MT Connect Challenge Monitoring and Control of Chatter Conditions with MTConnect Valerie Pezzullo Advisor: Dr. Laine Mears Clemson University

Transcription

1 MT Connect Challenge Monitoring and Control of Chatter Conditions with MTConnect Valerie Pezzullo Advisor: Dr. Laine Mears Clemson University Department of Mechanical Engineering Department of Automotive Engineering Clemson University International Center for Automotive Research (CU-ICAR) (561) /31/13

2 I. Abstract The MTConnect standard can be used to communicate machining process information regarding chatter conditions to the machine operator and to other machines to take automatic action for chatter avoidance. Chatter is the propagation of destructive vibrations in the toolworkpiece interaction. It is an undesirable phenomenon that can reduce part quality and increase tool wear. These consequences result in higher costs to replace damaged parts and tools as well as increasing the amount of machine downtime which can reduce the company s overall productivity. Currently, machine operators are able to correct for many machining errors due to their experience with the machine. Unfortunately as the experienced operators grow older, companies will hire new and relatively inexperienced operators. Without the same level of experience, new operators may not be able to meet the same quality levels. Once chatter can be detected audibly, damage to the workpiece may already have occurred. Therefore, an early identification and communication method with the machine tool is warranted to easily monitor and control the machine in the event of dynamic part damage. The proposed idea will provide a means to monitor and control cutting conditions to reduce and prevent chatter in the machining process and downstream processes within the machining system. II. Proposed Idea The goal of this proposed application is to use the MTConnect standard to communicate part-specific information (process parameters) about chatter identified in one operation of a machining system to downstream operations in order to avoid subsequent unstable conditions. This idea will use MTConnect as the communication protocol between the machine and the machine operator to relay machining process information. Certain machining process parameters, such as spindle speed, feed rate, and depth of cut, must be altered in order to reduce the occurrence of the undesirable chatter vibrations. Vibration information taken from machine sensors is used to identify chatter onset, adjustments to the machining process are made to avoid the vibration condition, and the machining design space causing the chatter for that specific part is communicated to downstream operations. These subsequent operations can then make changes to their own parameter sets in order to avoid chatter. The information will be sent to a user interface that will monitor the cutting conditions in real-time. The user interface can be either on a PC, a tablet, or a smartphone such as an Android device or an iphone. This will allow the information to be portable and independent of the user s location. The interface will organize the data in a graphical manner to show the cutting vibrations and values of all of the machining parameters from the machine and external sensors. The monitoring system will display the machine s state: whether it is behaving as normal, if the current cutting conditions are likely to produce chatter, or if chatter is detected. In addition to a monitoring system, a control system can be implemented to suppress chatter in the machining process if it does occur. The addition of a remote I/O monitor and controller, such as the National Instruments CompactRIO device can be used to relay the information from the external sensors and relevant signals from the machine through MTConnect to the user interface. The user interface will report the machine s state and if chatter is detected, either the operator will manually adjust the machining parameters or the controller can automatically adjust them via a connection outside of MTConnect. This is done because 1

3 MTConnect is currently read-only and the controller cannot write information to the machine through MTConnect. A high-level diagram of this process can be seen in figure 1. Figure 1 Communication between machine tool, controller, and user for the machine monitoring and control system Another facet of this idea is to communicate this information between machines. This would be useful in a multi-step machining process where the part goes from one machine to another. If the part was in a machining process that was close to chatter conditions, it would be desirable to communicate these results to the next machine that will work on this part so that the same conditions can be avoided. In this communication process, the first machine (machine #1) will send cutting parameter information through MTConnect and the remote I/O to the user interface. The user interface will also receive information from the sensors through the remote I/O. Additionally, machine #1 will send cutting parameter information through MTConnect to the second machine (machine #2). Machine #2 will send its information to the user in the same way as machine #1. Because MTConnect is currently read-only, the machines will only be able to communicate in a read-read manner. This means that machine #1 cannot directly tell machine #2 what to do, it can only send its information out to machine #2 and then machine #2 can decide what to do after the information is read. This communication of machining process information between machines will be helpful for the operator to choose suitable cutting parameters on machine #2 for the current part as well as adjusting the machining parameters on machine #1 for the next part. It can also be helpful to have the history of the part travel with it from one machine to the next. 2

4 Figure 2 Machine-to-machine communication with MTConnect to monitor and control cutting conditions related to chatter This idea would benefit several different areas of machining and the manufacturing industry. The human-machine communication would be easier via the readable and interactive user interface that would be developed. In addition to better communication, the detection and suppression of chatter in machining leads to better part quality, dimensional consistency, and the ability to salvage high value raw materials that would otherwise be discarded due to the effects of chatter on the material. This also leads to a reduction in the cost of replacing and re-machining parts as well as reducing tool wear and the cost of replacing tools. The amount of machine downtime would also benefit from the detection and suppression of chatter. If a part is exposed to chatter and is deemed unusable, both the part and the tool will need to be replaced and therefore the machine will be down for the amount of time it takes to replace the tool and part in the machine. Even if this only takes several minutes, this is precious time that could have been put to use in machining more parts. All of these combined make for a more productive machining process, and therefore a more productive manufacturing industry. III. Technical Requirements The technical requirements that are needed to implement this idea start with the machine tool. Ideally, any machine tool can be used. For the first phase of the idea (local chatter feedback), the machine that will be used to demonstrate this idea will be an Okuma horizontal CNC lathe which is available in our manufacturing laboratory. For the second phase of the idea (inter-machine communication), the previously mentioned lathe and an Okuma 3-axis CNC mill 3

5 available in our lab can be used. A feature that is internal in the Okuma 3-axis mill is a chatter suppression and controller called Machining Navi. This system changes the spindle speed to suppress chatter if it is detected. The results of this system can be seen in figure 3. Because the Machining Navi system is only present on our mill, an external chatter detection and suppression system using external sensors and the CompactRIO controller is required for use on the lathe. Both of these systems combined can be used to communicate chatter information to the user and between each of the machines. Figure 3 Okuma s Machining Navi chatter suppression system [1] A variety of sensors will be needed to monitor the cutting conditions and to detect chatter. A high-dynamic force sensor, developed at the CU-ICAR Manufacturing Laboratory at Clemson University, can be used to detect the forces between the tool and the workpiece and detect vibrations in the machining process. This sensor measures shear strain using several strain gauges on the tool and relates the voltage output to the forces observed using a regression model. A current sensor can be used to measure the current draw from the machine during operation and is connected to a power monitoring system from Caron Engineering known as Tool Monitoring Adaptive Control (TMAC). This information can be used to monitor the machine s power during operation. The machine will draw more current with an increase in force between the tool and the workpiece, and the force will vary due to vibrations and especially due to chatter. A few other sensors that can be used to detect vibrations are acoustic sensors such as microphones, accelerometers, and piezoelectric vibration sensors. Any of these sensors can be used to detect the vibrations caused by chatter and can be used along with the force sensor and the current sensor to notify the machine operator of these vibrations. Top Face Access for wires Figure 4 Force sensor setup on tool [2] 4

6 The remote I/O controller that will be used is a National Instruments CompactRIO, which is a reconfigurable remote I/O control and monitoring system. It can be configured with many different modules such as analog inputs and outputs, digital inputs and outputs, DC servo motor driver, inputs specifically designed for thermocouples, accelerometer and microphone inputs, serial communication, and more. It is designed to be used with LabVIEW and other related National Instruments software for monitoring and control. It communicates with a PC over Ethernet or it can be configured over a local network that can provide wireless communication. Other technical requirements involve a desktop or laptop PC, a tablet, and a smartphone that can be used to provide a user interface. The programming of the user interface depends on the device. On a Windows PC, LabVIEW can be used as a user interface that will directly communicate with the CompactRIO. Visual Studio can also be used to create a user interface that can receive the MTConnect information. If a tablet and a smartphone are used, the corresponding application developing software for either Apple or Android devices can be used to create a user interface. The machining process information received through MTConnect can be displayed on various user interfacing devices to alert the machine operator of any undesirable conditions and allows the operator to change the cutting parameters to correct for chatter. It also can allow the operator to set a manual or automatic mode so that the parameters can be changed by the operator (either remotely or in person) or automatically by the controller. Without this information provided through MTConnect, the machine operator would need to be by the machine s side throughout the entire machining process. Since the values of the cutting parameters such as spindle speed, feed rate, and depth of cut are currently locked in the machine, this information cannot be communicated remotely to the user. With MTConnect, the machine operator, or other support operations up to the plant manager, can have this information at his or her fingertips. A milestone that may be required to achieve the goal of controlling cutting parameters to suppress chatter conditions is the ability to have MTConnect as a read-write standard. This would allow the controller to talk back to the machine through MTConnect instead of externally. It would also allow for better machine-to-machine communication for better control operations. IV. Benefits This proposed idea of communicating chatter conditions to the user and to other machines can bring many benefits to the manufacturing industry. The communication of cutting parameters and conditions relating to chatter benefits the industry due to the realization of innovative user interfaces that are easy to use and aids machine operators in running machine tools. It also enables the manufacturing industry to monitor and control their machining processes to avoid chatter conditions and therefore increase part quality, reproducibility, and reduce waste of raw materials. It reduces the amount of tool wear as well as part defects and decreases the machine downtime that is needed to replace tools and parts if they need to be remachined. This reduces the cost of tooling and materials in the machining process and increases the productivity of the machine as well as the manufacturing process of the part itself. If more parts are being machined in a shorter amount of time with greater quality, the manufacturing industry will be able to sell more products and increase its profits. 5

7 REFERENCES [1] "MACHINING NAVI OKUMA ONLY-ONE TECHNOLOGY OKUMA CORPORATION." MACHINING NAVI OKUMA ONLY-ONE TECHNOLOGY OKUMA CORPORATION. Okuma, n.d. Web. 29 May < [2] Mehta, Parikshit, and Laine Mears. Machining Force Sensor Report. Rep. N.p.: n.p., n.d. Print. 6