Tap processing, which involves cutting internal threads (female threads) inside holes, is utilized by various machine tools as a means to efficiently process multiple threads. This article discusses the challenges that arise in tap processing and key points to eliminate processing errors in the final stage.
Tap processing refers to the operation of forming threads inside a pre-drilled hole using a specialized tool called a tap. This tool cuts female threads by ejecting chips through the grooves on the cutting edge sides as it rotates inside the hole.
Drill processing and reaming are often confused with hole processing, but they serve different purposes. Drill processing simply creates holes, reaming adjusts the holes to meet specific dimensions by enlarging them, and tap processing creates threaded holes for screws.
Challenges in tap processing include:
This is the most common problem in tap processing due to the high cutting resistance, making taps especially prone to breaking. Thin taps require particular caution. Chips clogging at the bottom of the hole can easily lead to breakage, necessitating reliable chip ejection. The smaller the diameter of the threaded hole being processed, the slower the pace of chip ejection, increasing the likelihood of chip clogging.
This is another common issue, where ejected chips wrap around the tap or chuck, leading to tool or workpiece damage. In mass production, where tap processing is performed continuously, chip entanglement tends to occur more frequently than in drilling.
Poor thread accuracy can lead to defective final products. While thread accuracy is checked using thread gauges or other measuring tools, caution is needed with sample inspections to avoid processing defects.
Solutions to improve tool breakage and accuracy issues include:
A significant cause of tool breakage is "chip clogging." Using the right type of tap for the hole (blind or through-hole) is crucial. Also, defects in the pilot hole (such as misalignment, incorrect diameter, or depth) can cause tap breakage, so high precision in the pre-drilling process is essential.
Use center-through type taps with coolant holes to flush chips away from the bottom of the hole, preventing clogging. Care should be taken not to insert the tap more than twice its diameter in one go to ensure chip ejection.
Use side-through hole taps with coolant holes. High-pressure coolant ejected from the sides of the tap helps wash away side chips, preventing clogging.
Chips can entangle when they fail to eject properly from the tap's grooves. Ensuring sufficient space between the fixture and the tool prevents chips from wrapping around the tool or chuck.
Various factors contribute to thread accuracy issues. Selecting the right tools and equipment and adjusting cutting conditions are crucial for preventing defective final products.
A specialized tap holder with a cushioning structure and expansion function helps absorb axial forces during tap withdrawal, preventing thread damage.
Modifying cutting conditions can improve thread shearing. Lowering the cutting speed for softer materials can reduce thread damage due to friction. However, too slow a speed may dull the tap, so adjusting cutting conditions to suit the tap and workpiece material is vital.
Coolant hole taps effectively prevent thread shearing caused by tip welding. Directly ejecting high-pressure coolant improves lubrication and prevents tip welding. Switching from water-soluble to non-water-soluble coolant can also reduce friction resistance.
Focusing on "chip ejection" can address many of the main causes of thread accuracy issues.
A broken tap during processing can lead to difficult removal and potentially scrapping the workpiece. Various methods, such as EDM or using a drill for tap removal, exist, but they require significant time and effort. Therefore, utmost care is needed to prevent tap breakage during processing.
This article explained the challenges in tap processing and key points to eliminate processing errors in the final stage. Tap processing is a fundamental metalworking technique. Effective chip ejection is crucial for preventing breakage and improving thread accuracy.
