Oliver Hentschel

Experimental investigations of processing the high carbon cold-work tool steel 1.2358 by laser metal deposition for the additive manufacturing of cold forging tools

In the field of tool making, Laser Beam Melting of metals has been already used to fabricate injection moulds with complex inner cooling channels made out of the low-carbon maraging tool steel X3NiCoMoTi18-9-5 (1.2709). Furthermore, laser metal deposition (LMD) is an established technology for the repair of worn-out tools and the deposition of wear resistance coatings based on metal matrix composites. However, at the moment, the processing of high-carbon tool steels for the additive manufacturing of complete cold forging tools has only been investigated to a limited extent. Within the scope of the presented research, the processing of the high-carbon cold-work tool steel 60CrMoV18-5 (1.2358) by LMD is analyzed in detail. In this context, geometrically simple cuboidal structures are directly generated on dissimilar substrate plates made out of the hot-work tool steel X37CrMoV5-1(1.2343) via the application of various process parameter combinations. The manufactured cuboidal structures are metallographically prepared and subsequently analyzed with respect to substrate bonding, relative density, defect formation, microstructure, chemical composition, and microhardness. In this context, the influence of the particle size distribution of the used tool steel powder on the LMD process itself and the resulting relative density are extensively researched. For this purpose, high-speed camera measurements of the powder particle stream were conducted in order to determine both the powder particle stream diameter and the lateral powder particle distribution with regard to the distance z from the powder nozzle. Furthermore, the influence of an additional substrate preheating (maximum preheating temperature of 400 °C) on the resulting microstructure and hardness of the additively generated samples is the subject of the presented investigations.In the field of tool making, Laser Beam Melting of metals has been already used to fabricate injection moulds with complex inner cooling channels made out of the low-carbon maraging tool steel X3NiCoMoTi18-9-5 (1.2709). Furthermore, laser metal deposition (LMD) is an established technology for the repair of worn-out tools and the deposition of wear resistance coatings based on metal matrix composites. However, at the moment, the processing of high-carbon tool steels for the additive manufacturing of complete cold forging tools has only been investigated to a limited extent. Within the scope of the presented research, the processing of the high-carbon cold-work tool steel 60CrMoV18-5 (1.2358) by LMD is analyzed in detail. In this context, geometrically simple cuboidal structures are directly generated on dissimilar substrate plates made out of the hot-work tool steel X37CrMoV5-1(1.2343) via the application of various process parameter combinations. The manufactured cuboidal structures are metallographicall...

Laser metal deposition of NiTi shape memory alloy on Ti sheet metal: Influence of preheating on dissimilar build-up

Lightweight and functional integration are two major drivers for additive manufacturing technologies. In order to integrate functionality, the use of smart materials like Nickel-Titanium (NiTi) shape memory alloys (SMAs) is a constructive approach. Generally, shape memory alloys are hard to machine and at the same time expensive materials. In this context, additive manufacturing processes like laser metal deposition are reasonable technologies to process these materials as the used powder can be recycled and near net shape geometry can be generated due to a layer-by-layer build-up process. For actuator applications, it might be reasonable to use hybrid systems, meaning just certain sections of a part are made of a shape memory material. One possible example is a NiTi shape memory element on a Ti sheet metal. Due to the varying coefficients of thermal expansion, a dissimilar build-up by means of laser metal deposition without any defects like cracks is challenging. In this paper, an approach that applies p...

Experimental investigation of direct diamond laser cladding in combination with high speed camera based process monitoring

Laser cladding is an established coating technology which is established as emerging technology for repair applications and for the fabrication of near net shape geometries. Within the scope of coating, repair and additive manufacturing applications single weld tracks are generated on a metal substrate by a laser beam and simultaneously injected metal powder. For coating applications, such as wear-resistant coatings, single weld tracks are positioned next to each other in order to form a continuous surface layer. Coatings against heavy abrasive wear often contain additional particles like tungsten carbide or diamond particles. However, by embedding wear-resistant particles like tungsten or diamond particles, varying applications can be addressed. For example, the cutting ability of industrial tools can be enhanced by embedding diamonds into a coating. In this paper, a novel approach, the direct embedding of diamonds without using a metal matrix during laser cladding is experimentally investigated. As diam...

Effect of Additive Manufactured Metallic Structures on Laser-Based Thermal Joining of Thermoplastic Metal Hybrids

In future, the use of tailored multi material parts consisting of thermoplastics and metals will increase especially in the field of automotive applications based on the pursuit of lightweight design. This provides completely new demands on automated manufacturing because dissimilar materials have to be joined reliably. A promising approach is the thermal joining by laser radiation which enables a non-contact, automated and reproducible production of thermoplastic metal hybrids. Thereby, laser radiation heats the metal and through heat conduction the thermoplastic melts and wets the metal surface. The surface topography of the metallic joining partner plays an important role for the strength of the hybrid joint. In this paper, a novel approach for the fast and flexible fabrication of part-adapted surface structures by means of laser cladding with powder injection is investigated. The aim of the performed experiments is to find out how the geometry and arrangement of additive manufactured line-like metallic structures affect the strength of the dissimilar joint. Therefore, the height and width of the structures are varied. The structure geometries are investigated by microscopy of cross-sections and laser-scanning microscope measurements. As substrate and powder material stainless steel is used. Finally, the metallic samples are joined with polyamide 12 by means of laser radiation and mechanically analyzed by tensile shear tests.

A New Process Chain for Joining Sheet Metal to Fibre Composite Sheets

Mixed-Materials parts have great light-weight potential for the automotive application to reduce the carbon footprint. But the joining of fibre composite plastic sheets to metal sheets is in practical application limited to adhesive bonding or mechanical joining with additional fastener elements due to the large differences in physical properties. A new process chain based on plastic joining without fastener elements is proposed and first results on the mechanism and on the achievable strength of the new joints are shown. The process chain consists of three steps: First joining pins are added to the sheet metal by an additive manufacturing process. In a second step these pins are pierced through the fibre composite sheet with a local heating of the thermoplastic in an overlap setup. In the third and last step the joint is created by forming the pins with the upsetting process to create a shape lock. The shear strength of the joined specimens was tested in a tensile testing machine. The paper shows that even with a non-optimized initial setup joints can be realised and that the new process chain is a possible alternative to adhesive bonding.

Analytic and experimental investigations on influence of harmonic generation on acousto-optical modulation

In application, laser power is modulated prior to harmonic generation to a large part. Consequently modulation characteristics are influenced as a result of the non-linearity of harmonic generation. Within this paper, straight-forward approaches to calculate modulation key parameters (rise time, fall time, bandwidth and contrast ratio) of an acousto-optical modulator prior to harmonic generation stage are presented. The results will be compared to experimental data for third harmonic generation (THG) of a 1064 nm fs-laser which is power-modulated by a TeO2-AOM prior to THG. In the latter case, rise time and fall time are significantly reduced to approximately 66% after THG both in experimental and analytical study.

Copper circuit traces by laser cladding with powder injection for additive manufactured mechatronic devices

Laser cladding allows for a fast, flexible and direct plotting of electric conductive structures on polymer based substrates. The surface of the substrate is selectively melted by a focused laser beam. Simultaneously, a metal powder is lead through a powder nozzle. This nozzle is oriented laterally or coaxially to the laser beam. As a result, a molten bath of substrate and powder material is created. After cooling and solidification a welding bead on the substrate surface is formed. With this generation of circuit traces mechatronic devices can be built up, especially for high current power electronic applications. In this paper copper circuit traces on polymere substrates, produced by laser cladding with powder injection are characterized for their optical, electrical and mechanical properties by measuring resistance, adhesive strengths and current-carrying capacity including the effects of simulated environmental influences.

Connection Strength of Additive Manufactured Tool Elements to the Substrate

In industry the increasing variety of products leads to shorter product life cycles. For parts made by forging processes this trend results in very high prizes, as the tool costs have to be assimilated with only few parts. To reduce the tool costs new, flexible processes have to be investigated and established in tool manufacturing. Laser based additive manufacturing is noted for its high flexibility and especially laser metal deposition (LMD) gets in the focus of the research as it allows adding material on free formed surfaces. Therefore it is already used for coating and repairing of forming tools. New investigations are made to qualify this process for the production of forging tools. The aim is to generate active elements onto a geometrical simple base unit. Within first investigations the manufacturing of high carbon hot work tool steel 1.2343 was analysed. The measured mechanical properties were similar to those of conventional manufactured material.The focus of this paper is the connection strength of the additively built structures to the substrate. Therefore cylindrical specimens for tensile tests are manufactured with the linkage zone in the parallel area, in which the highest tension will be achieved. To assess the strength of the connection a comparison with conventional manufactured steel will be made. Furthermore specimens produced with various settings will be tested to analyse the influence of the LMD process. Additionally post heat treated samples will be analysed to recognize the effect of the hardening on the strength of the specimens.

Tailor-Made Forging Tools by Laser Metal Deposition

The desire for individualized products forces the companies to a great diversity of combinable parts. This way, the clients can compile their personalized product. As this trend is not just limited on visual parts but also for functional components, laser additive manufacturing of metals is used more and more often in manufacturing. To bring more additive manufacturing into mass production, Laser Beam Melting and Laser Metal Deposition will be qualified for the use in tool manufacturing within the Bavarian research association “ForNextGen – Next Generation Tools”. The first subproject within this research association investigates the potential of Laser Metal Deposition in the production of hot and cold forging tools. Within initial tests optimized process, parameters for the processing of the hot-work steel 1.2709 are determined by single welding beads. The achieved density and the inner structure are analyzed within cubes that were built with the investigated parameters. As forging tools are usually made of high-carbon tool steel, the processing of materials with a rising percentage of carbon will be part of further investigations.