Design guidelines - Batelaan Kunststoffen B.V.

1 Design guidelines for the thermoforming process 1 1 Design guidelines for product engineers on the thermoforming process U aangeboden door: Batelaan Kunststoffen BV Veerpolder 8 2361KV Warmond T: 071-5613301 F: 071-5616701 Zonder schriftelijke toestemming van de ProducentenVereniging Thermoplasten (PVT) mag niets uit deze informatiemap worden verveelvoudigd en/of openbaar gemaakt door middel van druk, fotokopie, microfilm of anderszins, hetgeen ook van toepassing is op de gehele of gedeeltelijke bewerking. Deze informatiemap is gebaseerd op de trainingmodules, gerealiseerd in het kader van T-ForM.

2 Voor de eventuele aanwezigheid van (zet)fouten en onvolledigheden kan de PVT geen aansprakelijkheid aanvaarden. PVT, Postbus 420, 2260 AK Leidschendam, July 2008 Design guidelines for the thermoforming process 2 2 Contents Contents .. 1 1. Executive Summary .. 5 2. Introduction .. 9 Thin Sheet Thermoforming .. 9 Thick Sheet Thermoforming .. 10 Tooling .. 10 Literature .. 11 3. Thermoforming process .. 15 Bubble Forming .. 15 Cavity Forming .. 15 Drape Forming .. 17 Variations to Avoid Excessive Thinning .. 18 Cavity Forming with Plug Assistance .. 18 Billow Drape Forming .. 19 Snap-Back Forming.

3 19 Reverse Draw with Plug-Assist Forming .. 19 Twin Sheet Forming .. 19 Other Techniques .. 21 4. Tooling .. 23 Tooling Costs: Thermoforming versus Injection Moulding .. 23 Tooling: Design Considerations .. 23 Thermoforming Mould Design Criteria .. 24 Heat Transfer Considerations .. 26 Mould Temperature Control .. 27 Tooling Materials .. 27 Wood .. 30 Plaster .. 30 Sprayed Metal Alloys .. 31 Resin Tooling .. 31 Aluminium .. 33 Steel .. 33 Russian Tooling Practice .. 33 5. Proprietary resins and resin based materials for tooling .. 37 Axson EPO 4042 EPO4042/L Epoxy Casting Resin .. 37 Epon Epoxy Resins.

4 37 Fablite .. 38 Design guidelines for the thermoforming process 3 3 Polylite Polyester Resin .. 38 Metapor Epoxy/Aluminium .. 38 Espor .. 40 Vestalloy .. 40 WIS Tooling .. 41 Albright RT .. 41 Poly Steel .. 41 Microsyn .. 41 Ren-Shape (Vantico) .. 42 Polyurethane Machinable Slab (Ureol Board Axson) .. 43 Epoxy / Aluminium using Stereolithography (Escuelo Technica).. 43 Miscellaneous Materials .. 43 6. Tooling: plug 47 Plug Assisted Thermoforming .. 47 Plug 49 Acetal ( Delrin) .. 52 Hardened Felt .. 52 Syntactic foam .. 52 Wood .. 52 Resins .. 52 Hytac Syntactic foams.

5 52 Friction Between Plug and 54 Mould Plug and Heat Transfer .. 62 Plug Assisted Forming Experimental Work .. 62 7. Computerised process simulation .. 67 Background .. 67 Forming 70 Computer simulation literature summary .. 71 8. References .. 77 Appendix .. 80 Planoxal-50 Aluminium Data Sheet .. 81 RenShape BM 5055 .. 83 EPO 4042 / EPO 4042/L .. 85 LAB 1001 .. 87 PROLAB 89 Design guidelines for the thermoforming process 4 4 Design guidelines for the thermoforming process 5 5 1. Executive Summary This report reviews the choices that may be considered for thermoforming processing. Thermoforming is a broad technology genre so the report gives some background information to the various thermoforming process sub groups and links the tooling considerations to these technologies.

6 The tooling options for high pressure plug assisted, moulding which is a significant subgroup, is also discussed in some detail. This report considers the factors deemed to be important when selecting materials for the construction of moulds for the thermoforming process. It does not consider Design issues such as draft angles, corner radii and draw ratios because these should have been addressed during product Design . The selection of mould materials is dependent on several factors including cost, quantity and quality of parts required the capability and lead time of the toolmaker and the thermal characteristics of the material.

7 Additionally to comply with the dimensional and thermal requirements of the thermoforming process other tooling material requirements need careful consideration. The material must be capable of thermal cycling, be able to transmit vacuum from all areas of its surface, be robust but easily modifiable and be dimensionally accurate with known shrinkage characteristics. The literature confirms that aluminium is the mould material of choice for high volume production work, meeting all of the characteristics outlined above. The material is readily available, easily worked integrating into CAD/CAM systems and is relatively cheap.

8 Importantly it also offers excellent thermal conductivity: moulds are a fundamental part of the heat transfer process in thermoforming and determine the consistency of the mouldings from both a dimensional and quality perspective. Heat transfer characteristics maximises the efficiency of the production cycle and once the economics of scale become favourable it this characteristic that confirms on aluminium its dominant status. For prototype or low volume application other materials become worthy of consideration. In addition to the ubiquitous aluminium these can include resin (including metal filled systems) syntactic foam, composite board, plaster, and wood.

9 Prototype moulds and moulds for low volume applications are usually fabricated from more easily worked materials where the heat transfer benefits of aluminium associated can become secondary considerations. Data sheets for aluminium suitable for thermoforming tooling have been identified but none of the major suppliers make a point of supplying grades specifically for thermoforming. Design guidelines for the thermoforming process 6 6 Two non-aluminium materials were investigated; filled epoxy resin systems and machinable polyurethane board. These materials are indicated for several applications of which thermoforming tooling is only one.

10 Specific information linking the material to thermoforming is therefore limited, but data sheets for these types of materials used by the consortium partners have been reviewed Finally in the course of the study the literature unearthed a series of articles that linked thermoforming and tooling materials to process simulation. A brief synopsis of this area is included for completion. Design guidelines for the thermoforming process 7 7 Design guidelines for the thermoforming process 8 8 Design guidelines for the thermoforming process 9 9 2. Introduction Thermoforming usually describes a process whereby a thermoplastic sheet is heated sufficiently to soften it and then cooled to become solid again after forming to the required shape.