine.

2.2 Compression Bending:

Compression bending, a direct predecessor of draw bending, uses a bend die, clamp die, and pressure die. However, the static nature of the bend and clamp dies, combined with the rotating pressure die, results in a continuously moving line of tangency. This characteristic makes it challenging to improve bend quality by incorporating a mandrel. Attempts to use mandrels with a chain of balls often lead to undesirable humps in the tube bend, as the pressure die pushes the material over the balls. The inefficiency of mandrels in compression bending reinforces draw bending’s superiority in achieving optimal tube bend quality.

Conclusion:

In conclusion, draw bending emerges as the superior method for consistently producing high-quality tube bends. The ability to control material flow through the use of mandrel and wiper tooling sets draw bending apart from its alternatives, ram bending and compression bending. While each method has its merits, the draw bending process stands as the practical and effective choice for applications ranging from manufacturing agricultural equipment to automotive exhaust systems,.

The post The Superiority of Draw Bending: Ram Bending vs. Compression Bending appeared first on Bend Tooling.

Rotary-draw tube bending is a tool-intensive metal-forming operation.  The mandrel and wiper are critical to supporting the tube at the point of bend to produce consistently high-quality results.  The objective of this support is to plastically deform the tube along the arc of the bend with minimal distortion of its cross-section.  Therefore, the mandrel and wiper are primary elements in the rotary-draw tube bending operation.  This article covers an objective method of selecting the right mandrel and wiper for this task.

THE MANDREL-WIPER CHART

For many years, tube bending engineers have relied upon tables to specify the mandrel and wiper needed for a job.  These tables in the form of the familiar mandrel-wiper chart (see here) remain a convenient means of boiling down into standard recommendations the mathematical formulas and rules of thumb that go into this specification.

The typical mandrel-wiper chart displays the recommendations by wall factor vs. “D” of bend.  The wall factor is the tube outside diameter divided by the wall thickness.  The “D” of bend is the centerline radius of the bend divided by the tube outside diameter.  Where these two measures intersect on the chart is the mandrel and wiper recommended for that tube bend.

On most mandrel-wiper charts this recommendation indicates:  (1) Whether or not a mandrel is required for the tube bend; (2) if so, what the pitch and number of balls should be; and (3) whether or not a wiper is required.  Additional is sometimes also available.  The chart in Figure 1 also indicates whether standard tooling or high-pressure tooling is needed to make the tube bend.

For example, the tube bend is 2” TOD x .065” WT x 4” CLR.  The wall factor = 2” TOD / .065” WT = 30.8.  The “D” of bend = 4” CLR / 2” TOD = 2.0.  Using the mandrel-wiper chart here find the row with the largest wall factor equal to or less than 30.8.  That is Row “30”.  Similarly find the column with the largest “D” of bend equal to or less than 2.0.  That is Column “2”.  Find the recommendation at the intersection of Row “30” and Column “2”.  The value there is “R2W”.  (See Figure 2.)  The “R2” means that a regular-pitch 2-ball mandrel is required.  The “W” means that a wiper is also required.  The “W” has a further meaning:  Standard tooling, as opposed to high-pressure tooling, is sufficient to make the tube bend.  The distinction between standard and high-pressure tooling is explained below.

ZONES OF DIFFICULTY

It can be readily observed from an examination of the mandrel-wiper chart in Figure 1 that the greater the wall factor, the more difficult it is to make the tube bend.  Conversely, the greater the “D” of bend, the less difficult it is.  Therefore, the most difficult bends are at the lower left-hand corner of the chart, and the least difficult bend are at the upper right-hand corner.  Accordingly, the tooling recommendations sort themselves out into for four zones of difficulty.

The first zone, emanating from the upper right-hand corner, includes those bends that require no mandrel and no wiper.  This is because either the wall thickness relative to the tube diameter is heavy enough or the centerline radius relative to the tube diameter is large enough so that the tube material has sufficient strength to support itself at the point of bend.

The second zone includes those bends that require a standard mandrel but no wiper.  The third zone requires a standard mandrel and a standard wiper.  Finally, the fourth zone, emanating from the lower left-hand corner, includes the bends that are the most difficult because of very thin walls or very tight bend radiuses.  These bends require both a high-pressure mandrel and a high-pressure wiper for full control of the tube material at the point of bend.

With the advent of inserted mandrel and wiper tooling, it has become important to distinguish which tube bends are best suited to their use and which ones require their non-inserted counterparts.  This divide between inserted (or standard) tooling and non-inserted (or high-pressure) tooling comes when the extremes of thin walls and tight bend radiuses necessitate the application of relatively high radial pressure from the pressure die against close-fitting mandrels and wipers set at zero-rake.  Under these circumstances, higher pressure causes the tube material to be marked, distorted, or subject to excessive drag from the parting lines and other features that break the working surfaces of standard tooling – thus, the need for high-pressure tooling that has continuous working surfaces.

Therefore, the second and third zones call for standard mandrels and wipers for the most cost-effective tooling to make these bends, and the fourth zone calls for high-pressure mandrels and wipers.  If you are not using a modern mandrel-wiper chart that makes this important distinction between standard and high-pressure tooling, generally a recommendation from an obsolete chart for a close-pitch 5-ball mandrel and above should be interpreted as a call for high-pressure tooling.

ADJUSTING FOR SECONDARY PARAMETERS

As already indicated, the wall factor and the “D” of bend are the primary parameters in selecting the right mandrel and wiper for a tube-bending job.  The degree of bend and the tube material are also important.  However, the two-axis nature of a mandrel-wiper chart does not allow for a direct input of these secondary parameters.  Instead they must be taken in account by making adjustments to the recommendation produced by the intersection of the wall factor and the “D” of bend.

Like the wall factor, the greater the degree of bend the more difficult it is to make.  Because degree of bend is a secondary parameter, most mandrel-wiper charts are compiled on the basis of a 180-degree bend.  If the degree of bend is under 45 degrees, adjust the “D” of bend one column to the right (i.e., to the next higher “D”) for a suitable recommendation.

Adjustments for tube material can be similarly made.  Again most mandrel-wiper charts are predicated on an assumption about material:  The tube is a mild steel or other material with similar elasticity and plasticity.  This includes all non-stainless steels and most non-ferrous metals.  However, some materials are more difficult to bend and require firmer control at the point of bend.  To account for this, adjust the “D” of bend one column to the left (i.e., to the next lower “D”) for stainless steel, titanium, copper-nickel, and “T6” aluminum (e.g., 6061-T6) tubing.  Adjust two columns to the right for high-nickel stainless steel (e.g., 314 and 329 grades) and nickel alloy (e.g., Inconel) tubing.

CHART LIMITATIONS

All mandrel-wiper charts are limited by the practical range of rotary-draw tube bending.  The chart is most expansive in this regard.  First, it ranges from a wall factor of zero (i.e., solid rod), for which no mandrel or wiper is required, to “200” (e.g., a 2” TOD x .010” WT), which is very rare.  Second, it ranges from a “D” of bend of “3/4”, which is tightest tube bend suitable for rotary-draw tube bending (and then only in limited cases), to “12”, which seldom encountered because roll and press bending are usually more efficient.

Another important limitation is that mandrel-wiper charts are compiled for round tube.  It is possible to approximate the mandrel and wiper tooling needed for square, rectangular, oval, and elliptical tube from the chart .  Generally, they should be treated like the tougher materials to bend by adjusting the “D” of bend column to the left.  However, there is not a rule of thumb because the ratio of the major to minor axis, the corner radius, and the plane of bend (i.e., the “hard” or “easy” way) all must be factored into that adjustment.

Finally, all mandrel-wiper charts are limited by assumptions about the tooling and its set-up.  For example, this chart assumes certain best practices like the “forward nose” set-up of a link-type mandrel – as opposed to a cable mandrel, which is often set with the first ball at the line of tangency.  It also assumes certain specifications such as a precision nose radius for the mandrel instead of a larger high-production one and a nose diameter that is close-fitting (i.e., ND = TOD – WT x 2.21) rather than loose.

AFFORDABLE TOOLING

This objective method of using a mandrel-wiper chart to select the right mandrel and wiper for a tube-bending job opens the way to cost-effectiveness:

1. It specifies what tooling is sufficient to achieve process control.  The job is not under-tooled and so not unstable and unpredictable.  Nor is the job over-tooled and so more tooling is consumed per bend than is necessary.
2. A job under process control reduces the incidence of failure.  Failure, often from unbalanced forces being applied to the tube, tooling, or the machine, is expensive.  It disrupts the flow of work.  It scraps tubing.  It shortens tool and machine life.
3. Finally, process control increases productivity.  Fewer resources are needed in terms of labor, machine time, tooling and supplies, and overhead to get the job done.

Therefore, consult a modern mandrel-wiper chart to put yourself on the path to profitability in your rotary-draw tube-bending operations.

FAQ

1. What are the key factors in selecting the right mandrel and wiper for cost-effective tube bending?

The primary factors for selecting the correct mandrel and wiper are the wall factor (tube outside diameter divided by wall thickness) and the “D” of bend (centerline radius of the bend divided by the tube outside diameter). These two measurements are used in conjunction with a mandrel-wiper chart to determine the appropriate tooling. Secondary parameters like the degree of bend and tube material also influence the final selection and may require adjustments to the chart’s recommendation.

2. How does a mandrel-wiper chart work and what information does it provide?

A mandrel-wiper chart typically displays recommendations based on the intersection of the wall factor and the “D” of bend. At this intersection, the chart indicates:

• Whether a mandrel is required, and if so, its pitch and number of balls.
• Whether a wiper is required.
• Whether standard or high-pressure tooling is needed for the specific tube bend.

3. What do the “zones of difficulty” on a mandrel-wiper chart signify?

The mandrel-wiper chart categorizes tube bends into four zones of difficulty, based on the wall factor and “D” of bend. These zones dictate the type of tooling required:

• Zone 1 (least difficult): No mandrel or wiper needed.
• Zone 2: Standard mandrel, no wiper.
• Zone 3: Standard mandrel and standard wiper.
• Zone 4 (most difficult): High-pressure mandrel and high-pressure wiper.

4. How do tube material and degree of bend affect mandrel and wiper selection?

While not directly inputted into the chart, the tube material and degree of bend require adjustments to the chart’s initial recommendation. For bends under 45 degrees, you should adjust the “D” of bend one column to the right (to a higher “D”). For difficult-to-bend materials like stainless steel or titanium, adjust the “D” of bend one column to the left (to a lower “D”). Very high-nickel stainless steel or nickel alloys may require adjusting two columns to the left.

5. Why is using the correct mandrel and wiper crucial for cost-effective tube bending?

Selecting the right mandrel and wiper, as guided by a modern chart, is essential for cost-effectiveness because it ensures process control. This prevents both under-tooling (leading to unpredictable results and failures) and over-tooling (consuming more resources than necessary). Process control reduces failures, which are expensive due to scrapped tubing, disrupted workflow, and shortened tool/machine life, ultimately leading to increased productivity and profitability.

The post Selecting the Right Mandrel and Wiper for Cost-Effective Tube Bending appeared first on Bend Tooling.

The post The Mandrel Nose Placement Calculator appeared first on Bend Tooling.

Records from the U.S. Patent Office show that the history of the articulated mandrel for tube-bending can be traced back to the late nineteenth century when a series of segments were chained together to form the curves of a teapot spout. The modern mandrel was patented by Henry Spates in the late 1950’s and was initially used in the aircraft, shipbuilding, and hot rod industries. The Spates invention featured sturdy replaceable linkage which permitted the balls attached to the nose of the mandrel to rotate in all directions in a wrist-like motion, whereas earlier mandrels typically restricted the balls to an elbow-like motion in the plane of bend. The most significant improvement to the modern mandrel has been the inserted nose, a disposable component which takes the brunt of the wear, introduced by Bend Tooling Inc. in 1986. (See the photo for an example of this innovation.)

Because the mandrel had been recognized as the controlling element in draw bending, this continuum of improvement over the past century focused upon practical and cost-effective features of the mandrel to meet demands of better quality and performance. (See Note #2.) However, over the past twenty-five years the widespread use of pressure die assist and pressure die boost, especially with the convenient controls featured by most computer numerically controlled (CNC) machines, has allowed tube benders to apply force to control the flow of material at the point of bend through the pressure die instead of the mandrel. The effectiveness of this “high pressure” approach is limited; a fact many tube benders are now facing as bend applications become more extreme simultaneously with tightening tolerances. A return to basics with the aggressive use of the mandrel overcomes this problem, because the mandrel nose becomes once again the workhorse in a rotary-draw bend allowing the operator to reduce the machine pressure.

The key to maximizing the performance of the mandrel in a draw-bending set-up is its nose. The three factors to consider are the diameter of the nose (n), the radius of the nose (m), and position of the nose relative to the line of tangency (S). We recommend using the following formulas to calculate these values (see the illustration above for reference):

Mandrel nose diameter: n = t – ( w x 2.21 ). (See Note #3.)

Mandrel nose radius: If F is less than 50 then m = n x .1 else m = n x .02, where F = t / w.

Set-up position of mandrel nose: S = sqrt ( ( r + ( t / 2) – w )2 – ( r + ( n / 2 ) )2 ) + m.

For full information on how to optimize the use of the mandrel in your next set-up, we have detailed instructions and drawings in the “Four-Step Set-Up Procedure” in our free, downloadable Tube Bending Guide.

NOTE #1: There are isolated cases in which compression bending machines have been fixtured to mount a mandrel with a long chain of balls. Also, ram bending machines have been retro-fitted with complicated moving double-mandrel systems. The benefits of such improvements have been limited.

NOTE #2: Of course, not all draw bending applications necessitate the use of a mandrel. Most applications suitable for compression or ram bending, will not require a mandrel when produced on a rotary-draw bending machine. Also, “heart-shape” or “elliptical” die cavities, which slightly flatten the tube into the plane of bend, increase the range of non-mandrel draw bending applications. However, until there is wider use of the electric (i.e., servo-controlled) rotary-draw bending machine, these non-mandrel applications will remain at the margins of draw bending.

NOTE #3: This is the formula for single-walled tubing. For laminated (i.e., double-walled) tubing, use this formula for the mandrel nose diameter: n = ( t – ( wo x 2 ) ) – ( wi x 2.21 ), where wo = thickness of outside lamination and wi = thickness of inside lamination.

FAQ

1. What is “draw bending” and what makes it unique compared to other bending methods?

Draw bending, also known as rotary-draw bending, is a method that consistently produces high-quality tube bends. Its key distinction is that it fixes the “line of tangency” in space, allowing for the strategic placement of internal and external tooling, specifically mandrels and wipers. This precise control over material flow at the “point of bend” is what sets it apart from compression or ram bending.

2. What is the historical significance of the mandrel in tube bending?

The articulated mandrel has a long history, dating back to the late nineteenth century. Henry Spates patented the modern mandrel in the late 1950s, introducing sturdy, replaceable linkage that allowed the mandrel balls to rotate in all directions. A significant improvement was made in 1986 by Bend Tooling Inc. with the introduction of the inserted nose, a disposable component that absorbs the brunt of wear, further enhancing the mandrel’s practical and cost-effective features.

3. Why has there been a shift away from mandrel-centric control, and what are the limitations of this shift?

Over the past 25 years, the widespread use of pressure die assist and pressure die boost, particularly with CNC machines, has led many tube benders to rely on applying force through the pressure die rather than the mandrel for material control. However, the article highlights that the effectiveness of this “high pressure” approach is limited. As bend applications become more extreme and tolerances tighten, this limitation becomes evident, suggesting a return to aggressive mandrel use for better results.

The post The “Forward Mandrel” Secret of Tube-Bending appeared first on Bend Tooling.

This includes the wiper die. At first blush it is a simple tool. Often the wiper is a solid block machined to fit the gap between the bend die and the back tangent of the tube to be bent. Frequently the wiper die is an uncomplicated two-piece assembly in which the leading edge of the tool is a disposable insert. Other than size and material, there doesn’t appear to be much to the specification of a wiper die. Looks are deceiving.

The essential element of wiper die design is the feathered edge, so called because it is the sharp knife-like edge formed by the convergence of the tube cavity with the sweep of the radius face. The rest of the tool is nothing but mass to support the feathered edge and to provide sufficient surface area for mounting to the tube-bending machine. The geometry of the feathered edge is not as simple or obvious as it may appear. Precisely how this intersection of the tube cavity and the radius face is machined into a wiper has the primary impact upon the tool’s performance.

Before examining that issue, it will be useful to review the purpose of a wiper die. It serves two functions in the rotary-draw process. The first is to prevent a hump from forming at the trailing end of the inside radius of the tube bend. As the tube is being drawn into the bend, it becomes plasticized at the point of bend. The plasticized material behind the line of tangency flows into the curve of the bend die cavity that is sweeping away from the back tangent of the tube. Upon completion of the draw, if this deformation exceeds the elasticity of the tubing material, it will set as a hump, or a series of small humps, at the end of the bend. Fixturing a wiper die in the gap between the bend die and the tube stops the deformation from reaching that point by blocking the flow of the material into that gap.

Because all tubing materials have some elasticity – i.e., the property of resuming its original shape when stress is relieved – it is not necessary to fixture a wiper so that it fills the entire gap to prevent the formation of a terminal hump. A wiper can be raked – the angling of the feathered edge away from the line of tangency – so that it blocks no more than the flow of material before it exceeds its elasticity. The advantage of doing so is longer tool life. If you examine a worn wiper die that was set at little or no rake, you will observe that the tube cavity immediately behind the feathered edge is dished out from blocking the entire flow of material. This dishing cuts the life of a wiper die.

However, raking a wiper die to extend its life can be at odds with its second function: Full containment of the tubing material at the point of bend when bending under high pressure. Normally, high radial pressure as applied by the pressure die is not necessary in most draw-bending applications, especially if the mandrel nose is used aggressively. However, higher pressures cannot be avoided for bending materials such as 304 stainless steel or titanium – or even mild steel on an extremely tight centerline radius. These materials resist the compression that occurs as the intrados of the tube bend thickens during the draw. If the flow of material is not completely contained by tooling at the point of bend – the mandrel inside in the tube, the pressure die over the outside radius of the bend, the bend die over the inside radius ahead of the line of tangency, and the wiper set at zero-rake over the inside radius behind it – the compression will buckle the tube.

Therefore, tubing material (and to a lesser extent, bend specifications) will dictate whether or not a wiper can be raked. Those same factors also dictate the geometry of the feathered edge. In low-pressure bending in which elimination of the terminal hump is the only consideration and so the wiper can be raked, a simple-sweep geometry will suffice. In high-pressure bending in which the wiper must function as a backstop to the force of the pressure die and so the wiper must be set at zero-rake, an offset geometry is needed.

It is important to know that the simple-sweep feathered edge for low-pressure bending will not work well for high-pressure bending, and vice versa for the offset feathered edge. However, most suppliers of wiper tooling manufacture their wipers only with some variation of the simple-sweep geometry – i.e., the edge formed by the convergence of wiper’s tube cavity with its radius face. The exact geometry is usually determined not by how the wiper is to be used, but rather ease of manufacture. Even though the technology now exists to precision machine a feathered edge to completion, most simple-sweep feathered edges are at least partly made by manual honing or sanding. This creates even wider variations in the finished tool.

Often the end-user of hand-finished wipers partly compensates for discrepant feathered-edge geometry in two ways. First is by adjusting the rake. Second is by using aluminum-bronze as the material for the wiper to wear-in the desired feathered-edge geometry. However, both of these remedies work against process control in rotary-draw bending, because they are inherently variable or worse, unstable, and defeat attempts to standardize set-up parameters for a given tube-bending application. Bend Tooling has responded this problem by fully precision-machining to finish specifications the feathered edge, which entirely eliminates the variability of hand-finished wipers. (The photo below contrasts the quality of hand-finished feathered edges of wiper from a North American and a European tooling supplier with the fully precision-machined feathered edge of a Bend Tooling wiper shown above.)

However, even a fully precision-machined simple-sweep feathered edge is unsuited for a wiper set at zero-rake for high-pressure bending. To address this, Bend Tooling developed the offset feathered edge, called the Aero-Cut™. With the proper offset between the tube cavity and the radius face machined into the wiper die, the Aero-Cut™ feathered edge will maintain its integrity at the point of bend and provide sufficient containment of the material without deeply marking it. (In addition to this, Bend Tooling has also introduced a high-pressure wiper system specially designed from end-to-end for use at zero-rake under high radial and axial pressures. This new tool combines the best features of solid-body and inserted wipers while reducing the per-bend cost. Contact us for details.)

Fortunately, you can completely control what you get in a wiper die from your tooling supplier by taking into account the following design and manufacturing considerations of the feathered edge when specifying a wiper die:

• First is the material of the wiper. The non-nickel aluminum-bronzes remain the superior choice for steel, stainless steel, and titanium tubing. Untreated leaded steels are best for non-ferrous tubing. Harder materials, heat treatment, and coatings tend to make the feathered edge like an eggshell and lead to pre-mature failure as it fractures.

• Second is the geometry of the feathered edge. If the wiper will be raked, then simple-sweep geometry is required. If the wiper will be set at zero-rake to accommodate high-pressure bending of stainless steel, titanium, Inconel, or other similar tubing materials, then the feathered edge must have offset geometry.

• Finally, ensure that the feather edge is completely manufactured by machine. The feathered edge is a precision attribute of a wiper. If it is finished by manual methods, the soundness of its design will be compromised by the unavoidably wide variations in its manufacture by hand. Always insist upon a fully machined feathered edge.

The post The Wiper Feathered Edge appeared first on Bend Tooling.

If you are unsure of the link sizes you wish to order, please reference the dimensions below to find the correct size.

	A	B	C	D
#6 link	.472″	0.371″	.118″	.128″
#7 link	.623″	0.496″	.174″	.128″
#8 link	.750″	.621″	.197″	.258″
#9 link	.872″	.746″	.278″	.258″
#10 link	1.060″	.870″	.299″	.316″
#11 link	1.371″	1.119″	.364″	.316″
#12 link	1.750″	1.493″	.602″	.516″

CONFIDENTIALITY NOTICE: This drawing and all the information it contains is the property of Bend Tooling, Inc. and is CONFIDENTIAL. The recipient of this document and its information cannot use, distribute, reproduce, or replicate it in whole or in any part for any purpose other than to transact business with BTI.

DISCLAIMER: Although BTI links may be interchangable with other linkage systems and/or mandrel components we cannot guarantee that they are fully compatible. For best performacne we recommend using all BTI components for each mandrel system.

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