Generative Design of an EV Subframe and Validation for Manufacture

The problem

EV subframes carry the drive unit and suspension loads and must be light, stiff and cheap to make. Topology and generative methods suggest efficient forms, but the gap between an optimised shape and a part that a foundry or fabrication shop can make is where most of the benefit is lost. A method that links process choice to optimisation and validation is valuable to industry.

Objectives

• Define a subframe design space, load cases and process-specific controls.
• Generate concepts with Topology Studies for different processes and goals.
• Reinterpret each concept into a manufacturable parametric design.
• Validate designs for stiffness, strength, frequency and fatigue indicators.
• Compare processes for mass, performance and manufacturability, and quantify the loss from reinterpretation.

What you need

Key concepts

Generative design

Automatic generation of many design options from goals and constraints. In SOLIDWORKS desktop, the practical route is Topology Studies with manufacturing controls, run for several goals and processes.

Process-aware controls

Constraints that reflect how the part will be made, such as demould direction for casting or a constant section for extrusion. They narrow the gap between optimised and buildable shapes.

Reinterpretation loss

The change in mass or stiffness between the raw optimised result and the final parametric part. Measuring it tells you how much of the theoretical benefit is real.

Hard points

Fixed mounting locations for suspension, drive unit and body. They are preserved regions in the optimisation and must not move.

Step-by-step guide

1. 1

   Define requirements and hard points

   Define an example front subframe for a compact EV: suspension lower-arm pivots, drive-unit mounts, steering rack mounts and body attachment points as hard points. Collect example load cases such as vertical bump, braking, cornering, drive-unit torque reaction and a kerb strike. Set targets for mounting point stiffness, first frequency and factor of safety. Record packaging envelopes from neighbouring parts. Keep the coordinate set in a layout part used by every design.

   Checkpoint: A requirement document with hard point coordinates, load cases and targets, all marked as example values.

2. 2

   Build a baseline and design space

   Model a conventional baseline subframe, such as pressed steel side members and cross tubes, and analyse it to set reference values for mass and stiffness. Then build a design-space solid that fills the packaging envelope around hard points, checked with Interference Detection against drive unit, rack and body. Preserve material around every hard point with a margin for bushes and bolts.

   Checkpoint: Baseline mass and stiffness values, and a design space that passes Interference Detection.

3. 3

   Run Topology Studies per process

   Run Topology Studies with all load cases for three process families. For casting, add a demould direction and a minimum thickness. For extrusion-and-weld, use symmetry and look for straight load paths that suit constant sections. For sheet fabrication, use a thin-walled interpretation with symmetry. Use both Best Stiffness to Weight and Minimize Mass with displacement constraints. Use the same mesh size and load cases for every run so the results are comparable across processes.

   Checkpoint: At least six topology results (three processes by two goals) stored with their settings.

4. 4

   Check robustness of the results

   Vary mesh size, mass target and preserved-region margins for one process and see whether the main load paths stay the same. Load paths that appear in every run are robust; members that come and go are sensitive to settings. Record this so reinterpretation keeps robust paths and treats others as optional. Overlay exported meshes from different runs in one part to see the common load paths clearly. Save screenshots from the same view for each variant.

   Checkpoint: A robustness note identifying load paths present in all variants.

5. 5

   Reinterpret for casting

   Model a cast aluminium subframe with ribs and walls along the robust load paths, uniform wall thickness where possible, fillets and draft. Use Draft Analysis to check draft against the demould direction and Undercut Analysis for undercuts. Keep the part parametric so rib thickness and wall can change. Record mass against the raw topology mass. Keep minimum wall thickness at or above the value advised by the foundry, and add machining allowance on mounting faces.

   Checkpoint: A cast design that passes draft and undercut checks, with its reinterpretation loss in mass recorded.

6. 6

   Reinterpret for extrusion and sheet

   Build a second design from extruded aluminium members along straight load paths, joined with cast or machined nodes at hard points, using Weldments for members. Build a third design as pressed sheet halves welded into box sections using Sheet Metal. Check weld access, flat patterns and bend radii. Record mass for each. Use simple, constant sections for extrusions so that one die serves several members, and keep weld lines away from peak-stress regions found in topology.

   Checkpoint: Two further parametric designs with flat patterns or cut lists, and recorded masses.

7. 7

   Validate structurally

   For each of the three designs and the baseline, run Static studies for all load cases with the same fixture and loading method, Frequency for the first modes with drive-unit mass included, and a mesh convergence check at peak stress locations. Compute mounting point stiffness by applying unit loads at each hard point. Compare everything with the targets. Use identical mesh settings and refinement criteria for all four designs.

   Checkpoint: A validation table for four designs showing stiffness, stress, frequency and convergence results.

8. 8

   Assess fatigue and joints

   For a repeated bump or cornering load, run a Fatigue study with appropriate S–N data for each material, or a hand stress-life check if Simulation Professional is not available. For welded designs, note that weld fatigue follows weld detail categories in codes and that Simulation's parent-material S–N is not sufficient. Identify which design has the most fatigue-critical joints. Mark fatigue-critical locations on the drawings so they can be inspected on prototypes.

   Checkpoint: Fatigue indicators for each design, with the method and data sources stated.

9. 9

   Assess manufacturability and cost

   Run DFMXpress for basic rules and, if available, SOLIDWORKS Costing with consistent templates for casting, weldment and sheet metal. Record tooling needs, number of parts, weld length and inspection features. Where a supplier has given guidance, compare designs against it. Where not, state the assumption. Note lead time for tooling, since a casting tool can take much longer than a fabrication jig. Record any feature that a supplier would need to change before quoting. Keep cost results relative, because absolute values depend on templates.

   Checkpoint: A manufacturability table with cost estimates, tooling and part count for each design.

10. 10

    Compare and quantify the method

    Compare baseline and three designs on mass, stiffness, frequency, fatigue indicators, cost and part count. Quantify the reinterpretation loss for each process as the gap between raw topology and final validated mass at equal stiffness. Discuss which process kept most of the benefit and why, linking it to how well the process controls matched the final features. Plot each design on a mass against stiffness chart along with the raw topology points.

    Checkpoint: A comparison table and a reinterpretation-loss chart for each process.

11. 11

    Document and recommend

    Write the method as a repeatable procedure: requirements, design space, process-aware optimisation, robustness check, reinterpretation and validation. Include drawings of the recommended design with GD&T on hard points per ASME Y14.5 or ISO GPS. State limits: linear static and modal analysis, no crash or bush nonlinearity, and the need for physical rig tests to confirm stiffness and fatigue. Give the recommendation with conditions, such as production volume, under which another process would win.

    Checkpoint: A method document, a recommended design drawing with GD&T on hard points and a list of required physical tests.

Testing & validation

• Robust load paths identified across settings.
• All designs validated with the same load cases and convergence checks.
• Mounting point stiffness compared with targets.
• Draft, undercut, weld access and flat patterns checked per process.
• Reinterpretation loss quantified for each process.

Expected results

A documented process-aware generative method for an example EV front subframe, three validated manufacturable designs (cast, extruded and welded, pressed sheet), a baseline comparison and a measure of how much optimisation benefit each process keeps.

Take it further

• Compare SOLIDWORKS Topology results with a dedicated generative design tool on another platform for the same problem.
• Build a printed scale model of the recommended design and measure stiffness on a simple rig.
• Add bush stiffness and drive-unit dynamics with a Frequency study of the full assembly.

Viva and review questions

Learn it at DIYguru

These DIYguru courses and programmes teach what this project needs.