Bends with a CLR to OD ratio of 2 to 1 or above can be used without a mandrel. For example, a 1” OD with a 2” CLR. Mandrel bending is required for CLR to OD ratios below 2 to 1, requiring higher labor costs and tooling charges. Try to avoid a 1 to 1 ratio as this requires even more expensive tooling and labor cost.
Avoid having tangents of one bend blending into the tangent of an adjacent bend. It is best to have a straight distance between bend tangents so the tubing can be gripped. When one tangent is close to another tangent, special grips are required to grip the tubing.
Gripping and bending of tubing requires significant force. This will cause the wall to stretch and thin around the outside radii, and it will compress and thicken on the inside radii. The tighter the bend radii the greater this condition.
Try to allow for some straight distance from the last bend to the end of the tube. This will allow for the material compression/stretch condition around the tube bend, causing the ends of the tube to become unsquare. If the straight is too close the last tangent trimming & deburring will be required which adds cost, time, and tooling.
This is the condition in which metal wants to return to its original state or condition when bending force is applied. Spring back is a major consideration when selecting bend tolerance. To control this we must compensate by over-bending a few degrees. The harder the material the greater the spring back compensation factor required.
When designing a bent tubular part consider using soft, or annealed, tempered material when possible. This helps reduce spring back, reduces stretch/compression, and prevents wrinkling or breakage.