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NBC-9649 HY-PAK® Hem Welding
Automotive Panels

 

HY-PAK®
Hem Welding Requirements

  1. Weldable light-gauge material.

  2. Coated or uncoated materials.

  3. Ideally the thinner of the two materials no more than .048 inches thick.

  4. Typical materials are steel, stainless steel and their weldable alloys.

  5. Weld projections in thin-gauge material must be of sufficient column strength to withstand the weld force and the part must be designed for fast follow-up during the weld process.
  

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This HY-PAK® station produces rear decklids is integrated into a production line. Producing 120 parts per hour.
 

HY-PAK®
Hem Welding Features

  • HY-PAK® hem welding causes a minimal disruption of protective coatings where the electrode contacts the material. The galvanized coating on the automotive panels maintains its integrity providing full corrosion protection

  • HY-PAK® hem welding causes no marking of the show surface on coated or uncoated steel. Surface finishing is not required even on the most visible of surfaces.

  • HY-PAK® hem welding provides immediate, solid state joining of the inner and outer panels which eliminates slip between panels, greatly improving dimensional stability and repeatability.
  

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HY-PAK® Projection
 

HY-PAK®
Hem Welding Process

The HY-PAK® welding process facilitates the welding of thin materials with less energy and less force than typically required of standard processes. The features of the process also enable the welding of coated or pre-finished materials. Product design must be considered as a projection is usually required to concentrate the heat. Specially designed follow-up tooling provides for a rapid response during the weld. No special training is required to set up tooling and standard, inexpensive power systems are used.

  

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Newcor Standard Tab
 

Electrical Features

A typical weld pulse for spot or projection welding of light gauge sheet metal is a sixty hertz sinusoidal wave form with a duration of eight to sixteen cycles (approximately 150 to 250 milliseconds). The HY-PAK® process uses a weld pulse of less than one half of one cycle (four to six milliseconds). To get the required amount of energy to create a weld, higher currents are generated by using a transformer with a higher secondary voltage than normal.

  

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Indirect welding is used in hem welding for single sided access. As shown above, the finished surface is against the lower back-up and the current path would be from the weld electrode through the weld joint, through the inner panel back to the contact electrode. Indirect welding is used in hem welding for single sided access. As shown above, the finished surface is against the lower back-up and the current path would be from the weld electrode through the weld joint, through the inner panel back to the contact electrode.

 

Mechanical Features

With HY-PAK® welding it is possible to use a higher current and shorter weld time because of the mechanical system used to provide the weld force. Any solid state weld has the same requirements of heat or energy, and force for forging. If the force is inadequate during any period of the weld, the contact resistance between the mating surfaces will drastically increase, causing the part or the electrodes to become too hot. The result is molten material and expulsion. The HY-PAK® weld tooling is designed to prevent this. The mass of the electrode has been minimized by reducing the amount of tooling that has to move to follow the collapse of the weld, creating a highly responsive system.

When a weld joint starts to collapse, the electrode and associated tooling must accelerate to follow the material. Depending on the amount of mass, a force is required to accelerate the system. This force due to acceleration detracts from the force at the weld joint. Minimizing the mass allows as much of the force as possible to be applied to the weld joint where it is needed throughout the duration of the weld.
 

Material Requirements

As with the tooling, the mass of the part that must move during the collapse of the projection should be kept to a minimum. A tab in the flange stock is used in hem welding applications to minimize the amount of force required to move the part. This also allows for tight hem forming without collapsing the projection. A sharp linear projection is formed in the inner panel to concentrate the current and heat while distributing the force to prevent read through. Typical tab and projection are shown below.
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