Sheet stamping control.

Sheet stamping is most often cold, large-sized thick-walled structures are deformed in a heated state.

Depending on the types of technological operations (cutting, punching, bending, drawing, liquid stamping, explosion, rotational extrusion, etc.)

workpieces and parts may receive various defects, for the detection of which various types of controls are applied. There are the following types of control for sheet metal stamping:

control of raw sheet materials;  

control of die tools;  

control of technological processes of stamping;  

control of finished stampings.

List of defects of sheet materials in the initial state for strips

and for sheets and tapes are given in GOST 21014—88.

The stampability of steel is significantly affected by the size of the pearlite grain. Its definition occurs on an eight-point scale in accordance with GOST 5639-82

(ST SEV 1959-79). Defects of the original sheet materials may appear at the stage of transportation and storage (rust, dents, curvature, risks, etc.).

Defects of forgings from sheet materials can occur as a result of skipping low-quality sheet metal, including cracks and fractures, ruptures, slip bands (Chernov-Lüders lines), manifested in the form of local, banded grooves, which are formed as a result of local deformations, etc.

1. Control of source sheet materials.

The quality of sheet materials must first of all be ensured at the stage of forming rolled products, heat treatment, finishing and coating in accordance with current standards and specifications for finished rolled products. Acceptance of batches of sheet, strip and coiled material should be carried out by an external inspection of the PA stage of the entrance control with simultaneous verification of the certificate and passport for the rental batch. If necessary, the thickness of the sheet, the microstructure of the material on the witness samples can be checked and technological tests for microhardness and stampability can be carried out in relation to a specific type of technological operations of sheet metal stamping in accordance with the specifications and factory instructions.  

In technically sound cases, with increased demands on sheet quality, with automated and robotic sheet punching, the quality of rolled products can be checked automatically at the entrance to the process module by non-destructive methods (electromagnetic, eddy current, ultrasound, radiation, etc.).

2.Control die tool.

Die tools are a construction that has complex spatial interfaces in the working part. Inspection of stamps is carried out by visual inspection for external defects. The accuracy of the stamps is checked for compliance with design tolerances, the roughness of the working surfaces of the stamps, the accuracy of assembly and the relative position of the structural elements.

External examination monitors chipped, potholes, cracks, shells, risks, etc.

The roughness of the surfaces of the dies is controlled by samples. The highest surface cleanliness should have working surfaces of cutting, bending, exhaust dies, folding holders, cold extrusion dies, guiding surfaces of columns and sleeves.

Profile stamps controlled by racks with indicators on the control plate, templates; profile gages on the light slit, on the limit traffic jams, step line; coordinate measuring machines (CMM). Control using CMM is the most reliable. In this case, one-rack-mount CMM, CMM with a rotary table and universal CMMs can be used, allowing control to be performed by scanning. The control of the detachable parts of the stamps can be carried out using master punches and master dies for fine-tuning.

The accuracy of the assembly and the relative position of the die and the punch is crucial for ensuring the stamping without mechanical defects. Methods of controlling the relative position are given in table. one.

Table 1. Methods for controlling the relative position of the stamp parts

Controlled parameter. Control methods:

Feed pitch — Measurement on the test strip.

Fixing the workpiece in the punch die — With a probe.

The gap between the die and the punch when cutting — With the help of a probe.

Fit the punch and die during extraction — Control with the help of casts.

The course of the stamp — With the help of gauges, casts.

The coincidence of the axes of the matrix and the punch — Control with squares, levels, racks with indicators.

Wrapper holders — Tare key.

Certification of the stamp for cold stamping is generally the same as for hot stamping. The first parts after adjusting the stamp are subject to mandatory control, and periodic — during production, depending on the durability of the stamp. Certification of parts is most often carried out in the factory measurement laboratory.

3. Control of the stamping process.

With the introduction of robotic systems for sheet metal stamping, automatic punching machines and semi-automatic machines, the role of controlling the stamping process has increased. Most often it is conducted by contactless eddy current or pneumatic jet sensors.

Inspection of parts during cold forging. Receiving high-quality parts for cold forging depends on the source material and on the correct construction of the technological process.

At input control, the source material is controlled, at operational, the entire production process is controlled, at acceptance control — geometrical dimensions, internal and external defects and mechanical properties.

List of sources used:

1. Chupyrin V.N. Technical control in mechanical engineering. Designer’s Handbook. Under total ed. V.N. Chuprynin, A.D. Nikiforov. — M .: Mashinostroenie. 1987. — 512 p.

2. Chupyrin V.N. Technology technical control in engineering. M .: Publishing house of standards. 1990. — 400 pp.

3. GOST 21014-88 Rolled ferrous metals. Terms and definitions of surface defects.

4. R 50-609-40-01 Recommendations. Technological design technical control. Nizhny Novgorod. JSC «SIC CD». 2001. — 29 p.


Publication author: admin, 21 June 2019.