Studies have shown that the majority of forgers have adopted process simulation as an engineering tool.  As simulation matured, users moved from modeling unit processes to sequential processes.  Sequential processes were simulated in a manual, operation-by-operation procedure.  This could become time-consuming when many process or design variations had to be evaluated.  This was particularly true when variations came early in the sequence. 

Recent software developments have removed this obstacle.  Easy-to-use, multiple operation (MO) modeling tools now allow automated simulation of sequential processes.  This permits efficient modeling entire manufacturing process chains.

In the early days of forging simulation (1980s), ‘state of the art’ models were limited to one operation. A single-hit connecting rod platter (Figure 1) is a good example of a typical unit process.  The introduction of simulation allowed companies to predict part shape, die fill, defects, forming loads and die stresses.  No longer did manufacturers have to rely strictly on skill, experience and trials when developing processes.  Simulating an individual process was efficient and generally informative.

A deficiency with the unit process approach is that the initial workpiece starts with no prior processing history.  The initial geometry represents a “target” shape, not the actual shape output from the previous operation.  Mechanical, thermal and microstructural history is also missing.  These variables are important because they influence flow stress, which characterizes how the material plastically deforms. 

A more accurate solution was possible by capturing the effect of each operation on subsequent ones.  Thus, users began simulating operation sequences from their manufacturing process chain.

An automotive suspension component forged by LC Manufacturing provides an example of a sequential process.  Cross-wedge rolling was used to roll a billet into a preform that was then forged on a hammer.  A single simulation modeled the heat transfer, rolling and forging operations involved.  This permitted the geometrical, mechanical and thermal history from rolling to influence how the material flowed when forged. 

Simulation results (Figure 2) accurately predicted the part shape, flash, and die fill relative to the actual parts (Figure 3.)

Many products follow a similar process chain on their journey from raw material to final application. (Figure 4.)  First, an ingot is cast and then may be cogged, rolled, drawn or extruded down to a size suitable for manufacturing.  Billets and rings are cut from stock and used in forming operations. 

Primary forming operations may include forging, ring rolling, or shape rolling.  Then, parts may be heat-treated or machined to particular specifications.  Lastly, they are fastened or welded into assemblies that are tested and put into service.

For a given material, part performance in service is determined by its final geometry, residual stress state, and mechanical properties.  A part’s mechanical properties are the result of its chemistry, process and microstructure.  In an ideal world, it would be possible to simulate how the geometry, residual stresses and microstructure evolve through an entire process chain.  Then, it would be possible to predict the effect that manufacturing changes have on final part performance and life.