Maximizing welding productivity per square foot
Above: Adding more robots is a cost-effective solution because cell integration costs, such as PLCs, HMIs, tooling, safeguarding and utility drops do not increase.
Maximizing welding productivity per square foot
September 2018 - For manufacturers to gain maximum return on investment over a given payback period, many will obtain the most efficient workcell possible for handling a given application and part type. A larger workcell with additional robots can increase throughput, improve product quality, close the gap in available skilled workers and meet exacting customer demands.
Until recently, U.S. manufacturers were less concerned with floorspace compared to Asia-based manufacturers. This mentality is changing, however, as everything in production, including machine footprint, can become more efficient. Yaskawa Motoman makes a variety of standard welding workcells that can illustrate six factors that contribute to floorspace productivity.
Manufacturers looking to weld smaller parts that do not require positioning may consider an ArcWorld 1000 (single robot configuration).
Considerations
1. Part area: The space needed to support a product. For example, an automotive seat supplier has an obvious size difference between recliner brackets, front seats and 60/40 split rear seat frames for subassembly. Having enough space to effectively and efficiently position and produce quality parts with tooling is key. If a part must be reoriented, it will need a larger three-dimensional volume.
2. Workcell area: The entire workcell footprint or how much floorspace the robotic system encompasses. Choosing a robotic system based on footprint alone is not ideal and single-station workcells should be evaluated as a pair when comparing them to a two-station cell.
3. Safety area: An open space operators must occupy during positioner indexing to comply with safety regulations. Some manufacturers customize a robotic workcell with roll-up doors to secure the area. Suspending part bins for smaller parts inside this area helps use this space and improve ergonomics.
4. Operator/parts storage area: Where operators grab or place parts into the cell tooling. Cells with safety space potentially crowds an operator with part storage, which would require equipping a single-station workcell with a wider aisle. Single-station workcells are sometimes placed opposite each other, so the operator loads one and then services the other cell, working in the aisle.
5. Robot quantity: The number of arc welding robots in a workcell is also paramount when choosing a solution. Adding a second or third robot can nearly double or triple welding production with little to no impact on floorspace. This increases the “arc density” of a given workcell.
6. Cost: Many times, the robot is a smaller percentage of the cost when positioners, cell controls and tooling are included. Items such as laser sensors may raise cost but improve cycle time. A customer’s part and throughput requirements dictate how much they value cost-adding features when creating an extremely efficient cell.
Application ratios
When choosing the most productive workcell for a given application and part type, compare factors that impact workcell efficiency:
• Part area/workcell area = part to workcell area ratio or space utilization of cell
• Part/workcell X arc robot quantity = arc density or workcell productivity ratio
• Ratio of dollars to floorspace + number of arcs = value ratio
• Integration Costs (1x per workcell): PLC + HMI + power drops + tooling + etc.
Example 1: A job shop or automotive company may consider the ArcWorld C-52, a compact workcell for low- to medium-volume fabrication that has two flat table stations (an AWC-52S has headstocks for turning parts). This cell features:
• Reduced floorspace
• One six-axis Motoman robot
• Roll-up door
• Integrated welding package
• Maximum part size capacity of 760 mm by 700 mm
Selecting a smaller workcell based on part size may appear to be the best use of space, but after considering the smaller part size in conjunction with the total footprint of the workcell, the overall area efficiency of this cell is only 12 percent.
After calculating the part area to robot ratio and comparing it to the number of arcs, the AWC-52 workcell productivity ratio was still 12 percent efficient due to the single robot. Despite low entry cost, fast ramp-up time, tight footprint design and easy safeguarding capabilities, this workcell may fall short for some manufacturers.
A compact welding workcell designed for low- to medium-volume applications may be an ideal choice for a job shop or automotive company.
Example 2: Manufacturers looking to weld smaller parts that do not require positioning may consider the larger ArcWorld 1000 or 1200 (single or dual robot configuration). Pre-engineered for small- to medium-sized part production for medium-to high-volume welding applications, these feature:
• High-speed servo turntable (60 in. or 72 in. table)
• One or two six-axis Motoman robots
• Functional safety unit
• Integrated welding package
• Maximum part size capacity of 1,000 mm by 474 mm
Using the same subassembly comparison (as Example 1), the AW1000 cell was 10 percent efficient using the part area to workcell area ratio. Despite the introduction of a high-speed servo turntable, the safety area created unusable “dead space” during operation. On the positive side, the operator area required minimal movement from the operator, creating better ergonomics.
When the arc density was calculated in relation to the part area to workcell area ratio, it revealed that adding a robot (AW1200) increased the overall workcell productivity to 19 percent, making it a more productive use of floorspace than the smaller cell in Example 1
Example 3: Yaskawa’s AWIV-6000 series workcells provide the most efficient use of floorspace. Pre-engineered for medium- to high-volume part production, these feature:
• High-speed capacity, space-saving slim-line ferris-wheel positioner
• One to four six-axis Motoman robots
• Functional safety unit
• Integrated welding package
• Maximum part size capacity of 4,000 mm by 1,525 mm
Using the same comparison (Examples 1 and 2), the ArcWorld IV-6000 cells were 30 to 34 percent efficient using the part area to workcell area ratio. While the addition of a high-speed, slim-line positioner in relation to the part area and workcell area raised the efficiency of the cell, the presence of the safety section still created “dead space.” Some manufacturers use roll-up curtains to span the safety area to reduce the distance used by light curtains.
As in the ArcWorld C-series and 1000-series workcell examples, the presence of arc welding robots boosted the productivity factor. When the arc density was calculated in relation to the part area to workcell area ratio for each cell in the ArcWorld IV-6000 series, the findings were as follows:
• AWIV-6000SL part area/workcell with one arc robot and 2 m part span = 30 percent productivity ratio
• AWIV-6200SL part area/workcell with two arc robots and 3 m part span = 67 percent productivity ratio
• AWIV-6300SL part area/workcell with three arc robots and 3 m span = 101 percent productivity ratio
The arc density in relation to the part area to workcell ratio gave the ArcWorld IV-6300SL a greater percentage, making it the most flexible and productive workcell for Yaskawa standard configurations.
Compact workcells offer a reduced footprint but are not necessarily the most efficient use of floorspace. Job shops should evaluate the part size capacity in relation to the workcell footprint to determine the most flexible use of floorspace.
Evaluating the cost of different workcell configurations, including integration costs, can help manufacturers maximize the value of their factory floors. FFJ
Chris Anderson is associate chief engineer at Yaskawa America Inc.’s Motoman Robotics Division.
