The performance of a diamond tool is based on the protrusion rate. The protrusion rate inspection is a costly, labor-intensive activity in industry. Normally, about 20 to 35% of the protrusion rate is provided for the final inspection of diamond tools. There are five known methods used for the protrusion measurement: mechanical dial gage, electrical dial gage, surface roughness measuring machine, focusing by microscope, and manual comparison. In this study, a machine vision system was used as an inspection tool to determine the protrusion rate of a diamond tool. The method developed is a noncontact method without manual judgment. Three sets of field samples were used to demonstrate the proposed method for determining protrusion rate.
The diamond tool is a widely used tool for hard materials, such as concrete, asphalt, all sorts of stones and glasses, optical glasses, hardened alloys, tungsten carbide, and so on. The diamond used to make the tools could be from natural diamonds, artificial diamonds, or other types of superabrasive material, such as cubic boron nitride. The application of diamond tools includes lapping, polishing, grinding, sawing, drilling, cutting, turning, and so forth. Among all applications, about 20% of the diamond tools are used for hard material (such as stones) drilling. These types of tools consist of about 50 to 60% of the revenue of the diamond tool industry (Chen 1993).
The process for making a diamond tool is first mixing the diamond grinding material with a metallic or resin-type abrasive material. The tool is then formed through a "sintering" process (see Figure 1). At this point, the diamonds have not protruded from the tool surface. The next step in the process is "truing," that is to use a SiC or A1203 sand wheel to balance the centers of the inner and outer cylindrical surfaces. This is followed by "dressing," which causes the diamonds to protrude through the surface. Chen (1995) reviewed various truing and dressing methods. The finished tools are shown in Figure 2. The surface of the tool is shown in Figure 3.
The protrusion rate (PR) is defined as the ratio of the height (h) of the diamond above the tool surface and the diameter (d) of the tool. The ideal PR is h = 1/3d, shown in Figure 4. If excessive dressing occurs, that is, h>> 113, then the diamonds fall out easily. On the other hand, if insufficient dressing occurs, that is, h
Traditionally, there are five known methods used for the measurement of PR (Busch 1989, Chen 1993, Chen 1995, Sheiko et al. 1993, Weck 1984, Lo 1992):
(1) A mechanical dial gage to rotate the diamond tool with a fixed centering device and measure the variations in the surface smoothness using a mechanical dial gage.
(2) An electrical dial gage. This is similar to using a mechanical dial gage except that the gage is an electrical gage.
(3) A surface roughness measuring machine. This device is usually used to measure in flat surface roughness, and it can be set up for measuring the protrusions in a diamond tool.
(4) An optical microscope (Brinksmeier, Hoper, Riemer 1996). A sample object (i.e., a piece of coated diamond tool) is placed under a microscope, with the focus on the high and low spots to determine the PR.
(5) Manual comparison. This is similar to the surface roughness specimens normally used in a machine shop. The PR is determined by comparing the specimens and the diamond tool surface with the naked eye.
The first three methods must use a contact-type stylus, whose size can affect the measurement results. All five methods require extensive manual work and are difficult to automate. The objective of this study was to use a CCD-- based machine vision system to determine if PR can be automatically determined with a noncontact device.
Methods and Results
The original thought was to use a vision system to measure the protrusion rate of a diamond tool and compare the results using a traditional surface profilometer. Figure 5 shows the flowchart for this process.
The vision system used in this study consisted of a CCD camera (Toshiba IK-530S) with 256 x 256 pixel resolution, a TV monitor (SAMPO BMC-1202T), and an IBM-compatible PC with a frame grabber (HRT512-8 from Caten Systems). A Misutoyo SURF-400 profilometer was used to measure the surface roughness of the diamond tool. The idea behind this was that the protrusion rate, surface roughness, and diamond area from the CCD image might have a good correlation. Figure 6 shows the hardware and software setup.
Tuesday, February 27, 2007
Detection of machine tool contouring errors using wavelet transforms and neural networks
The accuracy and precision of computer numerical control (CNC) machine tools directly affect the dimensional accuracy of machined parts. Fast detection of machine tool contouring errors is required to guarantee the accuracy of the manufacturing process and, further, to eliminate errors through error compensation techniques. In this paper, several typical contouring error patterns of CNC machine tools (i.e., cyclic, backlash, scale mismatch, etc.) are presented. Detection of machine tool contouring errors is conducted in two steps using wavelet transforms (WT) and neural networks (NN). In the first step, wavelet transform is applied to contouring error signals to extract error features. In the second step, wavelet coefficients are grouped into proper input units for neural networks; that is, data were compressed by omitting unnecessary details. In this study, cascade-correlation (CC) neural networks are selected to recognize the seven basic patterns of CNC contouring errors. Multiple contouring errors can also be identified quantitatively in the WT-NN approach.Computer numerical control (CNC) machine tools are widely used throughout the manufacturing industry. Accuracy and good machining conditions are critical to the dimensional accuracy of parts produced using these tools. In general, CNC machine tool errors can be classified into four types:
1. Geometric errors of machine components and structures,
2. Errors induced by thermal distortions,
3. Deflection errors caused by cutting forces, and
4. Other errors-for example, those caused by servo errors of machine axes (for example, tracking errors) or numerical control interpolation algorithmic errors.1
Currently, two approaches exist for improving the accuracy of CNC machine tools: error avoidance and error compensation. The error compensation technique, which is an economical way to improve machine tool accuracy, was first applied by Hocken on a Moore NS CMM.2Error compensation identifies machine errors through either direct mapping or indirect modeling. Direct mapping of machine errors is accomplished through the use of precision artifacts and measurement instruments. Indirect modeling is performed using a kinematic model to express the error of tools relative to the position of parts. This technique was successfully applied to a multiaxis machine tool' and a CMM.4
The fundamental step in error compensation is the error identification technique, which can be classified as either direct or indirect. The feature-based error identification technique involves the measurement of machined parts. It involves tools such as pattern recognition, fuzzy systems, decision trees, expert systems, and neural networks.5 After the machine tool errors are detected with a feature-based method, inverse kinematic techniques and statistical methods can be used to identify individual machine error components. An adaptive error identification method was proposed by Mou.6,7 In this method, a feature-based comparison method is used to correlate the dimensional and form errors of a manufactured part to the systematic machine tool errors.
Compared with direct error component measurement, feature-based error identification is a more efficient way of estimating the components of machine tool error. Further, it is more useful for shop-floor applications of error identification.
The objective of this study is to develop an approach that can effectively detect the composition and amplitudes of error patterns from the machine tool contouring error signals. This approach is developed based on two techniques, wavelet transformations (WT) and neural networks (NN). The following sections describe the details of this approach.
Measurement and Classification of Machine Tool Contouring Errors
Accuracy and good machining conditions are critical to the dimensional accuracy of parts produced using CNC machine tools. Various machine errors affect the dimensions and forms of the resulting parts. Every type of machine error (such as backlash, axis reversal characteristics, vibration, nonsquareness, scale mismatch, and so on) can be reflected through how well a machine can interpolate a circle. Thus, machine errors can be revealed by measuring the circular cutting path of a CNC machine and comparing the path to predetermined reference error patterns.
1. Geometric errors of machine components and structures,
2. Errors induced by thermal distortions,
3. Deflection errors caused by cutting forces, and
4. Other errors-for example, those caused by servo errors of machine axes (for example, tracking errors) or numerical control interpolation algorithmic errors.1
Currently, two approaches exist for improving the accuracy of CNC machine tools: error avoidance and error compensation. The error compensation technique, which is an economical way to improve machine tool accuracy, was first applied by Hocken on a Moore NS CMM.2Error compensation identifies machine errors through either direct mapping or indirect modeling. Direct mapping of machine errors is accomplished through the use of precision artifacts and measurement instruments. Indirect modeling is performed using a kinematic model to express the error of tools relative to the position of parts. This technique was successfully applied to a multiaxis machine tool' and a CMM.4
The fundamental step in error compensation is the error identification technique, which can be classified as either direct or indirect. The feature-based error identification technique involves the measurement of machined parts. It involves tools such as pattern recognition, fuzzy systems, decision trees, expert systems, and neural networks.5 After the machine tool errors are detected with a feature-based method, inverse kinematic techniques and statistical methods can be used to identify individual machine error components. An adaptive error identification method was proposed by Mou.6,7 In this method, a feature-based comparison method is used to correlate the dimensional and form errors of a manufactured part to the systematic machine tool errors.
Compared with direct error component measurement, feature-based error identification is a more efficient way of estimating the components of machine tool error. Further, it is more useful for shop-floor applications of error identification.
The objective of this study is to develop an approach that can effectively detect the composition and amplitudes of error patterns from the machine tool contouring error signals. This approach is developed based on two techniques, wavelet transformations (WT) and neural networks (NN). The following sections describe the details of this approach.
Measurement and Classification of Machine Tool Contouring Errors
Accuracy and good machining conditions are critical to the dimensional accuracy of parts produced using CNC machine tools. Various machine errors affect the dimensions and forms of the resulting parts. Every type of machine error (such as backlash, axis reversal characteristics, vibration, nonsquareness, scale mismatch, and so on) can be reflected through how well a machine can interpolate a circle. Thus, machine errors can be revealed by measuring the circular cutting path of a CNC machine and comparing the path to predetermined reference error patterns.
Vertical Honing Machine produces bores from .750-8 in
Employing one motor for spindle and another for stroker, SV-10 Vertical Honing Machine can run traditional tools as well as DH-series diamond hone head, which offers 16 points of cutting action. Full bore profile display projects real-time graphical display of bore cross section, while zoom feature maximizes bore view. Variable spindle RPM and stroke speed allow infinitely variable crosshatch angle for any bore diameter and cylinder length combination.
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Sunnen's new SV-10 Vertical Honing Machine combines the latest technology with the consistency and dependability of Sunnen's legendary CV-616.
With two motors, one for the spindle and one for the stroker, the SV-10 has the capability to run traditional tools as well as Sunnen's new DH-series diamond hone head. Sunnen's expertise, with multiple-diamond honing on the top-of-the-line CK-21, is now available on the competitively-priced SV-10. The DH-series diamond hone, with 16 points of cutting action, is the choice for truly round bores. The mechanical stroke guarantees precision surface finish with consistent crosshatch angle in each cylinder no matter what tool is used.
Another new feature is the patented full bore profile display which projects a real time graphical display of the bore cross section. This feature actually displays the geometry of the bore ... there is no need for visualization and guesswork. A zoom feature maximizes the bore view. Also, during the cycle the SV-10 lets the operator dwell the honing tool anywhere throughout the bore. The dwell pointer can be moved to the position where the bore is visually smaller and the tool will dwell there as long as necessary.
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Sunnen's new SV-10 Vertical Honing Machine combines the latest technology with the consistency and dependability of Sunnen's legendary CV-616.
With two motors, one for the spindle and one for the stroker, the SV-10 has the capability to run traditional tools as well as Sunnen's new DH-series diamond hone head. Sunnen's expertise, with multiple-diamond honing on the top-of-the-line CK-21, is now available on the competitively-priced SV-10. The DH-series diamond hone, with 16 points of cutting action, is the choice for truly round bores. The mechanical stroke guarantees precision surface finish with consistent crosshatch angle in each cylinder no matter what tool is used.
Another new feature is the patented full bore profile display which projects a real time graphical display of the bore cross section. This feature actually displays the geometry of the bore ... there is no need for visualization and guesswork. A zoom feature maximizes the bore view. Also, during the cycle the SV-10 lets the operator dwell the honing tool anywhere throughout the bore. The dwell pointer can be moved to the position where the bore is visually smaller and the tool will dwell there as long as necessary.
Machine Tools are available with VDI-driven units
Mazak Quick Turn Nexus, Super Quick Turn, and Multiplex-series machine tools are offered with self-contained VDI-driven units that enable multiple part processes such as milling, drilling, and turning on same part in one setup. Available with KM interface or ER collet style, units feature sealed spindle bearings, recessed spindle configuration, and through-coolant capabilities up to 1,500 psi. Tool setups can be pre-staged offline.
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(LATROBE, PA) - Self-contained VDI-driven units from Kennametal for Mazak Quick Turn Nexus, Super Quick Turn, and Multiplex-series machine tools enable multiple part processes such as milling, drilling, and turning on the same part in a single setup. Available with either the Kennametal KM interface or standard ER collet style, setups can be accomplished accurately and efficiently. Since the units make offsets known quantities, tool setups can even be pre-staged offline for greater productivity gains. As Product Manager Curtis Rellick succinctly puts it, "Less setup time, more spindle time."
Individual driven units are designed to work specifically with each model variation of the Mazak machine tools for maximum equipment capability. The units feature high-precision gears and sealed spindle bearings for smooth operation, and a recessed spindle configuration that reduces spindle stress and increases bearing life. High-quality seals and O-rings enhance protection against external contamination. Through-coolant capabilities of up to 1500 psi are available.The driven units increase rigidity by design, enabling higher spindle speeds and feeds and longer tool life. Product life averages of three years before repair or rebuilding are required, compared to nine to 12 months for other drive spindles. One customer described the advantages of a driven unit running a four-tooth, 1.57-in. face mill rough-cutting cast stainless steel at 600 SFM at a depth of 0.07 inches taking a full 1-inch width of cut. "Our maintenance personnel were frequently rebuilding competitive units due to bad gear backlash and blown spindles from the heavy interrupted cut," he says. "Despite the pounding the Kennametal unit takes, we have experienced better tool life, increased surface finishes, and no downtime with broken spindles/gears. That translates into productivity and dollars that go right to the bottom line."
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(LATROBE, PA) - Self-contained VDI-driven units from Kennametal for Mazak Quick Turn Nexus, Super Quick Turn, and Multiplex-series machine tools enable multiple part processes such as milling, drilling, and turning on the same part in a single setup. Available with either the Kennametal KM interface or standard ER collet style, setups can be accomplished accurately and efficiently. Since the units make offsets known quantities, tool setups can even be pre-staged offline for greater productivity gains. As Product Manager Curtis Rellick succinctly puts it, "Less setup time, more spindle time."
Individual driven units are designed to work specifically with each model variation of the Mazak machine tools for maximum equipment capability. The units feature high-precision gears and sealed spindle bearings for smooth operation, and a recessed spindle configuration that reduces spindle stress and increases bearing life. High-quality seals and O-rings enhance protection against external contamination. Through-coolant capabilities of up to 1500 psi are available.The driven units increase rigidity by design, enabling higher spindle speeds and feeds and longer tool life. Product life averages of three years before repair or rebuilding are required, compared to nine to 12 months for other drive spindles. One customer described the advantages of a driven unit running a four-tooth, 1.57-in. face mill rough-cutting cast stainless steel at 600 SFM at a depth of 0.07 inches taking a full 1-inch width of cut. "Our maintenance personnel were frequently rebuilding competitive units due to bad gear backlash and blown spindles from the heavy interrupted cut," he says. "Despite the pounding the Kennametal unit takes, we have experienced better tool life, increased surface finishes, and no downtime with broken spindles/gears. That translates into productivity and dollars that go right to the bottom line."
Versatile Machine Tools
Okuma America Corporation is the US-based affiliate of Okuma Corporation, a world leader in the development of computer numeric controls (CNC) and machining technology, founded in 1898 in Nagoya, Japan.
Okuma is known for its technology leadership and world-class manufacturing, product quality, and dedication to customer service. Okuma products are used in the automotive industry, aerospace and defense, construction and farm equipment, energy, medical, mold and die, and fluidpower industries.
Machines include vertical and horizontal machining centers, lathes, double column machining centers, grinders, and wheel machines that offer users high throughput, high accuracy, and reliable solutions to production machining operations.
Using Mechatronics, our full-circle approach to equipment design, we build machines that have the exact balance of power, speed and size to meet most any application-machines that can hold tight tolerances, perform more sophisticated cuts, and create precision-crafted parts time and again.
Okuma has entered into a partnership agreement with the National hot Rod Association and has been named Official Machine Tool Sponsor of the NHRA. This partnership is part of Okuma's High Performance Motorsports Industry program.
Okuma is known for its technology leadership and world-class manufacturing, product quality, and dedication to customer service. Okuma products are used in the automotive industry, aerospace and defense, construction and farm equipment, energy, medical, mold and die, and fluidpower industries.
Machines include vertical and horizontal machining centers, lathes, double column machining centers, grinders, and wheel machines that offer users high throughput, high accuracy, and reliable solutions to production machining operations.
Using Mechatronics, our full-circle approach to equipment design, we build machines that have the exact balance of power, speed and size to meet most any application-machines that can hold tight tolerances, perform more sophisticated cuts, and create precision-crafted parts time and again.
Okuma has entered into a partnership agreement with the National hot Rod Association and has been named Official Machine Tool Sponsor of the NHRA. This partnership is part of Okuma's High Performance Motorsports Industry program.
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