There are two distinctive styles of hole punching. Dimple hole punching or piercing and Mandrel hole punching.
Dimple Style Hole Punching - The most cost-effective way to punch or pierce a hole in a round, square, or rectangular tube. There are two styles of dimple punching. Single-dimple and double-dimple. The double dimple version uses two individual punches that travel towards each other during the press cycle. Since this style punches without an internal support (mandrel), the punches create a dimple. The Single-dimple version uses a single punch that ravels from one side and continues through the tube. The tube is supported on the bottom-side of the tube so that as the punch travels through the tube it is supported and the second hole is "clean" or non-dimpled.
Two benefits to this style of tooling is that it is very inexpensive compared to mandrel style hole punching and the dimple can offer a space for a pan headed bolt to seat into the dimpled area keeping the bolt head flush with the tube. This is very effective for tubular assemblies.
Tooling can be designed to offer multiple holes in a row or multiple holes on different planes to be punched simultaneously.
Mandrel Style Hole Punching - Also a cost-effective way to punch round, square, or rectangular tubing. This method of punching uses an internal support so the outside diameter integrity of the tube is not altered. Holes may be punched one at a time or multiple holes in a row.
Mandrel style hole punching is required when tubes need to telescope or fit inside one another. The tooling required for mandrel hole punching is more expensive than dimple hole punching, but is more accurate and holds tighter tolerances.
Mandrel Hole Punching
Pierce (Dimple) Punching
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