Final report from
E F Craig

Project: Robot welds for Freight Liner a large US truck mfg.

Project Summary:

The following has been implemented at the --------- facility. Major changes were made in the existing welding programs of the ABB 2400 series robots. The program changes completed in the first week of Aug, were designed to improve the weld fusion potential and also to reduce the weld cycle times of both the HD and LD parts. The welding programs were put on discs and delivered to the engineering personnel.

The following welding recommendations to enhance the steel spray transfer weld quality and productivity.

* MIG GUN CONTACT TIPS: The benefits of recessing the robot contact tips inside the nozzle were proven with the test welds we made. The recessed tip greatly extends the tip life, reducing wire burn back potential and robot downtime. The recessed contact tip also enables increased wire feed rate with minimal increase in weld current. Instead of purchasing new tips or longer nozzles I had spacer sleeves machined which placed the nozzle in a lower position that provided protection for the tip.

* MIG GAS MIXES: The argon oxygen mix used at Gastonia is a low energy mix. To enhance the opportunity for superior weld fusion I used an argon + 15 CO2 mix.This gas mix provided improved weld fusion profiles in all the weld tests we carried out. As each robot will utilize the equivalent of a gas cylinder per shift per week, I would recommend that at this time you do not make changes to a bulk system and go with cylinders for the present. There appears to be restrictions to the gas flow in the 2400 cells, the gas flow rate was reduced by fifty percent from the flowmeter to the gun nozzle outlet. Ensure that 35 to 40 cuft/hr is available at the gun nozzle exit, restricted gas flow will effect a weld penetration profile.

* WELD POROSITY. Weld porosity is influenced primarily on your application by the lubricants left on the welded part surface. Operators do clean the parts, however more emphasis could be placed in improvements in this area.

* THE AUTOMATED ANTI SPATTER COMPOUND SPRAY SYSTEM is equipment and should always be regulated, especially when one considers the importance of the weld quality and the influence of liquids on weld quality. On my initial visit the anti-spatter system was set too high in one cell, resulting in excess anti spatter compound being ejected from the nozzle. Anti spatter compounds can add to the weld porosity and weld cracking potential. Operators should not be allowed to set this unit which has now been reset. The anti spatter should deliver a minuscule amount of compound after each nozzle clean cycle. The small amount of anti spatter compound does assist in the easy removal of the spatter in the nozzle ream cycle. The new welding program encompassed less nozzle cleaning requirements therefore (less anti spatter compound is used).

* THE WELD CYCLE TIME. As you are aware I have decreased the weld cycle time by 2 minutes per part resulting in a saving of over 3300hrs robot weld time per /100.000 parts for this one application. The same savings will also be generated on the LD parts. The weld time reduction is primary a result of changing the weld sequence, improving the deposition rates, improving the efficiency of the robot manipulations, removing the nozzle cleaning from every part and programming the cleaning action to occur for only one in five parts.

* WELD DATA: My objective with your welding application was to provide as much data as possible to enable optimum weld process control. Consistent weld quality from each shift is only achieved when all those involved in the robot application are aware of the variables that effect consistent weld fusion. As you are aware attaining consistent weld FUSION for this critical application is a sensitive issue, and any changes outside my recommendations will effect that weld fusion. The same process control logic also applies to attaining consistent weld productivity from each shift. It would be beneficial for weld process control data I provided if the data was placed on a poster size board in each of the robot cells involved in the application.

Please note that the most critical locations on your welds are the first and last 30mm of weld. It will be notable that when you cut and etch your weld samples you may note that one side of the weld indicates superior fusion than the other side, this results from the tendency of MIG towards lack of weld fusion on cold starts. Lack of weld fusion is also commom at the completion of the weld at the weld tie in. Please note that I am recommending that the weld speed be slowed down in the next table for these two critical areas. please ensure this data is reviewed and understood by the operators.

Freightliner should also be aware of any weld data we provide is data that has to be pre qualified and approved by your organization. The data can be changed and Imn sure as you review the application from a weld fusion potential that slight changes to the weld travel rates, wire feed rates, or gun angles will further enhance the opportunity for increased weld fusion potential. The bottom line is don't allow process changes without visual examination and approval of the weld fusion profile.

* THE MIG WIRE; As each drum of wire is replaced, the operator should examine the cast and helix as the wire is cold fed from the gun, and if required adjustments should be made to the wire straightner if necessary. Please note also the recommendation of the E70S-3 wire which will produce slightly less surface slag islands than the E70S-6 wire. IF Wire problems, equipment problems, part and fixture problems, occur ensure that each problem is documented in the robot cell log at present this does not appear to be taking place.

* EASY TEACH: Your ABB 2400 series robots, with the highly advanced S4 control, provides your organization with the ability to utilize unique tools which will have significant practical benefits. As you are aware few operators are proficient in programming and when training is provided much of it is quickly forgotten when the operator does little more than operate the programming. When an organization has at a specific location just a few robots its difficult to justify hiring a full time technician for programming, these factors unfortunately add greatly to the underutilization of the robots at your facility, and also add extensive time required for the programming when a prototype part is presented

* TRAINING: The most important step in maintaining consistent weld quality and productivity is to train the operators in the weld process requirements, its extremely important that the operators be aware of what they can change and what they must not touch, its also important that they have the ability to recognize the arc sounds, as the greatest diagnostic tool in a robot cell is the operators ears.

I wish to thank you for your cooperation and look forward to working with your organization in the future.

Yours Sincerely
E F Craig.

Weld Eng