What is precision blanking

Precision blanking has gained such a high level of interest and widespread popularity due to the enormous potential inherent in its basic principles.

This technology has now been upgraded by various designs and improvements and by the support of peripheral technologies.

It is a remarkable technology that not only improves the quality and performance of the finished product but also rationalizes the machining process, saves resources, and cuts costs.

The difference between precision blanking and general blanking

A plastic processing technique based on the development of general blanking technology, which uses toothed ring crimping to introduce crimping and counter-pressure to inhibit the tearing of the raw material during blanking, so that the material remains largely plastic until separation, resulting in a precision blanked part with low surface roughness, high dimensional accuracy, and good section quality.

In ordinary blanking, the material is separated by shearing through cracks near the die edge, and the part’s dimensional accuracy is low, generally below IT11.

The surface roughness is Ra12.5~6.3u m.

Fine blanking is the abbreviation of precision blanking, which is developed based on common blanking; it can obtain parts with smaller dimensional tolerances, higher dimensional accuracy, cleaner blanking surface, flat surface, perpendicularity, and good interchangeability than common blanking parts in one stamping stroke.

After fine blanking, the surface roughness of the parts can reach Ral .6~~0.2m, and the dimensional accuracy can reach more than IT9IT6, which can be directly used for assembly.

What are the requirements for precision blanking

Punching is not only required to produce parts by the shape of the drawing but also certain quality requirements, mainly referring to the quality of the cutting surface, dimensional accuracy, and shape error. The cutting surface should be straight, clean, and free from defects such as cracks, tears, laminations, and burrs. The part’s surface should be as flat as possible, i.e., the dome bend is small, and the dimensional accuracy should be guaranteed not to exceed the tolerance range specified in the drawing. When punching, the main factors affecting the quality of punching are the size and distribution uniformity of the convex and concave die clearance, the state of the die edge, the structure and manufacturing accuracy of the die, and the nature of the plate.

Commonly used precision blanking methods

Precision punching with strong crimping, semi-precision punching with a small gap and rounded edges, precision punching with a negative gap, reciprocating punching method

 

1.Powerful crimping process specification The use of extreme or very small punching gaps, up to 0.01-0.02 mm and independent of the material thickness, is used to ensure that the punching section is free of collapsed corners and burr bands. Because of the very small gap, the lower die cutter is very prone to bounce. The lower die cutter needs to be rounded to increase the service life and make the material easier to cut.

2.Small gap rounded edge punching is also called smooth punching. The direction in which the rounded edge is opened varies from one blanking process to another. In the case of a drop, it is opened on the concave die, which is sharp; in the case of a punch, it is opened on the convex die, which is sharp.

The small rounded edge is generally 10% of the thickness of the material to be punched, and the punching gap is 0.01-0.02mm when the punching force is 50% greater than in normal punching.

 This punching method suits materials with good plasticities, such as low-carbon steel, aluminum, copper, etc. The dimensional accuracy of the stamped parts can reach IT9~IT11, and the section roughness is Ra=0.5~0.63 micron.

 

3.Negative gap precision blanking method. The size of the convex die is slightly larger than the size of the concave die, forming a negative clearance punching method. Usually, the die has a clearance between the die and the die at the corresponding position.

4.In reciprocating punching, the die comprises two convex and concave dies, which are used to punch the sheet in both directions in steps.

Cutting. Therefore, on the cut-off surface of the part, two bright bands appear on the upper and lower sides while in the middle.

The tearing strip appears in between.

Advantages of precision blanking

1 .The section is pure shear separation under three-way compressive stress, and the stamping equipment simultaneously increases the main punching, pressing, and topping forces in three directions.

2.The dies are manufactured with high precision and very small clearances, and high-precision ball guides are used.

3.Small rounded corners on the die or die edge so that more material is squeezed into the deformation zone to increase the compressive stress.

4. The blanking process requires high equipment precision, die construction, materials, and press oil properties.

Disadvantages of precision blanking

1. The investment in a fine blanking machine is more than ten times that of a normal press.

2.The specialized nature of the fine blanking machine makes it unsuitable for multi-variety, small batch processes and is only feasible once the batch has reached a certain size.

3. Fine blanking technology is a relatively new and complex technology that requires advanced fine blanking machines and much advanced supporting equipment.

Factors affecting the quality of punched parts

1.pure metal punching raw material plasticity is better than alloy; impurity elements usually cause brittleness and reduce plasticity; various alloys have different effects on plasticity.

2.The organization of the metal of the blanking parts, single-phase organization, is better than multi-phase organization plasticity, the nature of the second phase, shape, size, number, and distribution state of the different.

3.Process deformation temperature, as the temperature rises during the punching process, plasticity also increases, but this increase is not simply a linear rise.

4. The increase in strain rate, both to reduce the plasticity of the metal and to increase the plasticity of the metal, the result of the combined effect of these two factors, ultimately determines the change in metal plasticity.

5.deformation mechanics conditions, in the main stress state, the more the number of compressive stress, the larger the value of the metal plasticity

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