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+--- Thread: Designing for Injection Molding (/showthread.php?tid=535)
Designing for Injection Molding - fftty127 - 09-13-2021
Injection molding machines perform a wide range of mechanical movements with differing characteristics. Mold opening is a low-force high-speed movement, and mold closing a high-force low-speed movement. Plasticizing involves high torque and low rotational speed, while injection requires high force and medium speed. A source of motive power is needed to drive these movements. The modern injection molding machine is virtually always a self-contained unit incorporating its own power source. Early machine frequency ran from a centralized source serving an entire shop or factory. In this respect, injection molding machines have undergone the same metamorphosis as machine tools.
Oil hydraulics has become firmly established as the drive system for the vast majority of injection molding machines and until recently was almost unchallenged as the power source. Put at its simplest, the injection molding machine contains a reservoir of hydraulic oil which is pumped by an electrically-driven pump at high pressure, typically at up to 2000 psi, to actuating cylinders and motors. High and low pressure linear movements are performed by hydraulic cylinders, and rotary movements for screw drive and other purposes are achieved by hydraulic motors. Hybrid machines, in which the screw is driven by electric motor while the linear movements remain hydraulically powered, are not uncommon.
Injection molding,such as commodity mold, is a prevalent manufacturing process utilized across a variety of applications, from full-scale productions of consumer products to smaller volume production of large components like car body panels.
The process involves a tool or mold, typically constructed from hardened steel or aluminum. The mold is precision machined to form the features of the desired auto part, and thermoplastic material is fed into a heated barrel, mixed and forced into the metal mold cavity where it cools and hardens.
With precise tooling and high-quality results, thin wall injection parts molding produces parts reliably and cost-effectively at large volumes.
Stratasys Direct has decades of experience in all phases of tooling, including part design, tool design, material sciences, post-processing and project management. Capabilities include injection molding, pad printing, silk screening, painting, EMI/RFI shielding and light assembly.
For streamlined operations, we offer Fast Track tooling, an operation that delivers parts in as little as ten days at volumes of 25 to 1,000 units.
Whatever the project, industrial designers, engineers and product designers may face some challenges when designing for plastic injection parts molding. The following details three mistakes designers should avoid for successful injection auto molded parts.
Mold drafts facilitate part removal from the metal thin wall mold. The draft must be in an offset angle that is parallel to the mold opening and closing. The ideal draft angle for a given part depends on the depth of the part in the mold and its required end-use function.
Allowing for as much draft as possible will permit parts to release from the mold easily. Typically, one to two degrees of drafts with an additional 1.5 degrees per 0.25mm depth of texture is sufficient.The mold part line will need to be located in a way that splits the draft in order to minimize it.
Sharp Corners
Sharp corners greatly increase stress concentration, which, when high enough, can lead to part failure. Sharp corners often come about in non-obvious places, such as a boss attached to a surface, or a strengthening rib, and the medical parts.In addition to reducing stresses, the fillet radius provides a streamlined flow path for the molten plastic, resulting in an easier fill of the mold, such as fiberglass mold. At corners, the suggested inside radius is 0.5 times the material thickness and the outside radius is 1.5 times the material thickness. A bigger radius should be used if part design allows.