The welding process, which is basically about joining metal parts together, depends on accuracy and precision. This is why metal parts that are due for welding have to be well-positioned and held together. This need for alignment is where tack welds come into play.
Tack welds are small temporary welds that hold parts together in preparation for the final weld. In most cases, they are little drops of welds that are just large enough to maintain the necessary gaps between pieces of metal parts. Tack welds are useful for every kind of welding process.
Here, we will be discussing everything you need to know about tack welds. You will learn about how tack welding works, its purposes, benefits, types, and forms. Plus, what you should do to achieve the highest quality tack welds.
What is Tack Welding?
Tack welding is the process of joining metal parts together along their length, using small and intermittent drops of welds. Tacks should be made at distances from each other suitable to achieve the required rigidity.
In tack welding, the number and size of tacks required depend on the size of the metal parts. Tacks should be large enough to hold the metal parts together and small enough to avoid interfering with the final weld.
What is the Purpose of Tack Welding?
Tack welding is a technique that helps you achieve proper alignment of metal parts before you apply the final weld. With tack welding, when done right, you can be sure of avoiding distortion after the final weld is complete.
Tack welds help you keep metal parts close or in place. Especially when you are to weld heavy objects that are difficult to hold together. Tack welds also ensure that the final weld is strong and of precise specification.
Why is Tack Welding So Important?
Tack welding solves crucial challenges in the welding process. The most important of which is accuracy and quality.
For instance, if you may want to produce a final work with a specific length, then you must ensure that you place the metals at the right distance from each other.
Without tacks, it will be almost impossible to deliver jobs with measurement accuracy. If the joint gap of the metal parts isn’t well placed, the final work will fall below expectations.
Consequently, if there is a challenge with the accuracy of joint gaps, this will negatively affect the quality of the final work.
More importantly, your metal parts shouldn’t move while the final welding is in progress. If your metal parts move before your final welding is complete, you will end up with distortions. Tacks reduce the possibility of moving metal parts by holding them rigidly in place.
“What about fixtures?” you may wonder. Well, it’s all up to you to decide. However, in many cases, tacks eliminate the need for fixtures, except when you are welding heavy metal parts.
Yet, you may also need tacks to complement the job of the fixture clamps. Tacks are still very much needed to reduce the stress produces by the fixture clamps.
How Does Tack Welding Work?
In most cases, tack welds are produced by the same process that executes the final weld. Some tack welding situations such as the ones for assembling aluminum alloys, will require a small and special welding tool that has been constructed for the process.
However, in the case of electron beam tacks, you will produce better tacks when you work with reduced power. Electron beam tacks are strong enough to replace fixtures.
Generally, the material requirements for tack welding are the same as those for the final welding. Although final welding does most of the work, it more or less continues from where the tack welding stops.
This point brings us to an interesting juncture. It is pretty easy to, because of the temporary work of tack welds, disregard their importance in the final weld result.
Many welders fail to apply diligence in producing tacks because they feel that tack welds are inferior to the final welds. They’ve got it all wrong. Tack welds are real welding. The quality of your tacks must be as high as that of your final weld.
Welding Cylindrical Pipes
For example, if you want to weld two (let’s say cylindrical) pipes together end-to-end, you must align the pipes. You will want to have the two ends at a similar distance from each other all across their circumferences. Tack welds will help you achieve that.
So, what you will want to do in this case, is to keep the ends of the pipes close to each other at a suitable distance. Now, it’s time to apply your tacks to keep the pipes in this position.
In this case, get a chip of metal, place it across the two cylindrical ends, and apply tacks to join the chip to each cylinder. Repeat the process several more times at different points on the cylinders.
Note that the sizes and number of cylindrical tack welds should depend on the thickness of the pipe walls and the circumference of the ends.
When you are done, the chips and the tacks will hold the cylinders in position without assistance. Now, the cylinders are ready for the final welding.
What Are the Challenges Involved in Tack Welding?
Like every other welding method, quite a few challenges accompany the use of tack welding for your projects.
They are:
- In cases where welds are defective and not perfectly done, joints of workpieces could tear apart while being moved from one place to another, turned, or hoisted. This could lead to serious injury to people or damage to machinery.
- Although tack welds primary purpose is to help create seamless, permanent welding, in some cases, it can do more harm than good and damage final welds. This can happen when defects like cracks, spatter, hard spots, or arc strikes occur.
- Tack welding involves the use of heat and pressure. The filler material gets heated, and the base material is also heated but to a lesser degree. Some defects could occur due to the quenching and cooling after the heating. For example, rapid quenching can cause cracks in the affected zone.
- Using specific methods such as shielded metal arc welding to apply tack welds during manufacturing can cause brittle regions and cracks. Such cracks tend to become bigger during the final welding process.
Tack Welding Procedure and Distortion Control?
Even if you are a beginner, you can get your tack welding done right, avoid defects, and produce high-quality final welding. To achieve all these, you must follow proper procedures and take a great deal of care.
Tack Welding Procedure
- Set Up the Welding Equipment
First, you must ensure that you set up your welding machine correctly and choose the right electrode. To be safe, refer to the manufacturer’s instructions.
After getting your materials ready, begin by ensuring that your workpiece, electrodes, and other materials are ready to go. Take care to choose the appropriate filler metal which should be compatible with the base metal.
- Prepare Your Materials
Before your welding begins, ensure that all your materials are ready for a smooth process. Remove any obstructions on your materials such as soot, oil, rust, or grinders. If you want to hold your materials with clamps, this is the time to get it done.
- Determine the Tack Weld Locations and Mark Them
Take a look at the length of the joint and determine the strategic positions for your tack welds. You can mark these positions just to ensure that you won’t make any errors.
- Begin Producing Your Welds
Touch the metal piece with your electrode and activate the welding arc. Ensure that your welds are small enough so that your workpiece doesn’t become a mess. Let the electrode move around the spot in a circular motion until you’ve formed a tack weld of a suitable size. Then move the electrode to the next spot to create another weld.
- Inspect Your Welds
After making your tack welds, ensure to carry out a proper inspection. Remember that tack welds are temporary and so, are subject to adjustments. Don’t hesitate to rework any welds that fail to come out right, even if it’s all of them.
Distortion Control
To prevent or reduce the chances of tack welding distortions, there are tips you should follow. Your most important considerations once you are about to weld your tacks would be direction and sequence.
It is best to begin building your tack welds first at the ends of the joints. Afterward, weld the centers of any distance between two welds until you have placed a weld at every appropriate spot
This technique helps prevent shrinkage. If you tack weld from one to another, the opposite end can suffer shrinkage which will make it close up its gaps and distort the work.
An alternative tack weld sequence would be to start from the middle of the joints. After placing the first weld in the middle, proceed to the next spot on the left, followed by the next spot on the right of the middle weld. By adhering to this sequence, you can avoid ending up with a distorted joint.
Materials Used in Tack Welding
One beautiful thing about tack welding is that there are several suitable materials for it. Let’s go over the various materials that can achieve a tack weld.
1. Stainless Steel
Tack welds are suitable for welding stainless steel. You can weld any stainless steel component including stainless steel pipes, aircraft parts, vessels, aircraft parts, and escalators.
2. Structural Steel
Structural steel is also suitable for tack welds. You can make tack welds for bridges, high-rise buildings, and parking garages.
3. Thin Gauge Materials
Tack welding is suitable for joining thin gauge materials like metal sheets.
4. Aluminum
Tack welding can be used on aluminum components. However, you must know that tack welds on aluminum are more likely to distort due to the material’s high thermal conductivity.
5. Cast Iron
As long as you are careful enough to prevent overheating of the metal, cast iron is also suitable for tack welds.
6. Other Materials
These include brass, copper, magnesium, and titanium.
Types of Tack Welding
There are several methods of tack welding. The application of these methods depends on how well-suited they are for specific projects and scenarios. However, here are the most common types of tack welding:
1. Standard Tack Weld
There are various types of tack welds. However, the standard tack weld technique is the most commonly used among welders.
For standard tack weld, the tacks are placed as support for the final welding procedure so they can help protect joints from breaking. Hence, they help hold workpieces together for the permanent weld.
While using this welding technique, one must consider the size of the tack welds. That is, the tacks must be large enough to hold the weight of the material being joined but also small enough that they are unnoticeable after permanent welding.
2. Bridge Tack Weld
This Bridge tack welding technique is used when materials naturally fit but still require a root opening. This method must be error-free and requires more skill than other tack weld techniques because the slightest mistake could ruin your workpieces.
Bridge tack welding is done by applying small tacks at a shallow depth. In cases where the weld gets too hot, it is wise to let the material cool down at intervals throughout the process.
3. Hot Tack Weld or Hot Tacking
Hot tack welding is another technique used to adjust gaps between metal pieces. You can force the gaps closed by depositing excess filler metal in the area and striking it with a hammer.
This method is suitable if you don’t mind affecting the weld quality. Also, hot tacks are called ‘dogs’ or ‘cleats.’
4. Ultrasonic Tack
Ultrasonic tacks are small tacks that are made on the joint of the edges of a workpiece with electric or gas welding machines. The machine creates short pushes or pulls through the joints at ultrasonic speed to push molten filler materials to create tacks.
5. Thermit Tack
Thermit tacking is a less popular type of tack welding. It requires a mixture of pure magnesium metal, aluminum powder, and iron oxide powder. This creates a reaction that’s often hotter than 4000 degrees Fahrenheit.
Four Forms of Tack Welds
Regardless of the type of tack weld you chose to employ, tack welds can take several different forms.
These forms are:
- Square
- Vertical
- Right angle
- Right angle corner
1. Square
Square welds are ideal for joining two metal parts at a right angle. The tack welds are done in squares and are known for their strength.
2. Vertical
You can apply tacks between two metal parts from the top to the bottom. Vertical tacks are great for pieces that you want to align vertically.
3. Right Angle
This form of tack welding is useful when the metal piece is perpendicular to each other. That is, they form 90 degrees when joined. In this situation, you will need to apply your tacks on the side of the bottom piece.
4. Right Angle Corner
When two metal parts are to join each other perpendicularly, you should use a right-angle corner tack weld. Not only are the metal pieces to form 90 degrees, but they will also produce a “T” shape when they are joined. Therefore, you will need to join the parts at their 90-degree point.
Practical Ways to Ensure High-Quality Tack Welds
Standard tack welds aren’t bigger than an inch but are most commonly between a half-inch and three-quarters of an inch. The strength of tack welding isn’t the size of the welds, it is in spreading small welds throughout the metal pieces.
So the first step to ensure high-quality tack welds is by keeping them as small as possible.
Advantages and Disadvantages of Tack Welding
Let’s examine the advantages and disadvantages of tack welding.
Advantages
1. It enhances the accuracy of your work
Tack welding is a technique that helps you achieve proper alignment of metal parts before you apply the final weld. This way, you can get results that comply with the specifications
2. It produces higher-quality jobs by reducing distortion
Many times, while welding is in progress, metal parts may shift from your desired position. Tack welding ensures that they don’t and so, there is no distortion in the final weld. Tack welding achieves this by making those little welds at different points of the metal part.
3. It saves cost
Tack welds save money. By eliminating the need to rework a weld after the final weld, you are sure to avoid unnecessary spending.
Also, using a non-consumable welding wire can save up more cost than using an expensive filler material.
4. It helps you achieve the welding at a faster rate
Tack welds, on many occasions, are a faster way to keep metal parts in place before achieving the final weld. That is, it is faster than using clamp fixtures.
Disadvantages
1. They are usually difficult to rework
While it is possible to rework a weld that wasn’t properly done, it is difficult to achieve that without negatively affecting the metal parts.
2. They can damage materials
Tack welding, especially for thin gauge materials can end up damaging the materials.
3. They could be expensive
If you decide to use filler materials over a non-consumable wire, you can end up spending way more than you could.
4. Could slow down work
Most times, tack welds require that you clean up the weld area after tacking. This process, especially if the welded area is large, can slow down the work.
Difference Between Spot Welding and Tack Welding
Just like tack welding, other welding processes finds application in various forms of welding. One such welding process is spot welding.
Spot welding is a welding process used for welding metal sheets together. In this process, the metal surface points in contact are joined by concentrating welding current on a spot using two electrodes.
Both welding processes share similarities and can be mistaken for the other. For example, they are both resistance welding processes. Therefore, it is important to know the difference between the two.
- While tack welds produce one weld at a time, spot weld produces multiple welds at the same time.
- Tack welds require less energy than spot welds and are more suitable for smaller welding projects.
- Due to the less heat required by tack welds, they are less likely to distort than spot welds.
- Tack welds produce weaker joints between the metal parts than spot welds. This is because tack welds only join the metals electronically, while spot welds join the metals atom to atom (fusion welding).
- Tack welds are slower to execute than spot welds.
- You can perform tack welds by hand but you must use special equipment for spot welds.
FAQs
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Before You Go
Tack welding is an important welding process that finds application in almost every form of welding activity. The primary purpose of tack welds is to hold metal pieces together so that the final weld is done without hassle.
Tack welds also ensure that your welds are accurate and comply with the specification. In addition, tack welds improve the quality of the welding process.
There are different types of tack welding. These are the standard, bridge, and hot tack welds. The type of weld you use depends on the nature of the work and the shape of the metal pieces.
Tack welds can speed up your welding process compared to using fixtures. They can also reduce your overall welding cost. If done right, they deliver some of the best quality welding jobs.
