COMPANY
The POM Group, Inc. is a full service provider of services and technologies for rapid product development. POM specializes in the design and build of mission critical tooling systems used to cast, stamp, or injection mold high volume products. POM's mission is to assist our clients in bringing new products to market with the shortest lead-time and lowest possible cost. We are a minority owned and operated business, certified by the Michigan Minority Business Development Council (MMBDC)
DMD™ (Direct Metal Deposition
DMD™ is a revolutionary additive metal process that fabricates fully dense, highly accurate molds and dies … in record level lead times. DMD is a laser-based fabrication technology that produces 100% dense metal products “from the ground up” using powdered metal. The first major advance in metalworking in decades, DMD produces tooling with superior material properties … in less time … and at a lower cost than is possible with traditional fabrication technologies.
The POM Group, Inc. is the winner of the 2002 PACE (Premier Automotive Suppliers' Contributions to Excellence) Award for its Direct Metal Deposition (DMD)® technology. The PACE award, sponsored by Automotive News and Cap Gemini Ernst & Young, LLP, recognizes creativity, excellence, and innovation in the automotive supply industry. The PACE Award, considered the most coveted of all automotive supplier awards, recognizes automotive suppliers from around the world who have embraced innovation to meet the growing service and quality demands of their customers; the world’s major automotive manufacturers
POM ADVANTAGE
Through a conbination of advanced metal fabrication technologies, highly skilled employees, advanced planning techniques and superior service, POM offers a complete solution to the high cost and long lead-time associated with designing and building tooling systems. POM's Advanced Product Development Center, located within Michigan's Automation Alley, houses the world's largest additive metal fabrication facility and offers 24/7/365 lights-out tooling fabrication, restoration and repair. POM's wide range of service offerings include:
• Tooling Design
• Tooling Performance and Predictive Modeling
• Tooling Optimization
• Reverse Engineering
• Tooling Reconfiguration (NuTool)
• Tooling Repair and Restoration (ToolRx)
• Additive Metal Changes to Existing Tooling
• Advanced Thermal Management Tooling (CoolMOLD)
• Tooling Surface Hardfacing (LaserCLAD)
Rapid Tooling Systems
Tuesday, November 27, 2007
Rapid tooling and it's faster in modeling
the next step in this project was to collect some information about rapid tooling and pom group.inc. this information was prepared by Don.
The "rapid" in rapid-tooling technology originally meant that molds could be made much faster than with conventional machining. That's still true. But in the last few years, RT technology has evolved toward building molds that provide up to 40% faster cycles than are possible with conventional technology. That emphasis on productivity accompanies a shift in RT applications from prototype to full production tooling.
Newer RT approaches can minimize or eliminate warpage and internal stresses caused by uneven cooling while boosting productivity by drawing heat more quickly from thick sections or other hard-to-cool features in the mold such as bosses or ribs. Tests of newer high-conductivity tools by at least two sources reportedly found that cooling time in the molding cycle could be set to zero and the process would still yield acceptable parts.
Conventional tool making is limited by two factors: One is the modest thermal conductivity of standard tool steels like H-13, P-20, or stainless, which are chosen for hardness and/or corrosion resistance. Cooling is also limited by reliance on straight gun-drilled channels in the mold base. Conventional mold makers can attempt to overcome these limitations with inserts of beryllium-copper or other highly conductive copper alloys, secondary cooling channels or "bubblers" in deep cores, and heat pipes or "thermal pins" that can reach into the body of the tool to extract heat.
Suppliers of rapid tool making techniques have developed two routes to improved mold cooling: building conductive metals into the tool from the start and/or incorporating cooling channels that conform to the part surface, no matter how irregular its shape. RT suppliers claim that either or both of these methods can do better than either bubblers or heat pipes. And the newer RT methods typically combine conductive metals with a tool steel to create a bimetallic structure that helps deliver better wear resistance than copper alloys or aluminum alone.
Some conductive alloys for conventional mold making have hardness values as high as 30 to 40 Rc, similar to P-20 steel. There are also methods of prehardening copper alloys and aluminum to similar levels, says metals supplier Bohler-Uddeholm. But today's RT techniques combine conductive metals with tool steels in bimetallic structures that provide high conductivity with hardness of 50 to 80 Rc—as high or higher than H-13 steel.
New developments with hard but highly conductive metals could give a needed boost to acceptance of rapid tooling, which has prompted great interest but only modest adoption by mold makers and molders. For the most part, RT approaches have found use in prototype and low-volume production. Now, so-called "bridge" tooling applications and high-volume jobs are within RT's grasp. "Basically, the goal now is to get the same tool life with the higher cooling rates for the faster cycles," says Jim Knirsch, president of RSP Tooling, a supplier of RT technology.
Bimetal layering methods
POM Group's Direct Metal Deposition technique produces a 99.8% fully dense tool component from metal powder. Commercialized in 1998, the process uses a 5-kw laser and powdered tool steel (D-2, H-13, P-20, stainless, or many other types). To make a highly conductive tool or component, the first step is to fabricate a core out of a conductive metal such as Ampco 940 chromium copper alloy. Then a steel shell is deposited on the core by DMD.
The process starts with a specially designed nozzle with separate orifices for the laser, the metal powder, and the inert gas that creates an oxygen-free environment. The layer-by-layer building of the tool follows a tool path generated from a CAD file. A small amount of powdered metal is injected through orifices in the nozzle onto a spot 1 to 2 mm in diam. As the powder reaches the substrate surface, the laser beam simultaneously melts the metal into a small pool, which cools quickly as the laser moves on. Build rate ranges from 2 to 9 cu in./hr. The shell is built up in layers of 0.5 to 1.25 mm to a near-net shape with 0.007 to 0.010 excess material that must be finished with conventional polishing or EDM. POM claims there is a true metallurgical bond between the core and shell, achieved with the aid of a proprietary metal-based "interface" or bond coat.
POM offers a five-axis DMD machine with a work area of 1 x 2 x 0.75 meter. Depending on the powder-metal alloy used, DMD can produce a steel shell with surface hardness as high as 62 Rc. Because of this, POM can use its technology to repair damaged tools. If a tool is being modified because of a design change in the part, just the area to be changed can be machined away and a new geometry added directly to the mold with DMD and machined to final dimensions. Unlike a conventionally rebuilt mold, there is no need to subject the entire mold to heat treating to harden the rebuilt section. Also, DMD can be used to add conformal cooling channels to slides, inserts, and lifters of old tools to reduce cycle time.
The Rapid Prototyping Center at the University of Louisville, Ky., has a DMD system from POM and is conducting extensive tests with bimetallic tools of chromium copper and H-13 steel to evaluate tool life and overall performance. A single-cavity tool ran PP with zero cooling time, cutting the overall cycle from 27 sec to 22 sec, while still producing acceptable parts. The Center is also testing the capabilities of DMD tools for aluminum die casting, which is a much harsher processing environment, says Tim Gornet, a research associate at the Univ. of Louisville Rapid Prototyping Center.
A second RT process involving bimetallic layering is RSP's Rapid Solidification Process, a metal spray deposition method that produces 99.5% to 99.8% fully dense cores and cavities. The process was developed at the Idaho National Engineering & Environmental Laboratory (INEEL) in a two-year consortium with 11 companies. The process uses a ceramic pattern built with the aid of stereolithography, SLS, or other rapid-prototyping process. Then molten steel is injected into the nozzle where it encounters a channeled flow of inert gas that conveys droplets 18 to 24 in. to the part surface. The droplets cool rapidly in flight and solidify instantly when they encounter the pattern. The nozzle can deposit up to 500 lb/hr of material. The spray deposition process mimics surface detail closely. To produce a skin/core structure, the deposited steel is heated, and then a layer of copper alloy is sprayed over it. Conformal cooling lines can be added to the tool by stopping the spray process, placing copper tubing, and then encapsulating it with more sprayed metal.
Says RSP's Knirsch, "Spraying the steel layer first allows for an even layer to be built. That will give us uniform heat transfer from the molding surface. The copper layer will vary in thickness across the mold. We let the copper make up the full depth of the insert."
The bond between the steel and copper is formed by the rough-spray technique, whereby the open surface of the steel is extremely rough. When the copper is sprayed over the steel, it infiltrates the nooks and crannies forming a strong physical bond, though not a metallurgical bond.
Mold components can be built in minutes to dimensional tolerances closer than ±0.002 in. Parts can be made up to 7 x 7 x 4 in. and a machine with larger capacity is planned.
The RSP process can be used with at least 10 different tool steels and with softer materials. When used with H-13, tool hardness can exceed the 60 Rc of a conventionally heat-treated H-13. This is due to the quick quenching of the sprayed droplets, which affects grain structure and strength. RSP tooling can also be heat treated and tempered.
RSP is evaluating high-chrome- content metals, which can deliver even higher hardness. It is also testing Inconel, a high-temperature, corrosion-resistant nickel-chrome-iron alloy. Future developments will also provide the ability to blend different metals during the spraying process.
The "rapid" in rapid-tooling technology originally meant that molds could be made much faster than with conventional machining. That's still true. But in the last few years, RT technology has evolved toward building molds that provide up to 40% faster cycles than are possible with conventional technology. That emphasis on productivity accompanies a shift in RT applications from prototype to full production tooling.
Newer RT approaches can minimize or eliminate warpage and internal stresses caused by uneven cooling while boosting productivity by drawing heat more quickly from thick sections or other hard-to-cool features in the mold such as bosses or ribs. Tests of newer high-conductivity tools by at least two sources reportedly found that cooling time in the molding cycle could be set to zero and the process would still yield acceptable parts.
Conventional tool making is limited by two factors: One is the modest thermal conductivity of standard tool steels like H-13, P-20, or stainless, which are chosen for hardness and/or corrosion resistance. Cooling is also limited by reliance on straight gun-drilled channels in the mold base. Conventional mold makers can attempt to overcome these limitations with inserts of beryllium-copper or other highly conductive copper alloys, secondary cooling channels or "bubblers" in deep cores, and heat pipes or "thermal pins" that can reach into the body of the tool to extract heat.
Suppliers of rapid tool making techniques have developed two routes to improved mold cooling: building conductive metals into the tool from the start and/or incorporating cooling channels that conform to the part surface, no matter how irregular its shape. RT suppliers claim that either or both of these methods can do better than either bubblers or heat pipes. And the newer RT methods typically combine conductive metals with a tool steel to create a bimetallic structure that helps deliver better wear resistance than copper alloys or aluminum alone.
Some conductive alloys for conventional mold making have hardness values as high as 30 to 40 Rc, similar to P-20 steel. There are also methods of prehardening copper alloys and aluminum to similar levels, says metals supplier Bohler-Uddeholm. But today's RT techniques combine conductive metals with tool steels in bimetallic structures that provide high conductivity with hardness of 50 to 80 Rc—as high or higher than H-13 steel.
New developments with hard but highly conductive metals could give a needed boost to acceptance of rapid tooling, which has prompted great interest but only modest adoption by mold makers and molders. For the most part, RT approaches have found use in prototype and low-volume production. Now, so-called "bridge" tooling applications and high-volume jobs are within RT's grasp. "Basically, the goal now is to get the same tool life with the higher cooling rates for the faster cycles," says Jim Knirsch, president of RSP Tooling, a supplier of RT technology.
Bimetal layering methods
POM Group's Direct Metal Deposition technique produces a 99.8% fully dense tool component from metal powder. Commercialized in 1998, the process uses a 5-kw laser and powdered tool steel (D-2, H-13, P-20, stainless, or many other types). To make a highly conductive tool or component, the first step is to fabricate a core out of a conductive metal such as Ampco 940 chromium copper alloy. Then a steel shell is deposited on the core by DMD.
The process starts with a specially designed nozzle with separate orifices for the laser, the metal powder, and the inert gas that creates an oxygen-free environment. The layer-by-layer building of the tool follows a tool path generated from a CAD file. A small amount of powdered metal is injected through orifices in the nozzle onto a spot 1 to 2 mm in diam. As the powder reaches the substrate surface, the laser beam simultaneously melts the metal into a small pool, which cools quickly as the laser moves on. Build rate ranges from 2 to 9 cu in./hr. The shell is built up in layers of 0.5 to 1.25 mm to a near-net shape with 0.007 to 0.010 excess material that must be finished with conventional polishing or EDM. POM claims there is a true metallurgical bond between the core and shell, achieved with the aid of a proprietary metal-based "interface" or bond coat.
POM offers a five-axis DMD machine with a work area of 1 x 2 x 0.75 meter. Depending on the powder-metal alloy used, DMD can produce a steel shell with surface hardness as high as 62 Rc. Because of this, POM can use its technology to repair damaged tools. If a tool is being modified because of a design change in the part, just the area to be changed can be machined away and a new geometry added directly to the mold with DMD and machined to final dimensions. Unlike a conventionally rebuilt mold, there is no need to subject the entire mold to heat treating to harden the rebuilt section. Also, DMD can be used to add conformal cooling channels to slides, inserts, and lifters of old tools to reduce cycle time.
The Rapid Prototyping Center at the University of Louisville, Ky., has a DMD system from POM and is conducting extensive tests with bimetallic tools of chromium copper and H-13 steel to evaluate tool life and overall performance. A single-cavity tool ran PP with zero cooling time, cutting the overall cycle from 27 sec to 22 sec, while still producing acceptable parts. The Center is also testing the capabilities of DMD tools for aluminum die casting, which is a much harsher processing environment, says Tim Gornet, a research associate at the Univ. of Louisville Rapid Prototyping Center.
A second RT process involving bimetallic layering is RSP's Rapid Solidification Process, a metal spray deposition method that produces 99.5% to 99.8% fully dense cores and cavities. The process was developed at the Idaho National Engineering & Environmental Laboratory (INEEL) in a two-year consortium with 11 companies. The process uses a ceramic pattern built with the aid of stereolithography, SLS, or other rapid-prototyping process. Then molten steel is injected into the nozzle where it encounters a channeled flow of inert gas that conveys droplets 18 to 24 in. to the part surface. The droplets cool rapidly in flight and solidify instantly when they encounter the pattern. The nozzle can deposit up to 500 lb/hr of material. The spray deposition process mimics surface detail closely. To produce a skin/core structure, the deposited steel is heated, and then a layer of copper alloy is sprayed over it. Conformal cooling lines can be added to the tool by stopping the spray process, placing copper tubing, and then encapsulating it with more sprayed metal.
Says RSP's Knirsch, "Spraying the steel layer first allows for an even layer to be built. That will give us uniform heat transfer from the molding surface. The copper layer will vary in thickness across the mold. We let the copper make up the full depth of the insert."
The bond between the steel and copper is formed by the rough-spray technique, whereby the open surface of the steel is extremely rough. When the copper is sprayed over the steel, it infiltrates the nooks and crannies forming a strong physical bond, though not a metallurgical bond.
Mold components can be built in minutes to dimensional tolerances closer than ±0.002 in. Parts can be made up to 7 x 7 x 4 in. and a machine with larger capacity is planned.
The RSP process can be used with at least 10 different tool steels and with softer materials. When used with H-13, tool hardness can exceed the 60 Rc of a conventionally heat-treated H-13. This is due to the quick quenching of the sprayed droplets, which affects grain structure and strength. RSP tooling can also be heat treated and tempered.
RSP is evaluating high-chrome- content metals, which can deliver even higher hardness. It is also testing Inconel, a high-temperature, corrosion-resistant nickel-chrome-iron alloy. Future developments will also provide the ability to blend different metals during the spraying process.
Monday, November 26, 2007
Sunday, November 25, 2007
S.L.S Metal powder& Test Results
1. Introduction
Selective laser sintering (SLS) is one of layered manufacturing technologies that can directly create component from powder-based materials layer by layer according to CAD model , and . It is much significant for metal parts to be manufactured via SLS process without the aid of any tooling because metal parts are always widely used and highly valued in the world. In present, it is competent for indirect SLS to fabricate metal parts through several steps. Firstly, a metal green shape composed of polymer binder and metal powders is usually formed via SLS process. Then polymer binder is burned out of the green shape and the shape is sintered at high temperature to be a porous metal part. Pores still in it, the sintered part should be infiltrated with low melting point materials such as resin, copper, brass and bronze to be a fully dense object finally. Thus, manufacturing metal parts via indirect SLS process is usually composed of two cycles which are SLS forming cycle and post furnace densification cycle, respectively.
As for steel parts, singular alloy powders such as 316, 316L, 420 stainless steel, 1080 steel and alike powders are used as indirect SLS processing powders previously. But not all types of steel powders can be purchased in the market, and it is also inconvenient for them to be produced due to the trouble of content control. Hence it is not an appropriate method to apply singular alloy powders to produce metal parts in SLS process.
2. Experimentation
2.1. Materials
Several alloy elemental powders are selected in SLS process, and they are electrolytic iron powder, deoxidized copper powder, carbonyl nickel powder and graphite powder (Table 1. Polymer powders with the diameter within 12 μm are used as a binder whose softening point is about 44 °C in the experiment. The powder materials listed in Table 1 are all irregular and they are blended with polymer binder in a 3D movement container to compose CEPS admixture. The weight ratio of polymer binder is 3% in each admixture.
Table 1.
The size and compositions of CEPS
Element
Size (μm)
1 (%)
2 (%)
3 (%)
4 (%)
5 (%)
Cu ≤45 8 8 8 8 8
Ni ≤7 0 0 4 4 0
C ≤45 0.5 1 0.5 1 0
Fe ≤45 Balanced Balanced Balanced Balanced Balanc
2.2. Experimental procedures
Metal green shapes were formed on the HRPS-II A SLS system manufactured by Huazhong University of Science and Technology (HUST) in China. The system is assembled with a continuous wave CO2 laser (wavelength = 10.6 μm). The power of CO2 laser is continuously adjustable from 0 to 50 W, and the laser beam spot is 0.2–0.25mm in diameter. To determine the appropriate SLS process parameters including laser power, scan speed, scan spacing, layer thickness and powder bed temperature, six terms of specimens (100 mm × 10 mm × 5 mm) were formed. There were five specimens in each term. Also provides the building orientation and the layer structure of a specimen. During SLS forming process, scan speed, scan spacing, layer thickness and powder bed temperature were kept 2000 mm/s, 0.1 mm, 0.1 mm and 35 °C, respectively, except laser power which was varied from 14 to 20 W. But as for a certain term of specimens, laser power was adjusted to a fixed value between 14 and 20 W. Then three points bending tests were carried out on a universal test machine after the specimens had been formed completely. The mean value of the bending strength of five specimens in one term was considered as the final result corresponding to a given laser power. Then the highest strength corresponding to one certain combination of parameters is obtained after the bending test, and the parameters in this combination were regarded as optimal ones. Metal green shapes (240 mm × 70 mm × 50 mm) of different composition in Table 1 were built on the HRPS-II A using optimal parameters subsequently. Meanwhile, the binder material was examined for the thermal gravity (TG) behavior in N2 at the heating rate of 10 °C/min to about 750 °C. Then the green shapes were degreased in a furnace in H2 environment according to the TG behavior of the binder material. After the binder had been burnt out, the green shapes were heated in a vacuum furnace at a heating rate of 15 °C/min from room temperature (RT) to 900 °C and 5 °C/min from 900 to 1200 °C, and then they are cooled naturally in the furnace after being sintered at 1200 °C/2 h. After the examination of the porosity of the sintered parts using Archimedes’ law, appropriate copper powder compact in which the volume of full dense copper is equal to the total volume of the pores in the sintered parts were placed on them before infiltration process. All the sintered parts were then infiltrated with molten copper in a sintering furnace in H2 environment at 1200 °C/1 h with a heating rate of 15 °C/min from RT to 1200 °C, and naturally cooled to RT. After infiltration process, the whole alloys except no. 5 alloy in Table 1 were thermally treated following the processes shown in Table 2 to modify their mechanical properties. Five tensile specimens (ASTM E8) were made out of each copper infiltrated alloys through linear cutting and then they were tensile loaded on a universal testing machine with the loading rate of 3 mm/min. Likewise, the average value of five data of a term of alloys was accepted for the final result. The copper infiltrated alloys of different composition were also examined for Brinell hardness using a 10 mm tempered steel ball with the load of 3000 kg and the loading time was 30 s. The final result was also the mean value of five data. Then samples were prepared from copper infiltrated alloys for examination by X-Ray diffraction (XRD), scanning electron microscope (SEM) using standard techniques.
The thermal treatments processes
Quenching temperature (°C)
Tempering temperature (°C)
1 850
2 800 200
3 890
4 830
3. Results and discussion
SLS parameters except laser power and powder bed temperature are universal ones in this SLS system. While both laser power and powder bed temperature are connected with powder materials, it is appropriate to keep the powder bed temperature at 35 °C which is close to the softening point of binder material . Then laser power can be determined by the green shapes’ maximum strength which is a vital factor in SLS forming cycle. This method is feasible because the strength of metal green shapes is only associated with laser power on the condition that other parameters are kept constant.
Polymer viscosity flow is formed when the polymer binder is heated by laser beam, and then it wets metal particles’ surfaces to bind them finally. Furthermore, the higher the laser power is, the higher the temperature of the flow is to lower its viscosity, which makes many more surfaces of the metal particles be wetted and bonded. Polymer binder even vaporizes and decomposes if laser power increases highly enough to cause binder flow temperature to rise up to its vapor or even decomposition point. But the bending strength of metal green shapes decreases simultaneously due to the excessive vaporization and decomposition of polymer binder. The relationship between the bending strength of metal green shapes and the laser power is shown in Fig. 2. Seen in Fig. 2, the strength reaches its peak value (2.41 MPa) when laser power approach 19 W. The strength drops if the laser power exceeds 19 W. Therefore, the appropriate value of laser power is 19 W and then the optimal SLS parameters are: laser power, 19 W; scan speed, 2000 mm/s; scan spacing, 0.1 mm; layer thickness, 0.1 mm; powder bed temperature, 35 °C.
4. Summary and conclusions
Metal green shapes composed of polymer bonded composite elemental powders (iron, copper, nickel and graphite) are formed via indirect SLS process. The operating parameters are as follows: laser power, 21 W; laser scan speed, 2000 mm/s; laser scan spacing, 0.1 mm; layer thickness, 0.1 mm; powder bed temperature, 35 °C. The bending strength of these green shapes is 2.41 MPa. After a series of post densification processes such as decomposition until 900 °C, sintered at 1200 °C and infiltrated with molten copper at 1200 °C, hybrid alloys composed of iron based alloy and copper are obtained finally.
Alloy elements (copper, nickel, graphite) can diffuse into γ-Fe during sintering and infiltration processes, and they distribute homogeneously after infiltration process. Quenched at different temperatures higher than 800 °C and then tempered at 200 °C, tempered martensite and precipitated α-Cu are the main RT microstructures of copper infiltrated Fe–8Cu–4Ni–0.5C and Fe–8Cu–0.5C alloys. Fe–Cu eutectoid still remains in copper infiltrated Fe–8Cu–4Ni–1C and Fe–8Cu–1C alloys to worsen the
mechanical properties of the two hybrid alloys. On the condition of the same content of carbon and copper, the addition of nickel enhances the strength of hybrid alloys due to the solution strengthening of nickel. The elongation of all the hybrid alloys is lower than 3%, the yield strength of them is over 400 MPa, the Brinell hardness of them is over 200 and the elastic modulus around 100 GPa. Compared to other hybrid alloys, copper infiltrated Fe–8Cu–4Ni–0.5C alloy has better mechanical properties.
A typical CEPS of iron based alloy system and steel parts fabricated with these CEPS via indirect SLS process are successfully presented in this paper. In addition, many more alloy elements such as molybdenum, titanium, vanadium and chromium can also be used as constituents of CEPS besides those powders mentioned in this experiment. With the introduction of CEPS to SLS process, the trouble of the preparation of powder materials is eliminated, and manufacturing steel parts via indirect SLS process becomes convenient either. The mechanical properties of these hybrid alloy parts can also be varied conveniently though changing the category and proportion of alloy element powders among CEPS. Therefore CEPS break a new direction for indirect SLS process to fabricate alloy parts.
Selective laser sintering (SLS) is one of layered manufacturing technologies that can directly create component from powder-based materials layer by layer according to CAD model , and . It is much significant for metal parts to be manufactured via SLS process without the aid of any tooling because metal parts are always widely used and highly valued in the world. In present, it is competent for indirect SLS to fabricate metal parts through several steps. Firstly, a metal green shape composed of polymer binder and metal powders is usually formed via SLS process. Then polymer binder is burned out of the green shape and the shape is sintered at high temperature to be a porous metal part. Pores still in it, the sintered part should be infiltrated with low melting point materials such as resin, copper, brass and bronze to be a fully dense object finally. Thus, manufacturing metal parts via indirect SLS process is usually composed of two cycles which are SLS forming cycle and post furnace densification cycle, respectively.
As for steel parts, singular alloy powders such as 316, 316L, 420 stainless steel, 1080 steel and alike powders are used as indirect SLS processing powders previously. But not all types of steel powders can be purchased in the market, and it is also inconvenient for them to be produced due to the trouble of content control. Hence it is not an appropriate method to apply singular alloy powders to produce metal parts in SLS process.
2. Experimentation
2.1. Materials
Several alloy elemental powders are selected in SLS process, and they are electrolytic iron powder, deoxidized copper powder, carbonyl nickel powder and graphite powder (Table 1. Polymer powders with the diameter within 12 μm are used as a binder whose softening point is about 44 °C in the experiment. The powder materials listed in Table 1 are all irregular and they are blended with polymer binder in a 3D movement container to compose CEPS admixture. The weight ratio of polymer binder is 3% in each admixture.
Table 1.
The size and compositions of CEPS
Element
Size (μm)
1 (%)
2 (%)
3 (%)
4 (%)
5 (%)
Cu ≤45 8 8 8 8 8
Ni ≤7 0 0 4 4 0
C ≤45 0.5 1 0.5 1 0
Fe ≤45 Balanced Balanced Balanced Balanced Balanc
2.2. Experimental procedures
Metal green shapes were formed on the HRPS-II A SLS system manufactured by Huazhong University of Science and Technology (HUST) in China. The system is assembled with a continuous wave CO2 laser (wavelength = 10.6 μm). The power of CO2 laser is continuously adjustable from 0 to 50 W, and the laser beam spot is 0.2–0.25mm in diameter. To determine the appropriate SLS process parameters including laser power, scan speed, scan spacing, layer thickness and powder bed temperature, six terms of specimens (100 mm × 10 mm × 5 mm) were formed. There were five specimens in each term. Also provides the building orientation and the layer structure of a specimen. During SLS forming process, scan speed, scan spacing, layer thickness and powder bed temperature were kept 2000 mm/s, 0.1 mm, 0.1 mm and 35 °C, respectively, except laser power which was varied from 14 to 20 W. But as for a certain term of specimens, laser power was adjusted to a fixed value between 14 and 20 W. Then three points bending tests were carried out on a universal test machine after the specimens had been formed completely. The mean value of the bending strength of five specimens in one term was considered as the final result corresponding to a given laser power. Then the highest strength corresponding to one certain combination of parameters is obtained after the bending test, and the parameters in this combination were regarded as optimal ones. Metal green shapes (240 mm × 70 mm × 50 mm) of different composition in Table 1 were built on the HRPS-II A using optimal parameters subsequently. Meanwhile, the binder material was examined for the thermal gravity (TG) behavior in N2 at the heating rate of 10 °C/min to about 750 °C. Then the green shapes were degreased in a furnace in H2 environment according to the TG behavior of the binder material. After the binder had been burnt out, the green shapes were heated in a vacuum furnace at a heating rate of 15 °C/min from room temperature (RT) to 900 °C and 5 °C/min from 900 to 1200 °C, and then they are cooled naturally in the furnace after being sintered at 1200 °C/2 h. After the examination of the porosity of the sintered parts using Archimedes’ law, appropriate copper powder compact in which the volume of full dense copper is equal to the total volume of the pores in the sintered parts were placed on them before infiltration process. All the sintered parts were then infiltrated with molten copper in a sintering furnace in H2 environment at 1200 °C/1 h with a heating rate of 15 °C/min from RT to 1200 °C, and naturally cooled to RT. After infiltration process, the whole alloys except no. 5 alloy in Table 1 were thermally treated following the processes shown in Table 2 to modify their mechanical properties. Five tensile specimens (ASTM E8) were made out of each copper infiltrated alloys through linear cutting and then they were tensile loaded on a universal testing machine with the loading rate of 3 mm/min. Likewise, the average value of five data of a term of alloys was accepted for the final result. The copper infiltrated alloys of different composition were also examined for Brinell hardness using a 10 mm tempered steel ball with the load of 3000 kg and the loading time was 30 s. The final result was also the mean value of five data. Then samples were prepared from copper infiltrated alloys for examination by X-Ray diffraction (XRD), scanning electron microscope (SEM) using standard techniques.
The thermal treatments processes
Quenching temperature (°C)
Tempering temperature (°C)
1 850
2 800 200
3 890
4 830
3. Results and discussion
SLS parameters except laser power and powder bed temperature are universal ones in this SLS system. While both laser power and powder bed temperature are connected with powder materials, it is appropriate to keep the powder bed temperature at 35 °C which is close to the softening point of binder material . Then laser power can be determined by the green shapes’ maximum strength which is a vital factor in SLS forming cycle. This method is feasible because the strength of metal green shapes is only associated with laser power on the condition that other parameters are kept constant.
Polymer viscosity flow is formed when the polymer binder is heated by laser beam, and then it wets metal particles’ surfaces to bind them finally. Furthermore, the higher the laser power is, the higher the temperature of the flow is to lower its viscosity, which makes many more surfaces of the metal particles be wetted and bonded. Polymer binder even vaporizes and decomposes if laser power increases highly enough to cause binder flow temperature to rise up to its vapor or even decomposition point. But the bending strength of metal green shapes decreases simultaneously due to the excessive vaporization and decomposition of polymer binder. The relationship between the bending strength of metal green shapes and the laser power is shown in Fig. 2. Seen in Fig. 2, the strength reaches its peak value (2.41 MPa) when laser power approach 19 W. The strength drops if the laser power exceeds 19 W. Therefore, the appropriate value of laser power is 19 W and then the optimal SLS parameters are: laser power, 19 W; scan speed, 2000 mm/s; scan spacing, 0.1 mm; layer thickness, 0.1 mm; powder bed temperature, 35 °C.
4. Summary and conclusions
Metal green shapes composed of polymer bonded composite elemental powders (iron, copper, nickel and graphite) are formed via indirect SLS process. The operating parameters are as follows: laser power, 21 W; laser scan speed, 2000 mm/s; laser scan spacing, 0.1 mm; layer thickness, 0.1 mm; powder bed temperature, 35 °C. The bending strength of these green shapes is 2.41 MPa. After a series of post densification processes such as decomposition until 900 °C, sintered at 1200 °C and infiltrated with molten copper at 1200 °C, hybrid alloys composed of iron based alloy and copper are obtained finally.
Alloy elements (copper, nickel, graphite) can diffuse into γ-Fe during sintering and infiltration processes, and they distribute homogeneously after infiltration process. Quenched at different temperatures higher than 800 °C and then tempered at 200 °C, tempered martensite and precipitated α-Cu are the main RT microstructures of copper infiltrated Fe–8Cu–4Ni–0.5C and Fe–8Cu–0.5C alloys. Fe–Cu eutectoid still remains in copper infiltrated Fe–8Cu–4Ni–1C and Fe–8Cu–1C alloys to worsen the
mechanical properties of the two hybrid alloys. On the condition of the same content of carbon and copper, the addition of nickel enhances the strength of hybrid alloys due to the solution strengthening of nickel. The elongation of all the hybrid alloys is lower than 3%, the yield strength of them is over 400 MPa, the Brinell hardness of them is over 200 and the elastic modulus around 100 GPa. Compared to other hybrid alloys, copper infiltrated Fe–8Cu–4Ni–0.5C alloy has better mechanical properties.
A typical CEPS of iron based alloy system and steel parts fabricated with these CEPS via indirect SLS process are successfully presented in this paper. In addition, many more alloy elements such as molybdenum, titanium, vanadium and chromium can also be used as constituents of CEPS besides those powders mentioned in this experiment. With the introduction of CEPS to SLS process, the trouble of the preparation of powder materials is eliminated, and manufacturing steel parts via indirect SLS process becomes convenient either. The mechanical properties of these hybrid alloy parts can also be varied conveniently though changing the category and proportion of alloy element powders among CEPS. Therefore CEPS break a new direction for indirect SLS process to fabricate alloy parts.
Tuesday, November 20, 2007
update on laser sintering project
We spoke to Professor Milan Brant on Monday at IRIS at Hawthron. He explained that they were waiting for a technician to cut the sample slices off for our group. We mentioned to him a piece of mild steel with a pilon of stainless steel welded on top of it. He responded by saying we could get a simple shape, eg. a cube, of laser sintering material.
We offered to him to cut up the samples ourselves, polish them and test them accordingly, considering the lab at Swinburne has the equipment required to perform our tests.
Professor Brant told us he will contact us within the next few days.
I perosnally Don will be polishing and etching the samples slices. From that point on, i intend to perform a microscopic examination of the grain structure and any firement. I particularly would like to see if the interzones between laser welded strings.
I personally Ian will be performing hardness testing on the samples, from there i can examine the level of hardness in each sample. I would like to see what the sample looks like through the microscope n the structure on top of the sample.
We offered to him to cut up the samples ourselves, polish them and test them accordingly, considering the lab at Swinburne has the equipment required to perform our tests.
Professor Brant told us he will contact us within the next few days.
I perosnally Don will be polishing and etching the samples slices. From that point on, i intend to perform a microscopic examination of the grain structure and any firement. I particularly would like to see if the interzones between laser welded strings.
I personally Ian will be performing hardness testing on the samples, from there i can examine the level of hardness in each sample. I would like to see what the sample looks like through the microscope n the structure on top of the sample.
Monday, November 19, 2007
Short Info about Heat treatment
as a part of this group I (Haroon) have to do heat treatment test on samples, which are going to be provieded to us. since the samples are not ready i will write abut the process and procedure of the waork later on. but beofre doing all those testings its better to know what heat treatment it self is?
Heat Treatment is the controlled heating and cooling of metals to change their physical and mechanical properties without changing the product shape. Heat Treatment is often associated with increasing the strength of material, but it can also be used to change certain manufacturability objectives such as improve machining, improve formability, restore ductility after a cold working operation. Thus it is a very enabling manufacturing process that can not only help other manufacturing process, but can also improve product performance by increasing strength or other desirable characteristics. Steels and alloys are particularly suitable for heat treatment, since they respond well to heat treatment and the commercial use of steels exceeds that of any other material. Metallic materials consist of a microstructure of small crystals called "grains" or crystallites. The nature of the grains (i.e. grain size and composition) determine the overall mechanical behavior of the metal. Heat treatment provides an efficient way to manipulate the properties of the metal by controlling rate of diffusion, and the rate of cooling within the microstructure. In carbon and low alloy steels, fast rates of cooling result in a high degree of hardness. The idea of heat treating a steel and alloy is to dissolve carbon onto the crystal structure and then retain this structure down to room temperature. This is happening only if the alloys have enough carbon. After the steels or alloys are heated, they are cooled in water in order the keep their structure and it’s done in room temperature. This process is called quenching. Quenched Steel and alloy are harder than those which are annealed.
Heat Treatment is the controlled heating and cooling of metals to change their physical and mechanical properties without changing the product shape. Heat Treatment is often associated with increasing the strength of material, but it can also be used to change certain manufacturability objectives such as improve machining, improve formability, restore ductility after a cold working operation. Thus it is a very enabling manufacturing process that can not only help other manufacturing process, but can also improve product performance by increasing strength or other desirable characteristics. Steels and alloys are particularly suitable for heat treatment, since they respond well to heat treatment and the commercial use of steels exceeds that of any other material. Metallic materials consist of a microstructure of small crystals called "grains" or crystallites. The nature of the grains (i.e. grain size and composition) determine the overall mechanical behavior of the metal. Heat treatment provides an efficient way to manipulate the properties of the metal by controlling rate of diffusion, and the rate of cooling within the microstructure. In carbon and low alloy steels, fast rates of cooling result in a high degree of hardness. The idea of heat treating a steel and alloy is to dissolve carbon onto the crystal structure and then retain this structure down to room temperature. This is happening only if the alloys have enough carbon. After the steels or alloys are heated, they are cooled in water in order the keep their structure and it’s done in room temperature. This process is called quenching. Quenched Steel and alloy are harder than those which are annealed.
Types of Laser Sintering machines
laser sintering machine has got different types which are used in different places for different purposes. here are some of main and important types of laser sintering machines
Metal Parts directly from CAD Data
EOSINT M 270 builds metal parts using Direct Metal Laser-Sintering (DMLS). The technology fuses metal powder into a solid part by melting it locally using a focussed laser beam. The parts are built up additively layer by layer. Even highly complex geometries are created directly from 3D CAD data, fully automatically, in just a few hours and without any tooling. It is a net-shape process, producing parts with high accuracy and detail resolution, good surface quality and excellent mechanical properties.
A wide variety of materials can be processed by the EOSINT M 270, ranging from light alloys via steels to super-alloys and composites. EOS has developed novel alloys especially for the DMLS process, and has also optimized and qualified standard industrial materials such as stainless steels for this machine. Further materials are continually being developed and qualified.
New Perspectives in Manufacturing with DirectPart
EOSINT M 270 is widely used to produce positive parts directly from CAD data. This application is called DirectPart. The components can be prototypes, series production parts or even spare parts. Whether the requirement is to deliver a functional metal prototype within one day, or to economically manufacture hundreds of individualized implants in bio-compatible alloy each week, EOSINT M 270 offers the solution.
Rapid and High-Performance Tooling with DirectTool
DMLS is well known as a leading technology for toolmaking, an application known as DirectTool. With its high accuracy and surface quality, EOSINT M 270 is an ideal platform for this application. The direct process eliminates tool-path generation and multiple machining processes such as EDM. Tool inserts are built overnight or even in just a few hours. Also the freedom of design can be used to optimize tool performance, for example by integrating conformal cooling channels into the tool. Increasingly, both strategies are combined to create improved performance in shorter time. DirectTool is best known for plastic injection moulding. However, the technology is also used for other tooling types including blow moulding, extrusion, die casting, sheet metal forming etc.
EOSINT M 270 is a state-of-the-art laser-sintering system. Its solid-state fibre laser offers high performance and reliability over a long lifetime. Fine focussing optics enable excellent detail resolution and part quality, while a variable focus diameter allows increased productivity and broad process control. The gas-tight process chamber offers an efficient use of a protective atmosphere. This enables a wide range of materials to be processed.
Metal Parts directly from CAD Data
EOSINT M 270 builds metal parts using Direct Metal Laser-Sintering (DMLS). The technology fuses metal powder into a solid part by melting it locally using a focussed laser beam. The parts are built up additively layer by layer. Even highly complex geometries are created directly from 3D CAD data, fully automatically, in just a few hours and without any tooling. It is a net-shape process, producing parts with high accuracy and detail resolution, good surface quality and excellent mechanical properties.
A wide variety of materials can be processed by the EOSINT M 270, ranging from light alloys via steels to super-alloys and composites. EOS has developed novel alloys especially for the DMLS process, and has also optimized and qualified standard industrial materials such as stainless steels for this machine. Further materials are continually being developed and qualified.
New Perspectives in Manufacturing with DirectPart
EOSINT M 270 is widely used to produce positive parts directly from CAD data. This application is called DirectPart. The components can be prototypes, series production parts or even spare parts. Whether the requirement is to deliver a functional metal prototype within one day, or to economically manufacture hundreds of individualized implants in bio-compatible alloy each week, EOSINT M 270 offers the solution.
Rapid and High-Performance Tooling with DirectTool
DMLS is well known as a leading technology for toolmaking, an application known as DirectTool. With its high accuracy and surface quality, EOSINT M 270 is an ideal platform for this application. The direct process eliminates tool-path generation and multiple machining processes such as EDM. Tool inserts are built overnight or even in just a few hours. Also the freedom of design can be used to optimize tool performance, for example by integrating conformal cooling channels into the tool. Increasingly, both strategies are combined to create improved performance in shorter time. DirectTool is best known for plastic injection moulding. However, the technology is also used for other tooling types including blow moulding, extrusion, die casting, sheet metal forming etc.
EOSINT M 270 is a state-of-the-art laser-sintering system. Its solid-state fibre laser offers high performance and reliability over a long lifetime. Fine focussing optics enable excellent detail resolution and part quality, while a variable focus diameter allows increased productivity and broad process control. The gas-tight process chamber offers an efficient use of a protective atmosphere. This enables a wide range of materials to be processed.
shot inf about laser sintering
Laser Sintering is an additive rapid manufacturing technique that uses a high power laser for example, a carbon dioxide laser to fuse small particles of plastic, metal, or ceramic powders into a mass representing a desired 3-dimensional object. The laser selectively fuses powdered material by scanning cross-sections generated from a 3-D digital description of the part e.g. from a CAD file or scan data on the surface of a powder bed. After each cross-section is scanned, the powder bed is lowered by one layer thickness, a new layer of material is applied on top, and the process is repeated until the part is completed.
Compared to other rapid manufacturing methods, SLS can produce parts from a relatively wide range of commercially available powder materials, including polymers nylon, also glass-filled or with other fillers, and polystyrene, metals steel, titanium, alloy mixtures, and composites) and green sand. The physical process can be full melting, partial melting, or liquid-phase sintering. And, depending on the material, up to 100% density can be achieved with material properties comparable to those from conventional manufacturing methods. In many cases large numbers of parts can be packed within the powder bed, allowing very high productivity.
SLS is performed by machines called SLS systems; the most widely known model of which is the Sinterstation SLS system. SLS technology is in wide use around the world due to its ability to easily make very complex geometries directly from digital CAD data. While it began as a way to build prototype parts early in the design cycle, it is increasingly being used in limited run manufacturing to produce end-use parts. One less expected and rapidly growing application of SLS is its use in art
Compared to other rapid manufacturing methods, SLS can produce parts from a relatively wide range of commercially available powder materials, including polymers nylon, also glass-filled or with other fillers, and polystyrene, metals steel, titanium, alloy mixtures, and composites) and green sand. The physical process can be full melting, partial melting, or liquid-phase sintering. And, depending on the material, up to 100% density can be achieved with material properties comparable to those from conventional manufacturing methods. In many cases large numbers of parts can be packed within the powder bed, allowing very high productivity.
SLS is performed by machines called SLS systems; the most widely known model of which is the Sinterstation SLS system. SLS technology is in wide use around the world due to its ability to easily make very complex geometries directly from digital CAD data. While it began as a way to build prototype parts early in the design cycle, it is increasingly being used in limited run manufacturing to produce end-use parts. One less expected and rapidly growing application of SLS is its use in art
Sunday, November 4, 2007
Update on Laser Sintering Project
We sent a letter to Milo Brant on the 25th of October 2007 about getting sample size pieces of mild steel with a continuous laser welded band on top of each sample.
When contacted, we were told that he's currently in the U.S. and would be returning on the 5th of November 2007 and would arrange for a technician to cut off a few samples for us to perform our tests on.
from the Laser Sintering Team
When contacted, we were told that he's currently in the U.S. and would be returning on the 5th of November 2007 and would arrange for a technician to cut off a few samples for us to perform our tests on.
from the Laser Sintering Team
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