STEPPED PUNCH

Abstract

A punch for forming a punched opening in a metal sheet having an elongated body with a first and second spaced apart ends. The first end is adapted to be held by a machine which, when activated, axially drives the body. The second end of the body includes an annular surface corresponding in shape and size to the punched opening as well as an extension which protrudes outwardly from and is surrounded by the annular surface. The extension has a length greater than the thickness of the sheet metal so that, as the punch is driven through the sheet metal, the extension forms a hole in the sheet metal smaller than the opening and thereafter the annular surface forms the opening of the desired size in the metal sheet.

Description

BACKGROUND OF THE INVENTION

I. Field of the Invention

The present invention relates generally to punches and, more particularly, to a punch for forming openings in metal sheets.

II. Description of Related Art

In the formation of metal parts, metal sheets are oftentimes stamped with metal punches to form the desired or required openings. The metal sheet is then formed into the desired end part by stamping. During that forming process, one or more openings may be formed within the metal sheet by metal punches.

For example, in the process of hot metal stamping, a metal sheet of carbon steel is formed into its desired shape by a die and then heated to an elevated temperature at which the metal forms into the austenite phase. At that time, metal punches are used to punch openings within the metal sheet. The stamped part is then rapidly cooled or quenched which transforms the metal from austenite to martensite. The martensite phase of steel is very hard and used in applications where very hard metal is required, e.g. crash barriers for automotive vehicles.

One problem in the hot stamping operation is that, when the heated part is punched by metal punches, a relatively large amount of flash is formed around a portion of the punched hole. When the part is quenched, that flash also hardens and must be removed. Such removal usually requires extensive grinding of the part which adds to the overall manufacturing cost of the part.

SUMMARY OF THE PRESENT INVENTION

The present invention provides a punch for forming a punched opening in a metal sheet that overcomes the above-mentioned disadvantages of the previously known punches.

In brief, the punch of the present invention comprises an elongated body having a first and second spaced ends. The first end is adapted to be held by a machine which, when activated, axially drives the body. That axial direction is typically normal to the surface in which the punched hole is formed.

The second end of the body includes an annular surface corresponding in shape and size to the desired punched hole in the metal sheet. An extension protrudes outwardly from and is surrounded by the annular surface.

The extension has a length greater than the thickness of the metal sheet so that, as the punch is driven through the metal sheet, the extension first forms a hole in the metal sheet smaller than the desired end opening in the metal sheet. As the punch is further driven into the metal sheet, the annular surface then contacts and forms the desired opening in the metal sheet. In practice, however, by first forming a small opening in the metal sheet, the formation of flash around the final punched hole is minimized. This is especially true when the punch is used in a hot metal stamping process.

BRIEF DESCRIPTION OF THE DRAWING

A better understanding of the present invention will be had upon reference to the following detailed description when read in conjunction with the accompanying drawing, wherein like reference characters refer to like parts throughout the several views, and in which:

FIG. 1 is an elevational view of a punch according to the present invention;

FIG. 2 is an end view of the punch; and

FIGS. 3 and 4 are fragmentary diagrammatic views illustrating the operation of the punch of the present invention.

DETAILED DESCRIPTION OF A PREFERRED EMBODIMENT OF THE PRESENT INVENTION

With reference to FIGS. 1 and 2, a punch 10 according to the present invention is shown. The punch 10 includes an elongated body 12 having a first end 14 and a second end 16. The first end 14 of the body is adapted to be mounted in a machine 18 (illustrated only diagrammatically) which, when activated, axially drives the punch 10 along the axis of the body 12. Furthermore, the punch 10 of the present invention is designed in particular for punching holes in heated sheet metal during a hot stamping process.

The body 12 includes a punch section 20 adjacent the punch end 16. This punch section 20 has a cross-sectional shape equal to the shape of the desired final hole in the metal sheet. The punch section 20 tapers outwardly into a mounting portion 22 of the body 12. This mounting portion 22 is greater in cross-sectional area than the punch section 20 and is dimensioned to fit into the machine 18.

Still referring to FIGS. 1 and 2, the punch section 20 terminates in an annular surface 24. This annular surface 24 is generally perpendicular to the direction 26 of movement of the punch 10 when driven by the machine 18.

An extension 30 of the body 12 protrudes axially outwardly from and is surrounded by the annular surface 24. This extension 30 terminates at the free end 16 of the punch body 12. Furthermore, the cross-sectional area of the extension 30 is preferably at least 70% of the cross-sectional area of the punch section 20. In addition, the end 16 of the extension 30 lies in a plane generally perpendicular to the punch axis 26.

A rounded chamfer 32 is preferably formed at the junction of the extension 30 and the annular surface 24. This chamfer not only relieves possible stress within the punch 10, but also prevents punch remnants from becoming stuck on the punch 10.

The entire punch 10 is preferably of a one-piece construction and formed from hardened metal. As such, both the free end of the punch extension 30 as well as the annular surface 24 of the punch section 20 are capable of forming holes in the metal sheet.

With reference now to FIGS. 3 and 4, upon activation of the machine 18, the machine 18 drives the punch 12 along its axis 26 toward the metal sheet 34. In doing so, the extension 30 first contacts the metal sheet 34 and punches a relatively small hole 36 in the metal sheet 34 as shown in FIG. 3. This punching operation also produces a small punched slug 38 from the metal sheet 34.

As the machine 18 continues to drive the punch 10 toward the metal sheet 34 to the position shown in FIG. 4, the annular surface 24 contacts the metal sheet and forms a hole 39 of the desired size in the metal sheet 34. This annular surface thus forms a slug 40 in the shape of a washer from the metal sheet 34. However, the chamfer 32 between the annular surface 24 and the extension 30 prevents the slug 40 from being stuck on the punch 10. The punch 10 is then retracted from the metal sheet 34 thus completing the hole 38 in the metal sheet 34.

In operation, it has been found that by using the two-step punch to form holes 38 in the metal sheets 34, very little flashing is formed around the punched hole 38. Indeed, in many cases, the flashing is so minor around the formed hole 38 that further removal or grinding of the flashing is unnecessary.

From the foregoing, it can be seen that the present invention provides a punch for forming openings in metal sheets and which is particularly useful during a hot stamp metal process. Having described my invention, however, many modifications thereto will become apparent to those skilled in the art to which it pertains without deviation from the spirit of the invention as defined by the scope of the appended claims.

Claims

1. A punch for forming a punched opening in a metal sheet comprising:

an elongated body having a first and a second spaced ends, said first end adapted to be held by a machine which, when activated, axially drives the body,

said body having a punch section axially spaced from said second end of said body, said punch section terminating in an annular surface corresponding in shape and size to the punched opening, and

an extension which extends axially outwardly from and is surrounded by said annular surface, said extension terminating at said second end of said body,

wherein said extension has a length greater than a thickness of the metal sheet so that, as the punch is driven through the metal sheet, said extension forms a hole in the metal sheet smaller than the opening and thereafter said annular surface forms the opening in the metal sheet.

2. The punch as defined in claim 1 wherein said punch is formed from hard metal.

3. The punch as defined in claim 1 and comprising a chamfer extending around a junction between said annular surface and said extension.

4. The punch as defined in claim 3 wherein said chamfer is formed on a radius.

5. The punch as defined in claim 1 wherein said body is a one piece construction.

6. The punch as defined in claim 1 wherein a free end of said extension lies in a plane perpendicular to said predetermined direction.

7. The punch as defined in claim 1 wherein said annular surface lies in a plane perpendicular to said predetermined direction.

8. The punch as defined in claim 1 wherein said extension is circular in cross-sectional shape.

9. The punch as defined in claim 1 wherein both said annular surface and said extension are circular in cross-sectional shape and wherein said extension has a diameter greater than sixty percent of the diameter of said annular surface.