Aluminum alloy with reducer end cover is an important part of small and micro low-speed motors. Die-casting process overcomes problem that machining center cannot process it in place and can greatly improve production efficiency. A mold structure with simple structure, reliable operation and beautiful casting parting surface is designed. Side gate feeding method is conducive to forming and convenient for removing gate waste; for irregular shape of end cover casting and two orthogonal bearing holes in space, it must be cut and finished to meet high-precision matching requirements of stop and machine base, bearing chamber and bearing. A set of milling fixtures with accurate positioning, reliable clamping without deformation, high turning accuracy, simple and reasonable structure, and convenient and fast operation is adopted.

Speed of AC drive motor can be around 960r/min, and when speed needs to be several tens of r/min, the simplest method is to install a reduction box at motor output shaft to output required final low speed. However, such a structure requires reduction box and end cover to be connected with screws, which is prone to loosening after long-term work and causes work failures; and it takes two sets of die-casting molds to obtain reduction box and end cover castings respectively. An optimized structure is to combine reduction box and end cover into one, as shown in Figure 1. Milling fixture used for cutting the end cover die-casting mold and end cover die-casting, two bearing chambers are more critical and must meet high precision requirements of end cover stop and bearing.

 

Figure 1 Schematic diagram of gearbox end cover

 

Figure 2 Assembly drawing of die-casting mold with gearbox end cover
1. Fixed mold plate 2, 17, 24, 30, 33, 35, 39, 40. Fastening screws 3, 41. Wedge block 4. Gearbox slider seat 5, 42. Inclined guide column 6. Gearbox slider 7. Gearbox slider bearing chamber core 8. Mounting hole core 9. Fixed mold core 10. End cover bearing chamber core 11. Moving mold cavity 12. Diverter cone 13. Gate sleeve 14. Guide sleeve 15. Guide column 16. Moving mold plate 18. Moving mold cover plate 19. Gate waste push rod 20. Push rod fixing plate 21. Pad 22. Moving mold bottom plate 23. Push plate 25. Push plate guide sleeve 26. Push plate guide sleeve 27. Casting push rod 28. Fixing pin 29. Reset rod 31, 38. Limit plate 32, 36. Compression spring 34, 37. Gasket 43. Outer edge slider
In view of particularity of casing structure, a side gate feeding method is adopted, which is conducive to filling and convenient for gate removal. As shown in Figure 1, core pulling mechanisms are set at A (joint between reduction gearbox body and end cover) and B (inner cavity of reduction gearbox) to ensure smooth ejection of casting; in order to decompose clamping force of end cover and reduction gearbox, end cover core 9 is set in fixed mold, and reduction gearbox core pulling mechanism is set in movable mold. Three arc windows in Figure 1 are used to dissipate heat for motor. Three arc bosses are set on the end face of fixed mold core to avoid complicated inlay.
Molten aluminum alloy is injected from gate sleeve 13. As injection punch is pushed in cold pressing chamber connected to it, molten aluminum alloy is pressed into movable mold cavity 11, mold is opened after pressurization and cooling. Two sliders 6 and 43 located in movable mold are respectively located in reduction box of end cover casting and at outer edge of end cover, thereby forming a large demoulding resistance. Based on 2mm gap between inclined guide column and inclined hole of slider, at the moment of mold opening, fixed and movable molds move horizontally first, and two sliders move core pulling later, so that end cover casting can be smoothly separated from fixed mold core 9; as mold opening continues, two sliders move core pulling along inclined guide column until they are separated from inclined guide columns 5 and 42; when mold opening is completed, all cores in end cover have been completely detached, leaving only casting shape in cavity. Ejection mechanism is started, and 5 push rods (one of which is a cold press waste push rod) can easily eject casting.

 

Figure 3 Milling machine fixture with reducer end cover
1. Handle 2. Positioning round pin 3. Clamp body locking screw 4. Opening gasket 5. Clamp body 6. Base 7. Rotating shaft 8. Pressure block screw 9. Compression spring 10. Indexing pressure block 11. Diamond pin
In order to meet assembly requirements with bearing and stator, obtained die casting needs to be processed in necessary subsequent processing so that two bearing chambers and stop sizes can be turned or milled to required accuracy, shape and position tolerances. However, due to special shape of end cover, even with support of turning fixture, it is impossible to complete processing of two spatial orthogonal bearing holes in one clamping during turning. Therefore, use of milling fixtures is considered to solve above problems, see Figure 3.
Clamp body 5 (see Figure 4) is placed on base 6 and flipped around rotation axis 7 between 0° and 90°, 0° and 90° are two working positions. Handle and clamp body jack are clearance-matched so that they can be pulled out immediately after insertion and flipping (otherwise it will hinder milling processing). At the same time, a fixing groove of clamp body 5 just passes through clamp body locking screw 3 on base. An open gasket 4 is inserted between fixing groove and head of clamp body locking screw 3, then screw 3 is tightened to limit last rotational freedom of clamp body. Based on high degree of dimensional consistency of die-casting parts, end cover casting adopts one-side two-pin positioning on clamp body, that is, a positioning round pin 2 and a diamond pin 11 are inserted into two diagonal holes in 4-φ5mm mounting hole of end cover respectively. When indexing block 10 is rotated to specified position, end cover parts can be locked by tightening block screw 8.

 

Figure 4 Clamp body

Part is a die-cast blank with an irregular shape. One-side two-pin positioning and end cover heat dissipation slot indexing clamping device is an ideal choice. It cleverly utilizes good dimensional consistency of die-cast parts, uses low-precision IT10 hole spacing mounting hole as positioning hole, preventing deformation of thin-walled end cover parts caused by universal clamping method such as three-claw or flat-nose pliers. Clamp body 5 is designed as a movable matrix that can be flipped 90°, two bearing holes that are orthogonal to each other in space can be easily completed in one clamping and milling. Opening gasket is selected as an important clamping element to avoid need to unscrew all clamping block screws. Fillet at intersection of right and lower sides of shaft hole of top view of clamp body 5 is 8mm. If it is smaller than its positioning size of 8mm, clamp body will be stuck when it is flipped.
End cover parts are difficult to be milled from aluminum blanks on a machining center. Die casting is a more suitable choice, but die casting accuracy is only about IT10. In order to improve dimensional accuracy of certain key parts by an order of magnitude, design and application of machine tool fixtures are particularly critical.