Cold forging process design presents a process layout problem. Due to the variety of working procedures and the complexity of the workpiece, it is very difficult to design a cold forging process without the designer’s knowledge and experience.

The case study presented here involves finite-element analysis of a multi-stage cold forging process for a heat pipe fitting made by Zoppelletto S.p.A., an Italian company operating in the cold forged components market for more than 50 years. Cold forging is the company’s core business and in the past 30 years Zoppelletto has evolved from a craft manufacturer into an advanced industrial enterprise, able to produce millions of specialty components and guaranteeing timely production for delivery.

Production focuses on five principal sectors: thermo hydraulic, oil-pressure hydraulic, automotive, office furniture, and hardware for bolts, hinges, etc.  Zoppelletto’s technical department has at its disposal the latest CAD-CAM capabilities for manufacturing production equipment and forging tools, engineered and produced in-house. For mass production of small or medium-sized components, multi-station automatic cold forging presses are used. In cold forging, initial materials are formed progressively to final shapes by automatic and synchronized operations, including shearing, upsetting, forward and/or backward extrusion and piercing. The development of forging simulation software presented the challenge of how best to introduce its use into forging companies. Its effective introduction has required advances in the user-friendliness of the simulation software and its application to a wide range of problems.

Planning a Production Process

Because the choice of a process plan affects the design, manufacture, and maintenance of the dies, cold forging research emphasizes improvement of process planning. The design of a multi-stage forging process sequence involves determining the number of preforms along with their shapes and dimensions. The best designs for preforming operations can be identified by their ability to achieve adequate material distribution; this is one of the most important aspects in the cold forging processes.

Traditionally, forging-sequence design is carried out using mainly empirical guidelines, experience, and trial-and-error, which results in a long process development time, and high production costs. Using computer-aided simulation techniques in metal forming before physical tests may reduce the cost and time of the process design.

Many computer-aided approaches based on approximate analysis and empirically established design rules have been published.

These techniques do not always provide detailed information concerning the mechanics of the process. However, the finite-element method has been shown to provide more accurate and detailed information, and thus has been widely adopted for simulating and analyzing various metalforming processes.

Finite-element analysis (FEA) has become one of the most widely used engineering tools and has been adopted in practically all fields of industry due to advances in both software capabilities and the availability of more powerful computers.

In addition, since FEA can simultaneously predict all the necessary stress-strain states in both die and workpiece, extensive applications of this method have been reported for large-scale deformation forging processes. Many researchers have focused on the effective strain, damage and flow patterns within the workpiece during cold forging processes. However, up to now, work on the process planning of cold forging has concentrated on rotationally symmetric parts. Work on non-axisymmetric parts has not been so actively pursued, due to difficulties of shape cognition and expression, calculations of the process variables such as forming load, effective strain, effective stress, and so on.

In this study, numerical simulations were carried out for the design of a cold-forged heat pipe fitting used in thermo-hydraulic applications. The simulation was performed using the Transvalor ColdForm software. A forging experiment of the heat pipe fitting also was carried out using the designed tool set. From a comparison of the results between the simulation and the experiment, it was found that the simulation showed good agreement with the experimental result.