292 CHAPTER 12 REVIEW QUESTIONS Avantages of ...

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292 CHAPTER 12 REVIEW QUESTIONS Advantages of using the backhand seave the electrode: 1. How does a welder set up the arc voltage and amperage for GMA welding? 2. In what unit is the wire feed speed measured? 3. What is the advantage of using a 6-second wire feed speed test rather than a 1-minute test? 4. What would be the ipm (inches per minute) if 24 in. of wire exit the contact tube in a 6-second test? 5. Why should the electrode wire be rewound back on the spool after a wire feed speed test? 6. List three terms that all refer to the relation of the gun to the work surface. 7. What effect does arc force have on the weld? 8. Describe the gun angle needed when welding thinner and thicker materials. 9. What is the difference between the forehand, perpendicular, and backhand techniques? 10. Which welding gun angle would be easier to weld on thin sheet metal without melting through? 11. Which gun angle is used for automated welding? 12. What are some advantages of a welding technique? 13. Why would a welder move or weave the ele during a weld? 14. What is electrode extension? 15. Describe how changes in electrode extension affect the weld bead. 16. What are tack welds? 17. Describe the characteristics of a good tack weld. 18. What is a lap joint? 19. How much buildup should be on a fillet weld made on a lap joint? 20. What might cause a lack of uniform width on a weld bead? 21. What might cause a lack of uniform buildup on a weld bead? 22. Describe an outside corner joint. 23. Sketch a tee joint.

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Sure, you want to learn how to MIG weld. And why not? MIG welding is extremely useful for repair work and fabrication.

MIG welding combines speed and versatility, making it one of the easiest welding processes to learn. Most people can run a nice bead fairly quickly with MIG welding equipment. It takes patience, concentration, and a few hours of practice.

MIG Explained

MIG stands for Metal Inert Gas and uses electricity to melt and join metal pieces. It's also referred to as GMAW (Gas Metal Arc Welding), MAG (Metal Active Gas) welding, or wire feed welding. Compared to other methods, MIG welding is the simplest way to weld.

Originally developed for welding aluminum during World War II to boost productivity, MIG welding can join various materials by changing the welding wire (electrode) and shielding gas. Here, we’ll focus on welding steel.

In simple terms, MIG welding works like a hot glue gun. A continuous, consumable wire electrode (instead of glue) and shielding gas are fed through a welding gun. A short circuit creates intense heat that melts the metal, allowing the pieces to fuse upon cooling.

MIG welding is versatile and can weld a wide range of metals, including steel, stainless steel, aluminum, and cast iron. It also offers several advantages:

• Produces a cleaner weld
• Requires less cleanup
• Allows for multi-position welding
• Easily joins metals of varying thickness

The Ins and Outs of a MIG Machine

A MIG machine consists of four key components: the power source, a tank of shielding gas, a welding gun, and a ground cable.

The Power Source: The exterior contains operating controls like the on/off switch, amperage and voltage controls, and transformer adjustment. Inside, you'll find the power supply (transformer, rectifier, and condensers) and the control side (circuit board, wire feed motor, main relay, and solenoid valve). A smooth wire feed system is crucial for a stable arc.

The Gas Tank: Situated behind the cabinet, the tank holds the shielding gas. The flowmeter reduces tank pressure to a usable level, allowing precise monitoring of gas flow.

The Welding Gun: Features a trigger that signals the machine to start welding current, wire feed, and gas flow. The replaceable copper contact tip transfers welding current to the wire. The gas nozzle directs shielding gas around the weld.

The Ground Clamp: Completes the circuit between the welder, gun, and metal being welded.

Start with Safety

Safety is paramount when learning MIG welding. While generally safe, the process involves significant heat and light. A good welding helmet, like today's auto-darkening helmets, is essential as it allows you to keep both hands free and automatically darkens when striking an arc.

Heavy-duty gloves and protective leather gear are also important for protection against splattering molten metal. Always work in a well-ventilated area and keep a charged CO2 fire extinguisher nearby.

The First Step

Clean the surfaces you plan to weld. A few swipes with a wire brush usually suffice. A clean surface prevents contamination and promotes a stable arc. Remember, more cleaning equals less welding time.

Since the electrode and gas auto-feed through the MIG gun, the technique is simple. Maintain a consistent gun position and orientation for a smooth arc. Hold the gun at a 45° angle and ensure you can see the wire. Maintain a constant arc length and speed.

Let's Get Started

We use the HTP® MIG 200, capable of welding up to 3/8" and thin sheet metal. Set the power switch to "On", attach the ground clamp, open the gas tank valve, and adjust the flowmeter to 15-25 cubic feet per hour. Choose the heat setting for your material thickness and adjust the wire feed rate using scrap metal. The correct setting produces a steady buzzing sound.

Set the wire feed too low, and you'll hear hissing; too high, and it will spit and pop.

The Tack Weld

Start with tack welds to avoid panel separation. Lay the gun edge on the work surface, point the wire, and pull the trigger. A molten puddle should form, joining the metals. Tack welds should be spaced two to three inches apart. After tacking, hold the gun at a 45° angle and guide it smoothly along the weld line, keeping the wire in sight.

Control bead width by adjusting gun speed. For less heat, turn up the heat and move faster; for more control, turn down the heat and move slower.

Next, Stitch Welding

Stitch welding is also straightforward. Set the machine to stitch weld mode, adjust the time, and start. The machine automatically performs overlapping tack welds, helping prevent warpage and burn-through. Stitch welding forms a continuous bead resembling a row of fish scales.

Once proficient in basic welding and stitch welding, you can explore techniques like plug and spot welding. Learning the basics of MIG welding involves practice. Think of these guidelines as a starting point. Actual welding practice will help you improve.

Source: HTP America, Inc.
(800) USA-WELD
www.usaweld.com

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