Metal deforming – By use of closed-die and coacting work-forcer – With stripping or ejecting from tool
Patent
1995-01-10
1996-08-06
Larson, Lowell A.
Metal deforming
By use of closed-die and coacting work-forcer
With stripping or ejecting from tool
72344, 72427, B21D 4500, B21D 4506
Patent
active
055422772
DESCRIPTION:
BRIEF SUMMARY
This invention relates to the removal of an article, formed from a metal disc by cooperation of a punch and die, from the punch and more particularly, but not exclusively to the removal of a drawn and wall ironed can body from the hollow punch of a press tool having a bottom shaping tool axially aligned with the punch.
In the mass production of cans from blanks cut from sheet metal, a cup is formed by a blank and draw tool and the cup is then redrawn and wall ironed in a long stroke press comprising a punch carried on a ram which drives the punch through a redraw die and a sequence of ironing rings making progressively smaller clearance with the punch so the can produced has a bottom wall substantially the same thickness of the sheet metal and side wall thinner than the bottom wall. One such wall ironing press is described in British Patent 1463026 (STANDUN) in which it is said that the ram moves at a rate in the order of 150 to 175 strokes per minute. This press used a mechanical stripper comprising a plurality of fingers arranged to surround the punch/ram so that on the return stroke the eared edge of the side wall of the can body strikes the stripper fingers which, after limited deflection to make complete contact with eared profile, lock to prevent the can body travelling back through the ironing rings as the ram retracts. GB-A-2181685 (METAL BOX) describes another form of stripper having deflectable fingers to engage with the eared edge. Whilst these deflectable finger strippers have been satisfactory at stroking rates of the order of 150 strokes per minute (roughly equivalent to linear speeds of about 180 meters per minute) improved processes having increased stroking rates of about 280 strokes per minute and greater are being introduced. At these increased speeds the free edge of the can strikes the stripper fingers at increased speeds which crumple the free edge.
Hollow rams and punches are customarily used so that the can interior is vented by air introduced through the punch during stripping. Various forms of knock out pad in the punch hollow have been proposed, such as are described in U.S. Pat. No. 3,402,591 (MAEDER) and U.S. Pat. No. 3,524,338 (BOZEK) but these knock out pads require a long actuating rod extending through the punch so adding mass to the ram and punch assembly and the complication of a mechanism to operate them.
In order to reduce the moving mass of the ram and punch assembly, punches have been proposed which rely on compressed air delivered through the ram hollow to not only vent but also push the completed can off the punch. In U.S. Pat. No. 3,771,344 WRIGHT/Crown Cork & Seal Co) and U.S. Pat. No. 4,164,860 (KAMINSKAS/Standun Inc) compressed air delivered through the ram assembly assists an external mechanical stripper.
U.S. Pat. No. 3,771,344 describes an assembly of dies, a ram and punch assembly movable through the dies and a doming pad in axial alignment with the end of the punch so that a concave dome is formed on the can bottom at the end of the ram stroke. The punch is provided with concentric passage ways which meet at a valve seat openable and closable by a valve having a dependent stem. The outer passage way is filled with compressed air at high pressure used for stripping and the inner passage way is filled with compressed air lower pressure to bias the valve to close on the valve seat. As the punch approaches the doming pad and flat can bottom is deformed to concave and presses on the valve stem to open the valve so that air at 100 psi is delivered to the interior of the can to vent and assist stripping during the return stroke. As the can leaves the punch, the valve is closed by the air pressure from the inner passage way so that no air is wasted during the return stroke. Bowever provision of the concentric passages for high pressure and low pressure air is a costly complication to the punch.
In U.S. Pat. No. 4,164,860 it is observed that although use of low air pressure in Wright's punch minimises risk of the stripping air blasting the freed can against the domi
REFERENCES:
patent: 4343173 (1982-08-01), Bulso, Jr. et al.
patent: 5056350 (1991-10-01), Moen et al.
patent: 5249449 (1993-10-01), Lee et al.
Butler Rodney
CarnaudMetalbox plc
Larson Lowell A.
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