Injection Mold Maker Tells Plastic Molding Design

• Posted by Jin hong July 9, 2021 - Filed in Arts & Culture - #Injection mold maker Plastic Compression Springs  - 429 views

  When it comes to forming plastics, design considerations given by Injection mold maker are similar to those associated with casting metals. It is critical to choose the right material among an extensive list of options based on

  (a) service requirements,
  (b) long-term effects (such as dimensional stability and wear), and
  (c) disposal at the end of the product’s life.
  Below is a list of general guidelines for the design of parts produced from plastics and composites:

  Since plastics are flexible materials, they can be used to produce many types of shapes and sizes. The production of complex parts with internal and external characteristics can be performed relatively simply and at a high rate. All three of these processes can create complex shapes with thin walls, which makes injection molding an ideal competitor with powder-injection molding and die casting. It is important to remember that when considering possible process substitutions, the materials involved and their distinct properties must be taken into consideration.
  The stiffness and strength of plastics are much lower than those of metals. The section shape and size must therefore be chosen carefully. Using the same design principles as I-beams and tubes, the section modulus of high-section steel can be achieved depending on the application. Simple means such as prescribing curvatures on parts can be used to stiffen large, flat surfaces. Venetian blinds, for example, have slats that are softly curved, yet stiff. For example, the hoods of garden tractors differ from one another in simple ways. They are made of sheet metal one time and plastic the next. A lightweight and stiff design can also be achieved by using fibers or particles.
  When selecting the appropriate shaping or molding process, the overall shape and thickness of the part are often a deciding factor. In addition to picking a specific process, the design should be such that the part and the die won’t pose challenges in terms of proper shape generation, dimensional control, and surface finish. Dimensional tolerances (particularly for thermoplastics) are not as small as in metalworking because of the low stiffness and thermal effects of this material. Injection molding, for example, tends to have much narrower dimension tolerances than thermoforming. Controlling the flow of material in the mold cavity is crucial in the casting of metals and alloys. Additionally, molecular orientation should be taken into consideration during the processing of polymer, especially when a polymer is extruded, thermoformed, or blown.
  If you wish to achieve the desired shape, avoid vast differences in cross-sectional area and section thickness. Also, avoid abrupt transitions in geometry. It is because thick sections are the last to solidify that sink marks (pull-ins) occur. Plastic parts tend to develop porosity when they contract in larger sections, as they do in metal castings, which is detrimental to product quality. Lack of stiffness, on the other hand, is likely to make removing thin parts from molds more difficult after they have been shaped.
  A low elastic modulus means that plastic shapes should be chosen properly to improve stiffness, especially when material savings are a concern. Considerations like the ones listed above are also required for the design of metal castings and forgings, as is the requirement for a minimum draft (often less than one degree) to facilitate removal from molds and dies. As a general rule, small parts should have a thickness of about 1 mm (0.04 in. ), while large parts should have a thickness of about 3 mm (0.12 in.).
  A high coefficient of thermal expansion (or similar physical properties) is an important consideration. When a part is designed or assembled improperly, it can warp (warp) or shrink unevenly. In most cases, plastics can be easily molded around metallic components and inserts, but their interfacial strength and compatibility with metals must be taken into consideration when they are assembled.
  Materials and their processing histories determine the final product’s properties. Polymers, for example, are strengthened and toughened by cold working. In contrast, residual stresses form in polymers due to their nonuniform deformation (even during simple rolling). Also, thermal cycling can cause these stresses in the part throughout processing. In the stress cracking process, such as for stress cracking, residual stresses (however they are created) play a critical role. As well, pressures that are applied to the part can relax with time, causing the part to distort over time.

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