Mold shops that recognize the potential of technology and equipment, and prioritize both accuracy and productivity will increase their competitiveness in the marketplace. The key is utilizing machines that are engineered to reduce the time-consuming elements of mold manufacturing, increase mold quality, enhance accuracy and eliminate opportunities for human error.

The mold-building process addresses a challenging combination of machining tolerances, further complicated by tedious workpiece setups that enable the machine to interact with the workpiece more precisely across machining and drilling steps.

Machines designed to handle specific moldmaking challenges—such as increasing throughput by eliminating many of the major time-intensive elements involved in creating a mold—are an optimal solution for mold manufacturers looking to gain an advantage. These machines have features that reduce the need for costly fixtures and extended changeovers, and enable a single setup for several machining processes while allowing operations to be performed on all four sides of a workpiece.

A mold on such a machine can be produced using a roughed-out workpiece that is clamped to the table with modular locating components. The part is milled on four sides and drilled at very high feed rates using high-performance gun drills and BTA tools. With the same setup and fixturing, compound angle machining, intersecting bores, pocketing and complex surface milling can be completed accurately and efficiently. Probing for critical features can then be performed. The mold manufacturer saves days in production time.

A capable machine also will meet the high tolerance demands of complex mold profiles. Features contributing to this include a rigid B-axis table that can handle heavy workpieces as well as high moment capacity. Another essential feature is a headstock carrying milling and drilling spindles that can tilt on an A axis without a loss in rigidity, and allows B-axis rotation at extreme angles and larger than typical travels. All of this leads to the elimination of tedious changeover work, which can save valuable time and effort that can then be applied to using advanced technology and creating better molds.

Machines that combine a range of machining and drilling operations, including high-performance milling and deep-hole drilling, can further increase efficiency. These feature multi-axis positioning and are equipped with capable headstocks with geared transmissions, and 50-taper spindles. A deep-hole drilling headstock capable of conventional gundrilling as well as BTA high-performance drilling will be five-to-seven-times faster than gundrilling alone to further increase productivity and maintain accuracy.

Highly productive machines take advantage of opportunities for automating the machining process as well, and they are extremely accurate in dynamic situations regardless of axis orientation. These machines typically are outfitted with several beneficial options, such as glass scales and direct-feedback angular encoders. They also are able to take advantage of volumetric compensation with a standard contouring control. Furthermore, workpiece probing, laser presetting and large-capacity automatic toolchangers allow unattended operation with greater versatility than previously possible. In addition, process feedback further improves a machine’s capabilities by allowing tooling to be pushed to the limit with the assurance of automatic cycle interruption before something catastrophic occurs.

Summary

The seamless integration of multiple technologies and operations in a single machine can be advantageous. Parametric 3D programming, sophisticated post processing, tool management and on-machine verification are common in more and more shops as the technology becomes affordable. Capable machines are engineered to optimize this technology, and this in turn drastically improves the process that competitive mold manufacturers use to succeed.

For a hydraulic cylinder to operate effectively, the cylinder’s ID must be precisely round and have a mirror-like surface finish to ensure a tight seal between it and the mating internal piston. This is commonly achieved through skiving and subsequent roller burnishing inside a tubular workpiece. Skiving uses a set of carbide blades positioned around the diameter of a tool to slice away chips and create a geometrically round bore. Roller burnishing, a cold-working process, uses multiple rollers to compress the peaks of material left behind after skiving to generate an extremely smooth surface finish. Burnishing also introduces a residual stress layer into the cylinder wall, which improves cylinder fatigue life.

These operations are sometimes performed in one pass using a combination skiving/roller burnishing tool on a BTA-style deep-hole drilling machine. However, UNISIG, a supplier of machines, tools and automation for deep hole-making applications, has recently designed machines engineered specifically to perform skiving and roller burnishing operations, noting increasing demand in the hydraulics market for such equipment. Its S-series machines use a single tool for both operations, achieving roundness tolerances of IT-8 or IT-9 and bore surface finishes as smooth as Ra 0.05 to 0.2 micron in one setup and one tool pass.

Sarang Garud, applications engineer for UNISIG, says that 80 percent of the S-series machine design is based on the company’s existing B-series (ballscrew-feed) BTA drilling machines. That said, he notes three distinct features that enable the S-series to be highly effective at skiving and roller burnishing:

Workholding

The tubes used for hydraulic cylinders are relatively thin. Care must be taken to secure the tube rigidly enough for the skiving and roller burnishing processes, but not so tightly as to deform it. Therefore, clamping cones are typically used to hold the tubes on both ends instead of three-jaw chucks. This clamping method also facilitates quick workpiece changeovers in automated environments. In addition, extra support must be provided along the length of the tube due to the inherently high length-to-diameter ratio of these workpieces. The S-series uses a V-shaped hydraulic clamp to provide this support.

Power Train

Thin cuts are taken during skiving. A skiving blade’s radial engagement with the workpiece might be just 2 mm and feeds might be 1 mm per revolution, per blade. However, each tool has two or three skiving blades, which multiples the effective feed rate. Similarly, the cold-working roller burnishing process requires a lot of torque and high spindle speed as it plasticizes and compresses the peaks that skiving leaves behind. As a result, the S-series features a more robust power train with higher horsepower motors and faster spindle speeds than conventional BTA drilling machines.

Rotary Union

A hydraulic circuit inside the skiving and roller burnishing tool expands the skiving blades and burnishing rollers during cutting operations. Therefore, the S-series has a rotary union at one end of the tool headstock to provide a hydraulic connection throughout the length of the rotating tool. Once the cutting pass is completed, the blades and rollers are retracted into the tool as it is removed from the tube. The tool continues to rotate as it is removed, but nylon guides on the tool and continuous coolant delivery prevent damage to the cylinder wall.

The S-series machines are available in skiving/burnishing diameters ranging from 1.5 to 12 inches and lengths to 45 feet (more machines available upon request). The machines can also be modified to perform BTA drilling, counter-boring, and other drilling and tube-finishing operations. In addition, tools can be configured to perform tube finishing on a variety of metals.