Mold Design Handling Metals for Moulds PDF

11.11.2024 Handling Metals for Moulds 1 Machinability of Steel Machinability (turning, drilling, milling) depends primarily on the structure of steel (which however depends on the content of carbon) and on alloying elements.  The formation of compounds that have a lubri...

11.11.2024 Handling Metals for Moulds 1 Machinability of Steel Machinability (turning, drilling, milling) depends primarily on the structure of steel (which however depends on the content of carbon) and on alloying elements.  The formation of compounds that have a lubricating effect, such as manganese sulfide (Mg + S), increases the strength of steel and improves its hardenability as well as its machinability.  Low carbon & manganese up to 1.5 % improves shape of the chips  Phosphorus in low concentrations improves breaking of chips & surface quality.  Lead is often added to low-alloy steels. The metal melts earlier and thus forms a lubricating film between the tool and the chips. This reduces friction and thus tool wear. Lead also improves chip breaking. Mould Design/WS 2024/2025. Michael Kaisser. Page: 2 11.11.2024 2 1  11.11.2024 Eroding Definition: Machining method in which material is spark eroding removed by means of electricity. There are two different processes: wire-cut eroding & spark eroding. In principle, any current-conducting metal such as aluminum, steel, copper, brass or iron can be machined. An electrode (graphite or copper) is moved to the workpiece at a small distance without touching it. Within the narrow gap between the object to be machined and wire-cut eroding the electrode, an electric current flows that generates extremely high temperatures between 8’000 - 12’000°C. This results in material removal by discharge via sparks. How much material is removed depends on the polarity, gap width, duration and intensity of machining, and other factors. Eroding is mainly used where highest precision and particularly tight tolerances are required. Mould Design/WS 2024/2025. Michael Kaisser. Page: 3 11.11.2024 3 Different Kinds of Eroding Spark Eroding (Video 5) Wire Cut Eroding (Video 6) Mould Design/WS 2024/2025. Michael Kaisser. Page: 4 11.11.2024 4 2  11.11.2024 Polishing of Moulds Mould Design/WS 2024/2025. Michael Kaisser. Page: 5 11.11.2024 5 Polishing of Moulds Quality of Steel: Influencing Kinds of polishing  Melt process  Stroke burnish (Strichpolitur)  Inclusions Factors  Gloss Finish (Glanzpolitur)  Mirror Finish (Hochglanzpolit.) Advantage polishing: Elements:  Surface finish Carrier-/ Polishing tool: S, Cr, Mo, Ni  Demoulding Felt Wood X 45 NiCrMo4  Optic appearance 40 CrMnMoS 86  Anti-corrossion  Safety against scratch & breaks Mould Design/WS 2024/2025. Michael Kaisser. Page: 6 11.11.2024 6 3  11.11.2024 Polishing of Moulds The same applies to surface quality as to tolerances: Not as accurate/good as possible but only as necessary Relatively Cost Surface roughness - micrometers Polishing is a cost factor & can account for between 10-30% of total mould costs Mould Design/WS 2024/2025. Michael Kaisser. Page: 7 11.11.2024 7 Coatings for Plastic Moulding  Moulds often subjected to highly abrasive &  For injection molding processes, abrasive, corrosive conditions due to fillers & resins, corrosive & frictional wear are important sticking of the parts to the mold & fretting of causes of reduced tool lifetime sliding parts.  Tools/Moulds (cavities, cores, ejectors,  Coatings for moulds & sliding parts can runners and sprue bushings) suffer abrasive significantly improve mould life, or reduce wear due to glass-filled plastics, corrosive scrap rates by improving demoulding wear due to outgassing of acidic gases from release, details and finish. resins, and frictional wear during processing and ejection steps  Two processes:  Physical Vapor Deposition  Chemical Vapor Deposition Mould Design/WS 2024/2025. Michael Kaisser. Page: 8 11.11.2024 8 4  11.11.2024 Different Coating Processes Physical Vapor Deposition (PVD) Chemical Vapour Deposition (CVD) Material to be deposited is converted into a vapor involves the use of chemical reactions to deposit state through physical processes like material evaporation or sputtering Material is heated until it turns into a vapor, which Gaseous precursors react or decompose on the then condenses on the substrate substrate surface, leading to the formation of a solid film In sputtering, atoms are ejected from a solid Gaseous precursors react or decompose on the target material due to bombardment by energetic substrate surface, leading to the formation of a particles, typically ions & then deposited onto the solid film substrate. Advantages Advantages  High deposition rates  excellent conformality  Ability to produce films  ability to deposit a wide range of materials Mould Design/WS 2024/2025. Michael Kaisser. Page: 9 11.11.2024 9 PVD-Process  PVD process is used for the deposition of coatings made of nitrides, carbides & carbonitrides Ti, Cr, Zr or Al alloys on a large range of tools & components  Applications include cutting & forming tools, moulds, mechanical comp., medical devices & ! products that benefit from the hard & decorative features of the coatings PVD (Physical Vapor Deposition) for producing metal-  Process temperatures: ~ 250-450°C based hard coatings by means of generation of partially ionized metal vapor, its reaction with certain gases & by  Coating thickness: ~2-5µm forming a thin film with a specified composition on the  Substrate materials: steels & non-ferrous metals, substrate. tungsten carbides & pre-plated plastics. Most commonly used methods:  Suitability for PVD coating is limited only by its  Sputtering: vapor is formed by a metal target being stability at the deposition temperature & bombarded with energetic gas ions.  Cathodic arc: uses repetitive vacuum arc discharges electrical conductivity. to strike the metal target and to evaporate the material. Mould Design/WS 2024/2025. Michael Kaisser. Page: 10 11.11.2024 10 5  11.11.2024 PACVD-Process  PACVD process is used for conductive & non- conductive materials at temperatures < 200°C  Coating thickness: ~ 2-3µm  Coating structure: amorphous + Broad range of substrate materials + No distortion of high precision substrates PACVD (Plasma Assisted Chemical Vapor Deposition) is + No post treatment necessary a vacuum based process used to deposit DLC (Diamond + Gaseous process for uniform coating of 3D Like Carbon) coatings. geometries without rotation PACVD process takes place in gaseous state. This makes it suitable for coating 3D components uniformly, + Green technology with respect to educts, without the need for rotation (→PVD). process and products PACVD is also known as Plasma Activated Chemical Vapour Deposition and Plasma Enhanced CVD. Mould Design/WS 2024/2025. Michael Kaisser. Page: 11 11.11.2024 11 CVP-Process  Process temperatures: ~900-1050 °C (HT CVD) ~720 - 900 °C (MT CVD)  Substrate materials are tungsten carbide, tool steel, HT-Nickel alloy, ceramic & graphite  Moulds/tools made of hardened steel requires heat threatment after coating to re-establish required hardness + Low stress Chemical Vapor Deposition (CVD): low stress coatings + Exceptional adhesion of the coating due to by means of thermally-induced chemical reactions. The formation of the diffusion bond material of the coating is supplied to the coating zone as vapor of the respective precursor. The vapor then either + High load bearing capacity decomposes or reacts with additional precursors, thus + Excellent coating uniformity, independent of producing a film on the substrate. The precursors are continuously fed into the reaction zone & by-products are part geometry removed. CVD service processes can be carried out under + Complex geometries, including certain inner vacuum or at atmospheric pressure. diameters Mould Design/WS 2024/2025. Michael Kaisser. Page: 12 11.11.2024 12 6  11.11.2024 CVA-Process + Reduce long term costs & increase efficiency. Costs are reduced due to longer-lasting components, which results in higher productivity. + CVA is an environmentally friendly process which results in not generating waste powders. + Remarkable resistance to high temperature oxidation & corrosion. Chemical Vapor Aluminizing (CVA) is based on the CVD process & is used for the production of diffusion aluminide coatings for high temperature applications. In the 900 - 1050 °C process, aluminum diffuses into the substrate to produce intermetallic compounds – aluminides. Aluminides offer remarkable resistance to high temperature oxidation & corrosion, e.g. for blades protection in the hot section of turbines. Mould Design/WS 2024/2025. Michael Kaisser. Page: 13 11.11.2024 13 7