Injection molding is a highly repeatable, highly scalable process. But there are a few best practices that ensure tolerance, form, fit, and function.
In a recent webinar onDesigning for Manufacturability without Compromising the Time-to-Market，约翰西多黎各拉副总裁兼客户服务Xcentric模具与工程，Xcentric模具与工程首席营销官员和Petro Tsarehradsky讨论了10个重要的最佳实践。
- Material choice。生产高质量的塑料injec一致ted modeled parts relies heavily on the chosen material. One source to explore is WhichMatWeb.com. There you can browse materials by name, type, performance, and characteristics. It’s a free site. Another option is go directly to material manufacturers.
Consider mixing materials. With today’s injection molding processes, you have the option to mix materials or include additives. Additives can be a way to enhance materials to meet your needs. One additive to consider is glass. Another is carbon fiber, which will add strength and static dissipation.
- Appropriate wall thickness。在您的材料选择旁边，在整个部分中保持均匀的壁厚至关重要。
墙壁厚度通常会确定机械性能，美容外观，易于模塑部分，以及部分成本。
Achieving an optimal wall thickness is a balance between strength and weight. A 10% increase in wall thickness provides about a 33% increase in stiffness with most materials. But avoid changing wall thicknesses within a design, going from thick to thin or from thin to thick over sections.
稍后将提到这一点，但肋骨和曲线可以为一部分提供强度而不诉诸增加壁厚。
- 草案。草案是设计成辅助部分从模具中移除的角度。包括设计中的草稿，以防止将喷射器引脚推入您的部件，尤其是在腔体或显示表面上。
草稿，年度，棘爪在弹射期间均易于摆脱霉菌。较少的选秀有时会在喷射期间损坏部件，称为阻力的条件，尤其是在分组线上。
A minimum recommended draft angle is a half a degree. A preferred draft angle is one and a half to two degrees, especially if you’re going to be adding textures.
- Runners and gates应设计并纳入一个模具ensure the consistent flow of material to fill the mold at the right pressure. A gate is the connection between the runner system and the molded part. The location and size of the gate is integral to the molding process.
- Appropriate tolerances.具有太紧耐受性的部分可能导致性能损失甚至部分失败。先进制造技术的一支技巧可以建议安全有效地达到精确规格的最佳方式。
Many factors come into play with tolerance, including materials, part complexity, tooling, and of course the injection molding process. A tight tolerance part for injection molding is plus or minus two thousandth of an inch. Starting with a good part design will ensure your tight tolerances.
If you have a tight tolerance chart, look at using low shrink rate materials such as ABS and polycarbonate materials, which have a low shrink rate. Thicker walls produce different shrink rates depending on the material, making repeatability difficult.
Higher shrink rate materials are going to be materials like nylons, unfilled nylons, polyethylenes, and polypropylenes.
Avoid tight tolerance areas around the alignment of mold halves, the parting line, or in moving mold components such as slides. If you have two parts coming together, such as in a housing, you may want to do a beauty reveal, where you can get away with hiding the mismatch.
- Ribs.肋骨通常用于结构增强。它们允许零件的更大的强度和刚度，而无需增加壁厚。
As a general rule, design ribs as approximately 60% of your nominal wall, or whatever the wall that the rib is joining, to minimize risk of sink. Glossy materials require a thinner rib, typically about 40% of the wall thickness. Thin ribs may be more difficult to fill in, especially once you start adding draft to them.
A proper rib design involves five parameters:
–Thickness, this affects cooling rate and degree of shrinkage, which may cause warp.
- 肋骨的高度不应超过肋骨基底厚度的三倍。
-地点。添加到非临界区域的肋骨实际上可以降低抗冲击性。
-数量。添加肋骨比移动它们更容易，因此它们应该谨慎使用。
— Moldability. Thin ribs can be difficult to fill. A good check is to request a mold flow and a manufacturability analysis through your injection molding provider.
- 老板用于定位，安装和组装。壁厚和高度是考虑的最大因素。老板设计特征周围的壁厚应为标称厚度的60％，类似于罗纹。
If a nominal part thickness is greater than one-eighth, the boss wall thickness should be around 40% the nominal wall. The height of the boss will also have a role. As a general rule, the boss height should be no more than two and a half times the diameter of the hole on the boss.
- Reduce undercuts.An undercut is any indentation or protrusion that prohibits the ejection of a part from a mold. Most commonly, it’s called an undercut, internal, external, or inaction. Undercuts typically increase mold complexity and can lead to higher mold construction costs. Use creativity and design them in a way where actions won’t be needed.
- 角落和过渡tie into wall thickness. Any sharp corners can cause molded in stress, just from the resin flow.
通过使用圆角来最小化压力，在内角，外角上添加RAD，并试图保持一致的壁厚。
- Thick and thin transitions.尽可能平稳地设计这些。尽量避免步骤;使用斜坡通过您的部件提高材料流动。
Follow these best practices in the following order to ensure an easy, cost effective molded part: materials, wall thickness, tolerances, draft, ribs, bosses, undercuts and corners, and transitions.
Leslie Langnau.
[email protected]
Filed Under:成型•注塑成型部件
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