production of injection molding tooling with conformal cooling channels using the three dimensional printing process.

by:INDUSTRIAL-MAN     2019-08-28
A solid free-form surface manufacturing process called 3D printing is applied to the manufacture of injection molds with cooling channels shaped with mold cavity.
The tool is made by laying a layer of stainless steel powder and selectively adding the powder to the layer through ink
Jet Printing of adhesive materials.
The unincorporated powder is removed from the green section that does not have such a definition.
The green part is sintering and infiltrating with copper alloy to produce a tool that is completely dense.
The penetration agent by lifting the tool above the free surface of the penetration agent pool in the crucible, resulting in a controlled negative pressure in the penetration agent, thus remaining outside the cooling channel.
Based on the consideration of transient heat transfer, the upper limit of separation of tool cavity and cooling channel is derived.
A set of tools was created to place a split ring and shaped cooling channel on both sides of the cavity and core of the tool.
The performance of the tool is compared to the performance of the tool group with a straight-line cooling channel.
The thermocouple buried in the core and cavity shows that the shape-preserving tool has no transient behavior at the beginning of the molding, while the tool for the straight passage requires 10-
The equilibrium temperature is reached in about 40 cycles [degrees]
The temperature is higher than the temperature of the coolant.
In a single molding cycle, the shape-preserving tool is also found to maintain a more uniform temperature inside the tool.
The gap in the molded open ring does not change with the cycle under the shape-preserving tool, but under the conventional tool. A 2-
D. The finite difference model accurately captures the observed temperature history of the mold with a shape-preserving cooling channel.
Injection molding of polymer components requires higher and higher quality and productivity of parts.
Correct thermal management of injection molds is the key to achieving simultaneous improvement of speed and quality.
The cooling channel placed in the tool manages the heat flow of the plastic.
The current manufacturing method limits the configuration of the cooling channel used for heating.
The freedom to create internal geometry by using a 3d printing process allows the manufacture of molds using complex internal cooling channels.
These cooling channels can be designed to be consistent with the molded cavity.
The shape-preserving channel produced with 3dp process provides the ability to control the mold cavity temperature more precisely throughout the process cycle.
This temperature control has the potential to shorten the cycle time and produce parts with lower residual stress.
Current mold cooling practice cooling in cavity geometry is usually done by wiring straight, drilled cooling channels around the cavity of the part.
These cooling pipe lines need to be drilled and the part injection system is avoided limiting the size and quantity of the cooling system and their proximity to the mold cavity.
Generally, it is not possible to place cooling channels in inserts, and they must be placed in supports or supports.
In this case, additional interfaces are generated, further hindering the removal of heat from the cavity.
Short and independent temperature control performance is optimal.
Compared with the series cooling circuit, the parallel cooling circuit is considered to be a better cooling method.
The short parallel circuit does not allow the coolant to heat up in the mold and provides a more consistent and uniform temperature control [1].
Cooling of core inserts is the biggest problem in most injection molding applications.
Generally, iron ore itself is not cooled.
Cooling occurs only in the mold base through coremount.
Without core cooling, the final heating of the core is inevitable.
Cooling of slender cores is usually done by using plug-ins made of materials with high thermal conductivity, such as copper, be-copper or high-
Strength of sintering copper
Materials [2].
When these plug-ins are pressed
Installed in a steel tool, an additional heat transfer interface is generated.
When in contact with a polymer melt, a reduction in tool life may be noted.
In the case of coolantis passing directly through the core, the baffle is a common cooling method.
The baffle usually uses a Fiat or spiral partition in the hole through the center of the core.
The inlet and return are separate.
This method provides the maximum cross-section for coolant flow.
The divider must be installed in the center of the hole to ensure that the coolant does not bypass the hole.
The most effective cooling of the slender core is achieved through the air bubble.
The feed pipe directs the coolant to the blind hole in the ore.
The diameter of both must be adjusted so that the flow resistance in the two cross sections is equal.
The blister is commercially available and is usually screwed into the core.
A problem with the baffle and bubble cooling system is that the necessary hollow center may result in a core insert with weak structure [2].
Some simple geometric shapes, such as cylinders and tapered cylinders, allow the use of a shape-preserving cooling channel, in which case the quality and productivity are greatly improved.
Current work provides a way to create shape-preserving cooling using the geometry of any molded assembly.
3d printing-
Application of 3D printing of injection mold [3DP]
Is the process of quickly manufacturing 3D parts directly from computer models [3].
Create an entity object by printing a sequence of two-
Dimension layer.
The production of each layer includes the diffusion of the thin layer of the powder material, and then selectively adds the powder to the layer through ink.
Jet Printing of adhesive materials. A continuous-
Jetprint head scans each layer of powder using computer-controlled x-y table.
Stitch separate lines together to form 2 Dlayers and stitch these layers together to form a 3D part.
Unbounce powder temporarily supports the unconnected part of the component, allowing the creation of highlighting, undercutting, and internal volumes.
After the process is completed, the unincorporated powder is removed leaving the final part.
The order of the 3D printing process is shown in the figure. 1.
3D printing can create parts in various material systems including ceramics, metals and polymers.
3D printing has been applied to the manufacture of ceramic shells for metal castings [4]
Structural and electronic ceramic elements5]
, Polymer appearance model, biology
Polymer and end
Using metal parts, the focus of this work is--
Metal injection mold]6].
In this work, use the capabilities of this process to create a high-complexity cooling channel that is compatible with the cavity.
Manufacturing Process overview the steps required to produce injection molding tools using 3d printing are as follows [7]: (1. )
Print the green component.
In this work, stainless steel spherical powder with an average size of 60 [mu]m (
Rutherford Anwar, New Jersey)
Scattered into layers.
A kind of water-based acrylic acid
Polymer emulsion (Acrysol WS-
24. Robben and Hans in Philadelphia)is ink-
Jet printed in order to combine the powder into a green part.
The bulk metal of the green part is about 58%, the polymer is about 10%, and the open hole rate is about 32%. (2. )Powder Removal.
Remove the green part from the powder bed.
In most cases, the movable spherical metal powder will fall off the green part.
Air may be needed in some areas-
Jet to clearpowder.
Then, under the action of gravity and air, the powder is removed from the shape-preserving cooling channel again (see below). (3. )De-Bonding and sintering.
The green parts are packed in ceramic powder and placed in the furnace.
The polymer adhesive is burned and the parts are lightly sintering to produce a metal skeleton (
The line contract is about 1. 5%). (4. )Infiltration.
Next, the skeleton is infiltrated by a metal alloy with a lower melting point than the base powder.
In this work, the penetration agent is a bronze alloy (
Copper 90%, tin 10% (weight).
Penetration technology is used to ensure that the cooling channel is kept without penetration (see below). (5. )Finishing.
Next, the mold plug-in will be done using traditional metal processing techniques (including machining and EDM.
Figure 2 shows photos of tool inserts in a green state and after penetration.
As mentioned earlier, spherical metal powders flow out of the cooling channel relatively easily under the action of their own weight and air pressure.
These techniques are sufficient to clear the cooling channels used in this work and will be introduced later.
In order to better evaluate the powder removal, a test assembly was manufactured with a winding channel crossed by the Channelsection 1.
25mm X 2mm with a total channel length of mm.
This channel is more demanding than the one used to produce the tool plug-in for this work and has also been successfully cleared.
Of course, there will be a channel geometry and length that will be difficult to clear.
However, the assessment of these limitations is left to future work.
Penetration of 3D printing plug-ins with alloy at lower melting temperature infiltrating porous metal prefabrication is a common practice for improving the strength of parts and removing residual pores [8].
This penetration technique relies on capillary action to attract the penetration into the pores of the bones.
In the penetration tool with a shape-preserving cooling channel, the challenge is to ensure that the channel remains permeable.
One way is to precisely weigh the amount of penetration required to fill the part, not the channel.
However, this approach will always lead to a slight deficiency
Penetration of parts (porosity)orover-
Channel penetration and blockage.
A new penetration method called \"stilt penetration\" was developed and illustrated in Figure 13.
During stilts infiltration, the Sintering metal part is placed on a porous metal stilts that lift it above the bottom of the Crucible.
The penetration agent is placed at the bottom of the Crucible and arranged according to the penetration temperature.
Melted bronze penetrates into stilt and sintering parts.
This infiltration process takes advantage of the differential pressure between the liquid penetrant and the surrounding atmosphere. The mettalo-
The static head of the molten liquid penetrant produces pressure below the ambient atmospheric pressure in the penetrant, which ensures that the penetrant does not fill a channel greater than a certain critical size (seebelow).
It is useful to understand the stilt height required to ensure that thata parts with a given size Channel are not filled with the penetration.
During penetration, the channel is assumed to be in a horizontal position.
The channel can be modeled as a capillary rise between two parallel plates with spacing between w.
Under the assumption that the wet angle between the permeability and the wall is zero, the capillary rise of themolten permeability is given: [rho]= 8780kg/[m. sup. 3][10]and [gamma]= 1 N/m [11].
Colunm 4 in Table 1 describes the experimental results.
The experimental results are in good agreement with the calculated maximum capillary rising equation. The one (
Minimum channel)
It is predicted that the penetration agent does fill and all the others remain clear.
The surface roughness inside the channel inside the hole skeleton will result in a larger capillary rise than predicted by Eq1 for two reasons :(i)
The surface roughness increases the contact week length between the penetration agent and the skeleton, and (ii)
Surface roughness can reduce Cross effectively
Section area of the tunnel.
Because of this, and because of the greater rise in the vertical channel, Eq 1 provides a reference point for the design height.
A secure design would be a multiple of two or three times the height predicted by Equation 1.
The capillary rise in the pores of Theskeleton itself can be predicted between 1 and 2 m, and soa is possible in the design of stil, even if it is a relatively small cooling channel.
How close is the mold design and testing distance?
A useful guide to shape-preserving cooling channel design is to consider how close they must be to the surface in order to have a significant impact on the temperature of the cavity surface.
This is essentially a transient heat transfer problem, where a thermal pulse from a molten polymer travels from the tool\'s surface to the cooling channel, where heat is removed from the system.
If we consider that before the injection, the tool is at an even temperature equal to the cooling temperature, we see that the first part of the heat entering the tool will be used to heat the part of the tool located between the surface and the cooling channel.
This observation can be used as 1-
A dimensional model that provides guidance for cooling channel placement. Consider a 1-
D. heat flow in the tool, where the distance from the mold surface to the nearest part of the cooling channel is d.
Let\'s assume that when the plastic is injected for the first time, the surface of the tool rises rapidly to the melting temperature ,[T. sub. m].
If the tool is in a steady state, the linear temperature distribution will develop from [T. sub. m]
On the surface [T. sub. c]
Temperature of coolant at the passage.
If the coolant does not take away the heat, the heat that must be transmitted to the tool in order to achieve this condition is: however, each unit of heat flows to the tool, compared to the straight slot insertion, the cycle time is set to 11 seconds.
Figure 12 compares the surface temperature of the mold near the gate (
Gate thermocouple hole)
For direct channel core insertion and conventional channel core insertion.
Each temperature swing represents a temperature.
The surface temperature data near the middle and ribs show similar results.
Figure 13 describes the core surface temperature of a 303 stainless steel blade with a straight slot in one shot.
The mold surface temperature history of the three mold surfaces is described (gate-middle-rib).
This number is the expansion of 19 thinking cycles (
After the upward cycle drift tends to be stable)in Fig. 12.
The timing of the three stages is depicted.
Because polystyrene plastic is hot, the temperature will rise rapidly during the filling stage.
This filling phase takes about 1. 0sec.
The surface temperature of the mold drops at 6.
5 Second cooling stage.
Finally open the mold and pop up the part.
This openstage takes about 3. 5 sec.
The mold still cools at this stage.
The mold is closed again and the cycle begins to end.
Figure 14 depicts a surface temperature map with a core insert with a shape-preserving channel. From Fig.
12, we see that there is a significant upward drift in the surface temperature during the injection molding of the straight channel chip.
After the first cycle is completed, the overall temperature of the mold surface rises.
The accumulation of heat in the mold surface material cannot dissipate within the specified cooling time.
The cooling channel is relatively far away from the forming surface, and due to the low thermal diffusion rate of the stainless steel material, it is not possible to remove heat from the forming surface quickly enough.
Observed upward drift of the surface temperature level of the 15-Post mold20shots.
The mold surface temperature with a chip conforming to the channel cannot prove this temperature drift. From Figs.
13 and 14 we see the temperature of the mold surface along the Ring (gate to rib)
More uniform in compliance with the cooling channel.
In addition, the temperature swing of about 15 [degrees]
C is on display in the straight results, and only 10 [degrees]
C is obvious in the shape-preserving channel results. Cavity (
Shaped Channel)
The surface temperature data have similar results.
As with the 3D printed Core plug-in, no upward drift of surface temperature was noticed, and the temperature on the surface of the mold along the perimeter of the cavity was significantly more uniform than that of the cavity with a straight hole.
Deformation Table 2 of the part shows the clearance of the part measured using a consistent cooling tool where the temperature of the cooling water is controlled separately for the core and cavity.
It can be seen that whenever the core and cavity are at the same temperature, the gap between the parts is about 1mm.
However, when the cavity is hotter than the core, the gap in the part is larger, and when the core is hotter than the cavity, the gap is actually completely closed.
These observations can be understood by recognizing that when the core is hotter than the cavity, the cavity side of the part freezes first.
With freezing and shrinking on the core side, thering is closed.
The upside down logic explains why the hot cavity causes the ring to open.
The 1mm gap for the temperature measurement of the equal core and cavity is less than 2.
The 16mm gap of the mold itself may be explained by the cylindrical geometry of the part.
The outer surface of the part has more heat transfer that can be used for cooling, and it is predicted first, even if the temperature of the core and cavity is the same.
Figure 15 shows the measurement results of two injection molding operations, one with a straight-line cooling channel and the other with a normal cooling channel.
In all cases, the temperature of the coolant flowing through the cavity and core is 1100.
It can be seen that for tools with formal cooling, the width of the gap remains the same, reflecting the good temperature control provided by cooling.
In contrast, in the case of a straight slot, the width of the gap begins to decrease and further decreases in the continuous part.
This reflects the fact that the core is heated more than the cavity, and that this temperature rise takes several cycles before reaching a stable state.
Modeling objectives and modeling assumptions to confirm our understanding of heat transfer in the shape-preserving Channel tool and lay the foundation for the design of more complex tools in the future, establishing a finite difference model for solving transient heat conduction problems.
The input of the model includes the thermal properties of the plastic (polystyrene)
, As well as the material of the stainless steel mold of the bronze penetration, the mold filling time in the simulated injection mold cycle, the cooling time and the pop-up time, the physical size of the cooling channel, the mold and the plastic melting area, coolant temperature and plastic melting temperature.
The model assumes that the wall of the cooling channel is at the temperature of the coolant flowing through the cooling channel.
This assumption is equivalent to the assumption that the heat flow resistance in the liquid in the channel is small compared to the heat flow resistance in the tool from the Channel to the mold surface.
Since the flow in the cooling channel is turbulent (
Filling stage, cooling stage and opening (ejection)stage.
According to the actual time of each stage in the simulated experimental injection molding operation, a given time increment is set for each stage.
In the \"filling\" phase, the plastic melt moves along the surface of the model steel block.
When the plastic moves along the surface of the mold, it cools.
This is modeled in the simulation by \"moving\" The plastic melt volume along the model steel block.
When the subcoil is moved, it retains the previous temperature and continues to cool as energy is lost to the steel mold roll.
Therefore, this filling stage simulates the cooling when the plastic melts along the surface of the mold.
The \"cooling\" phase only keeps the mold and plastic melting temperature at the end of the filling phase and continues the simulation.
Because the plastic melt has \"filled\" the cavity, the volume of the plastic melt is no longer moving.
At this stage, they continue to lose energy to the sub-volume of the steel mold surface.
This simulates plastic cooling.
The final stage of the injection mold cycle is the \"open\" stage where the mold is opened as a part that pops up from the surface of the mold.
This stage is modeled by removing the volume of plastic melts from the surface of the mold block.
Similarly, the start temperature of the steel mold roll is set to the final temperature of the cooling stage.
This process describes a single injection cycle.
Multiple cycles are modeled by using the mold block node temperature at the end of one cycle as the initial node temperature for the next cycle.
Simulation results figure 17 shows the finite difference simulation results of heat transfer of insert with shape-preserving channel during injection molding.
The results of this finite difference analysis can be compared with the experimental results of the surface temperature over time data of the 3D printing Core plug-in.
Figure 18 depicts a period of simulation and a period of experimental mold surface temperature data derived from gate thermocouple.
Figure 19 depicts the same blank at the rib thermocouple.
The simulation map has been moved on a time scale to synchronize the cycle start time with the experimental data.
The shape of the experimental and finite difference surface temperature maps is very similar.
Temperature rise of approximately 10 [molded surfaces]degrees]
C was observed in the experimental and simulation figures.
At the beginning of the cooling cycle, the difference in surface temperature between the mold surface of the gate and the mold surface at the rib is about 4-5[degrees]
C is detected in these two graphs.
Therefore, the model captures the stability well.
The state behavior, and the transient behavior of the mold surface temperature during the injection cycle, including as a function of the location of the cavity.
Discuss the comparison of cooling performance of two sets of blades (
A channel with a shape preservation and a channel with a straight through)
The same insert geometry is rendered.
Due to logistics, there is no printing and penetration of a set of 3d printing plug-ins with straight lanes.
On the contrary, the straight groove group is made of 303 stainless steel.
The mold material and mold thermal performance of the two sets of inserts are different.
This raises the question of whether different thermal properties will significantly affect the cooling performance.
The material properties of 303 stainless steel are used to simulate the design of the shape-preserving Channel (
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