Abstract : This article introduces the application of Delta Electronics' newly launched PUTNC-H6 series general-purpose CNC system on a high-speed CNC camshaft grinding machine. By selecting the H6 CNC system, significant improvements have been made in camshaft grinding quality, machining accuracy and efficiency, and safety protection.
Keywords: Camshaft, Grinding, CNC, Safety Protection
1. Introduction
CNC camshaft high-speed grinding machines are the main machining tools for producing automobile and engine camshafts (see Figure 1). They are mainly used for high-precision machining of non-circular contours of camshafts, and the machining accuracy requirements of the grinding machines are very high.
This paper utilizes the PUTNC-H6 series general-purpose CNC system to control the grinding wheel head feed, template changing, worktable movement, and grinding wheel dressing. The optimal number and amount of grinding wheel dressing can be selected to improve surface grinding quality and reduce grinding wheel consumption. The grinding wheel spindle system employs the latest linear velocity model, automatically compensating for changes in grinding wheel diameter and linear velocity process requirements to achieve constant linear velocity grinding. This significantly improves machining accuracy and efficiency, and avoids surface burns that are prone to occur during camshaft grinding.
The machine tool's main drive system adopts an AC servo motor and ball screw structure, ensuring precise feeding and reliable operation. Simultaneously, the machine tool features multiple automatic protection functions, effectively improving equipment safety.
Figure 1 Camshaft
2. Introduction to PUTNC-H6 General-Purpose CNC System
The PUTNC-H6 general-purpose CNC system (Figure 2) is a general-purpose CNC system developed by Delta Electronics based on the successful application experience of the previous H4 series general-purpose CNC system in industrial machinery. It has the following features:
Figure 2 PUTNC-H6 General CNC System
1) Split design, optional second auxiliary operation panel. The H6 series interface uses a high-definition color 8" LCD display, while the H6CL series uses a 10" LCD display. The display resolution and color brightness are significantly improved compared to the earlier H4 series products.
2) The latest PLC software and LCD interface editing software can modify the interface at will according to the different machine tool process requirements, and can create customized control solutions for different industrial machinery;
3) The CNC system can automatically identify voltage or pulse control mode, the resolution can be set up to 7 digits, and an external grating ruler can be connected to any axis to realize a full dead loop control architecture with a maximum response frequency of 2000kpps and higher control accuracy;
4) When the CNC system's command control mode is pulse type and open-loop control mode, it also has encoder pulse feedback function to compare whether the servo axis is in position, effectively preventing collisions.
5) Compared to previous Delta Electronics CNC systems, the optimized acceleration and deceleration curve model and 0.5μs processing response can smooth the tool path and effectively reduce the surface roughness of machined parts.
6) Supports a second set of software limit functions, which can be switched via PLC;
7) The PLC inputs and outputs adopt the latest split-type communication modules, which can be freely combined and expanded. The switch type of the input point supports automatic identification of both NPN and PNP types.
3. Machining process of camshaft workpieces
The CNC system of this grinding machine controls three servo axes: the X-axis drives the longitudinal feed of the grinding wheel head to determine the grinding dimensions of the cam; the Z-axis drives the transverse displacement of the worktable to change the cam position; and the Y-axis drives the template servo to change the corresponding cam template. The machining method for correcting the cam is similar to copy machining. The accuracy requirements for cam machining are: maximum lift error ≤ 0.05 mm, and cam surface roughness < 0.4 μm.
4. The dressing and compensation function of the grinding wheel is realized.
Grinding differs from turning. Grinding wheels are circular wheels made of abrasive particles and a binder, used to grind the surface of workpieces. During grinding, the grinding wheel and workpiece are in surface-to-surface contact. Abrasive particles and binder detach from the grinding wheel body, resulting in an uneven surface. Dressing involves using diamond tools to remove these unevennesses, sharpening the grinding wheel. After dressing, the diameter of the grinding wheel decreases accordingly, thus requiring a dressing compensation function. See Figure 3.
The Delta PUTNC-H6 CNC system utilizes the open nature of its LCD screen to consolidate all the necessary process parameters into a single interface. Chinese annotations and a conversational data input interface make it extremely convenient for operators to input process parameters.
At the same time, when the grinding program is invoked, the CNC system can utilize a wealth of macro program operation instructions to perform mathematical calculations for grinding wheel compensation.
Figure 3 Grinding wheel dressing settings diagram
5. Grinding wheel linear speed setting
After the cam is dressed, the diameter of the grinding wheel will decrease. In the early Siemens 802C CNC system, because the underlying variables of the CNC were not open to the machine manufacturer, the designers could only set the source of the spindle frequency converter to the frequency converter panel control and switch the speed by external terminals. The spindle speed needed to be calculated in advance according to an EXCEL spreadsheet, and then the corresponding parameters needed to be modified on the frequency converter panel, which was very cumbersome.
The solution using the Delta Electronics H6 CNC system primarily leverages the open underlying variables and open PLC computation features of this model. Based on the linear velocity model formula of the grinding wheel spindle system, users only need to input the corresponding grinding wheel diameter and linear velocity when replacing the grinding wheel. The CNC system can automatically compensate for changes in grinding wheel diameter and linear velocity requirements, thus achieving constant linear velocity grinding. Grinding wheel parameters are directly set and calculated on the CNC system, and the inverter operation is controlled by analog voltage, eliminating the need to modify inverter parameters. This significantly improves machining accuracy and efficiency, and avoids surface burns that are prone to occur during camshaft grinding. See Figure 4.
Figure 4 Grinding wheel linear speed setting diagram
6. Improvements in safety protection
Early versions of the Siemens 802C system lacked a CNC interface. Operators had to manually teach and dress the grinding wheel, record the current coordinates, and then input the corresponding data into the R-parameter interface. The input data lacked Chinese annotations, sometimes leading to errors that caused collisions and damaged grinding wheels. Other times, operators failed to notice the height difference between the workpiece and the diamond dressing tool, causing X-axis displacement and direct impact with the high-speed grinding wheel, resulting in the wheel breaking and flying out, creating a safety hazard.
Delta CNC system's solution addresses this problem from three aspects.
1) The data teaching method eliminates the need for cumbersome interface operations. Taking the grinding wheel dressing interface in Figure 3 as an example, the operator only needs to move to the corresponding position of the starting point of the diamond pen shown in the figure and click the "R34/R46" button. The CNC system will automatically assign the current X and Z axis mechanical coordinates directly to the corresponding key process variables, giving the operator no opportunity to set them, thus reducing the risk of setting errors to zero. For other minor related process parameters, they are all concentrated in a single Chinese parameter interface using an icon-based setting interface, greatly reducing the probability of setting errors.
2) Utilizing the system's two sets of soft limits, dynamic soft limit functions are implemented for the diamond wheel dressing position and workpiece grinding position. Because CNC processes NC programs using a pre-read mechanism, when the pre-read trajectory data exceeds the CNC's set soft limit, the CNC system will issue an alarm and prohibit axial movement, thus providing safety protection. Based on this, we combine the H6 CNC system's two sets of soft limit functions with the PLC's logic functions to determine the Z-axis table position, thereby determining to activate the corresponding X-axis safety soft limit. This provides software protection during diamond wheel dressing and workpiece grinding, completely avoiding high-speed impacts. Simultaneously, we utilize the H6 CNC system's mathematical calculation function to automatically adjust the "X-axis" system soft limit value based on the diameter change after grinding wheel dressing after the initial soft limit setting, achieving full-process safety protection. (See Figure 5.)
Figure 5 Soft limit protection setting diagram
3) MPG Handwheel Test. The MPG handwheel test is also a major feature of the H6 CNC system. Utilizing this feature, after the operator initially sets the parameters, they can run the NC program in test mode. The CNC system will run along the path planned by the NC. However, the feed rate is entirely determined by how fast the operator turns the handwheel. If mechanical interference occurs, the operator only needs to stop turning the handwheel, and the CNC system will stop feeding, thus completely avoiding collisions caused by incorrect parameter settings.
7. Delta CNC H6 and Siemens CNC 802C Scheme Comparison
Table 1 clearly illustrates the differences between using the Delta PUTNC-H6 CNC system and using the Siemens 802C CNC system.
Table 1 Comparison of solutions using Siemens 802C and Delta PUTNC-H6 CNC systems
8. Conclusion
This article provides a mechanistic overview of the application characteristics of the H6 system on camshaft grinding machines. For machine tool manufacturers, Delta Electronics provides customized control solutions that fully meet the control requirements of existing solutions. Furthermore, it considers the actual situations encountered by end-users, offering unique solutions from the end-user's perspective. This is the core competitiveness of Delta Electronics' H6 CNC system.
About the author:
Zhang Guangwei, born in September 1976, graduated from Luoyang Tractor College with a major in CNC technology. He is currently a senior application engineer in the Servo CNC Product Development Department of Delta Electronics Co., Ltd., where he is engaged in application support and product marketing for servo CNC products. He has 14 years of experience in the electrical industry.
