10 Tips for Designing Quality Molded Parts

Every detail of the injection mold design process is critical for avoiding problems with your final product. It’s best to start working with the molder early in the design process to avoid fatal flaws that could cost you time and money to fix. Luckily we’ve put together some top tips for you to keep in mind while designing your mold.

#1 – Discuss Material Options and Consequences

It’s important to work with your molder very early in your design process to choose the right resin. Semi-crystalline resins shrink more, and every material has different wall thickness and other requirements. You don’t want to discover late in the design process that the material you want to use won’t work for some reason.

#2 – Consider Wall Thickness, Shut-Off Angles, Tool-Bound Features, and Draft Angles

Every detail needs to be carefully thought out. Here are a few special points to pay attention to:

Shut-Off Angles

The shut-off angle refers to the minimum angle between the cavity and core, which can create an opening in a part that would otherwise require a cam or slide. Different molders and tool-makers will have different minimum angle requirements. While a minimum of 3° to 5° is most common, some molders may require a minimum of 8° to 10°. You’ll need to know your mold-makers requirements early in the design process.

Tool-Bound Features

Take advantage of groups of features formed by the same piece of the mold (core, cavity, slide, etc). They can be held to a tighter relative position tolerance than a group of features formed by different parts of the mold. This is ideal for features that need high relative tolerances, like sets of gear posts.

Draft Angles and Orientation

Drat angles make it easier to remove parts from the mold and reduce the odds of deformation and other problems. A part’s optimum draft depends on factors like wall thickness, material,  and shrink rate. You also want to consider which direction the draft should be oriented

#3 – Discuss Steel Safe Areas

It’s significantly easier for a tool maker to machine away steel in the mold to tighten up the clearances after initial test shots are molded rather than welding on additional steel. When you need tight tolerances like alignment features, snap fits, or interlocking parts, talk to the molder about whether to include steel safe areas in your design.

#4 – Keep in Mind Critical Tolerances

Tolerance variation can be affected by several variables, including process control, materials, and tool design. You must discuss reasonable critical tolerance specifications with your molder and consider options for possible mold revisions, if necessary. Molders may have many suggestions for maintaining tight tolerance control, like fixturing, post machining, and gate locations.

#5 – Save Money With Family Molds, Coring Out Parts, and More

There are many ways to save money on the manufacturing process. Some of the most common tips are:

  • Use family molds, where two or more different parts are shot in the same mold. Just make sure a good mold-flow analysis is performed to ensure every part fills properly.
  • Core out parts to reduce mass and material usage. Use walls and ribs to add strength instead. Keep in mind the rule of thumb to use a rib-to-wall thickness ratio of 40 to 60 percent of the thickness of the part’s surface.
  • Pass-cores let you create holes in a higher draft side surface or overhangs for features like snaps while still having a low-cost open shut mold. Creative designs can eliminate the need for slides.

#6 – Create Sealed Enclosures With Ultrasonic Welding

Ultrasonic welding can create weatherproof, strongly bonded assemblies for a low cost. It includes pressing two compatible parts into contact with each other; then, one part is excited with ultrasonic vibrations to fuse the parts. Some resins bond better than others, and amorphous resins like ABS and semi-crystalline resins like polypropylene (PP) have different optimal energy director geometry for different weld requirements.

#7 – Take Advantage of 3D Printed Prototypes…

Multi jet fusion (MJF) 3D printing can create parts that have nearly the same flexibility and strength properties as a molded nylon part, while stereolithography (SLA) can produce very fine features with a smooth surface finish that’s ideal for simulating part function and fitment.

#8 – …But Keep in Mind the Limitations of 3D Printed Prototypes

Remember that 3D printed parts will have different friction, wear, and tolerance properties than injection molded parts. They also won’t have knit lines or other features found only in molded parts. As a result, you need to keep in mind that test data might not accurately represent how a molded part would have performed.

#9 – Collaborate on Gate Location

Gate location is critical to nearly every attribute of an injection molded part, affecting appearance, tolerances, warpage, wall thickness, surface finish, molded in stresses, physical properties, and more. That’s why the gate location should be a collaboration between a molder, designer, and toolmaker.

#10 – Plan Ahead

In addition to designing the injection mold, you need to plan ahead for things like critical start-up phases, secondary operations and fixtures, and more. Each product includes critical milestones throughout each phase of development, such as: 

  • Regulatory compliance
  • Trade shows / Market Analysis
  • Tool design
  • Ordering steel
  • Machining molds
  • Sample shots
  • Texturing tools
  • Designing and building fixtures
  • Establishing quality standards
  • Optimizing production parameters
  • Pad printing
  • Painting
  • Labeling
  • Machining
  • Adding inserts
  • Assembly
  • Final product release

Let Us Help You Design Your Molded Parts

As you can see, designing molded parts involves many critical steps, many of which should be discussed with your molder before the design process has gotten very far. Contact us today to find out how we can help you design the perfect mold.

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