DESIGN TIP: Cutting Corners on Injection-Molded Parts

Sharp corners definitely have their place in part design, but they often spell trouble when injection molding plastic parts. Accordingly, designers should be aware of the pitfalls associated with “being square” when developing parts. Indeed, part accuracy, strength, and aesthetics suffer without the right amount of corner rounding and filleting.

This month’s design tip explores ways to strengthen injection-molded parts while reducing costs with proper placement of corner radii and fillet. You’ll learn about:

  • Material selection. Some plastics are more forgiving of sharp-cornered parts. Choosing the right one for your application is a necessary step towards accurate, functional parts.
  • Wall thickness. Beefing up adjacent walls may absorb some of the stress associated with sharp internal corners, but can create other design challenges.
  • Part geometry. Some parts are simply more “moldable” than others. Achieving proper form, fit and function depends on sound part design, a large piece of which is appropriate corner radii.

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DESIGN TIP: Metal 3D Printing Redefines Part Design

Metal 3D printing is helping to redefine part design, with capabilities to build ever-increasingly complex parts in less time and with little human intervention. Welcome to the industrial-grade 3D printing process of direct metal laser sintering (DMLS), which is the focus of our monthly design tip.

Med device developers are turning to industrial-grade metal 3D printing to produce a variety of prototype and end-use parts, including these components used for surgical instruments.

Through additive manufacturing technology, DMLS produces fully function metal prototypes and end-use parts, simplifies assembly by reducing component counts, offers virtually unlimited complexity with no additional cost, and works for a variety of industries, including the med device space (see part photo).

This month’s tip discusses:

  • A short overview of DMLS
  • Ways to avoid warping and curling with certain part features
  • Part orientation
  • Wall thickness considerations

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DESIGN TIP: Improving Part Design with Uniform Wall Thickness

Designing parts with consistent wall thickness is a fundamental rule of plastic injection molding, and ignoring it can lead to sink, warp and inaccurate or non-functional parts. Yet the functional requirements of consumer, medical, aerospace and industrial products often leave designers little consideration for the material flow and fill properties of plastic, both of which are at least partially determined by wall thickness.

Pay close attention to rib-to-wall thickness ratios. To prevent sink, the thickness of the rib should be about half of the thickness of the wall.

This month’s tip discusses:

  • Guidelines to avoid cosmetic defects associated with thin and thick features
  • Material alternatives to improve wall thickness consistency
  • Important questions to ask about material properties
  • The benefits of design for manufacturability analysis

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6 Ways to Cut Machining Costs

The left image illustrates resulting corner radii from milling. Consider adding reliefs to sharp corners (right image) to improve fit.

Machining gets a bit more complex every year, and as a result, it can be challenging to keep pace with the do’s and don’ts of part design. But lowering the cost of machined parts while improving functionality can still be achieved by a few relatively simple adjustments to your part design or material selection.

Small tool diameters add machining time so consider removing text or logos from machined prototypes.

This month’s tip discusses:

  • Machining corner holes
  • Deburring edges
  • Avoiding unnecessary text
  • Keeping an eye on thin features
  • Reducing part complexity
  • Selecting material alternatives

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13 Cosmetic Defects and How to Avoid Them

As with any manufacturing process, injection molding comes with its own set of design guidelines, and design engineers who understand these best practices will increase their chances of developing structurally sound and cosmetically appealing parts and products.

Learn about different cosmetic issues that commonly occur on injection-molded parts, and how to eliminate them to improve overall part appearance and performance. This month’s tip discusses sink, warp, flash, knit lines, drag, vestiges, jetting, splay and other cosmetic issues.

Read the full design tip here.