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One of the toughest metal forming operations on the planet and especially important for automotive and industrial use is exhaust pipe bending. Generally speaking exhaust pipe will not made of structural steel tube because it is exposed to heavy thermal cycling, vibration, backpressure and corrosive condensates, not to mention fitting it into an ever-shrinking engine bay. You will find plenty of results if you type “pipe bending company”, but you will struggle to find a job that is actually specializing in what it takes. Exhaust bending isn’t just a simple curve, it’s maintaining integrity of the mandrel and managing wall thinning along with orientation of the weld seam. Here are the distinguishing characteristics that separate excellent partners from adequate partners in exhaust bent tube applications.
Evaluate Their Mandrel Bending Capabilities and Tooling Inventory
The first and smallest difference between general pipe bender and an exhaust specialist is related to mandrel bending technology. Exhaust tubing frequently has to be bent into a tight radius, sometimes as low as 1.5-2 times the diameter of the tubing, but must not reduce the cross sectional area of the duct. This requires draw bending with a flexible ball mandrel or sand packed mandrel system which will provide support to the inner mandrel wall during the bending stroke. When looking at a potential partner, specific questions that should be addressed include what is the largest mandrel diameter they work with, how many ball segments they are able to fit, and has more than one mandrel set for common exhaust diameters such as 2.0", 2.5" and 3.0" stainless steel. Often a special manufacturer will have a tooling library that is indexed on the stainless grade - even though 409 stainless is different from 304 or aluminized steel. We have personalized mandrel moulds for every exhaust alloy that we process at Baorui, usually for exhaust production clients, we would like to ask our clients to check our tooling racks when they visit our factory. If any shop lacks the specific exhaust mandrel, it is probable that the compromise is the size of ovality or wrinkle formation.
Examine Their Material Knowledge and Weld-Seam Management
Exhaust tubes are almost never seamless. Instead they are made of welded tubes with a straight line seam run down the length of the tube. The tube's seam is a weak point to bend over the neutral axis (best is 45-90 degrees away from the compressions of the bend) unless the operator is experienced. Many suppliers do not get this angle perfectly and will end up splitting/thinning the exhaust bend in the tool.
You'll need to be careful in your initial inquiries of the suppliers. Ask them about the way their seams are set for bending. Do they use machine vision/seam detectors/sensors, manual indexes, or is it a visual call and is how do they determine the proper angle and degree to avoid thinning/splitting? Inquire about any thinning values have been given as a buffer or allowance to compensate wall. A good exhaust bend machine shop will have the engineering data available, as well as a thinning chart that includes parameters that influence the outcome and be able to advise the optimal process parameters to manage this. Baorui engineering will perform a rudimentary 2D cross section analysis (wall reduction, ovality analysis of the material for any given material for exhaust applications prior to signing off on any tool designs) before making a final decision.
Assess Their Quality Assurance and Measurement Protocols
It is essential to have proper quality control because exhaust pipe bending defect is a common situation after the plating or coating process. Water the "bed" and prepare them for forming. Check bend angle, spring back compensation and surface condition with inline laser profile scanners or coordinate measuring arms immediately after forming with a manufacturer. They should also have an internal wrinkle check procedure documented – which is best used for designs that do not allow high flow exhaust. Above all, ask for their statistical process control (SPC) information on past exhaust projects. Specialists will gladly provide the following: histograms of bend angle deviations, wall-thickness distribution and surface roughness averages. The protocol will also include a clear non destructive testing (NDT) procedure to identify micro-cracks in the outer part of the stretch zone, the extrados. Baorui has set up a special inspection station equipped with electronic comparators for each batch of exhaust products, and stores the conditions of the first, in-process and final inspection for at least five years. Exhaust safety-critical parts must be carefully selected for use with the manufacturer that doesn't treat quality the way it is supposed to be treated: as an ongoing process.
Verify Their Industry Experience and Application References
Last but not least, proof of a specialization does not come in the form of brochures but proof by history. Ask them for specific exhaust component applications like downpipe bends, catalytic converter housings, mufflers’ inlet pipes, EGR cooler pipes. The right specialists will ask for your project by vehicle platform codes, emissions targets (China 6b, EPA or Euro 6), the durability test cycles. They may also want to know material temper conditions because your exhaust bends might use anneal strips, or very lightly cold-rolled strips that help in getting the optimal compromise between workability and resistance. During conversations mention if they’ll ask the expected end-use operating temperature and cyclic fatigue life. This is clearly a sign of a specialist. Our passenger vehicle, commercial truck, off-highway vehicle clients, all our customers can attest to Baorui’s twenty-plus years in the exhaust bending knowhow. Our first response to your request to provide references would be, after a quick talk over some of the applications we’ve done; of course. If the supplier avoids the issue, or can’t speak on a granular level; this might be reason enough not to work with them.
Overall you would need to become as technically proficient in exhaust pipe bending as the candidate in order to make the best selection possible. We will require you know about mandrell tool depth, seam processing, accurately measurement capabilities and how they track the performance of the parts they’ve produced for some years. Working with us, you will find, would probably be welcomed! We at Baorui will answer all your questions with confidence since it shows that you do appreciate expertise and that you know exhaust forming. You will not waste a fortune in rework or, worse still, have costly field failures if you make the right choice.