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Stressed because multi-function lathes won't work? HOW TO IMPROVE THE EFFECIENCY OF A MULT-FUNCTION MACINE By Mike Wolf, Hartwig Applications Engineer
Manufacturing engineers approach us all the time looking for ways to improve existing processes, for help in creating processes for new parts. Frequent changes in production schedules, shortening product life, and accounting philosophies that require minimum inventories, demand manufacturing processes that combine machining operations but can be changed easily. If the processes are based on turning we look to multi-function lathes. These machines can turn, mill, drill, tap, sometimes on both ends of the part, and sometimes on any surface. Sounds great, doesn't it? Then why do some manufacturers seem to struggle with implementing these machines? There are three reasons.
First: Processing. Multi-function machines are ideal for a workpiece that has tight geometric relationships. A pattern of holes (even on an angle), which needs to be in a tight relationship with a turned diameter is best machined in the same set-up. Nothing beats a multi-tasking lathe for that. Similarly, an outside diameter, on one end of part is best machined in a sub-spindle lathe if it must be concentric to a bore on the opposite end. This is easy to understand. The difficulty comes when we are asked to maintain very tight tolerances (those would have been ground less than a generation ago). We have to consider that all the additional axis, tool changing, etc, naturally increases variability. Generally, we can get our customers where they need to be if we have access to their success on similar processes and parts, or if we can implement some sort of in-process or post-process gauging.
Second: Workholding. The task of adequately supporting a workpiece, yet being able to access every facet, can be difficult. Typically not enough thought goes into the workholding selection. On the plus side, most multi-function lathes provide interesting solutions by nature of their flexibility. Single turret machines might be available with steady-rests, and some are available with steady-rests that are position-able via a separate ball screw. This feature provides amazing flexibility. Dual turret machines not only offer the same flexibility by mounting a steady-rest on the lower turret, but also provide additional flexibility by mounting other static support or live centers on the lower turret.
Then there are workholding fundamentals that apply to any turning application. Using collet chucks (when possible) instead of three jaw chucks because they are smaller and create less tooling interference. Also, collets are typically faster to change than chuck jaws. When the need to use chuck jaws exists (most applications), use an axial locator that attaches to the face of the chuck instead of the surface of the chuck jaws. Yes, it is one more thing to change in a set-up, but the location will be much more consistent, inevitably leading to a quicker change over. Most importantly, when the jaws are machined, stamp an indentifying number in them (part number, size, etc), have them hardened, and put them into an appropriately indentified and accessible storage location.
Third: Documentation. Basically document everything. Take pictures and/or videos, and create set-up sheets that adequately describe the set-up (tooling, workholding, etc). Combine this information into set-up instructions that an operator can understand. If the machine has the ability, keep this information on the lathe's control for quick access. If not, put a computer with this information nearby. As previous articles suggested, keeping the tooling and workholding in organized storage locations will also help to minimize the change-over time.
Change-over time is defined as the time between the last part of one production run to the first "good" part of the next production run. Creating a durable process, having good workholding (and tooling), and recording the steps to complete a change-over are just things to consider, and they are absolutely required for a successful implementation of a multi-axis, multi-function machine. Hartwig has installed and created processes for several hundred of these machines. Call any office and talk to any application engineer for more ideas and help. We are happy to take your call.
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