CAD-based welding robot programming for lot sizes, big and small

2023-01-30 14:37:01 By : Ms. SC CarBeauty

FIGURE 6. A fixture used for locating and welding fireboxes is shown.

When first introduced in the late 70s and early 80s, robotic welding technology was seen as a panacea for welding high-volume, repeatable products. It didn’t take long before all the “low-hanging fruit” was picked, and robots were branded as effective only for high-volume applications. Lap Joint Flange

CAD-based welding robot programming for lot sizes, big and small

A lot has changed in the past several years.

I had the privilege of working with Petrosmith after the installation of their new robotic cutting and welding system, to help them get into full production, optimize their cutting and welding processes, and provide some hands-on practical training.

Petrosmith is a manufacturer of surface production equipment for the oil and gas industry. By nature, this business is a low-volume/high-mix environment. To automate the welding and cutting process in welded vessel parts, the robot system must have some innovative features to allow efficient welding of lot sizes as small as one.

Enter Cloos Robotic Welding and Autocam, a German software company that provides software allowing CAD-based “automated” programming.Cloos has been a purveyor of robotic welding systems in the U.S. for more than 30 years, specializing in customized robotic systems that can handle everything from small, high-volume parts to very large, low-volume weldments. Cloos is a single-source supplier of robotic welding systems, designing and building the robot, welding power sources, positioners, welding torches and cables, consumables, and software.

Autocam provides a software called Moses that can automatically generate robot programs from CAD drawings for plasma cutting and welding.

Together, they make a formidable team.

Petrosmith was looking to enhance their manufacturing capabilities and automate certain labor-intensive welding processes to address bottlenecks in their vessel manufacturing operation.

Mike Duffy, president of Petrosmith, Abilene, Texas, explained:

“Petrosmith wanted to bring additional value to our vessel operation, and adding robotic automation is a great way to differentiate ourselves from many of our competitors and address production constraints in our head fabrication area. Adding the robotic cell has allowed us to quickly weld small lot sizes for our custom vessel operation, as well as make repeatable, high-quality head weldments for use in some of the other more standardized vessel designs. I have previously had great experience working with Cloos, and what they bring to the table regarding a complete turnkey integrated solution for robotic welding. They did not disappoint here, as this system has exceeded our expectations, allowing us to utilize it on other labor-intensive weldments other than just heads.”

FIGURE 1. Petrosmith’s new robotic welding/cutting system.

Justin Hammond, vessel operations manager at Petrosmith, also understood that although employees may sometimes be concerned about the arrival of robotic automation, there really is no need for concern.

“It is always the first question when employees hear about robotic/automation implementation into their environment. This is the same thing for Petrosmith. Our goal was not to reduce head count, but rather focus on reallocation of resources to other parts of the operations where their skills could be better utilized,” Hammond said.

CLOOS provided a robotic system, including a 6-axis robot; a cutting table for cutting the heads; a 2-axis tilt and rotate positioner for welding components to the heads; a single, flexible fixture to locate and hold a variety of heads during welding; and the Moses software package; all integrated in a single, flexible system. The robot has a tool changer and can automatically change, as needed, between three tools: a single wire welding torch, a tandem welding torch, and a 400-amp Hypertherm high-definition plasma torch (see Figure 1).

The process starts with Moses, which contains a library of the physical components that will be welded, including the vessel heads, flanges, manways, and couplings, all in .dwg CAD format.

The programmer begins by importing a CAD model of the head into Moses (see Figure 2). He then locates and defines all the holes to be cut according to dimensions from the part prints. Then Moses calculates all the cutting paths and provides a complete robot program, which is ready to download to the robot to start cutting.

The same is true for welding. The parts that are to be welded to the head are added to the CAD model that was developed for cutting (see Figure 3). Then Moses calculates the welding paths complete with multipass welds where necessary, touch sensing, through-arc tracking commands, and everything else needed to generate the robot program. No post-editing is necessary: Moses provides a complete robot program ready to load into the robot.

Moses provides the ability to develop templates for different types of welds. For example, some heavy-walled heads will have groove welds around the flanges, so the robot must first fill in the groove, often a multipass weld, before welding the fillet weld on top of the groove, which is also a multipass weld. Templates save a lot of programming time: For example, an entire three-pass groove weld can be stored in a template and quickly assigned to a particular weld.

These templates (see Figure 4) can include the vareity torch angles needed for each pass and can allow for unique situations, such as the different welding torch angles needed to weld around flanges that are close to one another or are on the steep part of the head.

To handle the inevitable part tolerances, the robot searches for the beginning of the weld so it can strike the arc in the correct place, then uses real-time tracking to keep the weld in the joint the entire length of the weld. While tracking the first pass, the robot stores the actual position of the root pass. The subsequent passes are then offset to the desired distance from the root pass, which guarantees the weld is perfectly placed every time, even if the actual weld position varies in space.

In the cutting module, Moses provides for axial cuts (cuts where the flange or coupling will be parallel to the centerline of the vessel) or radial cuts (where the flange will be perpendicular to the surface of the head). It also allows for beveled cuts to provide for a groove weld, and the bevel angle is freely programmable. This beveling operation is a huge advantage for both part quality and cycle time. Imagine manually laying out, cutting, and beveling an axial hole on the sloped part of the vessel head (see Figure 5). Not only does this require a very skilled layout technician, but it is also quite time consuming. With the robot, it takes about a minute to actually search for and make the cut.

FIGURE 2. A head with flanges is programmed for welding.

The machine also marks the parts in low-amperage plasma marking mode to facilitate proper clocking of the head when it is manually located and tacked onto the vessel. As in welding, a touch-sense probe touches and locates the surface of the part before cutting to ensure the proper stand-off height when piercing. Then height sensing takes over during the cut to keep the stand-off height consistent throughout the entire cut.

After the holes are cut, the various parts are manually tacked in place, and a backing pass is manually welded inside the head. Then the tacked head is placed in the welding fixture, and the robot automatically drops off the plasma torch, picks up the welding torch, and performs all of the weld passes on the outside of the head.

The key to the whole process, and the technology that allows lots sizes of one, is of course the Moses software. While the robot is actively welding or cutting, the programmer can be working on the next program on a PC. The key to extracting a favorable ROI from a robot system is to keep it cutting or welding. That’s the only time it’s making money. By programming the next part while the robot is actively running production, the ROI is optimized.

I also worked with the Petrosmith team to add additional parts to the robot’s repertoire. We designed and built two welding fixtures in-house for locating large manways (flanges in the 18- to 24-in. dia. range) and fireboxes (see Figure 6).

These programs are written manually on the teach pendant the “old-fashioned” way since the programs are relatively simple and straightforward. The ROI was very good for these parts. A typical firebox takes four to five hours to weld manually, and about half an hour to weld with the robot. Of course, part fit-up, gap sizes, and repeatability are a challenge, and Petrosmith had to work on fine-tuning parts tolerances for robotic welding. But this is common in virtually every robotic welding application.

As of this writing, the system is being used for production parts, and many parts can be run in automatic mode, but there are still many parts yet to be programmed. Once a part program has been generated by Moses, it does not have to be reprogrammed; it can be saved both on the robot’s hard drive and on the PC that is connected to the robot via ethernet, and reused when needed. Even though many of Petrosmith’s products are low volume, many vessel types are repeatable so the programs generated will often be used again in the future.

The main advantage with this Cloos/Moses combination is that the programs can be generated from a library of standard parts, and this programming can be done offline while the robot remains in production. Flanges, manways, couplings, and vessel heads have industry-standard designs. As such, these CAD drawings can be used as standard features which Moses uses to build individual weldments and to calculate robot paths. Moses also can optimize the position of the welds to assure the best weld quality.

One goal of many robot users is to assign relatively unskilled labor to the robot, thinking that the robot will run perfectly as long as someone is there to simply load and unload parts. This may be true in some instances, but in many situations the robot operator should be more than just a button pusher. There are many applications that require an experienced welder to run the robot, and this is often the advice I give to my customers. This person may have to do more complex tasks such as post-weld inspection and repair, changing certain welding parameters as allowed, and simply recognizing when there is some kind of problem.

But with Moses, since the knowledge and experience is primarily trusted to the programmer (who certainly needs to be a skilled welder/robotic programmer), and the welding parameters are pre-proven and template-driven, the operator actually loading and unloading parts does not necessarily need to be an experienced welder. Keep in mind that one programmer with one seat [Is this the right word?] of Moses software can potentially write programs for more than one robot system.

The Cloos hardware and the Moses software can be scaled up to include complete vessels, and indeed there are companies in the U.S. that are using this same combination for cutting and welding complete vessels, including welding heads as described above, but also welding flanges and manways to the vessels themselves, and welding heads to vessels with girth welds.

FIGURE 3. A head with flanges is programmed for welding.

Often the girth welds utilize Cloos’s tandem welding process, a special welding process with a torch that includes two welding wires welding simultaneously, controlled by two separate welding machines, to provide very high deposition rates, fast welding speeds, and lower overall heat input, which can be a big advantage in ASME code welding of vessels.

For other industries with very low lot sizes and very high mix environments, which are not based on industry-standard CAD components, Moses may or may not be the best solution. However, the industry is ever evolving, and there may be a robotic solution just for you.

See More by Jim Berge

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CAD-based welding robot programming for lot sizes, big and small

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