Screws are a general term for fasteners, commonly used in daily spoken language. As an extremely widely used tool in industrial product production, there are some things you must know about screws. As designers who have long dealt with products, have you ever wondered about the manufacturing process of this inconspicuous but relatively important product? We will start with the basic knowledge of screws to explain the processing and manufacturing process of screw products.
I. Basic Knowledge of Screws
A. Relevant Terminology of Screws
1. Differences between Screws, Bolts, and Fasteners
2. Common English Expressions
￮ Screw (Screw/Bolt)
￮ Bolt (Bolt)
￮ Fastener (Fastener)
3. Definition of Threads
A thread is a shape with uniform helical protrusions on the outer or inner surface of a solid.
B. Functions of Threads
1. Fastening and Connecting Function
Applicable to most screw products at present.
2. Transmission Function (Displacement Function)
For example, micrometers used for QC dimension inspection.
3. Sealing Function
Such as the connection and sealing of pipelines.
C. Development History of Threads
• Machine Threads: Before assembly, drill holes and tap threads on the assembly first. The tapped internal threads are consistent with the external thread specifications of the screw, and assembly is carried out with a small torque.
• Self-Tapping Threads: Before assembly, drill holes on the assembly first, no need to tap internal threads, and assembly is carried out with a large torque.
• Self-Drilling Threads: Can be used directly on the assembly, and the screw drills holes and taps threads in one step.
D. Processing Methods of Screws
1. Turning
A method of removing material to make the material achieve the desired shape.
• Advantages: High processing accuracy, no mold restrictions.
• Disadvantages: High production cost, slow processing speed.
2. Forging
A process of extruding material through external force to make it deform to the desired shape.
• Advantages: Fast production speed, low cost, suitable for mass production.
• Disadvantages: Forming is limited by molds, and the mold cost for complex products is high.
3. Cold Heading: A process of extruding and deforming metal Steel Wire Coils without heating by using molds with external force. Cold heading is classified as a specific form of forging technology.
II. Screw Manufacturing Process
The general flow chart is as follows:
Steel Wire Coil (Coil) → Wire Drawing → Cold Heading (Heading) → Thread Rolling → Heat Treatment → Electroplating → Sorting → Packaging → Warehousing/Delivery
(Outsourced) (Outsourced)
1. Coil Process
Coil process refers to the original coil purchased from raw material manufacturers. A coil mainly includes the following parameters: A. Brand B. Product Name C. Specification D. Material E. Heat Number or Batch Number F. Quantity or Weight.
The main chemical components of carbon steel coils are: C, Mn, P, S, Si, Cu, Al. Among them, the lower the content of Cu and Al, the better.
2. Wire Drawing Process
Wire Drawing Process: To achieve the required wire diameter (e.g., drawing to 3.5mm).
3. Cold Heading (Heading) Process
3.1 Cold Heading (Heading) Process
Through the interaction between molds, the Steel Wire Coil is cut first, upset into a screw blank, forming the head, cross slot (or other head types), thread blank diameter, rod length, under-head fillet, etc.
Cold Heading Molds:
• Wire Guide Die: Cooperates with the cutter to cut the Steel Wire Coil to the required length.
• Initial Punching Mold (First Blow Mold): For initial forming.
• Finish Punching Mold: For forming the head type and slot type.
• Ejector Pin: For ejecting the blank.
Note: The design can be carried out according to customer requirements. Common head types include P-head, B-head, F-head, T-head, etc. Common slot types include cross slot, slotted slot, torx slot, hex socket slot, etc.
3.2 Cold Heading (Heading) Process for Ordinary Screws and High Deformation Screws
Process Flow: Cutting the Steel Wire Coil → First Blow Forming (Importing into the Main Cross Head Punch) → Finish Punching Forming → Blank Ejection
4. Thread Rolling Process
Thread Rolling Process: Roll threads on the cold-headed blank (thread forming is achieved through the interaction between the movable die plate and the fixed die plate).
Changes Before and After Thread Rolling: The smooth rod after cold heading is extruded by the die plates to form threads.
Equipment and Tools: Thread Rolling Machine, Thread Rolling Dies (Templates)
5. Heat Treatment Process
01. Purpose
To obtain higher hardness and strength of the screw after cold heading processing.
02. Functions
• Realize self-tapping and locking of metals.
• Improve the mechanical properties of metal parts, such as torsion resistance, tensile strength, and wear resistance.
03. Classification
• A. Annealing: (700℃ × 4hr): Elongate the structure → Polygonization (for cold-worked structures).
• B. Carburizing Heat Treatment: Add carbon elements to metal parts to improve their surface hardness (for metal materials with low carbon content). After carburizing, the surface of the metal part is hard (with more carbon atoms) while the core is soft (with fewer carbon atoms), thus introducing two indicators: surface hardness and core hardness.
• C. Quenching and Tempering Heat Treatment: Do not add elements to the metal, but change the internal structure of the metal through temperature changes to obtain better mechanical properties.
Process Flow: Incoming Inspection → Phosphorus Removal → Preheating → Quenching Heating (Zones 1-6) → Quenching (Oil Tank) → Air Drying → Post-Oil Cleaning → Tempering Heating (Zones 1-4) → Air Drying → Final Inspection → Delivery
6. Electroplating Process
Electroplated products gain the desired coloration and an anti-oxidation layer on their surface.
Process Flow and Raw Materials:
Raw Material Preparation → Degreasing and Cleaning → Water Washing → Pickling (Dilute Acid) → Water Washing → Electrolytic Degreasing → Water Washing → Activation → Water Washing → Zinc Plating → Water Washing → Activation → Passivation Treatment (Chromic Acid, Phosphoric Acid) → Water Washing → Hot Water Washing → Drying → Natural Cooling → Final Inspection → Finished Product
Raw Materials: Chromium Trioxide, Potassium Chloride, Chromic Acid, Nitric Acid, etc.
Conditions: 185°C, Time: 1-8 hours
Standard: ZB.S.S550 (Black Zinc Chromate Coating)
III. Introduction to Basic Configurations of Screws
To understand screws and bolts, it is necessary to first know their shape characteristics and functions. The basic configuration includes: A. Drive System B. Head C. Threaded Joint Part D. Lead-in and Tapping Part
1. Machine Screw
• Components: 1. Hexagonal Head (Drive System) 2. Head 3. Bearing Surface 4. Threaded Part (Joint Part) 5. Lead-in and Tapping Part
• Functional Dimensions:
￮ Needle Part: None (since the head type is integrated with the drive system)
￮ Head: Opposite Side, Wrench Height (Diagonal), Bearing Surface Diameter
￮ Threaded Part (Joint Part): Strength = Material Stress × Tensile Area (According to ISO 898-1 Clause 8.2: 3.1416/4 × {(Effective Thread Diameter + Minor Thread Diameter)/2}²)
￮ Lead-in Part: Ability to guide nuts. Too small a chamfer will cause difficulty in customer assembly.
2. Self-Tapping Screw
• Components: 1. Needle Part (Drive System) 2. Head 3. Bearing Surface 4. Threaded Part (Joint Part) 5. Lead-in and Tapping Part
• Functional Dimensions:
￮ Needle Part: Needle Type and Needle Depth. Incorrect needle type will prevent the wrench from being inserted; insufficient needle depth will cause drive slipping.
￮ Head: Too small an under-head radius (R) is prone to head breakage.
￮ Threaded Part (Joint Part): Self-tapping thread structure.
￮ Lead-in Part: Ability to guide nuts. Too small a chamfer will cause difficulty in customer assembly.
3. Triangular Thread Screw
• Components: 1. Needle Part (Drive System) 2. Head 3. Bearing Surface 4. Threaded Part (Joint Part) 5. Lead-in and Tapping Part
• Functional Dimensions:
￮ Needle Part: Needle Type and Needle Depth. Incorrect needle type will prevent the wrench from being inserted; insufficient needle depth will cause drive slipping.
￮ Head: Too small an under-head radius (R) is prone to head breakage.
￮ Threaded Part (Joint Part): Triangular thread structure (similar to self-tapping screws in function).
￮ Lead-in Part: Ability to guide nuts. Too small a chamfer will cause difficulty in customer assembly.
4. Screw Head Types
• CHEESE: Cylinder Head
• BINDING: Dome Pan Head
• PAN: Pan Head
• TRUSS: Truss Head
• FLAT: Countersunk Head (K-Head)
• HEXAGON: Hexagonal Head
• OVAL: Oval Head
• ROUND: Round Head
• WASHER: Washer Head
• PAN WASHER: Pan Washer Head
5. Screw Thread Types
• CHIPB
• MS
• TY-A
• TAPTITE
• TY-AB
• HI-LO
Fastenermachinetool can provide a full set of screw processing equipment, ranging from cold heading machine, thread rolling machine to packaging machine,since WE KNOW SCREW MACHINES AND TOOLS MAKING, also We know China Fasteners.
