SUMMARY

The production of products below the dimensions that can be produced with traditional molding technology is provided by micro molding technology. New technologies are used to process micro figures into the mold. In addition, micro products are molded thanks to the changes made in the design of the injection machine and injection parameters.

1. INTRODUCTION

Although micro-molding is mentioned today, the limit of a product to be a micro product has not been fully determined. After the point where traditional molding technology is insufficient, it is now in the field of micro molding technology. The lower limit, which can now be considered sufficient, is getting smaller in parallel with technological developments. The lower limit of moldability with current technology; It can be said to be 0.00013g in weight and 0.01mm in wall thickness. In this research, the issue of molding plastic products that are too small to be molded by traditional methods was examined.

Figure 1. Examples of micro products:

a) Micro water motor gearbox
Dimensions: 3 x 1 x 0.5 mm,
Mass: 0.325g
Material: Nylon b) Micro gear system. What appears next to it is a granule of plastic material.
Material: Acetal
Mass: 0.04mg c) World's smallest product produced by micro molding method
Length: 1.3 mm, core core diameters: 0.63 - 0.13 mm, Sprue inlet diameter: 0.076mm

If we give an example to micro products; micro gears, micro gearboxes, hearing aids, medical devices, micro motors, watch parts, electronic on-off switches, micro sensors, lenses, fiber optic materials, etc. In micro products; There are critical elements such as ribs, holes, protrusions, channels, clips. There are even inserts on the product or gradual injection process is performed.

Micro molding technology contains many difficult situations compared to traditional molding technology. For example, mold details are so small that the manufacturer may have to use a magnifying glass to see it. In addition, the injection parameters must be well designed in order to advance the melt plastic in narrow mold sections.

2. MICRO INJECTION MACHINES

Although micro injection machines have some differences compared to traditional machines, their working principles are basically the same. The method by which the molten plastic is transferred to the mold cavity can be shown as the biggest difference. In addition, the size of the equipment used is the biggest difference. For example, the diameter of the extruder screw is between 14-16 mm, the nozzle outlet diameter is 1.5 mm.

The diameter of the extruder screw used in micro injection machines cannot be made smaller than 14 mm. The smaller diameter extruder screw breaks by not responding to the pressure generated during injection. In addition, the smaller diameter extruder screw cannot feed the injection process. Cold runner type is generally used in micro molds. The engineering infrastructure required for the hot runner systems to be produced for micro molds is lacking.
If we explain the operation of the frequently used micro injection machine. The process starts with the 45 ° angled extruder screw advancing the molten plastic to the injection piston and feeding the vertical dosing chamber. After the scaling room is filled, the dosing process is started with the closure of the valve in front of the extruder screw. The dosing process is carried out with the adjusted amount of the dosing piston, which is vertical to the injection piston. Thanks to the sensitive servo motor controlling the dosing piston, dosing can be made with a volume sensitivity of 0.001 cc. After the dosing process is completed, the injection progresses, allowing the molten plastic to be filled into the mold pit.

Figure 2.Microsystem injection bench manufactured by Battenfeld company.

Dosing process should be done well. Insufficient dosing may cause the mold cavity not to be filled, and excessive dosing will cause the product to stick to the mold or damage the sensitive sections of the mold. In order to ensure the accuracy of the dosing amount, the movement of the injection piston is made with a 5 micron precision with a servo motor. The total injection process takes 0.020 seconds. High pressure and high melt temperature are required for the molten plastic to pass through narrow sections. Long-term storage of the plastic material at high temperatures will cause the internal structure of the material to deteriorate. Considering this situation, the molten plastic should not be kept at high temperatures for a long time. Although this time can take up to two hours in traditional injection molding machines, this time is reduced to two minutes in micro injection molds.

3. MICRO MOLDS AND MANUFACTURING TECHNOLOGIES

Viscous properties of plastic materials are taken into consideration when designing micro molds. Runners and distributors are made in very large sizes according to the product so that the material can fill the mold pit before it freezes. Another reason for doing this is that the transfer volume of the extruder screw is much more than the product volume. So much so that 1% of injected plastic 

We can take the two parts as a product. The 99% part is either going to waste or used as recycled material. However, since the products are used for very special purposes, it is not desirable to use recycled materials. The amount of material going to the garbage can be reduced up to 80% by making changes in the mold, providing both filling guarantee and sufficient amount of material. Although this reduction may seem small, it is a big gain in medical supplies that are very expensive (around 10USD / g).

While a 64-cavity mold can be produced in the traditional product scale, this value on the micro scale is very funny. Neither the desired tolerance precision nor the filling balance can be achieved in a multi-cavity mold. The number of eyes should be kept as small as possible. Surface quality is very important in micro scale products. Although the manufactured mold core surface looks smooth at first glance, it is seen that it cannot give the desired surface quality when looked closely. Therefore, the mold should be polished in a quality way.

The plastic materials from which micro parts will be produced should be chosen well. They are plastics with recommended high flow index and low viscosity at application temperature. In addition, glass fiber reinforced materials are not suitable for flow through narrow section channels. Special plastics used for the production of micro products are produced.
Thanks to the electronic signal sensors developed for the production of micro-scale molds, the production tolerance is reduced to ± 10 nanometers.

Technologies used in micro mold production; EDM, micro milling, etching, laser machining, UV lithography.

3.1. MICRO MILLING METHOD

The difference of micro milling cutters compared to conventional milling cutters is their small size and high machining precision. The stability of the axis movements of the machine is ensured by using sensitive servo motors and motion elements. While the processing precision of the traditional CNC milling machine can be 1-3 microns, the processing precision of the CNC micro milling machine goes down to 30 nanometers. Air-borne bearings are used to provide motion sensitivity. In addition, hydro-dynamic fluid supported bedding, which is still in the experimental stage, will be used for this purpose.

Diamond cutters are used in micro milling cutters. Small diameter diamond cutters up to 200 microns are produced. Extremely small details and smooth surfaces can be achieved with these cutters. In addition, the die halves are processed by making the diamond cutter an ultra-sonic vibration movement. The biggest disadvantage of diamond cutters is that they cannot machine steel materials. Instead of steel, nickel, aluminum or copper mold sets are processed. Carbide cutters are produced for steel die tools. In carbide cutters, cutters up to 125 micron diameter are produced. Thus, smaller details can be obtained. However, as smooth and smooth surfaces as a diamond cutter cannot be obtained.

3.2. EDM METHOD

Thanks to CNC EDM benches, mold cores of complex parts can be easily produced with 1.5 micron immersion precision. Since the machine axis accuracy is ± 2 microns, maximum measurement accuracy is ensured. Mold manufacturing is carried out using electro-wire erosion technology. In order to create small profiles, it is cut with 0.025 mm diameter wire.

3.3. UV-LITHOGRAPHY METHOD

Its technology, which is a brand new approach in mold and prototype production, is also used in micro mold production. The manufacturing process starts from a glass or silicon-based surface. The product geometry, which is divided into slices, is built layer by layer with the technology produced by each company. Starting from the lowest geometry, each layer is built and the core of the mold is formed. These mold cores are then coated with nickel or nickel alloys. Thus, the mold surface obtained is much smoother and smoother than that obtained with EDM and micro-milling.

Figure 4. Mold pit produced with UV-Lithography technology.
Printed plastic material: Nylon, gear diameter: 0.48 mm product wall thickness: 0.066 mm.

With the UV-Lithography method, indentations and details up to 10 microns can be easily created. Considering that this value is 100 microns in EDM and micro-milling technology, a very perfect precision emerges. Measurement tolerance up to ± 2 microns is provided for piece size. In addition, the problem of cores not meeting each other in multi-cavity molds produced by this method is eliminated. With this method, a mold can be made between 6-8 weeks and 5 million prints can be made for each eye. However, this method has problems that have not been solved yet. Mold production is expensive, since the mold is built only in the x and y axes, the production quality should also be considered when designing the mold core.

3.4. LASER ABRASION METHOD

Another method used in micro mold production is laser etching technology. 5 micron wide laser light beams with pulses of 10-100 nanoseconds onto the mold steel. 

preventing. Thus, the steel is abraded and the mold core is formed. The width of the light beam can be reduced to 355 nm. Small light beams are used in situations where surface quality is high. Although the width of the abrasive laser beam can be reduced this much, it should not be forgotten that there is a tolerance limit depending on the axis precision of the used machine. Long-term laser pulses cause thermal accumulation on the material. This situation adversely affects the mold surface quality.

4. FILLING ANALYSIS OF MICRO PRODUCTS IN COMPUTER ENVIRONMENT

As with macro products, the filling of micro products can be simulated in computer environment and the product quality can be predicted in advance. Miniature Tool & Die Inc. (MTD, Charlton, MA) and University of Massachusetts-Lowel’s Plastics Engineering Dept. (UML, Lowel, MA) organizations can make mold filling analyzes required for micro products thanks to the Moldflow flow analysis program they have prepared. While writing the program, the behavior of high temperature plastic material while passing through micro channels at high pressure has been taken into consideration. If traditional analysis programs are used, these pressure and temperature values ​​will be shown to us as lost their applicability.

Figure 5. An analysis and application simulated with Moldflow software.

5. CONCLUSION

It can be seen that as technology advances, the tools we use are getting smaller. Micro molding technology has also taken place in this downsizing and has become one of the biggest supporters of the progress. Micro molding is a very sensitive job in terms of the technology and methods used. Micro molding, a technology that pushes the boundaries of traditional molding technology, is starting to take its place in the ordinary products we use every day.

If we give an example to micro products; micro gears, micro gearboxes, hearing aids, medical devices, micro motors, watch parts, electronic on-off switches, micro sensors, lenses, fiber optic materials, etc. In micro products; There are critical elements such as ribs, holes, protrusions, channels, clips. There are even inserts on the product or gradual injection process is performed.

Micro molding technology contains many difficult situations compared to traditional molding technology. For example, mold details are so small that the manufacturer may have to use a magnifying glass to see it. In addition, the injection parameters must be well designed in order to advance the melt plastic in narrow mold sections.

2. MICRO INJECTION MACHINES

Although micro injection machines have some differences compared to traditional machines, their working principles are basically the same. The method by which the molten plastic is transferred to the mold cavity can be shown as the biggest difference. In addition, the size of the equipment used is the biggest difference. For example, the diameter of the extruder screw is between 14-16 mm, the nozzle outlet diameter is 1.5 mm.

The diameter of the extruder screw used in micro injection machines cannot be made smaller than 14 mm. The smaller diameter extruder screw breaks by not responding to the pressure generated during injection. In addition, the smaller diameter extruder screw cannot feed the injection process. Cold runner type is generally used in micro molds. The engineering infrastructure required for the hot runner systems to be produced for micro molds is lacking.
If we explain the operation of the frequently used micro injection machine. The process starts with the 45 ° angled extruder screw advancing the molten plastic to the injection piston and feeding the vertical dosing chamber. After the scaling room is filled, the dosing process is started with the closure of the valve in front of the extruder screw. The dosing process is carried out with the adjusted amount of the dosing piston, which is vertical to the injection piston. Thanks to the sensitive servo motor controlling the dosing piston, dosing can be made with a volume sensitivity of 0.001 cc. After the dosing process is completed, the injection progresses, allowing the molten plastic to be filled into the mold pit.

Figure 2.Microsystem injection bench manufactured by Battenfeld company.

Dosing process should be done well. Insufficient dosing may cause the mold cavity not to be filled, and excessive dosing will cause the product to stick to the mold or damage the sensitive sections of the mold. In order to ensure the accuracy of the dosing amount, the movement of the injection piston is made with a 5 micron precision with a servo motor. The total injection process takes 0.020 seconds. High pressure and high melt temperature are required for the molten plastic to pass through narrow sections. Long-term storage of the plastic material at high temperatures will cause the internal structure of the material to deteriorate. Considering this situation, the molten plastic should not be kept at high temperatures for a long time. In conventional injection molding machines this s

preventing. Thus, the steel is abraded and the mold core is formed. The width of the light beam can be reduced to 355 nm. Small light beams are used in situations where surface quality is high. Although the width of the abrasive laser beam can be reduced this much, it should not be forgotten that there is a tolerance limit depending on the axis precision of the used machine. Long-term laser pulses cause thermal accumulation on the material. This situation adversely affects the mold surface quality.

4. FILLING ANALYSIS OF MICRO PRODUCTS IN COMPUTER ENVIRONMENT

As with macro products, the filling of micro products can be simulated in computer environment and the product quality can be predicted in advance. Miniature Tool & Die Inc. (MTD, Charlton, MA) and University of Massachusetts-Lowel’s Plastics Engineering Dept. (UML, Lowel, MA) organizations can make mold filling analyzes required for micro products thanks to the Moldflow flow analysis program they have prepared. While writing the program, the behavior of high temperature plastic material while passing through micro channels at high pressure has been taken into consideration. If traditional analysis programs are used, these pressure and temperature values ​​will be shown to us as lost their applicability.

Figure 5. An analysis and application simulated with Moldflow software.

5. CONCLUSION

It can be seen that as technology advances, the tools we use are getting smaller. Micro molding technology has also taken place in this downsizing and has become one of the biggest supporters of the progress. Micro molding is a very sensitive job in terms of the technology and methods used. Micro molding, a technology that pushes the boundaries of traditional molding technology, is starting to take its place in the ordinary products we use every day.

If we give an example to micro products; micro gears, micro gearboxes, hearing aids, medical devices, micro motors, watch parts, electronic on-off switches, micro sensors, lenses, fiber optic materials, etc. In micro products; There are critical elements such as ribs, holes, protrusions, channels, clips. There are even inserts on the product or gradual injection process is performed.

Micro molding technology contains many difficult situations compared to traditional molding technology. For example, mold details are so small that the manufacturer may have to use a magnifying glass to see it. In addition, the injection parameters must be well designed in order to advance the melt plastic in narrow mold sections.

2. MICRO INJECTION MACHINES

Although micro injection machines have some differences compared to traditional machines, their working principles are basically the same. The method by which the molten plastic is transferred to the mold cavity can be shown as the biggest difference. In addition, the size of the equipment used is the biggest difference. For example, the diameter of the extruder screw is between 14-16 mm, the nozzle outlet diameter is 1.5 mm.

The diameter of the extruder screw used in micro injection machines cannot be made smaller than 14 mm. The smaller diameter extruder screw breaks by not responding to the pressure generated during injection. In addition, the smaller diameter extruder screw cannot feed the injection process. Cold runner type is generally used in micro molds. The engineering infrastructure required for the hot runner systems to be produced for micro molds is lacking.
If we explain the operation of the frequently used micro injection machine. The process starts with the 45 ° angled extruder screw advancing the molten plastic to the injection piston and feeding the vertical dosing chamber. After the scaling room is filled, the dosing process is started with the closure of the valve in front of the extruder screw. The dosing process is carried out with the adjusted amount of the dosing piston, which is vertical to the injection piston. Thanks to the sensitive servo motor controlling the dosing piston, dosing can be made with a volume sensitivity of 0.001 cc. After the dosing process is completed, the injection progresses, allowing the molten plastic to be filled into the mold pit.

Figure 2.Microsystem injection bench manufactured by Battenfeld company.

Dosing process should be done well. Insufficient dosing may cause the mold cavity not to be filled, and excessive dosing will cause the product to stick to the mold or damage the sensitive sections of the mold. In order to ensure the accuracy of the dosing amount, the movement of the injection piston is made with a 5 micron precision with a servo motor. The total injection process takes 0.020 seconds. High pressure and high melt temperature are required for the molten plastic to pass through narrow sections. Long-term storage of the plastic material at high temperatures will cause the internal structure of the material to deteriorate. Considering this situation, the molten plastic should not be kept at high temperatures for a long time. In conventional injection molding machines this s

Although urea can take up to two hours, this time is reduced to two minutes in micro injection machines.

3. MICRO MOLDS AND MANUFACTURING TECHNOLOGIES

Viscous properties of plastic materials are taken into consideration when designing micro molds. Runners and distributors are made in very large sizes according to the product so that the material can fill the mold pit before it freezes. Another reason for doing this is that the transfer volume of the extruder screw is much more than the product volume. So much so that we can take 1% of the injected plastic as a product. The 99% part is either going to waste or used as recycled material. However, since the products are used for very special purposes, it is not desirable to use recycled materials. The amount of material going to the garbage can be reduced up to 80% by making changes in the mold, providing both filling guarantee and sufficient amount of material. Although this reduction may seem small, it is a big gain in medical supplies that are very expensive (around 10USD / g).

While a 64-cavity mold can be produced in the traditional product scale, this value on the micro scale is very funny. Neither the desired tolerance precision nor the filling balance can be achieved in a multi-cavity mold. The number of eyes should be kept as small as possible. Surface quality is very important in micro scale products. Although the manufactured mold core surface looks smooth at first glance, it is seen that it cannot give the desired surface quality when looked closely. Therefore, the mold should be polished in a quality way.

The plastic materials from which micro parts will be produced should be chosen well. They are plastics with recommended high flow index and low viscosity at application temperature. In addition, glass fiber reinforced materials are not suitable for flow through narrow section channels. Special plastics used for the production of micro products are produced.
Thanks to the electronic signal sensors developed for the production of micro-scale molds, the production tolerance is reduced to ± 10 nanometers.

Technologies used in micro mold production; EDM, micro milling, etching, laser machining, UV lithography.

3.1. MICRO MILLING METHOD

The difference of micro milling cutters compared to conventional milling cutters is their small size and high machining precision. The stability of the axis movements of the machine is ensured by using sensitive servo motors and motion elements. While the processing precision of the traditional CNC milling machine can be 1-3 microns, the processing precision of the CNC micro milling machine goes down to 30 nanometers. Air-borne bearings are used to provide motion sensitivity. In addition, hydro-dynamic fluid supported bedding, which is still in the experimental stage, will be used for this purpose.

Diamond cutters are used in micro milling cutters. Small diameter diamond cutters up to 200 microns are produced. Extremely small details and smooth surfaces can be achieved with these cutters. In addition, the die halves are processed by making the diamond cutter an ultra-sonic vibration movement. The biggest disadvantage of diamond cutters is that they cannot machine steel materials. Instead of steel, nickel, aluminum or copper mold sets are processed. Carbide cutters are produced for steel die tools. In carbide cutters, cutters up to 125 micron diameter are produced. Thus, smaller details can be obtained. However, as smooth and smooth surfaces as a diamond cutter cannot be obtained.

3.2. EDM METHOD

Thanks to CNC EDM benches, mold cores of complex parts can be easily produced with 1.5 micron immersion precision. Since the machine axis accuracy is ± 2 microns, maximum measurement accuracy is ensured. Mold manufacturing is carried out using electro-wire erosion technology. In order to create small profiles, it is cut with 0.025 mm diameter wire.

3.3. UV-LITHOGRAPHY METHOD

UV-Lithography, which is a brand new approach in mold and prototype production, is also used in micro mold production. The manufacturing process starts from a glass or silicon-based surface. The product geometry, which is divided into slices, is built layer by layer with the technology produced by each company. Starting from the lowest geometry, each layer is built and the core of the mold is formed. These mold cores are then coated with nickel or nickel alloys. Thus, the mold surface obtained is much smoother and smoother than that obtained with EDM and micro-milling.

Figure 4. Mold pit produced with UV-Lithography technology.
Printed plastic material: Nylon, gear diameter: 0.48 mm product wall thickness: 0.066 mm.

With the UV-Lithography method, indentations and details up to 10 microns can be easily created. Considering that this value is 100 microns in EDM and micro-milling technology, a very perfect precision emerges. Measurement tolerance up to ± 2 microns is provided for piece size. In addition, the problem of cores not meeting each other in multi-cavity molds produced by this method is eliminated. With this method, a mold 6- 8 h 

5 million prints can be made for each eye. However, this method has problems that have not been solved yet. Mold production is expensive, since the mold is built only in the x and y axes, the production quality should also be considered when designing the mold core.

3.4. LASER ABRASION METHOD

Another method used in micro mold production is laser etching technology. It is the directing of a 5 micron wide laser light beam on the mold steel with pulses of 10-100 nanoseconds. Thus, the steel is abraded and the mold core is formed. The width of the light beam can be reduced to 355 nm. Small light beams are used in situations where surface quality is high. Although the width of the abrasive laser beam can be reduced this much, it should not be forgotten that there is a tolerance limit depending on the axis precision of the used machine. Long-term laser pulses cause thermal accumulation on the material. This situation adversely affects the mold surface quality.

4. FILLING ANALYSIS OF MICRO PRODUCTS IN COMPUTER ENVIRONMENT

As with macro products, the filling of micro products can be simulated in computer environment and the product quality can be predicted in advance. Miniature Tool & Die Inc. (MTD, Charlton, MA) and University of Massachusetts-Lowel’s Plastics Engineering Dept. (UML, Lowel, MA) organizations can make mold filling analyzes required for micro products thanks to the Moldflow flow analysis program they have prepared. While writing the program, the behavior of high temperature plastic material while passing through micro channels at high pressure has been taken into consideration. If traditional analysis programs are used, these pressure and temperature values ​​will be shown to us as lost their applicability.

Figure 5. An analysis and application simulated with Moldflow software.

5. CONCLUSION

It can be seen that as technology advances, the tools we use are getting smaller. Micro molding technology has also taken place in this downsizing and has become one of the biggest supporters of the progress. Micro molding is a very sensitive job in terms of the technology and methods used. Micro molding, a technology that pushes the boundaries of traditional molding technology, is starting to take its place in the ordinary products we use every day.