Stamping process and equipment selection
Prerequisites for stamping line planning
The printing production conditions in the factory face several important problems due to the increasing production of new models and the increase in quality standards in the printing industry. These problems require urgent solutions.
(1) Overload of large stamped parts
The production of large stamped parts is expected to intensify in the coming years and could reach or even exceed 150% of production capacity, according to the production program. The issue cannot be resolved because there is no capacity for mass production of large-scale stamped parts in the surrounding areas. To solve this problem, large-scale stamping production lines must be added.
(2) Quality assurance capability
With increasing quality requirements in the medium and heavy commercial vehicle market, the factory needs to improve its stamping quality assurance capabilities to meet quality standards, improve efficiency and reduce costs. Improving quality assurance capability is a comprehensive improvement project covering the entire stamping process, from raw material preparation to stamping production, storage and logistics. The factory must change and improve its production conditions and management level.
(3) Insufficient press tonnage
The introduction of high-quality commercial vehicle models has not only increased the large-scale parts production load at the factory (by 20 streams), but also the demand for press tonnage. Currently, the largest press has a nominal tonnage of 1,600 tons, but actual demand for the bulk exceeds 2,200 tons. Based on a comprehensive analysis, it was concluded that a higher tonnage press is required, with a maximum nominal tonnage of 2,400 tonnes, in line with the company's product development plan and industry rules.
(4) Low production efficiency and high labor intensity
The factory's stamping production lines are manual and low-efficiency, with SPH less than 240 times. Workers also face high labor intensity, moving more than 10t of quality in a single shift, with a maximum of 15t.
To resolve these issues and improve safety, environmental protection, inventory management and technology, the following actions are required:
(1) Clean, transform and integrate existing conditions to meet the needs of the phased construction of the “Centro de Estamparia” project.
(2) Upgrade a 630t unwinding shutter line.
(3) Add a new 2,400 ton automated stamping production line.
(4) Complete supporting facilities including mold processing, scrap line, lifting equipment, logistics equipment and station apparatus.
Production process and equipment
The production process of the stamping shop mainly involves the creation of stamping parts and parts, as well as auxiliary tasks such as mold testing and repair, stamping part repair, and waste transportation.
(1) Blank production
Blanking refers to the process of transforming coils into blanks necessary for the production of stamped parts. The production process involves:
- Coil Feed
- Unwinding
- cutting head
- Cleaning
- Leveling
- Feeding
- Suppression or cutting
- Stacking
To meet the demands of blank production, the workshop must have a fully automatic unwinding blank production line or a fully automatic slitting production line. The former can perform both cutting and trimming, while the latter is only suitable for cutting.
Figure 1 illustrates an example of a blind unwinding line.
Figure 1 Unwinding the blind line
Given the relatively high cost of an unwind cutting line, it is important to consider the cost-effectiveness of its configuration. Typically, one unwinding slitting line can correspond to the output of three fully automatic mechanical stamping production lines, and the choice of equipment should be based on the product and production requirements of the workshop.
(2) Printing Production
The stamping production process for large-scale cover parts includes deep drawing, cutting, flanging, forming, punching and shaping. The process is adjusted and matched based on the shape and structure of the printed parts.
For example, the typical production process for a door frame is as follows:
- Unstacking and feeding device
- Drawing training
- Trim and drill
- Oblique wedge cutting and drilling
- Flange Modeling
- off
For superior coverage, the process is:
- Unstacking and feeding device
- Drawing training
- Trim and drill
- Flange and oblique wedge shaping
- Shaping and drilling
- off
The arrangement of press connections for stamping production requires determining the number of presses based on the forming process of the stamped part and the shape of the stamping die. There are three, four, five and six orders, with four orders being the most commonly used. However, it is important to consider the complexity of mold design and the increased cost that can result from a complex die.
The parameters of the pressing equipment such as rated pressure, table size and clamping height must be determined based on the product process. The choice of the number of printing lines depends on the product, production and productivity of the printing line.
The formula is:
the number of pressing lines = ∑ (number of mold sets × production schedule) ÷ pressing line productivity (ASPM) ÷ equipment annual time base.
- The number of mold sets and production guidelines are established during the planning phase.
- The productivity of the press line is linked to the operating speed of the press and the mode of transportation of the stamped parts. The operating speed of the press is an inherent value of the equipment, and there are two ways of transporting stamped parts: manual loading and unloading and fully automatic loading and unloading (which can be divided into robot and manipulator). The transport speed of the manipulator is the fastest, followed by the robot, and the manual transport speed is the slowest. The cost of investment follows the same trend.
- The equipment's annual time base can be obtained from the “Design Standards for Machinery Factory Annual Time Base” or other relevant documents and regulations according to the company's system.
Figure 2 shows a fully automatic stamping production line with 1 2,400 ton press and 3 1,000 ton presses.
Figure 2 Automatic stamping production line 1×2400t+3×1000t
(3) Auxiliary Area
- Die repair
A simple machine repair setup is typically located in the stamping shop for convenient daily die repairs.
If the production line has a high loading rate, it may be necessary to establish a test press in the mold repair area. The specifications of the trial press must match those of the largest piece of equipment on the production line.
- Waste Transport
Stamping production generates punching waste, so it is advisable to set up a waste conveyor line to collect and dispose of waste, based on the press line.
- Repair of stamping parts
For online loading and unloading of stamped parts, a finishing area must be established to remove burrs and correct surface defects of the stamped parts.
Workshop layout and logistics
The workshop layout is designed based on the stamped parts production process.
The stamping workshop normally consists of areas for coil storage, unwinding and stamping production, blank stacking, mold stacking, mold maintenance, stamping production, temporary storage of stamped parts and maintenance of stamped parts, among others.
Additionally, the workshop includes a waste room, a forklift storage area, an office area and a lounge area.
Figure 3 illustrates the layout of the printing workshop.
Figure 3 Schematic diagram of the printing shop layout
The logistics flow in the stamping workshop is well defined, mainly including the following routes:
(1) The logistics route for stamping production is shown in Figure 4.
Figure 4 The logistics route of stamping production
(2) Molds, the logistics route of the molds is illustrated in Figure 5.
Figure 5 Logistics route of the stamping die
Civil engineering and public support requirements
Once the production program, technology and equipment of the stamping shop have been established, the necessary civil engineering requirements must be identified to meet production needs.
Civil work
(1) Workshop size
- Workshop extension
The size of the workshop is mainly determined by the type of die change in the press. There are three main forms of top die in the press: front top die, side top die and left and right top die. The upper front matrix has the smallest area, with a workshop with a span of 15 meters being sufficient. The upper side matrix has a slightly larger area and requires a workshop span of 24 meters. The upper left and right molds have the largest area and are mainly used in fully automatic production lines for greater efficiency, which requires a workshop span of 30 or 36 meters. The stamped parts warehouse requires a gap of at least 24 meters to facilitate transport with forklifts.
- Workshop duration
The length of the automatic stamping production area is generally about 60 meters, based on the layout of the press in the gap. The length of the die stacking area needs to be determined based on the number of dies. If there is only one stamping line, the length of the workshop is normally about 120 meters. If there are many matrices, the workshop may need to be expanded accordingly. The corresponding unwinding suppression period also requires a length of 120 meters.
- Column Distance
To accommodate large presses for transportation and minimize mold transportation and equipment maintenance costs, column spacing in the stamping shop is set between 9 and 12 meters.
- Workshop Height
The height of the pressing shop is determined by the height of the press. For large roofing pieces, the maximum press is usually 2,400 tons, with a height of 11 to 11.5 meters above the ground. The height of the top of the crane rail in the workshop, considering safety distances, is 13 to 14 meters, and the roof truss of the stamping workshop is fixed at a lower rope height of approximately 17 meters based on the selected height of the crane. The choice of press and crane has a significant impact on the height of the workshop. The height of the blind unwinding span is determined by the press on the blind unwinding line, with an upper rail height of 12 meters. The height of the stamped parts warehouse is based on the height and number of layers of the stamped parts stack, and for forklift transportation only, it is generally 7 meters.
(2) Architectural Forms
Press shop construction typically comes in three forms: concrete frame, steel frame, or steel-concrete frame, depending on the specific project requirements.
In the past, concrete was the main material used in the construction of stamping workshops. However, now, due to the cost-effectiveness of steel structure and its simple and efficient production and installation process, as well as the shorter construction period, steel structure has become the preferred material for most workshops. Press Shop.
The workshop floor must be clean and durable. Both epoxy resin flooring and high-strength, wear-resistant flooring are suitable options, while steel sand flooring is recommended for more demanding environments.
(3) Loading requirements
- Press Load:
The press load depends on the weight of the press itself, the weight of the die changing cart and the weight of the die. It is important to consider dynamic load when calculating press load, as mechanical presses generate a significant impact load during operation.
- Crane load:
In the stamping workshop, cranes with a capacity of 32t and 50t are usually used. Deadweight, wheel pressure, wheelbase and other parameters should be determined based on the crane's product specifications.
- Floor load:
Most of the stamping shop area, excluding the pressing line area, is used for mold stacking. Typically, the number of stacking layers is two, resulting in a floor load of approximately 100kPa. The stacking area of coils or sheets should be determined based on the stacking method. If specialized racking is used for stacking and exceeds the second floor, the floor load must be considered at 150kPa.
- Pipeline load:
The pressing workshop has water, electricity, gas, air and fire fighting pipes on the pillars, and their loads must be considered in the calculation. In addition, an electrical cabinet platform near the press line is generally required to accommodate the press and automation device power distribution cabinet, and the column load must also be taken into consideration.
(4) Press Foundation
The foundation of the automated press line in the pressing shop is a critical aspect of civil engineering and has three types: independent foundation, direct foundation and underground foundation.
An independent foundation refers to each press in the press line having its own separate foundation, not connected to each other. This method is the cheapest, but requires each piece of press equipment to be unloaded and transported individually within the workshop, which significantly impacts production and logistics in mass production. Therefore, this form is not commonly used.
Through foundation involves establishing the foundation for each press and installing a waste conveying line within the foundation to collect the stamping waste and transport it to the waste room. This form separates waste logistics from production logistics, making press maintenance more convenient, and is currently most widely used.
Basement foundation involves building a basement within reach of the press or placing the press line on the second floor. This shape creates a large space for the press foundation, which can also accommodate public power, power distribution facilities and some maintenance areas, effectively increasing the usable area of the workshop. However, this form is not frequently used due to its high cost.
The basis of the through-type press varies depending on the equipment, with product data differing between different suppliers. Typically, a 4-station press line pit has a net width of 9.5 m, a depth of 7 m and a length of approximately 35 m. A well must also be established for the main line of the waste transportation line, connected to the pressing well and arranged vertically. Its depth is equal to or less than that of the press pit, with an approximate width of 4m.
P public power auxiliary facilities
Public support facilities at press offices are generally basic.
Water, electricity and gas are essential for the equipment, while the decision to include facilities such as air conditioning, heating and dehumidification depends on the specific requirements of the project.
(1) Electricity:
Electricity is the main source of energy used in stamping factories, especially in the automatic stamping line and the unwind stamping line. As such, shop transformers are positioned as close to the equipment as possible.
(2) Compressed air:
The main areas of compressed air in the stamping shop include stamping equipment, mold repair and stamping part repair. Compressed air must meet the following quality standards: air source pressure of 6 bar, oil content of 25 mg/m3, particle diameter of 40 μm and particle content of 10 mg/m3.
(3) Cooling water circulation:
Circulating cooling water is mainly used in pressing equipment. The inlet water temperature must be 32°C, while the outlet water temperature must be 37°C. Soft or pure water is necessary to prevent scale damage to equipment.
(4) Other considerations:
- Fire protection:
The stamping workshop falls into production category E and does not have specific requirements for fire protection or smoke exhaustion.
- Environmental Protection:
The main environmental impact of the pressing workshop is the noise generated by the production of the press and the vibration and noise from the waste conveyor lines. To mitigate these impacts, the doors and walls of the pressing shop must use soundproof materials and the windows must have double vacuum glazing. Additionally, vibration isolation pads must be installed under the press to reduce the effects of noise and vibration on the surrounding environment. Furthermore, when planning the layout, consideration should be given to minimizing the proximity of homes, schools, hospitals and other civil facilities to the stamping shop.
Workshop staffing planning
Compared to manual lines, the number of workers per shift is significantly lower on automatic lines. This change in personnel requires a shift from manual stamping workers with high physical labor demands to highly skilled automation operators. As can be seen from Table 1, the physical labor intensity of workers is reduced.
| Production mode
Kind of work |
Automatic line staff structure | manual line personnel structure | Observation |
|---|---|---|---|
| Monitor | 1 | 1 | single line
single shift |
| Performance monitor | 1 | ||
| Stamp | 18 | ||
| Low paid staff | 1 | ||
| Website management | 1 | ||
| stamping operator | 1 | ||
| Preparing for automation | 1 | ||
| Engineering quality | 1 | ||
| Crane operator | two | 1 | |
| To check | two | 1 | |
| Packaging | 3 | 3 | |
| To repair | 3 | 1 | |
| Deliver | 3 | 3 | |
| Storage | two | 3 | |
| Total | 22 | 31 |
Compared to the manual line, the main factor behind the significant disparity in personnel is the focus on production stability and quality stability. The automated line has a production capacity three times greater than that of the manual line.
As a result, there is a need for a greater number of people to handle equipment and maintain dies to ensure stable production. Furthermore, a significant increase in the number of online inspectors is needed to detect quality problems early and maintain quality stability. It is important to note that new employees will need to be trained to acquire the necessary skills and qualities.
Conclusion
The pressing shop has a heavy workload and requires high standards of civil engineering and infrastructure. This article provides a comprehensive overview of various aspects involved in designing a stamping shop from an engineering design point of view. The aim is to serve as a reference guide for process technicians responsible for designing this type of workshop.
