Introduction
The cold forming industry operates in a highly competitive environment, driven by increasing demand in terms of quality and cost efficiency. Stricter tolerances, combined with zero-defect requirements imposed by industrial customers, rising raw material costs, and growing competition from Asian manufacturers, are forcing companies to rethink their process development and manufacturing validation strategies.
Traditional approaches based on trial and error, pilot production runs, and the scrapping of defective parts are no longer viable. They are slow, costly, and provide only limited understanding of defect origins, let alone reliable ways to eliminate them.
It is precisely to address these challenges that the finite element simulation software solutions, FORGE® and COLDFORM®, provide a decisive competitive advantage. By enabling the simulation of the entire cold manufacturing process, from billet to finished part, COLDFORM® gives engineers a level of process visibility that physical trials alone cannot achieve.
This article illustrates these capabilities through the example of a type of fasteners widely used across industries such as automotive, energy, and aerospace: hexagonal nuts.
Simulation of Multi-Stage Cold Forming of Hexagonal Nuts
Cold forming of hexagonal nuts involves several successive forging stages, each imposing a specific deformation on the part. Accurately reproducing such a manufacturing sequence through simulation requires precise material characterization, appropriate lubrication conditions, an accurate description of press kinematics, and a correct transfer of the part state between each stage. COLDFORM® addresses all these requirements. Tool geometries can be directly imported from CAD models. Material behavior can be defined using plastic flow curves from the software’s integrated database, covering more than 200 ferrous and non-ferrous alloys.
At each deformation stage, COLDFORM® simultaneously computes plastic deformation, friction-induced heating, and cooling through contact with the tooling, while ensuring the transfer of the mechanical state between successive stages. This continuity enables the representation of the accumulation of plastic strains, residual stresses, and work hardening throughout the process.
Detection and Diagnosis of Surface Defects in a Numerical Framework
By analyzing the distribution of contact pressures over the entire surface of the simulated part, engineers can immediately identify, at each forging stage, laps and underfilling zones within the tooling.
In the case of hexagonal nut manufacturing, this type of analysis typically highlights two categories of laps: those induced by the hexagonal geometry on the outer edges of the bearing face, and more subtle internal laps linked to material backward extrusion during the final forming stage. These latter defects are particularly difficult to detect and are a common cause of scrap at the end of production.
The marker grid functionality in COLDFORM® enables accurate tracking of material flow paths and the identification of surface defects related to flow behavior. It highlights regions where the flow pattern and dynamics promote local accumulations of material or lubricant, which may degrade the final surface condition, particularly on the bearing faces of nuts.
From Diagnosis to Process Optimization
The identification of a defect is only a first step. The main industrial challenge lies in the ability to quickly test corrective solutions without relying on costly physical trial campaigns. COLDFORM® allows to turn the analysis of a process-related issue into a systematic exploration of geometric and parametric variants. Starting from an initial configuration, different preform geometries or intermediate stages can be compared in order to assess their influence on material flow, die filling, and deformation stability. These results can be directly reused for similar product families.
Validation can then be extended to final operations such as piercing, where simulation allows tracking damage initiation and its propagation up to fracture.
Simulation of Fasteners with Integrated Functional Features
In certain fastener families, the primary mechanical fastening function is complemented by an integrated locking mechanism directly incorporated into the part geometry. Locking nuts with polymer inserts illustrate this principle, where a nylon element is brought into a constrained state within a cavity of the nut during a dedicated deformation stage.
The functional behavior therefore depends not only on the final geometry of the nut, but also on how the metallic material comes into contact with and compresses the insert during the forming process. The local distribution of forces and the closing kinematics become determining factors.
COLDFORM® enables this interaction to be represented by simultaneously tracking the deformation of the metallic wall and the response of the insert within the contact zone. The analysis focuses on the progressive evolution of pressure zones and the effective closure of the functional cavity. Several tooling configurations can then be tested to influence the location of contact regions and the way the material envelops the insert at the end of the cycle. This approach thus makes it possible to assess the influence of tool geometry on the final behavior of the part.
Conclusion
Cold forming of hexagonal nuts involves complex deformation sequences in which material flow and contact conditions directly determine the final quality of the parts. Surface and filling defects remain difficult to control without a detailed analysis of the process. COLDFORM® enables the simulation of the entire manufacturing chain, the identification of critical regions, and a better understanding of defect origins through deformation fields, contact pressures, and forming loads. Using numerical simulation with a tool such as COLDFORM® facilitates tooling and forming condition optimization while reducing physical trials, thereby helping to lower scrap rates and secure nut production.
