In many cases, MIG gun consumables may be an afterthought in the welding process, as concerns with equipment, workflow, part design and more dominate the attention of welding operators, supervisors and others involved in the operation. Yet, these components – particularly contact tips – can have a significant impact on welding performance.
In a MIG welding process, the contact tip is responsible for transferring the welding current to the wire as it passes through the bore, creating the arc. Optimally, the wire should feed through with minimal resistance while still maintaining electrical contact.
The position of the contact tip within the nozzle, referred to as the contact tip recess, is just as important. It can influence quality, productivity and costs in the welding operation. It can also affect the amount of time spent performing non-value-added activities that do not contribute to the operation’s overall throughput or profitability, such as grinding or blasting parts.
Impact on quality
Contact tip recess affects a number of factors that, in turn, can influence weld quality. For example, stickout or electrode extension (the length of the wire between the end of the contact tip and the work surface) varies according to contact tip recess – specifically, the greater the contact tip recess, the longer the wire stickout. As the wire stickout increases, voltage increases and amperage decreases. When this occurs, the arc may destabilize, causing excessive spatter, arc wander, poor heat control on thin metals and slower travel speeds.
Contact tip recess also affects radiant heat from the welding arc. Heat buildup leads to an increase in electrical resistance in the front-end consumables, which reduces the contact tip’s ability to pass the current along to the wire. This poor conductivity can cause insufficient penetration, spatter and other problems that could result in an unacceptable weld or lead to rework.
Also, too much heat generally reduces the working life of the contact tip. The result is higher overall consumable costs and greater downtime for contact tip changeover. Because labor is almost always the greatest cost in a welding operation, that downtime can add up to unnecessary increases in production costs.
Another important factor impacted by contact tip recess is shielding gas coverage. When the contact tip’s recess positions the nozzle farther away from the arc and weld puddle, the welding area is more susceptible to airflow that can disturb or displace shielding gas. Poor shielding gas coverage leads to porosity, spatter and insufficient penetration.
For all of these reasons, it’s important to utilize the correct contact tip recess for the application.
Types of contact tip recess
The diffuser, the contact tip and the nozzle are the three primary parts that comprise MIG gun consumables. The diffuser attaches directly to the gun neck and carries current through to the contact tip and directs the gas into the nozzle. The tip connects with the diffuser and transfers the current to the wire as it guides it through the nozzle and to the weld puddle. The nozzle attaches to the diffuser and serves to keep the shielding gas focused on the welding arc and puddle. Each component plays a critical role in overall weld quality.
Two types of contact tip recess are available with MIG gun consumables: fixed or adjustable. Because an adjustable contact tip recess can be changed to varying ranges of depth and extensions, it has the advantage of being able to meet the recess demands of different applications and processes. However, it also increases the potential for human error because welding operators adjust the recess by maneuvering the position of the nozzle or via a locking mechanism that secures the contact tip at a given recess.
To prevent variations, some companies prefer a fixed contact tip recess as a way to ensure weld uniformity and achieve consistent results from one welding operator to the next. Fixed contact tip recesses are commonplace in automated welding applications where a consistent tip location is critical.
Different manufacturers make consumables to accommodate a variety of contact tip recess depths, which typically range from a 1⁄4-in. recess to a 1⁄8-in. extension.
Determining the correct recess
The correct contact tip recess varies according to the application. A good rule to consider under most conditions is that, as the current increases, the recess should also increase. Also because less wire stickout typically results in a more stable arc and better low-voltage penetration, the best wire stickout length is generally the shortest one allowable for the application.
Here are a few guidelines:
- For pulsed welding, spray transfer processes and other applications greater than 200 amps, a contact tip recess of 1/8 in. or 1/4 in. is recommended.
- For applications with higher currents, such as those joining thick metals with large-diameter wire or metal-cored wire with a spray transfer process, a contact tip recess can also help keep the contact tip away from the high heat of the arc. Using a longer wire stickout for these processes helps reduce the occurrence of burnback (where the wire melts and seizes to the contact tip) and spatter, which helps extend contact tip life and reduce consumable costs.
- When using a short-circuit transfer process or low-current pulse welding, a flush contact tip with a wire stickout of roughly 1⁄4 in. is generally recommended. The relatively short stickout length allows short-circuit transfer to weld thin materials without risking burn-through or warping and with low spatter.
- Extended contact tips usually are reserved for a very limited number of short-circuit applications with difficult-to-access joint configurations, such as deep and narrow V-groove joints in pipe welding.
These considerations can help with the choice, but always consult the manufacturer’s recommendations to determine the right contact tip recess for the job. Remember, the correct position can reduce the opportunity for excessive spatter, porosity, insufficient penetration, and burn-through or warping on thinner materials.
Moreover, when a company recognizes contact tip recess as the culprit of such problems, it can help eliminate time-consuming and costly troubleshooting or post-weld activities such as rework.