Choosing the right robotic weld cell for your operation

If a company does much hand welding, it may have loose tolerances on the prints. However, a robot cannot work with these kinds of tolerances. A robot can maintain a good weld only if the parts are held to a tolerance of ± half the weld wire diameter. If this is not determined at the start, it can cause a lot of problems.

A robot can cause your company to do a lot of reverse engineering for the robot to perform, so you should review your fabrication procedures. Are the tolerances too loose? Do the parts in the assembly, before welding, have many gaps at the weld joints? Do external suppliers supply parts to print? Are the parts being supplied to the robot repetitively?

Look at your plant as a whole to detect all the areas that can cause a problem for the robot. Some parts may need to be redesigned and the tooling revamped to make them repetitive. Are check fixtures for individual components in place? Do you need to initiate a new quality plan? Will operators fabricating the components need more training and a new training manual?

Deciding to Purchase

Cost can be a major issue for smaller companies looking into the purchase of a robotic cell. A lower-priced cell with a small robot with limited reach and no integration can be useful for smaller items. A more complicated cell can be more than a smaller company can afford, but do your homework in this area also. Some lease packages give you the opportunity to purchase the complete system after the contract ends for as little as $1. This can help even small companies become competitive in the welding industry.

To determine your payback on the purchase, you'll need to find out what kind of production you'll get from this new system. A formula for weld time can help you figure out the parts per hour you can achieve for the most productive system.

In most instances, the cell indexes and the robot welds while the operator loads and unloads. This keeps the system busy. If in your system the operator waits while the robot welds, and the robot waits while the operator loads and unloads, add the weld time to the time it takes for the operator to load and unload. Both these times together make your total time for each welded assembly.

The formula is simple and surprisingly close. First, count the number of welds in your product. If you're welding a lot of circular welds that may be hard to access, count these areas as two welds and each doing half the total weld for that joint.

Let's say you have a total of 33 welds. Next add up all the lengths of each weld. In this instance it's 70 total inches.

Then determine what machine you'll be using and what travel speed (in inches-per-minute) you expect for the welding process. With 1¼4 inch-thick material, you may be able to travel 30 IPM in your weld program. With 60 seconds per minute, 60 sec. divided by 30 in. gives you a travel speed of 2 sec. per inch of weld, which will be used for this example.

Here are the calculation steps:

• Multiply the total number of welds by 2 sec. This 2-sec. interval is a calculation of air time for the robot moving from one weld joint to the next.
      2 sec. x 33 = 66 sec.
• Multiply the total inches of weld by 2 sec. This 2-sec. period is the travel speed calculated previously.
      2 sec. x 70 in. = 140 sec.
• Add 5 sec. for the positioner (if used).
      66 + 140 sec. + 5 sec. = 211
• So the total weld time per assembly is 211 sec.

Most robotic integrators quoting weld times typically add a 20 percent safety factor.

A robot can be useful tool in today's market. After you've planned, justified the cost, and decided to purchase a robotic welding system, it's time to do research.

Choosing the Right Integrator

Many factors are involved in choosing the right integrator. First, don't let money be the only issue. For your first system, you may want one completely integrated, delivered, and set up on your floor. A new robotic cell can be very confusing if it's unloaded on your dock and left for you to set up with no support.

A well-established and recommended robotic integrator can provide support and backing. Check with a few companies and get references. Travel to some of those references and see the integrators work. Talk to the operators that run the cells about any problems they've had. A good integrator will allow you to do this and will set up plant visits for you.

When choosing an integrator, keep in mind that most sell only specific robots–sometimes only one or two brands. It's just as important for you to choose the right robot as it is the integrator. Some robots are operator-friendly but may be lacking in the software department. Other robots are too complicated but are versatile in their abilities with the software.

Some robots are sold for welding but are better suited for material handling. These robots struggle to get into tight areas, so look for a small-end wrist where the torch attaches if access is a concern.

After you have chosen a robot and an integrator, it is time to decide on the cell that best suits your application.

Selecting the Cell

When looking at what to purchase, keep in mind that most cells fit most applications, but your application may be different. Take time to look at your application in all cells and find the best to fit your needs; then go further before you make a permanent decision.

Some cells are one-of-a-kind, unique to their specific application. With a little thought, you can come up with a special application that better fits your needs. This may cost a little more, but it can benefit your company in the long run. A good integrator can work with you on layouts of different cells with your product in mind. After you have decided which cell to purchase, it's time to decide on tooling.

Purchasing Tooling

The process of tooling involves putting individual piece parts together in a fixture, so that after welding a complete component is removed. Many companies have their own tooling engineers for welding. If your part is very simple with high production numbers, your engineer should be able to accomplish this task. But if your part is complex or has multiple components, robotic welding can be more complicated and repetitive than hand welding. It must allow complete access to the part for the welding torch and wrist.

Consider getting your first set of tooling from the integrator. After that, your tooling engineer can examine the tool and implement new ideas into the next set.

If you decide to let the integrator do the tooling, make sure that the trial run at its facility includes a trial run of the tooling. Complete integration should include all programming and a complete tool tryout.

Understanding Warranties

Your integrator should supply you with a complete breakdown in its quote of everything the cell includes, including warranties. Make sure that you will receive a package at delivery that has all the pertinent information regarding warranties of the items in your cell. Ask to see a copy of a previous purchaser's package. Make sure that a complete electrical schematic is included, along with a disk including your system's operating programs.

Many different components comprise a robotic cell. The integrator should accept responsibility for its specific components and what it has done to the cell only. All purchased items have a warranty from the manufacturer, and the manufacturer is responsible for repair or replacement.

Training

All those who will be responsible for the robot must receive proper training from the integrator in your facility. Training should include the master cell programs and the operation of your cell. Your employees won't be experts after this training, but they will know the basics and be able to get started when the cell arrives.

Make sure that those receiving training include one or two people who will be running the cell and two experienced workers who are likely to be with the company for a while. These last two can train future operators if those you have chosen do not work out or leave the company. Make the operators a part of the trial run so that they are familiar with the cell and feel that they are playing a major roll in this new cell.

Testing the System

A robotic cell can have a complicated master program to run the robot, postioner, and other peripherals. Make sure that all E-stops work and that the system runs as expected.

If you have any problems with your system, don't allow delivery until it has been fixed at the integrator's facility. Be cautious of problems that involve integration of components. It can be difficult to agree on whose problem it is. The integrator may say a problem is caused by the robot or welding machine, while the manufacturer of the robot or welding machine insists it's caused by the integrator.

After resolution of these problems and a successful trial run at the integrator's facility, the cell can be delivered to your facility. After delivery and setup, a trial run, which should be included in the contract, should be conducted at your facility. Be prepared for delays.

A system usually has bugs that need to be worked out. These bugs result from integration of such a complicated system, parts malfunctioning because of factory manufacturing errors, and the operators being uneasy with such a new and sophisticated product.

Plan for full production four to six weeks down the road. This gives time for your company to get used to the system and organize part flow to and from the system.

Michael Passmore is owner of Passmore's Jigs & Fixtures, 732 Boulder Place, Statesville, NC 28625, 704-878-2809, fax 704-883-8869, mike_capn@msn.com.