The discussion of high speed machining is still somewhat confusing.
There are many ideas and many ways to define high speed machining (HSM).
One of the main goals of high-speed machining is to reduce production costs through high productivity.
It is mainly used in finishing processes and is often used to process hardened die steels.
Another goal is to increase overall competitiveness by reducing production time and delivery time.
Definition of high speed machining
Our definition of high speed machining is described below:
HSM is not a high machining speed in the simple sense. It should be considered a process that is processed using specific methods and production equipment.
High-speed machining does not require high-speed spindle machining. Many high-speed machining applications are based on medium-speed spindles and large-size tools.
If the hardened steel is finished at high machining speeds and high feed conditions, the cutting parameters can be 4 to 6 times conventional.
In the roughing of semi-finished parts to semi-finishing, finishing and superfinishing of any size part, HSM means high productivity machining.
As part shapes become more complex, high-speed machining becomes more and more important.
High-speed machining is now mainly used on machine tools with a taper of 40.
High speed machining target
The main factors to achieve these goals are:
One (less frequent) setup of the mold.
Improve the geometric accuracy of the mold by machining, while reducing manual labor and shortening the test time.
Use CAM systems and shop-oriented programming to help develop process plans and increase machine and plant utilization through process planning.
Tools and workpieces
The low temperature can be maintained, which in many cases extends the life of the tool.
On the other hand, in high-speed machining applications, the amount of cutting is shallow, and the full depth time of the cutting edge is extremely short.
That is to say, the feed is faster than the heat.
Low cutting forces result in small, consistent tool bending.
This, combined with the constant machining allowance required for each tool and process, is one of the prerequisites for efficient and safe machining.
Since the typical depth of cut in high speed cutting is shallow, the radial forces on the tool and spindle are low.
This reduces wear on the spindle bearings, rails and ball screws.
High-speed cutting and axial milling are also good combinations. The impact on the spindle bearings is small. With this method, the tool with a long overhang can be used with little risk of vibration.
High-productivity cutting of small-sized parts, such as roughing, semi-finishing, and finishing, is economical when the overall material removal rate is relatively low.
High-speed cutting achieves high productivity in general finishing and excellent surface quality. The surface quality is often lower than Ra0.2μm.
The geometric accuracy of the mold is improved and assembly is easier and faster.
The surface texture and geometric accuracy of CAM/CNC production can be obtained regardless of the person or skill.
If the time spent on cutting is slightly more, the time-consuming manual polishing work can be significantly reduced.
It can often be reduced by 60-100%.
Some machining, such as quenching, electrolytic machining and electrical discharge machining (EDM), can be greatly reduced.
This reduces investment costs and simplifies logistics.
Adopt machining instead of electrical discharge machining (EDM), the mold life and quality are also improved.
Adopt high-speed cutting, the design can be changed quickly by CAD/CAM, especially without the need to produce new electrodes.
Due to the high acceleration and deceleration of the starting process and the stop, the guide rails, ball screws and spindle bearings produce relatively fast wear.
This often leads to higher maintenance costs.
Requires specialized process knowledge, programming equipment, and an interface to quickly transfer data.
It may be difficult to find and select senior technical staff.
There is considerable time for debugging and failure.
There is no need for an emergency stop during processing, resulting in many serious consequences for human error and software or hardware failure.
There must be a good processing plan.
Safety measures must be taken: use a machine with a safety cover and a debris-proof cover. Avoid large overhangs of the tool.
Do not use “heavy” tools and posts.
Regularly check the tools, posts and bolts for fatigue cracks.
Use only tools that indicate the highest spindle speed.
Do not use integral high speed steel (HSS) tools!
High-speed cutting requirements for machine tools
Typical requirements for ISO/BT 40 machines are as follows:
- Spindle speed range <40 000 rpm
- Spindle power >22 kW
- Programmable feed rate 40-60 m/min
- Fast transverse feed <90 m/min
- Axial deceleration/acceleration > 1g
- Block processing speed 1-20 milliseconds
- Data transfer speed 250 Kbit/s (1 ms)
- Incremental (linear) 5-20μm
- Or NURBS interpolation
- The spindle has high thermal stability and rigidity, and the spindle bearings have high pre-tension and cooling capacity.
- Air supply/coolant through the main shaft
- Rigid machine tool frame with high absorption vibration capability
- Various error compensation – temperature, quadrant, ball screw is the most important.
- Advanced preview function in the CNC.
Typical requirements for cutting tools of high-speed machining
High precision grinding with radial runout below 3μm.
The smallest possible protrusion and overhang, the maximum rigidity, the bending deformation of the tool as small as possible and the large core diameter.
In order to minimize the risk of vibration, cutting forces and bending, the cutting edge and contact length should be as short as possible.
Oversized, tapered shank, which is especially important at small diameters.
Fine grain matrix and TiAlN coating for high wear resistance.
Internal cooling holes for air cooling or coolant.
Robust micro-groove for high-speed cutting of hardened steel.
Symmetrical tools are best designed to ensure balance.
Tools using indexable inserts:
Designed to ensure a balance.
The high precision of the bobs on the insert holder and the blade is small, and the maximum radial runout of the main insert is 10μm.
Grades and geometries for high speed cutting of hardened steel.
The knife has a specific clearance to avoid friction when the tool bending (cutting force) disappears.
Cooling holes for air or coolant (end mill).
The knife is specifically marked with the maximum allowable speed.