**2. Injection moulding tools made from H13 material using the selective laser melting technology (industrial case study)**

One of the most important applications of the Selective Laser Melting (SLM) technology is the manufacturing of tools for the injection moulding process. Besides the advantages of the SLM process that consists in the fact that it is rapid, does not depend on the shape of the tool and it has reasonable costs as compared to the classical manufacturing technologies, there are some disadvantages as well. One of the major disadvantages of the SLM process is the accuracy, which is below the accuracy provided by some well-known classical technologies, such as grinding. The SLM technology looks quite simple in theory, but the process control is not so simple from the experimental point of view. The research started within the Technical University of Cluj-Napoca, in cooperation with Plastor SA Company from Oradea (Romania) and SLM Solutions GmbH Company from Luebeck (Germany) has proved the complexity of the SLM technology in the manufacturing of the injection moulding tools process. There are many important aspects that have to be taken into account, as mentioned above, when speaking about the accuracy of the manufactured injection moulding tools, in close-connection with the accuracy of the SLM process.

### **2.1. Finite element analysis used to estimate the shrinkage of the SLM tools**

The case study to be analyzed refers to the injection moulding tool components (punch and die) for a lid button of a grass-cutting machine manufactured by Plastor SA Company from Oradea (Romania) (see **Figure 3**).

 **Figure 3.** Injection moulding tools for a lid button (ProEngineer design).

 **Figure 2.** MCP Realizer II SLM 250 system from the Technical University of Cluj-Napoca.

**laser melting technology (industrial case study)**

this chapter of the book.

164 New Trends in 3D Printing

with the accuracy of the SLM process.

Part of the results obtained in this postdoctoral program, in cooperation with the SLM Solutions GmbH Company from Luebeck, Germany (best practice examples) are presented in

**2. Injection moulding tools made from H13 material using the selective**

One of the most important applications of the Selective Laser Melting (SLM) technology is the manufacturing of tools for the injection moulding process. Besides the advantages of the SLM process that consists in the fact that it is rapid, does not depend on the shape of the tool and it has reasonable costs as compared to the classical manufacturing technologies, there are some disadvantages as well. One of the major disadvantages of the SLM process is the accuracy, which is below the accuracy provided by some well-known classical technologies, such as grinding. The SLM technology looks quite simple in theory, but the process control is not so simple from the experimental point of view. The research started within the Technical University of Cluj-Napoca, in cooperation with Plastor SA Company from Oradea (Romania) and SLM Solutions GmbH Company from Luebeck (Germany) has proved the complexity of the SLM technology in the manufacturing of the injection moulding tools process. There are many important aspects that have to be taken into account, as mentioned above, when speaking about the accuracy of the manufactured injection moulding tools, in close-connection The 3D CAD models were imported afterward into the Ansys FEA program and the mesh was generated as illustrated in **Figure 4**. A mesh with a total number of 31.930 nodes and 18.618 elements for the punch and 28.276 nodes and 15.118 elements for the die, respectively, were generated within the FEA program.

 **Figure 4.** The mesh generated for the injection moulding tools—punch and die (Ansys 13).

Another important aspect consists in the introduction of thermal and mechanical characteris‐ tics of the raw material, as it was specified by the producer of the type of metallic powder that is commercially available for such applications: H13 Tool Steel material (see **Table 1**) [16–17]. The injection moulding tools were manufactured using the SLM 250 HL equipment from SLM Solutions GmbH Company in Luebeck, Germany from this type of material, having the same characteristics as the ones that were introduced within the finite element analysis (H13 Tool Steel material).

The next step of the finite element analysis consisted in the introduction of technological parameters within the Ansys program. The laser power, scanning speed and powder bed temperature were introduced as a subroutine into the analysis within the ANSYS APDL Heat Transfer Module.

Twenty finite element analyses were done using varied values of the technological parameters specified in **Table 2**, in order to find the combination of parameters that leads to an optimum closing of the active elements of moulds (see **Figure 5** and **Table 3**).


**Table 1.** H13 Tool Steel material properties.


**Table 2.** Technological parameters introduced in analysis using the APDL Heat transfer module.

Besides these technological parameters that were varied within the finite element analysis, there were also other important parameters that were specified, but were maintained constant during the analyses, such as the layer thickness (30 μm) and the hatching distance (20 μm). As it is possible to observe from the analysis, the value of technological parameters that leads to a minimum shrinkage in the case of punch and die made by SLM are different. If the temper‐ ature of the powder bed has the same value in both cases (176°C), the laser power and the scanning speed should be different, such as at the end the punch and die would fit by the closing point of view.


**Table 3.** Results of the finite element analyses.

The injection moulding tools were manufactured using the SLM 250 HL equipment from SLM Solutions GmbH Company in Luebeck, Germany from this type of material, having the same characteristics as the ones that were introduced within the finite element analysis (H13 Tool

The next step of the finite element analysis consisted in the introduction of technological parameters within the Ansys program. The laser power, scanning speed and powder bed temperature were introduced as a subroutine into the analysis within the ANSYS APDL Heat

Twenty finite element analyses were done using varied values of the technological parameters specified in **Table 2**, in order to find the combination of parameters that leads to an optimum

)

closing of the active elements of moulds (see **Figure 5** and **Table 3**).

**Property Value** Density 7.80 (g/cm3

Rockwell C hardness 54 HRC Tensile strength 1730 MPa Elongation 10.0% Specific heat at 20°C 460 (J/kg K) Thermal conductivity 28.6 (W/mK) Melting point 1020°C Poisson coefficient 0.3 Elastic modulus 200 GPa

**Technological parameter Varied value**

**Table 2.** Technological parameters introduced in analysis using the APDL Heat transfer module.

Laser power [W] 175 180 185 190 195 200 Scanning speed [mm/s] 250 300 350 400 450 500 Powder bed temperature [°C] 80 104 128 152 176 200

Besides these technological parameters that were varied within the finite element analysis, there were also other important parameters that were specified, but were maintained constant during the analyses, such as the layer thickness (30 μm) and the hatching distance (20 μm). As it is possible to observe from the analysis, the value of technological parameters that leads to a minimum shrinkage in the case of punch and die made by SLM are different. If the temper‐ ature of the powder bed has the same value in both cases (176°C), the laser power and the

Steel material).

166 New Trends in 3D Printing

Transfer Module.

**Table 1.** H13 Tool Steel material properties.

One may conclude that in the case of SLM technology it is very difficult to find a set of technological parameters that would be unique and universally valid in all cases of moulds manufactured by SLM from H13 Tool Steel material. The technological parameters to be used within the SLM process have to be different, according to the type and the shape of the metallic tools to be manufactured. The laser power and the energy density being applied on the scanned surface are obviously different if the injection moulding tools have thin walls or these tools are solid and massive in the entire structure of the material.

#### **2.2. Injection moulding tools made by SLM equipment and measurements**

Besides setting up the technological parameters, there is another important aspect regarding the accuracy issue, such as the support generating stage that is actually a pre-processing stage needed in the SLM process, in order to sustain the manufactured part onto the building platform of the machine.

The metallic supports have a wired structure and are needed because of the high stresses that occur during the welding process, having the tendency of severely deforming the manufac‐ tured models during manufacturing process, especially if welded connection is not good on the building platform starting with the first layers of the manufactured parts while manufac‐ turing. The metallic supports were generated, for the punch and die, using the Magics 15 software, as one may observe in **Figure 6**. The metallic supports are removed within the postprocessing stage.

 **Figure 6.** Supports generated for the punch and die using Magics 15 software.

The punch and die illustrated in **Figure 7** were manufactured on the SLM 250 HL equipment from SLM Solutions GmbH Company from Luebeck (Germany) presented in **Figure 8**, using the technological parameters presented in **Table 3**, as they were determined within the finite element analyses.

 **Figure 7.** The injection moulding tools made by SLM equipment.

Some measurements of the injection moulding tools were also made at the Technical University of Cluj-Napoca using a Zeiss Eclipse 550 CMM equipment. The conclusion was that the obtained results are comparable to the ones estimated within the finite element analysis (designed dimensions). The maximum value of shrinkage that has been experimentally determined has a value of approximately 80 μm, both in the case of the punch and die (see **Figures 9** and **10**).

The lowest values of deformations (less than 10 μm) were obtained in the case of the dimen‐ sions H1, used for the correct positioning of the punch and die. The mean value of the punch and die shrinkage has been determined in the interval of 30–40 μm, values that are comparable to the ones obtained in the case when the punch and die are produced by using similar technologies dealing with metallic powders such as Selective Laser Sintering (SLS) and Classical Sintering (CS).

software, as one may observe in **Figure 6**. The metallic supports are removed within the post-

The punch and die illustrated in **Figure 7** were manufactured on the SLM 250 HL equipment from SLM Solutions GmbH Company from Luebeck (Germany) presented in **Figure 8**, using the technological parameters presented in **Table 3**, as they were determined within the finite

Some measurements of the injection moulding tools were also made at the Technical University of Cluj-Napoca using a Zeiss Eclipse 550 CMM equipment. The conclusion was that the obtained results are comparable to the ones estimated within the finite element analysis (designed dimensions). The maximum value of shrinkage that has been experimentally determined has a value of approximately 80 μm, both in the case of the punch and die (see

The lowest values of deformations (less than 10 μm) were obtained in the case of the dimen‐ sions H1, used for the correct positioning of the punch and die. The mean value of the punch

 **Figure 6.** Supports generated for the punch and die using Magics 15 software.

 **Figure 7.** The injection moulding tools made by SLM equipment.

processing stage.

168 New Trends in 3D Printing

element analyses.

**Figures 9** and **10**).

 **Figure 8.** The SLM 250 HL equipment at SLM Solutions GmbH Company from Luebeck, Germany.

There are still other issues to be investigated in the near future such as finding a way for a better control of the SLM process.

The errors that occur during the SLM process can be compensated if precisely calculated scale factors would be applied in the pre-processing stage onto the 3D model that has to be manu‐ factured using the SLM equipment.

 **Figure 9.** Schematic draw of the dimensions measured in case of punch and die.

 **Figure 10.** Shrinkage values in microns determined in the case of punch and die.

#### **2.3. Testing the active element of moulds made by SLM at S.C. Plastor S.A. Oradea (injection moulding company from Romania)**

In order to test the active elements of the mould made by SLM technology within the Plastor S.A. company from Oradea, it was required the manufacturing of additional fixing plates using conventional technologies at Plastor SA, as it is possible to observe in **Figure 11**. These plates were mounted onto the injection moulding machine Arburg 370 CMD 800-325 - type that is available within Plastor SA Company from Oradea.

Before the injection moulding experiment were made, tests were required to be done using different finite element analyses through the Autodesk Simulation Moldflow Adviser pro‐ gram, in order to determine the plastic injection parameters, such as the injection pressure, filling speed, etc. Four types of plastic materials were tested, such as Acryl Butadiene Styrene – ABS, Polypropylene – PP, Polyamide armed with glass fibers - PA+30% GF and Poly Oxy Methylene– POM.

**Figure 11.** Active elements of moulds made by SLM mounted onto the plates manufactured at Plastor S.A. company from Oradea.

Applications of the Selective Laser Melting Technology in the Industrial and Medical Fields http://dx.doi.org/10.5772/63038 171

 **Figure 12.** Arburg 370 CMD 800-325 injection moulding equipment (Plastor SA Company Oradea).

 **Figure 10.** Shrinkage values in microns determined in the case of punch and die.

**moulding company from Romania)**

Methylene– POM.

170 New Trends in 3D Printing

from Oradea.

available within Plastor SA Company from Oradea.

**2.3. Testing the active element of moulds made by SLM at S.C. Plastor S.A. Oradea (injection**

In order to test the active elements of the mould made by SLM technology within the Plastor S.A. company from Oradea, it was required the manufacturing of additional fixing plates using conventional technologies at Plastor SA, as it is possible to observe in **Figure 11**. These plates were mounted onto the injection moulding machine Arburg 370 CMD 800-325 - type that is

Before the injection moulding experiment were made, tests were required to be done using different finite element analyses through the Autodesk Simulation Moldflow Adviser pro‐ gram, in order to determine the plastic injection parameters, such as the injection pressure, filling speed, etc. Four types of plastic materials were tested, such as Acryl Butadiene Styrene – ABS, Polypropylene – PP, Polyamide armed with glass fibers - PA+30% GF and Poly Oxy

**Figure 11.** Active elements of moulds made by SLM mounted onto the plates manufactured at Plastor S.A. company

After the mesh was generated and the optimum injection point was specified, as one could be observed in **Figure 13**, in accordance with the fiber plastic material orientation, the next step consists in determining of the injection moulding technological parameters, such as the filling speed, injection pressure, cooling time, etc.

 **Figure 13.** Optimum injection point and plastic material fiber orientation.

**Figure 14** presents the values obtained for the injection pressure and the filling time in the case of ROTEC® ABS 1001 FR V0/4 material. As it is possible to observe in these images, the injection pressure required in this case is 5.130 MPa and the filling time is 0.7437 seconds.

Regarding the other plastic injection technological parameters (filling speed, melting temper‐ ature, cooling time), it is important to specify the fact that these parameters have a significant importance in the plastic injection process. Filling speed depends on the injection pressure and the properties of the plastic material. The cooling time is directly correlated with the capacity of injection moulding tool to conduct the thermal energy at the end.

An important aspect regarding the finite element analysis that has been performed is repre‐ sented by the volumetric shrinkage at the end of the injection moulding process. As it is possible to observe in **Figure 15**, the volumetric shrinkage in the case of ABS plastic material were less than 4% for more than 90% of total part surface. In the clamping areas, the volumetric shrinkage values were higher, being closed to a value of 7%.

 **Figure 14.** Injection pressure and filling time in the case of ABS plastic material.

 **Figure 15.** Volumetric shrinkage at ejection at the end of injection moulding process.

The results obtained using the finite element analyses made using the MoldFlow program in the case of all plastic materials – Acryl Butadiene Styrene – ABS, Polypropylene – PP, Polya‐ mide armed with glass fibers - PA+30% GF and Poly Oxy Methylene– POM- are presented in **Table 4**.

The technological parameters presented in **Table 4** were used for the injection moulding tests that were made at Plastor SA Company from Oradea. All plastic materials were dried in an oven for three hours at a temperature of 80°C, with the exception of the Poly-propylene (PP) material which is not required to be dried. The maximum clamping force used during the injection moulding tests was 5 T for all four types of plastic materials that were tested.


**Table 4.** Results obtained using finite element analyses made by using Mold Flow program.

An important aspect regarding the finite element analysis that has been performed is repre‐ sented by the volumetric shrinkage at the end of the injection moulding process. As it is possible to observe in **Figure 15**, the volumetric shrinkage in the case of ABS plastic material were less than 4% for more than 90% of total part surface. In the clamping areas, the volumetric

shrinkage values were higher, being closed to a value of 7%.

172 New Trends in 3D Printing

 **Figure 14.** Injection pressure and filling time in the case of ABS plastic material.

 **Figure 15.** Volumetric shrinkage at ejection at the end of injection moulding process.

**Table 4**.

The results obtained using the finite element analyses made using the MoldFlow program in the case of all plastic materials – Acryl Butadiene Styrene – ABS, Polypropylene – PP, Polya‐ mide armed with glass fibers - PA+30% GF and Poly Oxy Methylene– POM- are presented in

The technological parameters presented in **Table 4** were used for the injection moulding tests that were made at Plastor SA Company from Oradea. All plastic materials were dried in an oven for three hours at a temperature of 80°C, with the exception of the Poly-propylene (PP)

**Figure 16.** Injection moulding tools mounted on the Arburg 370 CMD 800-325 testing machine from Plastor SA Ora‐ dea.

The injection pressure is different in accordance with the type of the plastic material that was tested. The injection pressure was for example 50 bars in the case of PP material and 210 bars in the case of ABS material. This fact was mainly caused by the fact that the PP material had a density of 0.9 g/cm3 as compared to the ABS material which had a density of 1.2 g/cm3 . In order to fill in the cavity with plastic material in the second case, a pressure difference of 160 bars is necessary.

The cooling time was adjusted differently in accordance with the plastic material that was injected into the mould. In the case of PA plastic material, a total time of 15 seconds is required, as compared with the ABS plastic material where the cooling time required is 50 seconds. This can be explained by the fact that the thermal conductivity coefficient is different in these cases. In the case of PA material, the thermal conductivity coefficient is 0.36 W/mK, while in the case of the ABS plastic material the value of this coefficient is 0.17 W/mK. The difference of 0.19 W/ mK is transformed to the time difference required to cool-down the material in a supplemen‐ tary period of 35 seconds.

#### **2.4. Conclusion**

As a conclusion of made research, it is possible to state that the Selective Laser Melting technology is easy to be understood in principle, but it is not so easy to be controlled. There are a lot of aspects that have to be taken into consideration when speaking about the accuracy of the injection moulding tools made by Selective Laser Melting (SLM), starting with the properties of the raw material, the optical system and ending with the scanning strategy or the technological parameters that are used in the manufacturing process. As related to the technological parameters (laser power, scanning speed, powder bed temperature, etc.), as it has been proven by the finite element analyses that were made, it is very difficult to find a set of technological parameters that would be unique and universally valid in all cases of moulds manufactured by Selective Laser Melting from H13 Tool Steel material. The accuracy of the injection-moulded tools made by Selective Laser Melting technology will be different, being dependent on the geometry of the tools (the size and the shape) and the accuracy of the process. Research still needs to be done in the future regarding the determination of scale factors that can be applied in the pre-processing stage onto the 3D model that has to be manufactured using the Selective Laser Melting equipment. The injection moulding tools were successfully manufactured on an SLM 250 HL equipment in the SLM Solutions GmbH Company from Luebeck (Germany) and tested in the injection moulding process of four type of plastic materials (Acryl Butadiene Styrene – ABS, Polypropylene – PP, Polyamide armed with glass fibers - PA+30% GF and Poly Oxy Methylene– POM) at Plastor SA Company from Oradea (Romania), as it is possible to observe in **Figure 17**.

**Figure 17.** Injected plastic materials obtained at Plastor SA Oradea using the injection moulding tools made by SLM.
