Several thread processing methods commonly used in CNC machining centers

Thread machining is one of the most important applications of CNC machining centers. The machining quality and efficiency of threads will directly affect the machining quality of parts and the production efficiency of machining centers.

The following is a summary of several threading methods commonly used in CNC machining centers, in order to enable technicians to reasonably select threading methods in processing and improve production efficiency.

1. Tap processing method

1.1 Classification and characteristics of tap processing

Using taps to process threaded holes is the most common processing method, and it is mainly suitable for threaded holes with small diameters (D<30) and low requirements for hole position accuracy.

In the 1980s, flexible tapping methods were adopted for threaded holes, that is, a flexible tapping chuck was used to hold the tap, and the tapping chuck could be used for axial compensation to compensate for the feed caused by the asynchronous feed of the machine tool and the spindle speed. Give the error to ensure the correct pitch. The flexible tapping chuck has a complex structure, high cost, easy damage and low processing efficiency. In recent years, the performance of CNC milling parts centers has gradually improved, and the rigid tapping function has become the basic configuration of CNC machining centers.

Therefore, rigid tapping has become the main method of thread processing at present.

That is, the tap is clamped with a rigid collet, and the spindle feed and spindle speed are controlled by the machine tool. Compared with the flexible tapping chuck, the spring collet has a simple structure, low price, and a wide range of uses. In addition to holding taps, it can also hold tools such as end mills and drills, which can reduce tool costs. At the same time, the rigid tapping can be used for high-speed cutting, which improves the efficiency of the machining center and reduces the manufacturing cost.

1.2 Determination of threaded bottom hole before tapping

The processing of the bottom hole of the thread has a great influence on the life of the tap and the quality of the thread processing. Usually, the diameter of the threaded bottom hole drill is selected close to the upper limit of the threaded bottom hole diameter tolerance,

For example, the bottom hole diameter of the M8 threaded hole is Ф6.7+0.27mm, and the diameter of the selected drill bit is Ф6.9mm. In this way, the machining allowance of the tap can be reduced, the load of the tap can be reduced, and the service life of the tap can be improved.

1.3 Selection of taps

When choosing a tap, first of all, the corresponding tap must be selected according to the material to be processed. The tool company produces different types of taps according to the different materials to be processed, and special attention should be paid to the selection.

Because taps are very sensitive to the material to be processed compared to milling cutters and boring tools. For example, using taps for processing cast iron to process aluminum parts is easy to cause thread loss, random buckles or even tap breakage, resulting in scrapped workpieces.

Secondly, attention should be paid to the difference between through-hole taps and blind-hole taps. The front-end guide of through-hole taps is longer, and the chip removal is front chip removal. The front end of the blind hole guide is short, and the chip evacuation is rear chip evacuation. Blind holes are processed with through-hole taps, and the depth of threading cannot be guaranteed.

Furthermore, if a flexible tapping chuck is used, it should also be noted that the diameter of the tap shank and the width of the square should be the same as that of the tapping chuck; the diameter of the tap shank for rigid tapping should be the same as the diameter of the spring jacket.

In short, only a reasonable selection of taps can ensure the smooth progress of processing.

2. Thread milling method

2.1 Characteristics of thread milling

Thread milling is to use thread milling tool, three-axis linkage of machining center, that is, X, Y axis circular interpolation, Z axis linear feed milling method to process threads.

Thread milling is mainly used for the processing of large-hole threads and threaded holes of difficult-to-machine materials.

It mainly has the following characteristics:

(1) The processing speed is fast, the efficiency is high, and the processing precision is high. The tool material is generally cemented carbide material, and the cutting speed is fast. The tool is manufactured with high precision, so the thread milling precision is high.

(2) Milling tools have a wide range of applications. As long as the pitch is the same, whether it is a left-handed thread or a right-handed thread, one tool can be used, which is beneficial to reduce tool costs.

(3) Milling is easy for chip removal and cooling. Compared with taps, the cutting performance is better. It is especially suitable for threading of difficult-to-machine materials such as aluminum, copper, and stainless steel. It is especially suitable for threading of large parts and parts of precious materials. Guarantee the quality of thread processing and the safety of the workpiece.

⑷Because there is no tool front guide, it is suitable for processing blind holes with short threaded bottom holes and holes without undercuts.

Classification of thread milling tools

Thread milling tools can be divided into two types, one is a machine-clamped carbide insert milling cutter, and the other is a solid carbide milling cutter. The machine-clamped tool is suitable for a wide range of applications. It can machine holes with a thread depth less than the length of the insert, or holes with a thread depth greater than the length of the insert. Solid carbide milling cutters are generally used to machine holes with a thread depth less than the tool length.

3. Pick-and-drop method

3.1 Characteristics of the pick-and-button method

Large threaded holes can sometimes be encountered on box-type parts. In the absence of taps and thread milling cutters, a method similar to lathe picking can be used. Install a thread turning tool on the boring bar for thread boring.

3.2 Precautions for pick-and-drop method

⑴After the spindle is started, there should be a delay time to ensure that the spindle reaches the rated speed.

(2) When retracting the tool, if it is a hand-ground thread tool, since the tool cannot be sharpened symmetrically, the reverse retraction cannot be used. The spindle orientation must be used, the tool radially moves, and then the tool is retracted.

(3) The manufacture of the arbor must be accurate, especially the position of the kerf must be consistent. If they are inconsistent, multi-tool bar processing cannot be used. Otherwise, it will cause confusion.

⑷ Even if it is a very thin buckle, it should not be picked with one knife when picking the button, otherwise it will cause tooth loss and poor surface roughness, at least two cuts should be made.

⑸ The processing efficiency is low, and it is only suitable for single-piece small batches, special pitch threads and no corresponding tools.