Over the years, Holden has developed a wealth of knowledge and expertise in the manufacture of complex curved aluminium products and components. We have been at the forefront of aluminium forming machine design and have built up a specialist work force, skilled in radial flow forming, stretch forming and roll forming.

Our facilities mean that we can curve a wide variety of sections from small to very large. Our experienced staff are always available with technical support at all stages of your product development.

Customer requirements fall into three categories:

STRETCH FORMING

Stretch forming is the most accurate, repeatable and fastest forming method, as well as being able to incorporate 2 and 3 plane bending into the tooling to give the most complex of shapes.

It is also possible to incorporate auxiliary operation such as piercing cropping and swaging into the tooling which in some cases can eliminate any subsequent operations and produce the finished components.

For symmetrical parts left and right hands can often be produced together from one length of section with a central cropping operation in the tooling to part left and right hands. For non symmetrical parts the tooling can incorporate separate bending movements for secondary bends.

Using positional controls for the major axis, such as rotation and stretch, the process can be adapted to incorporate compression bending in specific areas when components require very tight corner bends.  This is used to overcome the limitations of the material elongation when tighter bends are desirable.

I.e. traditional forming steel such as CR1 would a have an elongation value of 25 % where as Aluminium in 6063 T4 is restricted to around 14%.

For Example:-  A standard “U” channel having a depth of 25 mm will have a limiting internal radii of:-

• CR1 Steel, 100mm with the neutral axis for bending at R100mm
• Aluminium 6064 T4, 178mm with the neutral axis for bending at R178mm.

By moving the neutral axis to mid way of the 25 mm channel will place the inside into compression while retaining the out side as stretch then giving the following values for minimum inside bend radii.

• CR1 steel, 50mm with the neutral axis for bending at R62.5mm in CR1 steel
• Aluminium 6063 T4, 89mm with the neutral axis at R101.5mm in

For tighter radii the section can be reduced in the flange leg lengths allowing the neutral axis to be moved much closer to the outside edge and consequently greatly reduce the outside radii.  To prevent yielding at these points local clamps are introduced on both sides of the bend.

FLOW FORMING

Flow forming has lower set-up cost than stretch forming but is limited to single plane forming.  It is a very valuable method of forming hollow section where a floating mandrel can be positioned inside the hollow section which maintains the original cross sectional profile by preventing collapse during forming.  If the mandrel is not practical then other fillers can be introduced prior to forming in order top prevent collapse.  The materials used are common to other forming methods.

 Varying bend angles can be produced on common tooling with flow forming, up to a maximum bend angle of 180°, but the bend radii is governed by the tool being used. 

The theoretical minimum bend radii for flow forming is normally 3:1
We have however developed bending tooling to achieve a 1:1 bend radii. See diagram below.

In order to achieve such results the material being formed has to be controlled to very tight tolerances on it’s specification as well as dimensionally and it is very dependant on the extrusion profile.

The Flow Forming machines at H.A.T. have been enhanced in order to form very large cross sections such as bumpers and monorail stairs lift parts.

ROLL FORMING

Three roll forming machines have been in use for many years and have the advantage of economic tooling for shallow formed simple swept parts.   H.A.T has now invested in the latest CNC roll forming technology, which has many significant improvements over the original 3 roll machines and can now, with the use of a “Z” axis, roll complex three dimensional shapes and still with minimal tooling costs.  The advantage over Flow and Stretch Forming is that common tooling can be used for multiple radii, parabolic curves and edge forming in the same part. 

The part shown below is typical of what can now be achieved from CNC roll forming.

 For simple extrusion profiles such as rectangles and square section standard tooling can be used.  Material batch variations that cause form errors can be simply over come with program modifications rather than hard tool re-cuts. 

This machine can be used for prototype and development of products to aid customer designs and for low to medium volume production this machine can provide an economic solution to most forming requirements.

The length of formed components is only restricted by material handling and transportation limitations.

USING SUPPORTING INSERT OR FILLERS

The cross sections of the components should be carefully considered when designing parts that require forming and if possible avoid cavities that cannot be supported by the forming tools.

However if it is not possible to avoid cavities then insert fillers can be introduced which will prevent cross section collapse. The filler materials vary depending upon the application, from standard nylon 66 though to sacrificial aluminium and polyurethane.  For very low volume forming it is also possible to use ice as a filler material as well as low melt alloys.

In some higher volume production parts the filler insertion and withdrawal can be automated and be an integral part of the tooling.  For lower volume production it is normal to have separate remote operation for filler insertion and withdrawal.

We are pleased to offer advise and consult with customers through the component design phase in order to achieve  the  most practical and cost effective forming solutions.

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