Injection molding overview

Transcription

1 Injection molding overview This injection molding overview is designed to help our customers understand the process of injection molding and mold-making. Please read it fully as it helps to define what is expected of the customer and what you can expect from us. Injection molding is a manufacturing process for producing parts by injecting material into a mold. Injection molding has been a significant process for the plastics industry since it began in the late 1800s, and it is performed with a host of thermoplastic materials, including elastomers. During the injection molding process, material for the part is fed into a heated barrel, melted, mixed, and forced into a mold cavity under extremely high pressure and speed. The material then cools and hardens to the configuration of the cavity. Speed and consistency are vital to creating a successfully injection molded part. Because of the many variables involved in molding plastic parts, designs for such parts must be expertly and precisely developed. The part s material, the desired shape and features, the material of the mold, and the properties of the molding machine are just some of the many factors that must be taken into account in the design phase. At the same time, this level of detailed complexity also facilitates near infinite varieties of design considerations and possibilities. Therefore, when properly designed in the beginning, a part will be optimized for the injection molding process. Additionally, molds can be designed and machined to create a single cavity or multiple cavities. Furthermore, multiple cavities can be identical in shape in order to make multiple copies of the same part at once, or under some circumstances each cavity can be unique so that different parts are created during each injection cycle. In spite of even the best designing and machining efforts, a few cosmetic features are unavoidable, such as parting lines, sprues, gate marks, and ejector pin marks. Gate marks will form where the plastic delivery channels join the part s cavity inside the mold. Parting lines and ejector pin marks can form from minute misalignments, wear, gaseous vents, and/or other microscopic differences on the mating surfaces of the molds, as well as the surfaces of the cavity that come in contact with the melted plastic. 1

2 Mold making process at HPE The design and machining of the mold are critical in the ultimate outcomes of the part being molded. Each mold for each part is a complicated series of components that must work together within very close tolerances under extremely high temperatures and pressures. As the preceding overview illustrates, successful mold making is a complicated and technically challenging process. The sample image below illustrates how even a simple but typical mold contains an array of complex and interdependent parts and features. HPE brings numerous years of experience to the process, and we have established detailed design requirements and procedures to ensure successful and efficient mold making. We would like to review some of our mold making processes so that you may become more familiar with how your project will proceed at HPE. At HPE we divide mold-making into 5 stages 1) Part Model Evaluation, 2) Mold Design, 3) CNC Programing, 4) Machining, and 5) Assembly & Bench Work. STAGE 1 Part Model Evaluation: Because of the precise nature of injection molds (± ), this may be the most important phase of the mold-making process. After HPE receives your purchase order and deposit, we will conduct an extensive evaluation of your part s CAD model to verify that it will work with the injection molding process and produce your 2

3 desired part. We review a long list of criteria and factors required for good injection molding uniform wall thickness, acceptable draft and rounds, undercuts, side actions, and gate and ejector pin locations, among others. During this stage we examine the geometry and integrity of your CAD model as thoroughly as possible. Our goal is to discover and correct any possible flaws or inconsistencies in the beginning in order to make an accurate and reliable mold later. We review all drawings or other specifications provided to us, and we will update you about any findings and/or need for minor changes. If the changes are major however, we may need you to adjust your CAD model accordingly before proceeding. Whether any changes are needed or not, we also use this initial evaluation to be certain our quote matches the scope of your project number of cavities, materials, etc. STAGE 2 Mold Design: Once the CAD model for your part is evaluated and any adjustments finalized, HPE engineers and designers will create a detailed and accurate CAD model for the mold that will be used to make your plastic part. Cavities, slides, lifters, cores, and many other elements for the mold are designed at this time. This process is guided by detailed operational procedures and checklists that include numerous design reviews to better provide correct mold performance later. During this process, additional issues that escaped our initial evaluation might still surface. We may also find problems with the CAD model integrity or continuity if they become apparent at this stage. As with Stage 1, we will update you as needed during this process, as well as when we have completed this second phase of the project. STAGE 3 CNC Programming: After we have completed the CAD model for the mold, we will use that model to create CNC programs for machining of your mold on our state of the art machining centers. Similar to designing the mold, we adhere to documented procedures during this phase, as well numerous reviews of the programming. The programs will also be 100% computer verified before being sent to our CNC machines. And just as before, we may once again uncover an additional concern or two that escaped us previously. As always, we will regularly communicate our progress and findings so you can provide input as needed. STAGE 4 Machining and EDM Work: This is point at which the programming for the mold is executed and the CNC machines to make all the components of the mold, including any EDM electrodes if needed. HPE uses extremely accurate, ultra-high-speed machining centers that are automated to operate around the clock. During the machining stage, the mold components are periodically examined for overall fit, geometric accuracy, and surface finish so that any observed inconsistencies can be rectified as needed. 3

4 STAGE 5 Assembly and Bench Work: As soon as machining is complete, all necessary components are assembled to create a functional mold. Specific documented procedures are followed during this stage as well, and a number of tests are performed to confirm that the opening, closing, ejecting and other actions work smoothly and correctly. Texturing and/or polishing is not completed at this time. We will wait until first-article parts are molded and evaluated before the mold is polished or textured. Now that your mold is completely assembled and verified, we perform a First Article Molding run with the mold that tests its ability to make your plastic parts. This is done by using the mold to make plastic parts on an injection molding machine similar to the one illustrated on the left. The goal is to create parts that match your CAD model finalized in Stage 1 above, excluding any cosmetic requirements. Normally, after HPE has received your second and final payment for the mold, these parts will be sent to you for First-Article Approval. These First Article parts allow you to confirm that they match the CAD model and drawings finalized and agreed upon. This important step is your opportunity to examine the fit and function of the parts as they are intended to be used. Any objections to the parts must be documented by recording the measurements that deviate from the CAD model and drawings. After we receive your first-article report with documented measurements, we will develop an appropriate plan for any possible corrections. During this process, please remember that HPE can only be held to the drawings and CAD models agreed upon in the quote and Stages 1, and not the actual function of the part. If changes are needed to make the part function correctly, and if these changes deviate from the finalized CAD model, there will likely be additional fees especially when modifications to the mold are required. In order to faithfully serve all of our clients, it is necessary for us to cover any costs above and beyond originally agreed upon quotes. If needed, we can provide an additional quote that addresses any changes that may be needed on your mold and gladly make all adjustments requested until the parts produced by your mold function as desired. Once the first-article parts are approved, we will perform any polishing or texturing of the mold cavities. At this point, the mold is ready for production of parts. 4

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