What is CNC Machining?
CNC (Computer Numerical Control) Machining is a subtractive manufacturing process that involves using high speed, precision machines to remove plastic or metal from a block (“blank”) to create the design of a part. A CNC machine takes a specific set of code and uses that to cut out a part from a blank. The CNC machine code has a list of specific instructions on how to create the part. For example, the code will start off telling the machine where to place the tooltip, how fast the tooltip should spin and to what coordinates the tooltip should move to (CNC machines use coordinates on a set axis such as x, y and z axis). Machines commonly controlled in this manner include vertical milling machines, horizontal milling machines, lathes, routers and grinders. With CNC machining, parts can be cut out with extreme precision and can be easily replicated.
Benefits of CNC Machining
When starting a new plastic injection molding project, plastic prototype parts ensure a product’s design is sound. For most plastic parts, a CNC machined prototype will provide exactly what is needed for testing. CNC machining allows you to test the form, fit and function of injection molded parts without having to produce injection mold tooling.
Small Production Run
Since all you need is a proper CAD file, CNC machining is perfect for a small quantity of parts. Since there is no mold to create, you save money and time by directly creating the product on the CNC machine. That makes CNC machining perfect for runs under 100 pieces (once you get over 200 pieces it becomes cheaper to produce the parts with injection molding).
Quick Turnaround Time
Unlike in plastic injection molding where a mold has to be produced first, CNC machining doesn’t have that requirement. Once your files have been uploaded and approved, production can start right away. This cuts down production time dramatically.
High Quality Parts
CNC machining has many advantages. It is a more precise process than manual machining, and it provides exact repeatability. Because the computer controls the machine movement, the machine tools can all move precisely and simultaneously on their axes to create complex, three-dimensional shapes that would be almost impossible with manual machining. These qualities make CNC machining a good manufacturing process for jobs that require a high level of precision or repetition.
We will typically hold all tolerances to within +/- 0.2mm – 0.3mm. If there are critical areas on your part where tight tolerances are extremely important, you can specify that we hold tolerances tighter than 0.01″ (0.254mm).
For plastic parts, due to the materials available and the production process itself, CNC machining can produce more robust parts compared to 3D printing. Therefore, they can be subjected to the same conditions as the eventual injection molded production parts.
Materials for CNC Plastic Machining
CNC machining is a good choice for making prototypes and low-volume plastic parts. Since CNC machining can be done with different materials than used in the 3D printing process, for example, it is frequently used for situations where the prototype needs to be tested under the same conditions as the injection molded production parts will be subjected to, and thus made of the same material. There can also be better structural integrity of parts that are CNC machined compared to 3D printed, due to the nature of the manufacturing process. See more about CNC Plastic Machining.
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We currently offer the following materials for CNC machining:
- ABS, Black
- PMMA (Acrylic)
- PTFE (Teflon)
CNC Metal Machining
Our standard tolerance for CNC machined metal is +/- 0.002″, and you can also request tighter tolerances. The hardness of metal will also affect the length of time required to machine out a part. For example, using a harder metal like carbon steel requires a slower spindle RPM which will take more time to remove the material from the part. By using a softer metal like aluminum, a part can be cut out 4 times faster than a hard metal like carbon steel. Make sure you consider the type of metal when doing price estimation. See more about CNC Metal Machining.
Secondary CNC Machining Processes
Sometimes you may require additional processes done to your parts after they are CNC machined. We have the capability to perform many post-milling processes for you, such as painting and silk screening.
This can be especially useful for show pieces. There may be times when you need prototypes to have a special treatment because they are going to be used for a presentation to a customer, for internal use within your organization, or to display at a trade show.
The following is a list of the standard secondary processes we can do, which are available for selection in a dropdown menu in our interactive quotation system. In addition, we would be happy to discuss any custom process needs you may have.
- Silk screening
- Higher tolerance than +/- 0.01″ (0.254mm)
- Custom processes
- CNC Machined Plastic Tolerances
Types of CNC Machines
There are several types of CNC machines, each with its own functionality to machine different types of parts in different ways.
CNC mills generally start with a block (blank) of material and removes that material until only the desired part is left. A CAD file gets translated into G-code (or similar code). This code is then uploaded to the CNC mill, where it uses a program to control its spindle in a three-axis system (X, Y and Z). The code contains the coordinates for the part and the speed at which the spindle should spin. The CNC mill follows code in order and, once finished, the part has been cut out from the blank.
CNC lathes differ from CNC mills as they only move their spindles in a two-axis system (X and Y). CNC lathes take a blank and then spin it around at a high RPM. Any cuts made to the blank are uniform on all sides. CNC lathes are used for creating cylindrical pieces that need to have uniform cuts on all sides.
CNC Plasma Cutters
CNC plasma cutters use the same technology as other CNC machines. The main difference is that a plasma cutter cuts parts out of a large, flat metal blank instead of a block. It also only moves the tool tip along two axes.
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