Design_for_Stampings

Die and Punch Clearance

Force Curves – Using strain gages or other transducers to create force vs. displacement curves is a common tool for analyzing various clearance conditions. Poor clearance conditions result in less than ideal force curves (may put in curves???)
50 38 40 28 33 22
E.V. crane, Plastic Working in Presses, John Wiley and Sons, Inc., New York, 1948, p. 36
Die and Punch Clearance
Proper Clearance



Too Big – Blank ends up with rollover 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.
Work Hardening Annealing or Tempering Other processes that affect the mechanical properties of the material

Work and Energy

In terms of metal cutting:

Penetration
Roll Over + Burnish = Penetration
Percent Penetrations
Material Silicon Steel Aluminum % Penetration 30 60
.10 C Steel Annealed .10 C Steel Cold Rolled .20 C Steel Annealed .20 C Steel Cold Rolled .30 C Steel Annealed .30 C Cold Rolled
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 tons Work=(5.500)(.600)(.032)=.1056 inch tons*

Burnish – The rubbed or “cut” portion of the edge

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
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)
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 The sharper the punch the wider the burnish
Production Ramp up
Product Launch
Agenda

Cutting

Theory of Cutting Sheet Metal Forces for Cutting Die Cutting Operations


Properties of Metals (stress strain curve, spring back, etc) Forming
Forces for Cutting
For Cutting: In general 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

ቤተ መጻሕፍቲ ባይዱ

Bending Embossing and Miscellaneous Forming Drawing


Tooling Design Practices
Agenda

Cutting

Theory of Cutting Sheet Metal Forces for Cutting Die Cutting Operations
(Need to insert penetration chart page 10) *Most press flywheels are rated in inch ton capacity
Design for Stamping
Design for Stamping (DFS)

Assumptions
DFS will be “Design for Stamping” in this lecture DFS applies to sheet materials from .035 to .1875 Successful use of DFS is measured by:

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
Theory of Cutting

Assumptions
Theory of Cutting also applies to the trimming of forgings, extrusions and castings and the cutting of bar stock Sheet metal is anything <.125, Plate is anything >.125 These rules do not apply to very brittle materials such as magnesium
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.


Properties of Metals (stress strain curve, spring back, etc) Forming



Bending Embossing and Miscellaneous Forming Drawing


Tooling Design Practices