Pooling for Productivity
More pallets mean more parts per cycle in one setup
By Jim Lorincz
In stand-alone applications, in cellular configuration, and in multiple-machine installations in a wide variety of industries, HMCs have made their mark.
In high-volume production, automation has given manufacturers in industries from automotive to off-highway equipment to energy to electronics the ability to benefit from lean manufacturing capability. With the right automation, HMCs can run untended across a variety of complex workpieces, or be dedicated to a single part or a family of parts.
The right automation includes integrating a number of HMCs with a pallet delivery system, tending pairs of HMCs with robots, or servicing multiple in-line machines with overhead gantry systems. Increasingly, HMCs are being mixed and matched with other machine types, such as multitasking machines, mill-turns, and turning centers, to eliminate multiple setups, reduce labor, and reduce secondary finishing and machining operations.
Intevac Inc. (Santa Clara, CA) is a designer and manufacturer of the 200 Lean hard-disk sputtering system that deposits a highly engineered thin film onto disks used in computer hard drives. The capital equipment manufacturer selected two machines from Mazak Corp. (Florence, KY), the PFH-4800 HMC with a six-pallet Palletech system and an Integrex 200-IIIS multitasking machining center, as its production system. The goal was to make parts quickly and directly from engineering CAD systems for both rapidresponse prototyping and untended production.
The PFH-4800 HMC has enabled Intevac to bring parts in-house. "I picked a handful of parts from the 200 Lean to bring in house, and we saved 40-45% on them, not to mention major improvements in quality," says Hob Bosold, model shop manager. "The finishes we're getting are typically less than 4 Ra, which significantly reduces part detailing and polishing." Bosold says the Integrex does in one part setup what Intevac used to do in four or five operations with several machines, which included "a bridge mill big enough to park a car under, a couple of low-budget vertical CNCs, and three large horizontals."
Manufacturing spare parts for aerospace manufacturers such as Raytheon and Cessna, among others, led Product Manufacturing Corp. (PMC; Wichita, KS) to rely on two cells from Toyoda Machinery (Arlington Heights, IL) that literally mirror one another.
One cell features three FA450-III HMCs with two loading stations for 48 pallets, machining almost entirely aluminum. The second cell features three FA550-II HMCs with two loading stations and 28 pallets for machining a mix of aluminum, titanium, and steel workpieces.
Every pallet has tooling setup so that if a customer calls for a part, PMC can turn the order around in a day. Every HMC has a 120 or 230-tool magazine, so that all tooling remains right at the machine. The cells have been running two shifts for the last year and a half with more than 90% uptime to meet the product requirements of their customers.
With the increase in demand for its machining services, PMC is expanding its facility and credits the Toyoda FMS with enabling it to manage its speed-to-customer turnaround time.
HMCs are naturals for continuous production, whether as stand-alone machines or in cellular configuration. They have the advantages of ease of chip removal, avoidance of re-cutting chips, and a readily installed fourth axis.
"The benefits of mounting a number of parts on a greater number of pallets in pallet pools, which many machine tool builders are offering with their machines, are obvious," says Andy Popky of Tombstone City (Huntington Station, NY). "The manufacturer increases production, maximizes the workspace, and can machine three sides of the part simply by indexing the pallet 90°." Tombstones can easily be fitted with vises that multiply and maximize the number of parts to be machined.
Pallet pools offer manufacturers a number of strategies for untended production. A greater number of pallets holding a greater number of parts can be staged in queue for machining. Pallets can be identified with readable chips that contain machining information that matches programs stored in the control to the pallet. Pallets can be dedicated to a part or family of parts, and mixed and matched to be machined according to shop priorities.
Machine tool builders are offering pallet pools that can significantly extend the production capabilities of their machines, as well as offering readily expandable ATCs that can hold the tools necessary to machine a number of parts, and contain redundant tooling. Machine spindles can be equipped with load-detecting devices that monitor wear of tools, or signal broken or missing tools that can be automatically replaced.
HMCs with pallet pools offer a less complicated and less expensive alternative to FMS installations. Haas Automation Inc. (Oxnard, CA) has introduced its EC-400 pallet pool HMC with six pallets. The operator can assign programs to each pallet, schedule jobs, and set priorities by highlighting the pallet number on the control screen. Pallets on the EC-400 PP are 400-mm units with indexer load capacity of 454 kg. Standard equipment includes a 70-pocket sidemount toolchanger, 300-psi (2.1 MPa) through-spindle coolant, and 8000-rpm inline direct-drive spindle.
Haas is also extending its ECseries HMCs with the addition of the EC-630 with dual 630-mm pallets that can handle a 2640 lb (1197.4 kg) load. The machine has a separate protected station that allows the operator to safely load and unload parts or change a fixture on one pallet while parts are machined on the other. The EC-630 features a 40 x 32 x 35" (1016 x 812.8 x 889-mm) work envelope, 50-taper geared head spindle, and 50-pocket sidemount toolchanger.
To minimize setup times and increase productivity of the NH4000 DCG HMC, Mori Seiki USA Inc. (Rolling Meadows, IL) is offering the system with an optional six-pallet Carrier Pallet Pool (CPP). Operators control the CPP system directly with a built-in operating panel that facilitates untended operation.
The 15.7" (398.8-mm) square pallets of the NH4000 DCG feature a newly designed clamping mechanism that uses a two-face cone coupler. This feature permits high-thrust cuts near the top of the Y-axis travel due to box-in-box design characteristics that allow the NH4000 DCG to handle higher chip loads because of reduced deflection and vibration.
"Adding pallets and pallet pools doesn't necessarily reduce the compactness of the HMC if emphasis in machine design is focused on the efficient use of space," says Jim Devine of CNC Systems Inc. (South Windsor, CT), importer of Kiwa machining centers. Kiwa Machinery Co.'s KH-45G HMC offers multipallet system capability expandable in the field to six and eight-pallet APC units. The six and eight-pallet APCs have maximum workpiece size of 750-mm diam x 900-mm and 650-mm diam x 900 mm, respectively.
"The APCs are designed so that chips and coolant in the pallet pool return to the machine-side coolant, keeping the pallet pool a clean zone," explains Devine. The ATC magazine is also field-expandable in 40, 60, and 80-tool versions in a simple oval-shaped tool storage magazine, and in 80, 120, and 220-tool versions in a winding-chain ATC.
KGK International Corp. (Buffalo Grove, IL) introduced the Okuma & Howa Millac 44H HMC for cellular production or as a stand-alone machine for applications such as automotive, aerospace, and power-transmission parts manufacturing, among others. The 44H features boxway construction, 12,000-rpm spindle (15,000-rpm spindle optional), high-speed rapid traverse, and 410 x 460 x 470-mm X,Y,Z travels. The Okuma & Howa machines, which feature Fanuc controls, are being marketed under the Okuma name by KGK International.
NTC America Corp. (Novi, MI) is introducing a pallet-pool changer for its ZH5000 column-traverse HMC for stand-alone production in the medical device, aerospace, automotive, and general-purpose machining industries. A supplier of flexible machining systems to the automotive industry, NTC America also offers the ZH5000 with gantry loading or robot transfer. The ZH5000 features travel of 660 x 660 x 660 mm (X,Y,Z), rapid traverse of 60 m/min in all axes, and maximum loading capacity of 650 kg.
DMG America Inc. (Schaumburg, IL) has designed its DMC 80 H linear HMC with characteristics that make it adaptable to untended production, particularly in the automotive industry. Automation may be supplied in a manufacturing cell with a pallet station or other interlinked manufacturing systems. Machine characteristics include acceleration to 1.6 g, high rapid traverse speeds of 3937 ipm (100 m/min), 2.5 sec chip-to-chip times, and an NC rotary table speed of 90 rpm.
The DMC 60 H linear features linear drives and travels of 31.5 x 31.5 x 41.3" (800 x 800 x 1049 mm) in X, Y, and Z, and is controlled by the Siemens 840D Powerline CNC. Spindle speed of 18,000 rpm can be reached in 1.6 sec. Modular tool storage accommodates 45 tools. A chain magazine for 60 to 90 tools can be provided, as well as a shelf magazine for as many as 354 tools. A magazine can handle five tools to 31.5" (800-mm) long.
Heller Machine Tools (Troy, MI) has developed its MCH-C series HMCs to handle five-sided machining in a single setup from prototype to production volumes. The solution chosen was a universal horizontal machining center capable of handling all operations on a cast-iron engine block in a single setup, yet scaled for machining more than 90% of the parts that HMCs are used for today.
The Heller MCH-C series machines, which come in three different machine sizes, are intended for medical, automotive, and general-machining applications, with production rates from one part a day to 350,000 parts/year. The MCH-C machine series features an HSK-63 or 100 or CAT-50 spindle, a rotary table than can handle nearly three tons, and as many as 400 tools, as well as the ability to function as a stand-alone machine or as part of an FMS.
The most common pallet arrangement for HMCs is still the dual-pallet configuration. Enshu USA Corp. (Schaumburg, IL) has designed its JE80S HMC for stand-alone production, lean lines, or agile machining systems, particularly for the automotive and information technology industries. The dual automatic pallet changer can index to 1100 lb (499 kg) per pallet in 7 sec. The traveling column construction lends itself to automated loading.
The JE80S features axis travel of 31.5 x 31.5 x 31.5" (800 x 800 x 800 mm) and rapid traverse of 90 m/min, 1 g accel/decel, and a 29.5 hp (22 kW) gearless AC spindle that ramps to 15,000 rpm in 1.8 sec. Accuracy is 0.000080" (0.002 mm) with repeatability of +/-0.000040" (0.001 mm). The machine has a 60-tool ATC with tool-to-tool change time of 1.2 sec.
For heavy-duty machining, Johnford HMCs from Absolute Machine Tools Inc. (Lorain, OH) are designed with box-in-box construction for rigidity. The design keeps the spindle movement confined inside the boxshaped column casting, greatly reducing moving mass compared with a moving column design.
Johnford HMCs are available in two sizes, 500 mm and 630 mm, and two versions, 40-taper (HMC-500 and HMC-630) and 50-taper (HMC-500H and HMC-630H). The HMC-630H is available with a rotary APC unit with two rectangular pallets (800 x 630 mm). The HMC-500 is available with a rotary APC unit with two rectangular pallets (630 x 500 mm).
This article was first published in the July 2006 edition of Manufacturing Engineering magazine.