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aero-cut, aerospace cut, aircraft cut — An offset geometry specification for the feathered edge of a wiper.  Normally the radius face of a wiper is machined relative to the tube cavity so that the feathered edge is located at the line of tangency -- i.e., simple-sweep geometry.  Although this produces a fragile feathered edge, this wiper geometry is desirable for most lower pressure tube-bending applications.  For higher pressure applications, the aero-cut reduces the fragility of the feathered edge by offsetting the origin of the radius face relative to the tube cavity so the feathered edge is located behind the line of tangency.  The amount of the offset for the aero-cut is determined by the tube diameter and the centerline radius.  See feathered edge.

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aircraft quality — Obsolete marketing term for a higher grade of fit and finish for tube-bending tooling sometimes needed for high-pressure and exotic metal tube-bending applications frequently found in the aircraft industry.  Modern machining technology has improved readily attainable levels of quality to the extent that “aircraft quality” can be applied to the production of all tube-bending tooling.  Often the term now refers to tube-bending tooling that features older characteristics once preferred by the aircraft industry, such as solid-bodied mandrels and wipers instead of inserted ones.  Compare commercial grade and industrial grade.

alloy steel — In the limited context of tube-bending tooling materials, a steel that is alloyed with moderate amounts of chromium and other elements such as molybdenum.  Alloy steel is distinguished from stainless steel by having good hardening characteristics and is distinguished from tool steel by possessing better “toughness” after hardening.  See steel.

aluminum-bronze — A family of copper alloys sometimes used as material for perishable tube-bending tooling (i.e., mandrels, wipers, and static pressure dies).  Aluminum-bronze is preferred over alloy steel as the material for perishable tooling to bend carbon steel, stainless steel, titanium, and nickel alloy tubing because it tends to break down into fine particles instead of galling (i.e., welding relatively large pieces of itself) to the tubing as it wears.  Aluminum-bronze is available in various grades and names. 

arc — The curved section of a bent tube, as opposed to the straight unbent sections (i.e., tangents); the bend itself; the physical manifestation of the geometry of bend radius combined with degree of bend.  Compare tangent.  See geometry for illustration.

assist, assist pressure — An axial (or Y-axis) pressure function common to modern rotary-draw tube-bending machines; a pressure or speed setting driving the pressure (or follower) die forward; a pressure applied parallel with the axis of the tube to be contrasted with “direct pressure” which is applied radially (that is, in the X-axis) to the tube.  The importance of assist pressure is that it mitigates the drag caused by the tooling on the tubing at the point of bend, which helps to reduce wall-thinning and deformation of the extrados.  Compare direct pressure and boost pressure.

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axial pressure — See assist pressure.

back tangent — The straight section of the tube behind the line of tangency.  Compare forward tangent; also see tangent.  See geometry for illustration.

ball — A part of the mandrel assembly which supports the arc of the bend from flattening along the outside radius after the tubing material has passed through the point of bend.  The term ball is derived from the fact that geometrically it is the center segment of a true sphere; this is why a ball is occasionally called a “sphere” or “segment”.  Because of its spherical geometry, as opposed to the cylindrical geometry of the mandrel nose, the ball is not very effective in setting the tubing material into a circular cross-section at the point of bend.  For this reason, the mandrel should be fixtured so that the entire ball, or balls, rests past the point of bend — not in the point of bend or behind it.  See mandrel.

ball sub-assembly — The flexing portion of the mandrel assembly which consists of a series of balls linked together.  This is distinguished from a mandrel sub-assembly in that a ball sub-assembly does not include a mandrel nose insert.  See mandrel.

barrel — That part of a link which is nested inside of the bore of a ball when assembled.  See link.

B-axis — On CNC rotary-draw bending machine this is the rotary motion about the Y-axis, which is used to set (or orient) the tubing material in the plane of bend; the rotary axis of the collet.

bead — 1. A circumferential protrusion created in an end-forming process at the end of a tube.  If a bent tubular part requires a bead, it is usually beaded before it is bent.

2. See seam.

bend — Same as arc, which see.

bend data — A programming term for CNC tube-bending machines referring to the basic elements of motion which must be programmed into the machine’s controller to bend a tube.  The elements of motion are:

transport — Y-axis motion, which is the forward and backward linear movement of the tubing material relative to the line of tangency.

plane of bend or orientation — B-axis motion, which is the rotation of the tubing material about the Y-axis.

degree of bend — C-axis motion, which is the rotation of the bend die.

These bend data do not technically constitute a polar coordinate system, but there are to be contrasted with the XYZ rectangular coordinates commonly used in the automotive industry to specify tubular components.  The difference is that rectangular coordinates specify the location of the bend, whereas bend data specify the motion needed to make that bend.  

bend die — The primary tool on a rotary-draw tube-bending machine; the form against which the tube is clamped and then drawn around to produce a bend; less commonly known as the bend form or the radius die.  The essential specifications of a bend die are the outside diameter and the bend radius of the tube to be bent.  There are three basic types of bend die design:

inserted — Occasionally called a “spool die”, this popular design consists of two components:  the radius block and the clamp insert.  The radius block is notched at the line of tangency and then tapped.  The clamp insert is screwed into this notch, which completes the assembly.  The advantage of this design is that it is relatively inexpensive to produce, permits replacement of a worn clamp insert, and offers the greatest depth of bend.

teardrop — This single-piece design is essentially the same as the inserted design in function.  It is more expensive to produce but is necessary when the combination of tube diameter and bend radius create cross-sections too thin in the radius block to permit notching for a clamp insert.

platform — This is also a single-piece design that addresses applications too extreme for the teardrop, most commonly when the combination of tube diameter and bend radius create cross-sections too thin in the radius block to accommodate the bending machine’s bend post, pilot, or drive key.  The platform design remedies this problem by integrating the teardrop with a bottom plate with a bolt-hole circle, by means of which the bend die is screwed onto the bend head of the machine.

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bend form — A general term for the die containing the form of the bend.  In rotary-draw and compression bending, the bend form is the bend die.  In press bending it is the ram die.  See bend die.

bend radius — The radius of the arc of the bend.  This is a general term that does not precisely specify the radius, therefore it can mean inside radius, centerline radius, or any other arbitrary reference point.  When specifying a tube bend, it is necessary to state from which reference point the magnitude of the radius is determined.  The preferred reference point is the centerline radius for round tubing and the inside radius for square and rectangular tubing.  See centerline radius and inside radius.

bend specifications — The basic elements of machine, material, and bend that define a tube bend application; typically: make and model of the machine; shape, outside dimensions, wall thickness, and material of the tubing; radius and depth of the bend.  Other elements may also be significant, such as a large weld seam or an extremely short tangent between bends.  For most circumstances, six basic specifications are sufficient to define the applications:

tube outside diameter (TOD) — Usually specified in inches or millimeters.  Note that certain nominal “pipe” diameters vary considerably from their true diameters, therefore, the pipe system (e.g., IPS, EMT, K-type) must also be specified.

wall thickness (WT) — Specified in inches, millimeters, or wire gauge unless the material belongs in one of the pipe systems.  In that case, the schedule number or other wall thickness designator of the system should be specified.  If the wall thickness varies by 5% or more, it is advisable to specify the thickest wall dimension.

centerline radius (CLR) — Specified in inches, millimeters, or “D” of bend.  “D” is the ratio of the centerline radius to the nominal, not the true, outside diameter of the material: “D” = CLR / nominal TOD.  See “D” for details.

depth of bend (DOB) — Specified in degrees.

material (MATL) — Tubing material.

machine (MACH) — Make and model of machine.

Birmingham Wire Gauge, BWG — A system of measurements for tube wall thickness, in which a gauge number, from “36” for the thinnest wall to “0000” for the thickest wall, represents a certain wall thickness in decimal inches.  For example, “16-gauge” represents a wall thickness of .065 inches.

BWG #

inch

mm

BWG #

inch

mm

BWG #

inch

mm

BWG #

inch

mm

5/0

0.500

12.70

7

0.180

4.57

17

0.058

1.47

27

0.016

0.41

4/0

0.454

11.53

8

0.165

4.19

18

0.049

1.24

28

0.014

0.36

3/0

0.425

10.80

9

0.148

3.76

19

0.042

1.07

29

0.013

0.33

2/0

0.380

9.65

10

0.134

3.40

20

0.035

0.89

30

0.012

0.30

0 or 1/0

0.340

8.64

11

0.120

3.05

21

0.032

0.81

31

0.010

0.25

1

0.300

7.62

12

0.109

2.77

22

0.028

0.71

32

0.009

0.23

2

0.284

7.21

13

0.095

2.41

23

0.025

0.64

33

0.008

0.20

3

0.259

6.58

14

0.083

2.11

24

0.022

0.56

34

0.007

0.18

4

0.238

6.05

15

0.072

1.83

25

0.020

0.51

35

0.005

0.13

5

0.220

5.59

16

0.065

1.65

26

0.018

0.46

36

0.004

0.10

6

0.203

5.16

 

 

 

 

 

 

 

 

 

 

boost, boost pressure — 1. An axial (or Y-axis) pressure function found on some tube-bending machines which is similar to the common assist-pressure function but is distinguished from it by applying pressure to both sides of the tube behind the line of tangency.  (Assist pressure is applied only to the outside half of the tube at the line of tangency.)  Boost pressure pushes the tubing material through the point of bend as it is drawn forward around the bend die, which has the effect of increasing the flow of material from the tangent into the arc.  This increased flow is necessary only for tubing materials that do not become readily plastic at the point of bend or when wall thinning of the extrados must be kept to an extreme minimum.  Boost pressure is not otherwise recommended because it has the disadvantage of also exacerbating the wall thickening of the intrados.  Compare assist pressure and direct pressure.

2. Assist pressure; use of the term is this sense should be avoided to prevent confusion with first definition.

bore-mount — Same as reverse-mount, which see.  Also see wiper.

brass — A common, though technically inaccurate, term for the aluminum-bronze materials used for mandrel and wiper tools.

bronze — See aluminum-bronze.

brute link — An old type of link in which the balls of a mandrel assembly can swivel only in one plane.  Although brute links have the advantage of being heavy duty, they break if not properly oriented to the plane of bend.  Also brute links have the disadvantage of a relatively large pitch which limits their effectiveness for thin-wall and tight radius applications.  H-style universally flexible links have largely replaced brute links.  Compare H-type link.


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