Patent Application
20160256913
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.
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.
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:
With reference to
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
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
As the machine 18 continues to drive the punch 10 toward the metal sheet 34 to the position shown in
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.
