● Draft rough mold specifications based on product specifications, such as intended use and molding materials. Select molding contractors and external mold manufacturers with the Purchasing Section.● Mold layout: Consider parting lines, undercut treatment, gates (inlets for resin), molding shrinkage rates, and other factors; perform flow analysis while working with the product designer to determine the feasibility of the part design.● Design: Consider factors like moldability, machinability, mold life and ease of maintenance, temperature ● The precision machining is mainly performed using the machining center. Grinding machines and electrical discharge machining are also used to achieve high precision. Since molds are produced as single-item products, careful planning is essential to prevent processing errors.● The final finishing, including polishing and mold alignment, is done manually.● Molding trials are performed to check for molding defects and dimensions, based on which the mold is ● Mold conditions, like resin temperature, mold temperature, injection speed/pressure, and so forth, are The mold manufacturing siteThe site of the Mechanical Design R&D Group at the Head Office. Team leader Murakami, surrounded by various machines and tools, explains the complex structure of the molds, which resemble works of art.Injection mold and its structureInjection molding is the most common method used to mold plastic products. The molding process involves heating and melt-ing resin, injecting it into a cavity formed by the core (male part) and cavity (female part) of the mold, and then cooling it to so-lidify and create the product components.Work on an injection molding machineWith this injection molding machine, the resin is set on the top part and injected into a mold. The photo shows a plastic model distributed during tours for elementary school students, featuring Pixy, the official mascot of Rionet hearing aids.Designing precision molds that account for even the slightest resin shrinkageThe quality of molded parts depends on the quality of the mold.The main body that comes into contact with the back of the ear must have high water resistance to keep out sweat and moisture. Typically, highly waterproof products use rubber gaskets called O-rings inserted between the parts. However, using O-rings in hearing aids would make the product larger, resulting in discom-fort and inconvenience for users. This is why the parts must be formed so precisely that they fit together perfectly, without gaps.In summary, the work of the Mechanical Design R&D Group requires the high-precision mold processing capability that allows no tolerance greater than 0.02 mm when resin parts are assem-bled.The designers of hearing aid mechanisms may not necessarily consider the ease of mold manufacturing for resin parts. For this reason, Murata says, they must repeatedly hold discussions with mechanical designers to make adjustments.“You can design a hearing aid in 3D CAD, but manufactur-ing an actual product is a completely different matter. When we review the proposed drawings, we often say, ‘If you change the shape of such and such a part, we can make the mold.’ I under-stand certain aspects of the product may be non-negotiable, but any idea is meaningless if it’s not physically feasible. We engage in repeated exchanges to find mutually acceptable solutions. That’s part of our job.”In striving to create a better product, they go through multiple rounds of discussions with mechanical design engineers for each project. Typically, it takes two and a half to three months from the start of mold creation to completion.For parts manufacturing, resin heated to approximately 200°C is injected into a mold cavity, a process called injection molding. The resin is then cooled to around 50°C until it solidifies, at which point it’s released from the mold. The tricky part here is that resin contracts as it cools. Even a five-second increase in cooling time can change the shape. This means mold designers must account for the shrinkage rate. The rate and direction of shrinkage vary depending on the size and shape of the part, as well as the type of resin used. It is not as easy to achieve the desired results as in the simulation, according to Murata.“The rate and direction of resin shrinkage depend on material Initial planningMold designcontrol (cooling), then proceed with injection mold design.Mold machiningInjection moldingrepeatedly adjusted.adjusted to determine mass production conditions for each part.8The mold manufacturing process
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