Dr.-Eng. Ulf Schliephake
Area Sales Manager Scandinavia and Austria, Brechmann-Guss GmbH
Rapid Casting Part 3 Cost-Benefit Factor - Is the Additive Production of Molds and Cores Profitable?
This article series presents various possibilities along the product life cycle that innovative additive solutions offer to a tradition-conscious industry. In the third part, variants of Rapid Casting, costs and options in the spare parts business are considered.
Variants of Rapid Casting
On the basis of the previous experiences in the companies of the authors, one can roughly distinguish three different variants of Rapid Casting:
- Functional prototypes / series-like castings - produced by the fastest possible casting of components on the basis of the 3D data supplied by the customer without consideration of mold inclinations and undercuts with the least possible inspection effort (approx. two working weeks), if necessary also "next to the molding plant" or with the help of an adapter system in a molding plant. These components are not suitable for series production.
- Technical prototypes which are manufactured identical to the series in the series material under series production conditions and, if necessary, in the series test status (4s), which can later be manufactured in the conventional way without any modifications.
- Special case "unpourable" - in this case some shaping geometry sections of previously uncastable geometries are produced with printed molds
Which type is chosen, depends on the respective project and its possibility of implementation in series production. The majority of the projects carried out in the author's company were type technical prototypes. The first mentioned type belongs rather into the range of pure prototype service providers, which already times the floating up of not or badly stored cores by putting on of weights (and their holding down by an coworker) realizes. A procedure that cannot be implemented on a molding line and would cause corresponding problems during series production. Spare parts in very small quantities can be produced in the first mentioned as well as in the second mentioned variant.
Practically "nothing is impossible" in additive manufacturing - nevertheless, the cost-benefit factor must also be appropriate. The printing of molds and cores is far higher in relation to the raw casting price in series production, but in extreme cases it allows the delivery of prototypes (or very small series, or spare parts) in ten working days. In addition, the method preferred by the authors for sand casting of metals (cast iron, copper, aluminum), i.e. the use of a conventional (or printed) outer model made of pattern making plastic, offers the option of producing different design variants in one production batch without loss of time simply by varying the core geometries. An effect that is often used for the development of pumps and turbochargers, sometimes also using model equipment that has been in use for many years. This means that completely new parts are produced "from scratch" from partly existing model equipment, if necessary even for a different application (or a special solution with one-time requirement).
The time advantage is a circumstance that is used, for example, by the MAN foundry in Augsburg (Germany), which now produces many spare parts (mainly heavyweight hand-molded parts, some weighing more than 100 kg and with corresponding dimensions) for the large diesel engines produced in Augsburg from printed molds, if the pattern equipment used during earlier series production is no longer available. At first glance, EUR20,000 or EUR30,000 costs for the molds of only one component are an abstruse value. However, if one considers that the time a ship is in port is quickly calculated at EUR50,000 per day, these mold costs become "peanuts".
The same effect is used by customer foundries in the course of development projects of their customers. The time saved in product development or the penalty-free execution of a development project compensates very quickly for the costs of the process, which at first glance appear to be high. Especially since the time delay caused by the conventional procedure is often hardly evaluated - the designers are on site anyway and fixed costs do not play a role in traditional cost evaluations of purchasing.
This effect is generated even more clearly in spare parts production, as in the cost example for spare parts for a Danube bridge in Linz, for which exactly 4 housings (of a type that has not been manufactured for a long time) were required.
Options in the Spare Parts Business
An interesting train of thought in the focus of spare parts remanufacturing is also the use of reverse engineering for product optimization of spare parts: In the worst case, neither old drawings nor model equipment are available. The last available component to be replaced now may show the cause of failure, but certainly traces of wear or similar. What prevents the end customer from using modern development tools such as load analyses via FEM on the basis of the data created with reverse engineering and from adapting the spare part data accordingly? "The combination of additive manufacturing processes and modern engineering methods allows a controlled and fast change of geometry and functionality and enables a change of paradigm: The spare part offers the chance to be better than the original and is the starting point of an evolutionary product development"1.
It may even be necessary to rethink certain spare parts strategies: Today, in order to fulfill long-term spare parts obligations (10 years and more), model equipment is stored in order to perhaps supply something at a later date, or it is pre-produced in order to perhaps sell a few parts later. The corresponding calculation (if available at all) often does not work out, because despite the high leverage in the price calculation of sold spare parts, the costs of availability of a possible spare parts delivery are not calculated/are hardly calculable. In the sense of a holistic spare parts warehouse and production strategy with digitalization of the spare parts portfolio with the goal of data-based production (for castings with printed molds and cores), spare parts could be made available when needed. Indirect additive manufacturing is becoming the key in the spare parts production of castings - it represents a new business model.
A major obstacle to the use of cast prototypes in the product development process of cast components is the lengthy, time-consuming production of the shaping tools for the outer geometry and core required for the castings. With the indirect additive manufacturing (of the molds and cores) a production time of two weeks and more can be realized. This is accompanied by the abandonment of provisional prototypes (machined from the solid), so that ideally prototypes are produced in series status.
The time required for the product development process is drastically reduced. At the same time, a staged approach offers freedom of decision regarding the timing of the change from 3D print to conventionally manufactured cores and molds, or enables the inexpensive (and fast) production of variants in small batches. At the same time, the ability to quickly produce small batches is a core requirement in the spare parts business (Spare Parts on Demand).
In the end, Rapid Casting in its various forms represents a further alternative in terms of production technology. Just as the direct 3D printing of metal powders will not replace conventional manufacturing methods2, the majority of all castings will continue to be produced using conventionally manufactured tools3.
The process also offers the potential to "cast the uncastable anyway". This means that it shifts the application limits of the manufacturing process, but also requires completely new approaches in product development, because it offers unlimited design freedom. The simple reproduction of a conventionally manufactured component is a thing of the past for anyone using 3D printing. Components can be rethought.
1Junior, Volker; 3D scanning and Additive Manufacturing, New Value Creation Potential in Quality Assurance, Product and Process Optimisation; Vortrag tct live; Birmingham, 25. September 2012
2Die Revolution fällt (vorerst) aus, PRODUKTION, Magazin, 04/2016, S. 38-39
3Stahl, R.: How classic foundries remain competitive against 3D printing, ETMM, https://files.vogel.de/vogelonline/pdfarticles/744/9/744988.pdf, 27.08.2018