CNC Metal Machining For Prototyping
CNC machining is a process that involves using high-speed, computer-controlled, precision machines to remove metal from a blank, or block of metal, to create a part. Some components have complex geometries and require multiple operations from turning, milling and drilling, therefore CNC machines come in different configurations, including those with these multiple functions. Below we look at the different CNC machines used for prototyping parts made from metal:
Types of CNC machines used for metal parts
CNC Lathe – A lathe rotates the workpiece which is held in a chuck while a fixed cutting tool moves in an X, Y direction to remove metal from the workpiece. It is because of this rotational action of the workpiece; round symmetrical shapes are produced. The action of removing material in a lathe is known as ‘turning’.
CNC Mill – A mill holds the workpiece still while a rotating cutter removes material from the metal. A basic mill has three directions of freedom, X, Y, and Z, this machine is known as a 3-axis mill.
CNC Multi-axis Machines (Machining Centers) – The CNC machining center is an advanced manufacturing machine tool that can perform multiple machining functions that provide precision, quality, and high-quality surface finish. A CNC machining center can perform drilling, milling, and turning operations. These machines are often known as 5-axis machines. The three-axis refer to X, Y, and Z as mentioned above, the other two axis refers to the ability for the rotation around the X and Y axis, referred to as A-axis and B-axis. These two additional degrees of freedom provide a 360-degree cutting ability, hence the flexibility of a 5-axis machine to machine very complex components. In the diagram below there is a sixth axis, axis C, this is not generally included in machining centers as it has the same effect as the rotation of the spindle.
Image source: https://www.5-axis.org/
CNC Machining for Prototypes
Metal machining is ideal for small batch runs between 1 and 100 items. Suitable for both small and large parts provide a quick turnaround and lead-time. Most metals can be CNC machined directly from 3D CAD data. This method provides you with a functional and structurally sound prototype part for functional testing. This process is most suitable for producing prototypes where the final part will be metal.
CNC machining provides accuracy and consistency and can be used with a wide range of metals. Producing prototypes out of metal gives you the advantage of verifying and testing production design parts, allowing tests for stress, loading, temperature, strain, fatigue, and any other long term testing the part may need to be tested for.
When does it make sense to use CNC for prototyping metal parts?
- Tolerance – if you need to generate a prototype where you are checking fit where the tolerances are tight, CNC machining is capable of a standard dimensional tolerance of ± 0.005″
- Function and Performance – for very specific functional testing or performance testing, the end production-intent part is often the only way to verify and validate your design, CNC machining is a very good option in these cases.
- Quantity – whenever you need a larger quantity of prototype products for testing, say between 10 and 500, CNC machining can provide you with economic part costs as well as consistency, accuracy, and the required level of quality (surface finish, tolerances, limits, and fits) without investing in production tooling or other potentially expensive production methods.
Examples of CNC metal machined parts
Some of the typical industries that utilize CNC metal machining for their prototype testing are:
CNC Plastic Machining For Prototyping
CNC machining plastic prototypes makes perfect sense in that it provides production level plastic parts that are generally plastic injection molded where expensive tooling would have to be paid for and for prototype parts were very low volumes are required, capital investment in tooling is prohibitive.
The CNC machines available for plastic prototype machining are the same as those used for CNC metal machining as discussed above. However, about 80% of the plastic parts are CNC machined using the 5-axis machining centers, all the rest are usually turned on a lathe. One other advantage is that the cutting speeds and feeds will be much faster than metal, hence, shorter lead-times and an opportunity to test products quicker and bring them to market before your competitors.
For best optimization, use the production-intent plastic for the CNC machined parts, this will provide final product characteristics.
Some of the more common industries to utilize CNC machining for their plastic prototypes are: