Relay is an automatic switching element with isolation function, which is widely used in remote control, telemetry, communication, automatic control, mechatronics and power electronic equipment. It is one of the most important control elements. The earliest relay was an electromagnetic relay. It used phenomenon of magnetic force generation and disappearance of electromagnet under power on and off to control opening and closing of another circuit with high voltage and high current. Its appearance makes remote control and protection of circuit work smoothly. Relay is a great invention in history of human science and technology. It is not only basis of electrical engineering, but also an important basis of electronic and microelectronic technology. There are many types of relays, which can be divided into voltage relays, current relays, time relays, speed relays, pressure relays according to input amount. According to working principle, they can be divided into electromagnetic relays, inductive relays, electric relays, electronic relays, etc. It can be divided into control relays, protection relays according to use, and can be divided into presence or absence of relays and measuring relays according to change of input quantity. Main requirements for relay casing are sufficient strength, fatigue resistance, wear resistance, good heat dissipation and noise reduction. In order to meet lightweight requirements of mechanical and electrical products, relay casing is designed and manufactured with engineering plastics. This article introduces main points of injection mold design for Mueller relay housing in Germany.
Maximum external dimensions of German Mueller relay case are 101.00 mm x 55.8 mm x 32 mm, average plastic thickness of plastic part is 2.0mm, plastic part material is PA66, shrinkage rate is 1.012, and plastic parts mass is 78 grams. Technical requirements of plastic parts are that there must be no defects such as peaks, injection dissatisfaction, flow marks, pores, warping deformation, silver lines, cold materials, spray lines, bubbles, etc. Do not use mold release agents in molding of plastic parts.

 

As can be seen from Figure 1, plastic parts are divided into three units connected together, and each unit requires a side pull of slider. Plastic part has an inverted buckle, which needs to be demoulded forcibly. Inverted buckle is designed on the side of movable mold. Difficulty of mold design is forced demoulding of buckle. Since mold is a mold exported to Europe, mold design style is completely in accordance with European style design. Secondary ejection uses standard component Z169 of HASCO secondary ejection. The most commonly used European injection mold are German HASCO standard, German STRACK standard, German EOC standards, British DMS standards, American DME European specifications (metric standard parts), French ROUBARDIN standards and Austria's MEUSBURGER standards, the most famous of which is German HASCO standard.

 

 

Mold design cavity layout is 2. Mold base adopts HASCO standards, see mold design figure 2. Parts of HASCO mold base have good interchangeability. Select corresponding parts when ordering, and you need to assemble them yourself after it return. In ordering system of HASCO mold base, select corresponding specifications, system will automatically generate a mold base parts list with detailed specifications, quantities and codes.
Ball cage of HASCO standard guide bush is very long. When designing mold for second ejection of double-layer ejector plate, there will not be enough space to place ball cage of guide bush. At this time, it is necessary to cut off one or several balls on the top of ball cage with wire cutting(note that elastic retaining ring on the bottom of shaft cannot be cut off). There is a groove in the middle of two rows of balls on outer ring of ball cage, which is used for positioning when cutting.
Mold gating system uses a hot nozzle for injection molding. Hot nozzle grade is MoldMaster. After molten plastic enters parting surface, it enters two cavities through latent gate. PA66 requires a higher injection temperature and mold temperature. In order to prevent heat loss, heat insulation plates are usually added to mold moving plate and fixed plate. Another method is to mill processing grooves on moving plate and fixed plate to reduce contact area between mold plate and injection molding machine.

 

In order to facilitate design of slider core pulling system, mold cavity is layout linearly, and sliders are designed on both sides. Sliders on both sides need to be designed with a backhoe mechanism, and a wear plate is designed at the backhoe. Sliders are all driven by inclined guide posts, and wear-resistant plates are designed on slopes of sliders. Plastic part has a complicated structure. Bottom of slider core pulling mechanism is designed with a ejector pin. Mold needs to be designed to reset mechanism first and use an electronic travel switch to detect it.
There are certain difficulties in ejecting plastic parts. Plastic part has a complicated structure, and plastic bit has a larger tight force on moving mold. In addition, there is a buckle on bone position to make it difficult to get out of mold. For this reason, secondary ejection mechanism Z169 / 22 of HASCO has been designed. This ejection mechanism requires mold to have good rigidity. It is use of advantages of HASCO mold embryo. There are guide posts or guide sleeve positioning between mold plates. Both movable mold and fixed mold plate need to be designed with positioning rings. An ejector insert is fixed on inverse buckle part and fixed on lower thimble plate, and thimble is fixed on upper thimble plate. When ejecting for the first time, two layers of ejector plates are ejected together, and buckle part is released from movable mold. When ejection continues, ejector plate of lower layer stops, and ejector plate of upper layer drives ejector to completely eject plastic part.
Ejection principle of HA169's secondary ejection mechanism Z169 is shown in Figure 3.