Drill/Tap Centers Take to Milling
Thirty-taper doesn't mean machining lite anymore
By Jim Lorincz
It is reported that, not too long ago, before the current precipitous decline in machine-tool shipments, the number of 30-taper machines that were being manufactured and sold in Japan had surpassed the numbers of 40-taper and 50-taper machining centers. Conceived originally for high-speed drilling and tapping, typically as single-table platforms for machining aluminum and zinc die castings, 30-taper drilling and tapping centers have evolved into full-scale machining centers, while retaining the speed, flexibility, and ability to reduce cycle-times for which they were known and valued.
Introduced in the US in the early 1980s, 30-taper drill/tap/milling centers are used by manufacturers of die cast parts for a variety of industries, including automotive, small engine, pumps and valves, electrical, aerospace, and other commercial vehicles. Typical parts include automotive and motorcycle parts like racking housings, pump bodies, and throttle shafts, general machinery parts including gear cases, hydraulic transmission joints, camera panels, and distribution valves, as well as information-technology parts.
The progression in the development of the 30-taper drill/tap center has proceeded from basic single-table machines for high-speed drilling and tapping to machining centers equipped with twin pallet changers, or automation provided by dedicated robots. The range of materials machined has grown beyond the traditional aluminum or zinc die cast materials to include steel, stainless, cast iron, and even titanium for medical device applications.
Developments in the construction and design of 30- taper machines and advances in tooling and fixturing have made them a viable alternative to slower, larger machining centers. In fact, 30-taper machines may rival 40-taper and 50-taper HMCs in offering contract manufacturers a bankable advantage in quoting jobs that have formerly been exclusively the domain of the larger HMCs.
The numbers add up for contract manufacturers in quoting jobs with 30-taper machining centers. The principal reason is speed of processing. Speed is of the essence in reducing cycle times by minimizing non-cutting time with fast tool and pallet changes, and simplified changeover and fast setup times. Buying 30-taper machines requires less capital investment, switching over to 30-taper tooling, previously in limited supply, has become simpler as tooling manufacturers are developing the new tools required when changing to a new 30-taper tooling system.
The earliest 30-taper machines were difficult to employ for any but the lightest milling. But the new 30-taper machines feature heavier castings and larger spindle bearings to handle the axial loads generated in milling. Pallet changers have transformed 30-taper machining centers into production centers for a variety of parts. In addition, 30-taper drill/tap/milling centers feature high-speed spindles, fast rapid traverse, and high-pressure coolant capability, all intended to reduce cycle time and minimize non-cutting time. Machines can be equipped with fixturing such as a fourth-axis rotary table and tailstock, hydraulic and air clamping, probing, and light curtains for high production rates for the most complex components. Automation-ready drill/tap centers can be equipped with robots for untended operation.
For some companies, the transition to 30-taper machining has already produced tangible results in gaining new business, as well as maximizing throughput for existing customers.
Empire Die Casting (Macedonia, OH) produces zinc and aluminum die castings in its two foundries for several hundred customers in a variety of industries. In 2004, Empire acquired the first of three Brother TC-32B CNC tapping centers. Previously, machining die castings was performed exclusively on 500-mm and 630-mm HMCs, as well as various 40-taper VMCs.
Empire acquired two Brother TC-32B machines and one TC-32BN. One TC-32B is dedicated to one particular job with another machine serving as its backup. The TC- 32BN can be quickly changed over using the Ball Lock mounting system from Jergens Inc. (Cleveland) to run a variety of jobs. On one part, a housing for a hydrostatic transmission, the TC-32BN is face milling, machining Oring grooves, tapping flange mounting holes, tapping two 3/8" (9.5-mm) holes, tapping a seat, drilling a hole in the seat, and boring three different tight-tolerance bores.
One of Empire Die Casting's 30-taper machines, a TC-32B, is equipped with air and hydraulic clamping, a Nikken trunnion fourth axis with tailstock, and probing of every part to establish X, Y, Z datum planes. The Brother TC-32BN is the latest model from that company, and can hold 40 tools and handle 1000 psi (6.9 MPa) high-pressure coolant using a BT30 tool rather than the HSK 40A previously required—a higher priced tool somewhat limited on gage length.
"Our 30-taper machining centers are anything but weak, tiny little things for machining die castings," says Michael Garver of Yamazen Inc. (Westlake, OH). "As our machines have evolved into stronger, more-capable machining centers, we haven't lost the sheer speed in cutting, changing tools, and rapid traversing that have enabled our machines to minimize non-cutting time," says Garver.
When Brother developed its first drill tap center for its own use in manufacturing sewing machines, it also developed its own control with its patented "synchronous tapping." "Because of this and our unique spindle design, we can start and stop our spindle faster than the competition which gives us an advantage when it comes to tapping and tool changes," Garver explains. "Other advantages of the Brother machines are the ability to position the workpiece to the next feature to be machined while doing a tool change and the ability to change a tool while doing a pallet change. By the time the next part to be machined comes in the machine, the spindle is running at 16,000 rpm hovering above the part ready to cut with the proper tool."
Results are typical of the performance capability of the TC-32BN 30-taper machining centers. Says Garver: "The TC-32BN has rapids of 70 m/min with 1.5g's of acceleration and spindle acceleration from 0 to 16,000 rpm in 0.46 sec, and a chip to chip time of 2.1 secs, which is taken from the center of our X, Y travel with the spindle at 16,000 rpm. When it comes to a matter of a few seconds difference in reducing cycle times, these capabilities add up to increased productivity and competitiveness for job shops."
For untended operation, automation with robots is proving to be an effective and reliable way to improve production. Automation improves processing consistency by relieving operators of loading and unloading parts, either to a single-table machine or to dual pallet-equipped machines, and, of course, facilitates untended operation.
Recognizing the need to provide an integrated automation system for its Fanuc RoboDrill VMC, Methods Machine Tools Inc. (Sudbury, MA) developed the JobShop Cell, an automated production cell that is designed to fit the special needs of job shops. It provides fast setup for small to medium lot-size workpieces. The JobShop Cell is pre-engineered for simple installation, fast setups, quick changeovers, operator safety, and, above all, for production flexibility.
The JobShop Cell is readily adaptable to handle virtually any part that will fit in its 6" (152.4-mm) vise or chuck. It comes complete with inbound and outbound conveyors and guarding. The workhandling interface accommodates a variety of hydraulic or pneumatic workholding options. A fourth or fourth and fifth-axis table can be added to further increase the production cell's capability.
At the heart of the system is the Fanuc RoboDrill. "The RoboDrill is a fast, efficient, and affordable machining center that has expanded the capability of the 30-taper drill tap with beefed up castings and larger spindle bearings," explains Scott McIver, chairman and vice president of product development, Methods Machine Tools Inc. "The Fanuc RoboDrill VMC offers a 14-tool ATC, rigid tapping to 5000 rpm, accelerations to 1.5 g in X, Y, Z axes, rapid traverse to 2125 ipm [54 m/min], feed rates to 1181 ipm [30 m/min], high-speed reverse tapping, and thread milling." Options are available for 21 tools and for rigid tapping at 8000 rpm.
"Improving the structural components of the 30- taper machines was necessary because the early 30-taper drill/tap machines weren't strong enough to handle the axial load for milling except for light skimming. Beefing up the machines in the mid-90s immediately cut cycle times by as much as 60%," says McIver.
"The machine solved the drill tap and small light milling requirement of manufacturers, and, as time went on, more and more manufacturers began using the machine for milling steel and even titanium for medical applications. Any part that can fit through the door of the RoboDrill can be machined. We've machined parts from V-8 heads to entire castings for the rear of a car," says McIver.
Designed for job shops with small to medium lot sizes, the fully integrated production cell combines the milling, drilling, and tapping capability of the RoboDrill VMC with a fully interfaced Fanuc six-axis robot for automated loading and unloading of parts.
The six-axis Fanuc LR Mate 200iC robot has a payload of 11 lb (5 kg) and a double-gripper end-of-arm tooling. Features include a robot interface and robot side auto door, an inbound conveyor 12 x 60" (305 x 1524 mm) and an outbound conveyor 12 x 72" (305 x 1829 mm). Workholding interface for any combination of pneumatic or hydraulic valves, and chip management system, and two positive pressure nozzles for part blowoff are included. Larger Fanuc robots are available if your parts weigh more than 11 lb.
Methods is designing a Med Cell to automate loading and unloading of medical device parts with a 6" cube. The Med Cell is intended to be used with the Robodrill VMC or it can be adapted for turning applications on a small Nakamura CNC lathe. The Med Cell is intended to support the medical applications markets for smalllot production of 500–800 pieces with a quick changeover. A vision system can be added to identify parts of differing sizes.
Automation for the job shop is being offered in the Minuteman XA machine tending system from Accura Technics (Keene, NH). Accura is a manufacturer of grinding machines that it has equipped with this type of automation in the past. At the EASTEC exposition, Accura Technics displayed the machine-tending system interfaced with a 40-taper Mini Mill from Haas Automation (Oxnard, CA). "The system can be adapted to any number of machines, both smaller 40-taper machining centers and 30-taper drill/tap centers," says Pat Hurst, Accura Technics president.
"Small machines lend themselves well to this type of automation for parts under a 6" [152.4-mm] cube," says Hurst. "Typically there's not really room enough for ganging up vises. You might be able to use a couple, but weight capacity is another limitation." The Minuteman XA system features a six-axis Fanuc LR Mate 200iC robot with R-30iA controller. Workpiece weight is 11 lb (5 kg) and inbound/outbound conveyors are 6" wide x 48" long (152.4 x 1219-mm) with a 75-lb (34-kg) capacity.
Recent drill/tap machine entries include the DT-1 from Haas Automation (Oxnard, CA). The DT-1 is a high-speed drill and tap machine with full milling capabilities. The machine features a 20 x 16 x 15.5" (508 x 406 x 394-mm) work cube and a 26 x 15" (660 x 381-mm) T-slot table. A BT 30-taper spindle spins to 15,000 rpm and allows rigid tapping at speeds to 5000 rpm. The direct-drive spindle is a 15-hp (11-kW) vector drive system that provides 15 lb-ft (20.3 Nm) of continuous torque for milling and boring operations.
The DT-1 is equipped with a high-speed, 20-pocket, servo-driven toolchanger that swaps tools in 0.8 sec. Highspeed 2400 ipm (61 m/min) rapids combine with 1-g acceleration rates. Maximum cutting feed rate is 1200 ipm (30.5 m/min). A 45-gal (170-L) flood coolant system is standard, with options for a programmable coolant nozzle and high-pressure coolant available. The high-speed sidemount toolchanger swaps tools in 0.8 sec.
This article was first published in the August 2009 edition of Manufacturing Engineering magazine.