Handbook of Small Electric Motors MAZ Part 9 doc

CHAPTER 3 MECHANICS AND MANUFACTURING METHODS Chapter Contributors 3.1 3.1 MOTOR MANUFACTURING PROCESS FLOW* The basic manufacturing processes for electric ac and dc motors are shown in this section. Within each process, there are significant variables, each depending upon the manufacturing equipment, size and variety of the parts, electrical efficiency requirements, and economics. Each one of these process variables is described in the following text. 3.1.1 AC Motor Manufacturing Process Flow Figure 3.1 illustrates a basic ac motor manufacturing process flow. The first step is producing laminations.These laminations are separated into rotors and stators.The stator laminations, shown in Fig. 3.2,are then stacked into a core, and copper and/or aluminum wire is wound into the core, producing a wound stator core. An outer housing of some type is produced, and that is then wrapped around the wound sta- tor core, making a wound stator assembly.The wound stator assembly is then sent to motor assembly. Larry C. Anderson Axis SPA John S. Bank Warren C. Brown Peter Caine John Cocco Phil Dolan Leon Jackson Roger O. LaValley Bill Lawrence NMB Corporation Stanley D. Payne Derrick Peterman Karl H. Schultz Chris Swenski Harry J. Walters Alan W. Yeadon William H. Yeadon * Sections 3.1 to 3.9 contributed by Karl H. Schultz, Schultz Associates, except as noted. The rotor laminations in Fig. 3.3 are also stacked and then aluminum die cast into a rotor casting, shown in Fig. 3.4.A shaft is then produced, and this is assembled into the rotor, making it a rotor assembly, shown in Fig. 3.5. The rotor assembly is sent to motor assembly. Two end frames are produced and sent to motor assembly. At the final operation, the wound stator assembly, rotor assembly, two end frames, and miscellaneous parts are assembled into a complete motor. The motor is then tested, painted, and packed for shipment. 3.2 CHAPTER THREE FIGURE 3.1 Ac motor manufacturing process flow. FIGURE 3.2 Stator laminations. 3.1.2 DC Motor Manufacturing Process Flow The basic dc motor manufacturing pro- cess is illustrated in Fig. 3.6. Like ac motors, the first step is producing lami- nations for the pole piece and arma- ture. The pole-piece lamination is stacked with several other components into a pole piece assembly. The pole piece on dc motors may be of solid steel, as shown in Fig. 3.7. A housing is produced, and when the pole pieces are inserted, it becomes a frame and field assembly, shown in Fig. 3.8. This frame and field assembly is then sent to motor assembly. Brushes, with other components, are assembled into a brush assembly, as shown in Fig. 3.9, and this is then assembled on the frame and field assembly. The armature lamination is stacked into a core, which is then assembled onto a shaft, and copper wire is inserted or wound onto the core. The coils may be con- nected to the commutator as they are wound, as in Fig. 3.10, or connected after the coils are inserted into the core and shaft assembly, as in Fig. 3.11.This is a completed armature assembly which then goes to final motor assembly. The frame and field assembly, armature assembly, and miscellaneous parts are then assembled into a complete motor, as shown in Fig. 3.12. The motor is then tested, painted, and packed for shipment. MECHANICS AND MANUFACTURING METHODS 3.3 FIGURE 3.3 Rotor laminations. FIGURE 3.4 Rotor casting. 3.4 CHAPTER THREE 3.2 END FRAME MANUFACTURING The basic purpose of an end frame, sometimes denoted an end bell, end shield, or bracket, is to contain the shaft bearings and support the rotor assembly. It will also act as a heat transfer device. On open motors, the end frame will have slots for air to pass. On enclosed motors, the end frames will be solid, with no openings. A variety of end frames are shown in Figs. 3.13, 3.14, and 3.15. Like housings, end frames come in cast-iron, steel, zinc, or aluminum castings. Cast-iron castings are usually found on motors of 3 hp and larger. The service application is in the industrial market where severe conditions may exist. Materials are usually of about 30,000 lb/in 2 tensile strength and are free machining.The typical sequence of operations is a two-machine cell—a computer numerically controlled (CNC) machine prepares the bearing bore and end frame diameter, and a manual drill is used to prepare the holes for the housing attachment. The steel material is usually SAE 1010 to 1020. This type of end frame may be found on all types and sizes of motors.A coil is processed through a stamping press, and each part is drawn into form as a stamping. This is usually a progressive die operation. A self-aligning bearing is installed and lubricant is applied. Then the bearing is sized for the only machining process. Zinc or aluminum end frames are found on most motor types and sizes and gen- erally are castings. End frames are usually cast in a horizontal die caster. Because of its density, zinc is usually limited to end frames for motors 3 in in diameter or less. If the parts are small enough, more than one part is made at one time.This depends on the part and machine sizes.Also, on motors above 1 ⁄4 hp, a steel bearing insert is usu- ally die cast in the part. Following the die casting and part cooling, the part is trimmed. Many manufacturers have installed robots for this operation because of the heat and environmental conditions. FIGURE 3.5 Rotor assembly. FIGURE 3.6 DC motor manufacturing process flow. 3.5 3.6 CHAPTER THREE FIGURE 3.7 Solid steel pole piece. FIGURE 3.8 Frame and field assembly. MECHANICS AND MANUFACTURING METHODS 3.7 FIGURE 3.9 Brush assembly. FIGURE 3.10 Winding a commutator. 3.8 CHAPTER THREE FIGURE 3.11 Core and shaft assembly. FIGURE 3.12 Complete motor. MECHANICS AND MANUFACTURING METHODS 3.9 FIGURE 3.13 End frame. FIGURE 3.14 End frame. The bearing bore and housing end frame diameter of the end frame are then machined. This is done on either a CNC lathe or a special automatic machine, depending on size and volume. Some very small motors use an oil-soaked wick, as seen in Fig. 3.14, for lubrica- tion.This is inserted after machining. 3.3 HOUSING MATERIALS AND MANUFACTURING PROCESSES Housings, also known as frames, come in all types of materials and configurations. Basically, the housings are made in the same way for both ac and dc motors. The basic purpose of the housing is to cover the stator or pole-piece assembly, provide heat transfer and protection, provide a location for mounting the end frames, and serve as an attachment for other components, such as outlet boxes and lifting hooks. 3.3.1 Materials and Configurations The housings come in cast iron; in rolled, wrapped, and tube steel; and in both cast and extruded tube aluminum. Cast Iron. Castings are usually found on motors of 3 hp and larger. The service application is in the industrial market where severe conditions may exist. Materials are usually of about 30,000 lb/in 2 tensile strength and are free machining. In most cases, the mounting feet are cast as part of the housing. 3.10 CHAPTER THREE FIGURE 3.15 End frame. [...]... MANUFACTURING METHODS 3. 29 For automatic insertion of wedges, there is very definitely a desirable configuration Figure 3. 29 outlines this configuration for the bottom of the slot Note that at this point we are not too much concerned about the overall shape of the slot, only the shape of the slot nearest the bore Figure 3. 29 gives a few basic dimensions defining the desirable shape FIGURE 3. 29 Blade gap illustration... theory is very simple and consists of inserting a first layer of wire into a slot, compacting or deforming the wires into the back of the slot to fill all of the void spaces between wires, then inserting a second layer of wire As a simplified example, if a 92 percent slot fill is desired, a first insertion of 46 percent or half the total wires is inserted By the process of compaction, these wires are then... only 40 percent of the slot The remainder of the slot, 60 percent, is now available for the next insertion of 46 percent of the wire, which results in a 76 percent slot-fill insertion attempt on the second pass The second insertion falls within the range of feasibility based on present practice The use of the General Electric Electro-press process could also contribute to the feasibility of achieving... maintained and the process monitored continuously Process Options Several process options are shown in Figs 3.19a through 3.19e The optimally efficient process for electric motors is probably the one shown in Fig 3.19e Again, with the variety of machining options, a company must evaluate the requirements for electric motor efficiency and economics 3.6.4 Options for Attaching Rotor to Shaft There are basically... having the same number of slots Examination of the laminations within the same subgroup will then show that there are usually very small differences in the significant areas, as previously mentioned—for example, the slot opening and the wedge entry area Usually these small variations can be eliminated with little effect on the electrical performance of the final products Standardization of laminations therefore... assembled into a core in some fashion Permanent-magnet motors have air gaps on the order of 0.015 to 0.040 in per side Induction motors have air gaps on the order of 0.010 to 0.015 in These gaps must be held very consistent to avoid performance and noise degradation There are many methods for assembling stacks of laminations This section discusses some of the most common stacking methods with their positive... 0.080-in category With the advent of machine insertion, the operator restriction on wire size was removed A reasonable maximum wire size was then 13 or 14 AWG; however, a portion of the placer tooling also occupies a part of the slot opening, as shown in Fig 3.28.These two items resulted in larger slot openings, to the point where a majority of laminations are now in the 0. 095 - to 0.125-in category Even... hardened case * This subsection from Machinery’s Handbook 23, Revised Edition, Industrial Press, New York, 198 8, p 441 MECHANICS AND MANUFACTURING METHODS 3.15 Cyaniding A process of case hardening an iron-base alloy by heating in a cyanide salt Nitriding A process of case hardening in which an iron-base alloy of special composition is heated in an atmosphere of ammonia or while in contact with nitrogenous... and tube The material is usually SAE 1010 to 1020 This type of housing may be found on all types and sizes of motors Aluminum This material is also found on most motor types and sizes The cast housings may be produced for a size as large as NEMA 360 but are usually not found on motors rated below 3 hp The tubing may be found on the smallest motors up to about 25 hp The material is usually SAE 6061 3.3.2... stator There exist two major categories of pole configuration, lap winding and concentric The coil-insertion process has almost eliminated lap-type windings Although it is possible to insert some lap windings, it is almost impossible to achieve the slot fills and production rates of equivalent concentric windings Almost all of the lap-type motors, probably 90 to 95 percent, are hand wound This section . Because of its density, zinc is usually limited to end frames for motors 3 in in diameter or less. If the parts are small enough, more than one part is made at one time.This depends on the part. options are shown in Figs. 3.19a through 3.19e. The optimally efficient process for electric motors is probably the one shown in Fig. 3.19e. Again, with the variety of machining options, a company. for electric ac and dc motors are shown in this section. Within each process, there are significant variables, each depending upon the manufacturing equipment, size and variety of the parts, electrical