HERMACH MACHINE INC. IS BIG BELIEVER IN
TWO HEADS ARE BETTER THAN ONE CONCEPT
By: Tom Walsh
As everyone in the machining industry knows, the aero space market has radically changed during the past decade. With planes becoming much more sophisticated, the parts required have also become more sophisticated. To conserve and yet maintain structural strength, parts have more variations in thickness and are more complex in design. In turn, this requires that suppliers have the latest in software and machines that can respond to these demands.
Hermach Machine, Inc., Torrance, California, has served the aerospace industry since 1955 by providing 3, 4 and 5 axis machined parts and assemblies. With almost 40,000 sq.ft of manufacturing space, the company specializes in machining large structural members.
The majority of Hermach's machines are CNC with most of them two or three spindle. This is the case where two heads (and even three) are better than one. First of all, two or more spindles allow more productivity from each operator, and at the same time saves considerably in the cost of equipment. It is less expensive buying one machine with two or more spindles, than buying two or more complete machines. Then too, is the savings in floor space. One machine with two spindles (even though bigger) takes much less floor space than two machines with single spindles. Other savings are in the handling equipment, setup time, etc. Of course having multiple spindles is predicated on having enough production to keep the twin spindles running.
To ensure that Hermach stays competitive, the company recently acquired a Mighty Viper bridge VMC-4000GTDW with twin spindles. According to Ronald Chaplin, Hermach's President, 'The Viper really compliments the rest of the shop. It is really heavy-duty as we use it for machining 17-4PH stainless steel, which is a tough test on any machine. In fact, the machine weighs twice as much as a 30% longer bridge from another manufacturer. Big jobs demand massive support. Mighty's Meehanite cast iron frame ensures structure-free distortion and we really like this machine.
The spindles, gears, and spindle shafts of the Viper are all made of high grade alloy steel that is heat treated and precision ground. The spindles are supported by P4 Class precision bearings and automatic lubricating systems are used to ensure continuous cycling of the lubricant.
Mr.Chaplin stated that they were especially impressed with the slant beam concept, because of its exceptional rigidity. He commented, 'Mounted on this specially designed slant beam, the spindles are excellent for heavy duty cutting operations. Force is evenly distributed on the wide beam surface, allowing the cutting load on the Y axis to come as close as possible to the columns.'
Because the twin spindle bridge line is double wide, the beam has the kind of big travel required for large projects. Along with that is the uncompromising rigidity from its afore mentioned Meehanite cast iron frame. Especially heat treated to ensure that the structure remains distortion free for the duration of its life.
By using square box ways instead of linear motion guides, outstanding stability is achieved. All slideways are hardened to about HS 65. All mating surfaces have Turcite-B to minimize stick-slip and wear out. Furthermore, high precision ballscrews incorporated with pre-loaded double nuts and rigid coupling, ensure dependable positioning and repeatability. Travel on the V-4000GTDW is 160" X by 102.4" Y by 28" Z. Centerline distance between spindles on the twin is 40" and between spindles on the triple is 30".
Serving each spindle of the Viper bridge is an advance double arm-type automatic tool changer. Extremely fast, a high-quality hydraulic indexing motor stores and retrieves tools in a 20 tool capacity magazine. In addition, double screw-type chip conveyors are located below both sides of the table and provide fast and efficient chip disposal.
MELDAS CONTROL
Featured on the Viper bridge is a Mitsubishi Meldas CNC 530 controller. Providing a multi-window capability in a compact body, Meldas is extremely user friendly. Utilizing a 32-bit CPU, the controller allows up to six axis of simultaneous control. This all digital control is achieved by a paralel data bus link. It provides an instant display of detailed servo, I/O status, graphic tool path and ladder diagram. A totally enclosed dust-proof heat exchanger allows the controller to operate at consistent temperatures at all times, and it features alarm and self-diagnostic functions.
SOFTWARE IS IMPORTANT TOO
In order to meet the strict quality control and delivery requirements of aircraft manufacturers, Hermach has made a considerable investment in its CAD/ CAM programming capabilities. Since most aerospace disigns are performed on CATIA, a solid model program from IBM/ Dassault Systems, Hermach has the program. In order to keep one step ahead, Hermach also has NCL from NCCS for NC programming and VERICUT from CGTech for program verification.
In addition to being a design software, CATIA also has an NC multi-axis machining programmer module. This dedicated tool allows generation of continuous multi-axis tool paths on drafted, computer aided or warped surfaces. The system computes a high quality tool path even in a complex tool-geometry relationship including wireframe, surface and/or solid elements.
Hermach has been a user of NCL for more than a decade. NCL is a powerful CAM system which generates 2 through 5-axis NC tool paths and provides parametric 3D modeling. In particular, Hermach's NCL programmer likes the programs associativity capability. Any changes to the part model results in an immediate change to corresponding tool paths. Full parametric programming allows design and manufacturing data to represented as variables, which are easily modified to produce new designs and NC programs. The programming system makes program maintenance and updates easy. When engineering changes or program optimization are required, the programmer only has to change the affected area. NCL will altomatically rebuild any geometry associated with the change and regenerate the tool paths. Hermach has found that NCL excels in a production environment where machine time is critical. NCL recently released Version 9.0, which includes enhancements in X-window Graphics Display, Surface Display, and Net Surface.
In addition Hermach uses VERICUT, which uses computer simulation techniques to test tool paths without the expense and aggregation of actually machining prototypes. VERICUT provides complete interactive control over the part testing process by allowing a thorough examination of the part before it is actually machined.
The program provides cutting times and distances, cross-sectional data, the stock volumn at any time during the simulated trial, tool paths minimums and maximum, plus coolant, spindle and feedrate information. Programs from both CATIA and NCL are run through VERICUT.
Another program in use is PostWorks by NCCS. This is a complete universal postprocessor that runs any machine at Hermach. PostWorks is flexible enough to output very precise machine code, supports a wide veriety of complex machine tools, and has the capability to support special machne control features.
Hermach has a full complement of quality control CMM and standard measuring equipment including an automatic Sheffield RS-22, Apollo II Cordax CMM with 5 axis PH-9A probe system that is servo driven. The unit can handle parts 120" X by 48" Y by 40" Z.
TOOLING
Since the Viper us used for machining the tough metals, tooling is determined by the metal being cut. For example, on a 300 series stainless steel, a two inch cobalt 6-fluted cutter may be one of the tools used. It probably would be set at 190 rpm for .003 depth of cut at 2.75 ipm. Often the maximum amount of tools in the changer are used as most jobs are quite complex. Probably the biggest issue that is raised by the programmers is when a design calls for nonstandard cutter, such as calling for a .433" radius when the standard would be .500".
Chaplin concluded by stating, 'The key to an efficient operation starts right at the beginning of the process, i.e., maintaining integrity of the customer's data throughout the manufacturing process. Solid models provide an unambiguous part representation, reducing the chance of wrongly interpreting customer data. We analyze customer data in CATIA, develop NC programs with CATIA as well as with NCL and verify them with VERICUT. Approved programs are sent to the controls on the machine, with all operations working off original customer data. And with state-of-the-art equipment, such as our new Viper bridge, we are poised to offer complete machining facilities to our aerospace customers.'