Threads are one of the common geometric features in mechanical engineering, and usually refer to a spiral continuous part with a specific cross section made on the surface of a cylinder or cone.  According to its form, it is divided into external thread and internal thread, and according to its cross-sectional shape (tooth shape), it is divided into triangular thread, rectangular thread, trapezoidal thread, zigzag thread and other threads with special shapes. Different kinds of workpiece materials have different cutting difficulties due to their different mechanical properties and chemical compositions. The following Yixin Precision Metal and Plastic Ltd briefly introduces the selection of thread turning process for lower fasteners:
I. Selection of Thread Turning Technology
The pitch diameter of the thread is ensured by the total cutting depth of multiple feeds. There are three methods for turning triangular threads, namely, straight cutting, left and right cutting and oblique cutting.
(1) Straight-in method: use the middle slide plate to feed the tool, and cut the two blades and the tool tip at the same time. This method has a small error of tooth shape clarity, but the lathe tool has large stress, poor heat dissipation, difficult chip removal and easy tool tip wear. It is suitable for fine turning of small pitch threads and high precision threads.
(2) Left and right cutting method: The left and right cutting method is characterized in that the turning tool has only one cutting edge to cut, and at the same time of each cutting depth feed, the small tool holder is moved to the left and right for a short distance. The cutting is repeated several times, and the straight cutting method is still adopted at the end of the cutting to ensure the correct tooth shape and clear root. This method is applicable to threads with large pitch.
(3) Oblique cutting method: Turn the small tool holder by an angle to make the turning tool feed in the direction parallel to the right side of the thread, so that basically only one of the two cutting edges of the turning tool cuts. This method has the advantages of less cutting force, better heat dissipation and chip removal, and higher cutting rate. However, it is not easy to form a clear tooth shape and the tooth shape error is large. It is generally suitable for coarse turning with larger thread pitch.
Second, the thread turning tool material selection
In view of the difficulty in cutting stainless steel, tungsten cobalt hard alloy is selected as the turning tool material. Because tungsten cobalt alloy has superior toughness, wear resistance, high temperature resistance, grinding degree, adhesion resistance and thermal conductivity.
Three, the choice of thread turning tool angle
(1) the choice of front angle and nose angle
When cutting stainless steel materials, the chips are banded and the cutting force is concentrated at a larger front angle. When turning threads, the rake angle of the turning tool will affect the profile angle of the thread, because the profile angle of the thread turning tool with the rake angle will be larger than the tip angle of the turning tool, and the larger the rake angle, the larger the profile angle error will be.
(2) Selection of Turning Tool Rear Angle (Radial Rear Angle)
The function of the back angle is mainly to reduce the friction between the back of the turning tool and the surface of the workpiece. In order to improve the efficiency, hard alloy turning tools can use a smaller back angle during high-speed cutting.
(3) Selection of back angle of turning tool side edge
When turning a workpiece, it will affect the actual back angle of the side edge when turning the lathe tool. This problem is obvious when turning threads because the feed amount is small and negligible when turning the outer circle. The magnitude of its influence is determined by the helix angle.
Four, thread turning dosage selection
In order to overcome the defects of strong adhesion and poor heat dissipation of stainless steel, the use of vulcanized cutting oil is beneficial to reduce friction, reduce deformation, reduce cutting temperature, prevent cold working hardening of the blade, and improve the surface quality of threads.
These are the problems that need to be paid attention to in the thread turning process of fasteners. Reasonable setting of process parameters, selection of raw materials, cutting tools and cutting oil that meet the process requirements are the keys to ensure thread quality.
Yixin Precision Metal and Plastic Ltd was founded in 2004 and specializes in developing various stamping hardware and plastic small parts. Please feel free to contact us if you need. You can learn about us and our products on our official website, or you can directly send us e-mail inquiries.
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