RPT/RT BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS FACULTY OF MECHANICAL ENGINEERING DEPARTMENT OF POLYMER ENGINEERING

Transcription

1 B4 BUDAPEST UNIVERSITY OF TECHNOLOGY AND ECONOMICS FACULTY OF MECHANICAL ENGINEERING DEPARTMENT OF POLYMER ENGINEERING RPT/RT SMALL SERIES MANUFACTURING OF POLYMER PRODUCTS

2 LOCATION OF THE PRACTICE TABLE OF CONTENTS 1. AIM OF THE PRACTICE THEORETICAL BACKGROUND RAPID PROTOTYPING RAPID TOOLING REACTIVE INJECTION MOLDING THE MACHINES USED AT THE PRACTICE RECOMMENDED LITERATURE REPORT Small series manufacturing of polymer products 13/2

3 1. Aim of the practice The aim of the practice is to come to know the technologies of small series production techniques, with special regard to reactive injection molding (RIM), rapid protoyping (RPT) and the rapid tooling (RT) techniques essential for it. 2. Theoretical background The development time of different products and the time until they enter the market decreased significantly in the last years. The reason for this is the ever increasing market needs and the rapidly developing technology. Computer aided design (CAD) and manufacturing (CAM) and the appearance of different integrated systems lead the product development into new ways. The conventional, subsequent design and production processes are replaced by simultaneous product design. Intermediate checking and the efficient communication of those taking part in the design process play a great role in this process. Rapid prototyping (RPT) unites all these aspects well. In some phases of design prototypes produced by the means of RPT help find a compromise among the technical, ergonomic and design aims and also assist in expressing the requirements of the products. Although they can differ significantly concerning technical realization since there are different RPT technologies all over the world the principle of operation is the same in all cases: the models are prepared by adding material layer by layer. There can be three main reasons to create a prototype: The first, when one wants to examine the appearance of the product (model for visualization), wants to hold it in his/her hands in a real 3D form. This type of model is needed when the design of the product is being created or evaluated so there is no need to have the mechanical properties of the future part. The prototype has to be only a perfect geometric clone of it. The second reason is when one wants to examine the functionality of the product (functional model). In this case the mechanical properties of the prototype and in some other cases the material of it is important too. In the third case the prototype is the master sample for a mold which will create a small series of the required product. This product fulfils the above mentioned requisites and beyond those its manufacturing process the same as of the future product, cloning its properties perfectly. Small series manufacturing of polymer products 13/3

4 2.1. Rapid Prototyping (Additive manufacturing) Nowadays the range of materials that Rapid Prototyping uses to build models from are very wide (Fig. 1.). Liquid based Rapid Prototyping techniques are general, using polymeric materials mainly: Cross linking materials in one hand (SLA laser stereolitography) and thermoplastics in the other (FDM fused deposition modelling). Further technologies build the prototype from particles melting (SLS selective laser sintering) or binding (3D printing) the adjacent particles together. In addition there are techniques using plates or sheets to build from. The most simple is when sheets of paper is being cut and glued together to build up the part (LOM laminated object manufacturing).these techniques are all computer controlled. One needs a 3D model from any CAD system that can export in the STL (standard triangular language which describes the surfaces of the part with triangles) format. 1. Fig. Grouping of RPT technologies according to the raw materials D printing technologies 3D printing was developed by MIT (Massachusetts Institute of Technology). Several companies have purchased the license, and developed the technology further for commercial use. The most successful is Z Corporation, which introduced a 24-bit color printer in With this development it became possible to print full color 3D models, allowing the user to print out the model with the result of stress analysis or differentiating material or functions of a part by color. With 3D printing it is possible to manufacture any given shape, from a wide variety of materials. The main criteria for the material is that it should be available as powder, with small Small series manufacturing of polymer products 13/4

5 enough grain size, and adequate water soluble binder should be available. Z-Corporation offers cellulose, gypsum and ceramic powders with suitable binder. Before starting the printing process, layer of powder were laid down to guarantee the flat surface. During the production process the print head prints the binder material on the powder in the given cross section of the model. After printing the build piston lowers vertically one layer thickness distance, and the next powder layer is spread from the base material with the help of the leveling roller. These two steps repeat until the final geometry of the model is ready (2. Fig.). 2. Fig. How 3D printing works After the excess powder is evacuated, the rigid part is subjected to some kind of after treatment (Usually impregnation by some kind of resin and curing.). This procedure is fast, simple, relatively cheap and reliable. Since the product is in a powder bed, no additional support material is needed. The technology is also suitable for manufacturing ceramic mould for metal casting. Main disadvantages of technology are that it needs post treatment, accuracy is affected by the grain size of the material used and inner surface of the parts are hard to access. (How it works? - video) PolyJet - Objet technologies Objet Geometreis PolyJet technology is a novel RPT technology that combines the advantages of several previous technologies. An inkjet print head prints photo curing polymeric resin which is cured by integrated UV lamps unlike other technologies, where laser beam is used (SLA). In contrast to 3D printing where the unbounded powder serves as support, the PolyJet Small series manufacturing of polymer products 13/5

6 technology uses a special water-soluble support material that can be easily removed. Due to its building strategy, where the printed layer is solidified in one step while printing this technology is much faster and cheaper than technologies user laser beam. Its layer thickness is μm, with a resolution of 600 dpi in the building layer. A minimal wall thickness of 0.6 mm can be achieved, with a precision of ±0.05mm. (How it works? - video) 3. Fig. PolyJet process 2.2. Rapid Tooling Rapid Tooling, which was developed from Rapid Prototyping, is gaining an ever-growing ground in the field of polymer processing. Tools/molds/dies produced by RT are usually used for small series manufacturing of prototypes for precise measurements. They represent a big leap because opposed to conventional prototypes these are a perfect clone of the future product not only possessing the same mechanical properties but manufactured with the same processing technique. These days development is directed towards to be able to use this technique to mass produce parts. Various variants of Rapid Tooling can be found on the market from indirect tooling starting from a prototype to direct tooling (4. Fig.). Small series manufacturing of polymer products 13/6

7 4. Fig. Grouping of Rapid Tooling techniques The principle of the indirect branch of Rapid Tooling is using a prototype produced by a Rapid Prototyping technique as a master form for creating a mold/tool/die. It is much faster than using a master form manufactured by a conventional way (For example by machining.) and its accuracy is extensively satisfactory. Afterwards the master form can be cast around by another material, creating the mold withstanding the pressure, temperature and abrasive power of mass production. Silicone tooling belongs to the indirect branch of the Rapid Tooling techniques. Wax, polymer and low-melting metal parts can be manufactured that don t expose the mold to high pressure, temperature. The mold material is hot curing silicone rubber: addition product which cures without shrinkage and condensation product which in the other hand undergoes 2% shrinkage because of the evaporating alcohols. The most popular application of silicone tooling is when fast curing PUR resin is cast into the mold. In this case at least parts can be manufactured. The main advantage of this technique is that parts with undercuts can produced, inasmuch the mold can be pried open when getting out the finished parts (5. Fig.). (How it works? - video) 5. Fig. PUR casting into a silicone mold (1 Creating an RPT part with sprue and air escapes, layer of release agent, 2 Inclosing the part with silicone, 3 After cross-bonding of the silicone, creating a parting plane, opening the mold and removing the part, 4 PUR casting) Small series manufacturing of polymer products 13/7

8 There is no need to present a master form at direct tooling, this way it is a quicker and simpler technique than its indirect counterpart. These techniques are based on conventional PolyJet, SLA and SLS. (How it works? - video) 2.3. Reactive Injection Molding The injection molding is the most versatile technology of producing polymer (mainly thermoplastic polymer) products. Along the previously mentioned (B3 Injection molding) conventional injection molding there is numerous special injection molding techniques (For example: multi component injection molding, injection molding of cross-linking materials ). By RIM (Reactive Injection Molding) usually cross linking materials are processed. The main concept of this process is that two low viscosity fluids (monomers) are mixed and injected in a mold where the cross-linking takes place. When using polyol and isocyanate as components PUR is formed in the mold cavity through a polyaddition reaction. It is possible to produce composite parts by laying fabric or fiber in the cavity. The pot life of the mixture can be adjusted by adding additives to the mixture. (How it works? - video) RIM has several advantages compared to conventional injection molding, for example low processing temperature, injection pressure and clamping force (Table 1.). As a disadvantage the more complicated process (there is a chemical reaction in the mold cavity) and the non-recyclability of the part can be mentioned. Table. 1. Comparison of the main parameters of RIM and conventional injection molding Reactive Injection Molding (RIM) Conventional Injection Molding (Thermoplastic) Processing temperature ( C) Viscosity (Pa s) 0, Injection pressure (bar) 1-2 (non-expanded) (expanded) Cycle time (min) ,02-5 The machine used in the Lab Practice is a Dekumed Unidos 100 RIM machine equipped with a mixing head that means the mixing of the two components take place outside of the machine in the disposable head, so no solvent is needed for cleaning. This head has convincing intermixing results even with the most different mixture proportions and viscosities (6. Fig.). Small series manufacturing of polymer products 13/8

9 6. Fig. Scheme of the RIM machine PUR is used usually as a base material for RIM applications because its mechanical properties can be manipulated in a wide spectrum by additives (7. Fig.). 7. Fig. RIM materials Small series manufacturing of polymer products 13/9

10 3. The machines used at the practice Build size: 203x254x203 mm Layer thickness: 0,089-0,203 mm Build speed: ~ 25 mm/h Number of print heads: 1 (HP) Z310 3D PRINTER (8. FIG.) 8. Fig. Z810 3D printer Build size: 300x200x150 mm Layer thickness: 0,028 mm Build speed: ~ 6 mm/h Number of print heads: 2 ALARIS 30 DESKTOP PRINTER (9. FIG.) 9. Fig. Alaris 30 desktop printer Small series manufacturing of polymer products 13/10

11 4. Recommended Literature 1. T. Wholers: Wholers report 2008, Wohlers Associates, United States of America, A. Gebhardt: Understanding Additive Manufacturing, Hanser Publishers, Munich, C. K. Chua, K. F. Leong, C. S. Lim: Rapid Prototyping: Principles and Aplications, World Scientific Publishing Co. Pte. Ltd., Singapore, S. Upcraft, R. Fletcher: The rapid prototyping technologies, Assembly Automation, 2003/23, A. Rosochowsky, A. Matuszak: Rapid tooling: the state of the art, Journal of Materials Processing Technology, 2000/106, Osswald T.A., Turng L., Gramann P.J.: Injection Molding Handbook, Hanser Publishers, Munich, N. Hopkinson, P. Dickens: A comparison between stereolithography and aluminium injection moulding tooling, Rapid Prototyping Journal, 2000/6, (RIM) 9. (RPT, RT) Small series manufacturing of polymer products 13/11

12 REPORT Name: Grade: Neptun code: Date: Checked by: Head of practice: 1. The task Design the small series production, material selection. Production to different RPT technologies (PolyJet, 3D printing) and casting. Analysis the cost of production. 2. Basic, measured, and counted data: Product: pieces: 60 [db] mass: Material cost: 3D printing: ZP 131 powder: [Ft/kg] ZB 60 binder: [Ft/liter] PolyJet Objet: FullCure 835 model material: [Ft/kg] FullCure 705 support material: [Ft/kg] Köraform A42 silicon: 42A component: [Ft/kg] 42BW component: [Ft/kg] Biresin G26 (PUR): A component: 4000 [Ft/kg] B component: 4000 [Ft/kg] Small series manufacturing of polymer products 13/12

13 Direct manufacturing PolyJet Objet, Alaris 30 1 piece 60 pieces FullCure835- model material: FullCure 705 support material: Production time: Indirect manufacturing Master form Type of master form production: PolyJet Piece of master form: 1 Production time: 1,5 Silicon mold 1 piece 60 pieces Köraform 42A component: Köraform 42BW component: Curing time: Casting (PUR) 1 piece 60 pieces Biresin G26 A component: Biresin G26 B component: Curing time: Full indirect production time: Cost 1 piece 60 pieces Direct manufacturing [h] [h] [h] [h] [h] Alaris 30: [Ft] Z310: [Ft] Indirect manufacturing Master form: Silicon mold : PUR material: All together: [Ft] [Ft] [Ft] [Ft] Small series manufacturing of polymer products 13/13