Exchange of practical process technology for sheet metal products

Overview of sheet metal process
1. Definition

Sheet metal is a comprehensive cold working process for sheet metal (usually under 6mm), including cutting, punching/cutting/compounding, folding, welding, riveting, splicing, forming (such as car body), etc. Its remarkable feature is the same thickness of the same parts.

2. Basic process

Number blunt, blunt) - polishing - bending - fitter (boring, sink holes, tapping, riveting pressure) - welding  image - school - polishing - spraying back teeth - screen printing, assembly (school), packing

Two, the main process points of sheet metal

1, the number of flushing

1.1 Machining limits

1.11 Processing limits of sheet specification

1.111 Cold plate

Length: 0-2500

Width: 0-1250

Thickness: 0.8-2.5 (less than 1mm welding is very difficult, more than 2.5mm punching can not be processed (logarithmic punching loss is larger), can only take laser cutting, wire cutting, general punching (need open stamping die), milling, drilling and other means

1.112 Copper bar

Length: 0-1500

Width: 0-600

Thickness: 1-4mm, more than 4mm using shearing machine, general punching (need to open the die head)

1.1.2 Hole position limit

The distance between the hole and the hole, the hole and the edge

Factors to be considered: a. Overcome flanging effect;

B. Avoid punching the material. The harder the material, the greater the distance required;

C, avoid too large deformation, the denser the hole, the larger the deformation after processing.


The distance between the hole and the hole, the hole and the edge

Cold plate, red copper, brass, aluminum

0.5 T

Stainless steel

0.8 T

Note: T is plate thickness.

Minimum aperture


Minimum aperture

Cold plate, red copper, brass, aluminum


Stainless steel

1.5 T

Note: For square holes, the minimum side length is not less than 1.2mm. Too small square holes are easy to cause mold damage.

2. Bend

For design engineers, the main questions to consider are:

A. Bending interference problem;

B. Minimum hem: no less than 4 times the thickness of the plate, less than this limit may lead to greatly increased processing difficulty, or even impossible to process, in this case, should communicate with the process engineer.

C. Bending leads to the deformation of the hole: if the hole is too close to the bending line, it may be pulled and deformed by the mold.

Since bending is often determined according to the actual situation, maintaining the necessary communication with the process engineer can greatly provide design efficiency.

3, the general rush

Where possible, try to standardize, consistent, reduce mold costs, shorten the proofing cycle.

4. Fitter

Countersunk hole: It should be noted that the thickness of the plate is not less than the height of the countersunk screw head, otherwise the screw head will be higher than the plate, resulting in unstable fixation.

5, press riveting

5.1 If the thickness of the plate is less than 1mm, the riveting parts may fall off easily. In this case, the riveting parts can be increased or electric welding can be used after riveting to ensure the fastening strength.

5.2 Relationship between riveting screws and plate thickness


1.0 2.0 mm

2.0 2.5 mm

> 2.5 mm

Screw Specification

Below M5



5.3 Pressing riveting parts too far to the side will have two consequences:

A. After riveting, the edge of the plate will be deformed (the edge will bulge), and the hole will be offset 0.1-0.5mm to the edge;

B. The riveting position is too close to the hem, which will lead to the upper die cannot be pressed down: the distance between the outer edge of the riveting head and the hem is not less than 3mm.

5.4 The internal riveting of U-shaped bending parts should be taken into account whether the lower die can be attached to the workpiece. If other parts with relatively narrow internal space need the internal riveting, this problem should be taken into account.

5.5 The specifications of riveting parts should be unified as far as possible, which is convenient for suppliers to order, shorten the proofing cycle, and reduce the probability of riveting parts errors.

6. Welding

6.1 For the workpiece with relatively narrow internal space, if the inner side welding is needed, how to extend the welding torch should be taken into account.

6.2 When the thickness of the plate is less than or equal to 1mm, shrinkage holes or burning holes are easy to occur after welding, resulting in large welding deformation.

6.3 The welding of copper, aluminum and other materials is more difficult and requires higher technical level of welding workers.

7. Spraying

Spraying is mainly divided into the following three types (each including indoor and outdoor) :

Flat light: can be subdivided into matte, flat light, highlight, spraying layer thickness of about 60-90μm, about 90-120μm after back spraying.

Sand grain: can be subdivided into fine sand grain, coarse sand grain, spraying layer thickness of about 50-80μm, about 80-110μm after back spraying.

Orange lines: can be subdivided into small orange lines, large orange lines, spraying layer thickness of about 90-120μm, about 120-150μm after back spraying.

The thickness of the spraying layer in the position where the workpiece is easy to accumulate powder will exceed the above thickness.

7.1 Flat light: Advantages: beautiful appearance, good silkscreen effect; Disadvantages: spraying cost is high, spraying rework rate is high, it is easy to scratch, and the outer surface scratch can not be repaired, which is the most difficult to spray with highlight.

Avoid plain lighting if possible, especially for a large chassis. This is because a large chassis may be knocked during transportation.

7.2 Sand grain: advantages: not easy to scratch, spraying cost in the three lowest; Disadvantages: surface oil is not easy to remove, screen printing effect is not as smooth, orange.

7.3 Orange lines: Advantages: not easy to scratch, good screen printing effect, surface oil is easy to remove, spraying cost is slightly higher than sand lines, but far lower than flat. Cons: Slightly less aesthetically pleasing than flat.

7.4 The color of spraying should be as unified as possible, and the color of the company's mainstream products should be used to facilitate the supplier to order powder.

7.5 For each product, only one spraying color should be used to reduce the spraying cost (the processing time will be greatly increased when spraying multiple colors), and also reduce the probability of suppliers' spraying errors.

7.6 Silver powder should be avoided. Silver powder is a compound containing silver, the price of powder is twice that of ordinary powder, spraying is difficult, easy to produce bad products.

Three, sheet metal material introduction

1. Cold plate

Definition: Short for cold rolled steel sheet of ordinary carbon structural steel, hot plate is cold rolled and annealed to become cold plate.

Features: Good surface quality, high dimensional accuracy, due to annealing treatment, good machining performance, high surface quality, spraying adhesion. Common specifications for 0.5-2.5mm, more than 2.5mm material difficult to buy.

Common specifications: 2500*1250

Cost: Low

Materials are readily available.

2. Hot plate

Definition: Short for hot rolled steel plate.

Features: not annealed, machining performance is not good. The internal crystallization is not uniform, and the surface is easy to crack and rust. For the sheet metal of frequency converter, the hot plate is used when the plate thickness is greater than 2.5mm.

Cost: Low

Common specifications: 3000*1250

Materials are readily available.

3, galvanized sheet

Definition: A cold plate coated with zinc, generally referred to as a hot galvanized sheet. Galvanizing is a low cost, economical and effective means of corrosion prevention. About half of the world's production of zinc is used in galvanizing process. If the surface is not scratched, the corrosion protection period can exceed ten years.

Features: Machining performance is good, processing should pay attention to protect the surface, avoid scratches. Generally do not spray, spray adhesion is not as good as cold plate (before spraying do not do rust treatment, so as not to destroy the protective layer).

Cost: Slightly higher than cold plate

Common specifications: 2500*1250

Materials are readily available.

4. Electrolytic plate

Definition: Also known as electrogalvanized sheet, that is, the use of electrolysis, the formation of uniform, dense galvanized layer on the surface of the steel plate.

Features: machining performance is good, thin plate is not easy to weld, processing should pay attention to protect the surface, avoid scratches, generally do not spray, spraying sometimes pinhole (before spraying do not do rust treatment, so as not to destroy the protective layer). Compared with galvanized sheet, the corrosion resistance is better.

Common specifications: 2500*1250

Cost: High

Materials are not easy to buy, too few suppliers will not sell.

5, coated with aluminum zinc plate

Definition: A hot plating process is used to coat the surface of a steel plate with 55% aluminum and 43.4% zinc and 1.6% silicon.

Features: good machining performance, processing should pay attention to protect the surface, avoid scratches, generally do not do spraying treatment. Compared with galvanized sheet, corrosion resistance is better, high temperature is not easy to oxidation discoloration, beautiful appearance. The surface pattern is divided into large flowers, medium flowers and small flowers.

Common specifications: 2500*1250

Cost: High

Materials are not easy to buy, too few suppliers will not sell.

6. Copper material

It is mainly divided into red copper (also known as red copper), brass and bronze. At present, Guixi is the largest copper smelting base in Asia with high quality. Our company selects Guixi copper to purchase copper materials.

7. Insulation materials

7.1 Bakeries: high hardness, machining difficulty, easy to crack, the design should consider the hole location should not be too close to the edge, the edge should be greater than 2mm, too close to the hole will reduce the processing speed, and easy to produce waste. At present, bakelite is of the best quality as recommended by your company. However, the maximum thickness of bakeries in Taiwan Xindai is 50±1.5mm. Bakeries over 50mm can only be made of domestic materials (which need to pass the insulation performance test).

7.2 PVC: The hardness is between bakeries and nylon, the machining difficulty is small, the material can be tapped, the cost is the same as domestic bakeries, lower than Xindai bakeries.

7.3 Nylon: The material is soft, the machining is difficult, and the cost is similar to that of Xindai bakeries, so it is not recommended.

4. Suggestions on sheet metal design

1. Universal fasteners

2. Avoid opening special molds as the first choice in the design, and try to find alternative solutions as far as possible. It is not too late to open molds after the large batch.

3. It is suggested to communicate more with the process engineer of the supplier.

5. How to estimate sheet metal working cycle

Estimation of new product processing cycle:

Project expansion: 3 days below 55KW; Over 55KW: 3-5 days

Machining: 4 days

Spraying and assembly: 2 days

Vi. NCT mold introduction

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Pangyi Metalware (Shanghai) Co., Ltd.


Tel:13801763818(Mr. Pang)

Pangyi Metalware (Shanghai) Co., Ltd.

Add:No.555 Longpan Road, Malu, Jiading District, Shanghai, China

Pangyi Metaware (Shanghai) Co., Ltd.


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