Basic Of Metal Stamping : Tools and Dies Fixed Stripper

Stripper Designs

Stamping dies require some means of stripping the part from the end of the punch at withdrawal. Common types of strippers for accomplishing this include Fixed, Urethane and Spring. Stripping force varies based on part material type and thickness as well as punch-to-matrix clearance. This force ranges from nearly zero to as much as 25% of the force required to perforate the initial hole. Most applications do not exceed 10% of the perforating force.

Fixed StripperFixed strippers go by many names:
. Box . Bridge
. Channel . Positive
. Solid . Tunnel
A fixed stripper is a steel plate with a clearance slot that allows the part material to pass under it. This plate mounts to the die  etainer in a fixed  position. Clearance holes cut through the stripper plate let the punches extend through without interference. At withdrawal the part material hits the stripper, preventing it from lifting as punches retract. The part material strips from the end of the punch.

 

Fixed strippers have several drawbacks. They do not hold the stock strip flat and are unable to absorb impact and snap-thru hock. The result is poor part flatness and premature punch failure.
We generally do not recommend fixed strippers for high-volume or highprecision jobs. A typical clearance under the stripper is 11.2 times the material thickness - 1/16h to 1/8h is common clearance on the sides of the stock strip.

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Basic Of Metal Stamping - Die Type

There is 4 normal type of die in the metal stamping industries;

Punch Press

Perforation is generally the most severe operation performed in a die. That’s because the punch press applies forces ranging from a few tons to more than 1000 tons. Proper press alignment is essential. While die set has some effect on alignment during operation, it cannot offset poor press alignment.

Simple Die
A simple die typically perforates holes in a part or blanks out the part using punches in conjunction with mated lower die components (matrixes). Simple dies also commonly produce basic forms as well as perform notching and lancing operations.Simple dies require a press operator to load and unload parts and part material before and after each press cycle.

Compound Die
A compound die blanks and perforates a part at the same time in the same station. In most cases this operation perforates a hole or holes down, while the part blanks up. This allows slugs from those holes to fall through the die. This method leaves the part in the die, requiring some means of part removal.
Compound dies commonly run as single-hit dies. They can run continuously with a feeder, provided you can remove the part in a timely manner. Open Back Inclinable (OBI) presses - in the inclined position along with an air blowoff
- aid in part removal.
Advantages of a compound die include:
• Minimal space in the press
• All burrs in one direction
• Superior accuracy between holes and trim edges
• More economical to build than a progressive die
A disadvantage of a compound blank die is its limited space that tends to leave die components thin and weak. This concentrates the load and shock on punches and matrixes, resulting in tooling failures.

Progressive Die

Progressive dies provide an effective way to convert raw coil stock into a finished product with minimal handling. As aterial feeds from station to station in the die, it progressively works into a completed part. Progressive dies usually run rom right to left. The part material feeds one progression for each press cycle. Early stations typically perforate holes that serve as pilots to locate the stock strip in later stations.

There are many variations of progressive die designs. The design shown here illustrates some common operations and  terminology associated with progressive dies

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For any products, processes and parts inquiry,  or other technical support, feel free to contact any of our offices listed on the 'Contact Us' page. . Or check out our website at http://www.daepac.com