Uncover the advantages of plastic injection molding, what affects the cost of plastic molding, and how a finished part’s cost is estimated

Technologies overview

The technologies used to process polymers are numerous. The decision to use one technology over another is influenced by a variety of factors, which we shall cover next. One of the most frequent processing methods is injection molding. In addition to this technique, plastic components can also be produced using vacuum forming, 3D printing, milling, etc. Some plastic components are designed to be processed using such subtractive techniques as milling, drilling, and turning. When choosing processing modes, it is important to take into account the many characteristics of polymers that set them apart from other types of materials. Their mechanical properties depend on temperature and the rate at which a load is applied. They are ductile and can elastically recover their original shape. They also have a high temperature coefficient of linear expansion and low thermal conductivity and specific heat capacity. As a result, subtractive processing techniques are highly costly. Each of the technologies mentioned has benefits of its own.

It's a common misconception that plastic components ought to cost little. This is not usually the case. 

The first factor that affects cost is the quantity of parts produced. Particularly when producing thousands of products, the injection molding technique pays for itself. A 3D printer, for instance, which is undoubtedly unsuitable for mass production but will be a fantastic option for a small batch at a fair price, is better to utilize for an order of 10–20–30 pieces. While the cost of producing, for instance, a ten-piece batch of enclosures using plastic molding might reach thousands of dollars. 

The requirements of the product itself will be the second factor. Some polymers have particular ultraviolet treatments and are not intended for injection molding.

Every order is unique and demands a unique strategy.

When to choose injection molding. Brief overview of the process

Before commencing development, we first ask the customer about the batch volume. The choice of technology for the product’s manufacturing is significantly influenced by the quantity of items in the batch. Since the cost of injection molding tooling can approach tens of thousands of dollars, it is typically not reasonable to employ this technology for small batch production, batch of 10–20 pieces, or prototyping.

Cost comparison for injection molding and 3D printing

The part's shape plays a crucial role as well. It takes a lot longer and costs a lot more money to convert a 3D-printed functioning prototype for injection molding. The limitations of the plastic molding method, such as slopes, wall thicknesses, rounding radii, etc., must be taken into consideration during the early phases of development.

Let's now examine the injection molding technique in more detail. Injection molding is a technological process which involves injecting the raw material into an injection mold, where it solidifies. The components of an injection mold are movable punches and fixed dies with cavities for forming workpieces. Gating systems are used to feed material into the mold. The choice of a gating system is determined by the material being processed. Gating systems can be classified as cold-channel, hot-channel, and combined ones. Injection molding technology makes it possible to include metal elements into the parts, if necessary.

Injection molding is performed on special equipment called the injection molding machine. The industrial process is controlled by automation and electronics.

Plactic development, injection molding machine
EnCata's injection molding machine

There are many benefits to the injection molding procedure as compared to other processing technologies. But there are 3 of the most common ones. It is a waste-free technology, which reduces the amount of extra material and the cost of disposing of it. Second, post-processing is kept to a minimum. It is sometimes not even necessary. Cycle rate comes in third. One minute can be used to make the finished item. 

Advantages of injection molding

To improve material efficiency, hot runner injection molding is used. This helps to eliminate sprues and waste, which in turn enhances material use. Hot pressing, silicone molding, and vacuum forming processes all consume a lot more material irrationally than injection molding does.  For hot pressing, it is the extrusions that are needed to ensure the mold is filled. For silicone molding, these are the sprues and the process elements that ensure the molding silicone cavity is filled. For vacuum forming, these are the scraps of the plastic sheet, as well as the waste after rework of the part (e.g., when cutting holes for buttons or a screen). Therefore, the absence of waste is the primary benefit of the injection molding process.

The fact that an injection molded part requires no further machining is equally significant as the prior benefit. There are exceptions to every rule, thus there are rare circumstances where post-processing is essential. An easy illustration are chrome faucet knobs. Nowadays, they are almost never composed of metal; instead, mold companies create them from plastic that has been metalized to give it an organic appearance. Or auto bumpers. They are frequently constructed with a substance that fears UV light. Consequently, they need an extra covering. The majority of the time, however, engineers attempt to prevent any post-processing, including painting, sanding, and other mechanical processes. 

An injection-molded component may be finished right away, which makes it perfect for large manufacturing.

A further benefit of injection molding is that parts produced this way can have more intricate contours than those produced using subtractive techniques.

Molded parts of the Blood Container

This is because engineers employ tooling technology that they cannot afford in single-piece production in order to prepare for the creation of millennial pieces. Because of economies of scale, only a small portion of the total cost of the product will be attributable to the use of expensive technology. Such a technological approach in the context of plastic injection molds incorporates electrical erosion. We can create practically any mold using electroerosion without the need for undercuts. In the most extreme scenario, we simply take not just one, but multiple electrodes, arrange them how we choose, and obtain a solid piece. Additionally, the quality will be excellent, and practically any shape is conceivable. That is not possible with machining. For instance, if we need to create a triangular hole, a mortising machine will not be able to do the task, especially if the construction element is small.

However, we can easily create a triangular electrode and burn a hole with it. It is important to keep in mind that the electrode is milled and that electroerosion is a slow process. When combined, this comes at a significant expense.

What Influences Development and Production Costs

EnCata is frequently asked to estimate a part's cost after the customer's personnel has created it. Naturally, labor costs to prepare the item for production and create the mold will be influenced by the quality of the initial design. We might have to put a lot of work into redoing things if the initial 3D model ignores technological constraints like wall thicknesses. We had a customer who was very meticulous about design, and every millimeter of it was checked. Therefore, we were unable to reach consensus on significant design improvements for this project that would have decreased both development and production costs. It took over 400 hours to design a tiny enclosure with 3 parts that could fit in the palms of your hands.

When estimating labor costs for part production, the weight of the component, the equipment utilization factor, which influences the frequency of changeovers, and characteristics like the batch size are typically taken into account. If a batch of 1,000 pieces per month with a 20-second manufacturing cycle is requested, we will charge a price that is remarkably high. But because no retooling of the equipment is necessary if the product is produced for three consecutive months, the price will be then reduced.

Machine changeover is a crucial factor in determining how much a product will cost. While the production process may only take five hours, changeovers occasionally last six hours. The final cost of the part will be significantly impacted by this. On the other hand, the 6-hour changeover time has less of an effect on the ultimate price if the part is produced in two weeks and two shifts.

Finally, the core factors that affect plastic parts cost include:

  • The degree of difficulty in constructing the part and the tooling for it;
  • the product's look;
  • the manufacturing process selected;
  • the substance from which the product will be created.

First and foremost is the degree of difficulty. The future product's appearance comes in second. Making parts that resemble the iPhone for their body is currently quite popular. No wonder, either. The iPhone currently holds close to 50% of the global smartphone market, and everyone enjoys its aesthetic. The current iPhone has two shaped surfaces: two rectangular pieces of flat glass. This component appears difficult at first, but it is actually made for a straight molded connector; as there are no undercuts, nothing is prevented from opening after the cycle. Consequently, even if it is an iPhone body, making such a part is not expensive.

The axiom states that a part will cost less the simpler its mechanism is. The price of the finished product will be affected by any recesses, side undercuts, or grids that a part may have. This is due to the fact that a complex part with several holes and undercuts will require a greater tooling area and, as a result, be more expensive than a flat part without undercuts.

An illustration is the lid for cups in coffee spots, which was created by EnCata. The lid can be produced using injection molding or stamping. Because there is no waste left over after production, EnCata engineers chose the injection molding method. It is also the least expensive technique of the two viable options in terms of operational costs. The coffee cup lid is a part that is as simple as possible; it doesn't have any undercuts, bends, or frills, so the injection molding technique was also acceptable.

Cup covers from injectiom molding

Let's examine the algorithm for calculating the cost of a part. The two main elements that affect an injection molded part's price are its weight and how complicated it was to make. Depending on the weight of the finished part and the production process, specialists favor one injection molding equipment over another.

The two criteria used to rank all machines are the size of the working field, or the size of the tooling that the machine can handle, and the amount of plastic that the machine can inject at once. Now we can try to produce a simple sheet. The part might seem thin, small, and light. However, it will still require processing from a huge machine as there should be a large working field. Likewise, when producing a large, ribbed item, we may need a huge machine – not because the part won’t fit, but rather because a significant injection volume is necessary. Therefore, if you disregard the equipment's depreciation, you are left with three evaluation criteria: item weight, material usage, and labor.

What comes out of it all

The intricacy of the product design and the quantity of the product's production are the main factors that affect the cost of manufacturing a plastic item.

When producing a significant quantity of the product, using the injection molding method to make the parts is justified. This process has benefits in that it produces no waste and that injection molding machines can make parts quickly. The technology's biggest drawback is the high cost of tooling. When a product has a lot of plastic components, this can be a roadblock for entrepreneurs. Mold purchases might cost up to several hundred thousand dollars. However, if you want to build the part in big batches, the speed and quantity of goods produced more than make up for this drawback. With the right amount of sales of your product, you will be able to swiftly return your investment.

EnCata produces products using a variety of plastic processing techniques. We evaluate each project on an individual basis, assist the customer in selecting the manufacturing technique that will best produce the product, and then design the item specifically for that manufacturing technology. If injection molding is necessary, we have all the injection mold tooling needed to ensure that the custom plastic molding is produced to a high standard.