29 Sep Design for Manufacture: How to design parts optimally for cold forming
Cold forming is an effective and sustainable production method for precision metal parts. By deforming the material at room temperature through force rather than heat, it’s possible to create parts with very good precision, strength and repeatability, while generating little or no waste.
Not all designs, however, are equally well suited for cold forming. The process has some distinct advantages – as well as a few limitations – which engineers should be aware of early on. With the right design for cold forming in mind, companies can speed up development, cut tooling costs and ensure high-volume production goes smoothly.
In this blog post, we will cover the key points to designing parts for cold forming, from geometry and tolerances to material and secondary operations.
Why design for manufacture matters
An old saying “design drives cost” holds especially true in precision engineering. A part that is designed without a thought will typically need extra machining, extra material or many secondary processes. Each one of these adds cost and time.
Design for Manufacture (DfM) is the opposite of this. It means designing with the production method – in this case, cold forming – at the heart of the decision-making process. A few carefully considered changes at the design stage can make the difference between a part that runs trouble-free in production, and one that is difficult, wasteful or uneconomical to produce.
Key principles for cold forming design
1. Favour simple, symmetrical geometries
Cold forming is particularly suited to produce symmetric parts. Rotational features like shafts, pins, and connectors are very simple and include such standard features as concentric diameters, chamfers, and fillets. Extreme asymmetry or feature complexity can present challenges and may require secondary machining.
Tip: If an asymmetric feature is not critical, consider if it can be eliminated, or achieved as a follow-up operation.
2. Use gradual transitions
The forming process develops stress points at sharp corners and sudden changes in wall thickness which can result in cracking and material flow issues. Gradual transitions – fillets instead of sharp corners, tapers instead of abrupt steps – allow the material to flow more smoothly, help protect tooling and result in stronger components.
3. Respect minimum and maximum wall thickness
All materials have limitations as to how thin a wall they can be formed without rupture or how thick before flow becomes irregular. Aluminium for instance can have thinner walls than stainless steel because of the greater ductility of the aluminium. If you engage a forming specialist early, you will be able to produce sheet metal parts that are within the forming capability and not have to redesign later.
4. Plan for tolerances that match the process
Cold forming can produce very tight tolerances, often on the micron level. But not all features can be equally tight. It is easy to make a cylindrical diameter to very close tolerances, for instance, but a complex non-round surface may require secondary finishing.
Rule of thumb: Apply the tightest tolerances only to functional features. Tightening dimensions everywhere just adds cost without value.
5. Consider grain flow and strength
Unlike machining, which shears through a metal part’s grain structure, cold forming maintains and enhances the flow of grain in the metal. Parts manufactured by cold forming, therefore, have excellent strength and fatigue characteristics. Engineers can take advantage of the material characteristics by orienting load-bearing features of parts in line with the grain flow patterns formed by the forming process.
6. Choose materials wisely
Cold forming is most commonly applied to ductile metals including:
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- Copper – well suited for electrical components
- Aluminium – light in weight, very malleable
- Low-carbon steels – relatively cheap, decent mechanical strength
- Stainless steels – more difficult to form, but can be used for high strength, corrosion resistant parts if designed appropriately
Some high-hardness alloys may need other processes or hybrid forming/machining approaches.
7. Account for secondary operations
Even with optimal design, some features – such as very fine threads, complex slots, or surface texturing – may need finishing operations. Designing the part so that these areas are easily accessible to machining or surface treatment tools reduces complexity later.
Cold forming also integrates well with secondary processes such as heat treatment, plating, or assembly, so factor these into the early design stage.
Collaboration is key
One of the most critical elements in cold forming design is early involvement of your manufacturing partner. At Luvata Welshpool, our engineers can model material flow using industry leading software like DEFORM to identify potential problem areas and offer design recommendations before any tools are cut, saving both time and money and increasing the likelihood that your parts will be right first time.
Through close collaboration, design engineers and forming experts can reach that sweet spot of optimal functionality, cost and manufacturability.
Real-world benefits of optimised design
Benefits to the design of parts for cold forming include:
- Material is not wasted – savings of up to 80% compared to machining.
- Cycle time is reduced – cold forming is a high-speed, high-volume process.
- Strength is improved – due to favourable grain flow.
- Cost is reduced – not only per part but across the total production process.
The result is a competitive advantage for manufacturers and assemblers, in markets from automotive to aerospace to power distribution.
Design for manufacture is more than a cost-saving exercise. It’s a way of opening new opportunities for innovation. If you have a good grasp of cold forming principles, and work closely with experienced specialists, engineers can be surprised at the new potential of their components – parts that are stronger, lighter, greener and more cost-effective to make.
At Luvata Welshpool we have assisted companies worldwide in taking products from initial design right through to high volume production using optimised cold forming design. If you would like to discuss how your components could benefit, please contact our engineering team.