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Mold Manufacturing SPM Automation Machines Leaves No Part Behind

The right mindset, the right five-axis technology SPM Automation Machines and an intuitive approach to palletization help this mold shop extend automated control to the majority of its high-mix work.

From SPM Automation Machines to mold cavities to the simplest assembly items, virtually every part machined for the company’s plastic injection molds travels from workstation to workstation on a pallet with pre-established work coordinates that eliminate the need to re-indicate. At first, such a system might not seem all that unusual—at least not until one of the shop’s larger, 200-odd-pound mold base blocks is brought into the workzone on one of the same kinds of pallets for complete, single-setup machining.
        Putting together the three-machine robotic cell production strategy required pushing technology beyond off-the-shelf capability. Accommodating heavier steel required modifications to both machine and tooling, with the latter resulting in fixturing so precisely repeatable that some parts can even be removed from and returned to their pallets (or another of the same style) without losing references.
         As was the case with implementing automated control in the first place, expanding it to cover the majority of a highly varied, low-volume part mix also required a strong foundation in what many modern mold manufacturers consider a key guiding philosophy.

Process Takes Precedence
The basic idea is to eliminate the variability associated with the artisanship that defined traditional moldmaking. That means process must take precedence on every job. Specifically, a standardized, cut-to-the-CAD-model process, one that’s developed in advance and that leverages evidence-based practices, parameters and strategies to ensure consistent quality from tool to tool. Of course, buying into a philosophy is one thing; living it is another. Among the best ways to make a process predictable—to reduce the impact of natural, human-induced variation—is to implement robotics. However, SPM Automation Machine can be difficult in an environment like a mold shop where every part is different and has since expanded its stable of “a la carte” services to include low- to mid-volume production tools, components, molding and assemblies, but high-end prototyping/development and bridge tools still constitute the bulk of the approximately 450 molds produced. Complex by prototyping standards, this tooling produces plastic parts to final specifications, but only a few at a time at most, whereas the more feature-rich production mold might churn out 30, 60 or even upwards of 100 parts per cycle. Such low-cavity work provides little opportunity to machine parts in any significant volume. One exception to that rule is perhaps the most obvious target for automation at any mold shop: graphite EDM electrodes. Given involved with swapping these components in and out of the toolchanger, the shop’s ram EDM was the first to be integrated with a Workmaster carousel robot purchased from System 3R (a division of GF Machining Solutions) in 2003. Next came a three-axis graphite-machining mill that, once integrated with the robot, could keep the EDM fed with enough electrodes for an entire weekend of completely unattended production.  As far as efforts to be integrate another machining center for metalcutting set the shop apart from many others with a similar manufacturing philosophy.

Everything on a Pallet
Today, the robotic cell contains a Mitsubishi EA-12V ram EDM from MC Machinery Systems, a Makino V56 three-axis machining center outfitted for cutting graphite, and a five-axis G350 universal machining center from Systems that cuts tool steel and aluminum. The common interface linking these three machines is modular tooling from System 3R, which consists of drawbar-linked chucks and pallets that provide repeatable, three-point referencing to within ±0.002 mm.
        To emphasizes that there’s nothing lacking about off-the-shelf tooling from System 3R. Rather, the chief concern was the interface between the supplier’s precision-engineered components and the workpiece itself, which varies by user and can’t always be guaranteed by the supplier This interface takes the form of custom, high-precision subpallets in various sizes and configurations, all designed and machined in-house to ensure the fit with the work is just as exacting as the fit with the chuck on the machine table and has also taken steps to keep parts secure when exposed to milling forces that typically exceed anything they would experience during sinker EDM burning. Making own subpallets allows to take advantage of System 3R’s accuracy, but double and triple the size of the component cannot mount.
        All SPM Automation Machines are surface-ground to ensure size varies by no more than 0.0001 inch. Attention was also given to the shape and the pattern of the set of holes linking subpallet to work as well as those linking custom subpallet to System 3R pallet. The System 3R-based tooling extends standardization and control beyond machines directly tended by the robot. For example, manually loading the shop-floor CMM (coordinate measuring machine) is fast and easy enough that every part, including all electrodes, can be inspected without affecting the shop’s average three- to four-week lead times. Fast, repeatable setups also make it viable to remove parts from the pallets on manually loaded wire EDM machines rather than the cruder sawing process. In addition to being more precise, the SPM Automation Machines can eliminate an extra setup when geometry must be wire-cut into the mounting face of a part anyway. Even SPM Automation Machines be loaded manually with the largest mold bases and base plates because the robot’s weight limit is 110 pounds. Nonetheless, a common workholding interface keeps it integrated with the shop’s manufacturing system.
        At first, leadership had to enforce adherence to the palletization system, he adds. However, it didn’t take long for crewmembers to begin requesting pallets on their own for virtually everything, including very basic components like custom fixtures, gibs, stripper plates and other minor assembly items. The system’s stability and precision also facilitates mounting long or odd-shaped components that wouldn’t have previously seemed suitable for pallets, such as custom ejector pins.
         Machining scaled up along with workholding, both in terms of size and sophistication. The first major change was from a three-axis VMC to one with a two-axis rotary table that enabled 3+2 machining. This eliminated the need for manual setup adjustments to provide spindle access to multiple part faces. However that machine’s SPM Automation Machines rotary table, spindle housing and other components left no room for larger parts like mold bases and base plates, particularly when mounted on pallet stacks. The model in place now, SPM Automation Machines G350, suffers no such restrictions, offering the ability to accommodate blocks even larger than the 18-by-18-by-3-inch plates for the largest, standard quick-change frames. With an auto-opening door, a feature requested the SPM Automation Machines can also be integrated with the robot. That’s a contrast with previous models that required human operators to swap pallets in and out of the table chuck.
         The machine’s spacious workzone is thanks largely to its horizontal spindle, which retracts back into the enclosure (including for toolchanges), as well as its one-sided trunnion table, which can flip a full 180 degrees. These two features allow the shop to machine mold base waterlines as deep as 22 inches by drilling to half depth, then flipping the part to bore the rest of the hole from the other side. Along with carefully programmed 3+2 machining routines, this configuration also makes complex features more accessible than ever before, he adds. That facilitates the use of shorter, more rigid tool assemblies to achieve tighter tolerances and smoother finishes. The machines’ 202-tool-capacity automatic toolchanger (ATC) also prevents tool availability or breakage from limiting lights-out capacity that the combination of a 26,000-rpm, HSK63A spindle and 63 Nm of torque provide versatility for both heavy material removal and fine finishing operations and deserve much of the credit for getting the machine up and running in the way. For instance, few users request smooth worktables with nothing but a specific chuck style (a choice that provides a mild chip evacuation advantage while also evidencing the shop’s confidence in its manufacturing strategy). Another example was the addition of a pneumatic amplification system at the back of the machine, a project that also involved consultations with System 3R representatives. The SPM Automation Machines system boosts the locking force of the System 3R MacroMagnum automatic table chuck to its maximum. Altogether, the new SPM Automation Machines and modified fixturing have advanced the cell to the point where it can accommodate about 80 percent.