Analysis of Forming Process and Die Design of Connector Shield Spring

Time:2023-09-10 12:19:24 / Popularity: / Source:

1 Process Analysis

Figure 1 shows shield spring, part material is QBeMg1.9 beryllium bronze plate, plate thickness is 0.15 mm, surface of formed part is required to be free of pits, steps, burrs, deformation, cracks and other defects, production batch is not large. In order to save manufacturing costs, stamping and forming are carried out in different steps.
Die Design of Connector Shield Spring 
Figure 1 Shield spring

1.1 Part Analysis

Figure 2 shows three-dimensional structure of shielding leaf spring, which is similar to a lotus flower, with a through hole in the middle, and circumference is composed of 22 leaf springs. Roots of adjacent leaf springs have a circular transition, and top is concave. There are three more leaf springs on leaf spring. Circular gaps with a diameter of φ3 mm are evenly distributed, and each leaf spring plays a connecting role during assembly. Therefore, how to ensure diameter of inscribed circle of leaf spring is the key and difficult point in the forming of this part.
Die Design of Connector Shield Spring 
Figure 2 Three-dimensional structure of shield spring

1.2 Forming process

According to part structure analysis, there are 2 different forming schemes.
Scheme 1: blanking→cleaning→heat treatment→bending forming→punching→deburring→cleaning→heat treatment→inspection.
(1) Blanking. Blanking sheet into a blank, completing the one-time forming of central φ6 mm positioning hole, three φ3 mm circular holes, and 22 leaf springs.
(2) Bending and forming. On the basis of blank, top, middle and root of leaf spring are bent and formed at one time.
(3) Punching. Buckle shield spring upside down on punching die, punch out bottom hole, and complete punching of part.
Scheme 2: blanking→cleaning→heat treatment→bending forming I→bending forming II→punching→deburring→cleaning→heat treatment→inspection. Scheme 2 mainly divides the first bending forming of Scheme 1 into two formings, rest of process remains unchanged. Stamping forming process of parts is shown in Figure 3.
Die Design of Connector Shield Spring 
Figure 3 Stamping process
(1) Bending forming I. Top of leaf spring is bent and formed on the basis of blank to ensure stability of top features, and root of leaf spring is pre-bent to reduce springback of leaf spring during second bending.
(2) Bending Forming II. Root of leaf spring is bent and formed. Middle of 22 leaf springs is bent into a waist drum shape. Root of leaf spring is approximately perpendicular to bottom surface to ensure stability of root characteristics and complete basic shape of shielding leaf spring.
From analysis of above schemes, it can be seen that deformation of leaf spring in scheme 1 is large, top and root expand outward; in scheme 2, leaf spring is bent and formed in two times to ensure characteristics of top and root of leaf spring, so scheme 2 more reasonable.

2 Analysis of cause of deformation of shield spring

When formed shielding springs were put into storage for inspection, it was found that size of φ14.3 mm was out of tolerance, and forming consistency of each leaf spring was poor. Through analysis of production process of shielding springs, reasons for above problems were as follows.

2.1 Unreasonable stamping process

(1) Mold structure of bending forming II is shown in Figure 4. Leaf spring after bending forming I is placed in lower mold in forward direction. When bending and forming, it is positioned by middle positioning hole of shielding sheet spring, upper mold moves downward to complete forming of sheet spring, then upper mold moves upward. Due to special structure of part, shield spring has a small top and a large bottom structure. After bending, it will be tightly wrapped on upper mold. If shield spring is manually removed from upper mold, there is a possibility of deformation of leaf spring.
Die Design of Connector Shield Spring 
Figure 4 Bending Forming II Die Structure
1. Lower die base 2. Lower fixed plate 3. Die frame 4. Die die 5. Positioning nail 6. Guide post 7. Upper fixed plate 8. Backing plate 9. Upper die base 10. Punch 11. Push block
(2) Punching structure is shown in Figure 5. Shield spring is buckled upside down on lower mold, upper mold moves downward to complete punching. Considering removal deformation of leaf spring, outer diameter of lower mold is designed to be 0.05mm smaller than inscribed circle of shield spring. Due to relatively small tolerance, there will be deformation during manual pick-up, and shielding leaf spring will be obviously deformed. In Figure 6 (a), leaf spring on left side expands outward, and leaf spring on lower half of Figure 6(b) is concave inward.
Die Design of Connector Shield Spring 
Figure 5 punching structure
1. Lower die 2. Shield spring 3. Upper die
Die Design of Connector Shield Spring 
Figure 6 Shield spring after punching

2.2 Cleaning link

After removing burrs, put shielding spring into a circular carrier, use equipment for automatic cleaning and baking, and complete cleaning after 20 minutes. After inspection, no parts are found to be inserted or deformed, indicating that cleaning process does not affect deformation of leaf spring. .

2.3 Effect of material springback

Material of shield spring is beryllium bronze. Deformation factor is considered in mold design, and size of mold parts is designed accordingly. During stamping process, there is still reverse elastic deformation of a single leaf spring, which causes size of inscribed circle of shielding leaf spring to be inconsistent with design size. Considering influence of stress after forming, heat treatment is carried out after cleaning to eliminate stress generated during forming, and dimensions of parts are stable.

3. Improvement of mold structure

Due to deformation of parts after punching and impact of material springback, a shaping process is added after punching process to ensure that formed dimensions of parts meet requirements.
Figure 7 shows shield spring shaping die. During forming process, shield spring is deformed due to rebound and pick-up. Shaping die can eliminate two factors of springback and pick-up deformation. Mold design of pick-up link is very important. Considering convenience of taking parts, upper mold is designed according to size of inscribed circle of leaf spring to ensure that size of inscribed circle when shield spring is shaped. Root is designed to be smaller than size of inscribed circle, and springback compensation of part is considered. Shaping mold is composed of 4 quarter circles. It is open when it is not working. When it is working, the lower mold is embedded with a positioning core, top of positioning core is designed with a boss, which passes through inner hole of shield spring root and fits with bottom, is used for positioning when shield spring is shaped. When wedge moves downward and contacts slider, shaping die is closed to realize leaf spring shaping; when wedge moves upward and separates from slider, shaping die separates, and shielding leaf spring can be taken out from upper die to complete shaping. Leaf spring has a good size and no deformation, as shown in Figure 8.
Die Design of Connector Shield Spring 
Figure 7 Structure of plastic mold
1. Slider spring 2. Slider 3. Shaping insert 4. Shaping core 5. Upper die spring 6. Upper die base 7. Upper pad 8. Upper splint 9. Slanted wedge 10. Lower template 11. Positioning core 12. Lower backing plate 13. Lower mold seat
Die Design of Connector Shield Spring 
Figure 8 Shielding plate spring after shaping

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