Drawing of sheet metal

Claim 2

In a method of deep drawing a container from a sheet metal workpiece which comprises introducing the workpiece onto the first die of one set of punches of a deep drawing press having two opposed sets of interconnected, telescopically arranged punches relatively movable to an innermost punch, advancing a set of punches as a composite punch towards said first die and drawing said workpiece therethrough and advancing said punches to a second die, the improvement comprising the steps of storing energy created by relative movement between one of said punches and said innermost punch by compressing a fixed quantity of a compressible fluid medium, and transferring part of said energy directly to a punch in the opposed set of punches to assist movement of at least one of the telescoping punches of said opposed punch sets relative to the innermost punch of said opposed set of punches.

Claim 3

Deep drawing press apparatus of the type including a press head, at least one set of a plurality of telescoping punches carried by the press head for cooperation with a plurality of stationary draw dies whereby an initially substantially flat metallic workpiece supported on a first die is drawn progressively by said punches through said die to form a container upon movement of said press head towards said dies, at least one of said punches being movable in opposite directions relative to said press head during parts of the drawing operation, a control system for a relatively movable punch including means for storing energy generated in response to movement of said punch relative to said press head during one part of a drawing operation, said energy storing means comprising an accumulator containing a substantially fixed quantity of compressible fluid medium, a collapsible chamber containing a substantially fixed supply of a hydraulic fluid medium, means affording a direct and unrestricted connection between the collapsible chamber and said accumulator whereby a decrease in volume of said collapsible chamber effects a corresponding increase in pressure of the compressible fluid in said accumulator, means responsive to movement of said punch relative to said press head in one direction during a part of a drawing operation to collapse said chamber and increase the pressure in said accumulator in proportion to said relative movement, and fluid pressure-responsive means connected to said accumulator and constructed and arranged to receive the energy stored therein and assist in the further operation of said press, thereby decreasing the energy input requirement to the press substantially by the energy stored in the accumulator during the first-mentioned part of the drawing operation.

Claim 4

Deep drawing press apparatus of the type including a press head, at least one set of a plurality of telescoping punches carried by the press head for cooperation with a plurality of stationary draw dies whereby an initially substantially flat metallic workpiece supported on a first die is drawn progressively by said punches through said die to form a container upon movement of said press head towards said dies, at least one of said punches being movable in opposite directions relative to said press head during parts of the drawing operation, a control system for a relatively movable punch including means for storing energy generated in response to movement of said punch relative to said press head during one part of a drawing operation, said energy storing means comprising an accumulator containing a substantially fixed quantity of compressible fluid medium, a collapsible chamber containing a substantially fixed supply of a hydraulic fluid medium, means affording a direct and unrestricted connection between the collapsible chamber and said accumulator whereby a decrease in volume of said collapsible chamber effects a corresponding increase in pressure of the compressible fluid in said accumulator, means responsive to movement of said punch relative to said press head in one direction during a part of a drawing operation to collapse said chamber and increase the pressure in said accumulator in proportion to said relative movement, and fluid pressure-responsive means connected to said accumulator and constructed and arranged to receive the energy stored therein and assist in the further operation of said press, thereby decreasing the energy input requirement to the press substantially by the energy stored in the accumulator during the first-mentioned part of the drawing operation.

Claim 5

An apparatus as set forth in claim 2 wherein a hydraulic fluid makeup circuit is provided for supplying hydraulic makeup fluid to each control system.

Claim 6

An apparatus as set forth in claim 3 wherein the hydraulic makeup fluid circuit comprises a nonreturn valve and a pressure-sensitive relief valve operatively connected to a hydraulic reservoir.

Claim 7

An apparatus as set forth in claim 2 wherein holddown means are provided for holding the workpiece in position on at least the first die.

Claim 8

An apparatus as set forth in claim 5 wherein the holddown means comprises a blankholder operable by means of a hydraulic control circuit to move between a position in which the blankholder is biased away from the die and a clamping position in which said blankholder is adapted to hold a workpiece in clamping relationship with said die.

Claim 9

An apparatus as set forth in claim 6 wherein the blankholder is in the form of an annular ring.

Claim 10

An apparatus as set forth in claim 6 wherein a hydraulic fluid makeup circuit is provided for supplying hydraulic makeup fluid to the hydraulic circuit controlling the blankholder.

Claim 11

The press of claim 2 including a plurality of punches relatively movable with respect to said press head, and a control system for each of said punches.

Claim 12

An apparatus as set forth in claim 8 wherein the hydraulic fluid makeup circuit associated with the holddown means comprises a two-position valve for controlling actuation and relief of the hydraulic control circuit controlling operation of said blankholder, a hydraulic accumulator connected to the valve on the side thereof remote from the blankholder, and a nonreturn valve and a pressure-sensitive control valve arranged for connection to the hydraulic control circuit at a position between the valve and the accumulator and connectable to an hydraulic reservoir.

Claim 13

An apparatus as set forth in claim 9 wherein workpiece holddown means are provided on second and subsequent draw dies, holddown being effected by the punch immediately preceding that which is effecting the formation of the workpiece at that die.

Claim 14

An apparatus as set forth in claim 11 wherein the holddown pressure applied to the workpiece at any one of said dies is controlled by a spring-loaded attachment unit which comprises a pair of members resiliently spaced apart, one of said members being adapted to be fixedly connected to the press frame of said press, and the other of said members being adapted to be engaged by an abutment on the punch effecting holddown at that die, whereby to provide a workpiece holddown pressure less than the drawing pressure of said press.

Claim 15

An apparatus as set forth in claim 2 wherein each of the punches and dies are of circular cross section along at least part of its length.

Claim 16

An apparatus as set forth in claim 1, wherein the control system associated with each punch of one of the sets of punches is connected in common with the corresponding punch of the other of said set of punches.

Claim 17

An apparatus as set forth in claim 9 wherein a double-acting press is used and four sets of telescopically received punches are coaxially mounted in two rows of said press heads, which punches are arranged to cooperate with two opposed pairs of sets of stationary dies to produce four containers on each working stroke of the press.

Claim 18

An apparatus as set forth in claim 2 in which the punches are directed for either horizontal or vertical operation.

Claim 19

A method as set forth in claim 1 which further comprises removing a drawn workpiece from the innermost of the telescoping punches.

Claim 20

A method as set forth in claim 1 wherein the drawn workpiece is removed by ejecting same from the innermost of the telescopic punches by hydraulic and mechanical means.

Claim 21

A method as set forth in claim 15 wherein the hydraulic means comprises a plunger acting on the base of the drawn workpiece.

Claim 22

A method as set forth in claim 15 wherein the mechanical means comprises a stripper ring acting on the periphery of the open end of the drawn workpiece.

Claim 23

The press of claim 2 wherein said punch is movable between extended and retracted positions relative to said press head and wherein said punch is adapted to retract during the movement of said press head toward said dies and by engagement with a die of lesser cross-sectional dimension, said collapsible chamber being constructed and arranged to be collapsed in response to said retraction of said punch.

Claim 24

The press of claim 2 wherein said direct connection includes a cam-operated valve responsive to movement of said press head for locking the hydraulic fluid in said control system to prevent relative movement of a punch during a part of the drawing operation.

Claim 25

A press as set forth in claim 22 wherein at least some of the relatively movable punches are provided with radially extended flanges, a common casing formed as a cylinder slidably receiving said flanges, said flanges and casing defining each collapsible chamber operable during said one part in the drawing operation to increase the pressure in the accumulator, said casing and flanges also defining said pressure-responsive means for receiving the energy stored in said accumulator.

Claim 26

An apparatus as set forth in claim 2 including a second set of telescoping dies coaxially mounted on said press head in opposition to said first set and arranged to cooperate with a second set of opposed stationary dies to produce a container on each stroke of the press in opposite directions.