What should be paid attention to when processing the M1M2 self-locking tuning screw?
The M1/M2 self-locking tuning screw has the functions of self-locking and precise tuning, and the machining needs to focus on controlling thread precision, self-locking structural consistency, dimensional stability and surface quality. The following are the key points for attention in the whole process, covering core links such as material selection, cold heading, cutting, heat treatment, surface treatment and testing.
I. Material Selection and Blank Control
Project Precautions Accuracy/Parameter Requirements
H65 brass (commonly used in RF), 304 stainless steel and 40Cr (high strength) are preferred for material selection; M1/M2 specification avoids brittle materials and prevents processing/assembly fracture. H65 is selected as the conductive type, and 40Cr is selected as the strength type to be tempered to 220~250HB.
Wire accuracy: The diameter tolerance of cold-drawn wire is ±0.01~0.02mm, and the straightness is ≤0.05mm/m, so as to ensure the consistency of cold heading: φ0.83~0.98mm for M1 wire and φ1.8~1.98mm for M2 wire.
Cold heading is used for blank preparation batch, and precision cutting is used for single piece and small batch; Before cold heading, it is necessary to remove the scale and lubricate it to prevent the upsetting crack. The coaxiality of the cold heading die is ≤0.01mm, and the pressure parameters match the plasticity of the material.
Second, cold heading forming (preformed head and rod)
Multi-station cold heading control: the diameter of M1/M2 head is small (for example, the diameter of the pan head M1 is about φ1.6~1.8, and that of M2 is about φ2.4~2.8), so multi-station cold heading machine should be used for step-by-step forming to avoid eccentricity or cracking of the head caused by single-mode forming.
Coaxiality of the head: the positioning accuracy of the mold shall be ≤0.005mm, and the coaxiality of the head and the rod shall be ≤0.01mm to prevent sticking during tuning.
Allowance for rod: 0.1~0.2mm machining allowance should be reserved for self-locking structures (such as staggered threads and grooving) to avoid subsequent cutting damage to the matrix.
Three, self-locking structure and thread processing (core process)
The common structure of the self-locking tuning screw is staggered thread (the angle of two threads is staggered) or notched elastic structure, and the following points should be strictly controlled in processing:
Staggered thread machining
Double-thread design: M1 (pitch 0.25mm)/M2 (pitch 0.4mm) shall ensure the same pitch of two threads, and the diameter difference shall be controlled at 1.01:1~1.1:1, and the offset shall be 0.1p~0.8p(p is the pitch).
Cutting tool and programming: use customized thread turning tool or thread rolling wheel, and the positioning accuracy of numerical control system is ≤0.002mm to avoid thread disorder and broken teeth.
Grooving control: the axial grooving depth is 0.2~0.5mm and the width is 0.3~0.6mm, so as to ensure uniform elastic deformation and stable self-locking force at 5 ~ 15 nm (adjusted according to specifications).
Ordinary thread accuracy
The thread tolerance level reaches GB/T 197 6H, the tooth profile half-angle error is ≤ 1, and the surface roughness Ra is ≤ 0.8 μ m..
The starting end of the thread shall be chamfered by 0.2× 45 to prevent thread damage during assembly.
Four, cutting/grinding and special processing
Finishing/grinding: the cylindrical accuracy of the rod is IT6~IT7, the cylindricity is ≤0.003mm, and the surface roughness Ra is ≤ 0.4μ m; Using CNC lathe+cemented carbide tool, the cutting amount ap=0.05~0.1mm, f = 0.02 ~ 0.05 mm/r.
Grooving/drilling: High-speed steel drill/grooving cutter shall be used for oil hole and positioning groove, with groove width tolerance of 0.01 mm, and verticality between hole axis and rod part ≤0.01mm/100mm to avoid uneven stress during tuning.
Special processing: Special-shaped self-locking structures (such as elastic claws) are machined by wire cut EDM with surface roughness Ra≤0.2μm to avoid thermal deformation caused by wire cutting.
V. Heat Treatment and Surface Treatment (Performance and Protection)
Heat treatment: brass parts avoid high-temperature heat treatment and only undergo stress relief annealing (180~220℃, heat preservation for 1 ~ 2h); After quenching and tempering/surface quenching, the steel parts shall be tempered to ensure uniform hardness (for example, 40Cr surface quenching HRC58~62).
Surface treatment: brass parts are plated with silver (conducted by radio frequency), with a coating thickness of 5~10μm and a porosity of ≤0.5 pieces/cm; Passivation of stainless steel parts to prevent corrosion; Avoid the influence of too thick coating on thread matching accuracy.
Stress relief control: after heat treatment, use a straightener to correct, and the straightness shall be ≤0.005mm/m to prevent resilience deviation during tuning.
Six, quality inspection and process control
Accuracy requirements of testing tools for testing items
Dimensional accuracy CMM and thread gauge M1/M2 have a diameter tolerance IT6(±0.009mm) and a length tolerance of 0.02 mm.
Coaxiality of cylindricity instrument and dial gauge with form and position accuracy is ≤0.01mm, circular runout is ≤0.005mm, and verticality is ≤0.005mm/100mm.
Thread quality The tolerance of thread pitch diameter of thread comprehensive gauge and projector is 6H, and the error of tooth profile half angle is ≤ 1.
Self-locking performance The torque meter is disassembled and assembled repeatedly for 5 times, and the self-locking force is attenuated by ≤10%, without slipping or loosening.
Surface roughness tester and magnifying glass Ra ≤ 0.4μ m, without cracks, burrs and coating shedding.
Seven, batch production key process optimization
Unified datum: the whole process is based on the central hole of the rod to ensure the consistency of coaxiality of each process.
Solidification of process parameters: cold heading pressure, cutting speed and heat treatment temperature are recorded and archived to ensure batch consistency.
Dumb-proof design: the mold is equipped with positioning pins to prevent the processing angle deviation of staggered threads; After thread processing, 100% pass gauge inspection shall be carried out to prevent defective products from flowing into the next working procedure.
Eight, common defects and solutions
Causes of defect types and solutions
Tool wear and programming error of thread disorder, change tools regularly, optimize numerical control program, and increase thread detection stations.
Repair the positioning deviation of the eccentric cold heading die for the head, improve the die coaxiality, and increase the detection of coaxiality after cold heading.
The self-locking force is unstable and the groove depth/width is uneven. Optimize the groove cutter size and increase the on-line detection of groove width/depth.
Adjust tempering parameters due to bending heat treatment deformation of rod, increase straightening process and strictly control straightness.
