Welding large components such as heavy truck wheel hubs can be difficult and awkward for a variety of reasons. Complex geometries for recesses and spokes make heat distribution and weld access difficult. In addition, the thickness of high-strength steels or cast metals require more heat for penetration depth purposes of the welds. The extra heat can lead to distortion, cracking and residual stress. Sometimes, grease on the part’s surface or moisture in the air can cause thermal shock. Preheating parts prior to welding solves these problems.
How to know when to preheat
One of the most common situations where preheating is needed is when welding two large pieces together. “So, if you need to weld a large diameter pipe, say 20” in diameter, the mass is so large that heat added by the weld dissipates too quickly, and causes the weld to crack,” explains Kyle Bukoski, Sales and Applications Engineer at IDEA INDUCTION. “Putting heat into the area of the joint prior to welding will let the weld normalize slowly.”
Other joints that require preheating are parts made of high carbon steels, cast iron or critical components that will operate in cold environments, such jet engine or helicopter parts. Welding structural steel is another application that can benefit from preheating. “In this case, I’d suggest using a dual output unit for both heating cables for the large areas and a handheld coax for the finer placement heating,” Bukoski says.
If your project includes parts made of high carbon steel or cast iron, preheating is recommended to prevent thermal shock. “These metals are normally brittle and can self-destruct when introducing high heat in a localized area due to expansion factors. For these types of metals, a controlled ramp up and ramp down heating program would be required,” he says.
For shops that need to qualify their processes and assure the quality of their parts, induction preheating offers a point of control. According to Bukoski, “In this instance, we can add a pyrometer to the process. This will help to make sure that there is enough heating in the part prior to the welding. A PDI control loop that sends real time information back to the power supply tells it how much power is needed to get to temperature and to be able to hold a temperature with in a 20° range.”
Why induction heat works better than a flame
Unlike torches or ovens, induction heating delivers controlled, uniform preheat in less time — with no open flame, no emissions and no guesswork. Consider the following benefits:
- Speed – induction heats a part faster than any conventional method. Time spent on preheating while using induction can be up 80% faster, depending on the part size and target temperature.
- Precision – heat only the portion of the part that is needed without overheating nearby surfaces.
- Uniform – even distribution of heat minimizes thermal stress, prevents cracks and distortion, which is critical for thick or high-strength materials.
- Repeatability – automate temperature ramp-up and dwell time.
- Control – qualify your process and assure quality for industries like automotive, rail and heavy truck manufacturing.
- Energy efficiency – more than 90% of energy used to heat is converted. Gas or flame, by comparison, converts only 30-50%. In addition, you’ll keep your shop cooler since less heat is lost to the shop floor.
- Integration-ready – induction systems can be fully automated and integrated into welding cells, providing consistency without human error and a faster process in your shop.
- Less part handling – parts heat precisely and cool quickly, reducing the need to move parts between preheat and weld stations, thus lowering the risk of contamination or misalignment.
Bring your parts up to temperature using induction heating cables and generators before welding for faster and cleaner, safer and more consistent welds.
