Investment casting
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INVESTMENT CASTING FOUNDRY TECHNOLOGY

The Zollern factories The ZOLLERN GmbH & Co. KG is a company with worldwide operations, employing over 2400 employees in the business fields of transmission technology (automation, gears and winches, friction bearing technology), engineering elements, foundry technology and steel profiles. INVESTMENT CASTING • ZOLLERN Castings Technology – performance, experience and innovation • The Process • Tolerances and Surfaces • VDG Specification P 695 • VDG Specification P 690 • Shaping • Applications INVESTMENT CASTING 3 4 6 8 9 14 22

ZOLLERN CASTINGS TECHNOLOGY – PERFORMANCE, EXPERIENCE AND INNOVATION 2 3 In the field of castings technology, the ZOLLERN Company is not only one of the foremost names in Europe but also a highly respected exporter to some of the most important industrial notions in the world. After all, we have been making castings for around one hundred years. ZOLLERN helped to shape every stage in the development of the technology, from the production of simple cast iron at the end of the 19th century to the most modern technologies in use today. Our origins, however, go a lot further back. Prince...

THE PROCESS Investment casting is taken to mean casting into singlepiece ceramic shell moulds, eliminating the mould (pattern) parting line and the imprecision and flash associated with it. The characteristic feature of Investment casting is that the pattern is melted away and thus lost. The process is described by the following detail production steps. Surface quality The casting are produced without any trace of flash, and with an excellent surface finish. In many cases-expect for producing the required seat dimensions – there is no need for a follow-on machining process. Piece weights...

1 Patternmaking 2 Assembly of the casting unit 3 Immersion 4 Packing in sand 4 5 5 Shell mould 6 Melting out of pattern 7 Firing 8 Casting 9 Casting ejection 10 Release 11 Machining 12 Inspection 1 For every casting, a wax pattern has to be produced. Pattern are manufactured using an injection moulding machine in metal moulds made of soft metal alloy, aluminium or using wax. 2 The Patter are glued either individually (in the case of large workpieces) or in groups forming ‘clusters’ to a gating system (sprue, gates, feeder) which is also manufactured using wax. 3 up to 5 By repeated...

TOLERANCES AND SURFACES Using the investment casting method, economical dimensioning means ensuring that no tolerance is selected closer than necessary for the intended purpose. Dimensional tolerances, surface and machining allowances are generally laid down by the Technical Memorandum of the VDG (German Association of Foundry Specialists), P 690. The accuracy level D 1 is generally taken to be the free size tolerance for casting which demonstrate an average degree of complexity. Accuracy level D2 applies to casting dimensions within toleranced limits. Accuracy level D3 corresponds to the...

6 7 CLA [µinch] Ra1) [µm] Rz1) [µm] Rt1) [µm] N 1 1 0.025 0.22–0.30 0.24–0.40 N 2 2 0.050 0.15–0.60 0.49–0.90 N 3 4 0.1 0.8–1.1 0.85–1.45 N 4 8 0.2 1.0–1.8 1.10–2.40 N 5 16 0.4 1.6–2.8 1.75–3.60 N 6 Greatest nominal dimension 32 0.8 3.0–4.8 3.2–6.0 Investment casting Table 3: Surface qualities to DIN ISO 1302 N 7 63 1.6 5.9–8.0 6.3–10.0 N 8 125 3.2 12–16 13.0–19.5 N 9 250 6.3 23–32 25–38 Sand casting Table 2: Machining allowances depending on the type of machining (all values in mm) N 10 500 12.5 46–57 48–68 N 11 1000 25 90–110 95–130 N 12 2000 50 180–220 190–250 Allowance per surface over...

VDG SPECIFICATION P 695 INVESTMENT CASTINGS: TERMS OF DELIVERY Part 1: General conditions Part 2: Quality grades 1. Applications 1. General VDG Specification P 695 lays down the general technical terms of delivery for investment castings made by the lost wax method from standard and non-standard casting materials or metals. Additional, specific requirements relating to certain materials are laid down in separate standards. The present specification lays down various grades of external and internal quality for the condition of materials on delivery. The grades are subdivided in accordance...

VDG SPECIFICATION P 690 8 9 DIMENSIONAL TOLERANCES, SURFACES, MACHINING ALLOWANCES P690, 4th edition, February 1992 Directive compiled by the Special Committee on ‘Investment Casting’ GERMAN ASSOCIATION OF FOUNDRY SPECIALISTS Available from VDG-Center of Information Sohnstr. 70, 40237 Düsseldorf Tel. +49 (0) 211/68 71-254 Fax. +49 (0) 211/68 71-364 Email info@vdg.de www.vdg.de Slightly abridged version with the permission of the German Association of Foundry Specialists. 1. Definition and scope 1.1 Investment casting is a process by which a high surface quality can be manufactured through...

3. Dimensional accuracy 3.1 Contraction and shrinkage During the solidification and cooling of cast metals, a contraction of the volume naturally occurs as a result of shrinkage. Other factors influencing the production of instrument castings can result from the shrinkage of the lost pattern and the expansion of moulds during heating. The sum of these influencing factors is taken into consideration in the shrinkage allowance during the manufacture of injection moulds. The shrinkage allowance is based on experience values, depending on the contour of the casting, the ceramic shell and the...

4. Dimensional tolerances 4.1.2. Dimensions and shape of the casting The achievable accuracy level of the rated dimensions of an investment casting depends on the greatest dimension and the shape of the casting. If the rated dimension (GTA) exceeds the rated dimension range indicated for a certain accuracy level, the overall tolerance of the casting must be toleranced at the accuracy level (greatest tolerance field). Deviation outside the accuracy level must be agreed between the supplier and the buyer. 4.1 Linear dimensional tolerances Achievable dimensional tolerances on investment...