Understanding and Improving Modern CNC Milling

By Paul Coupe

CNC Milling

While CNC Milling has been around for more than 50 years, the technology is moving on and recent advances see automation of the entire process, from design right through to finished part. Such advances make it a technology that is readily available to all, for high or low volume quantities, prototyping to final parts and with lead times of as short as a day.

So, what has happened to make it so available, to democratise it for everyone?

To answer that question let’s first of all take a closer look at what CNC milling is exactly and then explore how it is evolving.


About cnc milling and machine tooling

What is CNC Milling?

Well first, despite their different approaches to removing material CNC drilling and milling, or a milling machine, and CNC turning, or a lathe, both remove material to produce a part. A machining centre often combines both methods and multiple tools, in one machine. All of them have multiple axis motion which drive cutting tools around and through the workpiece to shape exactly what you need.

The fundamental difference between the two is that a milling machine uses a spinning tool to make cuts on a workpiece, while a lathe spins the workpiece and a tool is applied to it.


How does CNC Milling work?

Before the advent of Computer Numerical Control, or CNC, both mills and lathes were manually operated.  As the name suggests CNC automated this process to make it more accurate, reliable and faster.

A skilled operator now programmes G-codes (which stands for Geometrical code) into the machine often via software. This controls the mill telling it which path to follow and how fast, so that it can drill, cut and shape the material to match the dimensions entered into the computer.

There are a number of different types of CNC mills, with the most common being 3 axis machines that traverse through the X, Y and Z axes to enable tooling to manufacture in 3 dimensions. 3 axis machines are able to produce more complex features by rotating and re-setting the workpiece to enable access from multiple angles. 

Five axis machines enhance this by adding two further directional movements, by rotation through the X and Y axis. It is ideal for creating complex and precise parts – but the downside is that using such technology might erode your budget as complexity adds cost.  Believe it or not 5 axes of motion should be able to define any 3D geometry. However, to hold the workpiece and rotate it freely in every direction is not practical, which means that there are now 6, 7 or even right up to 12 axis machines, but I would suggest that it is extremely unlikely that you will need to use these unless you require extremely complex parts – because the investment is huge, as is the size of the machine!


What’s next for CNC Machining?

As you can see a lot of evolution has gone into developing ever more complex CNC milling machines, that are getting bigger, more expensive to buy and need more skill to operate.  Even if you outsource your CNC machining you will pay more for this complexity as the specialist manufacturers have to recoup their investment.  If you have an extremely complex part that requires incredible precision and need it in large numbers then you may be able to justify the investment.  For the vast majority of jobs 3 axis or at a push 5 axis machining will be more than adequate.

After all there’s more than one way to solve a problem – for example constructing two or more less complex parts and then bolting, welding or joining them together as part of a secondary assembly process will generally be a better and cheaper solution than trying to machine an extremely complex single part.

So why is there all of this focus on developing new expensive and huge machines that offer ever diminishing returns? It’s a bit like Microsoft Office.  Most of us use Word but in truth we probably only use 20 percent of its capability and yet Microsoft keep on adding new features, most of which we will probably never need, use or are even aware of.

Instead of making ever smaller incremental improvements in the process, we think it’s better to improve the process itself.  This is where we can make the real gains.


Automating the process

Let’s go back to the beginning and examine the process of producing a part.

It all starts with the design engineer working on their CAD to design the part or component that they need.  Traditionally a skilled operator would take this and programme the G-code ready for CAM – or computer aided manufacturing. 

But once you’ve designed it why go through another step? Well, the good news is that you can turn your CAD this into G-code with many CAD packages – but we still need to go back a step.

After you’ve designed your part how do you know that it can be produced using CNC machining and to the tolerances that you want?  Your CAD should be the digital thread that links everything down the line with little or no human intervention.

After all, with Industry 4.0 we should all live in a connected world.  A lot of CNC machining still relies on having a skilled machinist.  When you send your design through it is generally a human who will need to check that it is manufacturable using the process they know.  If it isn’t okay, then they will need to feed this back to you so that you can redesign or tweak it.

At Protolabs we have automated that process.  Once you send your CAD through, our software will check it for manufacturability and produce a quote.  If there are any suggested or required alterations then the design for manufacturability report, which the software produces automatically, will show you on your CAD.  Once you are happy with your design and the manufacturing our software will produce the code needed for machining it exactly as specified on the quote.


Faster and more cost effective

This makes the process much faster and more cost effective, which can make a real difference for small and medium sized jobs or for prototyping and testing new parts.

Automation also makes this level of service the same for everyone, whatever the size of the project.  Traditional machine shops will understandably prioritise the projects that are worth more money to them – whether due to the size of the order or the complexity of the part needed – depending of course on their capabilities.

Automating the process levels the playing field, so that if you are prototyping or perhaps only need a small or medium number of parts then you still get the same speed and level of response. 

Because all this information is generated and collected right from the beginning we can cut and ship custom made CNC machined plastic and metal parts in as fast as 24 hours.  But if you don’t need it so quickly you can opt for a later delivery date and pay less – so you can even set your own terms and conditions automatically.

All of this process starts with your CAD, it means that after you have designed your part, we have a digital thread that we can use throughout the CNC machining operation – from your computer to final delivery.

Automation is about more than CNC milling and turning, it encompasses everything from design onwards. That is where the future of CNC milling lies.  It really is Industry 4.0 in action.

For additional help, feel free to contact a Protolabs applications engineer at +44 (0) 1952 683047 or [email protected]. To get your next design project started today, simply upload a 3D CAD model for an interactive quote within hours.

Tagged: CNC, Milling