Centerless cylindrical grinding is a grinding method suitable for mass production. It easily achieves high-power, high-speed grinding with wide grinding wheels, achieving a roundness of 0.005-0.001 mm and a surface roughness of Ra 0.1-0.025 μm. To achieve high-efficiency grinding, configuring an automatic loading and unloading system on the centerless grinding machine is essential. This system enables safer and more reliable automated operation, improves equipment utilization, reduces the number of operators, and lowers the labor intensity of workers. Previous research has often employed complex robotic arms and PLC electrical control systems; studies on simple structures with stable performance that meet the requirements are relatively few.
On-site equipment overview
As shown in Figure 1, a factory uses a Chongqing Grinding Machine Co., Ltd. M1080C model centerless cylindrical grinder to grind cylindrical magnetic materials. In this magnetic material grinding production line, a vibratory feeder is used for efficient and orderly feeding. However, the unloading configuration of the existing grinding machine's receiving equipment involves using an angle iron to create an inclined slide, which is welded to the machine tool. After grinding, the workpiece slides down the slide. An inclined support platform is built at the end of the angle iron using stainless steel sheet metal. A perforated receiving box is placed on the platform, and the sliding workpiece falls directly into the receiving box. The cutting fluid is recovered through the perforated receiving box along the inclined surface of the support platform and the cutting fluid recovery pipe.
On-site investigation revealed the following: First, due to the brittle nature of the magnetic material, the abrasive tip often breaks off upon impact as it slides down into the receiving box, resulting in a 10% scrap rate on the existing production line. Second, the fixed drop position of the workpieces leads to disorderly clustering, requiring manual separation, wasting manpower, and reducing production efficiency. Third, the fixed tilt angle of the slide rail cannot accommodate workpieces of different sizes, causing some workpieces to slide too quickly, while others slide too slowly or even remain stationary.
Therefore, the system technical requirements for this renovation project are as follows: the magnetic material dimensions are: diameter range φ2mm-φ30mm, length 30mm. The material is brittle with a density of 7.9g/mm^3. According to the factory's requirements, there are three main points: first, prevent the magnetic material from being bumped or struck, reduce end-face breakage, and lower the scrap rate; second, place the magnetic material systematically in the receiving box; and third, recycle and reuse the cutting fluid.
Mechanical mechanism design and working principle
Figure 2 is a schematic diagram of the finished product of the automatic grinding and collecting machine. The main components of the machine are the discharge chute, the collecting box tray, the moving platform, the frame, the chute mounting frame, the bellows cover, and the electrical control box.
Based on the requirements of buffering, sorting, and recovering cutting fluid, the overall mechanical structure is designed as shown in Figure 3. The workpiece motion trajectory is planned as shown by the arrows in Figure 3.
The buffer design focuses on two aspects: reducing the speed of the workpiece as it slides down and absorbing the impact force as it reaches the end. Friction is increased by changing the inclination angle and bending rate of the guide groove, and additional auxiliary buffer accessories are added to reduce impact. The device shown in Figure 4 effectively achieves both speed reduction and impact absorption.
As shown in Figure 4, the ground workpiece slides down from the top of the slide rail, along the discharge chute 3, and collides with the buffer pad 7 at the end of the chute. The impact force of the workpiece is absorbed by the buffer pad. The photoelectric switch 6 senses that the workpiece has reached its position and sends a signal to the controller. The controller outputs to activate the door opening cylinder 5 and the blocking cylinder 4. The door opening cylinder 5 pushes the door 8 to open, allowing the workpiece to slide down. The blocking cylinder extends to block the workpiece sliding down behind, forming a cycle.
The front adjusting rod 1 and the rear adjusting rod 2 extend and retract to change the tilt angle of the discharge chute 3, so that the workpiece can slide down smoothly, but the sliding speed is at a suitable level.
The sorting manufacturer requires that workpieces be laid flat in a single layer in the receiving box. Based on the specifications of the workpieces, a ramp rolling sorting method is used. Specifically, workpieces rolling down from the discharge chute through the opening door fall into the receiving box placed on the ramp, rolling along the ground to form a row. After one row is completed, the platform moves to a different position to arrange the second, third, and so on, until the entire receiving box is filled. Because the workpieces vary in size and rolling speed, the ramp should be adjustable, as shown in Figure 5.
As shown in Figure 5, the receiving box for collecting workpieces is placed on the ramp box. The ramp box can rotate around the hinge, and the tilt angle is designed to be adjustable. Based on calculations of the friction angle and on-site experimental measurements, the adjustable angle of 5-10 degrees can meet the requirements of producing various specifications of workpieces. A vertical support 1 with a groove, slider a2, slider b3, and ramp tray 8 constitute a double-moving-pair four-bar linkage. The vertical support 1 with the groove is fixed to the moving platform 7 with screws. Slider a1 can slide freely up and down the vertical groove in the form of a moving pair. Slider a2 is hinged to slider b3, and slider b3 can freely extend and retract in the groove 4 at the end of the ramp box 8. The ramp tray 8 and the moving platform 7 are hinged together by hinge 5. The dimensions of each component are designed based on strength and stability, and then checked until the design requirements are met.
As shown in Figure 6, a single-axis moving module is composed of a stepper motor, guide rail, lead screw, moving platform, nut, etc., to achieve intermittent motion.
As shown in Figure 7 (left), the receiving box slide rail surrounds three sides, with a notch on the fourth side. The bottom of the receiving basket is hollowed out, allowing cutting fluid to leak downwards. The fluid flows down the slope as shown by the arrow to drain port 1, and then is collected through the drain hose. The diagram on the right illustrates the receiving box replacement process. After the slide completes one stroke and the receiving box is full of bar stock, the full receiving box is pulled out from the left, while a new receiving box is simultaneously fed in from the right to complete the replacement.
Power control section
The stepper motor is a 57 stepper motor (112mm/3A, 2.8 Nm) with a matching DM542 driver. The driver uses an AC servo driver with a current loop for microstepping control, resulting in very low torque fluctuations, smooth low-speed operation, and virtually no vibration or noise. At high speeds, the torque is significantly higher than other two-phase drivers. The controller is the Hongda Intelligent Control HD1008 intelligent programmable single-axis stepper motor controller. The electrical schematic and wiring diagram are shown in Figure 8.
Conclusion
This equipment has been put into use, reducing the scrap rate of magnetic materials from 10% to less than 5%. The magnetic materials are neatly placed in the receiving box, facilitating subsequent testing and improving production efficiency. Simultaneously, automation has reduced the labor intensity for workers, decreasing the number of workers required per grinding machine from three to just one, saving labor costs and bringing significant economic benefits to the company.
