7. Large format CNC (Group Assignment)¶
What is CNC:¶
CNC stands for Computer Numerical Control, a technology that uses computer programs to automate and precisely control the operation of machine tools like mills, lathes, and routers. CNC enables highly automated, efficient, and repeatable manufacturing processes across various industries.
Group Assignment¶¶
In the group assignment we learned about how the CNC works, safety in using CNC, and about the speed of the spindle.
Safety procedures¶
1. Wear safety glasses to protect your eyes from flying debris.
2. Use sound-isolating headphones to safeguard your hearing.
3. If you have respiratory issues like asthma, wear a mask to avoid inhaling harmful dust.
4. Be sure to roll up your sleeves to prevent them from getting caught in the machinery.
5. Maintain a safe distance behind the marked line on the ground when the machine is in operation.
6. Remove any objects that could interfere with or get pulled into the device.
Runout¶
Runout refers to the deviation of a rotating component from its proper axis of rotation. To measure runout, a dial indicator is used to detect the radial movement of the tool as it is rotated. Runout can be minimized by tightening or replacing any worn tool holders, balancing workpieces, and ensuring proper spindle alignment. Taking these steps helps maintain the accuracy and precision of the rotating parts in the CNC machine.
Alignment¶
Alignment refers to the accurate positioning of the machine's components in relation to one another. To test the alignment, precision measurement tools like dial indicators and laser alignment systems are used to check for squareness, parallelism, and perpendicularity.
On this specific machine, the z-axis alignment is done automatically using the software and a basic plate. When the drill bit touches the plate, it closes an electrical circuit, allowing the software to determine the correct z-axis alignment.
To maintain proper alignment, machine components may need to be adjusted, worn parts replaced, and the entire machine recalibrated as necessary before any work begins. Ensuring precise alignment of all the machine's components is critical for its accurate and reliable operation.
Fixturing¶
Fixturing refers to the methods used to securely hold a workpiece in place during the machining process. Testing the fixturing can be potentially unsafe, so it's best to assess it carefully or through simulation to check for workpiece stability, vibrations, chatter, and any unwanted movement. Common fixturing techniques include using clamps, industrial adhesives, or directly drilling the workpiece into the CNC machine's bed. For this machine, screws are drilled into each corner as well as the middle of the workpiece to firmly secure it in place. Proper fixturing is crucial to ensure the workpiece remains stable and stationary during machining operations, preventing any accidents or damage to the part or the machine.
Speeds & Feeds¶
Speed refers to the rotational speed of the cutting tool, while feed rate is the rate at which the tool advances and moves into the material. To determine the optimal speed and feed settings, start conservatively and gradually increase them while monitoring tool life, surface finish, and chip formation. The specific speed and feed rate should be adjusted based on the workpiece material, tool geometry, and the desired results. For the MDF wood, the highest available spindle speed of 17,000 RPM provided the best results, paired with the slowest feed rate of 60 inches per minutes. Carefully testing and adjusting the speed and feed parameters is crucial to achieve the desired machining outcomes, maximize tool life, and avoid issues like premature tool wear or surface quality problems.
Materials¶
The material being machined in the CNC process is the primary factor that determines all the other required parameters, such as speed, feed rate, tool selection, and fixturing. The best approach is to test multiple materials and adjust the settings based on their machinability characteristics. The material chosen should be practical and appropriate for the intended application. In this case, MDF (Medium Density Fiberboard) wood was selected as the workpiece material. Carefully considering the material properties and conducting thorough testing is crucial to establishing the optimal machining parameters before starting the cutting process. This ensures the best possible outcomes in terms of part quality, tool life, and overall efficiency.
Toolpaths¶
Toolpaths refer to the programmed path that the cutting tool follows during the machining process. To test and validate the toolpaths, it is recommended to first run them through a simulation in a CAM (Computer-Aided Manufacturing) software. This allows you to identify any potential issues or errors before cutting the actual workpiece. After the simulation, it is advisable to perform a test cut on a small sample workpiece to further assess the toolpaths. Based on the results, the toolpaths can then be modified and optimized to improve cutting efficiency and part quality. Thoroughly testing and iterating on the toolpaths is a crucial step to ensure the CNC machine operates as intended and produces the desired outcome for the final workpiece.
