To address the machining challenges associated with the weak rigidity of the ore washer's thin-walled drum-specifically its susceptibility to deformation and chatter during clamping and machining, which compromises surface quality-finite element analysis was employed to optimize the design of a rational, cost-effective, and efficient support fixture. This initiative improved the manufacturing process for the thin-walled drum, enhanced machining efficiency, and effectively reduced production costs.
01
Introduction
The ore washer is a vital piece of equipment in mineral processing, typically utilized during the preparatory stage-prior to crushing, magnetic separation, and flotation-to wash clay lumps or gravel from the ore. The 2.1m × 4.5m ore washer featured in this project was custom-designed and manufactured for an overseas client. Its structure comprises several key components, including the feed section, drum section, drive assembly, support roller assembly, thrust roller assembly, and gear housing; the drum itself is the core component of the machine. A primary structural characteristic of this drum is its thin wall-measuring only 12 mm in thickness-classifying it as a thin-walled, low-rigidity drum compared to standard drum-type components. The central challenge in machining such low-rigidity drums is their lack of stiffness, making the control of deformation critical [1, 2]. During clamping and machining, the drum is prone to chatter, which can lead to dimensional and geometric tolerance deviations [3] and impair surface quality. Furthermore, there is a discrepancy between the drum's state during machining and its state during actual operation: while clamping involves securing the ends, the drum is supported by two riding rings (tires) during service.
Conventional solutions for machining low-rigidity drums focus on enhancing rigidity to minimize deformation caused by machine clamping forces and cutting forces. Our company previously manufactured an ore washer with a similar structure in 1995; however, due to the technological limitations of that time, the analysis of the thin-walled drum's rigidity relied largely on past experience and was limited to qualitative assessment. The process plan at that time involved designing a support fixture to reinforce the drum's rigidity; this fixture utilized a clamp-like structure secured around the outer circumference at both ends of the drum, supplemented by axial supports placed against the inner wall. With the aid of this tooling, the rigidity of the cylinder was enhanced, allowing the machining and manufacturing process to be successfully completed. However, the tooling weighed 2,035 kg-nearly as much as the ore washer cylinder itself (2,813 kg)-resulting in poor economic efficiency.
02
Structure of the Thin-Walled Ore Washer Cylinder
The cylinder is a key component of the ore washer assembly, featuring an integral welded structure where the cylinder wall is welded to the end caps. The internal rib structures differ between the two ends: the feed end has a larger opening, a greater number of ribs, and a relatively complex structure; the discharge end has a smaller opening, fewer ribs, and a simpler structure. The cylinder wall is made of Q345B steel with a thickness of 12 mm, a maximum outer diameter of 2,124 mm, a length of 4,819 mm, and an inner diameter of 2,100 mm; it weighs 2,813 kg. The areas requiring machining include the two outer cylindrical surfaces (Outer Diameter 1 and Outer Diameter 2) that interface with the riding rings, as well as the flange face at the feed end (see Figure 1). For Outer Diameters 1 and 2, the dimension is Φ2,124 mm, with a perpendicularity to the end face of 0.025 mm, a coaxiality of Φ0.15 mm, and a surface roughness of Ra = 3.2 μm.
Figure 1: 3D Model of the Cylinder
03
Optimization of the Support Tooling Scheme for the Thin-Walled Ore Washer Cylinder
3.1 Technical Approach for the Cylinder Tooling Scheme
Autodesk Inventor software was used to perform finite element analysis (FEA) on the cylinder to comprehensively evaluate its rigidity. Deformation simulations were conducted for both the cylinder's self-weight state and the state in which it is clamped on the machine tool. Based on the deformation analysis results, a manufacturing process plan was devised, the tooling structure was optimized, and a novel cylinder support tooling design was developed.
3.2 Finite Element Solid Modeling of the Cylinder
A 3D model was constructed using an "inside-out" approach based on the cylinder's structural configuration. During modeling, the cylinder structure was simplified, and the following assumptions were made:
1) The support components at both ends of the cylinder possess sufficient rigidity.
2) Defects such as incomplete fusion or cracks in the cylinder welds are not considered. 3) Material property changes at the cylinder weld seams are disregarded; the weld material is assumed to be identical to the base material [4, 5].
3.3 Load Calculation and Boundary Condition Setup
During the calculation process, the external loads acting on the cylinder consist primarily of two components: the structural weight of the cylinder itself and the clamping force exerted by the machine tool center. Based on component parameters and machine tool specifications-and after consulting the machine tool manual-the clamping force of the center was determined to be 20 kN.
Drawing on manufacturing experience with cylindrical components, the depth of cut during machining is minimal, and the impact of cutting forces is negligible; therefore, the effect of cutting forces on cylinder deformation is not analyzed. Based on this comprehensive analysis, the boundary conditions and load settings for the cylinder are established as follows:
(1) Cylinder Loads: Two load cases are considered. First, in the static state, only the cylinder's own weight is taken into account. Second, in the machine-clamped state, the clamping force from the machine tool center and the gripping force from the chuck jaws are considered; all other loads are disregarded.
(2) Boundary Conditions: In the static state, vertical displacement at both ends of the cylinder is constrained while axial displacement is left free to calculate the cylinder's self-deformation. In the machine-clamped state, axial and radial displacements are constrained at one end, while vertical displacement is constrained and radial movement is left free at the other end, simulating the loading conditions while clamped in the machine tool.
3.4 Finite Element Analysis of Cylinder Deformation
(1) Deformation in the Static State: Gravity is applied to the cylinder, and finite element analysis is used to calculate the deformation along the X, Y, and Z axes; details are shown in Figures 2 through 4.
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Figure 2 Deformation of the cylinder along the X-axis in the static state
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Figure 3 Deformation of the cylinder along the Y-axis in the static state
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Figure 4 Deformation of the cylinder along the Z-axis in the static state
(2) Deformation in the Machine-Clamped State: Axial and radial loads are applied to the cylinder, and finite element analysis is used to calculate the deformation along the X, Y, and Z axes while clamped in the machine tool; details are shown in Figures 5 through 7. Figure
Figure 5: Deformation of the cylinder along the X-axis while clamped
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Figure 6: Deformation of the cylinder along the Y-axis while clamped
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Figure 7: Deformation of the cylinder along the Z-axis while clamped
The finite element analysis results for the cylinder model-both in its static state and during the clamped machining state-are presented in Table 1.
Table 1: Finite element analysis results for the cylinder under different conditions (Unit: mm)
Figure
Data analysis, comparison, and study led to the following conclusions: the cylinder exhibits minimal deformation in its static state, whereas significant localized deformation occurs at both ends of the cylinder during the clamped machining process.
04
Support tooling scheme and verification process for the thin-walled ore washer cylinder
4.1 Optimized tooling scheme
Based on the low-rigidity characteristics of the cylinder, a new support tooling scheme was designed (see Figures 8 and 9). This tooling scheme consists of a set of four annular supports installed at the less rigid sections of the cylinder's inner wall. The outer diameter of the annular supports is adjustable to facilitate installation, and the tooling weighs 150 kg. Each annular support is composed of three arc-shaped plate segments, connecting plates, bolted fasteners, and wedges. Adjacent arc segments are bolted together; the outer diameter can be locally adjusted by varying the spacing between the connection holes. Once adjusted, the assembly is tightened using wedges and then fully secured with the bolted fasteners.
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Figure 8: Cylinder support tooling
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Figure 9: Installation scheme for cylinder support tooling
1-Shim plate 2-Machine tool tailstock end 3-Tailstock center
4-Annular support tooling 5-Workpiece 6-Chuck jaw 7-Machine tool headstock end
To ensure the thin-walled ore washer cylinder does not deform during machining, the following measures must be taken:
1) During the welding of the cylinder blank, the annular support tooling is welded to the inner wall of the cylinder; following the welding process, the cylinder-along with the annular supports-undergoes stress-relief annealing in a furnace. Since the annular support is welded to the cylinder body prior to annealing, the inherent rigidity of the cylinder is enhanced, thereby preventing deformation during the stress-relief annealing process.
2) Four backing plates were installed on the chuck at the headstock end to support the cylinder's end face, ensuring the clamping jaws gripped the cylinder's outer surface at the required location. A set of annular support fixtures was installed on the inner wall directly opposite the contact points between the clamping jaws and the cylinder's outer surface to prevent deformation caused by the clamping force. A process block was designed for the interface between the workpiece and the tailstock center; the design requirements for this block were that its external dimensions must accommodate the machining of the center hole, and the center hole itself had to be specified based on the machine tool's center angle and the workpiece's mass.
4.2 Verification Process
Following the implementation of the aforementioned process measures, a trial machining run was conducted after clamping the cylinder onto the machine tool. Dial indicators were used to check the cylinder's runout; the alignment accuracy was found to be less than 1 mm, fully satisfying the requirements of the machining plan. This alignment accuracy was essentially consistent with the precision of the welded cylinder blank, confirming that deformation during the clamping process was minimal. The cylinder machining process and the finished component are shown in Figures 10 through 12.
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Figure 10 Rough and finish machining of the cylinder
Figure 11 Process block at the interface with the machine tool center
Figure 12 Finished cylinder
By adopting the optimized cylinder support tooling scheme, the thin-walled cylinder for the ore washer was successfully manufactured. Inspection confirmed that all precision parameters met the drawing specifications. The optimized support scheme was validated in practice, which also confirmed the accuracy of the finite element analysis (FEA) results for the cylinder.
05
Conclusion
Through finite element analysis, the rigidity analysis of the ore washer's thin-walled cylinder was elevated from an empirical, qualitative approach to a quantitative one. This effectively improved the design quality of the manufacturing process and resulted in an optimized support tooling solution that is rational, cost-effective, and efficient. Practical verification demonstrates that this approach effectively reduces processing costs and shortens manufacturing cycles; it provides a scientific basis for the production of similar products and offers a valuable reference for other comparable items.
