Tips for Ultrasonic Welder Troubleshooting

Ultrasonic welding is a method that has been used since the 1940s to join thermoplastic and some metal materials to create a solid weld. During this process, high-frequency ultrasonic vibrations are applied to a specific area where workpieces are joined together under pressure. The vibrations cause the materials to form a solid weld without the use of high temperatures, glue or fasteners.

Because this method uses acoustics rather than heat or fastening materials, it offers many advantages. Some advantages of using ultrasonic welding include reliability, repeatability, low energy usage and savings on materials and labor.

However, while ultrasonic welding offers many advantages, it is an extremely delicate process that can result in various problems. Fortunately, most issues with ultrasonic welding can be traced back to problems in technique or welder settings.

Troubleshooting Common Ultrasonic Welding Problems

Despite being a delicate process, ultrasonic welding is relatively simple to troubleshoot. To help you determine how to fix your ultrasonic welding issues, we’ve developed an ultrasonic welder troubleshooting guide based on the Branson Ultrasonic Welder troubleshooting guide. Each problem is described in detail below, followed by the common causes of these problems and how to solve them.

1. Overweld

Overweld is when the resulting weld is more extensive than is specified. Overwelds can result in functional and aesthetic problems, altering the dimensions, finish and functionality of the part.

Problems: Overwelding often occurs because of excess energy that leeches outside of the intended area, affecting surfaces that are not intended to be welded. The following are the common causes of overwelding:

Too much energy is being put into the part.
The weld is being applied for too long, resulting in excess energy.
The weld travel distance, also known as the melt down distance or collapse, is too high.
The absolute distance is too high.

Solutions: The best way to reduce overweld is to reduce the amount of energy applied to the part. This can be done through the following means:

Reduce the pressure, trigger force and down speed used to reduce overall energy input.
Reduce the overall amount of time put into the weld.
Reduce the amplitude produced by the ultrasonic welder by changing to a lower ratio booster, digitally reducing the amplitude percentage, using amplitude profiling or using a lower gain horn.
Reduce the absolute distance by recalibrating the absolute distance and adjusting it accordingly.

When correcting an overweld, it is important to adjust each parameter individually rather than adjust them all simultaneously. You may also consider making sizeable parameter changes of 20 to 30 percent to induce opposite failure. This way, you can more easily gauge the efficacy of the change and work to find an optimal setting.

2. Underweld

An underweld is the opposite of an overweld — in these cases, the weld has not covered the entire area needed, so some areas are left untouched. This causes serious functional issues, as the part is not welded together strongly enough to meet specifications.

Problems: Underwelds most often occur for the opposite reason as overwelds — instead of too much energy being put into the part, too little energy is being put in. Additionally, underwelds may be caused by improper setup or cleaning. The following are the most common causes of underwelding:

Insufficient energy is being applied to the part.
The amount of time the weld is applied is too short.
The amplitude of the ultrasonic welder is too low.
The absolute distance is too low.
Energy is being lost into the fixture rather than focusing on the part.
The part is contaminated with mold release or moisture.
The part is set incorrectly on the anvil.

Solutions: Underweld is easily fixed with small adjustments in procedure and welder settings. This can be accomplished through the following steps:

Check all parts before welding to ensure that they are clean and free of moisture.
Recalibrate the base of the welder to ensure that it is level and makes full contact with the attachment before welding.
If energy is being lost into the fixture, change the fixture to a rigid material like aluminum or stainless steel.
Increase the pressure, trigger force or down speed to increase the energy applied to the part.
Increase the amount of time the weld is applied.
Increase amplitude by using a higher ratio booster or changing to a higher gain horn.
Increase the absolute distance.

With underwelding, it is generally best to check the setup and cleanliness of the parts before adjusting welder settings, as these problems are quickly and easily remedied. Once these aspects have been eliminated as possible causes, adjust welder settings one at a time to achieve desired results.

3. Non-Uniform Joint Weld

Non-uniform welds are both aesthetically unappealing and can have functional drawbacks. Non-uniform welds are not as strong in some areas as in others, meaning that the part may have a low-quality seal.

Problems: Faulty parts or fixtures most often cause non-uniform welds around the joint. Most often, these issues are caused by the following errors:

One part is improperly made or warped, or the wall is flexed so that it doesn’t fit properly to the other part.
The part is improperly cleaned, leaving behind mold release or moisture that can reduce the efficacy of the weld.
The parts are not properly aligned during setup.
Filler is accumulating in certain areas, resulting in more joint weld in some areas over others.
The horn, fixture and part are not parallel or have poor contact, resulting in a lower-quality weld.
The fixture on which the part rests is not sufficiently supported.
The horn of the ultrasonic welder isn’t producing a uniform amplitude.

Solutions: Non-uniform joint welds are most often fixed with simple part, equipment and setup testing and adjustment. Common solutions include:

Check the part for any signs of manufacturing error or warping. This may include checking the part’s dimensions and molding conditions for any inconsistencies. If the part is not made to specification, tighten tolerances and check molding conditions to ensure that parts are made correctly. If wall flexure is occurring, consider increasing wall thickness, adding internal ribs or modifying the fixture to prevent it.
Check the parts for any signs of mold release or moisture. If there is any evidence of improperly cleaned parts, update cleaning protocols appropriately.
Check the setup to ensure that parts are properly aligned before and during welding. Keep an eye out for proper alignment of mating parts and any shifting during the welding process.
Check the part for signs that filler is accumulating in one area over another. If this is an issue, make sure that you are using short fiber fillers and reduce the amount of filler used.
Check the setup to make sure that the fixture is firm and that the horn is making uniform contact with the part. If the setup is not right, shim the fixture as needed and test for parallelism.
If the fixture is insufficiently supported, you may want to either improve support or, in especially bad cases, change to a rigid fixture.
If the problem may be the horn, have the horn tested and modified or repaired to produce a uniform amplitude.

There are many more potential causes of non-uniform joint welds than most other ultrasonic welder issues, so be sure to be systematic in the troubleshooting procedure if this issue arises.

4. Part-to-Part Welds Inconsistent

In some cases, the weld on one part may differ from the weld on another. This poses a problem for a company’s overall production value, as production consistency is a point of interest for many clients.

Problems: There are numerous potential causes of part-to-part inconsistencies. Many of them relate to part, setup and procedure issues, including the following:

The parts are improperly or inconsistently cleaned, leaving behind mold release or moisture that can negatively affect weld consistency.
The ultrasonic welder is producing less consistent results due to maintenance issues or a drop in air line pressure.
The parts are made with poor-quality or incompatible materials, resulting in less consistent results.
Too much filler is being used or is distributed unevenly.
The parts are made inconsistently so that dimensions do not match from part to part.
The parts are designed in a way that they fit poorly.

Solutions: Many issues that lead to inconsistent weld results are fixable with basic changes at the process level, but higher-level issues may require more extensive fixes. Here are some potential solutions to help with part-to-part consistency:

Check the cleaning procedures to make sure that all parts are cleaned consistently to eliminate mold release and moisture.
Check the welder to ensure that it is functioning properly. If a drop in air-line pressure is the cause of the problem, check that your supply line capacity and compressor output supports the number of operating welders. If this isn’t the cause of the problem, have a professional check your welder to ensure that it is operating properly.
Check your materials to ensure that they are good quality and compatible. Poor-quality materials may have too much regrind in them. You can check for material compatibility by referring to your supplier specifications.
Check the amount and distribution of your filler. You may need to check molding conditions to ensure that filler is mixed thoroughly and not accumulating near weld areas. If possible, try to reduce the percentage of filler used and change the type of filler.
To check that parts are made consistently, check the dimensions of several parts. If inconsistencies are found, you may need to tighten tolerances and check molding conditions to ensure that parts are made more consistently.
In some cases, the design of the part may not facilitate consistent results due to poor part fits or incorrect joint design. In these cases, the design of the part may need to be adjusted.

Part-to-part weld inconsistencies can be caused by issues at any level of part design, so it is important to troubleshoot from the least complex to the most complex possible causes.

5. Marking

Marking is when the weld process causes a problem in the surface finish of a part. While marking doesn’t always affect the dimensions or functionality of a part, marking can negatively affect the aesthetic results.

Problems: Marking is often caused by the same problems as overwelding and non-uniform joint welds. Most often, marking results from setup and process errors, though some part fit issues can also result in marking:

The horn, fixture and part are not aligned properly, resulting in uneven contact.
The energy director is too large, resulting in the dispersal of energy beyond the weld area.
The horn of the ultrasonic welder heats up too much.
The part doesn’t fit properly into the fixture, causing the welder to hit areas that it isn’t meant to.
The part is designed with localized high spots along the surface, such as details or raised lettering.

Solutions: Most marking issues can be resolved by adjusting the setup or process, though some errors may require a slight part redesign if the issue persists.

Check the alignment of the horn, fixture and part. This may require making adjustments to bring everything level.
Reduce the size of the energy director to improve localization.
Troubleshoot the horn of the ultrasonic welder to determine if it is heating up too much. Some issues may require repair or setting adjustments.
Check the part to make sure that it sits properly in the fixture. If it doesn’t, check the dimensions of the part and the fixture. Resolving this issue may require increasing part tolerances.
If the part is designed with high spots that pose a consistent issue, consider redesigning the part to have recesses instead.

If the above solutions do not resolve the marking issue, use the solutions provided for overwelding, as marking is a common side-effect of overwelding.

6. Flash

Flash is a thin amount of excess plastic that appears at the joining point after welding. Flash can negatively affect the surface quality of the part, potentially affecting both the functional and aesthetic quality of the finished piece.

Problems: Flash is often caused by excess energy application and poor part design. Some of the most significant causes are listed below:

The weld is applied for too long.
The energy director is too large.
The joint is poorly designed or inconsistent.

Solutions: Flash is often fixed with slight adjustments in process, though consistent issues with flash may require slight part redesigns.

Reduce the weld time.
Reduce the size of the energy director or reduce the applied pressure.
Redesign the joint to direct flash appropriately and increase tolerances to minimize variation.

7. Misalignment

Misalignment of the assembly after welding is a significant problem as the faulty product will likely need to be scrapped.

Problems: Misalignment is most often caused by issues with part design and setup, though overwelding may also be a cause of error.

The mating parts are not aligned correctly before welding.
The fixture is not supported properly, resulting in movement during welding.
The parts are inconsistent or prone to warping.

Solutions: Misalignment most often requires adjustments to the part or fixture. These potential fixes are listed below:

Add alignment features like pins and sockets to the mating halves to help improve alignment.
Redesign the fixture with better support and alignment to minimize movement.
If the part is prone to wall flexure, redesign the part with ribs or thicker walls. If the parts are inconsistent, tighten tolerances and check the molding process to ensure that parts produced meet specifications.

If the above issues and solutions do not resolve the problem, troubleshoot for overwelding, another common cause of misalignment.

8. Internal Components Damaged or Welded

If a part includes internal components, these must remain untouched during the welding process. Unfortunately, damage to internal components is a frequent issue.

Problems: Internal component damage is often caused by procedural or design errors such as the following:

Too much energy is applied.
The weld is applied for too long.
The internal component is mounted improperly.

Solutions: Internal component damage can be rectified by making small changes to procedure, though some issues may require redesigns.

Reduce the energy applied by reducing amplitude, pressure or down speed.
Reduce the amount of time the weld is applied.
Redesign the part to ensure that internal components are mounted properly and isolated from the housing and any areas that require welding.

In some cases, you may have trouble because internal parts are physically welded along with their housing. In these cases, the problem is usually that the internal parts are made of the same material as the housing. The easiest solution to this issue is to change the material of the internal part so that it is incompatible with the housing material, or vice versa.

9. Melting or Fracture of Parts

Excess melting and fracture can result in a part becoming unusable, leading to excessive waste and longer lead times.

Problems: Melting and fracture are most often caused by issues in welding procedure and part design, including the following:

Too much energy is applied to the part.
The part is molded incorrectly, resulting in internal stress, flow lines and other problems.
The part features sharp internal corners.

Solutions: Melting and fracture can be resolved with small, relatively simple fixes like the following:

Reduce the weld time, amplitude or pressure to reduce applied energy.
Check the molding conditions and process parameters to ensure that parts are molded correctly.
Redesign the part with rounded corners instead of sharp corners.

10. Diaphragmming

Diaphragmming, also known as the “oil-canning” effect, occurs when a wall distorts outward to create a bubble. This issue negatively affects the aesthetic and functional value of the part, often resulting in scrapping the affected part.

Problems: Diaphragmming is often caused by issues in the welding process, though certain design choices exacerbate these issues.

The welder is applying too much energy to the part.
The horn used is wrong or is placed in the wrong area.
The part features a gate or a thin wall.

Solutions: Diaphragmming can be avoided by changing the welding process or redesigning features of the part specifically to avoid this issue.

Reduce the weld time or the amplitude used.
Eliminate horn contact over the area of concern or change the horn type to one with a nodal plunger or a vent hole. Also, check that the horn fits the part appropriately.
Redesign the part to change the shape of the gate or increase the thickness of the walls.

Choose GES Repair

The ultrasonic welding process can run into many problems, most of which can be resolved with some basic troubleshooting techniques. However, there may be situations where the problem is your ultrasonic welding equipment. In these cases, you need a repair shop you can trust with your equipment. GES Repair can help.

Contact GES Repair today to learn more about our ultrasonic equipment repair services and get a quote.