A
condensed version of the weld report issued:
The
following has been implemented at your 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 GUNS AND CONTACT TIP POSITIONS: The benefits of recessing the robot contact
tips 3 mm inside the nozzle were proven with the robot test welds made. The recessed
tip greatly extends the tip life, reducing wire burn back potential and robot
downtime. The recessed contact tip provides a lightly extended wire extension
which lowered the weld current . The reduction in current enabled me to increase
your wire feed rate decreasing the weld time.
Instead of purchasing new
tips or longer nozzles I had 3 mm spacer O ring sleeves machined, which when placed
behind the nozzle provided the correct tip position.
*
MIG GAS MIXES AND WELD FUSION: The argon 2% oxygen mix used at Gastonia is a very
low energy mix. To enhance the opportunity for superior weld fusion with my higher
speed welds, I used an argon + 15 CO2 mix.This gas mix provided improved weld
fusion profiles in all the weld tests we carried out and as this mix provided
higher weld voltage, the arc stability was improved.
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. Its part of the robot operators daily function
to ensure that 35 to 40 cuft/hr is available at the gun nozzle exit. The restricted
gas flow will effect a weld penetration profile and increase the weld porosity
potential.
* THE WELD POROSITY ISSUES. The weld porosity in the welds
is influenced primarily by the lubricants left on the welded part surface and
from your anti-spatter system. Operators do clean the parts, however more emphasis
could be placed in improvements in this area.
*
AUTOMATED ANTI SPATTER ROBOT SPRAY SYSTEM. This equipment in the robot cell should
be checked by maintenance weekly especially when one considers the importance
of the weld quality you desire and the influence of liquids on the 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.
Your operators
should not be allowed to set this unit which has now been reset. The anti spatter
liquid 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 robot weld cycle time by
2 minutes per part resulting in a saving of over 3300 hrs 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 outside each of the robot cells involved
with this 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
common 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 I provide is data that will require pre
qualification and approval by your organization. The data can be changed and I
am 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 macro 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 my 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 S4 control, provides your organization
with the ability to utilize unique tools which will have significant practical
weld benefits. As you are aware few of your programmers or operators are proficient
in the ABB programming and when training is provided much of it will be quickly
forgotten when the operator does little more than operate the existing programming.
As your rganization has just a few robots it's 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 control requirements, its extremely important that the operators be
aware of what they can change and what they must not touch. It's also important
that these individuals have the ability to recognize the arc sounds, as this is
an excellent diagnostic tool for a robot cell.
I would recommend the selection
of your most experienced operator and make him your robot technician. Send this
guy for training at the ABB robot school till he feels confident in his programming
ability.
I wish to thank you for your cooperation
and look forward to working with your organization in the future.
Sincerely. Ed Craig.
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