intro to rotary draw bending: an engineer’s guide to bending tubes
TRANSCRIPT
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 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
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
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)
Tight Radius Bending Material Considerations
• Ovality Requirements • Ovality % = Max OD - Min OD X 100 Nominal OD
5 Percent Ovality
Tight Radius Bending Material Considerations
• Wall Thinning Requirements • WT % = (Nom. - Min) / Nom X 100
Thin Wall Area
Tight Radius Bending Material Considerations
• 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
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
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 Machine Considerations
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
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
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
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
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
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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