Making the Cut

Using the wrong cutting tool – or a worn or damaged one – can lead to costly mistakes. Head of Engineering at MSC Industrial Supply Co. UK offers guidance to help you avoid a cutting tool catastrophe.

In manufacturing or engineering facilities, a good CNC machinist is trained to look and listen for the signs of wear and tear or damage on cutting tools. 

However, there are many environments where the operator only uses the tool infrequently and does not have the same level of training. Examples of this include maintenance and repair departments, prototype and development firms, and research facilities. In these environments the machine tool operators are not trained machinists, but are mechanics, technicians, design engineers, or academics. Naturally, their grasp of good practice in machining and cutting tool operation is unlikely to be at the same level as a machinist who uses a cutting tool every day. 

This gap in their knowledge can lead to the wrong tools being used, as well as failure to spot that a worn or damaged tool should be replaced. Edge wear and damage that would set off alarm bells on a shop floor are either missed or misunderstood. Other potential issues include using the wrong grade or geometry, with improper feeds, speeds, and depths of cut, making matters even worse. Fixing these issues can improve productivity and enhance a manufacturers’ bottom line.

With the right operator training and the right cutting tool for the job, you can achieve efficient and precise production of parts, enhance safety, and improve the tool’s working life.

Spotting wear 

There are many signs of cutting tool wear, including chipped or worn edges, notch wear on cutting tool at the depth of the cut line, discolouration of the tool or workpiece, build-up of material on the cutting surfaces, poor part quality and surface finish, and increased noise from the machine spindle. It is a long list, and even the most experienced machinists occasionally misdiagnose a problem. 

The most important thing to do is inspect tools often. If these signs become apparent, then take appropriate action, such as adjusting operating parameters or changing to a different grade, coating or geometry as required. 

Include tool holders

When you’re inspecting your tools, don’t forget to also examine the tool holders. Tool holders that are chipped and dented on their locating surfaces or exhibit a rust-like appearance known as fretting should be discarded. If you continue to use them, this damage will translate into poor tool life and part quality and may damage the machine tool as well. As with cutting tools, only swap them out for high-quality replacements. 

You don’t necessarily have to throw out tools that can no longer be used. There are companies out there who will regrind them for a fraction of the cost you’d pay for a new tool – many of these companies can also apply coatings or special grind to increase their effectiveness. These refurbished tools are ideal for lower-demand applications such as in maintenance and repair workshops.

Again, keeping your tools in good order will help them enjoy a longer second life. Generally speaking, you can get far more regrinds out of a cutting tool that’s been well cared for than one that’s been abused. 

The right tool

In many cases, the cutting tool might be used to cut different materials, such as aluminium one day, then stainless steel the next. You can settle for a multi-purpose tool with lower performance – but that can lead to excessive wear and tear. For example, if you need to drill a series of holes in a stainless steel component, or one made of superalloy, you can end up damaging your tools. By using a cutting tool designed specifically for these materials, you can save a lot of time and money in the long term.

Worn or chipped tools can also increase the load on expensive machinery, potentially causing damage to spindle bearings and electrical components, resulting in a big repair bill. They can also damage the part being created by generating enough heat to harden the material or snapping off unexpectedly deep inside a hole. A tool or material that snaps could injure the operator as well, which is why it is crucial for safety reasons not to overload tools. 

Hidden cost

One reason that facilities will settle for general-purpose machine tools is cost. High performance and application-specific tools have a higher up-front cost than general purpose. However, that does not mean they are more expensive. Spending a little bit more on an optimised cutting tool solution is an investment – more often than not, it saves you money in the long run. 

Replacing worn or damaged tools used for the wrong job is not the only hidden cost. Experts have noted that cutting tool consumption represents between 3 and 5 per cent of the total costs for producing a part. Because of this, a 30 percent decrease in tooling cost only reduces part cost by roughly 1 percent. In most operations, cycle time is much more important to profitability – and key to cycle time is the selection of high-performance tools that are optimised for the application. For example, spending a bit more on a coated tool almost always makes sense, as does switching to a tool with higher flute counts on finishing operations. Both reduce cycle time, which means higher productivity.

Evaluate and assess

In the same way as investing in the right machine tools will pay dividends, investing time in evaluating and assessing your tool portfolio will save you time further down the line. It is not always easy but set aside some time for testing new grades and geometries. These often require more aggressive machining parameters than expected - and unless applied properly, even an optimised cutting tool will fail. 

A great time to carry out this assessment is during a planned shutdown of your facility. Use this down time to evaluate what is working and what’s not - and do some testing and optimisation of new tools. Doing so can reap big benefits when the shop starts up again.[JH1]