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 for beauty 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.
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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.
One point to remember when buying plastic injection moldings from China or anywhere else is to be very specific about your requirements – in terms of plastic injection molding price, quality, lead time and so on – to your supplier and preferably to put it all in writing.
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:
Remember, material selection doesn’t end with picking the right plastic. As a buyer, you must be aware of the right molding conditions for your material and product. This includes injection temperature and pressure, mold temperature, ejection temperature, cooling time and cycle time. Given that plastic injection molded parts are getting more intricate by the day, it is also important to be aware of draft angles and undercuts (more on these in the next section). Naturally, all these decisions must be taken early to avoid delays, additional expenses, and stress mid- and post-production.
A plastic injection molded spoon among wooden beads1. Non-uniform walls: If your part has walls of varying thickness, the thinner sections will cool before the thicker ones. This will cause shrinkage and warpage in the thick sections. Walls with uniform thickness not only allow uniform cooling, they also ensure that the plastic flows and fills the mold cavity precisely. If you cannot avoid non-uniform walls due to design limitations, keep the variations as gradual as possible.
2. Thin versus thick walls: Apart from uniform wall thickness, the buyer must 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: A draft is a slight angle on the wall of a mold cavity 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. Parting line placement: The parting line is the line of separation on the molded part where the two mold halves meet. Its placement is a challenge in any manufacturing process. You’d like it to be as inconspicuous as possible for aesthetic reasons, but without compromising on the part’s functionality. The placement of the parting line requires your full attention because molten plastic tends to flow towards the parting line, which can cause flashes. Additionally, parting line placement impacts mold-making and post-processing costs.
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.
It is impossible to talk about plastics without talking about its impact on the environment. But as we grow into a more environmentally conscious society, the plastic injection molding industry is doing the same. Here’s how:
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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China’s plastic injection molding cost is much cheaper than of the USA or Europe. Sometimes, for the same quality, the cost generally will be only 50%. Usually, the injection mold is the most expensive part of the project, and can dramatically increase costs for small part runs. With such a competitive price from China, it can totally enhance your product market competitiveness.
If you are looking for a China plastic injection molding manufacturer to make your plastic molding parts, your first question was likely How much does the China injection molding cost to make my product? Is there any way to lower the mold cost in China?
The larger the part size is, the larger the mold size is, and needs more mold steel, mold cost will increase significantly.
The more complex part will require a more complex mold structure, which then leads to more mold costs. Reduce needless surfaces and corners or features as much as possible, which will save huge mold costs.
The plastic mold and injection molding parts costs will directly influence whether your project goes smoothly and success or failure. When you start to design a plastic part for injection molding, many factors you should consider, such as part complexity, part size, part surface, part material, mold cavity number, and production volume, will affect the price tremendously.
One cavity mold needs less time and process than multiple cavities mold (also called family mold), which will reduce mold cost, but rise the part unit price. If your production volume is small, then one cavity mold is enough; if the volume is large, you could consider multiple cavities mold.
The material cost will vary according to the type and quality of plastic you use. For example, if you choose high-cost fiberglass filler material, the mold material needs hardened steel, which also will increase the cost.
An attractive surface finish will add more processing cost and time, if the part surface is not very critical or the plastic part is invisible in the assembly product, you can choose a lower-level finish, such as SPI Finish B-3 or lower C grade.
3. How to Reduce the Plastic Injection Molding Cost in China
The best way to reduce the plastic injection molding cost in China is to find a professional plastic injection molding manufacturer. With their help, you don’t need to know so many skills to reduce the cost, they will do it for you.
However, finding a reliable plastic part supplier is not an easy thing, you can consider the following tips to reduce your plastic injection molding.
1) Save Cost From the Design
A professional plastic injection mold manufacturer knows well how to control the cost from the design stage. It is a very important skill because the design concept can determine the cost of the whole project.
The plastic injection mold manufacturer usually needs to hold a meeting in the early stage, it should consider the injection molding production, product assembly, and then find the best reasonable design. Engineers will design the mold according to this scheme, which can reduce a lot of costs.
2) One-stop Injection Molding Service
One-stop injection molding service includes mold design and manufacturing, product injection molding processing, plastic shell surface treatment (spray, screen printing, etc.), and other one-stop outsourcing services.
Why do so many plastic injection molding factories emphasize one-stop injection molding services? Because it can not only reduce the plastic injection molding cost but also save a lot of time.
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One-stop injection molding service can improve production efficiency greatly. The factory with one-stop service is also very professional and has enough strength to provide you with a better service.
3) Sample Test
A sample test is a must before you start your plastic parts mass production. You should require the injection molding factory to provide the proofing services. This process can tell you whether the molding factory’s production quality is good or not.
If the sample quality is poor, the next mass production goods are even worse. To avoid unnecessary loss, a sample test is the first thing you should do before you start your project.
4. Cost Estimating methods for plastic injection molding
Of course, we couldn’t totally rely on the plastic injection molding manufacturer to give us the price. We can use some methods to estimate the plastic injection molding cost. Here are some common methods to estimate the plastic mold parts cost.
1) Feature-based cost estimate
This feature-based cost estimation tool is suitable for plastic molding in production quantities (more than 10,000 pieces). Since it has a smaller impact on the cost of each component, more durable and expensive tools can be used. The material costs are estimated based on the geometry of the part, and current material prices are used.
In order to reduce production costs, a compatible injection molding machine was selected from a database of more than 50 machines, and the cycle time was estimated based on the part geometry, material properties, and machine specifications.
For the mold cost, use the standard mold size and mold category to select the appropriate mold base, and estimate the required mold processing based on the geometry of the part and other user specifications. These three costs (materials, production, and molds) are calculated for 4 different cavity arrangements (1, 2, 4, and 8 cavities) and provide the most cost-effective option.
2) Low-volume injection molding cost estimate
This feature-based cost estimation tool is suitable for injection molding in small batches (less than 10,000 units). Because of the great impact on the cost of each part, the rapid tool method (high-speed processing of 104 molds) is used to create molds. Material costs are estimated based on the geometry of the part, and current material prices are used. In order to reduce production costs, a compatible injection molding machine was selected from a database of more than 50 machines, and the cycle time was estimated based on the part geometry, material properties, and machine specifications.
For the cost of plastic molds, use the standard mold size to select the appropriate mold base, and estimate the required mold processing based on the geometry of the part and other user specifications. These three costs (materials, production, and molds) are calculated for 4 different cavity arrangements (1, 2, 4, and 8 cavities) and provide the most cost-effective option.
3) Standard estimate
This standard injection molding cost estimator does not require any part geometry but requires more input of process parameters to calculate a more accurate estimate. Material costs are estimated based on the number of parts and runners, and an up-to-date material database containing pricing, and customizable process parameters. For production costs, cycle time, as well as machine rate and labor rate must be specified. After adding mold cost, a detailed cost breakdown of material, production and mold costs is provided.
4) Plastic mold cost estimate
This feature-based cost estimator calculates the mold cost for plastic molding. According to the geometric shape of the part and the requirements of the mold, such as the number of cavities, use the standard mold size to select the appropriate mold base. The required mold processing is for the selected SPI mold type and the rapid plastic mold method can be selected for 104 types of molds or low-volume products.
5. China Plastic Injection Molding Cost FAQ
Here are some problems that our injection mold buyers faced:
1) Is 3d printing cheaper than injection molding?
If mass production is required, traditional molding methods such as injection molding are inseparable. Just need a separate product or sample, try 3D printing.
2) Is a small injection mold cheaper than a large injection mold?
The injection mold price is not only determined by the size of the product, but also according to the complexity of the structure of the product. Small injection mold requires higher accuracy, so the cost of production may be not cheap.
3) How do you know if you have got a good price for your plastic injection molding?
Plastic injection molding is a very competitive industry, there is no standard price at present. To win the customers, some plastic injection molding factories even don’t add any profits to the price, only add some processing charges.
Holly plastic has a client who needs a plastic mold for e-cigarettes, before contacting us, they worked with a plastic injection molding supplier in Dongguan. Because using poor material, their mold suction holes are easy to burst.
The price was nearly double that of the first supplier, and it really scared the customer. Because we need to use food-grade material to make this mold, this material will not deform at a temperature of 80 degrees, and it is a special non-toxic material. The client finally agreed to our offer, we finish this project together successfully. So you see, the price is not the only thing we need to consider!
4) Can I choose a small plastic injection molding factory in China as my partner?
In China, especially in Guangdong and Zhejiang, there are many small plastic injection molding factories, some of which can not only give you a great price but also guarantee quality. However, small may not mean cheap, it also means poor quality. Scientific team management can help small plastic mold factories lower the cost and improve the quality, if you find a professional engineering team, a small factory will help you save a lot of money and time.
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