Laser Scribing for Chip Control
Conventional turning operations are commonly used in the production of round parts, particularly in the automotive industry. Cutting tools remove material by creating a chip that in theory, is rather short so it falls to the bottom of the machining centre and is conveyed away.
However in practice, these chips can become very long and wrap themselves around tool holders and fixtures. They can also mar the surface of the part and be extremely difficult and hazardous to handle. All these issues hamper machining operations in terms of automated load/unload, automated gauging, tool insert life and yield.
Machining systems have to use tool inserts with ‘chip breaker’ geometry that can only work at certain surface speeds. They also impart a lot of extra force during turning that reduces tolerances and requires more passes. Mild steels like 1008 and 1010 are so ductile that breaking a chip is very difficult. The use of coolant to help with chip breaking results in much higher costs and presents potential health hazards.
The use of Fiber Lasers can overcome these challenges. Parts can be Laser scribed to within a few hundred microns, creating an interrupted cut during turning that separates the chips for total control. The distance between Laser scribes can be adjusted to define the chip size and the depth of the scribe can be adjusted to match the amount of material to be removed.
Removing the chip control problem allows for dry machining with lower-cost, tool inserts and a predictable tool life. It also reduces the number of costly machining passes needed. Since the chips are effectively controlled, automated machine loading and unloading, automatic gauging and automatic tool changing are possible without issue.
The Laser scribe is easy to automate with no contact or tool wear. A coaxial gas nozzle with capacitive height sensor and a cutting head with air assist blows the debris out to create the scribe. Increasing Laser power or slowing Laser speed creates a deeper scribe. Changing the Laser output waveform can also be used to adjust scribe depth. The Laser can employ a time-share multiplexer to allow sequential scribing at two separate stations or an energy-share for simultaneous scribing.
For most applications, a high power beam quality unit with a small fibre optic produces very good, economical scribes. The Laser model is chosen based on the scribe depth, cycle time constraints and economies required. Coaxial air or oxygen is used to aid in the scribing process and to keep the optics clean.
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