Holes are formed in tubular hydro-formed parts that may function, for example, as locator holes or for receiving fasteners.
Tubular parts may be hydro-formed in a die with a pressure medium, such as water, being injected inside a tubular blank to form the blank to a desired shape. The part may be pierced in the hydro-forming machine with a hydro-piercing tool.
A hydro-piercing tool includes a punch that is advanced to engage an outer surface of the part while the inner surface is supported by the pressure medium. Hydraulic cylinders are actuated to drive the punch through the part to form a hole. When the hole is formed a slug is removed from the part forming a hole.
Loose slugs created in the hydro-piercing process can create problems if not properly managed. Loose slugs can become trapped in the interior of the part and may cause a rattling noise. Loose slugs can damage the hydro-forming die if they are dislodged from the part and fall into the die.
Several systems have been developed in an effort to control slugs created in the hydro-piercing process. One proposal is to punch a slug leaving a short retaining tab attaching the slug to the part. The slug is then folded back on the tab into the interior of the part. This proposal may be acceptable for ductile steel materials, but is not suitable for other materials such as aluminum and high-strength steel. Folding the slug into the interior of the part on the tab when applied to aluminum may result in the slug being fractured from the part. In addition, edge cracks may tend to form on the part proximate the hole when the hole is formed.
Referring to FIGS. 1A and 1B, a specialized punch is proposed that has two recessed portions for forming tabs that hold the slug in place after punching the hole. This punch may be used for aluminum but undesirable distortion may occur proximate the hole. This punch may not be well suited for circular holes.
This disclosure is directed to solving the above problems and other problems as summarized below.