Visitors to the Gear Expo in Cincinnati saw an array of machining centers from leading machine tool builders machining gears, once the exclusive domain of highly specialized gear-generating machines. Multitasking machines and highly sophisticated programming and innovative cutting tools are bringing gear-making to the shop floor for the most commonly made helical and spur gears, not necessarily in high-production volumes, but sufficient to fill a need flexibly without dedicated gear-making machine technology.
Demonstrated at Gear Expo was Excel-Lent gear/gearbox design and analysis software, which has been developed by Excel Gear Inc. (Roscoe, IL) and written in Visual Basic .NET. This software has been written by engineers who also design and manufacture gears for their own use, according to company president N.K. "Chinn" Chinnusamy. Excel Gear’s experience includes the design, manufacturing, and quality analysis of its gear, gearbox, fluid bearing, spindle, CNC gimbal head, nutator, and special equipment production.
"Although commercial software has long been available in the gear industry, it has been too expensive or too complicated to be used by engineers without specialized gear-design knowledge. Our software is specifically designed with a user-friendly interactive input screen providing defaults and options in accordance with the AGMA [American Gear Manufacturers Association] 2001 standard." The users of Excel-Lent software can easily navigate through the input screens to edit, analyze and produce reports on the optimum gear and gearbox design for various industrial and other applications.
"This software is not designed for any specific industry," Chinnusamy explains. "It can be used for machine tools, heavy materials handling equipment, or even the wind-turbine industry. For the wind-turbine industry, for example, the designer needs a full understanding of all the operating loads on the gear members to arrive at the required power rating."
The key calculations performed are the AGMA power rating and load calculations, including bending strength geometry factor (J) and pitting resistance geometry factors (I). Output from the software is a single page of data printed in a format that is easy to read and interpret rather than the five or six pages of information typical of other commercial software, Chinnusamy observes.
The users of Excel-Lent need not be familiar with AGMA standards to use this software. Those who aren't gear engineers can also benefit from the gear engineering knowledge embedded in the software package. There are three sections in Excel-Lent: design, analysis, and gear dimensions. Any of the sections can be used individually to run calculations. On a typical job, according to Excel Gear, hundreds of hours typically spent doing the calculations can be saved.
The design section calculates the size of gears, based on minimal input by the user who needs to specify only the input rotational speed, gear ratio, power to be transmitted, and the material and heat treatments selected from the material tables of all commonly used materials in the industry.
Key values calculated are the diameter and face width of the pinion required to achieve the surface fatigue power rating and optimized DP or module (based on the calculated diameter) required for the bending fatigue power rating. The data are automatically exported to the analysis program for detailed analysis. The results are the power ratings for 5000–100,000 hr of B1 life (reliability factor of 1).
If required, other values such as face width or center distance may be entered but Excel Gear recommends leaving the face width and center distance values blank for optimized gear design. Design and analysis programs are used to design one gear stage in sequence on an external or internal spur and helical gear mesh.
The analysis program calculates the power rating of a gear set for 5000, 10,000, 25,000, 50,000 and 100,000 hr of B1 life (reliability factor of 1). Reliability factor of 1, 1.25, or 1.5 can be selected, as required. The user needs to input mesh type (spur, helical, internal and external), pressure angle, helix angle (if applicable), pinion speed, number of teeth in pinion and gear, material (from the list provided in the software), face width, DP or module and quality required. Crown and/or profile shift, if used, can also be entered.
The program will calculate the power rating of the gear set and show hp or kW capability along with torque, tangential force, and static capacity. Static capacity is based on yield strength and, if bending stress exceeds yield strength at any time, permanent deformation or even tooth breakage may occur. If the results are satisfactory, the user can print the single-page results only or, optionally, also print all the AGMA factors used in making the calculations.
The Excel-Lent software program lists commonly used gear material for the user to select. If the results are not as required, the user can select another material or change other design criteria as required to achieve the desired results. If a special material is desired, its yield, bending and contact stress numbers can be easily entered. If any of the required input data are missing, the program will prompt the user to supply what is missing. Metric or inch units can also be selected with just one click.
The program calculates the manufacturing dimensions for a new pinion and gear or calculates the dimension of a pinion or gear to mate an existing pinion or gear. This can be done for external gears, internal gears, or a gear rack. Users need only to enter the type of mesh (spur or helical, internal of external), pressure angle, helix angle (if helical gears), number of teeth in pinion and mating gear, DP or module and the quality of the gears.
The program will then calculate the center distance, dimension over pins, span measurement, form diameter, roll angles, and all gear tolerances to match the quality required (AGMA, DIN, or ISO). The program will calculate the helix angle required to match a specified center distance if the user chooses that option. The program displays plain English error messages when input is questionable or in error. "
Excel-Lent software further provides users the option to balance beam strength or specific sliding of gear and pinion, if desired. This is a key requirement for wind- turbine gears. The program will also calculate gear blank tolerances to achieve the desired quality level, if shaft and bore diameters are entered. Users can switch between inch and metric dimensions with one click.
For more information on Excel-Lent software and a test demonstration, go to www.excelgear.com, or telephone
Spindle Connection Maxes Power
When machining titanium, cutting speeds are of necessity relatively low due to thermal effects on cutting. The machining challenge is to maximize metal-removal rates to achieve production efficiencies, while dealing with low cutting speeds and considerably higher cutting forces. In response, machine-tool builders have improved stiffness of machine structures and damping on spindles which have been designed with high torque at low rotational speeds to minimize undesirable vibrations that deteriorate part quality and tool life. Although all of these advances add to greater productivity, the weakest point has often been the spindle connection itself, which must provide torque and bending capacity compatible with machine-tool specifications and the requirements for higher productivity.
The need for a stable connection comes in end-milling applications where projection lengths are typically greater, and the limiting factor is the spindle interface’s bending capacity. As an example, an indexable helical cutter with 250-mm projection from spindle face, 80-mm diam generates 4620 Nm of bending moment and less than 900 Nm of torque.
In the past, Kennametal and Krupp WIDIA initiated a joint program to develop a universal quick-change system in response to the need for a solution to this traditionally weak connection. The KM quick-change system that resulted has since been recognized as ISO standard 26622. The latest development from Kennametal is its next-generation spindle connection, KM4X. While some systems may be able to transmit considerable amount of torque, cutting forces also generate bending moments that will exceed the interface’s limits before torque limits are exceeded. The combination of the KM4X system’s high clamping force and controlled interference levels is said to produce a robust connection, extremely high stiffness, and restrained bending moment for improved performance in titanium machining.
KM4X engineering results in three times the bending moment resistant capacity compared to other tooling systems. This means shops can use their high-performance machining centers to increase speeds and feeds in difficult machining applications, thus gaining the full potential from the machine tool. KM4X can be retrofit to legacy machine tools, offering the added advantage of increasing throughput without having to invest in expensive additional capital equipment.
For more information on KM4X, go to www.kennametal.com, or telephone 800-446-7738.
Tool Selection Anytime 24/7
The importance of tool selection in maximizing productivity can't be underestimated. In fact, profitability in machining parts is dependent on the machine type, cutting tool, cutting, conditions, and the interaction between all of them. Iscar Metals Inc. (Arlington, TX) has developed Iscar Tool Advisor (ITA), a web-based tool selection software. Constructed on a unique mathematical algorithm, ITA puts tool selection on a scientifically objective and empirical technical basis. Best of all, it’s available 24/7 through Iscar’s web site.
The ITA application uses a parametric selection process to narrow down all possible tooling scenarios, taking into account cutting conditions, machine power, metal-removal rate, and cutting time. Even in a simple application, such as milling a 90° shoulder of low-alloy steel, measuring 10 × 10 mm, tools selected by ITA have delivered more productivity compared to manual tool selection done by industry experts.
Users need only enter a few mandatory fields (two to six) for quick results or complete more detailed fields specifying machine parameters, tool diameters, tool type, grade etc. The application provides the three best tooling options, but can display up to 25 tool recommendations per application search. Results include tool details, insert details, cutting conditions, power, metal-removal rate, and cutting time. Each search has a printable recommendation report available to the user.
ITA supports both inch and metric platforms and supports 25 different languages. Users can link to the Iscar electronic catalogue, 2-D and 3-D tool drawings, product videos, and pictures. ITA can e-mail a pdf file that includes the input and output for each application search.
ITA software is available free of charge, 24/7 with direct connection to an ITA support team. The application can be uploaded and used on any iPhone or iPod Touch, making all of Iscar’s technical information available and accessible via the internet, Wi-Fi, or mobile connection.
For immediate access to the Iscar Tool Advisor (ITA) software, go to www.iscarmetals.com/ITA.
This article was first published in the December 2011 edition of Manufacturing Engineering magazine. Click here for PDF.