Why Is The Titanium Alloy Frame Of IPhone15 A Difficult Material To Machine?

On September 13, Apple released the iPhone 15 series of mobile phones. It is worth mentioning that this is the first time that titanium alloy frames have appeared on smartphones. Titanium alloy is a lightweight, corrosion-resistant, and high-strength material. When used in smartphones, it can improve the overall strength, drop resistance, and scratch resistance of the phone. However, titanium alloy is a difficult-to-machine material, and the introduction of titanium alloy frames is also a challenge in CNC technology.

 

Why do we think titanium alloy is a difficult material to machine? Let’s learn about its related cutting processing characteristics.

01. "Heat" is the "culprit" that makes titanium alloys difficult to process.

The cutting force when processing titanium alloys is only slightly higher than that of steel of the same hardness, but the physical phenomena of processing titanium alloys are much more complex than processing steel, making titanium alloy processing faced with huge difficulties. The heat generated during the cutting of titanium alloy will not be quickly transferred to the workpiece or taken away by the chips. Instead, it will accumulate in the cutting area. The temperature generated can reach over 1000°C, causing the cutting edge of the tool to rapidly wear, crack, and generate chips. Knobs and rapidly worn blades generate more heat in the cutting area, further shortening the life of the tool.

 

02. Technological know-how for processing titanium alloys

On the basis of understanding the processing mechanism of titanium alloys and adding past experience, the main process know-how for processing titanium alloys is as follows:

High-pressure and high-flow cutting fluid is used to ensure the thermal stability of the machining process and prevent workpiece surface degeneration and tool damage caused by excessive temperature.

Machine titanium alloys in their softest state possible because the material becomes more difficult to machine after quenching, and heat treatment increases the strength of the material and increases blade wear.

Use a large tip radius or chamfer to get as much of the cutting edge into the cut as possible. This reduces cutting force and heat at every point and prevents local breakage.

 

03. Start with blades to solve titanium processing problems

The blade groove wear that occurs when machining titanium alloys is the local wear of the back and front along the cutting depth direction. It is often caused by the hardened layer left by the previous processing. The chemical reaction and diffusion between the tool and the workpiece material at processing temperatures exceeding 800°C are also one of the causes of groove wear.

Because during the machining process, the titanium molecules of the workpiece accumulate in front of the blade and are "welded" to the blade under high pressure and high temperature, forming built-up edge. When built-up edge peels off the cutting edge, it takes the insert's carbide coating with it, so titanium machining requires special insert materials and geometries.

 

04. Tool structure suitable for titanium processing

The focus of titanium alloy processing is heat. A large amount of high-pressure cutting fluid must be sprayed on the cutting edge promptly and accurately to remove the heat quickly. There are unique structures of milling cutters on the market specifically for titanium alloy processing.