Four solutions to reduce unscheduled downtime in welding lines
14 March 2016
The welding line is one of the harshest environments in a plant, so avoiding downtime is a particularly key challenge for plant personnel.
Root cause analysis of downtime in welding cells routinely points to a variety of factors that drive downtime to unacceptably low levels. Harry Vlap, European Product Manager for Industrial Application Products at Parker Hannifin reviews these causes and identifies how to reduce unscheduled downtime.
As the consequences of downtime are so costly, the challenge for automotive manufacturers is to anticipate and prevent problems from ever occurring. Being at the forefront of new automation and advanced production techniques, every advantage in both efficiency and quality should be taken. Whether it’s company-specific production systems, such as Chrysler’s adoption of World Class Manufacturing (WCM) from Fiat, or Toyota’s well documented lean principles, all plants are focused on getting as close as possible to the ultimate goal of zero waste, zero defects, zero breakdowns and zero inventory.
Solution one: scheduled inspection and maintenance
Welding lines follow the same maintenance patterns found throughout an automotive plant, including rigorous attention to detail and preventive maintenance. Far from being a luxury or a “nice to have,” this type of maintenance is a core requirement for today’s complex equipment and systems in such harsh environments. Weld line managers should focus on three key maintenance areas to assist in minimising downtime:
• For the weld cell in particular, keep components free from weld dust, splatter and other sources of contamination. Following strict maintenance schedules and inspections aids in uncovering equipment fatigue and wear.
• In an environment driven by lean, where on-site materials and inventories are discouraged, it’s important to balance the lean philosophy with practical realities of running a weld production line. In order to keep their lines up and running, have a ready supply of spare parts on site and nearby, particularly for damage-prone parts subject to high levels of corrosion.
• Automation systems today are driven by Programmable Logic Controllers (PLCs) that occasionally need to be updated. If remote connectivity is used, these systems need to be hardened and robust, protected against unreliable data interruptions and network tampering. As the “Internet of Things” and HMI-remote connectivity extends to the automated weld line, these data-driven factors become important elements of reducing downtime.
Solution two: adequate and continuous training
Operators of welding robots and weld automation systems today must adopt a “life-long learning” approach to their development, as new equipment and technology is continually introduced to their production lines. As automation technology and weld tools are constantly advancing and improving, ongoing training and advanced certifications should be core in ensuring equipment is used correctly and unscheduled downtime is minimised.
Plants that have the lowest downtime rates are typically those with operators and MRO (Maintenance-Repair-Operations) teams that fully understand how their machines function, for example they understand how to maintain and service weld tips and how to maintain the safety precautions around them.
Within a plant setting, the equipment is often heavy machinery becoming more dangerous through multiple fully automated machines operating in confined spaces, with precisely timed movements that use force capable of injuring or proving fatal for an operator. Over time, as tasks become routine, its human nature to become relaxed so ongoing training and refreshing of safety guidelines are important in advancing knowledge and ensuring compliance with all common safety and operation practices.
Providing cross-discipline training is also a good stop in ensuring a sufficient number of fully qualified operators are available to work across all shifts. Mutually beneficial to both the plant and employees, cross-training keeps employees engaged and creates opportunities for additional hours and line flexibility.
Solution three: upgrading machinery and preventing weld line equipment failure
Ingress of materials and substances, such as chemically treated water used to cool the welding guns or the molten metal during welding, can disrupt electrical connectivity and corrode or even melt components. This becomes evident in sparks coming from under the electrode or between the parts being welded, which as they fly, risk interrupting power to a weld robot or other critical component on the line. The increased introduction of automated weld tip dressers and changes to weld cells helps address the problem, but at the same time this introduces thousands of pounds worth of new equipment to be taken offline by water and spatter damage.
Weld spatter is the most visible culprit of downtime, causing a cascade-effect of problems that need to be controlled, minimised and ultimately eliminated. For the past ten years manufacturers have done a tremendous job in reducing weld spatter with successful strategies including improving control systems to minimise caustic materials, to improving the coatings.
Now, the focus has shifted to minimising the unwanted effects of corrosive weld water which can prove as big a challenge to productivity and safety as weld spatter. When a resistance spot weld is being made, force and current are applied through electrodes in the tips of the weld gun into the metal parts to be welded. Resistance heat is generated at the interface of metal parts, creating a pool of molten metal that quickly cools and solidifies into a round joint known as a “nugget.”
At the same time, the metal molecules become aligned in polarity, causing a very strong magnetic repulsion against the molten droplets created, launching them away from the metal parts. This is visible as spatter (expulsion) which can travel up to 10ft/3metres or more. With the capacity to potentially injure personnel in the area, set fire to materials, or damage cables, hoses and electronics, it’s vital to reduce the amount of electrical current being applied to minimise or eliminate the spatter.
Equipment failure can obviously lead to unscheduled downtime, but it’s a particularly crucial problem for automated weld production cells that equipment is upgraded and repaired where necessary. Components will naturally fail due to normal wear, but also inferior production quality, improper use (for example the wrong size of type for the application) or incorrect installation
Solution four: utilise water retract actuators to reduce water expulsion
Alongside investment in preventing expulsion of metal and better training of employees to prevent sparks, efforts need to be made to prevent water expulsion to reduce unnecessary maintenance costs. Water expulsion causes a variety of negative effects. Operators have complained of skin irritation as a result of exposure to weld water, most often after being exposed to water expulsion during tip changing. A corollary safety hazard occurs when weld water gathers in pools on the floor, creating slipping hazards.
Beyond potentially harming employees, the treated water can also damage weld line equipment and any nearby components as it sprays uncontrollably affecting floor surfaces beyond just causing slippery areas to avoid. American automakers are adopting the practice of their Japanese and European counterparts of coating dark grey plant floors with a lighter coloured surface.
This costly resurfacing helps with the ability to clearly see small items dropped on the floor, gives the plant a brighter look and provides better traction. However, these aesthetic benefits are ruined by weld water that’s expelled and allowed to remain pooled, since the chemically treated weld water destroys the coating.
Water Retract Actuators have been developed specifically to eliminate water weld expulsion in automotive facilities. When a weld tip needs to be changed, whether it has been redressed or not, the water supply is cut off and then the actuator pulls and holds with suction any water still left in the weld gun or in the water lines behind it. This innovative technology enables dry tip changes to be possible, improving safety, reducing costs and increasing productivity.
In conclusion, while water flow monitors work well in shutting off a water supply when a leak is detected, they don’t prevent the water already under pressure remaining in the line behind the weld tips from being expelled onto operators, equipment and the floor when the tips are removed to be changed.
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