When manufacturing or designing the plastic parts of products, there are different manufacturing techniques that are available. Before one starts with prototyping their part and finding out how much of the plastic parts would need to be produced, it is crucial to learn about the options that are available to you. It allows you to decide which method to select in order to ensure that your needs are met. There are two methods that normally come to mind when exploring your options. They include plastic injection moulding manufacturing and CNC plastic machining. This post compares the two to help you decide which one to opt for.
From speed to material selection and scale of parts production, it is important to find out what makes plastic moulding manufacturing and CNC plastic machining different. Even if you know a bit about the two options, it can be difficult to decide which one to select to create custom plastic parts. The decision can be complicated. However, this post aims to answer all the questions that you might have in mind so that you can choose the plastic manufacturing process which works best for you. Now, you should bear in mind that during the development life cycle, it is possible for the method to change. Both plastic moulding manufacturing and CNC plastic machining have their own pros and cons. Let’s start with understanding each process.
Plastic Moulding Manufacturing
As you might have already gotten an idea about the process, it involves injecting the material into a mould. The stock material is melted to do so. Then, it is forced into the mould at a very high pressure. After this, the part is left to cool down in the mould. Finally, it is ejected from the mould. This process continues until the next part. Thermoplastics are mostly injected into the moulds. They are also referred to as tools. The plastic is first heated to be injected. A well-made mould, loaded into electric or hydraulic machines allows precision parts to be made. Plastic injection moulding companies can help deal with the process.
CNC Plastic Machining
Unlike plastic moulding manufacturing that involves filling, CNC plastic machining is a process which generally begins with a block of the material which has its material layers removed by using the CNC machining. This is where a CNC laser cutter comes in handy. The process enables most of the different materials to be put to use. However, there are certain limitations to it. But, since the entire process is computer controlled, precise results are achieved. For those of you that do know what CNC is, it stands for computer numerical control. Computer-controlled machining helps cut the removal material. The information is pulled from a digital file which allows alterations to be made in production. The final product is produced as the computer breaks down the files into a series of different commands which enable the material to be used. Quick transition between physical parts and digital designs is also possible due to this.
So Which Process Should You Choose?
Generally, when deciding which process to choose, you need to look at it from a point of view where you trade off between different materials, volume, speed, design, surface finish, tolerances, and characteristics. Each of these is an important feature that needs to be considered.
- Speed
Understanding the speed offered by both plastic moulding manufacturing and CNC plastic machining is quite simple. CNC machining offers the fastest speed for low volume parts. For instance, if you require 15 parts in 3 weeks, CNC machining is the way to go. On the other hand, if you want 25,000 parts in 2 months, then, plastic moulding manufacturing is the perfect solution. Injection moulding needs time for the mould to be made and parts to be ensured. Thus, it could take anywhere from just a few weeks to even a few months. However, once it has been completed, it should not take much time for parts to be created using the mould. It is a relatively fast process. Investing in injection moulding will end up paying off in the long term.
- Volume
Another factor that needs to be considered is volume. It is important to look at independent of time. The main focus should instead be from the price part. The option that is cheaper depends on the volume you intend to produce. If you require just a few parts to be made such as a few hundred, CNC plastic machining would be cheaper. You would get some benefit out of the volume in the form of price. It will only be for up to a hundred. But, for larger volumes, you would be unable to add any other benefit. It is because of the distribution of the setup cost with the number of parts produced.
On the other hand, the real cost for each part of injection moulded parts is a lot less than machined ones. But, there is a large upfront cost that needs to be covered for injection moulding in order to create the mould itself. To determine the cost of each part, it is spread out over the amount of parts made. Thus, it will be possible for injected parts to be cheaper as compared to machined ones at a certain volume despite the high upfront cost of the mould. The gap in cost would become greater and greater as more parts are made. It is possible for a crossover to be achieved in as little as hundred parts or by 5000 parts.
- Material
When we look at the selection of materials offered by each option, CNC machining stands out. It provides a better selection of materials for creating parts. It can be an important deciding factor when there is a need for a specific plastic to be used or high performance plastic. Generally, harder plastics can be more easily handled with the machine than softer materials. As for injected moulded components, material selection tends to be quite limited. More high-performing materials can be created through injection moulding. It is a good idea to find a company that offers a variety of mouldable plastics so that you can work with more materials. However, there are still certain materials that would be near to impossible for the machine to produce. But, moulding can work with them like rubbers and similar flexible materials.
- Surface Finish/ Tolerance
Again, CNC plastic machining would win in this category. Offering use for more materials, a better surface, and a tighter tolerance, CNC machining seems to be the way to go when looking at surface finish/ tolerance. But, this does not mean that injection moulding does not offer any advantage. It offers the benefit of repeatability which CNC machining cannot offer. Besides, a great thing about moulds is that they can last for even the millionth of part without causing much wear and tear. It allows for the parts of a single batch to be identical with ones of the next batch. With CNC machining, more variability is common as each part is put into the machine. It is something that needs to be considered.
- Design
Now, you might be wondering that would the design change. If it does need to be changed, then, it might not be worth it to get a mould made just yet. Since moulds are difficult to make, it can be impossible to modify them many times to change the design. Even before that, the process of designing a part to machine is very different as compared to moulding. In both of the cases, a process can make features difficult or rather impossible to build through other processes.
If you are looking for more flexibility in design, you would need to go with machining. It lets you make many features easily which would be impossible or very difficult in moulding. Besides, it would be too expensive to do so in moulding. Some of the features which would be difficult to change include variable wall thickness, large walls, overhangs, and the like. But, injection moulding helps with deep features, living hinges, and square holes to be made more easily which machining would find expensive and too difficult.
The above should make it clear that making a decision between injection moulding and CNC machining is not as straightforward as one might think. Even in a single factor, there are many things that come at play and cannot be ignored. It might be best to opt for a two step operation if you require some of the benefits offered by both options in terms of price, design, features, and tolerances. The main feature could be injection moulded. As for the secondary feature, it would be a machining option which would provide the end result. It is a common technique that is adopted by some of the biggest companies across the globe. Besides just CNC machining, there are other manufacturing processes as well that can be considered. Besides, it is always better to know all of your options beforehand.
Questions To Ask?
To better understand how you can incorporate the abovementioned differences between the two methods, the following questions will help you choose the option that works best for you.
- How Many Customized Plastic Parts Are Required?
The first question that you should ask yourself is how many customized plastic parts would be required. Plastic injection moulding tends to be more affordable per part as compared to plastic machining. However, its upfront cost might be too steep if you only want to create a few hundred parts.
- Would There Be A Need To Change The Design Of the Part?
Before you decide to invest in a mould, you have to consider the design of the customized plastic part. It is financially inefficient for you to opt for one option without considering if you will need to change the design of the customized plastic part in the future. Go with machine if you need to alter the design from time to time. You cannot spend on mould if you require change of design since it is too difficult to change and financially not feasible.
- How Precise Should the Custom Plastic Parts Be?
To get plastic parts to offer the same design specifications, the better it would be to machine them. Achieve similar design specifications through machining.
Although injection moulding is also precise, there can be some differences from the initial specifications. If the product can be somewhat flexibility in terms of its specifications, you can still go with moulding.
- How Perfect Would the Plastic Parts Need To Be?
When you select plastic moulding manufacturing, you will encounter slight cosmetic imperfections which might be inacceptable. For instances, a slight flaw is possible by the gates of the moulds. Small depressions may be left when the knockout pins are removed from the part. It can be problem to achieve perfect surface smoothness with plastic injection moulding. Hence, CNC plastic machining would be much preferred if you cannot have any minor cosmetic defects.
- Is There A Need for An Advanced Specialty Plastic?
Finally, you also have to consider if advanced specialty plastic is needed. The selection of materials available are more limited if you opt for injection moulding as compared to machining. Soft and flexible materials like rubber can be moulded. But, high-performance and harder specialty plastics need to be machined. Thus, if you have an advanced specialty plastic in mind, you would need to choose machining.
Conclusion
Once you have gone over this entire post, you will have a better understanding over the differences between plastic moulding manufacturing and CNC plastic manufacturing. It can be difficult to decide which option to get. However, when you consider selection of advanced specialty plastics, cosmetic imperfections, flexibility of design, cost efficiency, turnaround times, and possible tolerances, you will be able to choose which option to pursue. There is bound to an option that you will find more appropriate.