Thinking Outside the Weld Cell
When looking at the overall expense and process of a welding operation, whether it is semi-automatic or robotic, the natural tendency is to focus primarily on the hard cost of equipment, including welding machines and consumables, and the labor associated with the welding process. This approach may seem logical given that the welding equipment constitutes an immediate upfront cost and the welding process is a company’s livelihood - it is what keeps parts moving through production. However, if purchasing supervisors and welding engineers consider that labor costs typically constitute over 80 percent of any welding operation, it is worthwhile to think outside of the welding cell to consider how the chosen welding process impacts pre- and post-weld labor costs, quality issues and overall throughput potential.
To that effect, this article will help companies identify possible ways to eliminate non-value added labor - labor that is not necessary to maintain a profitable and efficient welding operation—and improve their overall quality and productivity by using metal cored wire.
Addressing the Problem
Many companies use Gas Metal Arc Welding (GMAW) with solid wire for their chosen welding process and most of them also have pre- and post-weld areas for activities such as sandblasting, applying anti-spatter, grinding and weld repair. These activities are generally necessary to achieve defective-free, visually appealing parts. However, many companies don’t realize that there are ways to improve productivity and eliminate or significantly reduce labor costs associated with pre- and post-weld activities by looking at one simple factor in the welding process: the filler metal.
Look at a solid wire welding operation and ask one simple question: Why are there pre- and post-weld areas? Likely, the answer is: because they are necessary. As a general rule, solid wire does not weld well through mill scale or rust, so parts require pre-weld cleaning, such as sandblasting, beforehand. Also, because solid wire tends to generate spatter during welding, companies apply anti-spatter in the pre-weld area and maintain a post-weld area for grinding parts prior to powder coating or painting. Fundamentally, the labor in these areas is non-value added; it is not necessary to create parts. Rather, these pre- and post-weld activities are compensation activities—activities that balance out the shortcomings of the solid wire welding process.
Think for a moment what would happen to a welding operation if companies could eliminate non-value added labor in the pre- and post-weld areas. Could they reallocate that labor elsewhere to help improve throughput? To determine whether such an idea is viable, it helps to examine the differences between using solid wire and metal cored wire.
Pre-Weld Activities: Are They All Necessary?
In a perfect world, parts received for welding would be pristine - no dirt, no oil, no rust, no mill scale - and they could move straight to the weld cell. For a company using solid wire, what would happen if they did exactly that? Would solid wire be able to weld through those conditions and still meet quality standards? The answer is often no. In order for solid wire to burn adequately through mill scale, welding operators often need to increase their welding voltage. This adjustment causes the welding arc to lengthen and become less stable. As a result, the heat-affected area widens, undercut and burn-through problems increase and companies begin to encounter inherent weld quality problems. To prevent such problems, companies using solid wire avoid welding on mill scale or rust altogether and instead sandblast or grind it off.
Such activities add labor and can hinder throughput in two ways. First, pre-weld activities take money and minutes from the actual weld cell. Every minute spent on every part in the pre-weld area is one less minute spent welding and one less part produced. That brings forth a second concern: the time spent in the pre-weld area can become a bottleneck to productivity, causing welding operators to wait for parts to be sandblasted, ground or coated with anti-spatter.
To quantify how a bottleneck affects throughput, consider this real-world example. Company A, using solid wire, spends approximately 30 minutes in the pre-weld area, 10 of which they dedicate to sandblasting and four of which they use to apply anti-spatter. They use the remaining 16 minutes for fitting and tacking and/or lifting and moving parts (preparation activities). While Company A cannot remove pre-weld preparation activities, what about the other 14 minutes of time and labor? Could the company reallocate it toward welding parts and increasing throughput?
With metal cored wire, that reallocation is entirely feasible. Due to its inherent properties, metal cored wire offers two very distinct advantages over solid wire in terms of reducing pre-weld activities. One, metal cored wire welds through mill scale and/or rust while still achieving a smooth weld bead. Two, it requires lower voltage settings and produces a more rounded penetration profile than solid wire, allowing welding operators to gain more arc control. The more stable arc is one factor that helps to eliminate or significantly reduce spatter.
If Company A switches to metal cored wire, that extra 14 minutes of pre-weld labor can now move to the welding cell, increasing throughput in the pre-weld area by nearly 50 percent. That means more parts and more money at the end of the day. To that throughput gain, add the money saved by eliminating costs for anti-spatter and non-value added labor for cleaning (anti-spatter is notorious for coating floors and machinery). Further, eliminating the grinding associated with spatter could also reduce downtime and/or worker compensation costs associated with grinding injuries.
The Weld Cell and Beyond
While the weld cell seems the obvious place to look when considering labor costs, this area impacts throughput significantly less than many think. In fact, because metal cored wire costs about 50 percent more per unit than solid wire, evaluating throughput gains in the weld cell alone shows only a narrow segment of potential improvements. That is because metal cored wire typically presents greater opportunity for cost savings and improved productivity in the pre- and post-weld areas than in the actual weld cell.
Take Company A again. Using solid wire, the company spends about 40 minutes in the weld cell to produce a part: 20 minutes for arc-on time and 20 minutes for non-welding (arc-off time). If Company A implements metal cored wire in the weld cell, they could typically increase their deposition rate and travel speeds (both benefits directly related to metal cored wire) by 20 percent. As a result, they could gain four minutes of throughput, or an overall productivity increase of 10 percent. This gain seems comparatively small unless companies also consider that metal cored wire can help prevent rework and/or reject issues that originate in the weld cell.
As discussed earlier, the deficiencies produced by welding with solid wire, particularly on thinner parts, can be a root cause of companies needing to rework or reject parts, both factors that reduce productivity. Solid wire is prone to creating spatter in real world welding applications. When welding operators cannot maintain proper contact tip to work distance or gun angles, they exacerbate those spatter problems. Also, in robotic applications, the fingernail penetration profile of solid wire reduces the tolerance window with respect to the weld joint. Solid wire will more easily miss the joint and/or burn-through the part if part fit-up is not ideal and/or gap conditions exist. These factors generally increase the amount of rework or rejected parts compared to welding with metal cored wire. For every part that a company rejects or needs to rework, there are costs attached. First, there is the cost of the materials used to create the rejected part. Second, companies incur labor costs; for every part rejected, there is one less part that labor adds to the throughput total.
To quantify those losses, look at the cost per part and the number of parts rejected by using solid wire. The math is simple, but impressive. Again, if Company A makes 100 parts an hour at a material and labor cost of $1.00 per part and rejects 5 percent of those parts, then they are losing $5.00 per hour. That cost may seem small, but if Company A operates 7 days a week, 52 weeks a year at three 8-hour shifts per day, they stand to lose $43,680 annually in material and labor for rejected parts. They also compound losses by not producing those additional 43,680 parts for sale. With metal cored wire, the company could reasonably reduce their rejection costs to 1 percent or less, or in this example, from $43,680 to $8,736, while also increasing their throughput by 34,944 parts annually.
The labor required for post-weld rework associated with solid wire also represents significant cost. As with pre-weld areas, the labor here is non-value added, compensating for deficiencies of solid wire rather than contributing to throughput. If Company A spends 30 minutes grinding in the post-weld area because of using solid wire, then they are consuming 30 minutes of time and labor that could otherwise be spent creating quality parts and increasing throughput.
With metal cored wire, companies can drastically reduce issues like rejected parts, rework and post-weld clean-up by using a welding process that does not require compensatory acts. In short, weld it better the first time. Of course, no consumable can guarantee perfection, but metal cored wire has proven reliable in reducing rework and its associated labor cost by up to 80 percent. For Company A that means reducing post-weld activities from 30 minutes to six minutes, a gain that provides another 24 more minutes in the weld cell.
Will Metal Cored Wire Optimize All Operations?
For some welding operations using solid wire may be adequate, but many companies can achieve throughput gains by switching to metal cored wire. In the case of Company A, metal cored wire provides a total gain of 42 minutes to the welding operation—14 minutes in pre-weld, 4 minutes in the weld cell and 24 minutes in post-weld - by eliminating non-value added labor associated with solid wire. That company can now reallocate those 42 minutes to the weld cell to increase throughput of quality parts.
To realize the same potential, companies need to step outside the weld cell and look beyond the higher unit cost to determine if they are a viable candidate for metal cored wire. For the right candidate, that higher unit cost pales in comparison to becoming more productive, saving money on non-value added labor and producing quality products to better meet their customers’ needs.