design for stamping (dfs) terry sizemore edits from mark courtright, dwayne mattison, ravi...
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![Page 1: Design for Stamping (DFS) Terry Sizemore Edits from Mark Courtright, Dwayne Mattison, Ravi Ranganathan, Mac Lunn, Rolf Glaser](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649d9d5503460f94a874f8/html5/thumbnails/1.jpg)
Design for Stamping
(DFS)Terry Sizemore
Edits from Mark Courtright, Dwayne Mattison, Ravi
Ranganathan, Mac Lunn, Rolf Glaser
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References
■ Eary and Reed: Techniques of Pressworking Sheet Metal, 2nd ed. Prentice Hall
■ Boothroyd, Dewhurst, Knight: Product Design for Manufacture and Assembly, 2nd ed. Marcel Decker
■ Brallia: Design for Manufacturability Handbook, 2nd ed., McGraw Hill
■ Sizemore: EMU MFG 316 Lecture Notes■ Ulrich and Eppinger ■ SME Journal of Manufacturing Systems
Vol23, No3, 2004 (reference 1)
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Design for Stamping (DFS)
■ Assumptions■ DFS will be “Design for Stamping” in this lecture■ DFS applies to sheet materials from 0.026 to 0.1875 inches in
thickness (0.88-4.76mm)■ Successful use of DFS is measured by:
■ Material utilization percentage ■ Improvement in quality by decreasing Quality Loss
(Taguchi’s quality loss function)■ $$$’s of Die Cost Avoidance■ Number of processes eliminated■ Number reduced parts due to adding “Free” features■ Number of re-orientations eliminated
■ This list of metrics can be applied, not all are equal and you have to consider compromise for your design
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Product Development ProcessUlrich and Eppenger, 1995
Testing/Refinement
ConceptDevelopment
DetailDesign
SystemDesign
ProductionRamp up
ProductLaunch
MissionStatement Design for Stamping
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Agenda■ Cutting
■ Theory of Cutting Sheet Metal■ Forces for Cutting■ Die Cutting Operations
■ Properties of Metals (stress strain curve, spring back, etc)
■ Forming■ Bending■ Embossing and Miscellaneous Forming■ Drawing
■ Tooling■ Assembly■ Design Practices
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Theory of Cutting
■ Assumptions■ Theory of Cutting applies to the
trimming of forgings, extrusions and castings and the cutting of bar stock
■ Sheet metal is material <0.125” thick Plate is material >0.125” thick
■ Does not apply to brittle materials (i.e. magnesium)
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Analysis of Cutting
■ Forces applied by the punch and die are shearing forces, which apply a shearing stress to the material until fracture
■ Material deformation occurs in the plane of shear
■ As the tool wears and the clearance between the punch and die grow the material will begin to experience more tensile deformation and less shear deformation prior to fracture
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Characteristics of a Die Cut Edge
■ Roll Over – Flow of material around the punch and die ■ The larger the clearance the greater the roll
over■ Burnish – The rubbed or “cut” portion of the
edge■ The sharper the punch the wider the burnish
■ Fracture – The angled surface where the material separates from the parent material
■ Burr – The very sharp projection caused by a dull cutting on the punch or die.
General Rules: The more dull the tool the greater the burr. The softer the material the greater the burr.
*These characteristics are evident on both the hole and slug
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Penetration
Roll Over + Burnish = Penetration
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Percent PenetrationsMaterial % Penetration
Silicon Steel 30
Aluminum 60
.10 C Steel Annealed 50
.10 C Steel Cold Rolled
38
.20 C Steel Annealed 40
.20 C Steel Cold Rolled
28
.30 C Steel Annealed 33
.30 C Cold Rolled 22E.V. crane, Plastic Working in Presses, John Wiley and Sons, Inc., New York, 1948, p. 36
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Die and Punch Clearance
Proper Clearance■ Too Big – Blank ends up
with roll-over and/or a crown effect.
■ Too Small – Results in large stripping force and secondary shear. Secondary shear is when the fracture propagating from the punch misses the fracture propagating from the die.
■ When proper clearance exists, the fractures meet which yields a preferable break edge.
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Die and Punch Clearance
■ Force Curves – A common tool for analyzing various clearance conditions is by using strain gages or other transducers to create force vs. displacement curves. Poor clearance conditions result in less than ideal force curves.
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Other Characteristics
■ Dish Distortion■ Spacing Distortion – When holes are
punched next to each other in sequence distortion in the circularity and position of the first hole will occur. If possible punch closely proximate holes simultaneously. See attached table for recommended design practices. (insert figure and chart from page 20)
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Forces for Cutting
For Cutting:■ Ferrous stamping materials shear
strength is 70-80% ultimate tensile strength
■ Force=Shear Strength*Perimeter of Cut*Thickness
■ When calculating tonnage required it is recommended that ultimate tensile strength be used instead of shear strength to compensate for die wear.
Tonnage=(UTS*Perimeter*Thickness)/2000
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Forces for Cutting
■ Take caution in what number is used for shear strength or UTS. Consideration must be made for prior operations that may affect the material properties.■ Work Hardening■ Annealing or Tempering■ Other processes that affect the
mechanical properties of the material
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Work and Energy■In terms of metal cutting:
Work=average force*distance■Force: Since the force/displacement
curve for cutting sheet metal is nearly rectangular use the maximum force prior to fracture as the average force
■Distance: The distance used in this calculation is percent penetration (see earlier slide) multiplied by material thickness.
■This calculation assumes no secondary shear, which will require additional energy during cutting.
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Example
10 inch diameter aluminum blank made from .032 inch 3003 aluminum (3003 UTS is 11000 psi)
Force=(11000)(3.14)(10)(.032) =11053 lbs
Tonnage=11053/2000=5.5 tonsWork=(5.500)(.600)(.032)=.1056 inch
tons*
(Need to insert penetration chart page 10)
*Most press flywheels are rated in inch ton capacity
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Cutting Operations
■ Blanking – Material removed is the work-piece
■ Perforating – Material removed is scrap■ Piercing – Material removed is scrap■ Lancing – No metal removed, bending and
cutting■ Cut-off/Parting- Separating parts or
reducing scrap strip size■ Notching – Removing material from the
outer edges of the strip■ Shaving – Removing the break edge■ Trimming – Removing “Flash” from drawn
parts
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Blanking
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Bending
Bending - a metal forming process in which a force is applied to a piece of sheet metal, causing it to bend at an angle and form the desired shape. A bending operation causes deformation along one axis, but a sequence of several different operations can be performed to create a complex part.
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Perforating
*
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Piercing
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Lancing
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Cut-Off/Parting
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Notching
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Shaving
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Shaving
The shaving process is a finish operation where a small amount of metal is sheared away from an already blanked part. Its main purpose is to obtain better dimensional accuracy,
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Trimming
Punching away excess material from the perimeter of a part, such as trimming the flange from a drawn cup.
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Slitting
Cutting straight lines in the sheet. No scrap material is produced.
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Perforating
Punching a close arrangement of a large number of holes in a single operation.
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Dinking
A specialized form of piercing used for punching soft metals. A hollow punch, called a dinking die, with beveled, sharpened edges presses the sheet into a block of wood or soft metal.
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Parting
Separating a part from the remaining sheet, by punching away the material between parts.
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EmbossingEmbossing is a metal forming process for producing raised or sunken designs or relief in sheet material by means of matched male and female roller dies.
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DrawingDeep drawing is a metal forming process in which sheet metal is stretched into the desired part shape. A tool pushes downward on the sheet metal, forcing it into a die cavity in the shape of the desired part.
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Hydro-formingHydro-forming is a manufacturing process where fluid pressure is applied to a ductile metallic blank to form a desired component shape
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Agenda■ Cutting
■ Theory of Cutting Sheet Metal■ Forces for Cutting■ Die Cutting Operations
■ Properties of Metals (stress strain curve, spring back, etc)
■ Forming■ Bending■ Embossing and Miscellaneous Forming■ Drawing
■ Tooling■ Assembly■ Design Practices
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Stress/Strain Curves
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Geology of Stress Strain Curve
■ Elastic Region■ Yield Point■ Necking Region■ Ultimate Point■ Elongation■ Spring Back
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Spring Back
Spring-back is the material’s tendency to return to its original shape after forming. This must be anticipated in both the tooling and part design. Darts can be added in bendRadii to help the panel retain its shape. Designer should also anticipate that 90° flangesWill not be possible due to spring back of at least 3°. If 90° is required then additional process will be necessary.
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Stress/Strain Curves
Springback or the elastic strain, is then simply the amount of strain returned to the part as the stress returns to zero
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Agenda
■ Cutting■ Theory of Cutting Sheet Metal■ Forces for Cutting■ Die Cutting Operations
■ Properties of Metals (stress strain curve, spring back, etc)
■ Forming■ Bending■ Embossing and Miscellaneous Forming■ Drawing
■ Tooling■ Design Practices
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Forming Limit Diagram
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Embossing
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Drawing
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Bending
*
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Coining
*
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Embossing
*
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Projection
*
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Hydro-forming
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Agenda
■ Cutting■ Theory of Cutting Sheet Metal■ Forces for Cutting■ Die Cutting Operations
■ Properties of Metals (stress strain curve, spring back, etc)
■ Forming■ Bending■ Embossing and Miscellaneous Forming■ Drawing
■ Tooling■ Assembly■ Design Practices
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Transfer Dies
■ Most automotive stampings created by transfer press
■ Automation “transfers” part from die to die
■ First picture shows stampings transferred from the side
■ Second picture shows stampings transferred from the front and back
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Hydro-forming - Bladder press
■ Create only bottom half of the die (cheaper and faster)
■ Sheet metal placed over die■ Rubber-like material placed
over sheet metal■ High pressure water forms
part■ The dies are less expensive
than a transfer press but variable cost will be much higher due to significantly slower cycle times
■ More appropriate for low volume stampings
■ Can form more aggressive shapes than traditional draw forming
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Progressive Dies
■ Dies fed directly from steel coil
■ No need for blanking operation
■ Scrap gets cut away as part gets formed
Surfaces must be flanged instead of drawn home. This requires notches which reduce the strength of the part
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YouTube Videos on Progresisve Dies
■ http://www.youtube.com/watch?v=10vNgC4LpkQ■ http://www.youtube.com/watch?v=GKTDgBeEFik&fea
ture=fvwrel■ http://www.youtube.com/watch?v=IgEIt7fnHH4
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Rubber Pad Dies
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Forming Process Selection Chart
Transfer Dies Progressive Dies
Sheet Hydro-forming
Investment Required
H M L
Process Cycle Time
M H L
Part Variable Cost
M L H
Suitable Part Design
Class “A” PanelsClosure Inner
PanelUnderbody Cross
MembersTire Tubs
Reinforcement Brackets
Nut PlatesHinges
Similar to transfer dies
More aggressive shapes possible
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Agenda
■ Cutting■ Theory of Cutting Sheet Metal■ Forces for Cutting■ Die Cutting Operations
■ Properties of Metals (stress strain curve, spring back, etc)
■ Forming■ Bending■ Embossing and Miscellaneous Forming■ Drawing
■ Tooling■ Assembly■ Design Practices
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Design for Stampings
■Assembly Process is considered during the component design
■Assembly sequence and weld placement■Process Flow ■Assembly equipment layout■Equipment used and types of part joining
■Process to control variation■Part variation■Fixture variation ■Weld gun variation
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Welding Assembly
Design for welding includes manufacturing and assembly considerations during the component development stage
Weld points locations and access are considered during the component design
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Process Flow
• High level process flow development provides considerations for :• Design features for
needed for assembly • Assembly sequence • Preparation for floor plan
layout
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Assembly Floor plan - Process Flow
• Floor plan process flow provides:• Process Sequence• Welding times analysis• Fixture layout• Equipment placement• Robot programming• Part delivery and removal• Piece cost development• Capital expense evaluation
Floor plan layouts are a critical step during the design for welding process
Assembly equipment layout
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Assembly Floor plan
Floor plan shows sequence of operation of this assembly
Assembly equipment layout
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Assembly Equipment
■ Welding Type by equipment
■ Arc welding
■Robot with EOAT
■Pedestal Welder
■Holding fixture
■Robot EOAT
■Weld Nuts
■ MIG Welding
■Robot with EOAT
■ Laser Welding
■Robot
■ Ceiling
■ Tape
■ Dispensable Sealer
■ Fixture
■ Holding
■ Part Pass
■ Pedestal welder holding fixture
■ Joining
■Clinching
■Riveting
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Fixture Design Considerations
1. Parts are loaded in the assembly station (Figure2a)2. Tooling is closed, deforming the parts to a nominal position (Figure 2b)3. Parts are assembled / joined together (Figure 2c)4. Tooling and extra locators are released and theassembly springs back (Figure 2d)
Figure 2
Design for process Variation
The variation within the process needs to be controlled at each station
Reference 1
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Sources of Variation
■ Part Variation: In the absence of tooling variation, fixture position has no major impact on assembly variation in the presence of part variation. The final assembly variation is only a function of part deviation. The spring-back effect is totally compensated by the relocation effect when fixtures are moved to different positions.
Reference 1
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Sources of Variation
■ Fixture Variation: In the presence of fixture variation, assembly variation depends on fixture positions. A general rule for variation reduction is to avoid locating non-nominal fixtures close to welding locations and other fixtures. An optimal fixture position can be found.
Reference 1
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Sources of Variation
■Welding Gun Variation: In the presence of welding gun variation, assembly variation depends on the fixture positions. The guideline for fixture design is to move fixtures as far as possible from the locations of faulty welding gun. This minimizes any restraint to part deformation. In general, the optimal solution locates the fixtures such that they do not provide any support to the parts during the assembly process. However, this general solution is not feasible. Parts must be held or supported at a specific position before assembly.
Reference 1
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Agenda
■ Cutting■ Theory of Cutting Sheet Metal■ Forces for Cutting■ Die Cutting Operations
■ Properties of Metals (stress strain curve, spring back, etc)
■ Forming■ Bending■ Embossing and Miscellaneous Forming■ Drawing
■ Tooling■ Assembly■ Design Practices
![Page 69: Design for Stamping (DFS) Terry Sizemore Edits from Mark Courtright, Dwayne Mattison, Ravi Ranganathan, Mac Lunn, Rolf Glaser](https://reader036.vdocuments.mx/reader036/viewer/2022062516/56649d9d5503460f94a874f8/html5/thumbnails/69.jpg)
Stamping Applications
■ Can accommodate many functional features and attachment features
■ Natural uniform wall thickness■ Can incorporate
■ Springs■ Snap fit■ Tabs■ Spot welding
■ Material Thickness from .001 in to .790 in
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Production
■ 35 to 500 parts per minute■ 250000 per year minimum to justify
using progressive die■ Progressive Die should eliminate at
least two secondary operations before consideration
■ Short run press tooling – Short run is when the cost of the tool exceeds the cost of the parts
■ Punch presses should be used for low volume parts when possible
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Materials
■ Any material that can be produced in sheet can be press-worked■ Deep drawn parts require “Draw
Quality” steels■ Non-ferrous metals may require
modified processing or additional processing steps
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Design Recommendations
■Shaping and nesting on strip■Stamp multiple parts on same strip to increase
strip utilization■Design part/strip so part can be “cut-off”, not
“blanked”
■Holes■Diameter not less than T, spacing should be 2T
to 3T■1.5 to 2T between a hole and edge■1.5T + bending radius spacing between
surface and hole■ Use pilot holes
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Design Recommendations
■ Avoid sharp corners■ Improves tool wear■ Increases bur size■ Lowers stress■ Minimum radius of .5T or .03125
■ Be aware of grain direction and how it may change from blank to blank
■ Long sections should greater than 1.5T wide to avoid distortion and a weak problematic tool design
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Design Recommendations
■ Use stiffening ribs or darts when more strength is needed
■ Use extruded holes when threaded fasteners must be used (1.5 T is the max thread contact you can achieve; progressive dies can do better)
■ Set-outs – used for location, rivets, etc. ■ Height to be .5T
■ Be aware of the burr direction and how the mating part is installed in the hole
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Dimensional Considerations
■ Spring-back, die wear, material variation (temper, thickness, content) are sources of variation
■ Short run prototype stampings should represent the dimensional population of the production tooled parts to prevent system failures when part goes into production
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Material Utilization
There are two types of material utilization (MUD)
Engineering MUD and Process MUD
Engineering MUD is the part weight divided by the weight of the minimum amount of material required to make ONLY the outline of the part. This number will run between 80-90% for the average body structure stamping
Process MUD is the part weight divided by the weight of the blank that is used to make the part. This is what defines the cost for the part, as you have to purchase all of the material required to make the part. This number is much lower than the engineering MUD number and typically runs between 55-65% for the average body structure stamping