What are the metal CNC processing techniques?
CNC machining of metal is a high-precision, high-efficiency subtractive manufacturing technology. According to the cutting motion mode and the tools used, Metal Cnc Machining processes are mainly divided into the following four core types.
The following is a comparison of the mainstream metal CNC machining processes and their advantages and disadvantages:
- CNC milling
CNC milling is the most common CNC process. The workpiece is fixed and the multi-edged tool rotating at high speed moves on the surface of the workpiece to remove excess material. Common ones include three-axis, four-axis and five-axis milling.
Almost any geometry can be machined, including flat surfaces, grooves, gears and complex curved surfaces. Suitable for rough machining of large areas and high removal rates. Five-axis milling can process extremely complex aerospace, medical and other curved surface parts, reducing the number of clamping times.
Limited by the cylindrical appearance of the rotating tool, it is impossible to machine a perfect internal clearance angle (usually leaving an R angle). The milled surface will leave tiny tool marks, which usually require subsequent processes (such as sandblasting and polishing) to improve the appearance.
- CNC turning
Contrary to milling, CNC turning is a workpiece clamped on a chuck that rotates at high speed, while a single-edged turning tool moves in a straight line or curve to perform cutting. Usually used for processing rotary parts (such as shafts, classes, discs).
It is extremely fast when processing symmetrical axial parts such as cylinders, cones, threads, etc. Continuous cutting results in turned surfaces that are generally smoother than milled and have extremely high roundness and coaxiality. Compared with milling, turning tools have a simple structure and short processing time.
Only parts with rotationally symmetrical features can be machined. If the part has asymmetrical holes or slots, a "mill-turn" machine is required.
- CNC drilling and tapping
Use a rotating drill or tap to create round holes and internal threads on the workpiece. In CNC machining, this is usually performed as a secondary compound operation to milling or turning.
It can accurately locate hole positions extremely quickly and accurately, and process large quantities of threaded holes with standard specifications.
It can only process vertical or specific angle round holes and threads, and can’t be used for contour processing. It is easy to accumulate chips during deep hole machining. If the chips are not removed smoothly, it may easily lead to tool breakage.
- CNC grinding
A high-speed rotating grinding wheel is used as the main tool to perform micro-cutting on the workpiece surface. Usually used as the last finishing process for metal parts forming.
It can achieve micron-level dimensional tolerances and the surface can achieve a mirror effect. It can easily process hardened steel, carbide and other high-hardness metals that are difficult to cut with traditional milling cutters.
The processing speed is slow, the production efficiency is low, and it isn't suitable for removing a large amount of material for shaping. Equipment and grinding wheel wear costs are high.
In actual metal product development, most of them are a combination of multiple processes
Basic molding: First use CNC turning for shafts/cylinders or CNC milling for shells/special-shaped parts to quickly cut out the general appearance.
Local fine-tuning: When encountering a structure whose corners can’t be cleaned, use EDM to perform local corner cleaning or deep groove processing.
Surface and precision: CNC grinding is used for parts that require extremely high fit or require a mirror effect.
Post-processing: Combined with sandblasting, anodizing, PVD or physical polishing to hide CNC mechanical tool marks and achieve the ideal appearance and texture.
Sustainability in CNC machining can be achieved by improving energy efficiency, optimizing tool paths to reduce scrap, and recycling cutting fluids and metal residues.
Common problems in hole processing: Is the hole diameter too large/small, or the hole wall is rough?
The hole diameter is too large: drill bit swing error and boring tool compensation are too large;
Hole diameter is too small: drill bit wear, material extrusion rebound (aluminum, stainless steel);
Poor hole wall: poor chip removal, deep holes require tool retraction to remove chips.
Commonly used Cnc Processing materials and key points?
6061 Aluminum: easy to cut, good anodization, general structural parts; easy to deform
7075 aluminum: high strength, stick to knives, large oxidation color difference, stress-bearing parts
45# steel: high cost performance, easy to rust, needs surface anti-rust treatment
304 stainless steel: rust-proof, high cutting resistance, high tool wear, easy to work harden
Brass: light cutting, good finish, low hardness
TC4 titanium alloy: high strength, corrosion resistance, poor thermal conductivity, easy to burn the knife, high cost