Could You Optimize Your Robotic Process With a New Welding Consumable?
Robotic welding systems are a fixture in industries where speed and repeatability are required to maintain a high volume of production. Companies invest large amounts of capital on robotics, expecting a very fast payback and in many cases they achieve it. This return on investment can be attributed to both the robot itself and the welding consumable that is used. The automotive and metal fabrication industries, specifically, have become two of the biggest consumers for this technology.
Here’s a classic robotic “widget” scenario: Acme Widgets runs welding consumable type A in its robotic welding cells and produces 500 parts per shift. When switching to welding consumable type B, Acme Widgets increases its throughput to 700 parts while slightly increasing its overall variable cost. It is important to realize that, by looking past the initial increase in cost for welding consumable type B, Acme realized a 40 percent improvement in production.
As in the previous scenario example mentioned above, this article will discuss options for optimizing your expected returns on automation through proper welding consumable selection based on process merit and not unit cost. In particular, it will help you consider whether your robotic applications can benefit from a conversion from solid wire to metal cored wire and improve your return on your robotic system investment.
Why Robotics?
Robots deliver fast and accurate air movements during arc-off conditions, which helps reduce overall cycle times. A robot can repeatedly and precisely position a welding torch with accuracy to a few thousandths of an inch and can also deliver arc-on performance that far exceed the capabilities of a human operator. There are many quality robotic systems available on the market today, most of which are manufactured to the highest quality standards, delivering excellent longevity with minimal maintenance requirements.
Justifying automation can become quite simple: it’s man versus machine. On the other hand, to quantify and justify the weld process for robotics, it is important to look at other factors that contribute to the system. In this regard, the welding consumable for robotic systems can be an important, though often overlooked, area of opportunity for reducing the overall process cost.
The Importance of Welding Consumables in Robotics
Many companies invest large amounts of money on robotic systems, yet have not realized that an appropriate welding consumable selection for their application can yield significant savings and opportunities. Air movements, which generally represent 20 to 30 percent of the cycle time on average, are maximized by the robots’ speed and accuracy. Welding process speed and quality factor in the remaining percentage of the cycle that represents arc-on time. Therefore, using the most appropriate welding consumable for your application can contribute to optimizing the total cycle time and overall process cost.
When specifying welding consumables, the two most viable options are solid wire and metal cored wire. Between the two, there are recognizable differences in the unit cost, arc characteristics and performance and their impacts on the overall welding process.
Solid Wire Dominates Robotic Welding Industry
Solid wire has been the industry standard-bearer for both hand-held and robotic welding for many years. Its dominance in the industry is due primarily to availability and low unit cost. Solid wire is particularly effective on thinner gauge materials. In such applications, solid wire allows manufacturers to use a .035-inch diameter wire, for example, which is ideal for running low weld amperage applications. Solid wire applications, using small diameter wire, are particularly applicable to the automotive industry for welding thinner gauge material components. It is also a viable welding consumable for the manufacturing of metal furniture and thinner gauge metal applications where pulsed welding is used.
Solid wire begins to exhibit deficiencies (compared to metal cored wire) when increased travel speeds are necessary, especially on thinner gauge materials; the risk of burn-through increases on solid wire applications when higher heat input occurs. Other issues that can arise in solid wire applications include increased spatter, and a lesser ability to bridge gaps (the distance between the joint’s facing surfaces). Additionally, solid wires often have a restricted operating window and can create a “finger-like” penetration profile that may increase the risk of burn-through on thinner materials.
Due to the high usage of solid wire, the robotic welding industry has indirectly accepted solid wire deficiencies by introducing compensating activities (or non-value added labor to the end product) throughout the welding process. These activities include: using anti-spatter spray in the pre-weld stage, cleaning of spatter in the weld and post-weld stage and incorporating repair and rework stations, again in the post-weld stage.
Many of these compensating activities have become common practice for robotic welding. Companies often focus on the initial unit cost of wire versus the total process cost. Hence, even a solid wire that produces spatter and slower cycle times, while contributing to rework instances, has been accepted due to its lower upfront cost.
But how is this low unit cost approach impacting your total process cost and throughput opportunities and what limitations will it place on your robotic system investment?
Is Metal Cored Wire a Viable Option?
While solid wire is extremely applicable for a large number of welding applications, many could benefit from the use of metal cored wire. Here we will examine some key features associated with metal cored wire and how they reduce compensating activities associated with solid wire in the three weld stages.
At equivalent amperage settings, metal cored wires effectively carry higher current densities, as the current is primarily conducted through the outer sheath, compared to being conducted through a solid wire’s entire cross sectional area. This fact results in higher relative burn-off rates for metal cored wire and translates into the potential for increased deposition rates and faster travel speeds. In addition, metal cored wire provides excellent arc characteristics, smaller molten metal droplet transfer for large spatter reduction and a wider weld metal projection area for better bridging of part gaps. Metal cored wire also offers precise starting characteristics and improved wetting action to reduce undercut versus solid wire.
In certain robotic applications, the metal cored wire attributes listed above can be used to counter the compensating activities typical to solid wires. Here is an example of metal cored wire’s benefits with respect to higher deposition rates: a robotic system running .045-inch solid wire runs 420 inches per minute (IPM) and deposits 11.8 pounds per hour. At the same amperage, a .045-inch metal cored wire runs at 540 IPM and deposits 14 pounds of metal per hour. This fact translates to faster travel speed potential for an equivalent amperage and weld size.
Additionally, when using metal cored wire, it is common practice to increase wire diameter by one size over a solid wire without negative effects. This feature offers greater versatility on many material thicknesses and the potential to standardize on a single diameter of wire throughout the welding operation. While it easy to see that deposition rates are central to this argument, other factors are also critical in determining whether metal cored wire can lend itself to your robotic system.
Welding Stages, Activities and Cost
Solid wire unit costs are less than that of metal cored wire; it is an undisputable fact that often overshadows the consideration of metal cored wire for robotic applications. Looking beyond the unit cost of a particular welding consumable, however, may be worthwhile to optimize the investment for a robotic system.
A typical robotic system can be described in 3 distinct stages - pre-weld, weld and post-weld. Often the opportunity for cycle time improvement with metal cored wires has its biggest impact in the pre- and post-weld stages. The following describes how metal cored wire works in each of these stages and can help you determine whether a change of welding consumables is right for you.
Pre-Weld: Part tacking and loading are common activities of the pre-weld stage, but welding operators also spend large amounts of time for pre-cleaning activities (for example, sandblasting and grinding) prior to the robotic system doing its job. Metal cored wire has added deoxidizers in their core, which can reduce the need for such pre-cleaning activities. The reduced spatter characteristics of metal cored wire can also eliminate the need for anti-spatter spray applications.
Weld: As a rule, metal cored wire offers the opportunity to increase deposition rates significantly, a feature that provides the opportunity to weld on both thinner and thicker materials with lower heat input. Metal cored wire also provides stable arc initiation and smoother arc transfer. The molten metal droplets that are formed during welding, with metal cored wire, are smaller and their projection is generally wider. These factors provide a more effective and complete metal transfer and create less turbulence in the weld pool, which reduces spatter and improves deposition efficiency (the amount of wire actually placed in the weld).
Metal cored wire also allows part gaps to be bridged easier and reduce problems associated with part fit-up variance. This benefit is achieved by metal cored wires’ broader arc when welding and ultimately reduces the need for rework.
The bottom line is this: metal cored wire welds parts faster with less spatter, reduce rework and decrease the need for scheduled shutdowns to clean spatter from welding fixtures.
Post-Weld: Implementing metal cored wire often reduces or eliminates the need for post-weld spatter cleaning operations, along with repair and/or rework stations. This fact allows for potential re-allocation of labor elsewhere in the welding operation. Analyzing the cost of these activities also reveals the post-weld stage to be the greatest area of opportunity for optimizing robotic applications using metal cored wire.
Conclusion
When manufacturers choose to invest extra money to upgrade their operations to a robotic system, they may also wish to consider upgrading their welding consumable. While changing to a metal cored welding consumable is not ideal in every situation, there are many instances where robotic systems can benefit from the change. In fact, a large percentage of robotic applications in the automotive, manufacturing and heavy fabrication industries may be converted to the metal cored process and yield significant throughput gains. For companies who are struggling with additional costs and time for pre-weld, weld and post-weld labor activities, as a result of using solid wire, converting to metal cored wire may increase throughput and reduce overall welding costs.
Whatever the welding consumable, the goal is to determine which one—solid wire or metal cored wire—can help you optimize the potential of your robotic system and gain the return on investment that initially brought you to the decision to invest in welding automation. In many instances, metal cored wire may be a preferred consumable option to consider for optimizing throughput potential and lowering the overall welding costs of your robotic investment.