intro to rotary draw bending: an engineer’s guide to bending tubes

Tool School - Rotary Draw Bending Tooling An Engineer’s Guide to Bending Tubes

Tube Form Solutions Tool School

Rotary Draw Bending Tooling

Tool School Agenda:

• Introduction To Rotary Draw Bending

• Engineering Guidelines

• Tight Radius Bending

• Completing the Application Review

• Special Considerations & Applications

• Summary and Benefits

Introduction To Rotary Draw Bending

Introduction To Rotary Draw Bending Machine Axes

Introduction To Rotary Draw Bending Typical Interlock Style Tooling

Clamp Die Pressure Die

Mandrel

Bend Die

Wiper Die

Interlock

Introduction To Rotary Draw Bending Interlock (Spool) Bend Die

The Bend Die is used to form the tube and determines the radius of the bend

Non-Interlock Interlock



Non-Interlock

Wiper Die

Notch

Interlock

Wiper Die

Notch

Non-Interlock

Wiper Die

Notch

Interlock

Wiper Die

Notch

Introduction To Rotary Draw Bending Standard Bend Die Configurations

Introduction To Rotary Draw Bending Pedestal & Flange Mount Bend Dies

Pedestal & Flange Mount Bend Dies are required: 1. When Height Is Larger Than Width 2. For Small CLR (not enough material left for a

post through hole) Features of Pedestal & Flange Mount: • May or May Not Incorporate A Tool Post • Incorporates Platform For Stability

The Clamp Die is used

to grip the tube against

the Bend Die as the

Bend Die rotates

Introduction To Rotary Draw Bending Clamp Die

The Pressure Die presses

the tube into the Bend Die

and applies the pressure

required to bend the tube

Introduction To Rotary Draw Bending Pressure Die Assembly

The Mandrel supports the inside of the tube to prevent collapse and wrinkling during bending.

Introduction To Rotary Draw Bending Standard Pitch 4-ball Mandrel

Steel / Chrome Mandrels Are Used For bending: Steel, Copper, Aluminum, Bronze Tubing

Aluminum Bronze Mandrels Are Used For bending: Stainless, Titanium, Inconel Tubing

Close pitch mandrels are designed with less gap between

the balls

• Used for thin wall tubing and tight radius bends

• Utilize smaller link sizes

Introduction To Rotary Draw Bending Close Pitch 5 Ball Mandrel

The wiper die supports the tube on the inside of the bend to prevent wrinkles

Introduction To Rotary Draw Bending Typical Square Back Wiper Die

Steel Wiper Dies Are Used For: Steel, Copper, Aluminum, Bronze Tubing

Aluminum Bronze Wiper Dies Are Used For: Stainless, Titanium, Inconel Tubing

Introduction To Rotary Draw Bending Typical Wiper Die Tip with Close Approach Holder

Engineering Guidelines Requirements for Tool Design

Engineering Guidelines Requirements for Tool Design

• Material type

• Bend Criteria

• Tube O.D.

• Wall thickness

• Bend radius

• Max. Bend Angle

Engineering Guidelines Bend Criteria

The Bend Criteria required will determine the type of tools needed.

Bend Criteria is referred to as: • Ovality • Wall Thinning • Deformation • Marking • Other Customer Specifications

Engineering Guidelines Formulas

Wall Factor (WF)

D of Bend (D)

Difficulty Factor (DF)

D

WFDF

ODTube

RadiusCLRD

Wall

ODTubeWF

Engineering Guidelines Mandrel And Wiper Die Selection Guide

Engineering Guidelines Clamp Length Calculations

• D.F. 18 or less = 2 x TOD

• D.F 19 - 28 = 2.5 x TOD

• D.F. 29 - 56 = 3.0 x TOD

• D.F. 57 - 70 = 3.5 x TOD

• D.F. 71 - ?? = 4.0 and/or plug

Length

Engineering Guidelines Difficulty Calculation Examples

2.00 OD, .065 Wall, 4.0” CLR, Stainless

2.00 OD / .065 Wall = 30.7 Wall Factor

4.00 CLR / 2.00 OD = 2.0 D Factor

30.7 WF / 2 D = 15.3 Difficulty Factor

Per Guide; Requires 2 Ball Mandrel a Wiper Die and 4.00 Long Grip (2D)

Aluminum Bronze Mandrel & Wiper Die

Engineering Guidelines Difficulty Calculation Example

• 2.00 OD, .028 Wall, 3.00 CLR, Alum.

2.00 OD / .028 Wall = 71.4 Wall Factor

3.00 CLR / 2.00 OD = 1.5 D Factor

71.4 W.F. / 1.5 D = 47.6 Difficulty Factor

Per Guide; Requires 5 Ball Mandrel a Wiper Die and 6.00 Long Grip (3D)

Chrome Mandrel & Steel Wiper Die

Engineering Guidelines Real World Situation

Part Shape Distance Between Bends Is Shorter Than Engineering Clamp Length Guidelines

Engineering Guidelines Clamp Gripping Alternatives

• Surfalloy ( 6 grades available)

• Carbide Spray ( 6 grades available)

• Serrations ( Several options)

• Other

All Grip Applications Cause Marking

Tight Radius Bending

Tight Radius Bending Material Considerations

• Material type Stainless, Titanium, Aluminum, Etc.

• Material Elongation The plastic limit that the material can stretch

• Elongation percentage requirement formula for conventional machine

Elongation % = 0.50 X OD X 100

CLR


• Single Bend Vs Multi bends • Single Bend allows the outside wall to be drawn into

bend with out breaking (sample)

• Degree of Bend Required • Larger bend angles require more mandrel balls (To

support the clamp)

• Tooling clearance is an issue (Wiper Die) (Notch Bend die)


• Ovality Requirements • Ovality % = Max OD - Min OD X 100 Nominal OD

5 Percent Ovality


• Wall Thinning Requirements • WT % = (Nom. - Min) / Nom X 100

Thin Wall Area


• Tensile Strength

• Breaking point

• Yield Strength

• Point of permanent deformation

• Difficulty Factor

Tight Radius Bending Machine Considerations

• Sized for the bending torque required

• Boost • (Also called pressure die assist)

• Clamp die Support • Holder should support total length


• Heated Tooling Option • Required when bending pure titanium with tighter

than 3 D Bends

Typically the Pressure Die and mandrel are heated to increase the material elongation

Tight Radius Bending Machine Considerations Carriage Boost

• Forces additional material into bend reducing wall thinning and possibility of tube breakage

Compression

Elongation

Less draw

force needed

• Carriage boost applies force to end of tube

• Carriage boost, and pressure die assist movement is synchronized with C-axis position

Carriage Boost Assembly

Tight Radius Bending Machine Considerations Carriage Boost

• Carriage Boost

• Reduces clamp force requirement

• Allows tighter radius bends

• Required with materials with low elongation value and bends of 1.5 D or less

• Position Control Vs Pressure Control

• Position control electronically synchronizes the pressure die assist and/or the carriage boost to the bend arm position

• Push to Tangent

• Reduces material required (OD Collet Required)


Tight Radius Bending Hydraulic Pressures

• Keep Pressure die Pressure to min.

• Boost (Pressure die Assist) • 75% Of Pressure die starting point

• Boost Back Pressure (non mdl) • Increases amount of stretch

• Mechanical Pressure die setup Vs. Hydraulic Pressure setup • Should use hydraulic pressure method

Tight Radius Bending Tooling Considerations

• Tool Tolerances Must be Close

• Need Adequate Clamp Length

• Interlocking Tooling

• Deflections must be minimized: • Bend die, Bend Post, Wiper die, Wiper Holder, Wiper Die

Post, Tie Bars, and Clamp dies are major contributors to reducing deflections.

Definition:

a. firmly fixed or set

b. inflexible

Think Rigidity


• Mandrel fit • Establishes Ovality and controls wrinkling

• Static Pressure dies (non-mandrel) • Allow stretch of outer wall

• Serrations or Other Gripping Application Added to Pressure Die • Provides more frictional coupling


• Refer to the Basics in Tool Set Up • Bend die must be torqued. (Refer to machine

recommendation’s)

• Clamp die should not touch the bend die

• Monitor clamp die for slippage

• Pressure die should not touch the bend die

• Pressure die should travel at the same speed as the bend die


• The mandrel shank end should be adjusted to tangent point

• Too many mandrel balls may cause excessive drag

• Monitor mandrel lubrication

• Depending on material, too much lubrication or too little, or none may be what makes the part run successful.

• Wiper die alignment is very critical

• Do not apply too much rake angle

• Recommended - Zero to 1.5° of rake angle


• Wiper die deflection must be minimum

• Wiper die tip should reach near tangent

• Wiper die radius must fit the bend die radius

Special Considerations and Applications Elliptical Groove

Special Considerations and Applications Elliptical Groove

• Eliminates Need For Mandrel or Wiper Die

• Deforms Tube To an Ellipse

• Typically Used on Non-Cosmetic Applications

• Ovality is Estimated at .7 Times Difficulty Factor

Special Considerations And Applications Elliptical Groove

• Can Only Be Used When Difficulty Factor Is Less Than 19 On Steel

• Can Only Be Used When Difficulty Factor Is Less Than 10 On Aluminum Or Copper

• Isn’t Effective If Difficulty Factor Is Less Than 8 On Steel

Special Considerations And Applications Controlled Wrinkle Bend Die

Special Considerations And Applications Controlled Wrinkle Bend Die

• Used When D.F. IS More Than Elliptical Tooling Can Handle

• Usually Greater Than D.F. Of 20

• Can Only Be Used To Approx. D.F. 27 without the addition of a mandrel

• Allows Material To Flow Into Cavity

Special Considerations and Applications Reach Adjusted Tools

• Dedicated Tooling Sets

• Clamp And Pressure Die Lengths Are Compensated For CLR

• Tools Are Made To Tighter Tolerances

• All Tools Are Sized To The Largest CLR Used

• Dramatically Reduces Set Up Time

Summary

• Utilize the longest clamp length possible

• Always revert to the basics when experiencing problems with tight radius bending

• Use bending Difficulty Factor calculation to determine the tooling requirements

• Consider tooling automation features or reach adjust tooling to reduce setup time and improve throughput.

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