FORGING OF NON-FERROUS ALLOYS
A broad range of industries have come to rely on a steady supply of forged components in aluminum, copper and titanium non-ferrous alloys. More specifically the automotive and aerospace industries make heavy use of 6000 and 7000 series aluminum alloys, the consumer goods and industrial machinery (including plumbing supplies) industries rely heavily on parts forged in copper alloys such as brass, and the electronics industry makes use of forged copper components.
Forging of Aluminum Alloys
The 6000 and 7000 series of aluminum alloys have good mechanical properties, including high strength-to-density ratio, fatigue strength and resistance to corrosion, combined with excellent formability and machinability. Their formability qualities make it easy for them to be forged into aerospace and automotive parts.
The process takes one or more forging steps using a mechanical or screw press and this is followed by a flash trimming operation. Aluminum riveting and clinching are also very popular manufacturing processes for the automotive and aerospace industries, thanks to their lightness and reliability.
Forging of Copper Alloys
Copper alloys such as brass (CW617N and CW602N) are more commonly used in consumer goods and industrial machinery because of their extreme ductility and machinability and the fact that most of the scrap metal can be reused making them a very economical option for large scale production. On the down side, lead is often added in small concentrations (around 2%) to the alloy to enhance its machinability. The use of lead can pose a potential danger to drinking water when brass alloy is used for pipes and other plumbing components; new lead-free brass alloys such as CW510N also known as “Eco Brass®” have been introduced to avoid this issue but its ductility is obviously decreased.
The hot forging of brass, even when forging a hollow component with multiple holes, is usually performed in a single operation resulting in complex press kinematics (usually mechanical, knuckle or link-drive, and able to drive several punches simultaneously, commonly using a floating lower die).
Common Forging Defects in Non-ferrous Alloy Forging
Typical defects resulting from the hot forging of brass are under-fillings and superficial defects such as laps and folds (commonly near the punch head, where the material flow separates, but also as a result of the punch extraction, often resulting in a backwash).
The high formability of both aluminum and copper-based alloys combined with a complex shape of the die print often lead to gas entrainment in the forging process. The flash trimming management can also be a little tricky when dies are designed to prevent the flash from extending excessively in a radial direction. In such cases the flash often buckles creating laps.
Virtually Simulating the Non-ferrous Alloy Forging Process
The complex shape of the parts that are forged in non-ferrous alloys makes remeshing a very challenging and time consuming process. The complex kinematics of the tools (dies and punches) and the very thin layer of flash for these components further increase the challenge, with often 1+ million finite element meshes at the end of the computation. To keep total simulation run times within a few hours it is imperative that a scalable solver is used.
The choice of simulation software for the non-ferrous alloy forging process is very important. The software must be able to simulate press kinematics with the highest degree of fidelity which means it needs to include data for different mechanical presses (standard, knuckle, line-drive …) with floating dies and synchronized punches kinematics. It must include a large library of materials models including the most common classes of aluminum such as 6061, 6082 and 7075 and brass varieties such as CW617N and CW602N.
A good industrial example that illustrates how new numerical developments are helping design by simulation take over the “trial and error” design methods is the aluminum and titanium riveting process. New contact and friction algorithms as well as new damage and fracture criteria for material modeling now allow designers to take into account residual stresses and the damage of the rivets during the manufacturing process, therefore allowing greater precision and reliability in the structural design of the final component.
The initial single process simulations of the forging process are now giving way to automatic design optimization which produces more efficient results and better productivity. Using this method engineers can define their optimality criteria (minimum material volume, minimum die wear, …), their constraints (no under-fillings, keeping force of press below a given value …) and modifiable parameters (billet shape or position, process parameters such as temperature range or kinematics, …) and allow the optimization software to experiment with all the data input until an optimal output parameter is reached.
The Advantages derived from Virtually Simulating the Non-ferrous Alloy Forging Process
To simulate the non-ferrous alloy forging process means to minimize production defects through a better understanding of the material flow in the die cavities. Engineering Simulation of the process allows engineers to:
- test different configuration with changes in the billet dimension, its position with respect to the dies, the dies shape, all without having to physically produce the dies and test them in the real world
- increase collaboration with the customer who can evaluate and approve the proposed changes in the design on the basis of objective evidence provided by the software
- improve part quality, starting from the geometry to the elimination of folds and internal defects
- reduce scrap material (not so important for brass parts, where most of the flash is recycled)
- improve the die life by decreasing punches and insert stresses, deflection and wear
- make the correct press choice, avoiding overloading and balancing action on the press components
- reduce the time-to-market of the final product
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"The significant advantages obtained through simulation on a piece already in production have led us to use this innovative approach in the design of prototypes as well ... EnginSoft helped us to understand that simulation can give a significant boost to our competitiveness."
Fonderia Fratelli Maspero