Increasing Existing Robot Efficiency

Introduction

Manufacturing facilities spend enormous amounts of money on automation. The reason for investing in the equipment is typically to produce more goods with the same number of resources. Those resources include personnel/workers, time, floor space, etc. If a company can increase the amount of product they produce while still in the same building and with the same number of employees, they will generate more profit. For decades, robots have been implemented into manufacturing facilities to increase efficiencies. The next step is increasing the efficiencies of the robots. Companies who lower the cycle time per part push more parts out the door while maintaining the same overhead costs. This article begins with the physiological effects of robots on employees and ends with some ideas to increase robot speeds and decrease cycle times. Robotic cycle times are measured by timing how long it takes to load a part, have the work done to it (i.e. welded), and then get it unloaded. With factories who run tens of thousands of parts a year, a few tenths of a second per part add up to be significant. Let’s do a calculation to show just how significant a few tenths of a second can be. Imagine the cycle time for a part is 60 seconds (1min). If a factory works 8 hours a day with a 30-minute lunch and two 15 minute breaks, that leaves 7 hours left for work. Many robotic cells are installed with an assumed 85% uptime. This means 15% of the time the cell is down for maintenance, fixture change out, unplanned downtime, staffing shortages etc. Seven hours multiplied by .85 equals 5.95 hours of planned production time per day. 5.95 hours X 60 minutes per hour X 60 seconds per minute equates to 21,420 seconds. If the cycle time of a part is 60 seconds, then 21,420/60 means that 357 parts per day can be completed. There is no magical wand for saying how much efficiency your specific company could pick up. In some plants maybe all of this has already been done. In others maybe you can save 20% on cycle time with just the click of a few buttons. No matter the case, even a 2% decrease in cycle time saves 1.2 seconds on this part (60 seconds X .02) which allows the operator to produce 364 parts per shift (21,420/58.8). The increase from 357 to 364 parts per hour are essentially “free” parts because the labor and overhead were already going to be there anyway. If you’re not interested in numbers like those you wouldn’t have made it this far into the article. Let’s jump right in and make our automation work for us.

 

The physiology of automation

Before we can save cycle time we need to understand that automation can be demoralizing to workers. At the same time, it can make our jobs and lives much easier when used properly. The demoralizing side of automation is when the robot works faster than the operator can even dream of operating. In a perfect world, the operator should have 1-minute worth of work while the robot is doing 1-minute worth of work. Without even knowing it, an operator will make a game out of beating the robot and getting a “win” each time the cycle finishes. The opposite happens if the operator has 3 minutes’ worth of work to the robots 1 minute of work. In this case the operator has no incentive to work faster because no matter what they do the robot will still beat them. Factories have seen increased production rates by actually slowing their equipment down to match operator speeds. The remainder of this article is for the opposite problem and is focused on speeding up the robot so that the operator isn’t wasting time waiting for the robot.

 

Know your parts

Before changing anything in the program, first double check that the robot isn’t taught a weird path or a slower speed on purpose. Sometimes there are engineering reasons for certain programs, and it is important to understand these before modifying programs. Speak with the appropriate parties such as engineers or robotic programmers who originally wrote the program.

 

Speed up the air moves


The first and easiest thing to check for speeding up your robot is the air move speed. Robots typically measure this in a percentage with 100% being top speed for air moves.

 

Adjust the part clearance spacing

Robots go to the exact same spot and follow the exact path every time. With this in mind, move the air move points closer to the fixtures, clamps, etc. If the robot makes a weld, then moves over an obstacle, and makes another weld there is no reason to have the robot go higher than necessary. By dry running the program (running it with the weld turned off) watch and see where there is wasted movement. If the torch goes 8” up and over the fixture adjust it to 2” above. That saves 6 inches of air move time up and 6 additional inches of air move time back down. Small changes like this can make a big difference in the overall program.

 

Modify the Order of Welds

The quickest way to get somewhere is in a straight line. Use this theory for robotic programming as well. Have your program start on one side of the part and work towards the opposite side. A robot bouncing all around the part is wasted air move time. However, be careful with this one. Sometimes programs are written in special ways to help balance the heat input into the part. If you are working with a complex assembly, watch out when modifying the order of welds because it may affect the tolerances of the final part.

 

Knowing your move types

Robots typically have the option of linear moves, circular moves, or joint moves. A linear move goes in a straight line from point to point. These should be used when welding because it will make for a nice straight weld. Circular moves are used far less often but are implemented when welding an arc or circle. Joint moves are most common for air move applications. Joint moves do not necessarily move in a straight line but instead get the robot point to point in the fastest possible way. Joint moves should be used anytime the robot is moving in free space and its programmed path is not critical.

 

Path Smoothing

Path smoothing is a software setting that allows the robot to round off corners when applicable. The smoothing action has different names for different manufacturers, but it all accomplishes the same task. When smoothing is off or low the robot goes to the exact point that is programmed, stops for a split second, then to the next and the next. With smoothing turned on the robot rounds off the corners to save time and prevent unnecessary wear and tear. Path smoothing is commonly configured on a 1-5 scale. Welds should have the smoothing turned off because the robot needs to go to the exact point, whereas air moves are a great place to use path smoothing.

 

Adjust Pre and Post Flow

Preflow is the amount of time the shield gas flows before the weld begins. Post flow is the amount of time the gas is on after the weld is complete. Pre and post flows are both important for weld quality, but longer than necessary means wasted gas and wasted time. Remember that higher amperage welds require a longer postflow to protect the weld while it is still solidifying.

 

Change the weld position

Different weld positions have different benefits. For instance, welds made in the flat position have the best penetration whereas welds in the vertical down position have the quickest travel speeds. Sometimes a hybrid solution can be used as well. Even a 15-degree downslope will make a huge travel speed difference because gravity is helping to pull that weld down. Welds that are purely cosmetic or for sealing purposes are welded downhill all over the country to help speed up production rates. If the weld is considered structural make sure to do the proper weld verification testing after making any adjustments. Always refer to documentation like a WPS (Weld Procedure Specification) when applicable as well.

 

Invest in new technology

Cobots are new to the welding market. Cobot is a term that means collaborative robot. These machines work side by side with human operators. Customers of ours have found that even though the cobots have slower air move speeds, the overall production is increased compared to a traditional welding robot. The reason for this is that all the safety lockouts have been avoided via power force limiting and force sensors. Now the operator works directly with the robot and is no longer waiting for doors to open or avoiding light curtains. Some operators use a “loop” function as well. The loop function keeps the program running time after time so the operator is no longer even required to press the start button. When the operator needs the robot to stop, they just tap on the arm and the collaborative software brings everything to a stop until the program is restarted. Technology in welding power sources has improved travel speeds as well. New software technologies improve gap filling capabilities, offer improved travel speeds, decrease required rework, and have low spatter modes that decrease clean up time and save on consumable items like grinding wheels. If you’re running older equipment it may be time to discuss options for increased production and quality! 

Should you find yourself needing professional help with robotic programming, program modification, or consultation, reach out to Arc Solutions, Inc. today! We are an authorized service center and distributor of many trusted industrial brands. We have an automation team and engineering staff at your service. Reach us at 419-542-9272 or office@arcsolinc.com