Understanding the benefits of automating a welding process is easy for most end users – greater efficiency, greater precision which results in a better looking and stronger weld.
Although manufacturers understand the benefits, what is sometimes not understood is the difference between a part that is good for automation from one that is not. Manufacturers can struggle with the decision to automate, often stuck in the analysis paralysis of not knowing how to evaluate and which factors are critical.
In to many instances, manufacturers rush in haphazardly only to end up with an automated system that does not meet their requirements – the result is dusty robots placed in storage facilities and a lost investment.
Distributors already working with automation know that the manufacturer end-user wants and needs help in determining the best system for their requirements. For distributors new to the market, the decision by a customer to automate can be made much clearer and confidently by adopting the following points:
Production rate of a part needs to be evaluated to ensure the rate is sufficient to justify the expense of automation. Generally parts with low production rates are not cost effective for automation. Evaluating the production rate assist in determining the scope and level of automation. For example, intermediate production volumes are often good fits for flexible automated systems, such as robotic cells, that can be programmed to weld a broader range of parts to maximize the system’s utilization. Parts with higher quantities are typically ideal for dedicated systems that are designed to be highly
efficient at welding one type of part, or a family of parts with slight variation.
- Ensuring the technical capabilities of a facility match the level of automation selected is absolutely critical to evaluating automation systems
- Manufacturers seeking to automate must honestly evaluate their internal knowledge base when deciding to automate
- The human-to-machine interface, or controls, needs to be designed to fit the operator’s technical level
The size and weight of the part is evaluated next to determine the work envelope and load capacity of the system. Larger parts require robots with larger work envelopes, longer slides, possibly a robot transport unit with longer linear track, and larger positioning equipment with greater load capacities. A large part size commonly affects part accuracy. To note, large or complex parts require more programming. Each start, stop, or change in a weld path’s direction is an additional line of software to be written and debugged. This means more programming time which affects cost.
A part’s accuracy has the most influence over repeatability, and is therefore one of the most important areas of concern when evaluating an automation project. Part accuracy is more critical in automated welding, where any deviation greater than one wire diameter can be the difference between a good weld and a reject. Thermal expansion is also a source of dimensional error, particularly with long parts and high preheats temperatures.
Without some form of adaptive control, the weld torch’s programmed path will be the same every time, so it requires a part with accurate clamping points and geometry for the positioning and fixturing to be accurate. Joint gaps must also be consistent to tolerate the welding process.
It is still possible to automate parts with less than ideal accuracy using adaptive control, or a way for the system to detect inaccuracies and make adjustments accordingly.
Weld Acceptance Criteria
Weld acceptance criteria is a key variable that requires close consideration. Parts with partial penetration joints are preferred, whereas full penetration welds are more complex and require machined joints. Partial length welds are also preferred. Welding to an absolute edge rather than stopping just short of it increases the degree of difficulty and programming complexity. The aesthetic appearance criteria frequently dictate the welding process selection.
The welding process is evaluated to fit the best process for a project. Each process is unique in required equipment and operation costs, the degree of difficulty to automate, deposition rates and limitations. Furthermore, as technology advances, innovations can push some processes to the forefront which was previously not considered ideal for certain applications.
Robotic Plasma Transferred ARC Welding
Plasma arc welding (PTA) offers unique advantages like a more consistent current density due to its rigid columnar arc. The plasma arc resists deflection, making joint alignment more repeatable. PTA is unique in that filler metal can be added in a powder form rather than wire. This allows for more variety and blends of alloys unavailable in wire form, and powder is generally less expensive than wire. PTA equipment, however, is usually the most expensive arc welding process. Deposition rates are typically less than gas metal arc (GMA).
Submerged arc welding offers some of the highest deposition and lowest defect rates. Despite these benefits, submerged arc welding has historically been the least considered process for automation due to the constant management of flux and slag, and being limited to flat weld positions. However, advances in coordinated motion control and process sequencing have revived submerged arc welding for applications previously thought unviable.
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Different joint configurations alter the degree of difficulty to automate and must therefore be examined. Fillet and lap joints tolerate misalignment better and have surfaces for adaptive control measures like joint sensing and seam tracking.
Similar to part size, material thickness can affect a part’s accuracy. Thin parts commonly become less accurate as their flexibility increases and can be easily burned through. Thick parts are frequently inaccurate due to their production techniques, such as flame cutting, or liberal production tolerances.
The base material’s weldability is also evaluated before automating. Mild steel has good weldability due to its resistance to cracking and oxidation. High strength / low alloy steels often require a preheat process which adds complexity and equipment cost to the automated system. Aluminum’s weldability hinges on the part’s cleanliness. Stainless steel, high nickel alloys, titanium and other reactive metals require special measures to mitigate oxidation.
Technical Capability of Facility
One of the most neglected areas of evaluation is ensuring that the technical capabilities of a facility match the level of automation selected. The staff must be receptive to automation. Engineers, operators and maintenance personnel must be capable, trainable and willing to support the system once installed.
The human-to-machine interface, or controls, needs to be designed to fit the operator’s technical level. Simple is better, but some applications require complex controls and additional programming. Simplifying complex processes or, for instance, controlling complex motions of a robot without actually writing the pages of robot code on the fly, requires wizard-style software and graphical user interface.
Whether using internal resources, or utilizing the expertise of an automation specialist, a successful automated welding project requires leadership with a strong understanding of automation, welding and metallurgy. Additional considerations exist. However, these nine key points can help you guide an end user to identify and address the challenges of a project while it is in the planning stages and ensure a successful project in the end.
About the author:
This contribution to our integrator leadership series comes from Dan Allford, president of ARC Specialties located in Houston, Texas (www.arcspecialties.com)