Adding a lubrication step to a tube bending process is best done up front

When using gel or paste type lubricant, removal is more than likely going to be a necessary step in the fabrication process.

When baking a cake, you must combine all the ingredients to make a great tasting dessert. If you leave one out or forget a step in the preparation, the taste could be off, or your creation could be a total disaster. The same thought must go into your tube forming processes. Many metal fabricators are branching out, taking a stab at mandrel tube bending and other tube forming processes as demand for more tube and more sophisticated tube increases.

However, without a good knowledge base, a fabricator new to tube might relegate lubrication to the status of an afterthought. Addressing lubrication in the production stage rather than the design stage can be troublesome. Tough-to-bend parts may require extreme lubrication, and that can lead to undesirable residues on the finished part. The likely result is an unplanned and unbudgeted remedial step, a cleaning stage, incorporated at the end of the process.

Coming in Late

You’ve had a successful part runoff, and now the mandrel bender is in your facility. It’s time to ramp up production. As the program progresses, forming issues arise. Often the speed and throughput at normal production speed tend to introduce more heat and wear into the process. This increase in friction requires some lubrication if none was used in the runoff, or a more capable lubricant if one was used in the runoff. A lubricant supplier’s expertise might solve the problem, but the supplier can’t wave a magic wand and make your problems disappear. It’s going to take some time and some money.

When introducing lubrication for the first time in this later phase, most manufacturers usually aren’t prepared to deal with any resulting residue and must find a way to remove the excess lubricant or get approval from the end user to allow the residue to remain on the components. Depending on downstream processes, if even the slightest residue is not allowed, you must implement a residue removal or tube cleaning stage.

Another outcome is that, while some residue is acceptable, you have had to switch to a different lubricant that can withstand the greater-than-anticipated friction and heat buildup, and this more capable lubricant is also more viscous and leaves more residue than is acceptable, thereby requiring a deviation or another unforeseen processing step.

Both conditions introduce increased and unintended costs after the contract has been signed.

Start at the Beginning. The best way to avoid costly process step additions like cleaning is to think about lubrication in the engineering stages. Ask yourself a few insightful questions and you can determine whether a lubricant is necessary. Is the part a difficult configuration? Is the substrate a high-strength steel? Is it a thick material? Is the metal to be deformed substantially? A good rule of thumb is that if the metal is being moved enough to make it hot in the forming process, some lubrication is likely necessary.

In some cases, light lubrication can give the required performance while leaving very little residue. However, many times, a heavy- or extreme-duty lubricant is necessary to make the part. If this is determined up front, you and your team can build in a wipe or wash station to remove any unwanted residue. Of course, a lubricant’s chemistry and quantity determine how the removal stage is designed within the process. It’s a good idea to consult a reputable lubrication specialist in the design phase to help manage the frictional expectations.

Finding the Best Lubrication Option. Planning the lubrication operation starts with choosing the lubricant’s chemistry. A common choice is a vanishing lubricant. As the name implies, this type requires no removal steps. A vanishing lubricant can work well if the forming requirement isn’t severe and the end part must be dry to the touch. However, choosing such a lube requires careful consideration. Most vanishing oils are solvent-based and can introduce volatile organic compounds (VOCs) into the process. This may lead to even more design costs up front to handle the air quality and flammability hazards.

A vegetable oil applied in the smallest quantity possible, known as minimum quantity lubrication (MQL), substantially reduces the need to remove the remaining residue.

Other options are VOC-free vanishing products and minimum quantity lubrication fluids. These types leave little to no residue. Both options are lighter fluids and may need specialized application equipment. But if the part is difficult to form and beyond the metalforming capabilities of these lighter lubricants, heavier-duty options are available.

Tougher fluids like dilutable synthetics and soluble oils may offer more lubricity and be an option to avoid secondary cleaning processes, but it will depend on the dilution you are able to run. Even the lightest of these products need to be diluted with water out to about 5% to 10% concentration before the result is a light residue that may be acceptable for the end user.

Proper Coverage and Adhesion. Bends that were difficult (or impossible) years ago are becoming commonplace today. As OEMs design parts that are more sophisticated, fabricators find themselves dealing with parts that are more challenging to make. Mandrel-bent tube is rarely done with a generous bend radius anymore; a centerline bend radius that is equal to the tube’s diameter, a 1D bend, is becoming the norm in many applications. As the bend radius becomes tighter, friction and wear increase. Accompany this with harder materials, and many of today’s tube bending processes require extreme lubrication. This comes in the form of heavy fluids, gels, and pastes. It’s not just a matter of choosing the best one for the bend. The application process has to provide good coverage and adhesion.

Gels and pastes have been used for many years to provide the necessary amount of tool protection and forming performance, but they leave a residue. Applying these products is a matter of using the lightest film possible to get the desired results. Keeping the usage to a minimum helps in downstream operations, whether welding, wiping, cleaning, or painting. Hence, considering the use of these types of products in the design stage ensures a smooth process—application, bending, and removal.

Moving Forward After the Fact

If you find yourself developing a lubrication process in the latter stages of process development, it’s likely to require some research and a capital investment for lubricant application equipment, and you’ll lose some production time. You might get by with a light-duty product that leaves an acceptably small amount of residue, or none at all, but if you need a medium- to heavy-duty option, you’ll probably incur another capital cost and expenditure for a lubricant removal system.

The first step is to consider the various lubrication options and narrow them down until you have the optimal product. Second, make a test run of parts, optimizing the application to minimize the residue. Bear in mind that tool coatings can help as well. Finally, consult with the customer to determine if the residue is acceptable or not. If not, find out what your customer can accept, then discuss what residue will be acceptable. This can be defined with a dyne pen or an automated method.

If the residue from the bending process still exceeds your customer’s expectation, determine if wiping the residue from the surface is acceptable. This is normally a manual operation, so whether this is a workable solution depends on part volume. If wiping just doesn’t get the job done, the last resort is the costliest option: investing in cleaning equipment.

Cleaning operations can range from simple manual dip tanks to large, automated dip tanks or spray washers, either in-house or outsourced. If the project is small in scope, such as a workcell with a single bender, a midscale washing system brought in-house might be sufficient. An ultrasonic dip tank with a light cleaner also can be an interim or even permanent resolution.

Defining Lubrication Up Front

Lubrication requirements are best considered at the beginning when designers and engineers are developing the process. Having a lubrication specialist consult at this stage helps to ensure the right product is available to optimize the performance in a production setting and determine whether a residue is likely to remain and steps for removal. Knowing the right ingredients and steps involved to achieve the desired result will optimize the process and streamline costs, and it will certainly prevent a delay when production ramps up. And who knows—you might even win a prize at the local bake-off!