Design and application of CNC milling machine tool alignment instrument
When using tools and pads to determine the zero offset value, the tool should gradually approach the workpiece. When the distance between the tool and the workpiece is close to the thickness of the pad, a pad should be placed in the middle and pulled repeatedly. Based on the operator's feeling, when the tool, pad, and workpiece are in complete contact, the zero offset value of the workpiece coordinate system should be set. This method greatly tests the operator's experience and skills, takes a lot of time and has low accuracy. Improper operation can lead to the risk of knife collision, thereby increasing maintenance costs. Although it is convenient and safe to use professional tool setting tools to determine the zero offset value, the existing professional tool setting tools have relatively limited functions and can only complete one of the zero offset values for X and Y coordinates and Z coordinates. To complete the zero offset value setting for all coordinates, different tool setting tools need to be replaced, which takes a lot of time; In addition, professional tool setting is relatively expensive and requires high machine tool performance. General CNC milling machines are difficult to meet the requirements and require upgrading and transformation of the machine tool, which is costly and not suitable for some small and medium-sized enterprises
Enterprises adopt.
Design a tool alignment instrument that can simultaneously complete the zero offset values of X, Y, and Z coordinates. The structure is simple, the cost is low, the operation is convenient, and the accuracy is high. It can meet the problem of setting the zero offset values of the workpiece coordinate system for CNC milling machines and machining centers.
1. Structural design of CNC milling machine tool alignment instrument
1.1 Overall structural design
The CNC milling machine tool mainly consists of two parts, namely a chuck and an indicator. Among them, the chuck mainly includes a claw, a cylindrical shell, and a chuck core. The center position of the claw is equipped with a clamping space, which is used for clamping the cutting tool; The indicator mainly consists of a connecting shaft, insulation sleeve, battery, light-emitting diode, spring, indicator tube, connecting rod, contact, etc. There is a power supply and a luminous device inside the indicator tube, and a transparent hole is set on the side wall of the indicator tube, through which the luminous device can be observed whether it is emitting light; Connect the shaft to the power supply, and connect the power supply to the luminous element; The luminous element is connected to the contact, and the contact is coaxial with the clamping space [3].
When setting the zero offset value of the workpiece coordinate system, the gripper of the chuck body is clamped and installed on the tool on the machine tool. When the contact of the indicator is in contact with the workpiece, a closed circuit is formed, and the illuminated part of the indicator can emit light, achieving the purpose of tool alignment. Easy to operate, safe and reliable.
1.2 Indicator structure design
The indicator mainly consists of a connecting shaft, insulation sleeve, battery, light-emitting diode, spring 1, indicator tube, connecting rod, spring 2, and contact. The lower end of the indicator is a spherical contact, which is fixed in the arc-shaped hole at the bottom of the connecting rod by a spring. When subjected to radial force, it can swing left and right, and when external force is removed, it can return to its original state. When the contact contacts the workpiece on the side, it can buffer the force of the workpiece on the CNC milling machine tool alignment instrument, avoid deformation and damage to the tool alignment instrument, and reduce the accuracy of the tool alignment instrument. The material of the contact is a metal conductor with high hardness and wear resistance, which avoids frequent contact with the workpiece and causes wear, resulting in changes in the size of the contact and can also act as a conductor for conductivity.
The overall shape of the connecting rod is a T-shaped stepped axis shape, with a step hole in the middle. The large hole is used to place springs, and the small hole is used to connect wires; The cylindrical surface with a larger T-shaped diameter is located inside the cylindrical hole inside the indicator tube. It adopts an IT5-IT7 level H/g small gap fitting method. The larger cylinder is equipped with a compression spring on top of it, so that the connecting rod is always fixed on the clamp at the lower end of the indicator tube. When subjected to axial force, it can slide up and down, and when the external force is eliminated, it returns to its original state. When the contact of the lower end of the tool setting device contacts the upper surface of the workpiece, the connecting rod can move upwards to buffer the force of the workpiece on the tool setting device and prevent deformation or damage of the tool setting device (Figure 1).
Figure 1 Knife alignment instrument and indicator
The upper end of the spring is a transparent insulation tube, in which a light-emitting diode and a CR1025 battery are installed. The positive and negative poles of the light-emitting diode are connected to the contact battery with wires. When a closed circuit is formed between the light-emitting diode and the battery, the light-emitting diode will light up. The upper end of the battery is connected to the contact column of the connecting shaft, which is fixed in the middle hole of the insulation ring and connected with ordinary triangular fine thread. The upper end of the connecting shaft is screwed into the threaded hole at one end of the clamp through the thread for position fixation [4].
1.3 Clamp structure design
The chuck body is composed of a chuck core, a conical threaded ring, a clamp, and a cylindrical shell. The drill core has a claw holding hole and a tapered threaded ring holding groove. The threaded end of the claw is installed in the claw accommodating hole on the drill core, and is connected to the conical threaded ring in the accommodating groove on the drill core through threads. The unthreaded ends of the three claws form a clamping space for clamping the tool. The conical threaded ring is composed of two half circles, forming a whole circle, embedded in the conical threaded ring accommodating groove. The drill core is embedded with a cylindrical shell outside, and a small interference H7/p6 fit is used between the cylindrical shell and the conical threaded ring, which can transmit torque. When rotating the cylindrical shell, the conical thread ring is driven to rotate, and the conical thread ring drives the claw to expand and retract, causing the size of the accommodating hole between the claws to change, making it easier to install tools of different diameters and locking tools. Except for the connection with the conical threaded ring, the cylindrical shell and the drill core can rotate relative to each other without any special fitting requirements. A H9/d9 tolerance fit with a large gap is adopted, and the chuck structure is shown in Figure 2.
Figure 2 Clamp Structure
2. Usage of CNC milling machine tool alignment instrument
Taking the FANUC Series Oi Mate CNC milling machine as an example, this article introduces the usage method of the CNC milling machine tool alignment instrument (Figure 3): Rotate the cylindrical shell of the CNC milling machine tool alignment instrument to increase the accommodating hole between the three jaws, and deepen the tool on the tool handle into the accommodating hole between the three jaws, so that the tool tip contacts the bottom of the accommodating hole. Then, rotate the cylindrical shell of the CNC milling machine tool alignment instrument in the opposite direction, the jaws extend, the accommodating hole decreases, and the mutual position of the tool alignment instrument and the tool is fixed.
Figure 3 Installation of tool alignment instrument
When setting the zero point offset in the Z-axis direction, operate the CNC machine tool to gradually approach the upper surface of the workpiece zero point. When the warning of the tool setting instrument lights up, press the "OFF SET" button on the CNC milling machine operation panel to find the zero point offset setting interface. Enter the inherent length value of the numerical control milling tool setting instrument in the buffer area, press the "Measure" button or read the mechanical coordinate value displayed on the machine tool at this time, add it to the inherent length value of the tool setting instrument, and input the obtained value into the zero point offset setting interface to complete the Z-axis zero point offset setting.
When setting the zero point offset in the X-axis direction, operate the CNC machine tool to gradually approach the side surface of the workpiece in the X-axis direction with the contact of the tool setter. When the warning of the tool setter lights up, input the coordinate value of the tool setter in the workpiece coordinate system in the buffer area of the zero point offset setting interface, and press the "Measure" button to complete the zero point offset setting in the X-axis direction. The zero offset setting method in the Y-axis direction is the same as that in the X-axis direction [6].
3. Working principle of CNC milling machine tool alignment instrument
When the contact is in contact with the workpiece, the current will flow out from the positive electrode of the battery inside the indicator, pass through the connecting shaft, and reach the clamp part of the tool setter. The clamp is connected to the tool, and the tool is installed on the tool holder. The tool holder is installed on the machine tool, and the workpiece is fixed on the machine tool. The workpiece contacts the contact, and the contact is connected to the connecting rod. The connecting rod is connected to the positive electrode of the light-emitting diode through a wire, and the negative electrode of the light-emitting diode is connected to the negative electrode of the battery through a wire, forming a closed circuit that lights up the diode. When the contact leaves the workpiece, the circuit is disconnected and the light-emitting diode is extinguished. The principle of the control circuit is shown in Figure 4.
Figure 4 Circuit Principle
4. Conclusion
In order to solve the problem of zero point offset setting in CNC milling machines, a CNC milling machine tool alignment instrument is designed, which can complete the zero point offset value setting in the X, Y, and Z axis directions of the CNC milling machine workpiece coordinate system. At the same time, the use of tool alignment tools is introduced. The CNC milling machine tool alignment instrument mainly includes a chuck and an indicator, which is equipped with a button battery as the power source and a light-emitting diode as a warning device. When setting the zero offset of the milling machine, use the gripper on the chuck to fix the tool setter on the milling machine tool. When the contact of the tool setter contacts the workpiece, the machine tool, workpiece, tool, and tool setter form a closed circuit, and the warning device lights up. In the zero offset interface of the CNC milling machine, input the coordinate value of the tool in the mechanical coordinate system to complete the zero offset setting of the CNC milling machine. The use of this tool setting device can effectively save zero offset setting time and improve productivity, because there is an elastic device inside the tool setting device, which avoids the danger of improper operation and collision with the tool, reduces maintenance costs, has a simple structure, and is easy to operate.
Fund Project: Shandong Huayu Institute of Technology 2019 Campus level Research Platform: CNC Tool Manufacturing Technology Research and Development Center; Dezhou Enterprise R&D Program Project: Research and Practice of Tool Setting Device for CNC Milling Machine (DZSKJ202008)
