Tech Directions - December 2008 - (Page 18)

devices, an inverter can create just about any welding output imagined. In short, inverters can perform all welding processes equally well. For many schools, a CC/CV dc inverter with an output of 350 A at 60% connected to a give breaker. These primary power advantages can eliminate the need for expensive rewiring. ● Most important, an inverter offers advanced arc controls that enable students to become more proﬁcient faster. An inverter can make a good welder out of an average student while letting great students express their full potential. Advanced Stick Arc Control To provide operators with additional stick arc control, advanced CC welders offer arc force or “digi” control. This function enables operators to Increasing arc force (“dig”) makes it easier for tailor the shape of the this pipe welder to achieve good penetration on volt/amp curve to betan open root pass with an E6010 electrode. ter suit different joint conﬁgurations and electrode types, duty cycle meets most of their weland it can create an arc that expeding needs. This type of unit (Miller’s rienced operators describe as “soft” XMT 350 CC/CV for example) allows and “buttery” or “stiff and driving.” for training students on stick welding Under normal arc length condiand dc TIG welding in a broad variety tions, a stick electrode operates at of applications, as well as for training about 20 V. However, some welding students on the MIG and ﬂux cored situations demand shorter arc lengths, processes. For TIG-speciﬁc training such as when the operator has to and ac TIG welding on nonferrous push the rod into a tight corner or metals, an ac/dc TIG inverter (for into a deep bevel of an open root joint. example, the Dynasty 350) will offer the most ﬂexibility. In working with schools, I genSetting Arc Force erally recommend inverters because Individual operators have their they offer several advantages: own ideas about where to set arc ● This is the type of welding techcontrol, which is adjusted by a nology that industry is adopting, so knob on the machine’s front panel. it makes sense to train students on Some general recommendations the equipment they’ll use profesare: sionally. For open root welds on plate or ● Inverters are about one-ﬁfth the pipe, generally an XX10 or XX11 size and weight of conventional welelectrode is selected for the ﬁrst ders, so they take up very little space. pass. During this pass, the operator ● Inverters are more energy efﬁis trying to achieve full penetracient than other welders, which means tion. By adding arc control, usually they can pay for themselves through toward the high end of the scale savings in power consumption. (say 5 or 6 out of 10), the operator ● Some inverters offer the ability can control amperage (penetration) to connect to single- or three-phase by arc length. For deeper penetrapower over broad primary voltage tion, simply decrease arc length by ranges (e.g., 115 to 460 or 190 to pushing the rod into the joint. At 630 Vac). Also, inverters draw much this point (and only at this point), less amperage, reducing breaker the arc force control will kick in size or allowing more welders to be In these situations, stick electrodes are notoriously prone to living up to their namesake and “sticking the rod” (the voltage drops so low that the arc extinguishes itself). Arc force control overcomes this problem by increasing current when the voltage levels drop below about 20 V. The boost of current increases total power, keeps the weld puddle molten, prevents the rod from sticking, and eliminates a lot of operator frustration. Remember, inverters can adjust the welding output thousands of times per second. The speed of the human hand pushing an electrode closer to the joint is nothing compared with the speed of a microprocessor. Working with state-of-the-art welders is the difference between giving an accountant an abacus and giving him or her a computer. For schools that want to teach stick, TIG, and MIG welding (don’t forget about multiprocess CC/CV welders, which provide outputs for stick, TIG, MIG, ﬂux-cored, and air carbon arc gouging), choosing the right machine will help students succeed as quickly as possible. As a whole, industry desperately needs to add more skilled welding operators to its ranks. We owe it to students and trainees to provide them with the tools that will help them succeed. and provide the necessary boost of current. To reiterate: operators will only experience arc force when they reduce arc length to a point where voltage levels drop below 20 V on most machines. For electrodes not used on open root welds, increase arc control to the point where the electrodes don’t stick during arc starts or while welding (perhaps 2–5 on scale of 1 to 10). If you are TIG welding, set the arc control at 0 or switch it off. (If you have a welder with separate settings for TIG and stick, this won’t make a difference. Typically, the welder takes the arc control knob out of the circuit when set to TIG mode). 18 techdirections ◆ DECEMBER 2008

Table of Contents Feed for the Digital Edition of Tech Directions - December 2008

Tech Directions - December 2008 Contents Advertisers Index Technically Speaking Direct from Washington The Report Technology Today Technology’s Past Mastering Computers Digital Portfolios—Powerful Marketing Tool for Communication Students Choosing the Right CC Welding Unit—Student Success Depends on It Think Green—Increasing Awareness of Garbage and Recycling Think Green—Teach Students Smart Ways to Reduce Home Energy Use Go International! Build a Simplified Shortwave Receiver Mooresville Middle School Snags Web Site of the Month Gifts for Geeks More than Fun

Tech Directions - December 2008

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