TEMPERATURE ADAPTIVE CONTROL USING THE ADDITIVE MANUFACTURING FOR INJECTION MOLDING POLYMERIC PRODUCTS

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1 5 th International Conferene Advaned Composite Materials Engineering COMAT Otober 2014, Braşov, Romania TEMPERATURE ADAPTIVE CONTROL USING THE ADDITIVE MANUFACTURING FOR INJECTION MOLDING POLYMERIC PRODUCTS Teodoresu Drgahiesu Florin 1, Opran Constantin Gheorghe 2, Pasu Nioleta Elisabeta 3, 1 University Polytehnia, Buharest, ROMANIA, florin.teodoresu@ltp.pub.ro 2 University Polytehnia, Buharest, ROMANIA, opran.onstantin@ltp.pub.ro 3 University Polytehnia, Buharest, ROMANIA, nioletaelisabeta_pasu@yahoo.ro Abstrat: This paper presents the adaptive ontrol of the temperature in the injetion mold using additive manufaturing in order to ahieve the ontrolled and speifi ooling hannels in the omponents parts of the injetion molds of polymeri produts. The inreasing omplexity of tehnial harateristis by onstrution and tehnology of the polymer produts lead to inreasingly stringent speifiations for their dimensional stability and to ompliated injetion molds ost pries involving high reliability issues. The adaptive ontrol of the temperature in the injetion molds produed polymeri is the solution that solves these performane requirements. The main problems in the adaptive ontrol of the temperature by injetion molds is given by the thermodynami harateristis of ative plate material of the mold and by the distribution of the thermal fields and the ooling of the polymer produt injeted. The differential temperature ontrol of the various areas of the ative plaque avity by injetion mold using the onventional or assisted ooling systems lead to high manufaturing times and the bad quality of the produt. This paper presents ways to realize of speifi ooling hannels so that they will be onform to the ontour of the parts or integrated in the speifi heat ondutive material, embedded in the ative plate for the injetion polymer produt. It is also presents the tehnologies used to ahieve the speifi ooling hannels like diret laser metal forming, "diret metal laser sintering" (DMLS) and the method of introdution of high ondutivity material in the ative areas of the injetion molds plate. Eah type of produt requires a speifi onstrution tehnology to ahieve speifi.by reating these speifi hannels ours adaptive temperature ontrol in injetion mold ative areas resulting low manufaturing times and onformal quality. Keywords: temperature adaptive ontrol, additive manufaturing, injetion molding,diret metal laser sintering 1. INTRODUCTION Of partiular importane for injetion molds is that they allow obtaining produts injeted for material losses to a minimum, in ompliane with tehnial requirements. The injetion parts of omplex shapes, onave, must apply an injetion temperature ontrolled by the surfae of the part while maintaining pressure duration further. When opening the mold an our in parts molded internal tensions that an ause raking of parts (in ase more rigid amorphous thermoplastis suh as polystyrene shok-resistant PAS) or their deformation (in the ase of semi -rystalline thermoplastis suh as PE-polyethylene flexible. Temperature plays an important role influening mold: internal stress, deformation, dimensional auray, weight, surfae quality. Cooling time is determined by the temperature of the mold surfae. The heating equipment - ooling must ensure a onstant temperature of the mold with some limitations related to the ooling hannels position loser to the nest mold. The harateristi ooling time of the ooling proess during the longest part of the injetion yle representing approximately 68% of the total duration of the yle. To ahieve, in view of a high produtivity, short yle time, shall be provided redution measures for the ooling. Injetion tehnology, involves getting a time and ooling rate so as to ensure the quality presribed injeted part. By varying the ooling time and mold temperature (whih deter mines the ooling rate) is depleted the tehnologial possibilities of influening the proess of ooling in the mold. Although these tehnologial possibilities seem easy to ahieve, the ooling proess involves many tehnial diffiulties. This paper presents 104

adaptive ontrol temperature in the mold using manufaturing tehnologies through the generation of material to ahieve ontrolled and speifi ooling hannels in injetion molds omponents of polymeri produts.

2 adaptive ontrol temperature in the mold using manufaturing tehnologies through the generation of material to ahieve ontrolled and speifi ooling hannels in injetion molds omponents of polymeri produts. 2. COOLING SYSTEMS OF INJECTION MOLDS The higher the temperature of the thermoplasti material is higher, the more it is fluid filled lighter mold and injetion time are redued. Mold temperature is deisive phase ooling and solidifiation of the part. Table 1: Temperatures of major thermoplastis and molds Code Material The temperature Mould temperature of the molten [ C] material [ C] PS Polystiren ABS Arilonitril-butadien-styren Copolymer P.A.6 Polyamid P.A.6.6 Polyamid PP Polypropilene PMMA Polimetarilat Metil (Plexiglas) POM Poliaetatpolioximetilen PC Poliarbonat PTFE Politetrafluoretylene (Teflon) In terms of tehnology, ooling hannels position to the part, espeially in parts of omplex shapes is an intratable problem tehnologially. Suh a lassi mold LTPC existene in the laboratory of the University Politehnia of Buharest, for a ommon part, as well as an be seen in Figure 1 where the ooling hannels are driven on straight paths, trajetories relatively easily obtained in terms of tehnology. Retilinear trajetory ooling hannel an not be too lose to a piee of omplex size and different thikness. It is therefore very important that the ooling hannels position to make the play loser or mold nest. Figure 1: Making a mold ooling hannels for a ommon parts (made in Moldex 3D) Adaptive ontrol temperature inside the mold must however be optimized relative to the temperatures of the injeted material, mold temperature and ooling system after the injetion mold piee. The main problem is the ooling of injetion molds mold steel heat resistane. Depending on the quality of steel used typial thermal 105

3 ondutivity values are approximately 25 W/mk and down to about 12 to 15 W/mK, depending on the proportion of alloy additives. Tool steels are poor ondutors of heat as ompared to opper alloy or pure opper whih has a thermal ondutivity of approximately 390 W / mk. Figure 2 illustrates the situation of a onventional ooling heat the molds during the manufaturing proess [1]. Figure 2: The temperature in the injetion mold walls as ompared to the referene temperature of the ooling medium Although the distane from the ooling hannel to the wall of the mold avity is only 22 mm, the mold wall temperature inreases only about 19 C to a ore temperature of the ooling medium. If we onsider now the situation in the mold installation hannel, hannel ooling situation that is far away from the mold wall, or even a region whose thin-walled avity is ompletely enased in the polymer, the temperature differene between the ooling medium and the wall mould often reah values of 60 C and more. Suh hot spots are due to the onsiderable extension of the time of losing of the mold and also may affet the quality of parts and the injetion itself. The problem an be addressed only by the arrangement of ooling hannels so that they onform to the ontour or integrated in highly thermally ondutive material to be lamped tightly in tool steel workpiee regions. The polymeri material of the nest during a yle gives mold injetion mold body, the amount of heat Q, whih is alulated using the equation: Q=m(i 2 -i 1 ) kal m mass injeted part, kg; i 2 enthalpy of the polymeri material from entering the mold; i 1 enthalpy of the polymeri material to mold release. The enthalpy of the polymeri material is alulated using the equation: Δi= i 2 - i 1 = p (T Mp -T D ) [kal/kg) p speifi heat of the polymeri material kal/kg C; T Mp temperature of the material in the nest; T D mold release temperature; The amount of heat transfer of the piee is taken by mold and transported to the environment of moderation. The amount of heat Q is determined by the relationship: M Q S(Tp - TpT ) [W] where: λ M thermal ondutivity of the mold =0,197 [W/m K] δ Channel Tempering distane from the mold surfae,[m] S the ative ross-setional area of the mold,[m²] T p The average temperature of the wall of the avity =433 [k ] T pt hannel wall average temperature tempering =333 [K ] Heat transfer from the mold (solid medium) to the tempering environment (liquid medium) is by onvetion and an be expressed by the relation: Q=α T S T (T pt T T ) [W] where: α T heat transfer oeffiient tempering environment =1310 [w/m²k] S T ative surfae tempering hannels, [m²] T pt - hannel wall temperature tempering, =433 [k ] T T - ambient temperature tempering =393 [k ] Heat transfer oeffiient is alulated using the equation: 106

4 d 0,0668p e L T [3,65 ] d d 1 0,045(p e )² L where: d Channel Tempering diameter, [m] L Channel Tempering length, [m] [w/m²k] 3. MANUFACTURING TECHNOLOGY USE OF COOLING CHANNEL USING TECHNOLOGY GENERATION OF MATERIAL The inreasing omplexity and geometry of injetion molded parts and the more stringent speifiations for dimensional stability inreased the parts ost to put pressure in the injetion molds and enhane feasibility problems already diffiult. A reently launhed servie that has already gained attention is the diret laser metal forming (Diret Metal Laser Sintering-DMLS). This proess generates an insert molded from a metal powder bed, whih often is a material inserted in the original mold. A fine metal powder is plaed in a heated room built on a platform that an be lowered. A diret laser melting the powder layer, whih was initially leveled with a slide aording to a 3D model, to diretly form the ontour of the part webs, and the powder is welded to a monolithi workpiee subsequent to the final hardness about 52 Rokwell C (fig. 3). The onformal ooling, or the segmented mold ooling is a new tehnology that meets these halenges. Figure 3: Laser Sintering using the method of 3D generating metal powder diretly [2] The steel in the mold has a density of about 100%. If the position of the ooling hannel is in aordane with the shape of a part of the plasti material of the workpiee then is introdued into the 3D data set, whih is then further insertion of the printed preisely on the three-dimensional matrix in the form of a hannel. The advantage of the above-mentioned manufaturing proess is omplete freedom of design in reating hannel. Although the method does not require ooling medium flowing through onformal hannels, it provides adequate heat transfer due to high thermal ondutivity of the material. Heat ondutive needles, suh as opper of high purity whih an ahieve a thermal ondutivity of 390 W/mK an be inserted into the powder bed by taking the shape of the ontour. [1] 107

Figure 4: A 3D view of the inner ooling hanels of a tool insert, wih ould not be manufatured using onventional mahining [3] Figure 5: The mold for produing a liquid-ooled engine [3] ; Figure 6 :

ondutivity of the new omposite steel/opper is muh higher than that of the steel used in the mold onventional manner.

of the mold. Examples of building ooling hannels to ahieve a onsistent ooling using modern additive manufaturing tehnologies for material generating are shown in Figures 4, 5 and 6.

This segmentation is essential espeially for large surfae omponents beause then the form is usually operated at different temperatures - in aordane with the various areas of the part.

5 Figure 4: A 3D view of the inner ooling hanels of a tool insert, wih ould not be manufatured using onventional mahining [3] Figure 5: The mold for produing a liquid-ooled engine [3] ; Figure 6 : Eletroni Parts from ABS [3] In the ase where suh opper elements are welded or sintered high-purity (by diffusion bonding) plaed in the avities prior to the insertion of the mold, average thermal ondutivity of the new omposite steel/opper is muh higher than that of the steel used in the mold onventional manner. Depending on the design of the mold insert, suh items steel/opper an reah or even exeed the thermal ondutivity values, whih are usually arried out only by opper alloys are also used in the manufature of the mold. Examples of building ooling hannels to ahieve a onsistent ooling using modern additive manufaturing tehnologies for material generating are shown in Figures 4, 5 and 6. The position and shape of the hannels to be determined from the point of view of 3D additive manufaturing tehnologies being ahieved by the design and proper segmentation of the individual hannels. This segmentation is essential espeially for large surfae omponents beause then the form is usually operated at different temperatures - in aordane with the various areas of the part. This means that mold temperatures are tailored to speifi thermal balane of the piee. Suh segmentation is a segmentation hannels under different water temperatures and helps to influene and ontrol the ontration of individual areas play atively. [4] Figure 6 shows an example of an automotive ooling omply. The ore of eletroni parts ABS is about 300 mm long, 50 mm wide and about 100 mm in height. For the ABS-based ore, defining the shape is ontrolled two separate ooling hannels running beneath it. [5] In the narrower base region, the heat transfer opper-omposite steel pins provide for adequate heat removal. Plaing the lower half of a mold ore of a oolant tank for the engine shown in Figure 5 shows how impressive the different tehnologies interat to provide a viable solution. Spae ooling hannels in figure are projeted on a tehnial level of prodution possible, being designed only to supply the oolant ore regions and to allow appliation in hannel ross setions. In further narrow base regions an be observed opper pins embedded in mold steel needles remove heat effiiently, even in areas with narrow ontour regions. Figure 7 and Figure 8 is trying to ahieve ooling hannels made by generating a 3D printer. These tests were obtained by the Polytehni University of Buharest. 108

Figure 7: Cooling hannels made for a sample generated by 3D printing through the additive manufaturing tehnologies Figure 8: Physial part performed in a 3D printing mahine 4.

The ability to remove heat as quikly as the design of more effiient ooling hannels and the hoie of materials as appropriate and without making too ompliated mold, mold will inrease produtivity.

ostly proessing. A redution of yle time by an average of 30%, with lower rates for srap, an quikly lead to a redution in unit osts by 15% for injetable produts.

New tehnologies used to produe speifi ooling hannels and diret laser metal forming "diret metal laser sintering" (DMLS) and the method of introdution of high ondutivity material in the ative areas of

By reating these speifi hannels trough additive manufaturing tehnologies ours adaptive temperature ontrol in injetion mold ative areas resulting in low and quality manufaturing times omply.

6 Figure 7: Cooling hannels made for a sample generated by 3D printing through the additive manufaturing tehnologies Figure 8: Physial part performed in a 3D printing mahine 4. CONCLUSION Mold produtivity inreases with the quality and effiieny of the ooling system. The ability to remove heat as quikly as the design of more effiient ooling hannels and the hoie of materials as appropriate and without making too ompliated mold, mold will inrease produtivity. Copper-steel omposite solutions are not subjet to the disadvantages of the known opper-based alloys, suh as redued resistane to bending (due to the low modulus of elastiity), hardness and even less ostly proessing. A redution of yle time by an average of 30%, with lower rates for srap, an quikly lead to a redution in unit osts by 15% for injetable produts. Differential temperature ontrol of various areas of ative plaque avity injetion mold using onventional ooling systems or assisted stroke lead to high manufaturing quality and onform. New tehnologies used to produe speifi ooling hannels and diret laser metal forming "diret metal laser sintering" (DMLS) and the method of introdution of high ondutivity material in the ative areas of the plate as a ooling injetion molds omply with ontour. By reating these speifi hannels trough additive manufaturing tehnologies ours adaptive temperature ontrol in injetion mold ative areas resulting in low and quality manufaturing times omply. REFERENCES [1] Westhoff R., Conformal Cooling on the Advane, Kunststoffe International nr. 8/2006, Carl Hanser Verlag, pp.24-25, 2006; [2] Meyer R., Rapid Tehnologies in Automotive Engineering, ATZautotehnology nr /2008, volume 8, pp , 2008; [3] Conformal Cooling Irons out Prodution Problems, European Tool&Mould Making, pp 33-35, May 2014; [4] Metal Additive Manufauring to Grain Ground in Die and Mould, European Tool&Mould Making, pp 38-39, May 2014; [5] SASAM Projet, First European Standards at the European Level, ttmagazine, pp , July 2014; 109

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