Precision Grain Turning Boosts Product Manufacturing
To meet the processing needs of a specific product, modifications were made to the CNC lathe for enhanced safety protection. In conjunction with the requirements for grain drawing, research was conducted on turning processes, focusing on special fixtures, tools, and processing parameters. By optimizing turning processing technology, the grain processing requirements were successfully met while ensuring safety.
PART. 01 Preface
As modern weapons and equipment continue to develop, the structures of various warhead grains have become increasingly diverse. Traditional pressing and injection methods are no longer sufficient to meet product requirements. Process technicians in the industry have conducted extensive research on processing technologies tailored to specific product needs.
One of our company’s products features a disc-shaped, thin-bottomed grain. The traditional pressing forming process does not achieve the necessary density for this product. Therefore, we propose an innovative approach that involves pressing the grain blank and then turning the grain in stages to fulfill the product specifications.
To implement this new process successfully, we have made several enhancements. These include safety modifications to the processing equipment, the design of specialized fixtures and tools, the optimization of processing parameters, and the formulation of detailed operational steps. By considering the actual processing conditions, we have identified the most suitable processing technology for this grain.
PART. 02 Equipment safety modification
The 6150 CNC lathe was chosen as the turning equipment for the drug column based on the specifications outlined in the drawings. The equipment primarily consists of the machine tool itself, an electronic control system, and an operating system, as illustrated in Figure 1.
The main machine tool is located in an explosion-proof room, while the electric control system and operating system are housed in the control room. An adjustable-focus explosion-proof camera is installed in a suitable position within the explosion-proof room, and a monitoring display screen is positioned in the control room for real-time observation of the processing and debugging of the powder column.
The spindle motor, as well as the X-axis and Z-axis feed motors, utilize explosion-proof motors. Additionally, work lights have been replaced with explosion-proof lighting. The main power supply and control lines connect to a trench prepared in the explosion-proof room via explosion-proof flexible hoses from the main machine. Galvanized steel pipes are laid in the trench for routing, passing through an explosion-proof wall to connect to the electric control system and operating system in the control room. A 90° explosion-proof junction box and galvanized steel pipe are used at the trench’s turning point for transfer.
Once the equipment has been debugged and confirmed to be operational, the gap between the wire threading pipe and the reserved galvanized steel pipe in the explosion-proof wall is filled with explosion-proof cement. A patterned steel plate is placed above the trench. The explosion-proof room door and the equipment operation are equipped with a safety interlock system. This system ensures that when the explosion-proof room door is opened, the equipment cannot start or operate normally, thereby ensuring the safety of the processing operation.
The machine tool host consists of a lathe body, protective measures for the processing area, special fixtures, screw protection, a dust removal device, a tool holder, slide protection, and feed protection for both the X-axis and Z-axis, as illustrated in Figure 2.
Processing Area Protection: The processing area features semi-open protection; the front guard can be folded open while the rear guard is fixed in place.
Special Fixture: The fixture is constructed from non-ferrous metal.
Tool Holder: To meet product requirements, the tool holder utilizes a linear design. This arrangement effectively minimizes the risk of powder entering the tool holder gap when changing tools. Additionally, a rubber pad is positioned to prevent powder from entering the T-slot at the tool holder’s fixed location.
Dust Removal Device: A dust removal interface is located on the rear protective cover. One end connects to a material receiving box, while the other end connects to an explosion-proof vacuum cleaner, which collects waste material generated during processing.
Moving Parts Protection: The chuck is equipped with a claw protective cover to prevent powder entry during the turning process. A rubber cover protects the chuck wrench hole. Moving milling parts, including the machine tool slide, guide rail, and lead screw, are each fitted with telescopic protective covers to stop the waste powder from accumulating in friction-moving parts and to facilitate the cleaning of waste material.
PART. 03 Fixture design
Due to the special nature of the grain material, the clamping material in direct contact with the grain is made of copper alloy to ensure processing safety. The commonly used clamping methods of lathes can be divided into three categories: single clamp, one clamp and one top, and one clamp, one top and one support. The grain is a disc-shaped, thin-bottomed part, and a single clamp is used. The fixture is designed to match the shape of the grain. A standard self-centering chuck is used to weld the copper alloy tube blank. After welding, it is cut into three parts, and the fixture is fine-tuned to the equipment used for grain turning. The axial circular runout value of the fixture positioning surface is ≤0.02mm, which can effectively reduce the part processing size deviation caused by the fixture. The fixture is shown in Figure 3.
The charge is made from a fine granular explosive powder with a density of approximately 1.83 g/cm³. If the clamping torque is set too high, it can leave marks on the surface of the charge and cause deformation during machining. Conversely, if the clamping torque is set too low, the charge may rotate during processing, making it impossible to complete the task properly. To prevent these issues, use a torque wrench to manually clamp the charge at the specified torque.
First, calculate the approximate value of the required clamping torque. It is known that the maximum pressure on the surface of the charge is 1.6MPa, and the contact area between each claw and the charge is 805.9mm². The thrust on the claw can be calculated to be 1289N.
According to the formula
F＝2πMiη /（3t）（1）
Where F is the total clamping force (N); M is the input torque (N·m); i is the transmission ratio of the bevel gear pair; t is the pitch of the plane thread (m); η is the total efficiency of the chuck, η＝7%～17%.
The clamping torque M can be calculated as 3Ft/(2πiη) = (3×1289N×0.01m)÷(2×3.14×7×17%)≈5.17N·m. Based on this, the simulated grain column was processed and verified, and the clamping torque for the grain column processing was finally determined to be 4N·m.
PART.04 Tool Design
(1) Tool Material: Due to the limitations of the material used for the charge column and in accordance with the company’s safety regulations, the processing test utilized beryllium bronze and stainless steel tools for turning the charge column.
The homemade beryllium bronze tool tested with a hardness of 37HRC, while the stainless steel tool had a hardness of 39HRC. Under identical processing parameters, the beryllium bronze tool experienced faster wear and could not complete the normal turning process. Figure 4 illustrates the charge column processed by the beryllium bronze tool.
After conducting the processing test, it was determined that each blade tip of the homemade stainless steel tool could successfully process seven or eight charge columns. Consequently, the stainless steel tool was selected for turning the charge column.
(2) Tool structure: The tool structure features a 55° diamond inner hole design, tailored to accommodate the shape of the grain. The tooltip is produced with radii of R0.2mm and R0.4mm, respectively. When processing grains of the same size, the R0.2mm blade wears out faster than the R0.4mm blade. Therefore, the preferred blade tip for grain processing is the R0.4mm.
PART. 05 Determination of the program
To ensure operational safety, a simulated grain is used during trial cutting when determining the processing program. When pressing the grain blank, a simulated grain blank that matches the shape, size, and density of the actual grain blank is pressed simultaneously. This simulated grain blank is used for testing the cutting tool. Once the processing is deemed qualified, the actual grain is then processed.
1) The first round of the processing test uses a uniform cutting amount. After processing, the bottom thickness of the finished grain is only 3mm, resulting in a convex and deformed bottom plane. In the second round of processing, we employ a method that reduces the cutting amount while increasing the number of cycles. This approach aims to eliminate the deformation of the bottom plane caused by the processing parameters.
2) To enhance the surface quality of turning, we adjusted the tool processing trajectory from oblique cutting to straight cutting, while ensuring that the processing parameters were set correctly. After conducting verification tests, we observed a significant improvement in the surface quality of the grain column during turning. Figure 5 illustrates the oblique cutting process, while Figure 6 shows the straight cutting process.
The program for the oblique line cutting is as follows.
…
G0 T0101
X90
Z1
G1 X93.5 Z-0.6 F0.1
X-1
G0 X92 W1
G1 X93.5 Z-1.2 F0.1
X-1
G0 X92 W1
…
The program for the straight line cutting is as follows.
…
G0 T0101
X90
Z1
G1 X93.5 F0.15；Z-0.6 F0.1
X-1 F0.15
G0 X92 W1
G1 X93.5 F0.15；Z-1.2 F0.1
X-1 F0.15
G0 X92 W1
…
PART. 06 Operation steps
Once the CNC machining processing procedure has been determined through the simulation of the powder column, the next step is to process the powder column itself. The operator places the powder column into a specialized fixture and uses a torque wrench to clamp it at the designated torque level. Afterward, the operator starts the explosion-proof vacuum cleaner and exits the explosion-proof room, securely closing the explosion-proof door behind them.
While observing the monitoring system from the control room, the operator ensures that the door is properly interlocked before starting the power supply. The host machine is then operated through the operating system to commence the processing, ensuring safe human-machine isolation for the powder column during the turning operation.
Once the processing is complete and the equipment has stopped running, the operator confirms there are no safety hazards through monitoring and observation. Only then is the explosion-proof room door opened, allowing the operator to enter and clean up the waste material while also measuring the size of the powder column.
PART. 07 Conclusion
To ensure operational safety during the processing of a specific powder column product, the company has implemented safety enhancements to the processing equipment. By evaluating the structure of the powder column and conducting process tests, the appropriate materials, sizes, and processing parameters for the fixtures and tools have been identified. This thorough approach guarantees the quality of the processed powder column product. Through these efforts, the company effectively maintains high processing standards.
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Anebon team’s specialty and service consciousness have helped the company gain an excellent reputation among customers worldwide for offering affordable CNC machining parts, CNC milling parts, and CNC turning parts. The primary objective of Anebon is to help customers achieve their goals.