Manufacturing Processes - CNC Single Point Cutting Process
Single Point Cutting Tools
Single Point Cutting
Single point cutting fits in the category of machining as a manufacturing process. It involves the removal of metal from a workpiece using cutting tools that only have one primary cutting edge.
- Cylindrical turning on a lathe
- Facing on a vertical boring machine
- Internal boring on a horizontal boring machine or lathe
Single point cutting using standard tools and equipment is a good option for the production of small batches and 1 off items such as prototypes. Machines are flexible and can be used for the production of a large range of components without the need for dedicated tooling. Basic set up costs are relatively low.
High quality components can be produced through the management of feed rate, speed, depth of cut, cutting angles and tool types used. The skill and experience of the machine operator is also an important factor although the recent adoption of CNC machining for almost all types of single point cutting has moved the skills required to machine set up and programming rather than machine operation. This means that a manufacturer can hire less skilled labour to run the machines once the equipment has been set up for operation.
Most metals and polymers can be machined using single point cutting and it also possible to machine some ceramics. Cuttings form the majority of the material waste and they are typically quite difficult to recycle mainly due to contamination from lubricants and some changes in the microstructure as a result of the machining process which uses a shearing action for material removal. This as you can imagine will generate significant levels of stress and strains at the cutting edge.
Hardened or toughened materials can slow down cycle times and consideration needs to be given to tool wear if machining at high process rates for material removal. A basic requirement of a single point cutting tool is that it is harder than the material being cut, but even in that event there will be tool wear. The consequence of this is a need for frequent resharpening of the cutting edge and ultimately the tool may need to be replaced.
Another factor to consider when using a single point cutting tool is the generation of heat energy; mainly as a result of the primary shear taking place as the material is removed. A large proportion of this heat goes with the resulting material chip but there will still be a residual amount that stays with the parent material. This is why coolants are widely used in the single point cutting process. They typically also provide a secondary benefit of acting as cutting lubricants.
What are the optimum characteristics of Single Point Cutting Tools
- hardness even at high temperatures
- chemically inert
- resistant to wear
These characteristics have traditionally been found through the adoption of carbon and low alloy steels, although they did have a tendency to wear a little too easily. Being relatively easy to sharpen offset this problem to an extent but there was a clear need for further development of tooling which could perform better.
High speed steels provided an initial solution to the wear problem, which was mainly brought about as a result of high temperatures being present while machining that would have an adverse effect on the low alloy steels. The high speed steels are still considered to be an affordable and effective choice for cutting most materials, but more recently there has been an adoption of cemented carbide inserts.
Cemented carbide tips are used in conjunction with tool holders and are normally supplied in a triangular geometry which can now be rotated in the holder to provide a new cutting tip when it does wear simply by loosening a retaining screw and clamp. Early designs used brazing to secure the carbide tip in its holder which, for obvious reasons, made continued use of the tip after wear impractical.
Further improvements in wear resistance came in the form of ceramic coatings that could be used on both high speed steels and cemented carbide tools. Diamond is another cutting tool material but is pretty much limited to low temperature applications, despite it being the hardest known material available.
Single Point Cutting Tools
Single Point Cutting Tool Use in CNC Turning
CNC Programming Handbook
Multiple Point Cutting
The principles of multiple point cutting tools is much the same as for single point cutting tools but with the obvious difference of having more than one major cutting edge. They are used to remove material from metals, polymers and also some ceramics and composites.
Typical Multiple Point Cutting Tools
- Surface milling cutters
- Slot cutters
- Dovetail cutters
- Form cutters
- High speed drills
Most modern machines utilise standard milling cutters on CNC milling machines that are non dedicated. In other words they are set up and programmed on a job by job basis and can be quickly changed around to suit small batch or individual component production requirements such as prototype work. Producing 1 off articles isn't absolutely ideal due to the need to write supporting CNC programs. An exception to this statement might be if once a prototype has been produced and verified as fit for purpose, the programming code can then be utilized for further batch productions. So for high single component machining demand a better option may be standard milling machines with digital readouts.
CNC machines can of course also be used for high volume production but the machine then becomes tied up for long periods which effectively reduces flexibility.
Broaching is a slightly specialist process that is useful, for example, when producing key features in the bore of a tube, something that is difficult to do using standard machining practices.
The video below shows the level of adaptability of a CNC machine and how they can be used to produce components in 3D.
Multiple Point Cutting Tools
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