Developing your helix blank to achieve your finished helix dimensions is simple using the Design Calculator we provide but there are some crucial considerations.
Optimal results rely on two main design factors namely the maths and the mechanical properties of the material you are forming.
A third consideration is the balance between good design and the limits of your specific machine.
There is no exact or exhaustive reference table and experience is the best guide for what your machine can and cannot do. Following guidelines will assist you to achieve the best results from your machine and extend the wear life of your machine.
MATHEMATICALLY SOUND
We have seen just about every mathematical formula possible when it comes to designing helix blanks. The correct maths is critical to achieve perfect results.
In simple terms, when cold forming a helix, you can think of it as forming two helices at once (the outside helix and the inside helix) with the space between filled with metal. Your inside helix is always going to have greater pitch than the outside helix.
For example, a helix with finished dimensions 500mm OD, 100mm ID to pitch of 100mm will have the outside helix (the OD) with pitch of 20% and the inside helix (the ID) with pitch of 100%.
This means that when calculating the blank from finished helix dimensions, the ID and the OD calculations are independent of each other. Get this maths wrong and you might get a great fit to shaft, but your helix will be shy on finished OD. You could end up with your finished OD correct but have less than optimal shaft ID meaning poor fit and a lot of rework.
Our calculator is tried, tested, and proven for optimal fit-to-shaft precision with little to zero rework. It is simple to use and generates exact dimensions for the blank pattern.
The calculator can be found on the thumb drive included with this manual or by requesting electronic copy from support@helicalformer.com.
It is strongly recommended that any new design is well tested for fit before starting a long production run.
MECHANICALLY PROBABLE
Successfully cold forming any metal is a careful balance between design (the maths) and the mechanical properties of the grade and thickness of material you are forming.
Considering again for a moment that you are forming two helices (internal and external) with the faces filled with metal. The internal (shaft) helix will always have a far greater pitch than the external helix which means the material in the faces of the helix will deform at a different rate.
Successfully forming a helix relies on the permanent deformation of the blank but if there is physically not enough material in the internal helix to go the distance, you will see distortions and have less than optimal results.
This is because cold forming bends the material into a helix, it cannot stretch the material. It is deformation, not elongation, of the material that takes place in a cold forming process.
For this reason, you will find the there is a limit on smallest ID to OD which is also influenced by overall thickness and overall pitch of your design.
As a rule of thumb, when forming to 50% pitch or thereabouts, which is the maximum pitch any of our SD formers can form, ID should not be less than 35% of the OD of the helix when forming to the working thickness limit of the machine.
For example, on an HF30, the working thickness limit of the machine is 15mm. The jaw limit is 250 mm with a safe working limit of 200 mm
The largest diameter helix that could be formed on this machine at 15mm thickness would be about 600mm OD with a 200 mm ID to an overall finished pitch of 50% of the OD of the helix. In this example, 300mm.