Although we don’t offer welding services to put all your SendCutSent(™) parts together, welding is one of the fastest and most reliable ways to join two (or more) pieces to build just about anything you can come up with.
If you’re reading a whole article about welding defects and tips on how to avoid them, chances are you’re familiar with welding processes in general, but if not, never fear, we have articles on welding tips and tricks, MIG vs. TIG, and guides to various fastening methods.
Welding Defects in Laser and Waterjet Cut Parts to Avoid
What can get in the way of a great quality weld? While we’d all like to make that perfect stack of dimes each time we strike an arc, the reality is that shielding gas can run out, you can dip the electrode in the weld pool, your travel speed can be off, the welding current can be to high, low, or the position of the weld on the workpiece can be just plain bad.
Turns out that these, and a whole lot of other little things lead to irregularities which will fall under one of two headings: Discontinuities or Defects. We’ll get to the specifics of the classification in a bit, but know that things like weld spatter, cracking, and incomplete penetration are some of the big baddies in the list.
How to Design Your Laser Cut Parts to Prevent Welding Defects
Arguably, the most important factor for a successful weld is properly-prepared base materials. That, or having access to a welder. It’s still up for debate.
SendCutSend laser or waterjet cut parts are sent to you deburred and free from the mill scale when possible meaning minimal post-prep is required by you. Big time-saver.
When designing welded joints, make sure that there is adequate material around the weld area that is free from other features such as holes, press fit hardware, or bends, since the welding process is likely to damage these types of features.
Also consider your material choice: it’s a lot easier to successfully weld mild or stainless steel than it is to weld Titanium. Keep the grade of the material in mind as well: 7075 aluminum might be super strong, but unless you have a half a million dollars to blow on a friction stir welder, it’s best to stick with either 5052 or 6061.
Common Welding Defects
When the design criteria and material factors we looked at above are considered carefully, it can prevent some nasty problems down the road, which vary in seriousness from visual irregularities to catastrophic failures.
To try and gauge whether a part can be repaired, or whether it needs to be tossed, industries have different measurement classifications: While all weld defects are weld discontinuities, not all weld discontinuities are weld defects.
A weld discontinuity is any interruption in the normal structure of a weld. This can include internal discontinuities, such as weld inclusions and lack of fusion, as well as external discontinuities, such as cracks, porosity, and undercut.
A weld defect is a weld discontinuity that reduces the strength, durability, or aesthetics of the weld to the point where it is unacceptable. The acceptability of a weld discontinuity depends on the application and is typically defined by a welding code or specification. So let’s take a look at several of the more common weld defects:
Types of Welding Defects
Internal Welding Defects:
- Weld inclusions: Foreign materials, typically non-metals like oxides, that become trapped in the weld pool. Weld inclusions weaken the weld and make it more susceptible to failure. This defect is also known as slag inclusion.
- Welding lack of fusion: This is a defect that occurs when the weld metal does not fuse completely with the base metal. This can be caused by a number of factors, including improper welding technique, incorrect welding parameters, and contamination of the base metal.
- Poor penetration: This is a defect that occurs when the filler metal does not penetrate completely into the base metal. This can be caused by a number of factors, including improper welding technique, incorrect welding parameters, and inadequate joint design or preparation.
External Welding Defects:
- Welding cracks: These are linear separations in the weld metal or the base metal. Cracks can be caused by a number of factors, including residual stresses, thermal stresses, and hydrogen embrittlement. Cold cracking can occur as the part cools and residual stresses strain the weld/material interface. Hot cracks and crater cracking are two other pitfalls within this category. Be sure to preheat aluminum, and avoid rapid cooling of any heat affected zone, to mitigate these issues.
- Weld porosity: This is a defect that occurs when gas bubbles are trapped in the weld metal. Weld porosity can weaken the weld and make it more susceptible to failure.
- Welding undercut: This is a groove that is formed along the edge of the weld metal. Undercut can weaken the weld and make it more susceptible to corrosion.
- Over-roll/Overlap: This is a defect that occurs when the weld metal is deposited on top of the base metal without fusing with it. Over-roll/overlap can weaken the weld and make it more susceptible to failure.
- Burn through: This is a defect that occurs when the weld metal or arc melts through the base metal. Burn through can weaken the weld and make it more susceptible to failure and in some cases even blow holes in the parent material. To address this, control the heat input by lowering amperage and increasing travel or welding speed.
- Spatter: These are small globules of molten metal that are ejected from the weld pool. Spatter can be a nuisance to clean up, but it is generally not harmful to the weld.
- Under-fill: This is a defect that occurs when the surface of the weld bead does not completely fill the groove in the parent metal. Under-fill can weaken the weld and make it more susceptible to failure.
- Excess reinforcement: This is a defect that occurs when the filler metal is deposited too high above the base metal. Excess reinforcement can make the weld more susceptible to cracking, and increases the overall arc length of the weld.
- Mechanical damage: This is a defect that is caused by physical damage to the weld metal or the base metal. Mechanical damage can weaken the weld and make it more susceptible to failure.
- Whiskers: These are thin, hair-like protrusions that can grow on the surface of weld. Whiskers can cause short circuits and disrupt electrical currents. They can also be a nuisance to clean up.
How You Can Spot Welding Defects
The welding defects listed above are classified into two main types: internal defects and external defects. Internal defects are not visible to the naked eye and can only be detected using non-destructive testing (NDT) methods. External defects are visible to the naked eye and can be detected during visual inspection.
Common methods for testing welds:
- Visual inspection: This is the simplest and most common NDT method. It involves inspecting the weld for visible defects such as cracks, porosity, and undercut.
- Dye penetrant testing (PT): Uses capillary action to detect surface defects in welds. PT involves applying a dye penetrant to the weld surface and then removing the excess penetrant. Any defects in the weld will trap the penetrant and be visible under ultraviolet light or to the naked eye once a developer is sprayed onto the surface.
- Magnetic particle testing (MT): This method is used to detect surface and subsurface defects in welds. It involves applying a magnetic field to the weld and then sprinkling magnetic particles over the weld surface. Any defects in the weld will distort the magnetic field and cause the particles to accumulate.
- Ultrasonic testing (UT): This method is used to detect internal defects in welds. It involves using a high-frequency sound wave to probe the weld. Any defects in the weld will reflect the sound wave back to the transducer, which can be detected and displayed on a screen.
- Radiographic testing (RT): This method is used to detect internal defects in welds. It involves using X-rays or gamma rays to penetrate the weld and produce an image of the weld on a film. Any defects in the weld will show up as dark spots on the film.
The specific NDT method that is used to test a weld will depend on the type of weld, the materials being welded, and the requirements of the applicable code or standard. For example, PT and MT are often used to inspect welds in pipelines and other pressure vessels, while UT and RT are often used to inspect welds in critical structures such as bridges and buildings.
Turning Your Designs Into a Reality With SendCutSend
At SendCutSend, we love building cool things, and know that welding is an integral part of many great projects. Making sure your welds look great and the durability to stand up to stress over time is a huge part of the success or failure of your projects.
Welding defects can jeopardize the quality of your work, leading to issues ranging from visual irregularities to catastrophic failures. Familiarizing yourself with the different types of defects and their causes is an important part of the fabrication process.
Remember that proper preparation of base materials is key to durable welds and that SendCutSend laser or waterjet cut parts arrive at your doorstep deburred and free from mill scale, reducing your prep time. When designing parts for welding, ensure there’s enough material around the weld area without interfering features like holes, press-fit hardware, or bends.
To prevent welding defects, consider your material choice, as different metals pose varying challenges. Spotting welding defects involves visual inspection and in specialized cases, methods like dye penetrant testing, or magnetic particle testing, play pivotal roles in identifying hidden flaws.
FAQs About Welding Defects
What Are Welding Defects?
Welding defects are imperfections or discontinuities in a welded joint that can reduce its strength, or durability, as well as making things just plain ugly. Causes of weld defects are varied and include improper technique, incorrect weld machine settings, contamination of the base metal, and improper joint design, such as failure to fillet or chamfer the parent material.
What Are the Different Types of Weld Discontinuities?
A weld discontinuity is any imperfection in a weld. Although we’d like to think our welds are all perfect all the time, in reality, we have to determine if a discontinuity is bad enough to be considered a defect. Because discontinuities can be thought of as “minor defects” all the same internal and external classifications apply to discontinuities and defects.
What is the most common failure mode for a weld?
The most common failure mode for a weld is fatigue. Fatigue is often evidenced by cracking in the heat affected zone (HAZ). Cracks can form due to stress, improper cooling, or contamination, leading to catastrophic failure under load.
What welding method is most prone to defects?
Stick welding, or shielded metal arc welding, is a relatively inexpensive and versatile welding process, but it is also more prone to defects than other welding methods because it is a relatively manual process that uses a consumable electrode coated in flux. The flux melts and creates a gas shield around the weld pool, theoretically protecting it from contamination.