Parameter Settings for CNC turning of copper alloy threads
The parameter Settings for CNC turning of copper alloy threads can be carried out from aspects such as thread shape parameters, thread cutting parameters, feed rate and feed mode, and introduction/extraction distance.
Thread shape parameters
Thread direction: Select the outer diameter, inner diameter or end face/back face according to the processing requirements. When choosing between external thread or internal thread processing, the "Starting Position" text box is used to specify the Z-coordinate of the thread's starting point, and the "Ending Position" text box is used to specify the Z-coordinate of the thread's ending point. When the end face/back is selected, the "Starting Position" text box is used to specify the x-coordinate of the thread starting point, and the "Ending Position" text box is used to specify the x-coordinate of the thread ending point.
Thread parameters: including the setting of lead, thread Angle, top diameter of the thread, bottom diameter of the thread and thread cone Angle. The "Lead" text box is used to set the lead of the thread. There are two ways to represent it: the number of threads per millimeter length (teeth /mm) and the pitch (mm/ teeth). There are two parameters for setting the thread Angle. The "Included Angle" text box is used to specify the Angle between the two sides of the thread, that is, the thread Angle α. The "Thread Angle" text box is used to specify the Angle between the first edge of the thread and the vertical line of the thread axis, that is, the thread half-angle α/2. When setting the thread Angle, the "thread Angle" setting value should be less than the "included Angle" setting value. Generally, the "included Angle" setting value is twice the "thread Angle" setting value. The "Large Diameter" text box is used to specify the diameter of the top of the external thread, that is, the large diameter of the thread, which is also the nominal diameter of the thread. The "Thread Base Diameter (Diameter)" text box is used to specify the diameter of the external thread base, that is, the thread diameter. The "Thread Depth" text box represents the height of the thread. The "Taper Bottom Angle" text box is used to set the taper Angle of the thread. When the input value is greater than 0, the thread diameter increases linearly from the starting point to the end point. When the input value is less than 0, the thread diameter decreases linearly from the starting point to the end point.
Thread cutting parameters
NC code format: In the "NC Code Format" drop-down list box, three NC code formats for thread turning are provided: G32, G92, and G76. Among them, G32 and G92 are generally used for turning simple threads, while G76 is used for turning compound threads. However, not all CNC lathes can accept the commands of G92 and G76 threads.
The determining factor of the cutting depth: When the "Equal cutting volume" radio button is selected, the system sets the depth for each turn according to the same turning volume. When the "Equal Depth" radio button is selected, the system performs turning processing at a uniform depth (Z coordinate value).
The determining factors of the number of cuts: When the "cutting allowance for the first pass" radio button is selected, the system calculates the number of turns based on the specified turning allowance for the first pass, the cutting allowance for the last pass, and the thread depth. When the "Cutting Times" radio button is selected, the system calculates the cutting amount for each turn based on the set number of turns, the cutting amount of the last pass, and the thread depth.
Feed rate and feed mode
Feed rate: During the thread machining process, to achieve the best tool life, the workpiece diameter must not exceed 0.14mm of the thread outer diameter, and the feed rate should be avoided to be less than 0.05mm/r. The actual feed rate and the number of tool passes should be determined through experiments or based on the actual situation.
There are three feed methods for thread turning: radial, lateral and alternating. Radial feed is the most commonly used feed method. The chip formation is gentle and the blade wear is uniform, making it suitable for small-pitch threads. When processing large-pitch threads, poor chip control and significant vibration make it the preferred choice for working hardened materials such as stainless steel. Lateral feed can guide the chips in one direction, which can better control the chips and is suitable for cutting large-pitch threads and internal threads that are prone to chip removal problems. To prevent poor surface quality or excessive wear of the rear tool face due to friction at the rear edge, the feed Angle should be 1° to 5° smaller than the thread Angle. The axial feed rate for lateral feed can be simply calculated as 0.5× radial feed rate. Alternating feed is mainly used for cutting large tooth profiles. This method ensures uniform tool wear and a longer tool life.
Introduction/extraction distance: The servo system has a lag property. When processing threads, the starting position of the thread cutting will show an "advanced" phenomenon, while the ending position will show a "lagging" phenomenon, resulting in the pitch at both ends of the processed thread not meeting the processing requirements. Therefore, at the starting position of the thread cutting, the introduction distance δ1 of the tool should be considered, and at the ending position, the extraction distance δ2 of the tool should be considered. Generally, δ1=1.5P and δ2=P are taken; Empirical values can also be taken: δ1 is 2 to 5mm, and δ2 is half of δ1. For threads with a tool withdrawal groove structure, δ2 is generally taken as half the width of the tool withdrawal groove.
