Prototyping requires matching of the final product with the 3D design. The idea is to have a prototype that resembles the 3D file. Therefore, CNC prototype machining is very useful during prototyping. When CNC machining operate in a machine workshop, a file is sent directly from the design PC to the CNC machine. Using a computer program, the part is manufactured automatically without human interference. This reduces possible errors greatly and thus guaranteeing the quality of the final product.
Prototype Machining Technologies
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CNC Milling
This is a computer-controlled milling process. It involves the rotation of multi-point cutting tools that are controlled by a program to remove material from the workpiece. The program can vary the cutter direction, head speed, or even pressure as may be required. Consequently, the workpiece is machined to yield a custom-design prototype or product.
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CNC Turning
Traditionally, turning involves placing a cutting tool on a rotating head (such as the CNC lathe or turning center) to remove materials. The speed and depth of cut are then controlled by an operator. However, with CNC turning, the operations of the cutter are controlled by a computer program. It is most applicable to prototypes with cylindrical cross-sections.
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EDM/Wire EDM
Electric discharge machining (EDM) is the use of electric discharge to form any shape in metal. It is also called spark machining, spark eroding, die sinking, wire burning, or wire erosion. In EDM, a thin strand of wire is passing through a dielectric fluid is used to cut metal. The cutting process is numerically controlled. It has accuracies of +/- 0.00004” (0.001mm).
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One-stop Post Finish
Sometimes, a single prototype may require various forms of post-finish. Having these processes at a go minimizes the handling of the prototype and thus maintaining the quality. Some of the post-processes include polishing, painting, Chrome-plating, anodic oxidation, deburring, tapping, grinding, and so on. Combining such processes comes with expertise and experience.
Machining Materials
A large of materials can be used in CNC machining depending on the required finish. These include the following materials;
- Metals – All metals (such as steels, copper, brass, superalloy, and titanium among others) can be machines to manufacture prototypes.
- Plastics – All available plastics (such as ABS, Polyethylene Terephthalate (PETE or PET), High-Density Polyethylene (HDPE), Polyvinyl Chloride (PVC), Low-Density Polyethylene (LDPE), Polypropylene (PP), and Polystyrene or Styrofoam (PS)) are easily machinable.
Pros and Cons for Prototype Machining
Compared to other prototyping processes, CNC machining as applied to the manufacture of prototypes has the following pros and cons.
Pros
- CNC machining produces solid parts compared to injection molding for example. This means improved mechanical properties.
- It uses a variety of materials compared to some processes that may be material-selective. An example is the use of aluminum that cannot be used in 3D printing.
- CNC machining results in a high-quality surface finish. This means the prototype can be used as machined or require minimal surface finishing operations.
Cons
- Costly with low volume production. This can, however, be mitigated with low-volume manufacturing.
- CNC machining cannot produce a perfect corner due to the use of rotating cutting tools. On the other hand, a perfect corner is a week point. Therefore, this is not a big concern. Additionally, there is a limit to the depth of cavities with CNC machining compared to other prototyping methods.
Low Volume Manufacturing and Its Benefits
Low-volume manufacturing is the production of between 50 and 100,000 parts. It acts as the bridge between one-off prototyping and full production. Product developers all over are moving from mass production to low-volume production due to the following reasons;
- Design flexibilities – Designers and manufacturers want the freedom to make changes more easily without affecting the order. Low-volume manufacturing allows this with ease.
- Less costly – By default, the cost of production per unit reduces with the volume of production. This is not the case with low-volume production as you can still save on cost while manufacturing a small volume of your parts. This is done by avoiding investment costs in machines and using low-quality tools.
- Scaling up – Low-volume production allows the manufacturers and designers to streamline best practices to thus lowering cost production. This allows for ease of bridging to full production.
- Time to market – Businesses are striving to reduce the time-to-market to capture and/or retain market share. On the other hand, maintaining a large inventory is costly. As a result, low-volume manufacturing becomes a deal. That is, produce faster, reach the market, avoid the cost of inventory. The result is high profits.
There is no best way to enjoy the benefits of low-volume manufacturing than to engage experts in rapid prototyping.
Conclusion
That said, it is obvious that prototype machining is a very important process in manufacturing. The various types of machining processes can be combined to owing to the requirements of the prototype. This makes it easy to always arrive at the required prototype irrespective of its complexity. If you were to enjoy these benefits, then you would have to invest in high-cost CNC machines. This may not be justifiable for low volumes, prototyping, trial production, etc.
