Manufacturing process of ball screw nut housing
As a key bearing part of ball screw, ball screw nut housing needs to meet the requirements of high strength, high precision and wear resistance, and its manufacturing process covers material selection, precision machining, surface treatment and other aspects, the specific process is as follows.
First, material selection and pretreatment
ball screw nut housing materials need to take into account the strength and processing performance, the mainstream selection of high-carbon steel (such as S45C) or alloy structural steel (such as 40Cr):
High-carbon steel through the tempering treatment (quenching + tempering at high temperature) can be obtained by moderate hardness (HRC28-32), suitable for medium load scenarios; Alloy structural steels are carburized and quenched to achieve surface Alloy structural steels are carburized and quenched to a surface hardness of HRC58-62, with a tough core, suitable for heavy loads or high wear requirements (e.g. machine tool spindle nuts). material pretreatment stage needs to be annealed to eliminate the internal stress in the forging or rolling process, to avoid deformation during subsequent processing.
Second, blank molding
According to the size and structure of the nut shell, blank molding is divided into two types:
Forging blank: for large size or shaped nuts (such as flanged shell), the hot forging process will be used to forge the billet into a shape close to the finished product, through the forging grain refinement to improve the material density and mechanical properties;
Bar cutting: small and medium-sized nut shell can be directly used round steel bar, through the saw or laser cutting material, the blank length of 5-10mm processing allowance.
Third, rough machining
through the lathe, milling machine and other equipment to remove excess material from the blank, complete the shape and infrastructure processing:
lathe processing: turning the outer circle, end face and bore, to ensure that the bore and the outer circle of the coaxiality (tolerance ≤ 0.02mm), to lay the foundation for the subsequent processing of the thread;
Milling machine processing: if the shell with flange or mounting holes, milling the flange plane through the milling machine, drilling and tapping to ensure the perpendicularity of the mounting holes and the end face (tolerance ≤ 0.03mm). Rough machining needs to be aging treatment to further eliminate processing stress and avoid dimensional fluctuations after finishing.
Precision machining
The core process is the processing of internal thread and ball circulation groove, which directly affects the matching accuracy of the nut and the screw:
Internal thread processing: use the thread grinding machine to grind the internal thread, the accuracy can reach 6H level, the surface roughness Ra ≤ 0.8 μm, to ensure that the meshing gap with the screw threads is uniform;
Circulation groove processing: according to the ball circulation mode (internal/external circulation), the reverser mounting groove or elbow guiding groove is processed by EDM or special molding milling cutter, and the accuracy of groove position is controlled at ±0.01mm to ensure smooth ball circulation without stagnation.
End face fine grinding: use surface grinding machine to fine grind the flange end face or positioning surface, flatness ≤ 0.005mm/m, to ensure that the nut is installed with the equipment datum surface close fit.
Five. Heat treatment
According to the material characteristics of the selection of the appropriate heat treatment process:
high-carbon steel nut tempering treatment, balanced strength and toughness;
alloy structural steel nut carburizing quenching, strengthening the surface hardness and wear resistance;
low-temperature tempering after heat treatment is required to eliminate quenching stress, stabilize the flange. Eliminate quenching stress and stabilize the size.
Sixth. Final Processing and Precision Calibration
Further improve the accuracy of key parts through precision grinding or honing:
Fine grinding of thread surface, reduce the roughness to Ra≤0.4μm, reduce the friction and wear between the ball and the thread surface;
If the shell has sealing groove or dust-proof structure, it should be processed by coordinate grinding machine to ensure that the groove and the threads are not damaged; and to ensure that the groove and the threads are not damaged. If the housing has sealing groove or dustproof structure, it is processed by coordinate grinding machine to ensure the relative positional accuracy of the groove and thread;
Finally, the key dimensions (such as the internal thread center diameter and flange hole tolerance) are tested by coordinate measuring machine to ensure that it meets the requirements of the design drawings.
Seven.Surface treatment
Select surface treatment according to the use environment:
Phosphate treatment: form phosphate film on the surface to enhance the rust prevention ability and grease adsorption, suitable for humid environment.
Electroplating: galvanized or chrome plating can enhance corrosion resistance, chrome plating can also enhance the surface hardness (applicable to food machinery and other scenes that require cleanliness).
Blackening: black oxide film is formed on the surface through oxidation reaction, low cost and suitable for indoor dry environment of the nut shell. VIII. Pre-assembly testing
The finished product needs to pass two key tests:
Dimensional accuracy test: use thread plug gauge, micrometer and other tools to check the accuracy of internal threads, outside diameter tolerance and form and position error.
Performance test: After assembling the nut and screw, manually rotate it to detect whether there is any stagnation, or test the axial load carrying capacity and flexibility through the testing machine.
The core of the manufacturing process of the nut shell is "the balance of precision and strength". Through material optimization, precision machining and strict testing, we ensure that it can be both stable and load-bearing in the ball screw drive, and also can cooperate with the screw to achieve high-precision movement.
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