Related Glossary Terms
Shaft used for rotary support in machining applications. In grinding, the spindle for mounting the wheel; in milling and other cutting operations, the shaft for mounting the cutter.
- computer numerical control ( CNC)
computer numerical control ( CNC)
Microprocessor-based controller dedicated to a machine tool that permits the creation or modification of parts. Programmed numerical control activates the machine’s servos and spindle drives and controls the various machining operations. See DNC, direct numerical control; NC, numerical control.
- cutting speed
Tangential velocity on the surface of the tool or workpiece at the cutting interface. The formula for cutting speed (sfm) is tool diameter 5 0.26 5 spindle speed (rpm). The formula for feed per tooth (fpt) is table feed (ipm)/number of flutes/spindle speed (rpm). The formula for spindle speed (rpm) is cutting speed (sfm) 5 3.82/tool diameter. The formula for table feed (ipm) is feed per tooth (ftp) 5 number of tool flutes 5 spindle speed (rpm).
Milling cutter held by its shank that cuts on its periphery and, if so configured, on its free end. Takes a variety of shapes (single- and double-end, roughing, ballnose and cup-end) and sizes (stub, medium, long and extra-long). Also comes with differing numbers of flutes.
Rate of change of position of the tool as a whole, relative to the workpiece while cutting.
Device, often made in-house, that holds a specific workpiece. See jig; modular fixturing.
- numerical control ( NC)
numerical control ( NC)
Any controlled equipment that allows an operator to program its movement by entering a series of coded numbers and symbols. See CNC, computer numerical control; DNC, direct numerical control.
- quality assurance ( quality control)
quality assurance ( quality control)
Terms denoting a formal program for monitoring product quality. The denotations are the same, but QC typically connotes a more traditional postmachining inspection system, while QA implies a more comprehensive approach, with emphasis on “total quality,” broad quality principles, statistical process control and other statistical methods.
Main body of a tool; the portion of a drill or similar end-held tool that fits into a collet, chuck or similar mounting device.
Secures a cutting tool during a machining operation. Basic types include block, cartridge, chuck, collet, fixed, modular, quick-change and rotating.
Shops looking for a serious boost in productivity would do well to consider adding a state-of-the-art presetting-and-measuring unit to their collection of equipment. Presetting itself can shave valuable minutes off tool changes, increasing machine uptime. Presetting involves the use of a sophisticated unit that can hold the toolholder exactly the way it will be held in the spindle, while a measuring device such as an indicator or comparator gages the position of the tool’s cutting edge. By making the necessary adjustments while the tool is in the presetter, the operator can be assured that the tool will be ready to cut as soon as it is loaded into the machine tool.
The use of a presetter to measure and set tools off the machine can increase a shop’s productivity by at least 12% on every machine tool that is cutting with preset tools. Because of the benefits presetting offers, nearly all shops in the automotive industry worldwide use preset and measured tools. Studies conducted at facilities using preset tools have found that the presetters save shops at least 4.52 min. every time they change tools.
The following calculation shows how minutes saved on each tool change can add up to a significant increase in productivity:
- Minimum time saved with each tool change = 3 min.
- Number of tool changes per eight-hour shift = 20.
- Number of minutes saved per shift = 60.
- Calculated productivity increase = 12.5% (one hour saved for every eight hours of operation).
Figure 1: A sophisticated tool measuring-and-inspection system such as the profi AWV unit from Zoller can perform a variety of tool-management tasks in addition to tool presetting.
But saving time on tool changes is only one of the advantages modern presetters can offer. Today’s sophisticated presetting units feature integrated tool-measuring, tool-inspection, and data-storage capabilities (Figure 1). With their ability to remember specific setups and tool dimensions, state-of-the-art presetting units can become a vital part of a shop’s tool-management system.
Presetting Improves Quality
Presetting-and-measuring units not only allow operators to set tools faster than they can set them on the machine, they make it possible to set tools more accurately. The most sophisticated units can set tools with micron-level precision. These machines have special adapters that can hold any type of shank or taper in the precise position it will be held in the spindle. This ensures that the accuracy achieved at the presetter can be transferred to the application when the tool is moved from the presetter to the machine.
Some presetters can measure tools automatically, achieving an accuracy of at least ±2µm without operator intervention. Tools set and measured using this technology can start producing parts within dimensional tolerances as soon as they begin cutting chips. Because the operator knows the position of the tool’s cutting edge with certainty, a trial-cut period is not necessary. As a result, no scrap parts are produced.
Figure 2: The photorealistic input screen of a state-of-the-art presetting-and-measuring machine can guide the user through a program with easy-to-follow steps. This is the program for a radius-form endmill.
High-end presetting-and-measuring machines feature integrated computers and software that can guide operators through a measuring program (Figure 2). These systems also can perform a number of other tool-management tasks. In the computer’s memory, an operator can store significant data about the tool being set. This data can be recalled later to guide the setting of a replacement tool or to repeat the setup for another run of parts. Using tool data stored in the computer promotes repeatability, because every tool is set with nearly identical dimensions.
Such repeatable accuracy ensures the operator that the tool being loaded into the spindle is neither too long nor too short, thus reducing the chance that a wrong move by the machine will break the tool. When tools are not the correct length, the machine tool’s controller does not have an accurate idea of the tool tip’s location. This confusion can lead to costly mistakes.
While moving a cutting tool that is shorter than the machine tool has been programmed for, controllers frequently crash the tool into clamps and other fixture elements projecting above the surface of the workpiece. If a controller must compensate for a tool that is longer than the machine tool was programmed for, cutting conditions may be restricted, and this may lead to longer production times and greater tool wear.
During the preliminary period of an application, when the part program is being optimized, a tool of a specific length is used. Any modifications made to the program are made to achieve maximum performance with a tool of this particular length. By continuing to use tools of the same length throughout the application, the operator can run the CNC machine within the optimized program’s parameters, ensuring that productivity and output remain at their maximum levels and tool wear is minimized.
Because the operator cannot set tool length with accuracy if the tools are set on the machine, tool length varies with every tool change. Under these circumstances, the operator must make continuous corrections on the CNC machine to ensure that the correct cutting speed, feed, and depth are maintained.
Scrutinizing the Tools
Some presetters allow shops to inspect their tools’ cutting edges using video technology. During an application, operators can use this feature to measure the wear on tools that have already been used. By using a presetter’s tool-inspection capability to accurately gage wear during an application and changing tools only when they have worn past a certain point, the operator can get the full life out of the tools.
Without this capability, users must set up a schedule to change tools after cutting for a specified time or number of inches. When this is done, a cushion is typically built into the schedule to compensate for the tools’ varying wear rates. For safety, the operator makes the interval short enough to ensure that even the fastest wearing tool is changed before it breaks. As a result, most tools that are changed on a regular schedule are changed well before they have fully worn.
A presetter’s tool-inspection capability can be used for more than just monitoring tool wear. The unit can be used to inspect incoming tools as well. By comparing the as-received tools with the specified geometry for the tool, the user can monitor the tool suppliers’ quality levels.
Tool inspections also can be used to monitor part quality. This may be necessary in situations where it is too difficult or costly to inspect the part itself. In such circumstances, the operator must rely on tool-inspection data. If the tool is within tolerances, then the operator can assume that the cut produced by the tool is within tolerances. Using tool inspections for quality control requires a unit that can make extremely precise inspections and produce written reports of the measurements taken.
The Ultimate Presetter
When a presetter’s tool setup and inspection capabilities are combined with sophisticated software, the unit can perform the functions of a complete tool-management system, tracking tool components as well as whole tool assemblies. With a computerized system, the user can store data on individual components and select the relevant data when it is needed to assemble a complete tool.
This data can include inventory and supplier information, which the operator can reference to monitor the shop’s stock of tools and order replacement components in a timely manner. The orders can be printed out from the shop floor or faxed directly to the supplier from the computer.
For maximum efficiency, a shop can tie a presetter with the appropriate hardware into its in-house computer network. A fully integrated presetter can exchange data with other machines on the shop’s network quickly and directly. Tool lists for particular jobs can be downloaded to the presetter.
Once the measurements of these tools have been made, the presetter can generate the data in a CNC-compatible format and send this information to the distributive numerical control terminal or the machine that the tools are to be used with. This makes it unnecessary for the operator to program the data into the machine’s controller. Production can start as soon as the tools are loaded into the magazine.
The role of presetting-and-measuring machines in a shop’s operation has grown as the units have increased in sophistication and capabilities. The most advanced units have a full suite of tool-management functions and features. When fully employed, these features can help a shop improve productivity, quality, tool life, and inventory control, while reducing cycle time, downtime, and scrap.
About the Author
Christoph Zoller is president of Zoller Inc., Ann Arbor, MI.