The design of MIM parts is similar to plastic injection molding
time：2020-05-11Views：476 Author：Best Seiko
The design of MIM parts is similar to plastic injection molding. In the previous article, we introduced the guidelines for choosing the MIM process. Since it is not limited by the traditional metal forming process, part designers can reimagine new parts from a new perspective, imagine how the production process can reduce the weight of materials, how to combine multiple parts into one part or how to form functionality And decorative features. In order to make MIM parts (whether newly designed or replace parts previously produced by other processes) fully utilize the advantages of the MIM process in the design process and enhance the manufacturability, the following design guidelines are proposed. In this section, some information about the subsequent processing of sintering is also included. 1. MIM parts with simple process design are produced by the cavity formed by two half-molds combined with a plane. (Refer to reading: Structure of MIM Mold) Among them, the half-mold is composed of cores with uniform gaps installed in the other half of the molds. The uniform gaps are for forming parts with uniform wall thickness. Core molding is the structural feature inside the part, and cavity molding is the structural feature outside the part. All structural features of the design must be a molded part that can be released from the cavity and can be removed from the core by the ejector rod. When the complexity of MIM parts increases, you can add sliders, cores and other tools commonly used in plastic injection molding to form. While increasing the structural characteristics of the parts, the complexity of the parts increases. At this time, because the operating costs of tools and technical equipment related to general processing and subsequent processing or assembly operations can be eliminated, MIM parts can obtain economic benefits. At each stage of design, these benefits and costs must be carefully weighed against each other. When designing MIM parts, in order to fully obtain all the benefits of this process, the following key points must be considered: uniform wall thickness, thickness transition, core removal, draft angle, reinforcing ribs and spokes, chamfering With rounds, threads, holes and grooves, undercuts, pouring systems, parting lines, decorative features, sintered supports, etc. Each will be explained below. 1.1 Where uniform wall thickness is possible, the wall thickness of the entire MIM part should be the same. Different thicknesses can cause twisting, internal stress, holes, cracks and dents. It will also cause uneven shrinkage and affect dimensional tolerances and control. The part thickness is well in the range of 1.3~6.3mm. In order to make the wall thickness of MIM parts uniform, several commonly used methods for changing the shape are given. Manufacturability design of MIM parts (process design & post-sintering process)-uniform wall thickness Several commonly used methods to change shape 1.2 Thickness transition section In some cases, the uniform wall thickness cannot be met, so different thicknesses should be designed gradually transition. MIM parts manufacturability design (process design & post-sintering process) thickness transition 1.3 Core removal holes The use of core removal holes can reduce the cross section to within the guidelines and limits, achieve a uniform wall thickness, reduce material consumption and reduce or eliminate Cutting operations. The preferential direction is the direction parallel to the mold opening, in other words, the direction perpendicular to the parting line. Because the core rod is supported at both ends, it is better to use through-holes instead of blind holes. Blind holes use cantilever rods. MIM part manufacturability design (process design & post-sintering process) core removal hole 1.4 Demolding slope Demolding slope is a small angle on the surface, which should be parallel to the moving direction of the model part. For the mandrel, be particularly precise. The stripping slope is to facilitate the ejection and ejection of the formed part blank. The draft angle is generally 0.5 degrees to 2 degrees. The actual size of the release slope increases with the depth of the holes or recesses formed and the complexity of the parts or the number of cores. There are some situations where the draft angle is required. Manufacturability design of MIM parts (process design & post-sintering processing)-draft angle of draft and draft angle of 1.5. Reinforcement ribs and spokes Reinforcement ribs and spokes are used to reinforce thinner walls and avoid thick sections. In addition to increasing the strength and stiffness of the wall thickness, it can also improve the flow of materials and limit twisting. The thickness of the reinforcing rib shall not exceed the thickness of the adjoining wall. The structure needs thicker ribs, and multiple ribs should be used instead. The recommended ratio of ribs. It shows how to use the stiffeners and core removal holes to reduce the weight while maintaining the functional strength of the parts. The manufacturability design of MIM parts (process design & post-sintering process) The manufacturability design of MIM parts (process design & post-sintering process) reinforcement ribs and spokes 1.6 Chamfering and rounding are chamfering and rounding. Chamfering and rounding can reduce the stress at the intersection of structural features; eliminate sharp corners that may cause cracking and corrosion of structural features of the model, which facilitates the flow of injection material into the model and helps parts come out of the cavity, which is beneficial to molding operations Of. The manufacturability design (process design & post-sintering processing) of MIM parts is rounded and chamfered. 1.7 The internal and external threads of the thread can be formed by the MIM process, but compared with the screw core, the thread tapped Precise and cost-effective. In order to remove the model member from which the molded thread is screwed out, the external thread of the model part of the molded thread is well located on the parting line of the model construction. In order to maintain the thread tolerance of the thread diameter, it is generally stipulated that there is a small plane of 0.127mm on the parting line, as shown in Figure 7, which can ensure that the model is properly sealed, can reduce the trace of the parting line, and can avoid the thread Burrs are generated at the root, which can reduce model maintenance.