Manufacturing and engineering often go hand in hand. A beautifully designed part can never come to fruition unless it can be actually be machined, and so it is incredibly important for engineers to have a firm grasp on the CNC machining basics used in today’s manufacturing environment.

Learning about the machining process can not only help fine-tune an engineer’s design, but it can significantly reduce the finished part costs and limit potential delays in production. 

Below, we’ve outlined some of the basics of CNC machining as well as items an engineer should consider throughout their design process.

CNC Milling Basics

The CNC Mill is an incredibly powerful and versatile piece of equipment. Some of the most robust and intricate machining in the industry is performed on CNC milling centers, and more options are opening up all the time as technology grows to expand manufacturing capabilities. 

The capacity and complexity of CNC mills crosses a wide spectrum. Some shops rely on smaller, 3-axis machines for one-off or prototype jobs where part size and quantity are low. In larger, production environments there are massive multi-axis milling centers that can churn out parts with incredible efficiency. Whatever the size, shape or quantity of parts that a business needs to produce, there is a CNC mill that can be fitted to meet their needs, and they all function with the same principle set up.

Stock

This is the material from which a part will be machined. The part stock could be an existing component that needs to be modified, or it could be a chunk of raw material that will be trimmed down until only the finished part is left.

Work Holding

In a CNC Mill, the tooling/cutter moves around a stationary part that is held in a fixed position. Typical work holding involves one or multiple vises, clamps and/or fixtures to securely hold down parts/material so as not to become dislodged during the machining process.

Tooling

CNC mills use a wide variety of tooling to remove material from a workpiece, including drills, saws, end mills and more. The type of tooling used on a specific part will depend largely on the material required for the component, as well as the size and part geometry featured in the part’s design. In a CNC mill, the workpiece remains stationary while the tooling spins and travels around the part to remove material.

Items to Consider

  • Can we adjust the part size to fit within standard stock dimensions?
  • Can all part features be held/manufactured within mills machining envelope?
  • Would any part features require custom tooling?

CNC Turning Basics

CNC Lathes are a great option for machining pins, rollers, shafts, adapters, ferrules and many other turned components that feature a cylindrical profile. Lathes are incredibly efficient and can produce parts at a far higher rate than other CNC machines. Newer lathes can also be outfitted with milling features to increase their machining capabilities and limit secondary operations (i.e. drilling holes or milling slots.)

While the machining process on a lathe is similar to a mill in theory, there are a few key distinctions.

Stock

Lathes generally start with a piece of round bar or tube. Square or polygonal material can also be machined on a lathe with the proper work holding.

Work Holding

On a CNC lathe, the workpiece itself spins while the tooling remains stationary. It is held in a chuck and/or spindle and rotates at a high speed while the cutter travels across the material. On longer components, a tail stock can be used to support the weight of material and add rigidity throughout the machining process. The size of the part that can be machined on a lathe will be limited by the spindle/chuck opening, as well as the space between workpiece and tooling.

Tooling

Drills, boring bars, and OD/ID turning tools are all standard tooling on a CNC lathe. Most of these will include the tool holder and a cutting insert that move across the workpiece as it spins.

Items to Consider

  • Can we adjust part quantity to reflect standard bar lengths?
  • Can we adjust tolerance/surface finish to limit machining time?
  • Is mill/turn available at a specific shop to reduce secondary operations?

CNC Cutting Basics

Manufacturers can offer many different options when it comes to cutting material. The preferred method for a given component will depend largely on the size and material of the parts, as well as the precision and finish required of the cut itself. Common cutting methods include:

Waterjet Cutting

A waterjet cutter uses a high-pressure stream of water and garnet to cut through nearly any material. It is highly versatile and is not limited by material type, size or thickness (in most instances.) A waterjet cut leaves a very clean surface finish, though there can be a slight taper depending on the type and thickness of the material.

Laser Cutting

Laser is an incredibly powerful, precise and efficient cutting option. For thinner materials, the laser is probably the most cost-effective option on the market. It is able to cut with higher precision and less taper than a waterjet, but it does not perform well on harder/thicker/reflective materials. Lasers also introduce heat into a part, which should be taken into consideration if secondary machining processes are required.

Plasma/Flame Cutting

Plasma and Flame Cutters rely on a thermal process that uses high heat to quickly cut through material. This is a less precise method than laser or waterjet, but is highly efficient. While the surface finish is not as clean as with other methods, this is a fast and affordable option for cutting parts with wide tolerances, or for roughing out components that will be finish machined later.

EDM (Electrical Discharge Machining)

EDM, or electrical discharge machining is a process that uses an electrical current to displace material from a workpiece. EDM is less efficient than other cutting methods, and comes with a higher price tag, but is one of the most precise forms of cutting available today.

Items to Consider:

  • How important is surface finish on my cuts?
  • Will a part need to be machined after cutting (consider heat, taper, etc.)?
  • Can part size be adjusted to reflect standard plate dimensions (increase part yield)?