Injection Molding – Guide to Buying Manufacturing in China

Plastic injection molding, as you might already know, is a quick and efficient way of mass-producing plastic products such as food containers, furniture, retail packaging forbeauty products, and toys. It is very likely that any common plastic object you come across is a product of this manufacturing process. A molded part is created by injecting molten plastic at high speed and pressure into a metal mold and letting it cool and solidify to take on the shape of the mold.

What is my role as a buyer?

If you’re looking to buy plastic injection moldings, you must first understand that this kind of purchase requires a deeper involvement in the process. For example, if you are sourcing a particularly complex molded part, you might need to be involved in its design. There are numerous design decisions you need to take as these will determine your plastic injection molding price and quality. Taking informed decisions early on is critical as it will help you find and fix potential problems.

The process of buying a custom plastic injection molding starts with you, the buyer, providing the supplier with detailed 2D drawings showing material type, surface finish, tolerances (the accepted amount of dimensional deviation) and any specific critical dimensions along with a 3D design file of the part. If you go through a sourcing agent such as Sourcing Allies, we will act as the go-between. Most suppliers prefer 3D files in the STEP or IGES formats, which are the most widely accepted. Your initial design might need some tweaks and improvements, which can be made in collaboration with your supplier and sourcing agent.

从中国或其他任何地方购买塑料注射造型时要记住的一点是，您的要求非常具体 - 就塑料注塑价格，质量，交货时间等而言 -。

材料选择，以及为什么重要

A key decision a buyer must make pre-purchase is selecting the right plastic raw material. After all, the strength, durability, flexibility, functionality, appearance, and cost of the part all hinge on this choice. Given that there are more than 85,000 varieties of plastics out there, this isn’t an easy choice to make. But you can start by familiarizing yourself with the most popular plastics used in plastic injection molding and their properties:

• 丙烯腈丁二烯苯乙烯（ABS）：It solidifies quickly, has good impact resistance, is tough and sturdy, has a glossy appearance and doesn’t shrink easily when molded.ABS is used to make light and rigid partssuch as pipes, toys and golf stick heads. However, it melts or warps at temperatures above 93 degrees Celsius, making it unsuitable for parts that are subject to sustained and intense heat.
• Polycarbonates (PC):这些是一组坚硬，僵硬和坚硬的热塑性塑料，也以其热稳定性而闻名。自然透明，聚碳酸酯用于制作安全护目镜，防暴罩，紧凑的碟片和婴儿瓶。但是，对于需要一定程度的灵活性或颜色美学的产品，它们并不是理想的选择。
• Polypropylene (PP):This highly pliable thermoplastic is used for products that are flexible, lightweight, heat-resistant, and water-resistant. Food packaging, pipes, cables, bottle caps, washing machine drums and toys, for example. It can also be spun into fiber to make upholstery, carpets and rope. Polypropylene is often called the “steel of plastics” due to its versatility. However, it is difficult to dye or paint, is prone to UV degradation and is flammable.
• 尼龙：A class of plastics with high heat, chemical and wear resistance, nylons are also flexible, durable and flow easily around complex inserts. Toothbrushes, fasteners, and food packaging are some examples of nylon molded parts. However, nylons are prone to shrinkage. They also have poor dimensional stability, water absorption and heat resistance.
• Acetal:This stiff and strong thermoplastic has high dimensional stability, is easy to machine and has good wear resistance. It also offers great friction resistance, can be dyed easily and is pocket-friendly. Garden hose heads, zippers and valves are some products molded from Acetal. This plastic is unsuitable for products that will be used in environments where they are exposed to acids, UV rays and high temperatures.
• Polyethylene (PE):聚乙烯具有耐水性，非常适合防水零件。想想塑料购物袋。它也轻巧，灵活，柔软且负担得起。它具有高密度和低密度版本。低密度聚乙烯（LDPE）用于制作六包环，容器和计算机零件。它不适合在高温或恶劣的天气中使用。高密度聚乙烯（HDPE）具有高度的通用性，两者都很常见（乳液瓶, pipes) and uncommon applications (used in facial reconstruction procedures).

请记住，材料的选择不会以选择合适的塑料结束。作为买家，您必须意识到材料和产品的正确成型条件。这包括注入温度和压力，霉菌温度，弹出温度，冷却时间和周期时间。鉴于塑料注射模压零件在一天中变得越来越复杂，因此要注意草稿角度和缩小（在下一部分中详细介绍）也很重要。自然，所有这些决定都必须尽早做出，以避免延误，额外的费用以及后期和后期制作的压力。

常见的设计错误以及如何避免它们

1。Non-uniform walls:如果您的零件的墙壁变化不同，则较薄的部分将在较厚的部分冷却。这将导致厚部分中的收缩和扭曲。厚度均匀的墙壁不仅允许均匀冷却，还可以确保塑料流动并精确地填充霉菌腔。如果由于设计局限性而无法避免墙壁不均匀，请保持尽可能逐渐的变化。

2。Thin versus thick walls:除了统一的壁厚,买方必须的also consider the maximum wall thickness for a particular part. Thin walls mean a shorter cycle and lower production cost. Material selection plays a part here, so check with your supplier on the thickness specifications of the materials you are considering. As a general rule, thinner walls call for plastics that flow easily. Additionally, if your mold design requires a longer flow route, then thicker walls are more suitable.

3。Lack of drafts:墙上的草案是一个轻微的角度ca的模子vity so that its opening is wider than its base. This facilitates easy removal of the part from the mold. Without draft angles, a part can be damaged during ejection. Sometimes, even the mold might be damaged. The absence of draft angles might also result in the part warping or breaking due to stresses caused by cooling or ending up with a poor finish. Ideal draft angles vary from part to part, so make sure to consult your supplier on this. Overlooking draft angles during the design stage is a common mistake, one that should be avoided at all costs.

4.Sharp corners:When molten plastic flows across a sharp corner, it can cause stress formation in the material, leading to warpage and a defective product. Rounding off corners takes care of this problem by ensuring the material flows evenly in the mold cavity. However, stress concentrations vary with radius. Ensure your design incorporates uniform wall thickness with consistent inner and outer radii.

5.分开线位置：分隔线是在模制部分相遇的模制部分上的分离线。在任何制造过程中，其位置都是一个挑战。由于美学原因，您希望它尽可能不明显，但不会妥协该零件的功能。隔板的放置需要您的全部注意力，因为熔融塑料倾向于流向分隔线，这可能会导致闪光。此外，分开的位置会影响霉菌制造和后处理成本。

6.Too many undercuts:Undercuts are protrusions or depressions on a molded part that prevent it from sliding out of the mold. They are often used in complicated parts, such as medical equipment components, and in complex molding processes such as overmolding and insert molding. Undercuts add to cost, so they should be used sparingly or eliminated altogether.

塑料和污染辩论

如果不谈论其对环境的影响，就不可能谈论塑料。但是，随着我们成长为一个更加环保的社会，塑料注塑产业也在做同样的事情。就是这样：

• Recycled plastic plays a big role in plastic injection molding. While its performance might not be as good as new plastic, using it is a planet-friendly decision that can also lower production costs.
• 同样，塑料产品可以在回收后重新使用并重新使用。例如，回收的LDPE购物袋通常是第二次用作垃圾桶，地板，家具和镶板。
• 塑料注塑机在电源上运行。但是，随着技术进步，据说今天的设备比十年前的机器减少了20％至50％。另外，如果有选择，您可以通过液压机选择电动机，因为它更节能。

In terms of application, plastic can sometimes be a more environment friendly choice than other material. When used as an alternative to steel in aircraft components, it reduces fuel consumption because of its lower weight. Similarly, when used as insulation material in buildings, it aids in energy conservation.

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