CNC Machining Guide

1. What is CNC Machining?

CNC machining, or Computer Numerical Control machining is a form of subtractive manufacturing to produce parts and components made from materials such as metals and engineering plastics.

A process of manufacturing parts or components through material extraction, CNC machining uses pre-programmed computer software to relay a toolpath which tells the machine how and where to extract the material from a raw billet (block of material). 

The machine will take multiple step overs usually defined as a percentage of cutter diameter in order to produce the desired profile. The extraction is undertaken by motorised cutting tools.

CNC machining is suitable for producing both one-off/prototype quantities as well as high volume production.
 

3. What are the Benefits of CNC Machining?

CNC machining has many benefits as a manufacturing process which we outline here.

High Accuracy

The use of CAD means that CNC machining produces extremely high accuracy parts with tight tolerances. Penta has a general machine tolerance of +/-0.1mm geometric tolerance and a surface finish of 1.6µm (micrometer) but tolerances tighter than 0.01µm can be achieved where required. See PDF General Tolerances to DIN ISO 2768.

 

Cost Effective

A cost-effective manufacturing process of components, CNC machining can be used for prototypes, one offs and small to larger batch production. CNC machining is most cost effective for one off and small to medium batches. There are far fewer upfront costs associated with CNC machining than there are with many other manufacturing processes. In section 5 of this guide we compare CNC machining with 3D printing and injection moulding.

 

Efficient

CNC machining is associated with reasonably fast turnaround times. The set-up time is comparatively small to other manufacturing methods. This ties back to cost effectiveness as time is money! It is also easily repeatable. Once the design is created, it can be accurately repeated time and time again.

 

Range of Materials

A high number of materials can be CNC machined. Where other manufacturing processes can be quite limiting, CNC machining allows designers to select the most appropriate material, taking both the desired properties and cost into account. A good CNC machine shop will be able to help you with material selection if you require.

 

Superior Quality

CNC machined parts are associated with quality and excellent physical properties. Where high performance is required, CNC machining is an obvious choice.

 

 

5. Comparing CNC Machining to Other Manufacturing Methods

Clearly CNC machining isn’t the only manufacturing option so here we will compare with the other likely alternatives you may be considering.

 

CNC Machining vs 3D Printing

CNC machining is a type of subtractive manufacturing, 3D printing is additive manufacturing. This means that CNC machining starts off with a block of material and then undergoes a process to extract material resulting in a finished part. 3D printing involves a part being manufactured by building it up layer by layer using specialist machinery such as a laser or heated extruder.

CNC machining is associated with a very high degree of accuracy – hence why it’s often called precision machining. 3D printing tends to be able to offer more complex shapes than CNC machining.

Whilst CNC machining is compatible with a broad range of materials, 3D printing traditionally has more of a focus on plastics such as plastic resin and filaments.

More options to 3D print metals (metal powders) are being introduced, however in order to 3D print metals, much more expensive and high cost machinery is required. This could make the cost of 3D printing metals prohibitive, especially for prototypes.

Another big factor is that strength can be compromised with 3D printed parts and therefore it would not be suitable for all applications and industries.

 

 

CNC Machining vs Injection Moulding

Injection moulding is pretty much what it sounds like. It’s the injection of a material (in liquid form) into a mould in order to make the part. The material is then solidified to create the finished component. There are two major factors that can be prohibitive for injection moulding when it comes to lower volumes: time and cost.

Before the actual injection moulding process can take place, an initial prototype must first be made. This would be either CNC machined or 3D printed. Once the design has been finalised, a mould can then be designed and produced using this prototype. Only once the mould has been created can the injection moulding process begin. There is likely to be lots of testing at every stage of this process and tweaks or redesigns having to take place before everything is just right.

You can see that this process has consequences on both time frames and the cost of a project. Thus injection moulding should really only be considered when a high volume of components are required. For mass production, once the initial outlay has been recuperated, injection moulding becomes a cost-effective manufacturing process.

Less material is wasted during the injection moulding process as, like 3D printing, it is a form of additive manufacturing as opposed to CNC machining where material is taken away. Again this has an impact on cost but for low to medium quantities, CNC machining is still more cost effective.

Similarly to CNC machining, injection moulding is very good for consistency. Once everything has been set up, the parts produced should be as close to identical as is possible.

CNC machining is compatible with a far wider range of materials than injection moulding. Due to the nature of injection moulding and the fact that the material needs to be melted into liquid form before being returned to a solid state, it does rule out some materials whose properties would be compromised as a result of the process.

 

CNC Machining vs Manual Machining

CNC machining is much more accurate than manual machining; it’s much more precise and exactly the same process can be repeated in order to produce consistency across multiple parts.

Manual machining is sometimes favoured over CNC machining for prototypes and one off components where the set up time for CNC would not be cost effective.

CNC machines are significantly more expensive to purchase than manual machines so many CNC machining companies will usually have a plant list that includes some of each. This helps them balance their costs and pass savings onto their customers.

7. CNC Machined Part Applications

 

 

CNC machining can be used to manufacture parts for an endless number of applications. Components that can be CNC machined include: enclosures, heatsinks, connectors, brackets, housings, shafts, bushes, bearings, guides, manifolds, handles, casings, spacers… the list really does go on!

In terms of industries, CNC machining has been adopted as a popular machining process by many industries including:

• Aerospace
• Pharmaceutical & healthcare
• Computing & electronics
• Military & defence
• Marine
• Original equipment manufacturers (OEM).