"Mold Industry" 2001. No. 4 Total 242 40

Application of laser processing technology in mold manufacturing

Jiangsu University of Science and Technology (Jiangsu Zhenjiang 212013) Zhang Ying, Zhou Jianzhong and Dai Yachun

[Abstract] As laser processing technology becomes increasingly mature and the price of industrial high-power laser equipment gradually declines, the manufacturing process of products and molds has brought In order to achieve new changes, the laser optimization mold manufacturing process was analyzed and discussed in detail in three aspects: mold manufacturing, mold surface strengthening and maintenance, and mold replacement.

Keywords Mold laser process optimization

[ Abstract ]Wi t h t he mat uri ng of t he las e r p r oces si ng t echnology and t he dec r easi ng of p rice of t he

i ndus t rial la r ge - p owe r las e r e quipme nt , a new i nnovat ion was br ought t o t he manuf act uri ng

t echnology of t he p r oduct s and t he dies and moulds . molds f r om t hr e e asp ect s of

manuf act uri ng , s urf ace r ei nf orceme nt and mai nt e nance , and s ubs t i t ut ive dies or moulds .

Key words die and mold , las e r , t echnological p r oces s op t imizat ion

1 Introduction

Fierce market competition makes manufacturing companies respond to the market quickly

Requirements such as demand and first-time manufacturing success are increasingly urgent. In the conventional manufacturing system, the design, manufacturing and assembly and debugging of a large number of molds required for product production not only consume a lot of money, but more seriously, extend the production time.

The preparation time for product production is extended, thereby extending the new product development cycle,

forming a bottleneck in the manufacturing process. Therefore, how to quickly and effectively produce high-quality, low-cost molds and products has become a topic that people are constantly exploring. As laser processing technology becomes increasingly mature and the price of high-power laser equipment for industry declines, major changes have been brought to product and mold manufacturing processes. This article discusses the application of laser processing in mold manufacturing in three aspects: mold manufacturing, mold surface strengthening and repair, and mold replacement.

2 Mold Manufacturing

2. 1 Laser superposition manufacturing of molds

In 1982, Professor Nakagawa and others from the University of Tokyo in Japan proposed using

launched the laser superposition manufacturing method of molds and obtained a patent. The process flow is shown in the figure. 1. The principle is to superimpose multiple layers of laser-cut thin plates,

and gradually change their shape, and finally obtain the required three-dimensional geometric shape of the mold.

Japan has reached a practical stage in the laser superposition manufacturing of stamping dies. The convex and concave dies produced are of high quality and have high processing dimensional accuracy

— — — — — — — — — — — — — — — —

Date of receipt: August 10, 2000

It has reached ±0. 01mm, and the cutting thickness is 12mm.

After laser cutting, a hardened layer with a depth of 0. 1 to 0. 2mm and a hardness of 800HV is formed on the surface of the cut. It is used to punch 1mm thick steel plates. The self-cooling hardened layer can stamp 10,000 pieces. If it is flame quenched after laser cutting, 30,000 to 50,000 pieces can be stamped. Since the connection between the thin plates is simple,

using the superposition method to make the die can reduce the cost by half and greatly shorten the production cycle.

It has achieved significant economic benefits when used to manufacture composite dies, blanking dies and progressive dies.

Figure 1 Laser superimposed mold manufacturing process flow

Mold CAD and laser cutting are combined to form a complete mold CAD/CAM system

to realize sheet metal processing Cutting FMS is suitable for small batch production of multiple varieties. A manufacturing system that uses laser-cut thin plates to superimpose

synthesize arbitrary three-dimensional surfaces not only provides ideas for the implementation of FMS in the plastic processing

and mold fields, but also for internal

>

Mold manufacturing with complex internal structures, such as holes, mesopores and complex cooling pipes

is also an effective method to manufacture molds quickly and economically.

And can drive the development of other technologies such as solid phase diffusion.

2. 2 Rapid Mold Manufacturing

Mold CAD

Three-dimensional design

Two-dimensional shape

NC program

Laser

Cutting

Removal

Steps

Wound level

Finishing

Forming

Mold

Assembly

Assembling

Sheet

Link

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Finishing

NC Program

Mold Manufacturing Technology "Mold Industry" 2001. No. 4 Total 242 41

Rapid prototyping manufacturing technology ( RPM) is a manufacturing technology that emerged in the late 1980s. At present, RPM technology has developed more than a dozen process methods. Most of the methods for quickly manufacturing molds based on RPM technology are indirect molding methods, that is, using RPM prototypes to indirectly make molds.

(1) Production of soft simple molds (such as automobile panel molds)

Use silicone rubber, low melting point alloy, etc. to accurately copy the prototype into a

mold, or use metal spraying or physical evaporation deposition

to coat the surface of the prototype with a layer of extremely low melting point material alloy to make molds. The life of these simple molds is 50 to 5,000 pieces. Due to their low manufacturing cost and short production cycle, they are especially suitable for small batch production in the trial production stage of products.

Production.

(2) Steel mold production. RPM prototype — — — Three-dimensional grinding wheel

— — — Integral graphite electrode — — — Steel mold, a medium-sized and relatively complex electrode can generally be completed in 4 to 8 hours. Ford Motor Company of the United States

Using this technology to manufacture automobile panel molds has achieved satisfactory results.

Compared with traditional mechanical processing of molds, rapid mold manufacturing eliminates the need for rapid mold manufacturing

Time-consuming and expensive CNC processing is eliminated, the processing cost and cycle are greatly reduced

and it has broad application prospects.

3 Mold surface strengthening and repair

In order to increase the service life of the mold, it is often necessary to strengthen the mold surface

. Commonly used mold surface strengthening treatment processes include chemical treatment (such as carburizing, carbonitriding, etc.), surface composite treatment (such as overlay welding, thermal spraying, electroplating, etc.) Spark surface strengthening, PVD and CVD, etc.) and surface processing strengthening treatment (such as shot peening, etc.). Most of these methods have complex processes, long processing cycles, and large deformations after processing. Laser technology is used to strengthen and repair molds. It has the advantages of great flexibility, high surface hardness, short process cycle, and clean working environment, so it has strong vitality.

3. 1 Laser phase change hardening

Laser phase change hardening (laser quenching) uses laser irradiation to

the metal surface to make the surface very The high heating rate reaches the phase transformation temperature

degree (but lower than the melting temperature) to form austenite. When the laser beam leaves

, spontaneous austenite occurs by utilizing the heat conduction of the metal surface itself. Quenching causes the martensitic transformation of the metal surface to form a surface layer with high hardness and wear resistance, thereby strengthening the metal surface.

The equipment used is a three-axis CNC laser processing machine.

The main factors that affect laser intensification are laser power, spot size

and scanning speed. During the strengthening process, these parameters should be optimized

and appropriate laser processing parameters should be selected for specific materials. For common mold materials

CrWMn, Cr12MoV, Cr12, T10A and Cr-Mo cast iron, etc., after laser treatment, their structural properties are relatively normal

Regular heat treatment is generally improved. For example, when CrWMn steel is conventionally heated, it is easy to form network secondary carbides on the austenite grain boundaries, which significantly increases the brittleness of the workpiece and reduces the impact toughness. The service life is lower at the cutting edge or key parts of the mold. After laser quenching, fine martensite and dispersed carbide particles can be obtained, the network can be removed, and the maximum hardened layer depth and maximum hardness of 1 017. 2HV can be obtained. The hardness, resistance to plastic deformation and resistance to adhesive wear of Cr12MoV steel after light quenching are improved compared with

conventional heat treatment. For the punch made of T8A steel and the die made of Cr12Mo steel, the laser hardening depth is 0.12mm, the hardness is 1200HV, and the service life is increased by 4 to 6 times. Increase the number of items from 20,000 to 100,000 to 140,000.

For T10 steel, a hardened layer with a hardness of 1024HV and a depth of 0.55mm can be obtained after laser quenching; for Cr12, a hardness of 1000HV and a depth of 0 can be obtained after laser quenching. . 4mm hardened layer,

the service life has been greatly improved.

3. 2 Laser coating

Laser coating is to use laser to cover the surface of the substrate with a thin layer of coating material with

certain properties. Such materials can be metals or alloys, non-metals, compounds and their mixtures.

During the coating process, the coating layer is quickly combined with the substrate surface through

fusion under the action of laser. The main difference between it and laser alloying is that the chemical composition of the coating remains basically unchanged after laser action, and the components of the matrix basically do not enter the coating. Laser coating technology has a wide range of practical materials. The parent materials being studied include low carbon steel, alloy steel, cast iron, nickel-chromium-titanium heat-resistant alloy, etc. Research The added materials include cobalt-based alloys, iron-based alloys and nickel-based alloys.

Using laser technology on a 2kW CO2 laser with a powder feeder

, the surface of the 4Cr5MoV1Si steel substrate is coated with a layer of nickel-based high-temperature alloy

High-temperature wear-resistant alloy powder composed of WC + W2C particles

At the laser power P = 1500W, the powder feeding amount is 10g/min, and the workpiece moving speed is 2 Under the condition of ~3mm/s, a multi-pass overlapping large area high-temperature wear-resistant alloy was obtained. When the test temperature is 600℃, the hardness is 550~580HV0.2; when the temperature is 950℃, the hardness is 100~200HV0.2. It can be seen that at a high temperature of about 1000℃, the coating layer

still has high toughness and is an ideal high-temperature mold wear-resistant alloy

. In addition, the use of laser coating methods to repair worn punch dies

and drawing dies can greatly extend the service life of the mold and reduce the use cost of the mold

.

3. 3 Laser surfacing

For some automobile panel punching and trimming dies, in order to improve the service life

and save high-quality mold materials, the blade The mouth often adopts a layer of alloy with excellent properties overlayed on a poor

base material. In the past, the artificial oxygen-acetylene flame surfacing method was mostly used for cladding welding. Although this method has low equipment cost, "Mold Industry" 2001. No. 4 Total 242 42

But the power density is not high (10

2

～10

3

W/ cm 2

), and it is difficult to control accurately, so the quality and productivity of cladding welding are low. Since the 1970s

Plasma powder cladding technology has been successfully developed. Because

it has higher power density and better control performance, it has been successfully developed

It has been widely used. However, plasma cladding has problems such as short electrode life and high dilution rate of the base metal of the cladding layer.

Compared with the oxygen-acetylene flame surfacing method using the same material, the laser cladding method that has appeared since the 1980s has a finer and denser structure and a lower defective product rate.

Only 1/10 of the former. The speed of laser cladding is fast, and the productivity is 1.75 times higher than that of oxygen-acetylene flame cladding, while the amount of material used in cladding is only 1/2 of it. Moreover, the room temperature hardness of the laser cladding layer is about 50HV higher than that of oxygen-acetylene flame cladding. The quality of laser cladding is related to factors such as the beam mode, power and cladding speed of the laser.

4 Laser processing replaces mold stamping processing

4. 1 Laser cutting replaces punching molds for thin plate parts

Laser cutting replaces sheet metal parts and automobile body manufacturing The punching and trimming die has great potential.

Three-dimensional laser cutting technology began to be used in automobile body manufacturing in the 1980s due to its flexibility in processing and quality assurance. When cutting, you only need to use a straight support block to support the workpiece, so the production of the fixture is not only low-cost but also fast. Due to the combination with CAD/CAM technology, the cutting process is easy to control and can realize continuous production and parallel processing, thereby achieving high-efficiency cutting production.

There are two main types of lasers used for cutting plates, namely

CO2 lasers and Nd:YA G lasers, with power ranging from 100 to 1 500

W , because the vibration mode of lasers with power less than 1500W is single mode, the slit width is 0. 1 ~ 0. 2mm, the cutting surface is also very clean, and the output power When the power is greater than 1500W, the vibration mode of the laser is multimode, the slit width is nearly 1mm, and the cutting surface quality is poor. Because Nd:

YA G's laser can be transported through optical fibers, which is more flexible and convenient.

It is suitable for robots holding laser nozzles with program control for precise operation

operation, so it is mostly used in three-dimensional cutting. The main factors that affect the quality of laser cutting workpieces are cutting speed, focus position, auxiliary gas pressure, laser output power and mode.

Ford and General Motors in the United States, as well as Toyota, Nissan and other automobile companies in Japan, generally use laser cutting technology in automobile production lines.

It does not need to Using metal molds of various specifications, in addition to quickly

cutting various shapes of blanks quickly and conveniently, it is also used to cut and process large quantities of parts that need to be changed due to different specifications. Hole locations, such as car logo lights, vehicle frames, decorative lines on both sides of the body, etc. The trucks produced by General Motors have 20 types of holes in the door alone, with diameters ranging from <2.8 to <39mm.

The company uses Rofin-Sinar's 500W laser to pass through

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Connect to the welding head mounted on the robot through an optical fiber to cut these

holes. The processing of a door opening can be completed in 1 minute. The edge of the hole is smooth and the back

Smooth surface. The tolerance of <2. 8mm hole is 0. 03～0. 08mm,

The tolerance of <12mm hole is - 0. 25mm～ + 0. 03mm. The company's trucks and buses have 89 chassis with different hole diameters and hole configurations

. After optimized design, only 5 different chassis need to be stamped

The chassis is then laser-cut with holes with different configurations, which simplifies the process

, improves efficiency, and reduces costs.

In 1997, the National Natural Science Foundation of my country focused on the theory and technology of high-power CO2

and YA G laser three-dimensional welding and cutting

. Members of the research team of the National Industry-Academic-Research Laser Technology Center conducted systematic research on this and made recommendations for the application of three-dimensional laser processing technology in my country's automobile body manufacturing industry. A great contribution

. The center has carried out major engineering project research for the technological transformation of large state-owned enterprises such as FAW Car Company and Baoshan Iron and Steel Company, including the development of three-dimensional laser for the Hongqi extended sedan cover. Manufacturing process

Technology is used for the first time in my country's car production. In the experimental research on the laser large panel splicing process of thin

thick steel plates for automobiles, laser cutting was used for the first time to replace the precision cutting technology, and good technical experience was achieved

Economic effect.

Three-dimensional laser cutting is also very useful for processing after body assembly, such as opening luggage rack fixing holes, roof slide rail holes, antenna installation holes, and modifying the shape of wheel fenders. wait. It is used for contour cutting and correction in the trial production of new cars, which not only shortens the trial production cycle but also saves molds, fully embodying the advantages of laser cutting processing.

4. 2 Laser marking replaces die marking

Enterprises often need to put their own logo or specific logo on the parts they produce.

For symbols and numbers, the previous method was to use

die marking or molding, but the marking quality was not high. Using a CNC laser machine for marking is not only fast, but also overcomes the burrs, sharp edges and distortions that are common in die marking. Due to the use of computer control

, any complex pattern can be produced, eliminating the need for mold design, manufacturing and debugging, greatly shortening product development and manufacturing

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cycle, while also reducing costs. Because laser marking machines require low power, low cost, and beautiful marks, they are now used by most enterprises.

4. 3 Laser forming instead of bending die forming

The laser forming technology of metal sheets is a method that uses a focused beam to scan the metal plate at a certain speed. The surface of the material (scanning speed should be fast enough to prevent surface melting), causing the material in the heat zone to produce an obvious temperature gradient, resulting in non-uniformly distributed thermal stress, thus A method of plastically deforming sheet metal

. Compared with conventional forming methods, laser forming "Mold Industry" 2001. No. 4 Total 242 43

has many advantages: ① It is moldless forming, has a short production cycle and is flexible

Large, it is not restricted by the processing environment. By optimizing the parameters of the laser processing process and accurately controlling the heat action area and the distribution of thermal stress, the sheet metal can be formed without mold; ② Because of its It is a plastic processing method that only relies on thermal stress without the use of molds

to deform the sheet, so it is formed without external force; ③ It is non-contact forming, so it does not There are no problems such as mold making, wear

and lubrication. There is no mold sticking or springback phenomenon, and the forming accuracy

is high; ④ The sheet metal can be formed with complex shapes through composite forming. Special-shaped parts (such as spherical parts, conical parts, parabolic parts, etc.).

The essence of laser forming mechanism is the bending mechanism. When the laser heats the sheet, on the one hand, thermal stress is generated in and around the laser action area, and at the same time, the yield pole of the sheet in the heated area is reduced, thus

Cause the hot material in the thermal stress area to produce non-uniform plastic deformation

to realize the bending and forming of the sheet. Tests have shown that with each pass of laser scanning, the metal sheet can be bent by 1° to 5°, and different combinations of scanning trajectories and process parameters can produce different forming effects. With different degrees of deformation

, workpieces of various complex shapes can be obtained. The table in Figure 2

shows the conditions when the process parameters are laser speed power 1.5kW, laser beam diameter

5.4mm, material SUS304, thickness 1mm, and carbon coating surface

Below, the changing relationship between laser scanning speed and material bending angle.

Figure 2 Effect of laser scanning speed on bending angle

Many countries in the world have invested a lot of manpower and material resources

Special projects on laser forming technology Research and preliminary industrial applications have begun in some fields.

Professor HFrackiewicz of the Polish Institute of Basic Technology used laser forming to successively manufacture cylindrical parts, spherical parts, corrugated tubes and metal pipes, expanding and shrinking, and bending them into< /p>

Shaping, etc.; German scholar MGeiger and others combined laser forming with other processing

processes in the automobile manufacturing industry, and carried out flexible leveling and

of automobile panels. The forming of other formed parts, and computer closed-loop control of the bending forming process, improves the forming accuracy. The German company Trumpf developed the commercial laser forming multi-

purpose machine tool Trumat ic L 3030 in 1997. It is believed that with the deepening of research and the development of other related technologies, laser forming technology will gradually mature and enter the practical stage.

5 Conclusion

As an advanced processing technology, laser processing technology has been widely used in various industries at home and abroad. my country's machinery industry is It was also listed as one of the top ten technologies during the "Ninth Five-Year Plan" period. The National Natural Science Foundation of China also

funds the research on laser processing technology and laser processing equipment as a key research project, and clearly points out its main applications

The field should be in automobile manufacturing. As a tool, the production cycle, quality and cost of the mold directly affect the manufacturing process and sales of the product. As a universal processing tool, laser has great advantages in reducing mold manufacturing equipment, shortening mold manufacturing cycle, reducing manufacturing costs and ensuring mold quality. . How to apply laser processing technology in actual production to optimize the mold manufacturing process, and to improve and combine the traditional

mold manufacturing process requires us to make continuous efforts

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