Optimization of the Forging Process for a Kind of Flange

Take a flange forging process system optimization as an example, to provide a systematic thinking approach to optimize the process, reduce costs, improve efficiency, and enhance the core competitiveness of enterprises.

1. System optimization

The product is shown in Fig. 1, the material is 40Cr, the quality of forging is 2.485kg, and it is tempered. The billet Φ90mmx(58±1)mm with the mass of 2.90kg is used, and the utilization rate of the billet is 85.7%.
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Fig.1 Forging drawing
The conventional process flow is as follows: material preparation (automatic band saw machine) – heating (medium frequency) – upsetting to remove oxidation, pre-forging and final forging (2500t hot-die forging press) – edge cutting (315t press) – heat treatment (including quenching and tempering process, tempering production line) – shot blasting (GN15 shot blasting machine) – testing – packaging into storage.
For the above process flow, the whole process flow of human, machine, material, method, environmental elements of the system to optimize.

1.1 Product analysis

By analyzing the product, we firstly start from the use of forgings and fully understand the requirements of forgings. Since the flange is a high-speed moving part, the machining allowance is relatively large, and in order to ensure its final accuracy, the allowance is reset according to the characteristics of the forging process in the forging design, so as to reduce the cost and meet the accuracy requirements, and the die slope of the outer surface of the forging is changed from 2.5° to 1° [1].

1.2 Designing the process scheme

By re-evaluating the process flow, a reasonable process plan was designed.

1.2.1 Optimization of the downfeed process

In some forging enterprises, the focus is on the investment and improvement of forging equipment, and the process optimization of the downfeed process is often neglected, but it contains high economic benefits. Generally, sawing machines are used for downfeed, and semi-automatic and fully automatic band saws are commonly used, which have corresponding problems such as saw blade consumption, sawing loss, low downfeed efficiency, large space occupation, and contamination of sawing machine cutting fluid. Now many manufacturers use bar shear equipment, but the slope of the section is large, serious deformation. Bar shear combined with the use of constrained shear technology, it can well ensure the quality of the section, both to improve production efficiency and reduce production costs, mainly for large quantities of products, the requirements of the bar is not too large in diameter, the general diameter of 90mm or more bars should not be directly shear. Here, the original billet of Φ90mmx(58±1)mm is changed to Φ60mmx(112±0.5mm), and the bar is sheared by bar restraint, so that the accuracy of undercutting is greatly improved.

1.2.2 Optimization of heating process

Medium-frequency heating is one of the methods of less oxidation-free heating, with high heating efficiency and fast heating speed, which meets the requirements of mass production. Medium frequency heating adopts automatic loading mechanism, eliminating manual loading; the heating temperature is automatically sorted by infrared detection in three ways, and the temperature of the billet is stable after sorting, which provides conditions for the subsequent implementation of forging automatic line.

1.2.3 Forging process optimization

The billet is Φ60mmx(112±0.5mm), compared with the original Φ90mmx(58±1)mm, the deformation volume of upsetting step is increased, which is good for removing the oxide skin generated during heating. At the same time, due to the large deformation, after upsetting, pre-forging and final forging, the flow line of the metal is basically the same as the profile of the forging, which is conducive to the service of the part under high temperature and high pressure and high-speed alternating load conditions, and improves the performance of the forging.
As the beginning of the conventional open-die forging process, the corresponding forging accuracy will be lower than the precision forging process, there is a large die wear, low life and wrong die and a series of problems. If it can be changed to closed precision forging, it can not only improve the accuracy and eliminate the wrong die but also reduce the edge cutting process, eliminate the consumption of waste edge, save the edge cutting equipment, edge cutting dies and edge cutting operators, reduce the cost and improve the production efficiency. For this reason, modern forging process simulation technology is used to simulate the process and find the most reasonable forming solution.
Pro/E solid design software was used for the die design, and the solid was designed according to the forging drawing (as shown in Figure 2), and the corresponding shrinkage ratio was set according to the forging temperature to form the hot forgings, and the pre-forged parts were designed according to the principle of equal volume [2]. The tooling module of the software is used to design the pre-forging die and the final forging die (shown in Fig. 3), and the structure of the die is made by inserting blocks to reduce the die production cost, facilitate the replacement and improve the die life.
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Fig. 2 Forging model
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Figure 3 Pre-forging and finish forging dies
Deform 3D solid simulation software is used to verify and improve the design. It saves the cost of design trials, identifies problems in advance development, takes measures to reduce forging defects, shortens the development cycle, reduces development costs, and verifies the reliability of the die in advance.
The simulation involves: the forming process of the billet and possible folding and filling defects; the energy required for forging (from upsetting, pre-forging to forming steps), which is used as a basis for selecting equipment; whether the internal fiber flow of the forging is reasonable, requiring no sharp changes and basically consistent with the shape of the forging; changes in the temperature field of the forging, the heat generated in the deformation does not cause the forging temperature to rise sharply The temperature field of the forging changes, the heat generated in the deformation does not make the temperature of the forging rise sharply, forming overburning, nor does it decrease too quickly, causing the forming force to increase too quickly, while also meeting the requirements of forging afterheat quenching; the stress of the forging is within the range of use of the die, so that the die does not fail too quickly, thus improving the service life of the die and ensuring the stability of the quality of the forging process. The simulation results are shown in Fig. 4-11, which meet the design requirements.
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Fig.4 Pre-forging and finish forging dies
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Fig.5 Pre-forging
Make full use of modern technology and equipment to reduce the cost. The use of controllable energy forming equipment, program control, and automation with robots can eliminate the fluctuation of quality caused by the randomness of human operation, thus improving stability, reducing quality loss, and reducing labor costs. In the actual production, to ensure the match between pre-forging and final forging and the effect of final forging filling, the pre-forging energy is reduced by 5%~10%, and the final forging energy is increased by 5%~10% within the range of die stress. The quality of the process is optimized by making full use of modern monitoring, control and robotics.
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Fig.6 Finish forging
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Fig.7 Upsetting, pre-forging, finish forging load
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Fig.8 Temperature of the forging in the end
The electric screw press is simple in structure, reliable in operation, and programmable in energy [3]. The electric control part adopts the advanced technology of international famous brand companies, and is connected with the robot to form an automatic production line, which is a turnkey project and provides a better optimization platform for the process designer and layout. The equipment has a simple structure, low maintenance cost, low investment and short payback period.
Here, two robots are used for precise production control of the two electric screw presses in the forging process (as shown in Figure 12). One robot is responsible for taking the material from the intermediate frequency, upsetting and pre-forging the billet, and the other robot is responsible for putting the pre-forged parts into the final forging die cavity, and then taking out the final forging parts and quenching them in the forging afterheat quenching line, and so on. The die lubrication and cooling of the forging process is done by automatic spraying device, which is controlled by the electrical system integrated with the forging line, replacing the harsh environment and intensive manual operation with robot operation, reducing labor cost and improving process quality.
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Fig.9 Stress of the forging in the end of finish forging
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Fig.10 Metal flow in upsetting
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Fig.11 Metal flow of in the end of forging
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Fig.12 Layout of robots and equipments
As the closed forging process is adopted, the process of cutting the scrap edge, equipment and personnel consumption and the corresponding process quality loss are directly eliminated, and the forgings are quenched directly by forging waste heat.

1.2.4 Heat treatment process optimization

Forging waste heat quenching is a high-temperature deformation quenching, the use of this process to produce forgings with better performance than conventional heat treatment of forgings. By analyzing the metallographic organization of the forgings, it is found that the organization is coarser, but does not affect the use of forgings. Forging waste heat tempering compared with conventional tempering, saving the heating required for quenching, saving a heating energy loss, eliminating the need for quenching equipment and personnel operations, with significant economic benefits, in line with the national industrial policy of green manufacturing. Shot blasting process and subsequent inspection in the process optimization space is small, but is also an important process, shot blasting process in strict accordance with the requirements of the process documentation to implement the shot blasting time and attention to the ratio of old to new steel shot, inspection in strict accordance with the requirements of the work instructions frequency and project implementation of the inspection, fill in the inspection records.
Initially set the optimized process plan for: bar shear restraint – with automatic feeding and temperature sorting medium frequency heating – upsetting to remove the oxide, closed pre-forging and closed final forging forming (respectively 603t and 1000t electric screw press combined die forging, 2 ABB forging robot) – forging After heat treatment – shot blasting cleaning – inspection – packaging into storage.

2. Comprehensive benefit analysis

Through the optimization of the system, the comprehensive benefit analysis is as follows.

  • 1) Material saving. By understanding the customer’s requirements and communicating with the customer, the machining allowance of forging parts is reduced and the die slope is reduced. By using closed forging, the amount of raw material billets used is reduced.
  • 2) Reduction of material consumption. The consumption of saw blade is reduced, the cutting fluid is reduced, the cutting edge die is reduced, the service life of forging die is improved, and the consumption is reduced.
  • 3) Energy saving. The reduction of billet makes the heating consumption of excess material reduced. The use of forging waste heat quenching reduces the energy consumption of heating and quenching.
  • 4) Quality level is improved and quality cost is reduced due to the adoption of automated forging processes such as advanced robots.
  • 5) The customer’s finishing cost is reduced because the machining allowance is reduced, the quality is stable, and the overall efficiency is improved.
  • 6) The performance of finished products is improved and the fiber flow is more reasonable, so that the advantages of forging parts can be fully utilized.
  • 7) Reduce the operation of personnel, improve the stability of the process, and improve the efficiency.
  • 8) Less investment in equipment, low depreciation of fixed assets, short return on investment cycle.

3. Economic benefit calculation

The product batch is large, and the annual output of 300,000 pieces is calculated as follows: reduction of cost per piece (material saving + energy saving + reduction of tooling consumption + personnel salary + amortization of fixed assets) x 300,000 pieces; intangible benefits, such as stable product quality, customer satisfaction, environmental improvement, employee satisfaction, low cost and good benefit to the enterprise, market expansion to form the scale benefit, the enterprise will get high speed development, etc.

  • 1) Optimization benefits of the undercutting process. Reduce the consumption of saw blade and tool, reduce the loss of forging raw material sawing, improve the efficiency, improve the environment, and reduce the pollution of chip liquid. The consumption of saw blade for downfeed: 260 RMB per saw blade for downfeed, each saw blade for downfeed specification is Φ90mm, material is 40Cr, can saw 1000 pieces, then the cost of saw blade is 0.26 RMB per piece; using bar shear, tool price is 2000 RMB, can downfeed 100000 pieces, the consumption of tool is 0.02 RMB. The loss of sawing slit: 2mm sawing slit, specification is Φ90mm, material is 40Cr, quality is 0.1kg, material price is 5RMB/kg, sawdust is 1RMB/kg, then the loss of sawing slit is 0.4RMB.
  • 2) Material saving. Blanks Φ90mmx58mm, mass is 2.895kg; blanks Φ60mmx112mm, mass is 2.485kg, the price of scrap edge is 2 yuan/kg, saving 1.23 yuan.
  • 3) Energy saving. Medium frequency heating saves 0.205 yuan; heat treatment quenching saves 0.994 yuan.
  • 4) Reduce labor cost. The original forging line is operated by 5 people, after optimization only 1 person can maintain the production, according to 50,000 yuan / person, saving 200,000 yuan.
  • 5) Depreciation of fixed assets. 2500t hot die forging production line with total investment of 15 million RMB and electric screw press automatic production line with total investment of 5 million RMB, depreciated in 10 years and annual output of 1 million pieces, saving 1 yuan/piece, direct economic benefits: according to annual output of 300,000 pieces, saving 9200,710,000 RMB, in addition to saving 300,000 RMB in asset amortization and 200,000 RMB in personnel salary.

4. Problems that need to be improved

The machining allowance of forgings here is only related to the process dressing of forgings – the reduction of die slope, but not with the customer to achieve the real sense of reducing the machining allowance, further communication is needed to achieve from the beginning of product design to participate in the design of forgings, to make full use of modern forging technology, such as cold, warm We can make full use of modern forging technology, such as cold and warm forging, to achieve lean production. In addition, the choice of materials is also an important direction of forging process improvement. Although the use of forging waste heat quenching process, saving the cost of quenching and heating, but compared with non-quenched
Steel compared to a certain gap. This requires forging manufacturers and product designers, and even steel manufacturers to communicate and interact, and jointly promote the establishment of joint development, benefit-sharing mechanism. Through the above examples, we can see that innovation and process optimization have a very broad prospect and are good opportunities for the development of enterprises. Of course, management innovation can promote process improvement and technological innovation, and the two can promote each other, which will certainly inject vitality and provide development space for the enterprise.

5. Conclusion

By systematically optimizing the process, combining advanced equipment and mature automation technology such as forging robots, and using software simulation technology for verification, we can effectively reduce the production cost of forgings, improve the quality of the product process, improve the production environment, promote green manufacturing, obtain better economic benefits, and enhance the core competitiveness of enterprises.

Authors: Ding Jingen,Xu Baoguo,Xu Hao

Source: China Flange Manufacturer – Yaang Pipe Industry (www.steeljrv.com)

(Yaang Pipe Industry is a leading manufacturer and supplier of nickel alloy and stainless steel products, including Super Duplex Stainless Steel Flanges, Stainless Steel Flanges, Stainless Steel Pipe Fittings, Stainless Steel Pipe. Yaang products are widely used in Shipbuilding, Nuclear power, Marine engineering, Petroleum, Chemical, Mining, Sewage treatment, Natural gas and Pressure vessels and other industries.)

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References:

  • [1] Forging and Pressing Society of Chinese Engineering Society. Forging and pressing manual volume 1 forging [M]. Beijing: China Machinery Industry Press, 1993.
  • [2] Zhan Yougang. Pro/ENGINEER English wildfire version of the tutorial — special module [M]. Beijing:Tsinghua University Press,2004.
  • [3] RICCARDO Bossi. Forging system using “direct drive hao screw press” [C]. Proceedings of the 3rd Asian Forging Conference. Beijing: China Forging and Press Association, 2010:135-141.

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