Product diagram of ATM teller face shell is shown in Figure 1. Maximum external dimensions of product are 509.57 mm*599.44 mm*226.43 mm, average thickness of plastic parts is 4.0 mm, material of plastic parts is PA66+30GF, shrinkage rate is 1.002, and weight of plastic parts is 2860 grams. Technical requirements for plastic parts are that there should be no defects such as peaks, incomplete injection molding, flow lines, pores, warpage, silver lines, cold materials, spray lines and other defects.

 

Figure 1 ATM teller machine shell product diagram

As can be seen from Figure 1, plastic part belongs to a large-scale shell, shape is a rectangular hollow sinking, and there are multiple bone-position reinforcing ribs on the back. There are multiple screw columns on the back of shell and sunken square hole on the back, which needs to be designed to push out cylinder. Difficulty of mold design is a reasonable gating system design to solve problem of floating fiber and ejection system design of large plastic parts to ensure that plastic parts avoid deformation during ejection process.

 

Plastic parts belong to large plastic parts, and molds belong to large molds. Mold cavity layout is 1 cavity. For large plastic parts, choice of gate position is very important. Gate can not be designed on the outer surface of plastic part, so gate position can only be selected at the edge of sinking rectangular hole. Size of plastic parts is large and process is long, so 3 side gates need to be designed, as shown in mold design diagram 2. Mold base of large mold is non-standard mold base 8590, straight body mold base structure. Two taper positioning blocks are designed for each edge of mold base, which is beneficial to accurate positioning when closing mold. Fixed mold adopts original design, and movable mold adopts mosaic structure.
ATM teller face shells have high requirements on geometric tolerance of plastic parts. Therefore, mold cooling is critical during injection process. Reasonable cooling is an important factor to ensure that plastic parts do not warp. Fixed mold cooling adopts combination of straight-through water transport and pond cooling. Movable mold adopts pond cooling. It should be noted that when buying mold base, water transportation needs deep hole drilling, and straight waterway needs to be processed directly in mold base factory. Water delivery diameter is ø10.
Ejection of plastic parts adopts push block, ø8 and ø12 ejector pin, and cylinder to eject. Mold plate of large mold has a heavy weight, and eject plate must be designed with a torso guide. Because ejection stroke is large and ejection force is large, eject by ejector pin and cylinder alone will definitely cause excessive stress on the plastic part and ejection deformation. Therefore, push block is designed to push out at the edge of plastic part. Bottom of push block is ejected by a ejecor pin with a diameter of 16 and fixed with M10 screws.
Design of push block is divided into 4 push blocks, one on each side, and adjacent push blocks are separated by inserts at the corners. Upper and lower push blocks are fixed with three screws to eject pin. Length of two push blocks on the left and right is very long, and 6 eject pins are fixed with 6 screws respectively.

 

 

 

Figure 2 ATM teller face shell mold drawing

Facsimile cover product is shown in Figure 1. Maximum external dimensions of product are 478.0 mm*230.35 mm*61.95 mm, average thickness of plastic parts is 2.30 mm, material of plastic parts is ABS, shrinkage rate is 1.005, and weight of plastic parts is 208.95 grams. Technical requirements for plastic parts are that there should be no defects such as peaks, incomplete injection molding, flow lines, pores, warpage, silver lines, cold materials, spray lines and other defects.

 

 

Figure 1 Fax machine face shell product picture

This is facsimile cover of Epson Corporation of Japan. As can be seen from Figure 1, shape of plastic part is very complicated, there are multiple key holes on the top surface of face shell, and there is a full circle of bone positions on the back of each key hole, overall shape is complex. There is a window above hole of plastic part, and there is a large area opening in the middle of plastic part, flow of plastic in these parts is restricted. Therefore, design of gating system should meet filling of plastic. Parting surface of plastic part is an irregular curved surface. Clamping line at the front and back mold package R of edge should be uniform, and step difference should not exceed 0.03mm. Processing of parting surface should be processed in one time by a high-speed machine, and a new knife should be used. It is not possible to manually file and repair oil stone.
Large plastic parts, such as printer, fax machine casing parts, and larger ones, such as automobile parts, are becoming more and more complicated for beauty. Appearance tends to be more complex curved surfaces, which puts high demands on the mold. Selection of steel for large molds is critical. Due to rapid replacement of Japanese mold products, soft molds are often used for molds. Soft mold steel has not been heat treated. When cutting steel, best hardness is HRC38. When hardness is less than HRC38, it is difficult to obtain good surface roughness. When hardness is higher than HRC38, cutting force increases, tool wear increases, spindle heat and tremor are also unfavorable for processing. Japanese mold steel NAK80 is a pre-hardened mold steel with a hardness of HRC38~41, which is just right for hardness range that is beneficial to processing. Therefore, this set of molds is manufactured with NAK80.
Japanese mold parts generally need to use MISUMI brand mold parts according to customer requirements. Reset spring of eject plate mostly uses Japanese Dongfa purple spring, which is different from steel used by MISUMI reset spring, difference between heat treatment and elastic coefficient is also very large. According to author's experience, life of Dongfa purple spring in Japan is significantly longer than that of MISUMI return spring, but obvious strength of Dongfa purple spring is small. When used in large molds, it is necessary to comprehensively consider reset force of ejector system. If spring force is insufficient, 2 to 4 return springs need to be added.
Plastic parts belong to large plastic parts. Mold cavity layout is 1 cavity. Mold base is a non-standard fine nozzle mold base 6585. Mold design is shown in Figure 2. Attention should be paid to design of large fine nozzle molds:
1. For safety reasons, design a straight mold as much as possible;
2. Exhaust tail of guide post and guide sleeve;
3. When A plate is thick, carefully calculate opening distance of mold. If opening distance of front mold is too large, you need to consider whether strength of nozzle edge is sufficient;
4. Condensate of gating system is long, it is easy to be deformed and overturned. It is necessary to add an anti-rotation column to facilitate grasping of robot.
5. Panel and nozzle plate need to be designed with cooling water.

 

6. Nylon switch is fixed on A plate, and B plate is pulled. Note that there is no need to drill exhaust hole on the top of switch.
7. Oblique roof oil groove adopts intersecting concentric circles with a depth of 0.8, without cross type.
8. Lower frame of mold core adopts a squeeze block structure, which is convenient for frame matching.
9. Both front and rear mold blanks should be designed with positioning pins to improve mold rigidity.
Ejection of plastic parts adopts ejector pins, cylinder and straight ejection to ensure stable ejection and no deformation of plastic parts.

 

 

 

 

Figure 2 Mould drawing of fax machine face shell

 

Figure 3 mold photo