Injection moulding process productivity can be compromised by de-moulding issues caused in many instances by increasing part and polymer complexity.
An effective and traditional method to overcome these issues is to apply coatings to the mould surface to reduce adhesion and friction enabling moulded parts to be ejected quickly. This coating process occurs after the machining operations (i.e. milling, EDM machining etc.) have been completed - and, as such, adds time and cost to the whole manufacturing process.
A new, less time-consuming approach using advanced EDM die-sinking technology has been developed by GF Machining Solutions.
In essence the new approach can be adopted by mould makers with access to the company’s latest AgieCharmilles FORM P and FORM X die-sinking machines that are equipped with the high-performance and digital Intelligent Speed Power Generator (ISPG) and 3DS - an onboard, intelligent surface texturing technology that can be accessed directly from the machines’ HMI control.
3DS technology smoothes out the distance between the peaks and valleys on the mould surface, but not to a point where the peaks are eliminated. 3DS stretches the surface RSM (Root Mean Square) value, without affecting the Ra value and, because the peaks are more evenly spread out the surface that is created in the mould, prevents sticking.
Owing to the reduced surface friction moulds can be filled faster (shaving seconds off the moulding process) and moulded parts can be ejected quickly and effortlessly.
For manufacturers that make millions of injection-moulded parts, this enables significant cycle time reductions and the ability to make hundreds of thousands of additional parts.
The surface finish achieved using 3DS also reduces the likelihood of residue sticking to the mould after the plastic is injected. This is a particular problem that grows steadily worse after repeated injections, leading to uneven surface finishes on parts.
While a polished surface finish may seem ideal for every mould, this is not always the case.
A highly polished finish requires significantly more pressure to inject the liquefied plastic into the mould. If the finish is too flat, or too smooth, the plastic sucks to the surface – like two pieces of glass with water in between them. This exceptionally strong suction effect slows the flow of plastic into the mould.
Additionally, greater ejection force is required to push the moulded part out of the cavity because the smooth surface causes it to stick - and if the newly-formed part is still warm and a bit soft, the ejector pins will push into it and deform its surface.
The optimised 3DS surface finish ensures less force is needed to eject a moulded part. And even if tiny plastic particles are still present, the amount is not enough to contaminate the surface.
In operation, a die-sink EDM machine with 3DS – after rough burning a mould cavity surface – follows the standard finishing operation but then activates the new 3DS function for the last two or three burn settings to deliver and ensure the enhanced surface finish. The machine uses the same standard finishing electrode and the machining cycle time remains unchanged because, instead of using the last standard finishing parameters, the 3DS setting is simply implemented.
3DS technology is proven and successful. One GF Machining Solutions customer using 3DS technology recently reported a 30 percent reduction in maintenance costs. This same company has also been able to leave the mould in the moulding press 30 percent longer without having to clean the mould surface and interrupt production.
This type of surface finishing has other applications outside of mould making. Any part that comes into contact with fluid, for example, will benefit from advanced surface quality to facilitate the fast and smooth flow of fluids.
3DS is available on advanced AgieCharmilles FORM P and FORM X series of die-sinking machines from GF Machining Solutions.