By Robert Levy – CEO TFGUSA
© Copyright 2017
Precision: How Accurate Do You Need It?
As you design a part for near net shape cold forming, it is important to
realize that holding tight tolerances is possible, but the tighter the
tolerance, the more costly to manufacture.
As engineers, it is our responsibility to design and develop a part to perform
a task: and equally as important, we must design that part to be manufactured
economically. The key element to successful design is Function Analysis; the
ability to study a part thoroughly and understand what function it must perform,
then designing that part to do that job. Look at a part objectively and determine
what it has to do. Ask yourself all of the functional questions you have been
taught as engineers.
The design of a part does not have to be personal testimony to your drawing
and engineering skills, rather it should be a design to do the job and be
The following information will provide the guidelines needed for the
development of a near net shape cold formed part.
Cold Forming Precision: How Accurately Can You Make It?
The accuracy to which cold formed parts can be produced is predicated on a
number of important manufacturing conditions, the most important being:
- The type and condition of the machinery
- The accuracy of the tooling
- The quality of the material
- The type of lubricant used
Therefore, one of the most important, but neglected, procedures in the
development of a production part is the communication between the Design
and the Manufacturing Engineering.
Whether designing a part for assembly or production, talk with the engineers
as soon as you have your initial design on paper. The importance of involving
these people is multi-faceted.
They know what tolerances the machinery will hold, how efficiently it will run and
what changes will be necessary to produce your part. An added benefit sometimes
achieved is some design assistance to help make your part run the first time it
goes on the machine. Remember, they have been responsible for those machines
for years, and they know what they can do.
Now that you know what the part must do and how you are going to produce
it, keep in mind these guidelines.
- Practical tolerances on all dimensions
- Stay away from sharp comers, undercuts and chamfers
- Specific geometry
- Practical concentricity, flatness and parallelism
- Practical surface finish requirements
- Material – what is best for cold forming?
- Mechanical properties
The tolerances demonstrated on Figure 1 are typical for a production run.
Closer tolerances are obtainable, but the cost of production increases substantially.
Surface finishes produced by quality cold forming tooling are very good and
generally require no finishing other than that required to hold close tolerances.
These differences in surface finish are predicated on:
- The condition of the materia! before forming
- Substantial material savings
- The type of cold working
- The lubricant used
- The finish and condition of the tooling
Near net shapes formed to the tolerances previously mentioned can be
machined or ground to final configurations to meet a specific need.
As with cold heading and forming, the quality and precision of the finished
part is directly related to the condition and quality of the machinery.
Why Cold Forming To Near Net Shapes?
The most obvious reason for cold forming is cost savings, and this savings is
generated in a number of ways:
- Substantial material savings
- High production rates
- Added strength
- Consistent quality, because only good quality material will stand up to cold forming pressures
Selecting The Right Part For Cold Forming
The most important factor in choosing a part for cold forming.
Will the volume support the tooling and development costs? The following
size to volume recommendations are general requirements needed to
offset set-up and tooling costs while keeping prices competitive.
Will the part lend itself to cold forming? Because of the
many complex guidelines used in designing a cold formed part, I strongly
recommend that you contact an expert engineer in cold heading to assist
you. Establishing the operating sequence is very complex and requires a
strong knowledge of cold forming design perimeters, as does the design of
the tooling. Most of our suppliers have a qualified engineering staff to work
Cold forming generally produces a very strong part, but not all
materials have good. cold forming properties. Material selection will
depend strongly on the configuration of the part and the type of secondary
operations that will be required. The material selection guides (Figures 11
through 15) give a general ranking of the material for cold forming. These
rankings were developed through years of testing by National Machinery
and are considered very reliable.
Generally, cold forming will produce a more economical
part than will a material removal process. However, price is dependent
upon complexity and volume.
We sincerely hope you found this article informative and valuable.
We welcome your comments or suggestions regarding this article
or other subjects you would like to see us write about.
The Federal Group USA