When it is done correctly, robotic welding can provide manufacturers with significant productivity gains, as well as an excellent return on investment (ROI). However, robotic welding can be a complex process, especially if you are a new robot programmer.
While the best course of action for learning robotic programming is to acquire training from your robot brand OEM, it never hurts to implement expert-proven robotic welding tips and tricks from the start. As with any specialty process, there are steps that you must take when programming a weld sequence and certain things to avoid.
General Do’s and Don’ts of Robotic Welding Programming
The gas metal arc welding (GMAW) process is the same for robotic welding as it is for semiautomatic welding. Some of the practices outlined in welding codes can help to “control” the application of robots for the fabrication and manufacturing world. Examples include the setup and use of established weld procedures for various joint conditions common in your operations. Other welding-related tips can help simplify the process.
Create an Arc File library based on weld size, and name each file clearly and concisely. For example, ASF#1 is a 3⁄16-in. horizontal fillet; ASF#2 is a 3⁄16-in. flat fillet; ASF#3 is a ¼-in. horizontal fillet; and so on. Use corresponding numbers for arc start and end files.
Weave files should match the arc files for each weld size. For example, ASF#1 uses WEV#1; ASF#2 uses WEV#2, etc.
Remove speed tags on process moves if you want to use the weld speed specified in the arc
Keep weld programs small (less than 100 to 200 points). Having too much in one program can make editing confusing. Always label each weld with a line comment on the move before the arc start. Use logical subroutines to keep program size manageable, such as a program for each positioner orientation if there are many weld locations on a multisided part.
Focus on torch/arm posture for weld joints, and then add air-cut moves in between welds that flow smoothly.
Keep a master part for programming. This part should be labeled with weld numbers and arc size file numbers, which allows for a quick reference for weld adjustment. A part print with weld locations and program points noted can serve the same purpose.
Keep a log or change record for the robot workcell where technicians can note the date, time, and reason for changes. Robots may have the ability to log changes to programs, but they may not include the reason for changes.
Do not create programs with improper control axes, especially if the system is equipped with coordinated positioners or multiple robots.
Do not create or use multiple weld settings (wire feed speed and voltage) on many different weld locations with the same joint type. Use travel speed to adjust the heat or fill for various joint fit-ups. Wire feed speed and voltage control the “burn” of the wire and can be adjusted to reduce spatter. Travel speed has the most pronounced effect on heat, as noted by heat input:
Heat Input = (Amps x Volts) / Travel Speed
Welding Torch Do’s and Don’ts
A critical factor for robotic welding is choosing the right weld gun for the task at hand. More so, the ability to program and maneuver a weld torch with the utmost efficiency is equally important. Here are some tips to keep in mind for the business end of the robot.
• Use a torch alignment tool. Most manufacturers sell them and most will work for multiple torch models. The reason is a 45-degree torch from a manufacturer is not always the same as a 45-degree torch in a robot workcell. Before doing any programming, place the torch in the tool and ensure the bend is correct. If it is not, use the tool to bring the bend in line, guaranteeing a correct angle on the torch. Moreover, if you should ever need to replace the torch, you can place the new torch in the alignment tool before you install it.
Create and maintain a good tool center point (TCP), as well as a check job, which confirms the TCP location and alignment before touching up points. Robot suppliers and integrators may have gauges or tools to help automate this process.
If you are searching for weld joints, go through your search routine and shift “on” before touching up points. If you don’t do this you will lose the relationship between your searches and your weld points.
Program all weld points with the same wire stick-out length (the distance between the contact tip and the weld joint). You can create a “teach tip” by drilling out a contact tip and inserting a sharpened tungsten or drill bit with the desired stick-out. The teach tip will be straight and can help negate the effects of wire cast on TCP location. If you are using the actual weld wire, be sure to clip the wire to the same length when programming with either welpers or a gauge.
Never touch up a position for one defect on one part. Ensure there is no defect in the part or upstream process. You do not want to change a point to fit an out-of-spec part, as in-spec parts will not weld correctly after the change.
Don’t select your robotic torch based on which consumables are in your tool crib. While it is convenient to have the same parts in a plant, many continue to use different torch neck angles or dated designs because maintenance keeps the same spare parts lists.
Don’t use extended torch necks or narrow nozzles unless it’s absolutely necessary. Extended necks will result in less repeatability and are more prone to damage. Smaller nozzle diameters will clog with spatter more frequently and require more reaming.
Power Source Considerations
Advances in inverter technology and faster processors have led to more precise weld process control, which has benefited robotic welding. Power source brands offer unique technologies with powerful yet easy-to-use interfaces that help achieve high-quality welds.
Most manufacturers offer multiple process variations for a given wire type, size, and gas combination. These generally can be changed by the robot program to provide optimal welding characteristics for a variety of joint conditions, even if they exist on the same part. Additional considerations include:
Keep track of the welding process selected from the power source in addition to the individual weld settings, such as wire feed speed and voltage. This may be a comment in the weld program if it is not associated with the instructions for weld settings.
Set up or program the weld processes that apply to your operation into the power source programs or robot selection tables. Even if they are not used on a specific part today, they will be in a known program location for future use.
Do not make changes locally from a power source panel if you are relying on the robot to control the sequence. A process or parameter may be changed on the power source for temporary or expediency reasons, but older programs may reference this changed setting and result in unexpected results.
While you may be familiar with how important using proper torch angles are in welding, robot programming adds the variable of creating the motion most efficiently and quickly. A good robot program will prevent the robot from performing exaggerated positions/postures and balance the motion of the torch orientation with the robot arm position.
All nonprocess moves should be joint moves (noninterpolated motion). Moves where an axis is moving more than 180 degrees should be made in two moves to ensure smooth motion.
Keep the robot posture as close as possible to the home position. Try to keep the default posture and don’t wind up the robot into an odd posture if it is not absolutely necessary.
Keep the wrist—more specifically, axis 5—pointing downward so that the angle of the torch creates the work angle with the weld joint (if the joint is horizontal).
Do not use major axes (such as axis 1, 2, and 3) movement to position the torch angle. The most efficient motion will use the wrist axis to orient the torch, while the motion of the base axis performs translational motion only.
Do not use excessive torch motion creating a singularity of any axis (axis 4 and 5 mainly) during the weld process.
Implementing robotic welding is not a task to take lightly. Any steps you take to make programming a smoother, more effective process can optimize production. This is particularly true when you have multiple personnel maintaining multiple robotic workcells.
From better weld quality to improved consistency, you can experience many benefits when using robotic welding. Using these tips and tricks should help you reach your goals more efficiently.
By Chris Anderson