Frame Robot Weld Report:
Customer Tier 0ne Supplier.
Big Three Truck Frames. 2003.
This tier one company declared bankruptcy
less than two years after this report was written.
It's the intention of this report to deal with the root causes of the numerous robot / manual weld issues found on a new tier one robot truck frame weld line.
Every frame manufactured on the new robot line today requires extensive manual weld rework. Your weld repair personnel report that approximately fifty percent of the total robot frame welds require rework, of approx. 60 - 80 welds per frame. Of the sectioned welds that daily require macro examination of the weld fusion, 12 - 15 % of the welds tested revealed lack of weld fusion. The numerous weld repairs are providing a patched product, which provides a poor visual weld appearance. Both the in-plant weld process and robot cell equipment decisions are negatively impacting the potential weld productivity and quality potential.
The MIG weld transfer mode selected for the majority of the robot and manual frame welds is the "globular weld transfer mode". This weld mode produces poor fusion, erratic weld transfer and extensive weld spatter. The traditional MIG process offers short circuit, globular and spray transfer and electronic MIG weld equipment offers the pulsed MIG mode.
For consistent weld quality on parts over 2 mm, spray transfer is the preferred mode for frame welds.
While in the plant I had many opinions presented to me on the causes of the extensive robot / manual weld process issues. In the eighteen months since this robot project commenced, the lack of management resolutions for most of the weld issues in this plant comes from the fundamental fact. The majority of the managers and supervisors who provided an opinion are simply not qualified on the subject of robot / manual weld process controls.
Of the 140 arc welding robots in the plant, 88 are dedicated to the frame subassembly parts and 52 robots make the frame welds. At this time, many of the frame robots average a down time of > 60 minutes per- shift. None of the robot cells have logs to report real world robot down time. The robot weld log is an essential tool for robot PM, robot efficiency and weld process issues resolution.
The primary causes of robot down time as verbally reported by the shop robot technicians are;
[a] Inconsistent part dimensions and gaps.
In general and from a robot weld perspective, the majority of frame parts that I have viewed do not have serious dimensional deviation issues or excessive, oversized gaps. Of greater concern in the robot cells is the lack of effective robot programmed weld process data that that can compensate for moderate part gaps which unfortunately are too typical.
[b] Unacceptable weld joint dimensional deviation.
Again the robot programming process data that is applied or the equipment purchased addresses this common issue. The ABB robots should have been purchased with the Bulls Eye (BE) automated TCP control. The automated TCP control is one of the key outstanding patented features of an ABB robot. With optimum robot program points established, the TCP control automatically maintains the pre-programmed weld points (weld wire position and weld gun angle to work) through control of the robot's tool center point. At this time with no controlled TCP and lack of effective process data, the operators have to resort to shutting down the cells to make what they believe are effective program point adjustments.
The reality is without process training and the correct equipment, this manual band aid approach by the operators results in extensive manual intervention and less than optimum robot program points that create numerous weld issues that impact productivity and weld rework.
Note: From a product launch perspective. The investment in the purchase of the TCP equipment (approx $3000 a unit) makes a lot more sense than the purchase of the 140 Miller Invision "pulsed power sources" especially as the Pulsed MIG mode is not used on this application. If the pulsed mode had been used it would have created more weld problems.
If management could see through the salesmanship that surrounds the costly pulsed weld equipment they would be aware that it's erratic performance has not been suited for high weld speed, steel applications. The prime choice would have been the much lower cost traditional MIG equipment.
If a Miller, Delta Weld with built in interface had been purchased instead of the Miller Invision, the savings of approx. $2000 per unit, $280,000.00 in total would have gone a long way to paying for the Bulls Eyes equipment for the robots.
[c] Robot / Manual Weld process issues:
The management selection of the incorrect wire diameter, 0.052 (1.4mm) at the start of the project and the resulting globular weld transfer, that results when optimum spray transfer weld current cannot be applied, along with inappropriate, robot weld process data are the fundamental primary causes for most of the robot weld issues.
As extra shifts commence at this plant, and the facility ramps up to attain it's target robot weld production, without a major change to the weld process and without the implementation of effective management influenced weld process controls, there will be a rapid escalation of in the manual weld rework and an extensive loss of productivity through increased robot down time. The robot down time has the potential to increase to a minimum average range of 90 minutes per shift eventually to a potential loss of weld production equal that of 14 + robots.
From a mechanical weld integrity perspective, the over welding that takes place on these frames may today compensate for the inconsistent, unacceptable robot weld quality, however the poor weld quality end product produced indicates to your big three customer a general lack of manufacturing expertise and provides a product that does not reflect the shop floor employees efforts or the robot's true welding potential
There are many reasons as discussed in this report for the extensive weld issues that prevail. With many robot automotive / truck installations the last thing that is often given consideration for the robot line are the actual welds. After 50 years of use, it's inexcusable in 2003 to find the universal MIG weld process confusion and management apathy that surrounds this simple two-control weld process. With a short course in weld process control training any engineer or technician in your facility should attain the ability to simply look at the part's gage thickness, which determines the optimum weld wire diameter. With the wire and thickness the desired weld transfer mode is selected. The transfer mode and thickness instantly determine the required wire feed rate, travel rate, weld voltage and the correct shielding gas.
My robot / manual process control teaching method provides this data and all the other necessary weld data. The training program enables personnel to instantly set a robot without "playing around with the controls or reading crib notes.
Robots do not need the input of skilled welders. Robots need weld process data that is developed from a robot process control program, a program not generally taught in industry or in educational facilities that teach technicians or welding engineers. The refreshing reality for those involved with the robot weld production is when it comes to robot MIG welding there are no gray issues. There is however universal weld process ignorance and process myths combined with the influence of excessive salesmanship. Management and engineers simply have to take ownership of this important process.
Management Robot / Weld Responsibility.
If you hand over the factory process keys to confident yet untrained workers, inexperienced supervisors, it should not be a surprise to find that your plant has extensive robot / manual weld process issues. In any established manufacturing environment it's natural to find on the shop floor great resistance to manufacturing changes. The required changes have to first be understood, supported and driven by all managers, engineers and supervisors involved. I met with the production manager of the robot line that suffers the most weld issues. This man has no weld process experience; he does however have great tunnel vision and a closed mind approach to the required robot weld process issues and the changes required.
It's important to note that the weld issues at this plant are not derived from the weld shop floor. The weld shop personnel did not select the inappropriate weld equipment or incorrect size (052) weld consumables. The robot personnel have no control over the parts or the fixtures. The robot personnel did not turn down the automated TCP equipment, and the hundred plus personnel that daily make robot weld process changes did not turn down robot process control training.
Weld best practices and robot process optimization should commence at the design, prototype and launch stage. At this frame facility, the production pressures and the overall lack of weld process expertise, by many of the key production personnel are causing process apathy and poor shop floor moral. This is the attitude, why change the way we do things, (better the devil we know than to accept the risk of the unknown). To make changes to an entrenched chaotic process in a project of this scope requires management input and support to provide direction for the weld teams.
To address the root cause of the primary robot / manual weld issues, all involved have to walk the same production path, agree on the necessary actions, take responsibility for the process ownership and then provide the leadership and time lines necessary to make the weld changes successful.
The Welding Resolutions
Robots: After robot weld process control training for all those involved, "including management". With the change to the 0.045 weld wire, and reduction of CO2 content from 15 to 10%, the robot weld process changes will be easy to implement. The process changes I recommend will increase the robot weld production by 20%. I will make the required changes in any of your cells. As I do not play around with robot weld data the changes will be made quickly. The data I provide will ensure you attain your desired production in a consistent manner. The new data will greatly reduce the required weld rework, to less than 5% and reduce the weld spatter by at least 70%. . As the new robot weld programs are produced, I will develop 3 simple standard weld schedules that will be applicable to all the robot welds in the plant.
Note: Before the ABB robot programs are changed, it would be highly beneficial to get control of the robot TCP with the installation of Bulls Eyes in the cells.
During the new robot programming, it would be beneficial if I worked with the tooling manager as he understands the parts and fit issues so I would use his expertise to ensure that the process changes made are geared address the future weld dimensional issues.
For the manual weld repairs. I would change the wire sizes for the manual welders, give them an 035 1 mm wire and provide them with weld data that is actually designed for manual MIG weld repairs.
The Robot Process Control Training Program.
Obviously the robot process control training is an essential part of this package. Who attends the training is key to the long-term success of this project. I will repeat that it's essential that all personnel including managers, supervisors, QA and engineer should be given the robot weld process control training. The bottom line with the frame robots, when it comes to weld decisions that impact the weld production or quality all the plant's weld decision makers should lead and ensure all those involved walk the same production path.
I provide effective, unique, simple robot weld process control training and have already developed the necessary training resources, (used in by both Magna and Dana). Another key issue to the success of the process changes is accountability and responsibility. I would not consider taking on this project unless I was given full responsibility for the robot weld changes.
The large 052-weld wire used at your plant appears to be influenced by the Ford Dearborn approach to welding frames. In that plant they have managers that lack process expertise, managers who believe bigger weld wires must mean more production. You are likely not aware that for more than a decade almost every frame robot welded frame built at the Dearborn facility with the over sized wires has required extensive manual weld rework.
With robot weld issues when the root causes are not addressed, there is a tendency in the weld shops towards looking for an easy quick fix, or look for a "sales influenced solution" like changing to a more costly MIG power source, try the magic three part weld gas mix or the special coated contact tips, etc. As I sit here writing this report the production manager at this facility, a man who does not want to hear about the use of a smaller size weld wire or process control training is hinting that he believes changing the weld wire to a "copper coated MIG wire or changing to a three part gas mix is the solution to the frame weld issues.
Note: In 1997 I was asked by Ford to analyze there numerous (over 160 weld issues) at the Dearborn Frame facility. I not only analyzed all the issues in a 10 day period I had the opportunity on a weekend to set up the future 1998 frame line with my new recommendations for the prototype frames. At the end of that weekend, for the first time in the Dearborn history of the frame line, frames meeting both the weld productivity and quality expectations were produced. However due to union issues and management indifference, my process changes were not implemented.
A FEW PROCESS CONTROL WELD FACTS:
Weld Wire Size. Here are some welding facts that apply to both copper coated and none copper coated weld wires. The 0.052 (1.4 mm) MIG weld wire selected by your facility is too large for the gage parts welded. To attain stable, minimum weld spatter with the spray weld transfer using the 052 wires requires weld current > 290 amps. Due to the thin gages welded on the frames and to avoid weld burn through, the majority of the robot and manual welds at the plant are welded in the 240 to 290-amp range. Stable spatter free, spray transfer with a 0.045 wire are attained > 250 amps.
As the >290 amps cannot be used with the 052 wires due to weld burn through issues that would occur on the 2 to 4 mm parts, the plant's reactions has been to either lower the weld current typically 240 to 260, lower the weld voltages to 20 - 24 volts or increase the wire stick out which further lowers the weld current. This weld data results in erratic globular transfer. With globular weld transfer, the weld produces large erratic weld droplets which cause excess weld spatter and can result in poor weld fusion. However the primary concern for the excess, globular weld spatter generated is on its affects on the fixture equipment, the fixture switches and on blocking the robot MIG gun contact tips and nozzles.
The number one weld process problem at the plant that leads to robot down time is "wire burn back" to the contact tips caused by either inappropriate weld start data, (process training) or the globular weld drops which adhere around the contact tips bore, restricting the MIG wire as it exits the contact tip. As the weld robot weld production increases the globular weld spatter issues will increase becoming a prime cause of robot down time.
The over sized weld wires and globular weld transfer also provide convex welds with poor appearance. Most of the welds are 20 to 30 percent larger than they need to be this requires slower weld travel speeds impacting cycle times.
I hope we can in future work together at the front end of your projects to implement effective Robot Best Weld Practices that will ensure a smooth transition from the part inception to the weld production.
Sincerely Ed Craig: