DPSS Micromachining Puts Shine on Industrial Molds
- Saturday, 01 April 2006
Modular diode-pumped solid state (DPSS) lasers make it easy to tailor laser sources to micromachining applications, such as steel and ceramic molds.
Lasers are now used to micromachine virtually every type of material, including metals, plastics, glass, and ceramics. Micromachining is a highly diverse market that uses flash-pumped, diode-pumped solid-state (DPSS), and excimer lasers. Excimer lasers provide more average power at shorter wavelengths, enabling more precise micromachining, but as DPSS lasers have added increased average output power to their lower acquisition and operation costs, small footprint, improved mode operation, and high-repetition pulse rate, DPSS systems are grabbing a larger share of the micromachining market.
As DPSS lasers find themselves in a wider number and variety of applications, it is causing manufacturers to reevaluate how they design these laser sources to meet the application-specific needs of micromachining, which change with material type and micromachining process. The result is a split in DPSS lasers to include standardized systems built for volume applications, and modular designs that provide the level of customization micromachining applications require, without excessive non-reccurring engineering costs.
An interesting niche application for laser micromachining involves creating precision mold forms for small parts by three-dimensional (3D) micromachining, or 3D ablation. Lasertec (Dublin, Ireland), a company recently acquired by the Sauer division of Gildemeister (Bielefeld, Germany), manufactures a workstation intended for the production of precision molds and dies, mainly from stainless steel, carbide steel, and ceramic. These molds are then used to produce large numbers of plastic parts for toys (most notably model trains), electronic plugs, and connectors. These parts may have overall dimensions as large as 300 × 200 mm, but are often smaller than 10 mm. From a laser micromachining viewpoint, this is a somewhat unusual application because these small molds are high-value products used to create many thousands of parts. The dominant process parameters are surface finish and dimensional precision more than process speed, which is a secondary issue.
In practice, the engineer first designs a mold using conventional CAD software package. Once the design is finalized, the data is exported in a standard triangle format — the same format used in laser sintering. In this format, the data is divided into thin layers with thicknesses between 0.5 and 5 μm, depending on the desired surface quality (roughness). These layers are defined by a polygonal surface mesh consisting of triangular facets. The workstation then etches each successive layer by use of a focused laser beam.
To start the system, the operator mounts a blank material on an X-Y stage, which moves the mold in two dimensions (2D) relative to the focused laser beam. The beam is vector scanned over the substrate using twin-axis galvanometer mirrors (θX, θY). A fifth degree of motion is provided by a Z-shifter that moves the focus position of the final beam delivery lens, which is mounted on a linear scanner. This enables shapes such as balls and spheres to be created. In addition, the beam delivery system is set up to allow the beam to be inclined relative to the workpiece at angles up to ±20°. This enables the system to create pockets with vertical walls.