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Permanently prepositioned by resistance welding, weld fasteners provide strong and reliable fastener foundations. With OHIO Weld Fasteners in place, mating parts can be rapidly assembled with power equipment. There is no need to hold OHIO Weld Fasteners because they are fused to the component part. OHIO Weld Fasteners will not work loose under shock, torque, or vibration.

OHIO Weld Fasteners are available in two types; spot weld and projection weld fasteners. Spot weld fasteners can be welded with the same electrodes, weld settings and equipment used in normal production of components and assemblies.
OHIO Weld Fasteners produce primary fastener foundations faster and more efficiently for less in-place cost than many other fastening methods. The wide variety of Ohio Weld Fasteners are helping metal working companies turn out components with predictable strength, durability and performance. The three basic requirements for producing a good resistance weld involveHeat, Time and Pressure. The proper relationship and control of these elements assure the finest weld.

Heat Heat balance is extremely important to good welds. Proper heat balance occurs when bringing the fastener and the component to the welding temperature simultaneously. Heat or current balance occurs when the distribution of heat between the fastener and the part is equal.

Some variables which affect the heat:

1. The weld time is too long.
2. The welding current is too high.
3. Low electrode pressure.
4. Electrode diameter is too small.
5. Improper electrode alignment.
6. Improper adjustments in changing metal thickness.
7. Unclean fastener or part.

Adjusting the heat or current with a regulator changes the ratio of primary to secondary voltage. Most OHIO Weld Products require from 5,000 to 20,000 secondary amperes to produce enough heat to make the weld. Set the regulator at a point where current will not cause flashing or sparking when the weld occurs. A Duffer's current meter will determine accurate short circuit secondary ampere readings. This is an accurate method for determining correct current settings.

Time Time, expressed in cycles, is the second most important factor enabling a good weld. One cycle represents 1/60 of a second. The weld time should be as short as possible and the weld should occur in one hit. Repeated hits add nothing to the strength or appearance of the weld and may damage the work. An average weld takes from three to fifteen cycles. There are three groups of time in resistance welding and they are all important.

Squeeze Time

The time from the application of the electrode until the application of the welding current.

Weld Time

The time which the current flows through the work during the weld process.

Hold Time

The time that pressure remains on the electrodes after the end of the flow of welding current.

Pressure

Pressure plays a key part in welds. Pressure assures good electrical contact of the welded part of the Sheet In projection welding, pressure also forces the projection into the sheet after the metal reaches fusion temperature. Extreme pressure will cause projections to flatten out before reaching weld heat. Not enough pressure causes flashing, spitting, burning and discoloration.

Photo courtesy of: T. J. Snow Company

Required Equipment

All standard OHIO Weld Products, except those with ring projections, require from 300 to 1,200 pounds pressure at the electrodes. A force gauge checks the pressure at the electrodes. The selection of the proper type and size of welder depends on the work the welder is to perform. OHIO Weld Fasteners weld with the simplest type of press or rocker-arm welder. Production requirements may call for large automated machines. KVA (Kilovolts Amperes) determines welder size. Many OHIO Projection Weld Screws weld with press welders as small as 20 KVA, while others will require units as large as 200 KVA.

Projection and Spot Welders

Projection welding uses a press welder (above left) because the air cylinder is directly over the electrodes and the travel is straight line. In addition, good alignment and equalized pressure is achieved at the tips.

Spot welding can and usually use rocker-arm welders (above right) although press type welders will also work. When welding OHIO Spot weld Fasteners, manufacturing can use the same equipment, electrodes, and settings used in regular production welding. Air cylinders, a motor and cam or foot treadle supply electrode force. Machines are available from 10 KVA to 75 KVA or greater. OHIO Spot weld Screws and Nuts are welded with spot welders which range in size from 30 KVA to 75 KVA.

About Projection Welding

Projection welding uses relatively large electrodes to insure coverage of the entire projection area. The more bearing surface, the longer the electrode life. Electrodes should be located directly on the center line of pressure application to insure accurate alignment and good contact for quality welds. In projection welding, heat is localized in the weld projections of the fastener. On OHIO parts, these carefully located projections cause the current to be concentrated in small areas as it flows between the fastener and the parent part. Welding occurs as the projections fuse with the surface of the parts.

About Spot Welding

The spot welding principle involves placing the two pieces to be welded between two copper or copper alloy welding tips. An electric current of sufficient strength is passed through the entire area under the electrode tip, welding the pieces together. This differs from projection welding in that the heat concentration depends on the size and shape of the electrode tip rather than on the size, shape and the number of projections used.

Because the size and shape of the electrode tip directly affect the size of the weld, it also determines the strength of the weld in shear. Thus, control weld size and strength by maintaining a uniform tip contact area. Tip diameters must be changed for each thickness of metal to be welded.

In spot welding, indentations and discolorations appear in the weld area. This is caused by metal being drawn up to form the weld nugget or growth between the fastener and the part. It is possible to reduce this indentation (and discoloration) by using a flat electrode on the side where minimization of these marks is desired.
An important advantage of spot welding is it can be utilized to attach fasteners where the assembly itself is being spot welded. This eliminates extra setup time and adds to the flexibility of the basic welding equipment.

Spot Welding (left)
Projection Welding (right)

Trouble Shooting Welding Problems

Faulty welds can be eliminated or minimized by avoiding some of the easily overlooked pitfalls in resistance welding. Some of the basic requirements are that the material to be welded is of good welding quality and is free of oil, dirt and foreign matter of all kinds.

Spot welding electrodes must be kept dressed to proper size. Mushroomed tips prevent necessary localizing of heat for proper welding. Projection welding electrodes must be kept aligned for optimum and uniform pressure.

On through the hole applications, allow sufficient clearance between part and parent material to prevent shunting of current into material. When using jigs, fixtures and stops for locating devices are insulated from the electrode body.

Welds can be traced to a variety of factors such as the weld setup, electrodes, the control system, the selection of fasteners, the machine, the operator or the process itself. The following check list can be helpful in isolating trouble areas

1. The weld setup; incorrect heat, time or pressure.
2. The electrodes (faulty design, lack of insulation, need for dressing).
3. The welding machine (mechanical, electrical, water or air inadequacies).
4. The electronic controls (tube failures, etc).
5. The parts being welded (poor design, wrong material and projection design or location).
6. The metal to which the parts are welded (Is it good welding quality?).
7. Jigs, fixtures and the feeding devices (are they effective?).
8. The operator (the human element).

Welding Diagnosis

• Figures 1, 2, and 3 illustrates the results of welds made with improper electrodes.
• Figures 1 and 2 also show indentations made by electrodes which did not cover the entire head of the weld screw, which is mandatory in perimeter projection welding. Since the projections are fairly close to the of the screw head, both of these welds failed to fuse all of the projections resulting in weak welds.
• Figure 3 shows the weld spatter in the screw threads caused by poor or complete lack of insulation. Whenever the screw or nut is welded through a hole in a sheet, the lower electrode must be insulated.
• Figures 4 and 5 show the results of improper weld setups.
• In figure 5, the operator attempted to offset the lack of pressure by increasing the heat. You can see the expulsion and discoloration has increased. In addition, the sheet metal area around the weld has been weakened at the weld point.

Projection Weld Maintenance Tips

Do ...

Do maintain a supply of electrodes to minimize downtime due to electrode change.

Do dress the face of electrodes on a lathe.

Do use a RWMA, Group A, Class 3 copper on the sheet side.

Don't ...

Don't use a file to dress electrodes.

Don't store electrodes where face damage can result.

Don't use a pipe wrench to remove the electrodes.

Spot Weld Maintenance Tips

Do ...

Do maintain a standby supply of electrodes at the welder.

Do dress electrodes periodically with an approved Spot weld tip dresser.

Do change tip diameters to adjust to each thickness of metal to be welded.

Don't ...

Don't use a file to dress electrodes.

Don't store electrodes where face damage can result.

Don't use a pipe wrench to remove the electrodes.

Helpful Hints

To assure perfect alignment, both the faces and the axis of the electrodes must be parallel. Check this by inserting a piece or carbon paper and a sheet of plain white paper between the electrodes and applying pressure with the weld cycles turned off. The resulting impression on the plain paper will indicate the alignment of the electrodes.Utilize a water jacket whenever possible and locate it as close as possible to the welding surface.Keep material to be welded free form oil, dirt and other foreign matter. Follow welder size and setting recommendations made by The Ohio Nut and Bolt Company.