Weld Repair Done Right
Eagle Group casting facilities consistently receive top marks in customer satisfaction, scrap rates and return rates, but even with our commitment to quality and rigorous product development process, our castings occasionally require post-solidification adjustments prior to delivery. "Across all of our 2,000-plus part numbers, under 10% of castings fall out for repair," according to Eagle Alloy Chief Sales Officer, Jeff Cook, "and some part numbers have 1% or less." While the percentage is small, the cost of scrapping repairable defects can raise part price and delay delivery. For those reasons, many world-class casting facilities strongly recommend that customers allow weld repair at the foundry's discretion.
How Welding Fits into High Quality Casting Production
The Steel Founder's Society of America (SFSA) states that "welding is routinely used as a part of the production process to manufacture the highest quality castings." Still, many casting customers prefer to avoid welding altogether. A single instance of weldment failure–or even industry rumors–can cause the customer to lose faith in the process. But when weld repair is done right, it is a very reliable and repeatable process that should never result in part failure, or even diminished quality.
As a casting facility, it's important for the Eagle Group to work with welders we trust. Krause Welding and Machining, a second generation, family-owned business in our area, has been handling our weld repairs for decades. Based on their knowledge and experience, the following guidelines can help ensure defect-free weld repairs for cast parts.
Starting the Weld Repair Process: Customer Requirements
The first step in weld repair is to evaluate the customer's requirements. The casting facility and their customer should have an agreement in place describing areas that cannot be welded and areas that will be machined. Welding technicians must take all of these requirements into consideration before deciding how to approach the repair.
Evaluating Castings for Weld Repair
Every casting defect is different, and every part must be evaluated before beginning weld repair. Cosmetic defects, like sand inclusions or gas porosity, are easier to repair than structural defects. Sand inclusions can sometimes be burned out with a hot melt weld, but other times must be excavated. More severe cosmetic defects always require excavation. Cracks are where experience really becomes key. If a crack on a casting–even a cosmetic surface crack–is not fully excavated and welded correctly, it can easily reform during heat treatment.
The material of the casting also plays a role in deciding the weld repair strategy. Softer materials, like some grades of steel, are much easier to repair through welding. Harder alloys can crack very easily, and must be welded at lower temperatures. For carbon steels, welders must carefully clean the welded area to ensure that no carbon is left; otherwise, gas porosity can form in the welded area.
First Steps Are Key to Successful Weld Repair
According to Brian Krause, owner of Krause Welding and Machining, the first layer of the weld is key to the success of the repair. The welder must apply enough heat and filler rod so that the bottom gets completely filled, with no defects whatsoever. After the first weld, the process involves filling in the cavity and making sure the edges are fused to the hole. Throughout the process, the welding technician must make sure to apply the correct amount of heat to melt the material together without causing additional cracking.
Weld Repair for Castings: What Not to Do
When weld repaired cast parts do fail, it's often a result of incomplete evaluation or improper technique. The following mistakes must be avoided in order to ensure successful weld repairs.
- Using too much heat: this can lead to cracking, especially on hard alloys.
- Using too little or too much filler: this can lead to weak bonds between the welded area and the cast part. With hard alloys, excessive filler can also lead to cracking.
- Entrusting repairs to inexperienced operators: it takes knowledge, experience and hands-on training to be able to properly evaluate a defect and apply the correct technique in weld repairing.
The final result of a successful weld repair is a casting that performs just like a non-welded casting in any performance test administered by the customer. When weld repair is done right, repaired parts are just as strong and just as ductile as non-welded parts. They also last the same amount of time, even with repeated use.
To see for yourself, check out our case study on weld repair showing that welding (done right) results in nearly identical testing results.
Tags: Casting Defects, Welding
Written by Mark Hollenbeck
Mark Hollenbeck is Senior Sales Engineer at Eagle Alloy. He has been with the company since 1995.