Hemming Technology

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by Dave Bishop

The right tooling will boost the productivity of your press brake

The process of placing hems on the edges of sheet metal goes back almost as far as the press brake itself. It is a fairly simple operation that improves cosmetics, eliminates the exposure of sharp edges and burrs in areas where the part would otherwise be dangerous to handle, adds strength to the finished part, and can almost always be performed in two steps on a press brake.

Initially, hemming on a press brake required two sets of tooling and two different set-ups. The first was an acute angle punch and die, which were used to make the initial 30° bend. The second set of tooling consisted of a flattening punch and die that were used to flatten the 30° bend to create the hem. Later, with the advent of two stage hemming dies, it became possible to perform hemming operations with a single acute angle punch and a hemming die in a single set-up when forming mild steel, stainless steel, and aluminum in the range of 14 ga. (.075 in./2.0 mm) and thinner. Together they create an acute angle bend of 28-30° during the first bend and then flatten that bend to create the hem during the second bend.

While two stage hemming dies work exceptionally well in handling most hemming operations, they can accommodate only one V-opening and therefore are limited to handling one to two material thicknesses. This also limits them to forming 90° bends in one to two material thicknesses. As such, they are fairly limited in terms of their versatility.

This can require fabricators to purchase two to three different sets of hemming dies to hem multiple material thicknesses. As hemming dies are normally sold in a length
of 515 mm (20.28 in.) for New Standard and American Style
tooling applications, and in a length of 835 mm (32.87 in.) in European tooling applications, filling the full length of a press brake requires the purchase of multiple units. Understandably, purchasing multiple units of two or more hemming dies can be expensive.

New Standard Style acute angle punch with U-shaped hemming die.To provide metal fabricators with hemming dies that provide greater flexibility, faster tooling changes, and those that are better suited for high production environments, various press brake tooling manufacturers have introduced what are commonly known throughout the industry as “Dutch hemming tools” or “hemming tables.” Today’s Dutch hemming tools or hemming tables have several features that are not found on standard hemming dies. They include the following:

  • Upper table is opened and closed with hydraulic cylinders as opposed to mechanical springs
  • Upper table is lowered to the bottom position before each bend for maximum accuracy
  • Offered with hydraulic and manual die clamping
  • Uses standard off the shelf New Standard and American Style acute angle dies with V-openings ranging between 6 mm (.236 in.) and 24 mm (.945 in.)
  • Can hem materials ranging from 0.5-3.0 mm (.020-.120 in.) mild steel, 0.5-2.0 mm (.020-.080 in.) stainless steel, to 0.5-3.0 mm (.020-.120 in.) aluminum.
  • Available with optional hardened flattening jaws for maximum life, which are especially valuable when hemming stainless steel, perforated parts, and parts that are cut on a plasma machine
  • During periods of inactivity, the upper table remains in the closed position. It can then be used as a standard die holder for dies with V-openings up to 24 mm (.945 in.)
  • Never needs to be removed from the press brake when bending materials ranging from 0.5-3.0 mm (.020-.120 in.) mild steel

The benefits of a flexible hemming system that sets up quickly and only rarely needs to be removed from the press brake for metal fabricators that typically bend only light gauge materials is virtually immeasurable. This technology is especially beneficial to companies that produce appliances, audio equipment, metal cabinets, computer chassis, refrigeration equipment, office furniture, metal furniture, cooking equipment, hospital equipment, prison equipment, etc. to name a few.

If this technology is of interest to you, your press brake and press brake tooling suppliers will assist you with all the details to ensure a successful implementation. SMT

David Bishop is business development manager with Wila USA.


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