This guide is an excellent starting point for anyone who has questions or is interested in learning about bending tooling. Easy to understand diagrams and images are accompanied by clear information, walking readers through the basics of bending tooling.

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

2. Tube Form Solutions Tool School
Rotary Draw Bending Tooling

3. Tool School Agenda:
• Introduction To Rotary Draw Bending
• Engineering Guidelines
• Tight Radius Bending
• Completing the Application Review
• Special Considerations & Applications
• Summary and Benefits

4. Introduction To Rotary Draw Bending

5. Introduction To Rotary Draw Bending
Machine Axes

6. Introduction To Rotary Draw Bending
Typical Interlock Style Tooling
Clamp Die Pressure DieMandrel
Bend Die
Wiper Die
Interlock

7. 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

8. Non-Interlock Interlock
Non-Interlock Interlock
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

9. 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

10. 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

11. 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

12. 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

13. 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

14. 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

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

16. Engineering Guidelines
Requirements for Tool Design

17. Engineering Guidelines
Requirements for Tool Design
• Material type
• Bend Criteria
• Tube O.D.
• Wall thickness
• Bend radius
• Max. Bend Angle

18. 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

19. Engineering Guidelines
Formulas
Wall Factor (WF)
D of Bend (D)
Difficulty Factor (DF)
D
WF
DF
ODTube
RadiusCLR
D
Wall
ODTube
WF




20. Engineering Guidelines
Mandrel And Wiper Die Selection Guide

21. 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

22. 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

23. 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

24. Engineering Guidelines
Real World Situation
Part Shape Distance Between
Bends Is Shorter Than
Engineering Clamp Length
Guidelines

25. Engineering Guidelines
Clamp Gripping Alternatives
• Surfalloy ( 6 grades available)
• Carbide Spray ( 6 grades available)
• Serrations ( Several options)
• Other
All Grip Applications Cause Marking

26. Tight Radius Bending

27. 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

28. Tight Radius Bending
Material Considerations
• 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)

29. Tight Radius Bending
Material Considerations
• Ovality Requirements
• Ovality % = Max OD - Min OD X 100 Nominal OD
5 Percent Ovality

30. Tight Radius Bending
Material Considerations
• Wall Thinning Requirements
• WT % = (Nom. - Min) / Nom X 100
Thin Wall Area

31. Tight Radius Bending
Material Considerations
• Tensile Strength
• Breaking point
• Yield Strength
• Point of permanent deformation
• Difficulty Factor

32. 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

33. Tight Radius Bending
Machine Considerations
• 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

34. 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

35. • 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

36. • 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 Machine Considerations

37. 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

38. 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

39. Tight Radius Bending
Tooling Considerations
• 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

40. Tight Radius Bending
Tooling Considerations
• 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

41. Tight Radius Bending
Tooling Considerations
• 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

42. Tight Radius Bending
Tooling Considerations
• Wiper die deflection must be
minimum
• Wiper die tip should reach
near tangent
• Wiper die radius must fit the
bend die radius

43. Special Considerations and Applications
Elliptical Groove

44. 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

45. 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

46. Special Considerations And Applications
Controlled Wrinkle Bend Die

47. 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

48. 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

49. 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.

50. Leading Tube Bending and End Forming Company
Our goal at Tube Form Solutions is to empower people who design. Our
focus is to help our customers materialize their ideas by providing the tools
and information to help them transform their concepts into reality.
We are a tube bending company dedicated to providing exceptional,
innovative products, technical support, and customer service.
We do not just sell CNC Tube Benders; Tooling or Fixtures’ we provide
solutions to Tube Forming.
We help you get everything you need quickly and accurately for precise
bending and end forming so you can continue to lead the tube forming
industry