CNC Tube Bending for Locomotive Pipework

A locomotive carries a surprising amount of pipework. Air lines feed the brakes and auxiliary equipment, fuel lines supply the injection system, oil and water lines connect pumps, coolers and the engine. Each pipe follows its own path around frames, brackets and other equipment, and a replacement that is slightly wrong will not fit, or will fit only under stress.

CNC pipe and tube bending is how these parts are reproduced accurately and repeatably. This article explains what it involves, what information a bender needs, and how to order pipework when all you have is the old pipe.

Where bent pipework is used on locomotives

Typical bent pipe and tube parts include:

• compressed air lines between the compressor, reservoirs, air dryer and brake equipment;
• fuel lines, including supply and return lines;
• lube oil lines to and from pumps, filters, coolers and the turbocharger;
• cooling water pipes between the engine, radiators and other coolers;
• hydraulic and sanding lines, depending on the design;
• handrails, guards and tubular frames, which use the same bending process for structural parts.

Why CNC bending?

Pipes can be bent by hand, but CNC bending has clear advantages for rail parts:

• Repeatability. Once a pipe is programmed, every copy matches the first, which matters when you order a batch for several locomotives.
• Accuracy. Bend angles, lengths between bends and the rotation between bend planes are controlled, so the pipe fits without forcing.
• Consistent bend quality. Correct tooling limits flattening (ovality), wrinkling and wall thinning at the bends.
• Less fitting stress. A pipe that is forced into place is loaded before the system is even pressurised, which can lead to cracked fittings and leaks.

The data a tube bender needs

To make a bent pipe, the bender needs:

1. Material: for example carbon steel, stainless steel or copper, and the specification if one applies.
2. Outside diameter and wall thickness.
3. Centreline bend radius, which depends on the tooling available for that diameter.
4. Bend data: the straight length before each bend, the bend angle, and the rotation of each bend relative to the previous one. This is often written as a list of length, rotation and angle values for each bend.
5. End details: flares, ferrules, flanges, threads or weld preparations.
6. Tolerances, if the drawing specifies them.

On a drawing, the same information may be given as coordinates of the pipe's centreline at each bend point. Either form can be converted for programming.

Making pipework from a sample

Often the drawing is lost, but the old pipe is still available, perhaps bent, crushed or corroded. Pipes can still be reproduced:

• Measure the old pipe carefully, recording diameters, wall thickness, straight lengths and bend angles. Photographs from several angles help.
• Correct for damage. A pipe that has been knocked or forced out of shape must not be copied exactly. The fixing points on the locomotive are the true reference.
• Check the end fittings, including thread type and size, so the new pipe connects properly.
• Confirm the fit on a locomotive or a template before making a batch.

Deomac's re-engineering service designs and manufactures parts from a sample, drawing or part number, and pipework is a good example of where working from a sample saves time.

Design limits to keep in mind

Pipe bending has practical limits:

• Minimum bend radius. Bending tighter than the tooling allows flattens or wrinkles the pipe.
• Straight length between bends. The bender needs some straight pipe to clamp between bends. Very close bends may need to be made as separate pieces and joined.
• Wall thinning. The outside of a bend stretches and thins. Thin-walled pipes bent tightly lose more strength at the bend.
• Ovality. Some flattening is normal; too much restricts flow and weakens the pipe.

If a pipe has always been difficult to make, a small change to the bend radius or the routing can make it much easier to produce, as long as it still fits and the system's engineering requirements are respected.

Cleanliness and testing

For fluid lines, how a pipe is finished matters as much as its shape:

• Clean the bore. Scale, swarf and debris inside a fuel, oil or air line can damage pumps, injectors and valves. Pipes should be cleaned and flushed after bending and welding.
• Cap the ends. Fit caps until installation to keep dirt out.
• Pressure test where required, especially for air and fuel lines.
• Protect the outside with the coating or plating specified.

Pipe and tube bending at Deomac

Deomac's services include CNC pipe and tube bending, with tooling for pipes up to 74 mm diameter, alongside welding and fabrication, CNC turning, milling, and laser and plasma cutting. That combination means bent pipes, welded flanges, machined fittings and brackets can be made together.

To get a quote, send:

• the drawing, or the old pipe or good photos and measurements;
• material, outside diameter and wall thickness, if known;
• end fitting details;
• quantities and the required date.

Use the contact page to send your requirement. If the part already has a catalogue number, check the parts list first.

Related reading

• EMD and GE engine spares: a buyer's guide, which covers lubrication and cooling parts
• Weld repair or replace? deciding on rail parts, for fabricated assemblies that include bent tube

Summary

Accurate pipework makes the difference between a quick fit and a frustrating one. Give the bender complete data, or a sample that is measured with care, respect the limits of bending, and finish fluid lines clean and tested. CNC bending then makes every pipe in a batch the same.