Why bending copper tube is harder than it looks
Bend a thin-walled tube tightly enough and, without the right support, the outer wall thins and the inner wall wrinkles inward — both of which reduce the tube's pressure rating and restrict refrigerant flow exactly at the bend. Getting a clean, round bend at a tight radius is a controlled forming process, not just mechanical force applied to metal.
Mandrel and roller-die bending
Production bending typically uses a mandrel — a close-fitting internal support, often a series of articulated balls — that holds the tube's cross-section round as it's bent around a die. Roller dies support the tube from the outside during the bend, keeping wall thickness even around the bend's circumference. The mandrel and die combination is selected to match the tube's outer diameter, wall thickness and the bend radius specified for the part.
CNC bending for repeatability
Modern production lines use CNC-controlled bending equipment that can be programmed with the exact bend angle, rotation and feed length for a given part, and repeat it precisely across a full production run. This matters for coils and manifolds with several bends in sequence, where a small error early in the sequence compounds into a part that doesn't fit by the final bend.
Inspection after bending
Bent tube is checked for ovality (how far the cross-section has deviated from round), wall thickness at the bend's outer radius, and overall dimensional accuracy against the part drawing. Parts that fall outside tolerance are rejected before they reach the next operation — bending errors are far more expensive to catch after a part has already been brazed into a larger assembly.