The design and selection of mold materials is something that mold designers must carefully consider, so that the materials can meet the requirements of strength, plasticity, hardness, wear resistance, impact toughness and fatigue strength of the designed mold.
1. Mould formwork
The template is a frame structure that supports the mold core and is connected with the molding equipment. In the past, many sand casting enterprises used the method of sand casting blank to make the mold template and core into an integrated cast iron material in order to save trouble and facilitate mold production. Because the role and pressure of template and core are very different for sand core casting mold. Therefore, in order to give full play to the advantages of different materials and the needs of different parts of the mold, most sand casting enterprises have selected and processed the mold template and core respectively. Because the main function of the template on the mold is to realize the connection between the mold core and the molding machine, and give consideration to the needs of parting and modeling. In the molding process of sand casting, the template and core usually need to be heated to 30 ~ 70 ℃. Therefore, the formwork material must have sufficient strength and hardness within this temperature range. Generally, using cast iron as template can meet the requirements of mechanical properties and hardness in the molding process.
2. Mold core
The mold core is the core of the mold and the key part of forming sand castings. Therefore, for the core material, we must choose high strength and hardness,. Materials with excellent plasticity and wear resistance, high impact toughness and fatigue strength are used as mold core materials. Generally, according to the type of mold and the basic requirements of sand castings, different types of mold steel should be selected as the core material. In addition, the inlay method shall be used to inlay the rough machined die core into the template, and then carry out subsequent finishing, so as to avoid inaccurate positioning of the die core and template caused by multiple assembly, and ensure the accuracy of the processed die.
3. Gating system
The main function of the gating system on the mold is to provide a mold filling channel for liquid metal to enter the mold cavity of sand casting during pouring. In the molding process of sand casting, the gating system and mold core must also withstand the impact and friction of molding sand and air flow for a long time. The overall weight of the die should also be considered in the design. Therefore, wear-resistant high alloy cast aluminum or surface chromium plating materials with high hardness and high heat resistance are generally selected as the gating system.
4. Core box
The core box is generally made of high-grade cast iron by machining. When cast iron is used as the base material for the hot core box, the core box is generally required to be heated to 210 ~ 300 ℃ during the core making process, and the decarburization of cast iron used in the long-term thermal environment should be fully considered. Therefore, low carbon equivalent cast iron should be used for the hot core box to prolong the service life of the hot core box; In addition, the sand shooting nozzle of the core box must be in contact with silica sand with high air flow for a long time during the core making process, and the sand shooting nozzle must have sufficient wear resistance. Therefore, the sand blasting nozzle must be quenched, and the hardness shall reach 40 ~ 48hrc, and then the sand blasting nozzle shall be embedded into the core box by inlaying.
5. Ejector rod
The top core rod is a rod-shaped top core device installed in the core box and used to eject the sand core of sand mold casting. Its function is mainly to take out the sand core of sand mold casting after the core box is opened. On the premise of ensuring a certain strength, the main consideration is that the top of the top core rod should have good wear resistance. Generally, A3 steel can be used for processing, and the available 45# steel with slightly higher requirements can obtain a wear-resistant hardness of 40 ~ 48hrc after heat treatment.
6. Lower core frame
The lower core frame is a lower core device installed on the molding machine. Its purpose is to accurately lower the sand core, cold iron or filter screen prepared before molding into the corresponding position of the mold cavity. During the molding process, the lower core frame needs to repeatedly clamp objects such as sand mold casting sand core into the mold cavity. The material requirements for the lower core frame are generally based on lightweight and wear resistance. Therefore, cast aluminum or resin materials are generally used as the frame of the lower core frame, and wear-resistant steel sheets are used as the clamping surface and contact point of sand mold casting sand core, cold iron or filter screen, so as to reduce local wear caused by friction during long-term use.
7. Locating pin and locating pin sleeve
Locating pin and locating pin sleeve are widely used in sand casting mold. They are the accurate positioning of templates, core boxes, lower core frames and other modules that participate in limiting mutual cooperation. In sand casting production, we should use the mutual cooperation of locating pin and locating pin sleeve to realize positioning and prevent the error of installation position and direction. The matching accuracy of locating pin and locating pin sleeve directly determines the dimensional accuracy of sand castings. Therefore, the precision requirements of sand casting molds are particularly high. Based on the function and purpose of locating pin and locating pin sleeve, their materials must be able to withstand the impact and friction in the process of frequent mutual cooperation. The 45# steel can be quenched and tempered + semi finishing + high frequency surface quenching + low temperature tempering to obtain a wear-resistant material with a hardness of 55 ~ 58hrc; GCr15 steel can also be subject to salt bath step quenching + low temperature tempering, and the hardness after treatment can be as high as 58 ~ 62Hrc. After the design of sand casting mold and the preparation of materials, it can be put into the substantive sand casting mold processing process. However, before machining, the manufacturing feasibility of the designed sand mold should also be ensured. Especially for the small engraving on the sand mold, we must pay attention to whether the existing cutting tools can meet the needs of machining. If not, we should consider EDM; For the parts of sand casting mold with special deep recess, whether the tool handle is long enough shall also be considered. If it is not long enough, the deep recess shall be processed by layered processing method, and then assembled to the corresponding position of sand casting mold.