The control of dimensional tolerances for copper castings is a critical step in the casting process, which directly affects the quality, performance, and assembly accuracy of the product. Copper alloys have good thermal conductivity, wear resistance, and corrosion resistance, and are widely used in fields such as machinery, electronics, and construction. However, copper castings are susceptible to various factors during the casting process, leading to dimensional deviations. Therefore, it is crucial to reasonably control the dimensional tolerances of copper castings. The following discusses in detail the control methods of dimensional tolerances for copper castings from the aspects of casting technology, mold design, material selection, and post-treatment.

1、 Optimization of Casting Process

Choose the appropriate casting method

The dimensional tolerance of copper castings is closely related to the casting method. Common casting methods include sand casting, metal mold casting, die-casting, and centrifugal casting. The accuracy of different casting methods varies:

Sand casting: suitable for castings with complex shapes and large sizes, but with low dimensional accuracy and tolerances generally ranging from CT8-CT12 levels.

Metal mold casting: With high dimensional accuracy and tolerances up to CT6-CT8 levels, it is suitable for small and medium-sized castings.

Die casting: High precision, with tolerances up to CT4-CT6 levels, suitable for large-scale production of small precision castings.

Choosing the appropriate casting method according to product requirements can effectively control dimensional tolerances.

Control the pouring temperature and speed

The pouring temperature and speed directly affect the shrinkage rate and dimensional stability of castings. Excessive pouring temperature can lead to increased shrinkage and dimensional deviation of castings; Low pouring temperature may cause incomplete filling. Therefore, pouring parameters should be optimized based on the melting point of copper alloys and the structure of castings.

Reasonably design the sprue and riser system

The design of the sprue and riser system affects the solidification sequence and shrinkage compensation of castings. A reasonable sprue and riser system can reduce defects such as shrinkage and porosity, ensuring the dimensional stability of castings.

2、 Mold design and manufacturing

Mold size compensation

Copper alloys undergo shrinkage during the solidification process, so the shrinkage rate needs to be considered in mold design. Usually, the shrinkage rate of copper alloys is 1.5% -2.5%. The mold size should be compensated according to the shrinkage rate to ensure that the casting size meets the requirements.

Improve mold accuracy

The machining accuracy of molds directly affects the dimensional tolerance of castings. High precision machining equipment (such as CNC machine tools) should be used to manufacture molds, and the dimensional errors of the molds should be strictly controlled.

Design of Mold Cooling System

A reasonable cooling system can uniformly control the solidification rate of castings and reduce dimensional deviations caused by uneven local shrinkage.

3、 Material selection and control

Choose the appropriate copper alloy

The shrinkage rate and flowability of different copper alloys are different. For example, brass has a low shrinkage rate and is suitable for manufacturing castings with high dimensional accuracy requirements; Bronze has a higher shrinkage rate and requires stricter process control.

Control the quality of raw materials

The composition and purity of raw materials affect the performance of castings. The composition of copper alloys should be strictly controlled to avoid uneven shrinkage or deformation of castings caused by excessive impurity content.

4、 Post processing and detection

Heat treatment control

Copper castings may undergo dimensional changes during heat treatment. The heat treatment process should be optimized according to the alloy type and product requirements to reduce deformation.

machining

For castings with high dimensional accuracy requirements, the dimensions can be further corrected through mechanical processing (such as turning, milling) to ensure that the tolerances meet the requirements.

dimension measurement

Use tools such as coordinate measuring instruments, calipers, and micrometers to detect and correct deviations in casting dimensions in a timely manner. For large-scale production, sampling testing or automated testing equipment can be used.

5、 Common problems and solutions

Size too large or too small

Reason: Insufficient or excessive compensation for mold size, improper control of pouring temperature.

Solution: Recalculate the shrinkage rate and optimize the mold size; Adjust the pouring parameters.

Casting deformation

Reason: Uneven cooling and improper heat treatment process.

Solution: Optimize the cooling system; Adjust the heat treatment process.

Local dimensions exceed the tolerance

Reason: Local wear or unreasonable design of the mold.

Solution: Repair or replace the mold; Optimize mold design.

The control of dimensional tolerances for copper castings requires comprehensive consideration from multiple aspects such as casting process, mold design, material selection, and post-treatment. By optimizing process parameters, improving mold accuracy, strictly controlling materials, and strengthening testing, dimensional deviations can be effectively reduced to ensure casting quality. In actual production, a reasonable control plan should be developed based on specific product requirements and production conditions, and the process should be continuously optimized to meet the increasing demand for precision.