The problem
Motor housings in EVs carry bearing loads, mount the motor to the vehicle and often contain a coolant jacket, all in a thin-walled casting. A design that ignores casting rules leads to porosity, hot tears and machining scrap, while one that ignores loads cracks at mounts. Combining structural and casting thinking at the design stage is a practical M.Tech-level skill.
Objectives
- Model a housing with stator bore, bearing seats, mounting feet and a cooling jacket.
- Apply casting rules: draft, uniform walls, fillets, ribs and machining allowance.
- Analyse bearing loads, mount loads and thermal stress with SOLIDWORKS Simulation.
- Check frequencies to avoid resonance with motor and road excitation.
- Review castability qualitatively and document machining and casting drawings.
What you need
Tools and toolboxes
- SOLIDWORKS Part with Configurations — As-cast and as-machined configurations of the same housing with draft, ribs and machining allowance.
- Draft Analysis and Thickness Analysis — Check draft and find thick sections; Thickness Analysis is part of SOLIDWORKS Utilities, so use section views if your licence lacks it.
- SOLIDWORKS Simulation (Static, Frequency) — Bearing and mount load cases, and natural frequencies of the housing.
- SOLIDWORKS Simulation (Thermal) — Steady-state temperature from stator losses with convection to the coolant jacket; thermal studies need Simulation Professional or Premium.
- SOLIDWORKS Flow Simulation (optional) — Coolant flow and pressure drop through the jacket.
- SOLIDWORKS Drawings — Casting and machining drawings with datums, draft notes and machining allowance.
Software
- SOLIDWORKS 2023 or later
- SOLIDWORKS Simulation Professional or Premium
- SOLIDWORKS Flow Simulation (optional)
Extra parts and data
- Casting alloy datasheet — Mechanical and thermal properties of a die-cast or gravity-cast aluminium alloy, which differ from wrought alloys in the default library.
Key concepts
- Directional solidification
- A casting should solidify from thin far regions towards thick regions near the feeders, so shrinkage is fed by liquid metal and porosity is avoided.
- Hot spots
- Thick junctions that solidify last and tend to shrink and form porosity. They are reduced with coring, uniform walls and fillets.
- Machining allowance
- Extra material on surfaces that will be machined, such as bearing seats and mounting faces, so cast surface defects and draft are removed.
- Shrink fit stresses
- A stator pressed or shrunk into the housing creates hoop stress in the housing wall, which adds to service loads.
Step-by-step guide
- 1
Set requirements and loads
Define an example motor: stator outer diameter 200 mm, stack length 120 mm, two bearings, a foot or flange mount, and a water-glycol jacket. List loads as example values: radial bearing loads from a belt or gear drive, motor torque reaction at the mounts, a 5 g vertical shock, and stator losses of about 1.5 kW as heat. Choose a casting process, such as high-pressure die casting or gravity casting, because it sets minimum wall and draft.
Checkpoint: A load and requirements table with process, material, loads, temperature limits and a target factor of safety.
- 2
Model the as-machined geometry
Model the housing as finished: stator bore with interference fit tolerance, bearing seats with shoulders, mounting faces and holes, and a sealing face for the end cover. Use global variables for wall thickness, stator diameter and stack length so the housing can be resized. Create the cooling jacket as a helical or axial channel by a sweep cut or by splitting into an inner and outer shell.
Checkpoint: A fully defined as-machined model driven by global variables, rebuilding without errors when stack length changes.
- 3
Create the as-cast configuration
Add a configuration for the as-cast part: add machining allowance on every machined face, apply draft to walls along the die opening direction, add generous fillets at junctions and core out thick bosses. Keep walls close to a nominal thickness, for example 5 mm, and transition gradually. Use Draft Analysis with the pull direction to confirm draft and Thickness Analysis, or section views, to find thick regions.
Checkpoint: Draft Analysis passes at the minimum angle and no region exceeds about 1.5 times the nominal wall without a stated reason.
- 4
Add ribs and mounts
Add ribs from the mounting feet to the bearing bosses to carry torque reaction and shock, with drafted sides and a rib thickness below the wall thickness. Add fillets at rib roots. Model end-cover bolt bosses with cored holes where practical. Keep ribs aligned with the die opening if possible to avoid side cores, and record any that need one.
Checkpoint: Ribs connect the load path from bearings to mounts with no undrafted faces.
- 5
Run static load cases
Assign a casting aluminium alloy from the datasheet as a custom material. In a static study, fix the mounting holes using bolt connectors or fixed faces, apply bearing loads with Bearing Load on the seats, motor torque as a moment, and a separate 5 g shock case with remote masses for the stator and rotor. Add mesh control at rib roots and bearing seats and refine the mesh until peak stress changes by less than about 5 per cent.
Checkpoint: Converged stresses with factor of safety above the target for each case, and bearing seat deflection under a stated limit.
- 6
Check frequencies
Run a frequency study with the same fixtures and remote masses. Find the first few modes and compare them with excitation sources: motor electrical frequency at speed, gear mesh frequency and road input. If a mode is close to a strong excitation, stiffen ribs or change the mount. Record mode shapes as images for the report. Use the same mesh controls as the static study and confirm the first frequencies change by less than about 2 per cent with a finer mesh.
Checkpoint: No housing mode falls within a stated margin of a main excitation frequency at operating speeds.
- 7
Run a thermal study
In a thermal study, apply the example stator loss as heat power on the stator bore contact, a convection coefficient on the jacket walls for the coolant and natural convection on the outer surface. Use a thermal contact resistance at the stator interface. Run steady state and check housing temperature. Then import the temperature field into a static study to see thermal stress combined with the shrink-fit pressure.
Checkpoint: Peak housing temperature is under the alloy's limit and the combined thermal plus mechanical stress keeps factor of safety above the target.
- 8
Check coolant flow (optional)
In SOLIDWORKS Flow Simulation, create an internal flow project with the jacket lids, set an inlet volume flow, an outlet environmental pressure, and water-glycol as the fluid. Run and check pressure drop and velocity distribution. Look for dead zones where velocity is low and redesign the channel if needed. Check the solution with a goal convergence plot and a mesh refinement.
Checkpoint: Pressure drop within an example pump budget and no large stagnant zones in the jacket.
- 9
Review castability
Without a dedicated casting simulation tool, do a structured qualitative review: sketch a modulus map (volume to cooling surface ratio) of main sections, check that sections thicken towards where the feeders or gate would be, and identify hot spots at rib and boss junctions. Propose gate and feeder locations. If your institute has casting simulation software, run it and compare. Record redesigns such as extra coring or fillets.
Checkpoint: A castability review with a modulus sketch, proposed feeding, hot spots identified and the changes made.
- 10
Drawings and report
Create a casting drawing from the as-cast configuration with draft notes, parting line, general casting tolerances and critical cast surfaces, and a machining drawing from the as-machined configuration with datums, GD&T on bearing seats and the stator bore, and surface finish. Write the report with loads, convergence, results, castability review and limitations, stating that results need physical validation such as strain gauge or modal tests.
Checkpoint: Two linked drawings and a report covering structural, modal, thermal and castability results with stated limitations.
Testing & validation
- Mesh convergence on peak stress within about 5 per cent.
- Hand check of bearing seat stress or hoop stress agrees with simulation in order of magnitude.
- Frequencies are compared with excitation sources at operating speed.
- Thermal results are within material limits and coupled into a stress study.
- Castability review identifies hot spots and the redesign addresses them.
Expected results
A cast motor housing with as-cast and as-machined configurations, converged structural, modal and thermal results, a castability review with changes made, and casting and machining drawings.
Research angle for your M.Tech thesis
Investigate how casting constraints such as minimum wall, draft and directional solidification limit lightweighting of motor housings, and compare topology-optimised and rule-based rib layouts for mass, stiffness, thermal performance and castability. The strongest work validates results with casting simulation or a cast sample.
Take it further
- Run a Topology Study on the rib layout to save mass.
- Run a fatigue study on the mounts using an example duty cycle.
- Compare a die-cast and a gravity-cast design for wall thickness and mass.
Viva and review questions
Why do you need two configurations?
The casting supplier needs the as-cast shape with draft and machining allowance, while the machine shop needs the finished shape with tolerances. Configurations keep both linked to one model.
Where would you expect porosity and why?
At thick junctions such as rib roots and bearing bosses, which solidify last. I reduced them with coring and fillets and placed feeders to supply those areas.
Why combine thermal and structural studies?
The housing expands when hot, changing the stator fit pressure and adding thermal stress. Studying them separately could miss a combined case that exceeds the allowable stress.
Learn it at DIYguru
These DIYguru courses and programmes teach what this project needs.