Machining the inner bore and stops of the motor base is crucial in motor base manufacturing. It can be done on a lathe or a boring machine. Different motor manufacturers will tailor specific machining processes according to the specific structure of their products, but the fundamental requirements of the process remain unchanged: the coaxiality of the stops at both ends with the inner bore of the motor base, the perpendicularity of the end faces of the stops relative to the central axis, and the tolerance requirements with mating components. Today, Ms. will participate in a brief discussion, and we welcome everyone to actively leave comments and share their opinions.
Lathe machining base process
Motor bases for H200 and smaller sizes are generally machined on horizontal or hexagonal lathes, while bases for H225 and larger sizes are generally machined on vertical lathes.
When machining the first end stop, the outer circle and both ends of the machine base blank must be aligned to ensure that the wall thickness of the machine base is approximately uniform after machining. When machining the other end stop, the first end stop and the end face are used for positioning. To ensure the coaxiality of the two ends stop, a cast iron chassis is first fixed on the lathe worktable, and the chassis stop is precision machined to achieve a suitable tolerance fit with the first end stop of the machine base. The chassis manufactured in this way serves as a stop positioning jig. When fixing the first end stop of the machine base onto the positioning jig, the dust on the contact surfaces should be cleaned to ensure a tight contact between the machine base stop and the end face and the chassis.
Because the locating lug's stop is precision machined on the lathe's working face, the centerline of the locating lug's stop is perfectly aligned with the centerline of the lathe's worktable. Therefore, using the locating lug's stop to position and machine the second end stop and the inner circle ensures the coaxiality of both end stops and the inner bore, and that the circumferential runout between the end face and the centerline of both end stops does not exceed tolerance. During clamping, apply force evenly around the machine base along the axial direction to press the machine base firmly onto the locating lug. After rough machining, the clamping force must be appropriately loosened before finish machining to prevent deformation of the machine base due to excessive clamping force.
Boring machine base processing technology
Use the machined base plane as a reference surface to fix the machine base to the worktable. Single and small batch production can be carried out on a universal boring machine. Align the axis of rotation on the worktable according to the markings on the machine base. Secure the base with bolts and bore the inner circle and stop.
Mass production is carried out on a dedicated combination machine tool. The machine automatically aligns its axis using two reamed foot holes on the base and pins on the positioning base plate. The positioning base plate is then automatically aligned with the machine tool's axis. The base feet and positioning plate are pressed onto the worktable by bolt plates or pneumatic clamps, and then machining is performed. Because the end stops and inner diameter are machined in a single setup, coaxiality is guaranteed by the machine tool's precision and is less affected by errors generated during positioning. Therefore, this machining method is relatively stable and reliable. During machining, the clamping force acts on the feet, minimizing the impact of machine base deformation caused by the clamping force.
Analysis of common reasons for non-compliance
After machining, the deformation of the machine base stop and inner circle, as well as the deviation of their coaxiality, are common quality problems in production. The causes can be basically attributed to the following factors.
●Improper clamping, excessive clamping force, unclean chassis stop contact surfaces, and excessively loose chassis stop fit are the main causes of machine base deformation and coaxiality deviation. Therefore, it is essential to operate according to the process specifications. The clamping force must be appropriately relaxed before finishing; this point should never be overlooked.
● Due to the internal stress in castings or weldments. The magnitude of the internal stress depends on the structural shape, material, and manufacturing method of the blank of the machine base. Welded machine bases, cast steel machine bases, and high-strength cast iron machine bases should undergo stress-relieving annealing. Ordinary gray cast iron machine bases should be left to stand for an appropriate time after casting for a so-called "natural aging" treatment to relieve internal stress before machining. However, for workpieces with very strict deformation restrictions, stress-relieving annealing must be performed after rough machining before finish machining.
● Due to substandard cast iron materials. For example, excessive free graphite in the iron reduces the strength and rigidity of the machine base, making it prone to deformation.
● Poor rigidity of the machine base. If the design does not consider that the stress on the machine base during clamping and cutting is much greater than that during normal operation, the designed machine base is too weak and prone to deformation. Therefore, it is necessary to appropriately increase the wall thickness or add reinforcing ribs, or use materials with greater strength and better rigidity.
●Due to inherent machine tool errors and the influence of measurement temperature, the machine tool should be maintained regularly, and measures should be taken to eliminate the influence of measurement temperature.
