Method and apparatus for superplastic forming

1. A method of forming a workpiece comprising the steps of:

providing a forming apparatus, the forming apparatus having an upper die member, a punch and a blank holder, the upper die member having a cavity, the punch having a forming surface and the blank holder operative to move between a first, open position and a second, closed position;

placing a workpiece between the upper die member and the blank holder when the blank holder is in the first, open position;

moving one of the upper die member and the blank holder to place the blank holder in the second, closed position thereby sandwiching the workpiece between the upper die member and the blank holder;

moving the workpiece sandwiched between the upper die member and the blank holder against the punch such that the punch engages the workpiece and draws a portion of the workpiece sandwiched between the upper die member and blank holder into the cavity in the upper die member;

supplying gas pressure to the cavity wherein the gas pressure acts against one side of the workpiece to press the workpiece against the forming surface of the punch until forming of the workpiece is completed;

withdrawing the punch; and

moving the upper die and blank holder to the first, open position and removing the formed workpiece.

2. A method of forming a workpiece as set forth in claim 1 including the die cavity having a non-forming surface and the step of keeping the workpiece spaced from the non-forming surface of the die cavity during the forming operation.

3. A method of forming a workpiece as set forth in claim 1 including the step of providing at least one passageway extending to and terminating at the forming surface of the punch; and

venting any pressure between a lower surface of the workpiece and the forming surface of the punch as the workpiece is pressed against the forming surface of the punch.

4. A method of forming a workpiece as set forth in claim 1 including the step of using the blank holder to remove the workpiece from the punch; and

separating the upper die from the blank holder to position the upper die and blank holder in the first, open position.

5. A method of forming a workpiece as set forth in claim 1 including the step of using the blank holder to control the amount of workpiece material drawn into the cavity;

monitoring the temperature of the forming apparatus; and

modifying the pressure exerted on the workpiece by the blank holder based on and as a function of the temperature of the forming apparatus.

6. A method of forming a workpiece as set forth in claim 1 including the step of monitoring the temperature of the forming apparatus; and

varying the gas pressure supplied to the cavity based on and as a function of the temperature of the forming apparatus.

7. A method of forming a workpiece as set forth in claim 1 including the step of applying a lubricant to the forming surface of the punch to facilitate workpiece removal.

8. A method of forming a workpiece as set forth in claim 1 including the step of using the punch to guide the blank holder and configuring the punch and blank holder based on thermal expansion properties of the punch to reduce binding of the punch and blank holder during operation of the forming apparatus.

9. A method of forming a workpiece as set forth in claim 1 including the step of raising the upper die first to cool the workpiece prior to raising the blank holder to lift the completed part off the punch.

10. A method of forming a workpiece comprising the steps of:

providing a forming apparatus operative to move between a first, open position and a second, closed position;

providing the forming apparatus with a first die member having a cavity and a punch, the punch having a forming surface;

providing a blank holder operative to move between a first, workpiece loading position and a second, forming position;

providing a cushion system supporting the blank holder and operative to exert a force against the blank holder and the first die member;

heating the first die member and the punch to a predetermined temperature;

placing a heated workpiece on the blank holder when the blank holder is in the first, workpiece loading position;

moving one of the blank holder and first die member to place the blank holder in the second, forming position to sandwich the workpiece between the upper die member and the blank holder;

moving one of the first die member and the punch to press one side of the workpiece against the forming surface of the punch to draw a portion of the workpiece into the cavity of the first die member and begin the forming process;

continuing the forming process by maintaining contact between the punch and the workpiece and applying gas pressure to the workpiece to press a workpiece against the forming surface of the punch until forming of the workpiece is completed; and

moving the forming apparatus to the second, open position to remove the formed workpiece.

11. A method of forming a workpiece as set forth in claim 10 wherein the step of continuing the forming process by maintaining contact between the punch and the workpiece includes the step of maintaining a space between the workpiece and a surface of the die cavity of the first die member such that the workpiece does not contact the non-forming surface of the die cavity during the forming process.

12. A method of forming a workpiece as set forth in claim 10 including the step of providing a forming process including a press ram;

using the press ram to maintain a pressure seal between the first die member and the workpiece and increasing press ram force as necessary to maintain the pressure seal.

13. A method of forming a workpiece as set forth in claim 10 including the step of monitoring the temperature of the forming apparatus; and

varying the gas pressure applied to the workpiece based on and as a function of the temperature of the forming apparatus.

14. A method of forming a workpiece as set forth in claim 10 including the step of providing at least one passageway extending to and terminating at the forming surface of the punch; and

venting any pressure between a lower surface of the workpiece and the forming surface of the punch as the workpiece is pressed against the forming surface of the punch.

15. A method of forming a workpiece as set forth in claim 10 wherein the step of moving the forming apparatus to the second, open position to remove the formed workpiece includes the step of moving the blank holder in relation to the punch to remove the workpiece from the punch; and

after removing the workpiece from the punch, separating the first die member from the blank holder whereby the formed workpiece rests on the blank holder.

16. A method of forming a workpiece as set forth in claim 10 wherein the step of moving one of the blank holder and the first die member to the second, forming position includes the step of moving the first die member in a direction toward the blank holder; and

continuing movement of the first die member until the first die member engages the workpiece placed on the blank holder whereby continued travel of the first die member acts against pressure exerted by the cushion system such that the pressure exerted by the cushion system controls flow of workpiece material drawn into the cavity by the punch.

17. A method of forming a workpiece as set forth in claim 16 wherein the pressure exerted by the cushion system varies dependent upon forming apparatus temperature.

18. An apparatus for forming a workpiece comprising:

an upper die shoe and a lower die shoe, said upper die shoe and said lower die shoe operative to move between a first open position and a second closed position;

a die member having a cavity connected to one of said upper die shoe and said lower die shoe, said cavity having a non-forming surface;

a punch, connected to one of said upper die shoe and said lower die shoe and positioned opposite said die member, said punch having a forming surface, said forming surface configured to form the workpiece in a final workpiece shape wherein when said upper and lower die shoes are placed in said second closed position, said punch extends into said cavity and remains spaced from said non-forming surface of said die cavity;

a blank holder supported by a cushion system;

a gas pressure source force applying gas to said cavity; and at least one passageway extending to and terminating at the forming surface of the punch.

19. An apparatus for forming a workpiece as set forth in claim 18 wherein said apparatus provides a gas pressure seal only between the upper surface of the workpiece and upper die member wherein gas pressure in the cavity forms the workpiece on the forming surface of the punch.