The following RWMA Q & A articles were published in the Welding Journal and are available here.
- September 2014 by Jerry Gould
Q: Reducing energy consumption is a constant theme in our production facility. Our industrial engineering staff look at the instantaneous power demands of our resistance welding systems and see this as an area where improvements can be made. How is energy consumed during resistance welding, and how do system changes affect these energy requirements?
A: Resistance welding has historically been considered a high-productivity, low-energy-input, low-cost joining technology. Resistance welding processes are typically characterized by very short processing times... Read More
- May 2014 by David Bellish
Q: Our company has only used manually operated pneumatic PED welding machines in the past. However, due to increased production requirements, we are currently in the process of designing a new robotic cell with servo weld guns. I have heard there are different philosophies on how to handle the equalizing on servo robotic guns. Can you explain?
A: Servo robotic guns have been around for more than 15 years, and the methods used for equalizing have changed along with the weld gun's evolution. To make the best choice in regard to the method for equalization, it is best to have a good understanding on what equalization is and why it is necessary in the first place. Read More
- March 2014 by Roger Hirsch
Q: I am trying to weld a 0.031-in.-thick steel ring to a 0.093-in.-thick steel oil filter thread ring – Fig. 1. The ring is about 3 in. in diameter and has six small projections. This is being done in one hit on a 250-kVA press welding machine. The part is in a nest to align components. The problem is that some of the projections are good; some are low on strength or have no fusion. We also noticed burn marks on the flat part near the projections.
A: Welding large parts with multiple projections can be a challenge. The last part in your question regarding burn marks near the weld zones gives me a clue as to what is happening. I am betting that the fixture holding the parts in line is actually preventing the two parts from completely coming together. This often happens when fixtures are used. It is important that the fixture does not restrict vertical movement of either part during the entire weld sequence. Read More
- January 2014 by Tom Snow
Q: One of our resistance welding machine operators recently lost part of his finger when it was crushed between the electrodes of the machine. How can we protect our operators from similar injuries in the future?
A: Forging forces ranging from several hundred to several thousand pounds are required to properly resistance weld metal together, so resistance spot and projection welding machines can be dangerous if care is not taken to protect the operator. Read More
- November 2013 by Donald F. Maatz Jr.
Q: We are resistance spot welding on galvanized coated parts and experiencing what we consider to be short electrode life. We start each production run with welds that barely meet their size requirements but finish with expulsion so severe we end up destroying the electrode face. We are hesitant to change the weld schedule due to the small initial weld size and have instead focused on the current stepper, to little effect. The water flow, electrode cap size, weld force, secondary current, and weld time are all in line with RWMA guidelines. Any ideas would be appreciated.
A: Your question intrigues me. If it is assumed that all other aspects of your resistance spot welding (RSW) application are within acceptable industry norms, and that you are welding parts with a coating that is not too detrimental (they all are to a certain extent) to the electrode caps, you may actually have a current stepper boost issue. Read More
- September 2013 by Tyler Alexander
Q: Our automotive end user has asked us to prove our resistance fastener welding process is capable because our pushout values are fairly inconsistent. What factors influence capability in resistance projection welding?
A: A number of factors influence the final result beyond the primary adjustable variables. Fundamentally, resistance welding relies on precise control of current, force, and time; however, by definition, resistive heating is the reason for the formation of the resistance weld. Read More
- July 2013 by Donald F. Maatz, Jr.
Q: We are considering changing our steel source for several of the parts we produce; however, one of the new materials is not approved by the automotive original equipment manufacturer (OEM). What approval process are they talking about? The proposed replacement appears to be the same as our existing one.
A: The process of joining two materials together is something that never really crosses your mind when you purchase a motor vehicle. In fact, it is almost something that is assumed since your driving of the final product is proof that it can be done. However, as with many things, a little digging reveals there can be much more to this process than meets the eye. Read More
- May 2013 by Roger Hirsch
Q: I am trying to make resistance welding seams using a single-phase constant current welding control and am having a hard time holding the tolerance required for this military project. We are using a 150-kVA seam welding machine with 3/8-inch-wide welding wheels on 0.040-in. CRS. The welding transformer tap switch is set to the #1 position. I checked the learn table in the control and see that we are in the 25-30% range so I know I am not overworking the welding machine. Do you have any suggestions?
A: The problem here is a misunderstanding of how a resistance welding machine works. Because you are using the control in this very low heat percentage range, the output of the welding transformer is a series of very small heat pulses and a lot of spaces in between. Read More
- March 2013 by Eric Pakalnins
Q: Our company is in the process of quoting the resistance spot welding of several small automotive assemblies. We must provide the customer with metallographic results using AWS D8.1M:2007, Specification for Automotive Weld Quality – Resistance Spot Welding of Steel. This standard contains a large amount of information. Could you review and discuss the metallographic information I need to know to satisfy my customer's request?
A: Before discussing the metallographic requirements of AWS D8.1M:2007, it is important to understand the specification's scope. This specification applies to resistance spot welds in automotive steels and is intended to define their desired weld quality. Read More
- January 2013 by Tom Snow Kay
Q: Our company needs extra spot welding capacity because production is increasing. We have an old spot welding machine in storage that has not run in years. Should I try to get it going or buy a new one?
A: As with many things in life, "it all depends." Spot welding machines are among the most durable of production machines and the "three Rs" of machine maintenance can easily be applied – repair, retrofit, or rebuild. Read More