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Improved welding solutions for automotive exhaust systems using advanced welding

In today’s automotive industry, complex exhaust systems with multiple connections and various material combinations require a new approach when it comes to welding them. New designs are shifting the limits for efficiency and new government regulations are moving toward innovative ways to reduce emissions. For exhaust system manufacturers, advanced welding technology is the answer.

In response, Fronius released its TPS/i series of welding power sources that provide an adaptive arc, specialized processes and modular design, meeting the demands of welding today’s exhaust systems.

pmc technology

The standard

For years, the common method to weld exhaust systems was the standard pulsed GMAW process in combination with metal-cored or solid stainless wire. In general, the majority of the applications use ferritic stainless for the base material and 409 or 439 filler material for corrosion and high-temperature corrosion resistance, respectively.

Today’s exhaust components, however, operate at higher temperatures and therefore require higher quality welds, reduced distortion and minimized spatter. For example, new designs of emission control systems, such as diesel particulate filters (DPFs) and selective catalytic reduction (SCR) control, require new materials that can operate around 800 to 1,000 degrees C. Furthermore, new coatings, such as aluminized stainless and multi-sheet type joints comprised of different materials, are being used.

Such changes in design and material selection complicate the task of the weld engineers responsible for joining the product for final assembly. Regardless of the exhaust component and type of joint and material used, there are some major goals to be achieved: high travel speed welding and reduced scrap while producing quality welds without defects.

Above standard

Fortunately, exhaust manifolds, catalytic converters, mufflers and other exhaust components can be joined together using one welding platform: the TPS/i welding system. All of these exhaust components are possible due to the high versatility and flexibility of the welding system, which allows a dedicated solution for each individual application.

exhaust system within a vehicle
Fronius’ TPS/i welding platform is applicable for a complete automotive exhaust system.

Such flexibility and precision welding is possible due to unique TPS/i features. The main process in the TPS/i platform to be deployed is the PMC (pulse multi-control), an advanced pulse GMAW process that contains functions such as the arc length stabilizer and penetration stabilizer. This is combined with specifically designed waveforms for all material combinations from the touchscreen parameter control display.

Functions of the arc length stabilizer include:

  • Automatic adjustments to changes in weld environment (sheet thickness and part variation).
  • Constant arc length due to machine-controlled adjustments.
  • Freedom from adjustments when the weld joint changes, such as when welding a butt joint to a T-joint.

The arc length stabilizer forces short arcs, advantageous for welding, via a short-circuit current control and keeps them stable even with a variable stick-out or external interference.

Functions of the penetration stabilizer:

  • Minimizes burn through and lack of fusion, ensuring weld quality across the seam.
  • Performs ultra-fast regulation of wire feed speed to compensate for part fit-up and inconsistent torch access.
  • Maintains penetration even through changes in contact-tip-to-work distance.

The penetration stabilizer is used to set the maximum permitted change in the wire feed speed to ensure that the welding current and hence the fusion penetration is kept stable or constant with variable stick-out.

fronius weld profile
Perfect penetration and profile. For weld profile, the smooth weld toe transition into the base material will avoid stress raisers during thermal cycles where the exhaust components expand and contract. If the angle of the transition is too tight, there is a danger of stress-induced cracking and failure of the joint. Typical penetration is 10 percent in almost all standards, depending on the type of joint. With 15 to 20 percent penetration, there will be a statistic “buffer” zone that ensures penetration will not go below the 10 percent required and a “safe buffer” is created.

The main advatage of dedicated waveforms, or synergic lines (a Fronius term), is the time saved not having to find the desired weld parameters. On a typical welding machine, multiple trials and a certain level of welding expertise are needed to achieve the desired results.

Specifically for exhaust systems, Fronius has created a large synergic lines library encompasing all filler materials and gas combinations used in the industry, from standard solid and metal-cored stainless wires to specialty high-alloy steels for speciality applications.

What is the practicality of such capabilities? It is clear from production feedback that PMC technology delivers what is required in today’s automotive exhaust industry. From 50 percent more travel speed compared with the standard pulsed process to carefully controlled heat input, the technology ensures full functionality of the welded component (such as a butterfly valve).

Precise, clean welds are now possible using the PMC technology process. So clearly, there is an advantage with using PMC when rework needs to be minimized or when thin-gauge material, which is becoming very common, is being joined to prevent burn-through. Conversely, penetration is precisely controlled in thicker materials without issues such as lack of fusion.

Fill in the gap

The arc is controlled in a manner that doesn’t heavily affect the base material or critical components inside the welded parts. Thin, high-strength materials and inconsistent gaps are common when welding exhaust components. Precise arc control helps bridge gaps due to poor fit-up which is a reality of production.

When it comes to automotive production environments, inconsistent gaps are a given regardless of what parts are being joined (such as the exhaust system, engine cradle, frame and ride control). Causes include wear and tear on the stamping machines, lost machine calibration while cutting blanks, or inappropriate fixturing and clamping or lack of maintenance of these devices.

In the automotive industry specifically, due to price pressure per component, it is almost impossible to ensure 100 percent perfect fit-up of components and joints before welding.

The TPS/I system, however, which is used for manual or robotic applications, excels in every aspect of welding exhaust systems – all materials, all thicknesses, all joints, all while compensating for inconsistent part fit-up. One machine handles a variety of materials and weld configurations. Today’s stricter standards require better solutions and the TPS/i platform was designed to meet those challenges – as well as those of the future.

Fronius USA LLC

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