Manufacturing Engineering Magazine August 2018
About the time that the equivalent of a couple of vertical machining centers are going full bore out in the shop, you’ll know that it’s time to make that commitment to a major investment in horizontal machining center technology to keep up with your order book. Your mix of complex parts and families of parts, in combination with longer and regularly recurring production runs, will make it much easier to justify what four-and five-axis HMC technology can deliver, including a choice of automating technologies for untended machining.
HMC are equipped with twin pallets for tombstone-mounted parts as standard, but can be automated with pools of six or more pallets, linear flexible manufacturing systems fed by stockers and tended by rail-guided, overhead gantry robots, or pedestal-mounted six-axis robots. Table loads are such that HMCs readily handle just about anything that automotive, general engineering, power generation, or energy industry applications can throw at them. Workpieces range from large, boxy engine blocks to oil field drill bits, housings and manifolds, and myriad families of tombstone-mounted components.
Horizontals Provide Versatile Production
DP Tool & Machine Inc. is a contract machining shop that has benefited from horizontal machining center technology in meeting demands from a customer base scattered across industries as diverse as automotive, food and beverage, health imaging, machinery, oil and gas, and power distribution. DP Tool’s seven HCN 5000 horizontal machining centers are part of a two-level Mazak Palletech high-rise automation system that features a rail-guided robot, 60-pallet capacity stocker and Mazak’s Smooth PMC cell controller that oversees all operations and helps DP Tool take full advantage of the cell’s flexibility.
With the Palletech Automation System, one operator can, at times, keep all seven HCN 5000s running by serving the load/unload stations and keeping up with required tool changes. The system features a fully automatic programmable presetter and Mazak’s Smooth PMC software. While initially acquired for one big production job, additional machines were added, and the cell’s flexibility allows the shop to fill in production ups and downs with other work to keep the cell’s schedule full and it constantly producing.
What we do is load a production job, then fill in any available space with just-in-time jobs and we usually dedicate the high volume work to maybe three of the HCNs, while short run jobs go to the other four with 160-tool capacity magazines. The cell is very flexible and we can set it up to meet our specific needs, running certain jobs during the day and others overnight.
Of course, shops don’t have to adopt a full-scale FMS. They can simply add a pallet pool to the horizontal machine. All the major HMC builders offer them.
Match the HMC to the Job
HMCs are a good solution for job shops or larger manufacturing operations. Though there are limited in X- and Z-axis travels range due to the horizontal concept, in length we are very flexible. The biggest advantage of the machine is in the serial production, where you have the same parts for a certain period of time. Of course, it could be also for job shops so there they can prepare the next job on the setup station.
At IMTS, Zimmermann Inc. is displaying a new horizontal machining center concept. The new FZH six-axis HMC features a patented M3ABC six-axis milling head option and a redesigned water-cooled traveling column to increase penetration into the material, increasing rigidity and eliminating the lever effect. The model range is especially useful for efficient machining of standard aluminum and carbon fiber components for the aerospace industry.
The FZH models can be equipped with the VH30/VH40 two-axis milling head for high precision and repeatability in the A and C axes or the new M3ABC three-axis milling head (A/B/C) which offers improved efficiency, especially when milling structural parts with its increased swiveling range.
Greater Throughput Spurs HMC Users
The main attraction for purchasing is their throughput. Loading more parts on the table and addressing more sides on the workpiece increase output and minimize setups. It also helps that with our horizontal pallet changers, loading/unloading parts takes place as the machine continues to run. Essentially, people are starting to understand owning a horizontal machine can help them stay competitive and manufacture parts more accurately and at a higher rate.
All Kitamura horizontal machines have a standard two-station APC (automatic pallet changer) with an option to increase the number of pallets with pallet pools in the field “which in a sense is automation. Multiple pallet systems allow the customer to load parts one time and monitor the machine until all pallets are completed, consequently freeing operators for other tasks like QC [quality control] or tending other machines. In addition to making chip evacuation simpler (aided by gravity), HMC design accommodates larger automatic tool changer (ATC) capacity and allows robotic automation without interference with machining or parts changing, each of which is done in its own separate compartment.
Michael Cope, product technical specialist of Hurco Companies Inc., agreed that HMC use is growing among job shops as well as larger manufacturing operations for many of the same reasons that five-axis machining is growing, namely turnaround time, increased productivity and the ability to react quicker to customers’ changing needs and demands.
Due to their speed and versatility, HMCs with their common built-in pallet changers lend themselves very well to automation. With the built-in pallet changer, automated loading and unloading can be achieved a little more seamlessly than with a traditional vertical machining center. With JIT manufacturing causing everyone to look at more efficient ways to produce parts, and because horizontal machines are very automation friendly, they are a good choice for untended machining operations.
Automation Made Easier
While automation setup with any type of machine is complicated, HMCs seem easier because of the volume of their production output, according to Ben Hu, marketing director of YCM Technology Inc. The time to recover the costs/investment is always the primary concern in HMC purchasing. Popular sizes are 500/630 mm with a minimum 60-120 tool capacity for small job shops and 240 tools and up for major factories. Greater tooling capacities allow more complex jobs with minimum setup time, especially with multi-pallet cell configuration.
At IMTS, YCM is exhibiting the NH500A 6 APC and targeting industries like automotive that produce high volumes of parts. The NH500A has a 30 ho (22-kW) 20,000-rpm spindle and a 500 x 500 mm pallet. The high rigidity T-base foundation with rib construction is combined with a one-piece casting spindle headstock and dual-wall column design. The direct-drive spindle features precision ceramic ball bearings and high-precision roller-type guideways on all axes. The precision pallet indexing system accommodates a six-pallet APC.
Getting automated is made still easier because of the wide array of ready-to-install technologies available. The desire to implement untended machining concepts requires significant engineering time committed to get to that state. Not many smaller shops can afford the engineering expense and time. However, when they do, their business will grow quickly.
FMS-type systems that share pallets among multiple machines are themselves a productivity-enhancing option, but are a bit more difficult from a setup and startup standpoint. Kitamura’s dedicated pallet pools (one machine to one pallet pool) are easier to operate from the get-go. The customer sees quicker results and saves on floor space when compared with linear-style pallet systems.
Fully Integrated Fifth Axis
To meet the demand for still more complex part machining, Makino Inc. will demonstrate the newest addition to its family of high-capability HMCs, the five-axis a500Z, at IMTS. Makino is adding a factory-built and fully integrated “Z-type” fifth axis to its four-axis nx-series HMCs to handle more complex part geometries and do it in a minimum number of workholding setups and machining operations.
The secret of the integration is a kinematic arrangement of the a500Z to minimize the force path lengths both through the spindle as well as through the workpiece. The result, according to the company, is the ability to efficiently transfer both cutting loads and reactive forces into the machine’s three-point leveled bed. The resulting rigidity maximizes both metal removal rates and perishable tool life.
The a500Z’s standard 14,000-rpm high-power spindle offers output capabilities of 49.6 hp (37-kW) peak power and 223 ft-lb (303 N•m peak torque. An optional 20,000-rpm high-speed spindle is offered for users utilizing primarily small diameter tools for high-speed machining. Rapid rates for all linear axes are 2362 ipm (60 m/min) and a B-axis rotation rapid rate of 45,000 degrees per minute. The a500Z handles workpieces of up to 24.8″ (630 mm) by 19.9″ (500 mm) high with payload weights up to 880 lb (400 kg).
HMC Series for Five-Axis Production
Newly introduced to North America, HF Series five-axis horizontal machining centers from Heller Machine Tools are designed for machining complex prismatic parts from lighter, smaller workpieces to heavier workpieces up to 800-kg table load. In the series of two machines, the fifth axis is provided by the workpiece on a swiveling trunnion with rotary table or a pallet changer for higher volume production. Four spindle packages are available based on the material they are to process. Spindle speeds up to 18,000 rpm and torque up to 354 N•m are available.
According to Heller, the main target groups of the HF series are the general engineering machine industry and automotive suppliers. The two new machine models include the HF 5500 with a work area of 900 x 950 x 900 mm (X/Y/Z), and the smaller HF 3500 with a work envelope of 710 x 750 x 710 mm (X/Y/Z). With three linear axes in X, Y and Z and two rotary axes in A and B integrated into a rotary table on a trunnion, the HF machines are designed for five-sided machining and simultaneous five-axis machining. What we do is load a production job [on the high-rise automated system], then fill in any available space with just-in-time jobs.
The HF machines may alternatively be equipped with a lift-and-rotate pallet changer for series five-sided production. Standardized pallet automation solutions may be supplied by Fastems or Schuler. Unlike conventional five-axis machining centers, Heller’s HF Series is not only based on single-part clamping, but also provides the possibility of multiple clamping or the clamping of very large components, for example transmission cases using “window-type” fixtures.
The NC toolchanger is equipped with two NC axes for short idle times and consistent operation, according to Heller. The chain-type tool magazine capacities are: HSK 63: 54, 80, 160 or HSK 100: 50, 100, 150 tools. As standard, Heller offers the SC63 SpeedCutting unit (18,000 rpm, 100 N•m) equipped with an HSK-A 63 spindle taper as standard with options available.
Sizing Up the Job for Selecting the Right Size HMC
Selecting the size of machine tool for a job shop is never an easy task. There are a lot of factors to consider. First and foremost is the budget. Customers must decide what is justifiable with reference to current projects or projects they want to approach in the future. Secondly, customers need to analyze the size of parts they are machining and whether loading one part on the table or loading multiple parts to increase throughput is needed. Furthermore, analyzing parts will dictate the number of tools, magazine size selection, and tool sizes. Factoring in material for selecting taper size is the key. Some materials with wear-resistant properties will require larger taper and machining will be less difficult.
Machine capacity must be reviewed along with overall machine size, spindle power, rigidity, and accuracy with regard to how these specifications relate to specific applications. Reliability of the machine needs to be factored into the purchase as well to ensure that the machine is always up and running. Finally, space and power must be considered.
Customers who are interested in purchasing a particular machine must make sure that they have enough space to move the machine into the shop, specifically the entrance and ceiling clearance, and have sufficient space to place the machine. With regard to production shops, machine selection is a bit easier, since they usually have one part to spec the machine for, so the decision to select the machine would be based on the size of this part or the number of parts on the fixture.
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