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Design for Custom Plastic Parts
Customizing or developing custom parts from scratch can stretch over a large portion of the overall turnaround time. It is said that the design stage contains 70-80% of the product costs. The decisions made at the design stage determine the complexity of the product, its material, and manufacturability. Thinking about the manufacturing technique in advance is very important. For example, it is easier to design a hole under the overhanging part of a plastic snap-fit joint so that you can manufacture the joint as part of the molding. Otherwise, you would have to employ additional CNC machining. Naturally, such things are not required if you 3D-print the part.
Selecting The Manufacturing Process for A Custom Part
Once you have established the design, or even better, while establishing the design, you should consider the manufacturing process.
Usually, there are two main considerations that influence this choice. The technical and economic factors. The first one is absolute because it is determined by the requirements you’ve set for the design. Say, you want one part with minimum porosity. Then, the 3D-printing options are out of the question because sintered parts are more porous compared to alternatively manufactured parts. However tempting the advantages of 3D-printing may be in creating one custom part, you just won’t do it since the part will break when it starts working due to porosity. There is, of course, a way to overcome this. That is when you know that the product material will be porous so you strengthen the design for it to work.
Now, as you’ve established the range of manufacturing techniques that will ensure your part will work when installed, it is time to choose the one that will provide you the part faster at a smaller price.
Each manufacturing technique has the initial tooling costs and the ongoing processing costs.
The first group consists of fixtures, injection molds, assembly equipment or even machine tools that are required to manufacture the part.
The second group is calculated based on the number of parts in the batch. It consists of materials, cutting tools, packing (if present) and other expendable elements. The cost of those increases with each part to be manufactured.
In order to choose the optimum manufacturing processes, a thorough assessment of time and costs is required. In order to save you some time, I’ve rounded up the most popular manufacturing technologies for custom plastic fabrication.
Rapid Plastic Manufacturing Technologies
If we talk about custom plastic fabrication parts, we usually imply a small batch or even just a few parts. In this case, ongoing costs are almost nonexistent. The main problems are the initial costs and the time required to prepare all of the necessary tooling.
Modern technology has developed a number of techniques with minimum tooling costs and preparation time. Each of them is best for a certain number of parts to be produced.
Plastic Vacuum Urethane Casting
Plastic Urethane Casting is a modern method of rapid prototyping. If you need to manufacture a small batch of parts with good surface finish and properties, urethane casting is a perfect choice. You require a master model of your part (metal wood or plastic) and a special silicone liquid. By suspending the master model over a tank and pouring the silicone into the tank, you will get a hard casting form that can withstand up to 20 uses if you want more parts, you can manufacture multiple forms from the same master model. In order to prevent cavities and increase material property, the whole process is done in a vacuum chamber. That way, air bubbles will get to the surface faster after the plastic has been cast into the form.
In general, Vacuum Casting forms take around 15 days to be made by a professional custom plastic fabricator and the initial cost of the process is the highest among the three rapid prototyping technologies mentioned. However, with larger batches, this method is the best since it offers minimal manufacturing time per part and minimal material waste.
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Custom Plastic 3D-Printing
3D-Printing is a comparatively new technology that uses a laser to sinter a plastic thread or a plastic powder layer by layer. The laser beam mimics the contours of the corresponding cross-section of the part. After sintering one layer, the next layer of material is set and the laser sinters the next section. 3D-printing processes are not as developed as the other methods but they offer a lot of advantages for plastic custom parts fabrication. Firstly, no tooling is needed at all. All the supports and fixtures are sintered from the same material, however, the material itself is much more expensive. Secondly, the complexity of the parts may be practically boundless. Since the part is “grown” from scratch, the tool has no obstacles and may produce practically any kind of geometry. Custom plastic fabricator companies often use this manufacturing method to create master models for casting processes.
Despite all of its advantages, 3D-printing is quite slow and the material for it is very expensive. In addition, the surface quality of the printed part leaves much to be desired. That is why it is mostly used to produce under 5-10 newly designed parts.
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CNC Machining of Plastic Parts
CNC machining is the oldest and yet quite a young process among the rapid manufacturing techniques. CNC systems have been developed to a mass-production degree recently but the machining has existed for a long time. Custom plastic fabrication processes employ metal cutting machine tools working at special speeds and feeds with specialized cutting tools. CNC machining is the absolute winner if you need high precision and surface finish. However, the process requires fixtures. In most cases, standardized fixtures are enough but it is not absolute. So, there may be a part, which will require the manufacturing of specialized fixtures thus prolonging the preparation time considerably. Apart from that, every kind of CNC machine tool requires an NC program that tells it what to do. The more complex the part, the longer it takes to write and fine-tune the program, however, it may be used later for a larger batch. In addition, using standard blanks to produce custom parts generates up to 75% of material waste.
Source: WAYKEN RAPID MANUFACTURING
Generally, CNC machining is good for 10-30 parts up to the moment when a large amount of waste becomes a serious concern.
