The CNC lathe or turning center can be an extremely valuable asset for a plastic injection mold making company. Many shops have yet to realize just how accurate and versatile these machines can be.
With the addition of live tooling it is possible to achieve highly accurate, complex operations while maintaining an excellent surface finish. Often it is possible to eliminate the need for surface grinding, CNC milling, and mold polishing. This naturally saves time and money, which is a good thing!
My first experience with the CNC lathe occurred when I was given the task of building a lens mold for police cars. These lenses are rather complicated, with multi-faceted surfaces designed to reflect light. While I was figuring out how to manufacture the lens core and dreading the prospect of cutting all those facets on the manual lathe, the CNC guy approached me with the good news that he could easily do it on his new turning center.
This was in the early days of CNC and he had very little software to work with, but, being the clever fellow that he was, he turned the core in approximately two hours, complete with the threads around the base.
I was amazed at the accuracy and finish, not to mention the speed with which the core was turned. Another impressive fact was that the threads had to stop at a specific location to time the core to the cavity. Naturally, the two fit together perfectly the first try.
Nearly every injection mold contains round components, such as core pins and cavity inserts. Typically, these are roughed out on a manual lathe, heat treated, finish ground and then EDM’d. The CNC lathe can produce the same work in a fraction of the time, enabling toolmakers to focus on other tasks.
Round components are frequently found to be advantageous over rectangular or square ones for several reasons. Fitting can be much easier, machining may be simpler, and standardization of sizes can enable mold designers to accomplish more is less space.
The use of electrode holders, such as System 3R or Erowa enables the CNC lathe to produce round electrodes quickly and accurately with almost no set-up. The grinding operation may often be eliminated, once again enabling the toolmakers to focus on other jobs.
Repetitive jobs can make use of the tool-changing robot, which loads electrodes into the CNC turning center, removes it to be inspected by the CMM, offsets loaded into the CNC EDM, then loads the electrode into the EDM.
This process obviously requires considerable up-front planning, yet shops have managed to do this all over the world. As companies experience the retiring of skilled help and the subsequent lack of up-and-coming toolmakers, scenarios such as that mentioned above become more common.
Creativity is key
The use of the CNC lathe or turning center is limited only by the imagination and creativity of the mold maker and mold designer. While it may seem, at first glance, that there is not really that much use for the CNC lathe in an injection moldmaking shop, those that own one discover uses that were previously unknown.