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How To Make Injection Molds: The Complete Process

How To Make Injection Molds
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    The injection mold is a tool for producing plastic products and a tool that gives products a complete structure and precise dimensions. Injection molding is a kind of processing method used in large quantities of some products with a complex shape. It refers to a method of injecting hot melted plastic into a mold cavity under the promoting action of high pressure exerted by the injection molding machine and getting the molded product after cooling and solidification.

    The injection mold can be categorized into thermosetting plastic mold and thermoplastic plastic mold according to molding characteristic, and into transfer mold, blow mold, die casting mold, thermoforming mold, hot press mold (compression mold), injection mold etc. according to molding process. Among them, hot press mold can be divided into overflow, semi-overflow and non-overflow types according to the handling way of overflow material.This blog post will serve as a complete guide to making injection molds.

    Step 1: Injection Mold Design And Development Process

    The modern mold design is digital mold design, which is based on the traditional mold design, fully utilizing digital design tools to improve mold design quality and shorten the design cycle. Mold design process is a thinking process of creativeness based on the designer’s rich experience and knowledge. It’s not only the auxiliary design referencing existing experience and knowledge but also accumulation and innovation based on these foundations.

    Mold design belongs to the category of mechanical design. In the early stages, mold design primarily relied on manual drafting. It usually brought serious problems into the assembly and precision of the manufactured molds. Along with the development of computer technology, the design method of molds is gradually transforming from traditional manual drafting to computer-aided design. Great changes have been brought into the design of molds. In the meantime, the application of CAE for the stimulation and optimization of the design processes has turned into a mainstream in mold design.

    Step 2: Accepting The Task Assignment

    Currently, there exist three types of injection mold design task assignments.

    The first kind is when the customer assigns with reviewed plastic part drawings and reviewed technical requirements. The second type is that the client provides a physical sample. Here, one needs to create a 3D model, then generate 2D engineering drawings, and after that, execute the mold design.

    The second category is when there are plastic part samples, prototypes, and physical products provided by the client. The works will be reverse engineering of the plastic part, creating a 3D model, generating 2D engineering drawings, and then mold design.

    The third category is when the client has approved plastic part drawings, technical requirements, and mold drawings. In such cases, the mold is designed based on real production conditions.

    Evidently, the three kinds of task assignments differ greatly in their responsibilities and workload.

    For the second type, the manufacturer should go about it with great caution. The drawings of plastic parts obtained after reverse engineering need to be approved by related departments before mold design can start.

    The general task assignment of molding plastic parts is submitted by the plastic part designer. Content in the task assignment: formally reviewed plastic part drawing (including material grade, color, and transparency, etc.) and plastic part specification or technical requirement (such as number of production quantity). The proposal of a mold design task assignment should be done by a technical process engineer based on the task assignment of molding plastic parts. Then, with the plastic part molding task assignment and the injection mold design task assignment, mold designers execute mold design.

    Step 3: Collection Of Raw Data-Analysis And Digestion

    In the process of designing, it is necessary to get some key basic information and data, including plastic part drawing conforming to the standard or plastic part sample, production volume requirements, production efficiency requirements, equipment model, and parameter requirements of plastic part production factory; Furthermore, the data include equipment and manufacturing technology level of the mold manufacturing factory. Then, raw materials and data are analyzed and digested as follows:

    • Analyze the drawings of plastic parts: The purpose should be understood by analyzing the manufacturability, such as the geometric shape and dimensional accuracy of the plastic part.
    • Analyze the process documents: Whether the molding method, molding equipment, plastic material grade, mold type, and other requirements stated in the process task assignment are reasonable and feasible should be reviewed.
    • Familiarization with relevant reference materials and technical standards: The usually referred-to reference materials include the Plastic Materials Handbook, Plastic Technical Standards, Plastic Mold Design Handbook, and Molding Equipment Manuals. The usually referred-to technical standards include the Mechanical Drawing

    Standards and Plastic Mold Standards.

    Step 4: Determine The Mold Structure And Obtain A 3D Mold Drawing

    The ideal mold structure should combine both the process technical requirements of the plastic part with the production economic requirements. Process technical requirements consist of three aspects : making the geometric shape of the plastic part, its dimensional tolerance, and surface roughness meet the requirements. While production economic requirements mean to minimize the cost of the plastic part, maximize the production efficiency of the mold, ensure its long service life, and guarantee ease of operation, maintenance, safety, and reliability.

    Based on the mold structure determination, draft the diagram of the mold structure, including the mold outline dimensions and key structural dimensions of components. Then verify adaptability between the mold structure and the parameters of the injection molding machine selected, make necessary adjustments to finalize the mold structure and its parameters.

    During the molding assembly structure, the total structure of mold and the assembly relationship of each component including fastening and positioning shall be designed precisely and rationally.

    Step 5: Mold Testing

    A set of molds is only 70% to 80% complete in its entire manufacturing process by the time design and assembly are finished. Such problems as discrepancies between predicted and actual shrinkage, the ease of mold release, the effectiveness of cooling, and the effect of dimensions, positions, and shapes of gates on precision and appearance of the product have to be tried out through mold trials. Therefore, it is very important to check the mold qualification through mold testing and to choose an appropriate molding process for this part.

    Conclusion

    Injection mold manufacturing is a very complex process that involves several stages, each requiring a certain dose of creativity, precision, and technical expertise. From the initial design, using digital tools and state-of-the-art simulations to optimize mold structure and functionality, right down to mold testing, which involves adjustments necessary for the production of high-quality plastic parts, each step in producing the desired results is important. Understanding the requirements of the plastic part, selecting the right materials, and using the appropriate technology for mold design and manufacturing-are some of the major factors that play a very important role in ensuring production efficiency and mold longevity. The ultimate aim is a mold that meets technical specifications while offering benefits in terms of overall production cost-effectiveness.

    Final Thoughts

    As someone with 15 years of experience in injection molding service, I can confidently say that the process requires a deep understanding of both the technical and practical aspects of mold design and manufacturing. From precise 3D modeling to material selection and thorough mold testing, every step is crucial to producing high-quality, cost-effective plastic parts. In my experience, working with a skilled team and advanced technology makes all the difference. At Ultirapid, we specialize in creating custom injection molds that meet the most stringent requirements. For example, we recently worked on a project for an automotive client, where our mold design reduced cycle time by 20% while maintaining exacting tolerances. If you’re looking for reliable, efficient mold production, we’re here to help.

    Faqs

    What Components Does The Production Cost Of Mold Manufacturing Consist Of?

    Roughly speaking, the cost distribution is as follows: 65% for cutting, 20% for workpiece material, 5% for heat treatment, and 10% for assembly/adjustment. This clearly demonstrates the importance of good metal cutting performance and an excellent overall cutting solution for cost-effective production.

    What Are The Main And Common Processing Steps In Mold Manufacturing?

    Manufacturing always involves a cutting process, which should at least be divided into three types of operations: roughing, semi-finishing, and finishing, and sometimes even superfinishing (mostly in high-speed cutting applications). Residual material milling is, of course, performed after the semi-finishing operation in preparation for the finishing process. In each operation, it is crucial to ensure that an evenly distributed allowance is left for the next operation. If the toolpath direction and workload change infrequently, the tool life may be extended and become more predictable. If possible, finishing operations should be carried out on dedicated machines, as this will improve geometric accuracy and quality in a shorter setup and assembly time.

    Why Are Round Insert Mills Most Commonly Used As The Tool Of Choice For Roughing Molds?

    When using a shoulder mill for rough milling of cavities, a large amount of step-like cutting allowance may need to be removed, causing changes in cutting forces that affect geometric accuracy. In contrast, round insert mills offer advantages in roughing and semi-roughing due to their variable chip thickness, allowing for higher feed rates and smoother cutting action. Round inserts are suitable for various materials and multi-directional milling, making them a more economical and efficient choice.

    At Ultirapid, we specialize in CNC Machining, Injection Molding, Sheet Metal Fabrication, and 3D Printing.

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