PMMA Light Guide Prototyping
This is one of many light guides we’ve made for the automotive industry. The part was made by high Speed CNC Milling from solid PMMA block, and polished by hand. We use 4 axis or 5 axis milling to achieve the twist sharp. R 0.15mm cutter and more than 20000 RPM to ensure maximum transparence of the teeth. No hand finish on these feature at all. So the parts are absolutely true to the design geometry, and without blemish. The customer was more than happy when they received the part.
Prototyping of small metal assembly by two methods; DMLS vs CNC.
The designer created this two-part ring assembly with internal space for a micro SD card. Initially they opted for prototyping by DMLS (direct metal laser sintering) – arguably the most accurate additive manufacturing process for metal parts. As the geometry features deep recesses and thin wall sections, fabrication by conventional methods seemed challenging.
After receiving DMLS parts from Europe, the designer decided to explore other options. The CAD files were sent to 3ERP, and we made several units by CNC machining (in 316 Stainless steel.) Since the depth of the recess is more than ten times the width, we used electrostatic discharge machining for this feature.
The CNC parts we provided compared favorably with the DMLS parts, and we received orders for the next design iterations.
This case study highlights several advantages of CNC machining over existing DMLS capabilities;
Surface finish; the titanium ring exhibits rough texture as a result of the layer-by layer DMLS fabrication process. DMLS parts are not 100% dense, therefore impossible to finish in the same way as CNC parts.
Accuracy; the titanium ring did not assemble as well as the rings made by CNC. Imperfect fit on DMLS parts could be attributed to surface irregularity or warped geometry.
Cost; the ring made by DMLS was much more expensive than the CNC alternative. Of course, titanium is more expensive than steel – but even if the DMLS ring had been made in steel, material costs would have been higher due to processing cost of the powdered stock. The price of DMLS machinery is another factor.
Whilst DMLS came off second best in this example, there are many applications where its strengths outweigh the drawbacks, and it makes the difference between impossible and possible. If your project requires fabrication of tricky components, feel free to contact us.