Profile Rolling Process Design: Case Study

The rolling process is aimed at achieving or forming a desired cross-section and required thickness by successively pinching or compressing a flat / profiled strip. The rolling process, as with all processes, needs proper design. This section presents the design of the rolling process based on the hierarchical design technique. This methodology has been used successively for designing aircraft engine components for one of the largest aircraft engine manufacturers. A sample rolling shape has been selected for the design example and is presented in this paper.

Conceptual Design: Design Matrix for Plane Rolling

The objective in a hot rolling process is to achieve a desired microstructural configuration and desired shape without violating any constraints of the process. The microstructural requirements are easily translated into mechanical properties which may be desired. The microstructural requirements can be defined by the functional requirements of the process which are related to the rolling design parameters, the strain, the strain rate and the temperature. The design parameters are dependent on the machine parameters or process parameters which can be modified by the operator. Thus, each stage of the rolling process has certain requirements, constraints and design variables. The requirements and the design parameters can be mapped in each stage and later concatenated to provide the global picture. The functional requirements, the design parameters and the process variables for hot strip rolling are listed below :

Functional Requirements - {FRs}

• thickness / shape, t
• grain size, d
• volume fraction, _

Design Parameters - {DPs}

• average strain, _
• strain rate, _
• temperature of strip, T_w
• mean stress, __m
• thickness, t

Process Variables - {PVs}

• average reduction ratio per pass, r
• number of passes, n
• roll speed, V_R
• starting strip temperature, T_B
• roll force, F
• back tension, f_b
• front tension, f_f
• friction, _
• roll diameter, R

Preliminary Design

A software package developed at Ohio University for the design and analysis of the rolling process, ROLLCAD2.0, is employed for the preliminary design stage. ROLLCAD2.0 is a design tool which works within the AutoCAD environment and offers the versatility of the AutoCAD drafting features combined with the geometric and analyses tools of the software package. Moreover, the ROLLCAD2.0 execution time is extremely small which makes it ideal for conducting a parametric study, or to obtain quick results on a shop floor, or to conduct preliminary design studies as presented in this paper. ROLLCAD1.0 has various design and analysis modules which were utilized in this design process. They include :

• Process Design : consists of geometric design tools for generating roll pass designs, preform designs, or to generate intermediate pass designs. Roll pass designs are initiated at this stage and are fine tuned after further analysis. The geometric design tools include area/volume mapping, thickness mapping, lateral material flow mapping, etc.
• Material Sizing : Based on the information from the geometric models in the process design stage, the raw material configurations and the final material sizing are determined. This tool permits the designer to plan ahead of time and order raw materials according to the machine specifications.
• Analysis Models : After roll pass designs, analyses models employing a modified slab analysis approach for simulating the profile rolling and ring rolling processes are used. Results from these analyses modules are employed for the initial design and to tweak roll pass designs to meet all the requirements.
• FEM Interface : Upon completion of the preliminary design, a finite element interface can be invoked to generate an FEM model for the final analysis.

ROLLCAD2.0 was employed to generate the roll pass design for the profile shown in figure 2. A 0.5" thick starting stock was selected for the profile rolling process. Based on the workability limit of the material and the roll force requirements, a two pass rolling operation was employed. This software package has been validated with actual experiments and predicts results within 5-10% of the experimental ones. Therefore, this software package has a great deal of reliability in predicting the material hardness, workability limits, roll force, and the temperature. However, finite element model needs to be invoked to determine the material fill and for the confirmation of the design.

Final Design

The final design stage employs finite element analysis of the rolling process. A 0.5" thick and 2.8" wide rectangular stock was employed as the starting material. A two pass rolling operation was designed to achieve the desired shape. The objective of the finite element analysis is to determine the material fill, which is one of the most important criteria in profile rolling. Moreover, the roll pass design is also confirmed using finite element models. Finite element models are quite accurate (about 3-5%) and provide an accurate local distribution of process parameters. Lack of material fill in figure 4 results from insufficient elements along the circular portions. However, the material fill for the design looks acceptable for this situation and therefore, an optimal design is achieved.

To see the resume of the expert associated with this case study, see the link below.