Stress Relief Aging of Dalian Motor Housing Castings
Motor housings are thin-walled shell castings. Residual casting stress forms after pouring and cooling. If such stress is not released, deformation, out-of-roundness and coaxiality deviation tend to occur after boring and sealing surface machining, resulting in rotor-stator rubbing and poor sealing after assembly. The core purpose of aging treatment is to homogenize and release internal casting stress and stabilize geometric dimensions. For Dalian motor housings, suitable aging solutions are selected according to material, precision grade and production cycle. The process follows casting pretreatment, aging method selection, process control and re-inspection & traceability to mitigate deformation risks.
Preliminary cleaning and pretreatment of casting blanks are preparatory steps for aging of Dalian motor housings. Before aging, ingates, risers, flash and burrs shall be removed, and adhered sand and loose sand inside the cavity cleaned. Defect welding repair must be completed prior to aging, as welding introduces new stress which shall be relieved collectively in subsequent aging. Check the shell for casting defects such as cold shuts and cracks; defective workpieces shall be isolated in advance. Support points shall be arranged on rigid flanges or bases instead of the thin-walled barrel at a single point, to avoid additional bending stress from self-weight. Spacers shall be inserted between stacked workpieces to prevent plastic deformation caused by extrusion and guarantee aging performance.
Selection of aging schemes lays the foundation for stress control of Dalian motor housings. Three mainstream options are available: natural aging, thermal aging and vibratory aging. Natural aging means placing blanks outdoors to release stress slowly via day-night temperature variation; it requires a long cycle and suits high-precision small-batch orders. Thermal aging, namely stress-relief annealing, delivers remarkable stress removal and is the primary process for cast iron motor housings. Vibratory aging features high efficiency and low energy consumption, suitable for mass delivery and tight lead-time shells; it is usually applied after rough machining and before finish machining to eliminate secondary stress induced by machining. Composite aging can be adopted for high-specification motor housings: thermal aging after casting as the base treatment, followed by vibratory aging after rough machining for further stress homogenization.
Temperature rise, holding and cooling control in thermal aging are critical procedures for Dalian motor housings. For cast iron motor housing stress-relief annealing, the temperature is generally kept between 500℃ and 550℃. Slow heating is required to avoid new stress caused by excessive temperature difference inside and outside the shell. Holding duration is adjusted according to wall thickness and extended for thicker sections. Workpieces must be furnace-cooled slowly after heat preservation; direct air quenching at high temperature is forbidden, for rapid cooling regenerates residual stress. Airflow passages shall be reserved inside the furnace instead of dense stacking to ensure uniform furnace temperature and prevent shell warping induced by local temperature deviation. Temperature gauges shall be calibrated regularly for zoned furnace temperature monitoring to avoid material property degradation from overheating.
Tooling and parameter tuning for vibratory aging adapt to mass production of Dalian motor housings. Motor housings are flexibly supported on rubber pads to isolate rigid ground conduction. Vibrators are mounted on rigid shell sections away from thin-walled vulnerable zones. Sweep frequency test is first carried out to determine the resonance range and set vibration parameters. Short-duration vibration under resonance triggers minor plastic deformation at high-stress positions and homogenizes residual stress. Watch the shell during vibration to prevent collision from excessive amplitude. Vibratory aging curves shall be printed and filed after treatment as acceptance records. Vibratory aging is mainly used for stress relief after rough machining and cannot fully replace thermal aging after casting.
Dimensional re-inspection and process flow control after aging secure the treatment effect of Dalian motor housings. After aging, workpieces shall cool naturally to room temperature and rest for a period before dimensional inspection. Recheck the form and position tolerances of sealing surfaces, inner cavities and mounting datums, compare with pre-aging records and identify abnormal deformation. Qualified blanks are stored in separate zones with batch marking, recording material grade, aging method, process parameters and treatment time. Finished blanks shall be handled gently during transfer. Lifting points are set on base flanges; clamping on thin-walled barrels is prohibited to avoid new stress from external force.
Machining sequence arrangement reduces secondary stress accumulation of Dalian motor housings. Appropriately allocate machining allowance: reserve finish allowance after rough machining and arrange one aging process after roughing to release cutting stress before finish machining. Removing all allowance at one time is not allowed, for heavy cutting stress will offset previous aging results. Cutting parameters shall be optimized in finish machining to lower stress generated by cutting heat and force. For customers with strict requirements on coaxiality and sealing surface roundness, aging nodes shall be specified in process documents, and aging procedures shall not be omitted to shorten lead time.
Long-term storage and batch traceability maintain dimensional stability of Dalian motor housings. The blank storage area shall be dry to prevent rusting, and the supporting layout shall be consistent with that used in aging. Shells of different batches and materials are managed separately. Mature aging parameters are reused for repeat orders. If casting formula or shell structure is modified, first-piece aging test shall be performed to track post-machining deformation before mass production. Ledgers are established to trace aging processes in case of dimensional drift.
In summary, aging treatment for motor housing castings is not an independent procedure. Processes shall be matched according to precision requirements, with strict control over heating, supporting, cooling and machining rhythm. Through blank pretreatment, proper aging selection, tight parameter control, post-aging re-inspection and process optimization, Dalian motor housings release residual stress from casting and cutting, reduce deformation risks in subsequent machining and field operation, and stabilize motor assembly accuracy.
