The discussion on high-speed machining is still somewhat confusing.
There are multiple ideas and definitions to describe high-speed machining (HSM).
One of the primary objectives of high-speed machining is to enhance productivity and minimize production costs.
It is generally applied in finishing procedures and is frequently utilized for processing hardened die steels.
Another aim is to elevate overall competitiveness by shortening production and delivery time.
Definition of high speed machining
The following is our definition of high-speed machining:
High-speed machining (HSM) is not simply machining at high speeds. It is a specific process that utilizes specialized methods and production equipment.
The use of high-speed spindles is not always necessary for HSM. Many applications of HSM involve medium-speed spindles and large-size tools.
When machining hardened steel, cutting parameters can be 4 to 6 times higher than conventional methods if high machining speeds and high feed conditions are used.
HSM is ideal for increasing productivity in roughing semi-finished parts, semi-finishing, finishing, and superfinishing parts of any size.
As part shapes become more complex, high-speed machining becomes increasingly crucial.
Currently, HSM is mainly utilized on machine tools with a taper of 40.
High speed machining target
The main factors to achieve these goals are:
- Minimizing the frequency of mold setup.
- Enhancing the geometric accuracy of the mold through machining, reducing manual labor and shortening the testing time.
- Utilizing CAM systems and shop-oriented programming to aid in developing process plans and increasing machine and plant utilization via process planning.
Tools and workpieces
Maintaining low temperatures can often prolong the lifespan of a tool. However, in high-speed machining applications, the cutting depth is usually shallow, and the cutting edge is in contact for a very short time. This means that the feed rate is faster than the heat generated.
As a result of the low cutting forces involved, the tool undergoes minimal bending, which combined with a consistent machining allowance, is essential for efficient and safe machining. The shallow cutting depth in high-speed cutting also reduces radial forces on the tool and spindle, which helps to minimize wear on spindle bearings, rails, and ball screws.
High-speed cutting and axial milling are a great combination since they have a minimal impact on spindle bearings. This method also allows the use of tools with long overhangs with little risk of vibration.
When it comes to high-productivity cutting of small-sized parts, such as roughing, semi-finishing, and finishing, it’s more economical to have a relatively low overall material removal rate.
High-speed cutting is an effective method for achieving high productivity and excellent surface quality in general finishing. The resulting surface quality is often as low as Ra0.2μm. This method also improves the geometric accuracy of molds, making assembly easier and faster.
Moreover, regardless of a person’s skill level, the surface texture and geometric accuracy of CAM/CNC production can be obtained. Although cutting time may increase slightly, it can significantly reduce time-consuming manual polishing work by up to 60-100%.
Some machining processes, such as quenching, electrolytic machining, and electrical discharge machining (EDM), can be greatly reduced, thereby lowering investment costs and simplifying logistics. By adopting machining instead of EDM, mold life and quality can also be improved.
Furthermore, using high-speed cutting enables quick design changes through CAD/CAM without the need to produce new electrodes. However, due to the high acceleration and deceleration during the starting process and stopping, guide rails, ball screws, and spindle bearings can wear relatively quickly.
This often results in increased maintenance expenses.
It requires specialized knowledge of the processes, programming equipment, and an interface to transfer data quickly.
Finding and selecting senior technical staff can be challenging.
Debugging and failure can take a significant amount of time.
Not having an emergency stop during processing can lead to severe consequences in case of human error or hardware or software failure.
A well-planned processing strategy is necessary.
Safety measures must be implemented, such as using a machine with a safety cover and debris-proof cover, avoiding large tool overhangs, not using “heavy” tools and posts, regularly checking for fatigue cracks in tools, posts, and bolts, and using only tools that indicate the highest spindle speed.
Integral high speed steel (HSS) tools should not be used.
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
Solid carbide:
Achieve high-precision grinding with radial runout below 3μm by incorporating the following features: minimize protrusion and overhang, maximize rigidity, reduce bending deformation of the tool, and use a large core diameter.
To minimize the risk of vibration, cutting forces, and bending, keep the cutting edge and contact length as short as possible. Additionally, use an oversized, tapered shank, especially for small diameters.
Use a fine-grain matrix and TiAlN coating to ensure high wear resistance. Incorporate internal cooling holes for air cooling or coolant to improve performance.
For high-speed cutting of hardened steel, use a robust micro-groove. Design symmetrical tools to ensure balance.
Tools using indexable inserts:
This design aims to achieve a balance by incorporating several features. The bobs on the insert holder and blade have high precision, and the maximum radial runout of the main insert is 10μm. Additionally, grades and geometries have been selected for high-speed cutting of hardened steel.
To prevent friction when the tool bends due to cutting force, the knife has a specific clearance. Furthermore, cooling holes have been added for either air or coolant (in case of end mills).
Lastly, the knife is marked with the maximum allowable speed for user safety.
