brass hot Stamping Practical Guide
As an advanced processing method with minimal cutting, forging(called hot stamping) technology has significant advantages in the production of copper alloy products - it can ensure good mechanical properties of the parts and achieve efficient mass production. It is widely used in hardware products such as pipeline valves, pipe fittings, nuts, etc. However, many practitioners often encounter problems such as mold fragility, difficulty in determining specifications, and inaccurate temperature control in practical operations. Today, based on professional materials, we will share the core experience of copper alloy hot stamping, focusing on dismantling the key points for improving mold life, determining copper rod specifications, and hot stamping temperature control techniques.
1. Copper alloy stamping core parameters: temperature control is the foundation
The hot stamping temperature directly affects the plasticity of copper alloys, mold life, and product quality. It is necessary to strictly avoid the brittle zone to ensure smooth metal flow.
hot stamping temperature range:
The commonly used copper alloy hot stamping temperature is 650-890 ℃, which needs to be adjusted according to the grade: brass (such as H62, HPb59-1) is recommended to be 650-720 ℃, bronze (such as QAl9-2) is recommended to be 700-890 ℃, and pure copper (T1-T3) is recommended to be 650-900 ℃.
Key principles:
The temperature should be 150-250 ℃ lower than the melting temperature of the metal to avoid overheating and coarsening of the grains. At the same time, the brittle zone around 500-700 ℃ should be avoided to prevent cracking of the parts.
Heating specifications:
Using resistance furnace or flame heating, the heating speed is based on the principle of "rapid heating+short-term insulation", and the insulation time is calculated according to the thickness of the billet, generally not less than 20 minutes, to ensure uniform temperature inside and outside the billet and uce oxidation and decarburization.
2. Copper alloy hot stamping mold design: 4 keys to extend service life
The punch mold works under high temperature and high pressure, and in response to the flowability characteristics of copper alloys, the following designs need to be optimized:
Mold material selection:
Priority should be given to using high-temperature resistant and wear-resistant hot work mold steel, such as 3Cr2W8V, 5Cr4W5Mo2V, etc. The core of the concave mold can adopt a composite structure, with heat-resistant alloy steel for the inner layer and high-strength material for the outer layer, ucing costs and improving crack resistance.
Optimization of cavity structure:
Large rounded corners are used at the transition of the mold cavity (recommended to be selected at 0.5-4mm according to the height of the component) to avoid stress concentration caused by sharp corners; The inner hole core pulling adopts a combined structure to uce the risk of core mold breakage; The concave mold is set with a demolding slope of 10 '~30' to facilitate the detachment of the workpiece and uce mold wear.
Gap and Work Belt Design:
The clearance between the convex and concave molds should be controlled at 0.08~0.15mm to adapt to the thermal expansion and contraction characteristics of copper alloys; The length of the concave mold working belt is adjusted according to the material. For brass parts, it is 0.8-1.5mm, and for pure copper parts, it can be appropriately extended to balance the accuracy of the parts and the difficulty of demolding.
Lubrication and cooling design:
Lubrication channels should be reserved on the working surface of the mold, using graphite+engine oil or molybdenum disulfide high-temperature lubricants to uce metal flow friction; A cooling groove can be installed on the back of the mold to avoid long-term high temperature causing the mold to soften.
3. Copper rod specification determination: precise calculation+trial mold verification
The specifications of copper bars directly affect material utilization and product quality, and should be determined according to the principle of "conservation of mass+process margin":
Core calculation formula
The quality of the billet is m=the quality of the workpiece m1+the quality of the flash edge m2; the length of the billet is h=m/(ρ× A) (ρ is the density of the copper alloy, about 8.3-8.4g/cm ³, and A is the cross-sectional area of the copper rod).
Key margin control
The diameter of the copper rod should be close to the diameter of the concave mold cavity, generally 1-1.5mm smaller than the mold cavity, to uce metal flow resistance; A surplus thickness of 5-10mm should be reserved for the length to avoid insufficient filling of the parts. The surplus thickness can be adjusted through trial molding.
Trial mold verification and adjustment
Before mass production, a trial punching is requi to adjust the specifications of the copper rod according to the filling situation and flash thickness of the parts. Generally, the flash thickness should be controlled at around 0.5mm to ensure a material utilization rate of over 95%.
4. Practical tip: uce defects+improve efficiency
After cutting the copper rod, it is necessary to clean the burrs and oxide scale on the end face to avoid pressing into the surface of the workpiece and affecting the quality;
The mold needs to be preheated to 200-300 ℃ before hot stamping to prevent sudden cooling and cracking of the mold;
The edge cutting of the workpiece adopts cold cutting technology, and the clearance between the convex and concave molds is selected as 0.04~0.06mm according to the hardness of the copper alloy to avoid residual burrs.
5、 How to improve the lifespan of molds?
✔ Reasonable R value (most important)
✔ Reasonable classification surface
✔ mold preheating
✔ Copper material temperature remains stable
✔ Mold surface coating
✔ Top pin and material pushing structure buffering treatment
✔ Avoid excessive overheating of copper materials
✔ Reasonable depth of flying edge groove
Each item can increase lifespan, but the most crucial is:
Temperature stable+sufficient rounded corners+no forced buckling
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